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Sökning: WFRF:(Horellou Cathy 1967)

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1.
  • Adam, R. M., et al. (författare)
  • The XXL Survey: LI. Pressure profile and Y SZ -M scaling relation in three low-mass galaxy clusters at z∼1 observed with NIKA2
  • 2024
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 684
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The thermodynamical properties of the intracluster medium (ICM) are driven by scale-free gravitational collapse, but they also reflect the rich astrophysical processes at play in galaxy clusters. At low masses (∼1014M) and high redshift (z≳1), these properties remain poorly constrained, observationally speaking, due to the difficulty in obtaining resolved and sensitive data. Aims. We aim to investigate the inner structure of the ICM as seen through the Sunyaev-Zel’dovich (SZ) effect in this regime of mass and redshift. We focused on the thermal pressure profile and the scaling relation between SZ flux and mass, namely the YSZ-M scaling relation. Methods. The three galaxy clusters XLSSC 072 (z=1.002), XLSSC 100 (z=0.915), and XLSSC 102 (z=0.969), with M500∼2×1014M, were selected from the XXL X-ray survey and observed with the NIKA2 millimeter camera to image their SZ signal. XMM-Newton X-ray data were used as a complement to the NIKA2 data to derive masses based on the YX-M relation and the hydrostatic equilibrium. Results. The SZ images of the three clusters, along with the X-ray and optical data, indicate dynamical activity related to merging events. The pressure profile is consistent with that expected for morphologically disturbed systems, with a relatively flat core and a shallow outer slope. Despite significant disturbances in the ICM, the three high-redshift low-mass clusters follow the YSZ-M relation expected from standard evolution remarkably well. Conclusions. These results indicate that the dominant physics that drives cluster evolution is already in place by z∼1, at least for systems with masses above M500∼1014M.
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2.
  • Adami, C., et al. (författare)
  • The XXL Survey VIII. MUSE characterisation of intracluster light in a z similar to 0.53 cluster of galaxies
  • 2016
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:A7
  • Forskningsöversikt (refereegranskat)abstract
    • Aims. Within a cluster, gravitational effects can lead to the removal of stars from their parent galaxies and their subsequent dispersal into the intracluster medium. Gas hydrodynamical effects can additionally strip gas and dust from galaxies; both gas and stars contribute to intracluster light (ICL). The properties of the ICL can therefore help constrain the physical processes at work in clusters by serving as a fossil record of the interaction history. Methods. The present study is designed to characterise this ICL for the first time in a similar to 10(14) M-circle dot and z similar to 0.53 cluster of galaxies from imaging and spectroscopic points of view. By applying a wavelet-based method to CFHT Megacam and WIRCAM images, we detect significant quantities of diffuse light and are able to constrain their spectral energy distributions. These sources were then spectroscopically characterised with ESO Multi Unit Spectroscopic Explorer (MUSE) spectroscopic data. MUSE data were also used to compute redshifts of 24 cluster galaxies and search for cluster substructures. Results. An atypically large amount of ICL, equivalent in i' to the emission from two brightest cluster galaxies, has been detected in this cluster. Part of the detected diffuse light has a very weak optical stellar component and apparently consists mainly of gas emission, while other diffuse light sources are clearly dominated by old stars. Furthermore, emission lines were detected in several places of diffuse light. Our spectral analysis shows that this emission likely originates from low-excitation parameter gas. Globally, the stellar contribution to the ICL is about 2.3 x 10(9) yr old even though the ICL is not currently forming a large number of stars. On the other hand, the contribution of the gas emission to the ICL in the optical is much greater than the stellar contribution in some regions, but the gas density is likely too low to form stars. These observations favour ram pressure stripping, turbulent viscous stripping, or supernovae winds as the origin of the large amount of intracluster light. Since the cluster appears not to be in a major merging phase, we conclude that ram pressure stripping is the most plausible process that generates the observed ICL sources. Conclusions. This is one of the first times that we are able to spectroscopically study diffuse light in such a distant and massive cluster, and it demonstrates the potential of MUSE observations for such studies.
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3.
  • Adami, C., et al. (författare)
  • The XXL Survey: XX. The 365 cluster catalogue
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical. Aims. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detected clusters suitable for cosmological studies. The main goal of present article is to make public and describe the properties of the cluster catalogue in its present state, as well as of associated catalogues of more specific objects such as super-clusters and fossil groups. Methods. Following from the publication of the hundred brightest XXL clusters, we now release a sample containing 365 clusters in total, down to a flux of a few 10-15 erg s-1 cm-2 in the [0.5-2] keV band and in a 1′ aperture. This release contains the complete subset of clusters for which the selection function is well determined plus all X-ray clusters which are, to date, spectroscopically confirmed. In this paper, we give the details of the follow-up observations and explain the procedure adopted to validate the cluster spectroscopic redshifts. Considering the whole XXL cluster sample, we have provided two types of selection, both complete in a particular sense: one based on flux-morphology criteria, and an alternative based on the [0.5-2] keV flux within 1 arcmin of the cluster centre. We have also provided X-ray temperature measurements for 80% of the clusters having a flux larger than 9 × 10-15 erg s-1 cm-2. Results. Our cluster sample extends from z ∼ 0 to z ∼ 1.2, with one cluster at z ∼ 2. Clusters were identified through a mean number of six spectroscopically confirmed cluster members. The largest number of confirmed spectroscopic members in a cluster is 41. Our updated luminosity function and luminosity-temperature relation are compatible with our previous determinations based on the 100 brightest clusters, but show smaller uncertainties. We also present an enlarged list of super-clusters and a sample of 18 possible fossil groups. Conclusions. This intermediate publication is the last before the final release of the complete XXL cluster catalogue when the ongoing C2 cluster spectroscopic follow-up is complete. It provides a unique inventory of medium-mass clusters over a 50 deg2 area out to z ∼ 1.
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4.
  • Andersson, Christer, 1948, et al. (författare)
  • Radioastronomy for students
  • 2005
  • Ingår i: International Amateur-Professional Photoelectric Photometry Communications, Proceedings of `Global Hands-On Universe 2004", St. Petersburg, Russia, July 2004. ; 100, s. 49-54
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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5.
  • Asabere, B. D., et al. (författare)
  • Mid-infrared dust in two nearby radio galaxies, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36)
  • 2016
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:A20, s. 1-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Most radio galaxies are hosted by giant gas-poor ellipticals, but some contain significant amounts of dust, which is likely to be of external origin. Aims. In order to characterize the mid-IR properties of two of the most nearby and brightest merger-remnant radio galaxies of the Southern hemisphere, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36), we used observations with the Wide-field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12 and 22 mu m and Spitzer mid-infrared spectra. Methods. By applying a resolution-enhancement technique, new WISE images were produced at angular resolutions ranging from 2 ''.6 to 5 ''.5. Global measurements were performed in the four WISE bands, and stellar masses and star-formation rates were estimated using published scaling relations. Two methods were used to uncover the distribution of dust, one relying on two-dimensional fits to the 3.4 mu m images to model the starlight, and the other one using a simple scaling and subtraction of the 3.4 mu m images to estimate the stellar continuum contribution to the emission in the 12 and 22 mu m bands. Results. The two galaxies differ markedly in their mid-IR properties. The 3.4 mu m brightness distribution can be well represented by the superposition of two Sersic models in NGC 1316 and by a Sersic model and an exponential disk in NGC 612. The WISE colors of NGC 1316 are typical of those of early-type galaxies; those of NGC 612 are in the range found for star-forming galaxies. From the 22 mu m luminosity, we infer a star-formation rate of similar to 0.7 M-circle dot yr(-1) in NGC 1316 and similar to 7 M-circle dot yr(-1) in NGC 612. Spitzer spectroscopy shows that the 7.7-to-11.3 mu m PAH line ratio is significantly lower in NGC 1316 than in NGC 612. The WISE images reveal resolved emission from dust in the central 1'-2' of the galaxies. In NGC 1316, the extra-nuclear emission coincides with two dusty regions NW and SE of the nucleus seen in extinction in optical images and where molecular gas is known to reside. In NGC 612 it comes from a warped disk. This suggests a recent infall onto NGC 1316 and disruption of one or several smaller gas-rich galaxies, but a smoother accretion in NGC 612. While the nucleus of NGC 1316 is currently dormant and the galaxy is likely to evolve into a passive elliptical, NGC 612 has the potential of growing a larger disk and sustaining an active nucleus. Conclusions. NGC 1316 and NGC 612 represent interesting challenges to models of formation and evolution of galaxies and AGNs.
