Observing the host galaxies of high-redshift quasars with JWST: predictions from the BLUETIDES simulation

The bright emission from high-redshift quasars completely conceals their host galaxies in the rest-frame ultraviolet/optical, with detection of the hosts in these wavelengths eluding even the Hubble Space Telescope (HST) using detailed point spread function (PSF) modelling techniques. In this study, we produce mock images of a sample of z = 7 quasars extracted from the BLUETIDES simulation, and apply Markov chain Monte Carlo-based PSF modelling to determine the detectability of their host galaxies with the James Webb Space Telescope (JWST). While no statistically significant detections are made with HST, we predict that at the same wavelengths and exposure times JWST NIRCam imaging will detect ∼ 50 per cent of quasar host galaxies. We investigate various observational strategies, and find that NIRCam wide-band imaging in the long-wavelength filters results in the highest fraction of successful quasar host detections, detecting > 80 per cent of the hosts of bright quasars in exposure times of 5 ks. Exposure times of > 5 ks are required to detect the majority of host galaxies in the NIRCam wide-band filters, however, even 10 ks exposures with MIRI result in < 30 per cent successful host detections. We find no significant trends between galaxy properties and their detectability. The PSF modelling can accurately recover the host magnitudes, radii, and spatial distribution of the larger scale emission, when accounting for the central core being contaminated by residual quasar flux. Care should be made when interpreting the host properties measured using PSF modelling

A Significant Excess in Major Merger Rate for AGNs with the Highest Eddington Ratios at z \u3c 0.2

Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (AGN). After studying the connection between major mergers and AGNs with the highest Eddington ratios at z = 2, we here expand our analysis to z \u3c 0.2, exploring the same AGN parameter space. Using ESO VLT/FORS2 B-, V-, and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios , and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. We combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. With a best estimate of fm,agn = 0.41 ± 0.12 for the AGN host galaxies and fm,ina = 0.08 ± 0.06 for the inactive galaxies, our results imply that our AGN host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. We conclude that although major mergers are an essential mechanism to trigger local high Eddington ratio AGNs at z \u3c 0.2, the origin of of this specific AGN subpopulation still remains unclear

Limits to Rest-Frame Ultraviolet Emission From Far-Infrared-Luminous z~6 Quasar Hosts

We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous $z\simeq{}6$ quasars and the $z=5.85$ hot-dust free quasar SDSS J0005-0006. We perform 2D surface brightness modeling for each quasar using a Markov-Chain Monte-Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of $m_J>22.7$ mag and $m_H>22.4$ mag, corresponding to stellar masses of $M_\ast<2\times10^{11}M_\odot$. These stellar mass limits are consistent with the local $M_{\textrm{BH}}$-$M_\ast$ relation. Our flux limits are consistent with those predicted for the UV stellar populations of $z\simeq6$ host galaxies, but likely in the presence of significant dust ($\langle A_{\mathrm{UV}}\rangle\simeq 2.6$ mag). We also detect a total of up to 9 potential $z\simeq6$ quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1.4''-3.2'', or 8.4-19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of -22.1 to -19.9 mag, and UV spectral slopes $\beta$ of -2.0 to -0.2, consistent with luminous star-forming galaxies at $z\simeq6$. These results suggest that the quasars are in dense environments typical of luminous $z\simeq6$ galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the $z\simeq6$ quasar host galaxies and better constrain their stellar mass and dust content.Comment: 22 pages, 13 figures. Accepted for publication in Ap

Major mergers are not the dominant trigger for high-accretion AGNs at z ∼ 2

Research over the past decade has shown diminishing evidence for major galaxy mergers being a dominant mechanism for the growth of supermassive black holes (BHs) in galaxies and the triggering of optically or X-ray-selected active galactic nuclei (AGNs). For the first time we test whether such a connection exists at least in the most "plausible" part of parameter space: the highest specific accretion rate broad-line AGNs at the peak epoch of BH activity around z = 2. To that end we analyze two samples-21 AGNs with L/L-e(dd) > 0.7 and 92 stellar mass-and redshift-matched inactive galaxies-observed with HST/WFC3. We remove the AGN point sources from their host galaxies and avoid bias in visual classification by adding and then subtracting mock point sources to and from the comparison galaxies, producing matched residual structures for both sets. The resulting samples are joined and visually ranked according to distortion strength by 10 experts. The ensuing individual rankings are combined into a consensus sequence and from this we derive the merger fractions for both samples. With the merger fractions f(m,)(agn) = 0.24 +/- 0.09 for the AGN host galaxy sample and f(m,ina) = 0.19 +/- 0.04 for the inactive galaxies, we find no significant difference between the samples. This finding is consistent with previous studies for different AGN populations, and we conclude that even BH growth at the highest specific accretion rates and at the peak of cosmic AGN activity is not predominantly caused by major mergers

A significant excess in major merger rate for AGNs with the highest eddington ratios at z < 0.2

Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (AGN). After studying the connection between major mergers and AGNs with the highest Eddington ratios at z = 2, we here expand our analysis to z 0.3, and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. We combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. With a best estimate of f(m, agn) = 0.41 +/- 0.12 for the AGN host galaxies and f(m, ina) = 0.08 +/- 0.06 for the inactive galaxies, our results imply that our AGN host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. We conclude that although major mergers are an essential mechanism to trigger local high Eddington ratio AGNs at z < 0.2, the origin of greater than or similar to 50% of this specific AGN subpopulation still remains unclear