| 1. |
- Adam, R. M., et al.
(författare)
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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
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 684
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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)
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The XXL Survey VIII. MUSE characterisation of intracluster light in a z similar to 0.53 cluster of galaxies
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:A7
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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)
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The XXL Survey: XX. The 365 cluster catalogue
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
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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)
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Radioastronomy for students
- 2005
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Ingår i: International Amateur-Professional Photoelectric Photometry Communications, Proceedings of `Global Hands-On Universe 2004", St. Petersburg, Russia, July 2004. ; 100, s. 49-54
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Asabere, B. D., et al.
(författare)
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Mid-infrared dust in two nearby radio galaxies, NGC 1316 (Fornax A) and NGC 612 (PKS 0131-36)
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592:A20, s. 1-16
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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)
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Radio astronomy in Africa: the case of Ghana
- 2015
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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
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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)
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CONSTRAINS ON THE QUINTESSENCE FROM OBSERVATIONAL DATA
- 2011
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Ingår i: Romanian Reports on Physics. - 1221-1451 .- 1841-8759. ; 63:3, s. 852-861
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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)
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The XXL Survey IX. Optical overdensity and radio continuum analysis of a supercluster at z=0.43
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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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)
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Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 519:Article Number: A29
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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)
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Structure, dynamical impact and origin of magnetic fields in nearby galaxies in the SKA era
- 2015
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Ingår i: Proceedings of Science. - 1824-8039. ; 9-13-June-2014
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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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