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6.
  • Asabere, Bernard Duah, et al. (författare)
  • Radio astronomy in Africa: the case of Ghana
  • 2015
  • Ingår i: Proceedings of SAIP2014, the 59th Annual Conference of the South African Institute of Physics, edited by Chris Engelbrecht and Steven Karataglidis (University of Johannesburg, 2015). - 9780620653916 ; , s. 296-301
  • Konferensbidrag (refereegranskat)abstract
    • South Africa has played a leading role in radio astronomy in Africa with the Hartebeesthoek Radio Astronomy Observatory (HartRAO). It continues to make strides with the current seven-dish MeerKAT precursor array (KAT-7), leading to the 64-dish MeerKAT and the giant Square Kilometer Array (SKA), which will be used for transformational radio astronomy research. Ghana, an African partner to the SKA, has been mentored by South Africa over the past six years and will soon emerge in the field of radio astronomy. The country will soon have a science-quality 32m dish converted from a redundant satellite communication antenna. Initially, it will be fitted with 5 GHz and 6.7 GHz receivers to be followed later by a 1.4 - 1.7 GHz receiver. The telescope is being designed for use as a single dish observatory and for participation in the developing African Very Long Baseline Interferometry (VLBI) Network (AVN) and the European VLBI Network. Ghana is earmarked to host a remote station during a possible SKA Phase 2. The location of the country on 5 degree north of the Equator gives it the distinct advantage of viewing the entire plane of the Milky Way galaxy and nearly the whole sky. In this article, we present the case of Ghana in the radio astronomy scene and the science/technology that will soon be carried out by engineers and astronomers.
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7.
  • Badescu, A. M., et al. (författare)
  • CONSTRAINS ON THE QUINTESSENCE FROM OBSERVATIONAL DATA
  • 2011
  • Ingår i: Romanian Reports on Physics. - 1221-1451 .- 1841-8759. ; 63:3, s. 852-861
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated a flat Universe where the quintessence has been approximated by the first order Chebyshev polynomials. We used different cosmological measurements: angular diameter, luminosity distance and the Hubble parameter to constrain it. The first two types of measurements favor a time dependent quintessence with a value of the quintessence at the present epoch higher than in the cosmological constant case. Hubble parameter measurements support a Universe close to the one given by the cosmological constant case.
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8.
  • Baran, N., et al. (författare)
  • The XXL Survey IX. Optical overdensity and radio continuum analysis of a supercluster at z=0.43
  • 2016
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
  • Forskningsöversikt (refereegranskat)abstract
    • We present observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward a sub-field of the XXL-North 25 deg(2) field targeting the first supercluster discovered in the XXL Survey. The structure has been found at a spectroscopic redshift of 0.43 and extending over 0.degrees 35x0.degrees 1 on the sky. The aim of this paper is twofold. First, we present the 3 GHz VLA radio continuum observations, the final radio mosaic and radio source catalogue, and, second, we perform a detailed analysis of the supercluster in the optical and radio regimes using photometric redshifts from the CFHTLS survey and our new VLA-XXL data. Our final 3 GHz radio mosaic has a resolution of 3 ''.2 x 1 ''.9, and encompasses an area of 41'x41' with rms noise level lower than similar to 20 mu Jy beam(-1). The noise in the central 15'x15' region is approximate to 11 mu Jy beam(-1). From the mosaic we extract a catalogue of 155 radio sources with signal-to-noise ratio (S/N) >= 6, eight of which are large, multicomponent sources, and 123 (79%) of which can be associated with optical sources in the CFHTLS W1 catalogue. Applying Voronoi tessellation analysis (VTA) in the area around the X-ray identified supercluster using photometric redshifts from the CFHTLS survey we identify a total of seventeen overdensities at z(phot) = 0.35-0.50, 7 of which are associated with clusters detected in the XMM-Newton XXL data. We find a mean photometric redshift of 0.43 for our overdensities, consistent with the spectroscopic redshifts of the brightest cluster galaxies of seven X-ray detected clusters. The full VTA-identified structure extends over similar to 0.degrees 6x0.degrees 2on the sky, which corresponds to a physical size of similar to 12x4 Mpc(2) at z = 0.43. No large radio galaxies are present within the overdensities, and we associate eight (S/N > 7) radio sources with potential group/cluster member galaxies. The spatial distribution of the red and blue VTA-identified potential group member galaxies, selected by their observed g -r colours, suggests that the clusters are not virialised yet, but are dynamically young, as expected for hierarchical structure growth in a Lambda CDM universe. Further spectroscopic data are required to analyse the dynamical state of the groups.
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9.
  • Basu, K., et al. (författare)
  • Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
  • 2010
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 519:Article Number: A29
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We aim to demonstrate the usability of mm-wavelength imaging data obtained from the APEX-SZ bolometer array to derive the radial temperature profile of the hot intra-cluster gas out to radius r(500) and beyond. The goal is to study the physical properties of the intra-cluster gas by using a non-parametric de-projection method that is, aside from the assumption of spherical symmetry, free from modeling bias. Methods. We use publicly available X-ray spectroscopic-imaging data in the 0.7-2 keV energy band from the XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data from the APEX-SZ experiment at 150 GHz to de-project the density and temperature profiles for a well-studied relaxed cluster, Abell 2204. We derive the gas density, temperature and entropy profiles assuming spherical symmetry, and obtain the total mass profile under the assumption of hydrostatic equilibrium. For comparison with X-ray spectroscopic temperature models, a re-analysis of recent Chandra observation is done with the latest calibration updates. We compare the results with that from an unrelaxed cluster, Abell 2163, to illustrate some differences between relaxed and merging systems. Results. Using the non-parametric modeling, we demonstrate a decrease of gas temperature in the cluster outskirts, and also measure gas entropy profiles, both of which are done for the first time independently of X-ray spectroscopy using the SZE and X-ray imaging data. The gas entropy measurement in the central 100 kpc shows the usability of APEX-SZ data for inferring cluster dynamical states with this method. The contribution of the SZE systematic uncertainties in measuring T-e at large radii is shown to be small compared to XMM-Newton and Chandra systematic spectroscopic errors. The total mass profile obtained using the hydrostatic equilibrium assumption is in agreement with the published X-ray and weak lensing results; the upper limit on M-200 derived from the non-parametric method is consistent with the NFW model prediction from weak lensing analysis.
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10.
  • Beck, R., et al. (författare)
  • Structure, dynamical impact and origin of magnetic fields in nearby galaxies in the SKA era
  • 2015
  • Ingår i: Proceedings of Science. - 1824-8039. ; 9-13-June-2014
  • Konferensbidrag (refereegranskat)abstract
    • Magnetic fields are an important ingredient of the interstellar medium (ISM). Besides their importancefor star formation, they govern the transport of cosmic rays, relevant to the launch andregulation of galactic outflows and winds, which in turn are pivotal in shaping the structure of halomagnetic fields. Mapping the small-scale structure of interstellar magnetic fields in many nearbygalaxies is crucial to understand the interaction between gas and magnetic fields, in particularhow gas flows are affected. Elucidation of the magnetic role in, e.g., triggering star formation,forming and stabilising spiral arms, driving outflows, gas heating by reconnection and magnetisingthe intergalactic medium has the potential to revolutionise our physical picture of the ISMand galaxy evolution in general. Radio polarisation observations in the very nearest galaxies athigh frequencies (3 GHz) and with high spatial resolution (500) hold the key here. The galaxysurvey with SKA1 that we propose will also be a major step to understand the galactic dynamo,which is important for models of galaxy evolution and for astrophysical magnetohydrodynamicsin general. Field amplification by turbulent gas motions, which is crucial for efficient dynamoaction, has been investigated so far only in simulations, while compelling evidence of turbulentfields from observations is still lacking.
