| 1. |
- Jolly, Jean Baptiste, 1990, et al.
(författare)
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LINESTACKER: A spectral line stacking tool for interferometric data
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:3, s. 3992-4010
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Tidskriftsartikel (refereegranskat)abstract
- LINESTACKER is a new open access and open source tool for stacking of spectral lines in interferometric data. LINESTACKER is an ensemble of CASA tasks, and can stack both 3D cubes or already extracted spectra. The algorithm is tested on increasingly complex simulated data sets, mimicking Atacama Large Millimeter/submillimeter Array, and Karl G. Jansky Very Large Array observations of [C II] and CO(3-2) emission lines, from z ∼ 7 and z ∼ 4 galaxies, respectively. We find that the algorithm is very robust, successfully retrieving the input parameters of the stacked lines in all cases with an accuracy ≳90 per cent. However, we distinguish some specific situations showcasing the intrinsic limitations of the method. Mainly that high uncertainties on the redshifts (∆z > 0.01) can lead to poor signal-to-noise ratio improvement, due to lines being stacked on shifted central frequencies. Additionally, we give an extensive description of the embedded statistical tools included in LINESTACKER: mainly bootstrapping, rebinning, and subsampling. Velocity rebinning is applied on the data before stacking and proves necessary when studying line profiles, in order to avoid artificial spectral features in the stack. Subsampling is useful to sort the stacked sources, allowing to find a subsample maximizing the searched parameters, while bootstrapping allows to detect inhomogeneities in the stacked sample. LINESTACKER is a useful tool for extracting the most from spectral observations of various types.
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| 2. |
- Stanley, Flora, 1990, et al.
(författare)
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A spectral stacking analysis to search for faint outflow signatures in z ∼6 quasars
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms that potentially affect the evolution of the host galaxy. However, systematic millimetre (mm) observations of outflows are only now becoming possible with the advent of sensitive mm telescopes. In this study we used spectral stacking methods to search for a faint high-velocity outflow signal in a sample of [C II] detected, z ∼ 6 quasars. Methods. We searched for broad emission line signatures from high-velocity outflows for a sample of 26 ∼ 6 quasars observed with the Atacama Large Millimeter Array (ALMA), with a detection of the [C II] line. The observed emission lines of the sources are dominated by the host galaxy, and outflow emission is not detected for the individual sources. We used a spectral line stacking analysis developed for interferometric data to search for outflow emission. We stacked both extracted spectra and the full spectral cubes. We also investigated the possibility that only a sub-set of our sample contributes to the stacked outflow emission. Results. We find only a tentative detection of a broad emission line component in the stacked spectra. When taking a region of about 2″ around the central position of the stacked cubes, the stacked line shows an excess emission due to a broad component of 1.1-1.5σ, but the significance drops to 0.4-0.7σ when stacking the extracted spectra from a smaller region. The broad component can be characterised by a line width of full width at half-maximum FWHM > 700 km s-1. Furthermore, we find a sub-sample of 12 sources, the stack of which maximises the broad component emission. The stack of this sub-sample shows an excess emission due to a broad component of 1.2-2.5σ. The stacked line of these sources has a broad component of FWHM > 775 km s-1. Conclusions. We find evidence suggesting the presence of outflows in a sub-sample of 12 out of 26 sources, which demonstrates the importance of spectral stacking techniques in tracing faint signal in galaxy samples. However, deeper ALMA observations are necessary to confirm the presence of a broad component in the individual spectra.
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| 3. |
- Bernhard, E., et al.