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11.
  • Bender, A. N., et al. (författare)
  • Galaxy cluster scaling relations measured with APEX-SZ
  • 2016
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 460:4, s. 3432-3446
  • Tidskriftsartikel (refereegranskat)abstract
    • We present thermal Sunyaev-Zel'dovich effect (SZE) measurements for 42 galaxy clusters observed at 150 GHz with the APEX-SZ experiment. For each cluster, we model the pressure profile and calculate the integrated Comptonization Y to estimate the total thermal energy of the intraclustermedium (ICM). We compare the measured Y values to X-ray observables of the ICM from the literature (cluster gas mass M-gas, temperature T-X, and Y-X = MgasTX) that relate to total cluster mass. We measure power-law scaling relations, including an intrinsic scatter, between the SZE and X-ray observables for three subsamples within the set of 42 clusters that have uniform X-ray analysis in the literature. We observe that differences between these X-ray analyses introduce significant variance into the measured scaling relations, particularly affecting the normalization. For all three subsamples, we find results consistent with a selfsimilarmodel of cluster evolution dominated by gravitational effects. Comparing to predictions from numerical simulations, these scaling relations prefer models that include cooling and feedback in the ICM. Lastly, we measure an intrinsic scatter of similar to 28 per cent in the Y - Y-X scaling relation for all three subsamples.
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12.
  • Béthermin, Matthieu, et al. (författare)
  • CONCERTO: High-fidelity simulation of millimeter line emissions of galaxies and [CII] intensity mapping
  • 2022
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 667
  • Tidskriftsartikel (refereegranskat)abstract
    • The intensity mapping of the [CII] 158-μm line redshifted to the submillimeter window is a promising probe of the za>4 star formation and its spatial distribution into large-scale structures. To prepare the first-generation experiments (e.g., CONCERTO), we need realistic simulations of the submillimeter extragalactic sky in spectroscopy. We present a new version of the simulated infrared dusty extragalactic sky (SIDES) model including the main submillimeter lines around 1 mm (CO, [CII], [CI]). This approach successfully reproduces the observed line luminosity functions. We then use our simulation to generate CONCERTO-like cubes (125-305 GHz) and forecast the power spectra of the fluctuations caused by the various astrophysical components at those frequencies. Depending on our assumptions on the relation between the star formation rate and [CII] luminosity, and the star formation history, our predictions of the za∼6 [CII] power spectrum vary by two orders of magnitude. This highlights how uncertain the predictions are and how important future measurements will be to improve our understanding of this early epoch. SIDES can reproduce the CO shot noise recently measured at a4;100 GHz by the millimeter-wavelength intensity mapping experiment (mmIME). Finally, we compare the contribution of the different astrophysical components at various redshifts to the power spectra. The continuum is by far the brightest, by a factor of three to 100, depending on the frequency. At 300 GHz, the CO foreground power spectrum is higher than the [CII] one for our base scenario. At lower frequencies, the contrast between [CII] and extragalactic foregrounds is even worse. Masking the known galaxies from deep surveys should allow us to reduce the foregrounds to 20% of the [CII] power spectrum up to z∼ 6.5. However, this masking method will not be sufficient at higher redshifts. The code and the products of our simulation are released publicly, and can be used for both intensity mapping experiments and submillimeter continuum and line surveys.
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13.
  • Butler, Andrew, et al. (författare)
  • The XXL Survey XVIII. ATCA 2.1 GHz radio source catalogue and source counts for the XXL-South field
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • The 2.1 GHz radio source catalogue of the 25 deg(2) ultimate XMM extragalactic survey south (XXL-S) field, observed with the Australia Telescope Compact Array (ATCA), is presented. The final radio mosaic achieved a resolution of similar to 4.8" and a median rms noise of sigma approximate to 41 mu Jy/beam. To date, this is the largest area radio survey to reach this flux density level. A total of 6350 radio components above 5 sigma are included in the component catalogue, 26.4% of which are resolved. Of these components, 111 were merged together to create 48 multiple-component radio sources, resulting in a total of 6287 radio sources in the source catalogue, 25.9% of which were resolved. A survival analysis revealed that the median spectral index of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz sources in the field is alpha = 0.75, consistent with the values of -0.7 to -0.8 commonly used to characterise radio spectral energy distributions of active galactic nuclei. The 2.1 GHz and 1.4 GHz di ff erential radio source counts are presented and compared to other 1.4 GHz radio surveys. The XXL-S source counts show good agreement with the other surveys.
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14.
  • Carretti, Ettore, et al. (författare)
  • Magnetic field strength in cosmic web filaments
  • 2022
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 512:1, s. 945-959
  • Tidskriftsartikel (refereegranskat)abstract
    • We used the rotation measure (RM) catalogue derived from the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2) at 144MHz to measure the evolution with redshift of the extragalactic RM (RRM: Residual RM) and the polarization fraction (p) of sources in low-density environments. We also measured the same at 1.4 GHz by cross-matching with the NRAO VLA Sky Survey RM catalogue. We find that RRM versus redshift is flat at 144 MHz, but, once redshift-corrected, it shows evolution at high significance. Also, p evolves with redshift with a decrement by a factor of similar to 8 at z similar to 2. Comparing the 144-MHz and 1.4-GHz data, we find that the observed RRM and p are most likely to have an origin local to the source at 1.4 GHz, while a cosmic web filament origin is favoured at 144 MHz. If we attribute the entire signal to filaments, we infer a mean rest-frame RRM per filament of RRM0,f = 0.71 +/- 0.07 rad m(-2) and a magnetic field per filament of B-f = 32 +/- 3 nG. This is in agreement with estimates obtained with a complementary method based on synchrotron emission stacking, and with cosmological simulations if primordial magnetic fields are amplified by astrophysical source field seeding. The measurement of an RRM0, f supports the presence of diffuse baryonic gas in filaments. We also estimated a conservative upper limit of the filament magnetic turbulence of sigma(RRM0,f) = 0.039 +/- 0.001 rad m(-2), concluding that the ordered magnetic field component dominates in filaments.
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15.
  • Ceraj, L., et al. (författare)
  • The XXL Survey: XLIII. The quasar radio loudness dichotomy exposed via radio luminosity functions obtained by combining results from COSMOS and XXL-S X-ray selected quasars
  • 2020
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 642
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied a sample of 274 radio and X-ray selected quasars (XQSOs) detected in the COSMOS and XXL-S radio surveys at 3 GHz and 2.1 GHz, respectively. This sample was identified by adopting a conservative threshold in X-ray luminosity, LX [2-10 keV] ≥ 1044 erg s-1, selecting only the most powerful quasars. A number of previous studies on the origin of radio emission in type-1 quasars have focused on the radio loudness distributions, some claiming to have found evidence for bimodality, pointing toward the existence of two physically different mechanisms for the radio emission. Using available multiwavelength data, we examined various criteria for the selection of radio-loud (RL) and radio-quiet (RQ) XQSOs and found that the number of RL/RQ XQSOs changes significantly depending on the chosen criterion. This discrepancy arises due to the different criteria tracing different physical processes and due to the fact that our sample was selected from flux-limited radio and X-ray surveys. Another approach to study the origin of radio emission in XQSOs is via their radio luminosity functions (RLF). We constructed the XQSO 1.4 GHz RLFs in six redshift bins at 0:5 ≤ z ≤ 3:75. The lower-1.4 GHz luminosity end shows a higher normalization than expected only from AGN contribution in all studied redshift bins. We found that the so-called "bump"is mostly dominated by emission due to star-forming processes within the host galaxies of XQSOs. As expected, AGN-related radio emission is the dominant contribution at the higher-luminosity end of RLF. To study the evolution of the XQSO RLF, we used a combination of analytic forms from the literature to constrain the "bump"due to star formation and the higher-luminosity AGN part of the RLF. We defined two 1.4 GHz luminosity thresholds, Lth;SF and Lth;AGN, below and above which more than 80% of sources contributing to the RLF are dominated by star formation and AGN-related activity, respectively. The two thresholds evolve with redshift, which is most likely driven by the strong evolution of star formation rates of the XQSO host galaxies. We found that both the lower and higher luminosity ends evolve significantly in density, while their luminosity evolution parameters are consistent with being constant. We found that the lower-luminosity end evolves both in density and luminosity, while the higher-luminosity end evolves significantly only in density. Our results expose the dichotomy of the origin of radio emission: while the higher-luminosity end of the XQSO RLF is dominated by AGN activity, the lower-luminosity end is dominated by the star formation-related processes.
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16.
  • Clarke, A. O., et al. (författare)
  • Signatures from a merging galaxy cluster and its AGN population: LOFAR observations of Abell 1682
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 627
  • Tidskriftsartikel (refereegranskat)abstract
    • We present LOFAR data from 110-180 MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio, and X-ray data. Our images of 6 arcsec in resolution at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At a resolution of 20 arcsec we see diffuse emission throughout the cluster over hundreds of kiloparsecs, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectrum emission (having a spectral index of α < -2.5). Furthermore, we identify a new region of diffuse steep-spectrum emission (α < -1.1) as a candidate for a radio halo which is co-spatial with the centre of the cluster merger. We suggest its origin as a population of old and mildly relativistic electrons left over from radio galaxies throughout the cluster which have been re-accelerated to higher energies by shocks and turbulence induced by the cluster merger event. We also note the discovery of six new giant radio galaxies in the vicinity of Abell 1682.
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17.
  • Eyles, R. A. J., et al. (författare)
  • The XXL Survey XXXIX. Polarised radio sources in the XXL-South field
  • 2020
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 633
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We investigate the properties of the polarised radio population in the central 6.5 deg(2) of the XXL-South field observed at 2.1 GHz using the Australia Telescope Compact Array (ATCA) in 81 pointings with a synthesised beam of FWHM 5.2 ''. We also investigate the ATCA's susceptibility to polarisation leakage. Methods. We performed a survey of a 5.6 deg(2) subregion and calculated the number density of polarised sources. We derived the total and polarised spectral indices, in addition to comparing our source positions with those of X-ray-detected clusters. We measured the polarisation of sources in multiple pointings to examine leakage in the ATCA. Results. We find 39 polarised sources, involving 50 polarised source components, above a polarised flux density limit of 0.2 mJy at 1.332 GHz. The number density of polarised source components is comparable with recent surveys, although there is an indication of an excess at similar to 1 mJy. We find that those sources coincident with X-ray clusters are consistent in their properties with regard to the general population. In terms of the ATCA leakage response, we find that ATCA mosaics with beam separation of less than or similar to 2/3 of the primary beam FWHM have off-axis linear polarisation leakage less than or similar to 1.4% at 1.332 GHz.
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18.
  • Farnes, J.S., et al. (författare)
  • Source finding in linear polarization for LOFAR, and SKA predecessor surveys, using Faraday moments
  • 2018
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 474:3, s. 3280-3296
  • Tidskriftsartikel (refereegranskat)abstract
    • The optimal source-finding strategy for linear polarization data is an unsolved problem, with many inhibitive factors imposed by the technically challenging nature of polarization observations. Such an algorithm is essential for Square Kilometre Array (SKA) pathfinder surveys, such as the Multifrequency Snapshot Sky Survey with the LOw Frequency ARray (LOFAR), as data volumes are significant enough to prohibit manual inspection. We present a new strategy of 'Faraday Moments' for source-finding in linear polarization with LOFAR, using the moments of the frequency-dependent full-Stokes data (i.e. the mean, standard deviation, skewness, and excess kurtosis). Through simulations of the sky, we find that moments can identify polarized sources with a high completeness: 98.5 per cent at a signal to noise of 5. While the method has low reliability, rotation measure (RM) synthesis can be applied per candidate source to filter out instrumental and spurious detections. This combined strategy will result in a complete and reliable catalogue of polarized sources that includes the full sensitivity of the observational bandwidth. We find that the technique can reduce the number of pixels on which RM Synthesis needs to be performed by a factor of ≈1 × 10 5 for source distributions anticipated with modern radio telescopes. Through tests on LOFAR data, we find that the technique works effectively in the presence of diffuse emission. Extensions of this method are directly applicable to other upcoming radio surveys such as the POlarization Sky Survey of the Universe's Magnetism with the Australia Square Kilometre Array Pathfinder, and the SKA itself.
  •  
19.
  • Finet, F., et al. (författare)
  • Predicted multiply imaged X-ray AGNs in the XXL survey
  • 2015
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:2, s. 1480-1492
  • Tidskriftsartikel (refereegranskat)abstract
    • We estimate the incidence of multiply imaged active galactic nuclei (AGNs) among the optical counterparts of X-ray selected point-like sources in the XXL field.We also derive the expected statistical properties of this sample, such as the redshift distribution of the lensed sources and of the deflectors that lead to the formation of multiple images, modelling the deflectors using both spherical and ellipsoidal singular isothermal mass distributions. We further assume that the XXL survey sample has the same overall properties as the smaller XMM-COSMOS sample restricted to the same flux limits and taking into account the detection probability of the XXL survey. Among the X-ray sources with a flux in the [0.5-2] keVband larger than 3.0×10-15 erg cm-2 s-1 and with optical counterparts brighter than an r-band magnitude of 25, we expect ~20 multiply imaged sources. Out of these, ~16 should be detected if the search is made among the seeing-limited images of the X-ray AGN optical counterparts and only one of them should be composed of more than two lensed images. Finally, we study the impact of the cosmological model on the expected fraction of lensed sources.
  •  
20.
  • Fletcher, A., et al. (författare)
  • Magnetic fields and spiral arms in the galaxy M51
  • 2011
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 412:4, s. 2396-2416
  • Tidskriftsartikel (refereegranskat)abstract
    • We use new multiwavelength radio observations, made with the VLA and Effelsberg telescopes, to study the magnetic field of the nearby galaxy M51 on scales from 200 pc to several kpc. Interferometric and single-dish data are combined to obtain new maps at lambda lambda 3, 6 cm in total and polarized emission, and earlier lambda 20 cm data are rereduced. We compare the spatial distribution of the radio emission with observations of the neutral gas, derive radio spectral index and Faraday depolarization maps, and model the large-scale variation in Faraday rotation in order to deduce the structure of the regular magnetic field. We find that the lambda 20 cm emission from the disc is severely depolarized and that a dominating fraction of the observed polarized emission at lambda 6 cm must be due to anisotropic small-scale magnetic fields. Taking this into account, we derive two components for the regular magnetic field in this galaxy; the disc is dominated by a combination of azimuthal modes, m = 0 + 2, but in the halo only an m = 1 mode is required to fit the observations. We discuss how the observed arm-interarm contrast in radio intensities can be reconciled with evidence for strong gas compression in the spiral shocks. In the inner spiral arms, the strong arm-interarm contrasts in total and polarized radio emission are roughly consistent with expectations from shock compression of the regular and turbulent components of the magnetic field. However, the average arm-interam contrast, representative of the radii r > 2 kpc where the spiral arms are broader, is not compatible with straightforward compression: lower arm-interarm contrasts than expected may be due to resolution effects and decompression of the magnetic field as it leaves the arms. We suggest a simple method to estimate the turbulent scale in the magneto-ionic medium from the dependence of the standard deviation of the observed Faraday rotation measure on resolution. We thus obtain an estimate of 50 pc for the size of the turbulent eddies.
  •  
21.