(författare)
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Evidence for a mass-dependent AGN Eddington ratio distribution via the flat relationship between SFR and AGN luminosity
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:1, s. 436-450
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Tidskriftsartikel (refereegranskat)abstract
- The lack of a strong correlation between AGN X-ray luminosity (L-X; a proxy for AGN power) and the star formation rate (SFR) of their host galaxies has recently been attributed to stochastic AGN variability. Studies using population synthesis models have incorporated this by assuming a broad, universal (i.e. does not depend on the host galaxy properties) probability distribution for AGN specific X-ray luminosities (i.e. the ratio of L-X to host stellar mass; a common proxy for Eddington ratio). However, recent studies have demonstrated that this universal Eddington ratio distribution fails to reproduce the observed X-ray luminosity functions beyond z similar to 1.2. Furthermore, empirical studies have recently shown that the Eddington ratio distribution may instead depend upon host galaxy properties, such as SFR and/or stellar mass. To investigate this further, we develop a population synthesis model in which the Eddington ratio distribution is different for star-forming and quiescent host galaxies. We show that, although this model is able to reproduce the observed X-ray luminosity functions out to z similar to 2, it fails to simultaneously reproduce the observed flat relationship between SFR and X-ray luminosity. We can solve this, however, by incorporating a mass dependency in the AGN Eddington ratio distribution for star-forming host galaxies. Overall, our models indicate that a relative suppression of low Eddington ratios (lambda(Edd) less than or similar to 0.1) in lower mass galaxies (M-* less than or similar to 10(10-11)M(circle dot)) is required to reproduce both the observed X-ray luminosity functions and the observed flat SFR/X-ray relationship.
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| 4. |
- Del Moro, Agnese, et al.
(författare)
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Luminous and Obscured Quasars and Their Host Galaxies
- 2018
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The most heavily-obscured, luminous quasars might represent a specific phase of the evolution of the actively accreting supermassive black holes and their host galaxies, possibly related to mergers. We investigated a sample of the most luminous quasars at z approximate to 1 - 3 in the GOODS fields, selected in the mid-infrared band through detailed spectral energy distribution (SED) decomposition. The vast majority of these quasars (-80%) are obscured in the X-ray band and 30% of them to such an extent, that they are undetected in some of the deepest (2 and 4 Ms) Chandra X-ray data. Although no clear relation is found between the star-formation rate of the host galaxies and the X-ray obscuration, we find a higher incidence of heavily-obscured quasars in disturbed/merging galaxies compared to the unobscured ones, thus possibly representing an earlier stage of evolution, after which the system is relaxing and becoming unobscured.
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| 5. |
- Falstad, Niklas, 1987, et al.
(författare)
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CON-quest: Searching for the most obscured galaxy nuclei
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 649
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Tidskriftsartikel (refereegranskat)abstract
- Context. Some luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) host extremely compact (r < 100 pc) and dusty nuclei. The high extinction associated with large column densities of gas and dust toward these objects render them hard to detect at many wavelengths. The intense infrared radiation arising from warm dust in these sources can provide a significant fraction of the bolometric luminosity of the galaxy and is prone to excite vibrational levels of molecules such as HCN. This results in emission from the rotational transitions of vibrationally excited HCN (HCN-vib); the brightest emission is found in compact obscured nuclei (CONs; ςHCN-vib > 1 L⊙ pc-2 in the J = 3-2 transition). However, there have been no systematic searches for CONs, and it is unknown how common they are. Aims. We aim to establish how common CONs are in the local Universe (z < 0.08), and whether their prevalence depends on the luminosity or other properties of the host galaxy. Methods. We conducted an Atacama Large Millimeter/submillimeter Array survey of the rotational J = 3-2 transition of HCN-vib in a volume-limited sample of 46 far-infrared luminous galaxies. Results. Compact obscured nuclei are identified in 38-13+18% of the ULIRGs, 21-6+12% of the LIRGs, and 0-0+9% of the lower luminosity galaxies. We find no dependence on the inclination of the host galaxy, but strong evidence of lower IRAS 25 μm to 60 μm flux density ratios (f25/f60) in CONs (with the exception of one galaxy, NGC 4418) compared to the rest of the sample. Furthermore, we find that CONs have stronger silicate features (s9.7 μm), but similar polycyclic aromatic hydrocarbon equivalent widths (EQW6.2 μm) compared to other galaxies. Along with signatures of molecular inflows seen in the far-infrared in most CONs, submillimeter observations also reveal compact, often collimated, outflows. Conclusions. In the local Universe, CONs are primarily found in (U)LIRGs, in which they are remarkably common. As such systems are often highly disturbed, inclinations are difficult to estimate, and high-resolution continuum observations of the individual nuclei are required to determine if the CON phenomenon is related to the inclinations of the nuclear disks. Further studies of the in- A nd outflow properties of CONs should also be conducted to investigate how these are connected to each other and to the CON phenomenon. The lower f25/f60 ratios in CONs as well as the results for the mid-infrared diagnostics investigated (EQW6.2 μm and s9.7 μm) are consistent with the notion that large dust columns gradually shift the radiation from the hot nucleus to longer wavelengths, making the mid- A nd far-infrared "photospheres"significantly cooler than the interior regions. Finally, to assess the importance of CONs in the context of galaxy evolution, it is necessary to extend this study to higher redshifts where (U)LIRGs are more common.