  • Fletcher, A., et al. (författare)
  • Magnetic Fields and Spiral Structure
  • 2004
  • Ingår i: Proceedings of "How does the Galaxy Work?", Granada, Spain, June 2003, eds E.J. Alfaro, E. Perez, J. Franco, Astrophys. and Sp. Sci. Library, Springer-Verlag. ; , s. 315-
  • Konferensbidrag (refereegranskat)
  •  
22.
  • Fotopoulou, S., et al. (författare)
  • The XXL Survey VI. The 1000 brightest X-ray point sources
  • 2016
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:A5
  • Forskningsöversikt (refereegranskat)abstract
    • Context. X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). Usually, a combination of deep and wide surveys is necessary to create a complete picture of the population. Deep X-ray surveys provide the faint population at high redshift, while wide surveys provide the rare bright sources. Nevertheless, very wide area surveys often lack the ancillary information available for modern deep surveys. The XXL survey spans two fields of a combined 50 deg(2) observed for more than 6Ms with XMM-Newton, occupying the parameter space that lies between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. Aims. This paper marks the first release of the XXL point source catalogue including four optical photometry bands and redshift estimates. Our sample is selected in the 2-10 keV energy band with the goal of providing a sizable sample useful for AGN studies. The limiting flux is F2-10 keV = 4.8 x 10(14) erg s(-1) cm(-2). Methods. We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources by means of a likelihood ratio test. We improve upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift category (passive, star forming, starburst, AGN, quasi-stellar objects (QSO)). Additionally, we assign a probability to each source that indicates whether it might be a star or an outlier. We apply Bayesian analysis to model the X-ray spectra assuming a power-law model with the presence of an absorbing medium. Results. We find that the average unabsorbed photon index is = 1.85 +/- 0.40 while the average hydrogen column density is log i = 21.07 +/- 1.2 cm(-2). We find no trend of Gamma or N-H with redshift and a fraction of 26% absorbed sources (log N-H > 22) consistent with the literature on bright sources (log L-x > 44). The counterpart identification rate reaches 96.7% for sources in the northern field, 97.7% for the southern field, and 97.2% in total. The photometric redshift accuracy is 0.095 for the full XMM-XXL with 28% catastrophic outliers estimated on a sample of 339 sources. Conclusions. We show that the XXL-1000-AGN sample number counts extended the number counts of the COSMOS survey to higher fluxes and are fully consistent with the Euclidean expectation. We constrain the intrinsic luminosity function of AGN in the 2-10 keV energy band where the unabsorbed X-ray flux is estimated from the X-ray spectral fit up to z = 3. Finally, we demonstrate the presence of a supercluster size structure at redshift 0.14, identified by means of percolation analysis of the XXL-1000-AGN sample. The XXL survey, reaching a medium flux limit and covering a wide area, is a stepping stone between current deep fields and planned wide area surveys.
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23.
  • Govoni, F., et al. (författare)
  • A radio ridge connecting two galaxy clusters in a filament of the cosmic web
  • 2019
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6444, s. 981-984
  • Tidskriftsartikel (refereegranskat)abstract
    • Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.
  •  
24.
  • Guglielmo, V., et al. (författare)
  • The XXL Survey: XXII. the XXL-North spectrophotometric sample and galaxy stellar mass function in X-ray detected groups and clusters
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The fraction of galaxies bound in groups in the nearby Universe is high (50% at z ∼ 0). Systematic studies of galaxy properties in groups are important in order to improve our understanding of the evolution of galaxies and of the physical phenomena occurring within this environment. Aims. We have built a complete spectrophotometric sample of galaxies within X-ray detected, optically spectroscopically confirmed groups and clusters (G&C), covering a wide range of halo masses at z ≤ 0.6. Methods. In the context of the XXL survey, we analyse a sample of 164 G&C in the XXL-North region (XXL-N), at z ≤ 0.6, with a wide range of virial masses (1.24 × 1013 ≤ M500,scal(Mo) ≤ 6.63 × 1014) and X-ray luminosities ((2.27 × 1041 ≤ L500,scalXXL(erg-s-1) ≤ 2.15 × 1044)). The G&C are X-ray selected and spectroscopically confirmed. We describe the membership assignment and the spectroscopic completeness analysis, and compute stellar masses. As a first scientific exploitation of the sample, we study the dependence of the galaxy stellar mass function (GSMF) on global environment. Results. We present a spectrophotometric characterisation of the G&C and their galaxies. The final sample contains 132 G&C, 22 111 field galaxies and 2225 G&C galaxies with r-band magnitude <20. Of the G&C, 95% have at least three spectroscopic members, and 70% at least ten. The shape of the GSMF seems not to depend on environment (field versus G&C) or X-ray luminosity (used as a proxy for the virial mass of the system). These results are confirmed by the study of the correlation between mean stellar mass of G&C members and L500,scalXXL. We release the spectrophotometric catalogue of galaxies with all the quantities computed in this work. Conclusions. As a first homogeneous census of galaxies within X-ray spectroscopically confirmed G&C at these redshifts, this sample will allow environmental studies of the evolution of galaxy properties.
  •  
25.
  • Guglielmo, V., et al. (författare)
  • The XXL Survey: XXX. Characterisation of the XLSSsC N01 supercluster and analysis of the galaxy stellar populations
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Superclusters form from the largest enhancements in the primordial density perturbation field and extend for tens of Mpc, tracing the large-scale structure of the Universe. X-ray detections and systematic characterisations of superclusters and the properties of their galaxies have only been possible in the last few years. Aims. We characterise XLSSsC N01, a rich supercluster at z ∼ 0.3 detected in the XXL Survey, composed of X-ray clusters of different virial masses and X-ray luminosities. As one of the first studies on this topic, we investigate the stellar populations of galaxies in different environments in the supercluster region. Methods. We study a magnitude-limited (r ≤ 20) and a mass-limited sample (log(M ∗ Mo) ≥ 10.8) of galaxies in the virialised region and in the outskirts of 11 XLSSsC N01 clusters, in high-density field regions, and in the low-density field. We compute the stellar population properties of galaxies using spectral energy distribution (SED) and spectral fitting techniques, and study the dependence of star formation rates (SFR), colours, and stellar ages on environment. Results. For r ≤ 20, the fraction of star-forming/blue galaxies, computed either from the specific-SFR (sSFR) or rest-frame colour, shows depletion within the cluster virial radii, where the number of galaxies with log (sSFR/ yr-1) > -12 and with (g - r) restframe < 0.6 is lower than in the field. For log(M ∗ Mo) ≥ 10.8, no trends with environment emerge, as massive galaxies are mostly already passive in all environments. No differences among low- and high-density field members and cluster members emerge in the sSFR-mass relation in the mass-complete regime. Finally, the luminosity-weighted age-mass relation of the passive populations within cluster virial radii show signatures of recent environmental quenching. Conclusions. The study of luminous and massive galaxies in this supercluster shows that while environment has a prominent role in determining the fractions of star-forming/blue galaxies, its effects on the star formation activity in star-forming galaxies are negligible.
  •  
26.
  • Heald, G., et al. (författare)
  • Magnetic Field Tomography in Nearby Galaxies with the Square Kilometre Array
  • 2015
  • Ingår i: Proceedings of Science. - 1824-8039. ; 9-13-June-2014
  • Konferensbidrag (refereegranskat)abstract
    • Magnetic fields play an important role in shaping the structure and evolution of the interstellarmedium (ISM) of galaxies, but the details of this relationship remain unclear. With SKA1, the 3Dstructure of galactic magnetic fields and its connection to star formation will be revealed. A highlysensitive probe of the internal structure of the magnetoionized ISM is the partial depolarizationof synchrotron radiation from inside the volume. Different configurations of magnetic field andionized gas within the resolution element of the telescope lead to frequency-dependent changesin the observed degree of polarization. The results of spectro-polarimetric observations are tiedto physical structure in the ISM through comparison with detailed modeling, supplemented withthe use of new analysis techniques that are being actively developed and studied within the communitysuch as Rotation Measure Synthesis. The SKA will enable this field to come into its ownand begin the study of the detailed structure of the magnetized ISM in a sample of nearby galaxies,thanks to its extraordinary wideband capabilities coupled with the combination of excellentsurface brightness sensitivity and angular resolution.
  •  
27.
  • Heald, G., et al. (författare)
  • Magnetism science with the square kilometre array
  • 2020
  • Ingår i: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
  •  
28.
  • Heesen, V., et al. (författare)
  • Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
  • Tidskriftsartikel (refereegranskat)abstract
    • Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc 2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC [(ΣSFR)hyb] a , where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > -0.65; Iν ν α ), the relation becomes almost linear at both frequencies with a 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l = 1-5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13-1.5) × 10 28 cm 2 s -1 at 1 GeV. Conclusions. A RC-SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z 10 using 140 MHz observations.
  •  
29.
  • Heesen, V., et al. (författare)
  • Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation
  • 2023
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 670
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The existence of magnetic fields in the circumgalactic medium (CGM) is largely unconstrained. Their detection is important as magnetic fields can have a significant impact on the evolution of the CGM, and, in turn, the fields can serve as tracers for dynamical processes in the CGM. Aims. Using the Faraday rotation of polarised background sources, we aim to detect a possible excess of the rotation measure in the surrounding area of nearby galaxies. Methods. We used 2461 residual rotation measures (RRMs) observed with the LOw Frequency ARray (LOFAR), where the foreground contribution from the Milky Way is subtracted. The RRMs were then studied around a subset of 183 nearby galaxies that was selected by apparent B-band magnitude. Results. We find that, in general, the RRMs show no significant excess for small impact parameters (i.e., the perpendicular distance to the line of sight). However, if we only consider galaxies at higher inclination angles and sightlines that pass close to the minor axis of the galaxies, we find significant excess at impact parameters of less than 100 kpc. The excess in |RRM| is 3.7 rad m-2 with an uncertainty between ±0.9 rad m-2 and ±1.3 rad m-2 depending on the statistical properties of the background (2.8σ - 4.1σ). With electron densities of ∼10-4 cm-3, this suggests magnetic field strengths of a few tenths of a microgauss. Conclusions. Our results suggest a slow decrease in the magnetic field strength with distance from the galactic disc, as expected if the CGM is magnetised by galactic winds and outflows.
  •  
30.
  • Heesen, V., et al. (författare)
  • Exploring the making of a galactic wind in the starbursting dwarf irregular galaxy IC 10 with LOFAR
  • 2018
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:2, s. 1756-1764
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role; they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby starburst dwarf irregular galaxy IC 10 using observations at 140MHz with the Low-Frequency Array (LOFAR), at 1580MHz with the Very Large Array (VLA), and at 6200MHz with the VLA and the 100-m Effelsberg telescope.We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic ray transport models for pure diffusion and advection.We find that a diffusion model fits best, with a diffusion coefficient of D = (0.4-0.8) × 10 26 (E/GeV) 0.5 cm 2 s -1 , which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of ≈50 km s -1 , as expected for a cosmic ray-driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc-halo interface.
  •  
31.
  • Heesen, V, et al. (författare)
  • Nearby galaxies in the LOFAR Two-metre Sky Survey I. Insights into the non-linearity of the radio-SFR relation
  • 2022
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 664
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Cosmic rays and magnetic fields are key ingredients in galaxy evolution, regulating both stellar feedback and star formation. Their properties can be studied with low-frequency radio continuum observations that are free from thermal contamination. Aims. We define a sample of 76 nearby (<30 Mpc) galaxies with rich ancillary data in the radio continuum and infrared from the CHANG-ES and KINGFISH surveys, which will be observed with the LOFAR Two-metre Sky Survey (LoTSS) at 144 MHz. Methods. We present maps for 45 of them as part of the LoTSS data release 2 (LoTSS-DR2), where we measure integrated flux densities and study integrated and spatially resolved radio spectral indices. We investigate the radio-star formation rate (SFR) relation using SFRs derived from total infrared and H alpha + 24-mu m emission. Results. The radio-SFR relation at 144 MHz is clearly super-linear with L-144mHz proportional to SFR1,4-1,5. The mean integrated radio spectral index between 144 and approximate to 1400 MHz is = -0.56 +/- 0.14, in agreement with the injection spectral index for cosmic ray electrons (CRE5). However, the radio spectral index maps show variation of spectral indices with flatter spectra associated with star-forming regions and steeper spectra in galaxy outskirts and, in particular, in extra-planar regions. We found that galaxies with high SFRs have steeper radio spectra; we find similar correlations with galaxy size, mass, and rotation speed. Conclusions. Galaxies that are larger and more massive are better electron calorimeters, meaning that the CRE lose a higher fraction of their energy within the galaxies. This explains the super-linear radio-SFR relation, with more massive, star-forming galaxies being radio bright. We propose a semi-calorimetric radio-SFR relation that employs the galaxy mass as a proxy for the calorimetric efficiency.
  •  
32.
  • Heesen, Volker, et al. (författare)
  • Stellar feedback in dwarf irregular galaxies with radio continuum observations
  • 2019
  • Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 14:S344, s. 255-258
  • Konferensbidrag (refereegranskat)abstract
    • Low-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind.
  •  
33.
  • Heesen, V, et al. (författare)
  • Warped diffusive radio halo around the quiescent spiral edge-on galaxy NGC 4565
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
  • Tidskriftsartikel (refereegranskat)abstract
    • Context . Cosmic rays play a pivotal role in launching galactic winds, particularly in quiescently star-forming galaxies where the hot gas alone is not sufficient to drive a wind. Except for the Milky Way, not much is known about the transport of cosmic rays in galaxies. Aims. In this Letter, we present low-frequency observations of the nearby edge-on spiral galaxy NGC 4565 using the LOw-Frequency ARray (LOFAR). With our deep 144 MHz observations, we obtain a clean estimate of the emission originating from old cosmic-ray electrons (CRe), which is almost free from contamination by thermal emission. Methods . We measured vertical profiles of the non-thermal radio continuum emission that we fitted with Gaussian and exponential functions. The different profile shapes correspond to 1D cosmic-ray transport models of pure diffusion and advection, respectively. Results. We detect a warp in the radio continuum that is reminiscent of the previously known H I warp. Because the warp is not seen at GHz-frequencies in the radio continuum, its minimum age must be about 100 Myr. The warp also explains the slight flaring of the thick radio disc that can otherwise be well described by a Gaussian profile with an FWHM of 65 arcsec (3.7 kpc). Conclusions . The diffusive radio halo together with the extra-planar X-ray emission may be remnants of enhanced star-forming activity in the past where the galaxy had a galactic wind, as GHz-observations indicate only a weak outflow in the last 40 Myr. NGC 4565 could be in transition from an outflow-to an inflow-dominated phase.
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34.
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35.
  • Horellou, Cathy, 1967, et al. (författare)
  • Dark Energy and the Evolution of Spherical Overdensities
  • 2004
  • Ingår i: Proceedings of XXXIXth Rencontres de Moriond, La Thuile, Italy, Mar. 28-Apr. 4, 2004, eds. Y. Giraud-Héraud, J. Trân Thanh Vân. ; , s. 155-
  • Konferensbidrag (refereegranskat)
  •  
36.
  •  
37.
  • Horellou, Cathy, 1967, et al. (författare)
  • Gas and Star Formation in the Interacting Galaxies NGC 6872/IC 4970
  • 2004
  • Ingår i: in Proceedings of "The Neutral ISM in Starburst Galaxies", Marstrand, June 2003, eds. Aalto S., Huettemeister S., Pedlar A., Astronomical Society of the Pacific Conf. Series, San Francisco. - 1583811826 ; , s. 69-72
  • Konferensbidrag (refereegranskat)
  •  
38.
  • Horellou, Cathy, 1967 (författare)
  • Leve The Big Bang Theory!
  • 2011
  • Ingår i: Populär astronomi. ; :3, s. 24-25
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
  •  
39.