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| 6. |
- Grimmett, L. P., et al.
(författare)
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A binning-free method reveals a continuous relationship between galaxies' AGN power and offset from main sequence
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 495:1, s. 1392-1402
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Tidskriftsartikel (refereegranskat)abstract
- Studies investigating the relationship between active galactic nucleus (AGN) power and the star formation rates (SFRs) of their host galaxies often rely on averaging techniques - such as stacking - to incorporate information from non-detections. However, averages, and especially means, can be strongly affected by outliers and can therefore give a misleading indication of the 'typical' case. Recently, a number of studies have taken a step further by binning their sample in terms of AGN power (approximated by the 2-10 keV luminosity of the AGN), and investigating how the SFR distribution differs between these bins. These bin thresholds are often weakly motivated, and binning implicitly assumes that sources within the same bin have similar (or even identical) properties. In this paper, we investigate whether the distribution of host SFRs - relative to the locus of the star-forming main sequence (i.e. RMS) - changes continuously as a function of AGN power. We achieve this by using a hierarchical Bayesian model that completely removes the need to bin in AGN power. In doing so, we find strong evidence that the RMS distribution changes with 2-10 keV X-ray luminosity. The results suggest that higher X-ray luminosity AGNs have a tighter physical connection to the star-forming process than lower X-ray luminosity AGNs, at least within the 0.8 < z< 1.2 redshift range considered here.
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| 7. |
- Harrison, C. M., et al.
(författare)
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Do AGN really suppress star formation?
- 2019
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 15, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- Active galactic nuclei (AGN) are believed to regulate star formation inside their host galaxies through "AGN feedback". We summarise our on-going study of luminous AGN (z ∼0.2-3; LAGN,bol 1043 erg s-1), which is designed to search for observational signatures of feedback by combining observed star-formation rate (SFR) measurements from statistical samples with cosmological model predictions. Using the EAGLE hydrodynamical cosmological simulations, in combination with our Herschel + ALMA surveys, we show that - even in the presence of AGN feedback - we do not necessarily expect to see any relationships between average galaxy-wide SFRs and instantaneous AGN luminosities. We caution that the correlation with stellar mass for both SFR and AGN luminosity can contribute to apparent observed positive trends between these two quantities. On the other hand, the EAGLE simulations, which reproduce our observations, predict that a signature of AGN feedback can be seen in the wide specific SFR distributions of all massive galaxies (not just AGN hosts). Overall, whilst we can not rule out that AGN have an immediate small-scale impact on in-situ star-formation, all of our results are consistent with a feedback model where galaxy-wide in-situ star formation is not rapidly suppressed by AGN, but where the feedback likely acts over a longer timescale than a single AGN episode.
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| 8. |
- Lindroos, Lukas, 1986, et al.
(författare)
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Measuring size evolution of distant, faint galaxies in the radio regime
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:3, s. 3544-3554
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Tidskriftsartikel (refereegranskat)abstract
- We measure the evolution of sizes for star-forming galaxies as seen in 1.4 GHz continuum radio for z = 0-3. The measurements are based on combined VLA+MERLIN data of the Hubble Deep Field, and using a uv-stacking algorithm combined with model fitting to estimate the average sizes of galaxies. A sample of similar to 1000 star-forming galaxies is selected from optical and near-infrared catalogues, with stellar masses Me-circle dot approximate to 10(10)-10(11) M-circle dot and photometric redshifts 0-3. The median sizes are parametrized for stellar mass M-* = 5 x 10(10) M-circle dot as R-e = A x (H(z)/H(1.5))(alpha z). We find that the median radio sizes evolve towards larger sizes at later times with alpha(z) = 1.1 +/- 0.6, and A (the median size at z approximate to 1.5) is found to be 0 ''.26 +/- 0 ''.07 or 2.3 +/- 0.6 kpc. The measured radio sizes are typically a factor of 2 smaller than those measure in the optical, and are also smaller than the typical H alpha sizes in the literature. This indicates that star formation, as traced by the radio continuum, is typically concentrated towards the centre of galaxies, for the sampled redshift range. Furthermore, the discrepancy of measured sizes from different tracers of star formation, indicates the need for models of size evolution to adopt a multiwavelength approach in the measurement of the sizes star-forming regions.