  • Horellou, Cathy, 1967, et al. (författare)
  • Magnetic field tomography, helical magnetic fields and Faraday depolarization
  • 2014
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 441:3, s. 2049-2057
  • Tidskriftsartikel (refereegranskat)abstract
    • Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three-dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along the wave's propagation path to the observer). In order to proceed, reliable methods are required for inverting the signals observed in wavelength space into useful data in Faraday space, with robust estimates of their uncertainty. In this paper, we examine how variations of the intrinsic angle of polarized emission psi(0) with the Faraday depth phi within a source affect the observable quantities. Using simple models for the Faraday dispersion F(phi) and psi(0)(phi), along with the current and planned properties of the main radio interferometers, we demonstrate how degeneracies among the parameters describing the magneto-ionic medium can be minimized by combining observations in different wavebands. We also discuss how depolarization by Faraday dispersion due to a random component of the magnetic field attenuates the variations in the spectral energy distribution of the polarization and shifts its peak towards shorter wavelengths. This additional effect reduces the prospect of recovering the characteristics of the magnetic field helicity in magneto-ionic media dominated by the turbulent component of the magnetic field.
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40.
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41.
  • Horellou, Cathy, 1967, et al. (författare)
  • Sicken attans liten söt antenn!
  • 2008
  • Ingår i: Populär Astronomi. - 1650-7177. ; 9:4, s. 28-29
  • Tidskriftsartikel (refereegranskat)
  •  
42.
  •  
43.
  •  
44.
  • Horellou, Cathy, 1967, et al. (författare)
  • The XXL Survey: XXXIV. Double Irony in XXL-North: A tale of two radio galaxies in a supercluster at z = 0.14
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We show how the XXL multiwavelength survey can be used to shed light on radio galaxies and their environment. Methods. Two prominent radio galaxies were identified in a visual examination of the mosaic of XXL-North obtained with the Giant Metrewave Radio Telescope at 610 MHz. Counterparts were searched for in other bands. Spectroscopic redshifts from the GAMA database were used to identify clusters and/or groups of galaxies, estimate their masses with the caustic method, and quantify anisotropies in the surrounding galaxy distribution via a Fourier analysis. Results. Both radio galaxies are of FR I type and are hosted by early-type galaxies at a redshift of 0.138. The first radio source, named the Exemplar, has a physical extent of ∼400 kpc; it is located in the cluster XLSSC 112, which has a temperature of ∼2 keV, a total mass of ∼1014 Mo, and resides in an XXL supercluster with eight known members. The second source, named the Double Irony, is a giant radio galaxy with a total length of about 1.1 Mpc. Its core coincides with a cataloged point-like X-ray source, but no extended X-ray emission from a surrounding galaxy cluster was detected. However, from the optical data we determined that the host is the brightest galaxy in a group that is younger, less virialized, and less massive than the Exemplar's cluster. A friends-of-friends analysis showed that the Double Irony's group is a member of the same supercluster as the Exemplar. There are indications that the jets and plumes of the Double Irony have been deflected by gas associated with the surrounding galaxy distribution. Another overdensity of galaxies (the tenth) containing a radio galaxy was found to be associated with the supercluster. Conclusions. Radio Galaxies can be used to find galaxy clusters/groups that are below the current sensitivity of X-ray surveys.
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45.
  • Iacobelli, M., et al. (författare)
  • Studying Galactic interstellar turbulence through fluctuations in synchrotron emission: First LOFAR Galactic foreground detection
  • 2013
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 558, s. 721-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. The characteristic outer scale of turbulence (i.e. the scale at which the dominant source of turbulence injects energy to the interstellar medium) and the ratio of the random to ordered components of the magnetic field are key parameters to characterise magnetic turbulence in the interstellar gas, which affects the propagation of cosmic rays within the Galaxy. We provide new constraints to those two parameters. Methods. We use the LOw Frequency ARray (LOFAR) to image the diffuse continuum emission in the Fan region at (l,b) ∼ (137.0, +7.0) at 80′′ × 70′′ resolution in the range [146, 174] MHz. We detect multi-scale fluctuations in the Galactic synchrotron emission and compute their power spectrum. Applying theoretical estimates and derivations from the literature for the first time, we derive the outer scale of turbulence and the ratio of random to ordered magnetic field from the characteristics of these fluctuations. Results. We obtain the deepest image of the Fan region to date and find diffuse continuum emission within the primary beam. The power spectrum displays a power law behaviour for scales between 100 and 8 arcmin with a slope α =-1.84 ± 0.19. We find an upper limit of ∼20 pc for the outer scale of the magnetic interstellar turbulence toward the Fan region, which is in agreement with previous estimates in literature. We also find a variation of the ratio of random to ordered field as a function of Galactic coordinates, supporting different turbulent regimes. Conclusions. We present the first LOFAR detection and imaging of the Galactic diffuse synchrotron emission around 160 MHz from the highly polarized Fan region. The power spectrum of the foreground synchrotron fluctuations is approximately a power law with a slope α ≈-1.84 up to angular multipoles of ≤1300, corresponding to an angular scale of ∼8 arcmin. We use power spectra fluctuations from LOFAR as well as earlier GMRT and WSRT observations to constrain the outer scale of turbulence (Lout) of the Galactic synchrotron foreground, finding a range of plausible values of 10-20 pc. Then, we use this information to deduce lower limits of the ratio of ordered to random magnetic field strength. These are found to be 0.3, 0.3, and 0.5 for the LOFAR, WSRT and GMRT fields considered respectively. Both these constraints are in agreement with previous estimates. © 2013 ESO.
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46.
  • Johansson, Daniel, 1980, et al. (författare)
  • A LABOCA survey of submillimeter galaxies behind galaxy clusters
  • 2011
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 527:14
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Submillimeter galaxies are a population of dusty star-forming galaxies at high redshift. Measuring their properties will help relate them to other types of galaxies, both at high and low redshift. This is needed in order to understand the formation and evolution of galaxies.Aims. The aim is to use gravitational lensing by galaxy clusters to probe the faint and abundant submillimeter galaxy population down to a lower flux density level than what can be achieved in blank-field observations.Methods. We use the LABOCA bolometer camera on the APEX telescope to observe five clusters of galaxies at a wavelength of 870 μm. The final maps have an angular resolution of 27.5" and a point source noise level of 1.2–2.2 mJy. We model the mass distribution in the clusters as superpositions of spherical NFW halos and derive magnification maps that we use to calculate intrinsic flux densities as well as area-weighted number counts. We also use the positions of Spitzer MIPS 24 μm sources in four of the fields for a stacking analysis.Context. Submillimeter galaxies are a population of dusty star-forming galaxies at high redshift. Measuring their properties will help relate them to other types of galaxies, both at high and low redshift. This is needed in order to understand the formation and evolution of galaxies.Aims. The aim is to use gravitational lensing by galaxy clusters to probe the faint and abundant submillimeter galaxy population down to a lower flux density level than what can be achieved in blank-field observations.Methods. We use the LABOCA bolometer camera on the APEX telescope to observe five clusters of galaxies at a wavelength of 870 μm. The final maps have an angular resolution of 27.5" and a point source noise level of 1.2–2.2 mJy. We model the mass distribution in the clusters as superpositions of spherical NFW halos and derive magnification maps that we use to calculate intrinsic flux densities as well as area-weighted number counts. We also use the positions of Spitzer MIPS 24 μm sources in four of the fields for a stacking analysis.Results. We detected 37 submm sources, out of which 14 have not been previously reported. One source has a sub-mJy intrinsic flux density. The derived number counts are consistent with previous results, after correction for gravitational magnification and completeness levels. The stacking analysis reveals an intrinsic 870 μm signal of 390 ± 27 μJy at 14.5σ significance. We study the S24 μm–S870 μm relation by stacking on subsamples of the 24 μm sources and find a linear relation at S24 μm
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47.