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| 9. |
- Scholtz, J., et al.
(författare)
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Identifying the subtle signatures of feedback from distant AGN using ALMA observations and the EAGLE hydrodynamical simulations
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 475:1, s. 1288-1305
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Tidskriftsartikel (refereegranskat)abstract
- We present sensitive 870 μm continuum measurements from our ALMA programmes of 114 X-ray selected active galactic nuclei (AGN) in the Chandra Deep Field-South and Cosmic Evolution Survey fields. We use these observations in combination with data from Spitzer and Herschel to construct a sample of 86 X-ray selected AGN, 63 with ALMA constraints at Ζ = 1.5-3.2 with stellar mass > 2 × 10 10 M ⊙ . We constructed broad-band spectral energy distributions in the infrared band (8-1000 μm) and constrain star-formation rates (SFRs) uncontaminated by the AGN. Using a hierarchical Bayesian method that takes into account the information from upper limits, we fit SFR and specific SFR (sSFR) distributions. We explore these distributions as a function of both X-ray luminosity and stellar mass. We compare our measurements to two versions of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical simulations: the reference model withAGNfeedback and the model without AGN. We find good agreement between the observations and that predicted by the EAGLE reference model for the modes and widths of the sSFR distributions as a function of both X-ray luminosity and stellar mass; however, we found that the EAGLE model without AGN feedback predicts a significantly narrower width when compared to the data. Overall, from the combination of the observations with the model predictions, we conclude that (1) even with AGN feedback, we expect no strong relationship between the sSFR distribution parameters and instantaneous AGN luminosity and (2) a signature of AGN feedback is a broad distribution of sSFRs for all galaxies (not just those hosting an AGN) with stellar masses above ≈10 10 M ⊙ .
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| 10. |
- Scholtz, Jan, 1992, et al.
(författare)
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The impact of ionized outflows from z - 2.5 quasars is not through instantaneous in situ quenching: The evidence from ALMA and VLT/SINFONI
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 505:4, s. 5469-5487
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Tidskriftsartikel (refereegranskat)abstract
- We present high-resolution (-2.4 kpc) ALMA band 7 observations (rest-frame λ - 250 μm) of three powerful z - 2.5 quasars (Lbol = 1047.3–1047.5 erg s−1). These targets have previously been reported as showing evidence for suppressed star formation based on cavities in the narrow H α emission at the location of outflows traced with [O III] emission. Here, we combine the ALMA observations with a re-analysis of the VLT/SINFONI data to map the rest-frame far-infrared emission, H α emission, and [O III] emission. In all targets, we observe high velocity [O III] gas (i.e. W80 - 1000–2000 km s−1) across the whole galaxy. We do not identify any H α emission that is free from contamination from AGN-related processes; however, based on SED analyses, we show that the ALMA data contain a significant dust-obscured star formation component in two out of the three systems. This dust emission is found to be extended over ≈1.5–5.5 kpc in the nuclear regions, overlaps with the previously reported H α cavities and is co-spatial with the peak in surface brightness of the [O III] outflows. In summary, within the resolution and sensitivity limits of the data, we do not see any evidence for a instantaneous shut down of in situ star formation caused directly by the outflows. However, similar to the conclusions of previous studies and based on our measured star formation rates, we do not rule out that the global host galaxy star formation could be suppressed on longer time-scales by the cumulative effect of quasar episodes during the growth of these massive black holes.
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