  • Johansson, Daniel, 1980, et al. (författare)
  • Molecular gas and dust in the highly magnified z similar to 2.8 galaxy behind the Bullet Cluster
  • 2012
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 543, s. Article Number: A62 (pp. 1-10)
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The gravitational magnification provided by massive galaxy clusters makes it possible to probe the physical conditions in distant galaxies that are of lower luminosity than those in blank fields and likely more representative of the bulk of the high-redshift galaxy population. Aims. We aim to constrain the basic properties of molecular gas in a strongly magnified submm galaxy located behind the massive Bullet Cluster (1E 0657-56). This galaxy (SMM J0658) is split into three images, with a total magnification factor of almost 100. Methods. We used the Australia Telescope Compact Array (ATCA) to search for (CO)-C-12(1-0) and (CO)-C-12(3-2) line emission from SMM J0658. We also used the SABOCA bolometer camera on the Atacama Pathfinder EXperiment (APEX) telescope to measure the continuum emission at 350 mu m. Results. CO(1-0) and CO(3-2) are detected at 6.8 sigma and 7.5 sigma significance when the spectra toward the two brightest images of the galaxy are combined. From the CO(1-0) luminosity we derive a mass of cold molecular gas of (1.8 +/- 0.3) x 10(9) M-circle dot, using the CO to H-2 conversion factor commonly used for luminous infrared galaxies. This is 45 +/- 25% of the stellar mass. From the width of the CO lines we derive a dynamical mass within the CO-emitting region L of (1.3 +/- 0.4) x 10(10)(L/1 kpc) M-circle dot. We refine the redshift determination of SMM J0658 to z = 2.7793 +/- 0.0003. The CO(3-2) to CO(1-0) brightness temperature ratio is 0.56(-0.15)(+0.21), which is similar to the values found in other star-forming galaxies. Continuum emission at 350 mu m from SMM J0658 was detected with SABOCA at a signal-to-noise ratio of 3.6. The flux density is consistent with previous measurements at the same wavelength by the Herschel satellite and BLAST balloon-borne telescope. We study the spectral energy distribution of SMM J0658 and derive a dust temperature of 33 +/- 5 K and a dust mass of 1.1(-0.3)(+0.8) x 10(7) M-circle dot. Conclusions. SMM J0658 is one of the least massive submm galaxies discovered so far. As a likely representative of the bulk of the submm galaxy population, it is a prime target for future observations.
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48.
  • Johansson, Daniel, 1980, et al. (författare)
  • Submillimeter galaxies behind the Bullet cluster (1E 0657-56)
  • 2010
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 514:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Clusters of galaxies are effective gravitational lenses able to magnify background galaxies and making it possible to probe the fainter part of the galaxy population. Submillimeter galaxies, which are believed to be star-forming galaxies at typical redshifts of 2 to 3, are a major contaminant to the extended Sunyaev-Zeldovich (SZ) signal of galaxy clusters. For a proper quantification of the SZ signal the contribution of submillimeter galaxies needs to be quantified. Aims. The aims of this study are to identify submillimeter sources in the field of the Bullet cluster (1E 0657-56), a massive cluster of galaxies at z similar or equal to 0.3, measure their flux densities at 870 mu m, and search for counterparts at other wavelengths to constrain their properties. Methods. We carried out deep observations of the submillimeter continuum emission at 870 mu m using the Large APEX BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope. Several numerical techniques were used to quantify the noise properties of the data and extract sources. Results. In total, seventeen sources were found. Thirteen of them lie in the central 10 arcmin of the map, which has a pixel sensitivity of 1.2 mJy per 22 '' beam. After correction for flux boosting and gravitational lensing, the number counts are consistent with published submm measurements. Nine of the sources have infrared counterparts in Spitzer maps. The strongest submm detection coincides with a source previously reported at other wavelengths, at an estimated redshift z similar or equal to 2.7. If the submm flux arises from two images of a galaxy magnified by a total factor of 75, as models have suggested, its intrinsic flux would be around 0.6 mJy, consistent with an intrinsic luminosity below 10(12) L-circle dot.
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49.
  • Kierdorf, M., et al. (författare)
  • The magnetized disk-halo transition region of M 51
  • 2020
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 642
  • Tidskriftsartikel (refereegranskat)abstract
    • The grand-design face-on spiral galaxy M 51 is an excellent laboratory for studying magnetic fields in galaxies. Due to wavelength-dependent Faraday depolarization, linearly polarized synchrotron emission at different radio frequencies yields a picture of the galaxy at different depths: observations in the L-band (1-2 GHz) probe the halo region, while at 4.85 GHz (C-band) and 8.35 GHz (X-band), the linearly polarized emission mostly emerges from the disk region of M 51. We present new observations of M 51 using the Karl G. Jansky Very Large Array at the intermediate frequency range of the S-band (2-4 GHz), where previously no high-resolution broadband polarization observations existed, to shed new light on the transition region between the disk and the halo. We present the S-band radio images of the distributions of the total intensity, polarized intensity, degree of polarization, and rotation measure (RM). The RM distribution in the S-band shows a fluctuating pattern without any apparent large-scale structure. We discuss a model of the depolarization of synchrotron radiation in a multi-layer magneto-ionic medium and compare the model predictions to the multi-frequency polarization data of M 51 between 1-8 GHz. The model makes distinct predictions of a two-layer (disk-halo) and three-layer (far-side halo "disk"near-side halo) system. Since the model predictions strongly differ within the wavelength range of the S-band, the new S-band data are essential for distinguishing between the different systems. A two-layer model of M 51 is preferred. The parameters of the model are adjusted to fit to the data of polarization fractions in a few selected regions. In three spiral arm regions, the turbulent field in the disk dominates with strengths between 18 μG and 24 μG, while the regular field strengths are 8 - 16 μG. In one inter-arm region, the regular field strength of 18 μG exceeds that of the turbulent field of 11 μG. The regular field strengths in the halo are 3 - 5 μG. The observed RMs in the disk-halo transition region are probably dominated by tangled regular fields, as predicted from models of evolving dynamos, and/or vertical fields, as predicted from numerical simulations of Parker instabilities or galactic winds. Both types of magnetic fields have frequent reversals on scales similar to or larger than the beam size (∼550 pc) that contribute to an increase of the RM dispersion and to distortions of any large-scale pattern of the regular field. Our study devises new ways of analyzing and interpreting broadband multi-frequency polarization data that will be applicable to future data from, for example, the Square Kilometre Array.
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50.
  • Kolokythas, Konstantinos, et al. (författare)
  • Evidence of AGN feedback and sloshing in the X-ray luminous NGC 1550 galaxy group
  • 2020
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 496:2, s. 1471-1487
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results from Giant Metrewave Radio Telescope and Chandra observations of the NGC 1550 galaxy group. Although previously thought of as relaxed, we show evidence that gas sloshing and active galactic nucleus (AGN) heating have affected the structure of the system. The 610 and 235 MHz radio images show an asymmetric jet-lobe structure with a total size of similar to 33 kpc, with a sharp kink at the base of the more extended western jet, and bending of the shorter eastern jet as it enters the lobe. The 235-610 MHz spectral index map shows that both radio lobes have steep spectral indices (alpha(610)(235) >= -1.5), indicating the presence of an old electron population. The X-ray images reveal an asymmetric structure in the hot gas correlated with the radio structure, as well as potential cavities coincident with the radio lobes, with rims and arms of gas that may have been uplifted by the cavity expansion. The X-ray residual map reveals an arc-shaped structure to the east that resembles a sloshing cold front. Radio spectral analysis suggests a radiative age of about 33 Myr for the source, comparable to the sloshing time-scale and dynamical estimates of the age of the lobes. An estimate of the mechanical energy required to inflate the cavities suggests that the AGN of NGC 1550 is capable of balancing radiative losses from the intragroup medium (IGM) and preventing excessive cooling, providing that the AGN jets are efficiently coupled to the IGM gas. In conclusion, we find evidence of sloshing motions from both radio and X-ray structures, suggesting that NGC 1550 was perturbed by a minor merger or infalling galaxy about 33 Myr ago.
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