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Register a new userA Catalog of AGN Host Galaxies Observed with HST/ACS: Correlations between Star Formation and AGN Activity
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We present the Advanced Camera for Surveys Active Galactic Nuclei (ACS-AGN) Catalog, a catalog of 2585 active galactic nucleus (AGN) host galaxies that are at redshifts 0.2<z<2.5 and that were imaged with the Hubble Space Telescopes Advanced Camera for Surveys (ACS). Using the ACS General Catalog (ACS-GC) as our initial sample, we select an AGN subsample using Spitzer and Chandra data along with their respective established AGN selection criteria. We then gather further multi-wavelength photometric data in order to construct spectral energy distributions (SEDs). Using these SEDs we are able to derive multiple AGN and host galaxy properties, such as star formation rate, AGN luminosity, stellar mass, and nuclear column density. From these data, we show that AGN host galaxies tend to lie below the star-forming main sequence, with X-ray-selected AGN host galaxies being more offset than IR-selected AGN host galaxies. This suggests that there is some process, possibly negative feedback, in AGN host galaxies causing decreased star formation. We also demonstrate that there is a positive trend between star formation rate and AGN luminosity in AGN host galaxies, in individual redshift bins and across all redshift bins, and that both are correlated with the stellar mass of their galaxies. This points towards an underlying link between the stellar mass, stellar growth, and SMBH growth in a galaxy.
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We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog (Assef et al. 2018) with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts of z~3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts of z=0.2-0.3, with relatively blue W1-W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs, relative to those of normal star forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with Eddington ratio. This result is consistent with a version of the `receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.
We investigate the location of an ultra-hard X-ray selected sample of AGN from the Swift Burst Alert Telescope (BAT) catalog with respect to the main sequence (MS) of star-forming galaxies using Herschel-based measurements of the star formation rate (SFR) and stellar mass (mstar) from Sloan Digital Sky Survey (SDSS) photometry where the AGN contribution has been carefully removed. We construct the MS with galaxies from the Herschel Reference Survey and Herschel Stripe 82 Survey using the exact same methods to measure the SFR and mstar{} as the Swift/BAT AGN. We find a large fraction of the Swift/BAT AGN lie below the MS indicating decreased specific SFR (sSFR) compared to non-AGN galaxies. The Swift/BAT AGN are then compared to a high-mass galaxy sample (COLD GASS), where we find a similarity between the AGN in COLD GASS and the Swift/BAT AGN. Both samples of AGN lie firmly between star-forming galaxies on the MS and quiescent galaxies far below the MS. However, we find no relationship between the X-ray luminosity and distance from the MS. While the morphological distribution of the BAT AGN is more similar to star-forming galaxies, the sSFR of each morphology is more similar to the COLD GASS AGN. The merger fraction in the BAT AGN is much higher than the COLD GASS AGN and star-forming galaxies and is related to distance from the MS. These results support a model in which bright AGN tend to be in high mass star-forming galaxies in the process of quenching which eventually starves the supermassive black hole itself.
We analyze a suite of $30$ high resolution zoom-in cosmological hydrodynamic simulations of massive galaxies with stellar masses $M_{ast} > 10^{10.9} M_odot$, with the goal of better understanding merger activity in AGN, AGN activity in merging systems, SMBH growth during mergers, and the role of gas content. Using the radiative transfer code textsc{Powderday}, we generate HST-WFC3 F160W synthetic observations of redshift $0.5 < z < 3$ central galaxies, add noise properties similar to the CANDELS survey, and measure morphological properties from the synthetic images using commonly adopted non-parametric statistics. We compare the distributions of morphological properties measured from the synthetic images with a sample of inactive galaxies and X-ray selected AGN hosts from CANDELS. We study the connection between mergers and AGN activity in the simulations, the synthetic images, and the observed CANDELS sample. We find that, in both the simulations and CANDELS, even the most luminous $(L_{rm bol} > 10^{45}$ erg s$^{-1})$ AGN in our sample are no more likely than inactive galaxies $(L_{rm bol} < 10^{43}$ erg s$^{-1})$ to be found in merging systems. We also find that AGN activity is not overall enhanced by mergers, nor enhanced at any specific time in the $1$ Gyr preceding and following a merger. Even gas rich major mergers (stellar mass ratio $>$1:4) do not necessarily enhance AGN activity or significantly grow the central SMBH. We conclude that in the simulated massive galaxies studied here, mergers are not the primary drivers of AGN.
We investigate the relation between AGN and star formation (SF) activity at $0.5 < z < 3$ by analyzing 898 galaxies with X-ray luminous AGN ($L_X > 10^{44}$ erg s$^{-1}$) and a large comparison sample of $sim 320,000$ galaxies without X-ray luminous AGN. Our samples are selected from a large (11.8 deg$^2$) area in Stripe 82 that has multi-wavelength (X-ray to far-IR) data. The enormous comoving volume ($sim 0.3$ Gpc$^3$) at $0.5 < z < 3$ minimizes the effects of cosmic variance and captures a large number of massive galaxies ($sim 30,000$ galaxies with $M_* > 10^{11} M_{odot}$) and X-ray luminous AGN. While many galaxy studies discard AGN hosts, we fit the SED of galaxies with and without X-ray luminous AGN with Code Investigating GALaxy Emission (CIGALE) and include AGN emission templates. We find that without this inclusion, stellar masses and star formation rates (SFRs) in AGN host galaxies can be overestimated, on average, by factors of up to $sim 5$ and $sim 10$, respectively. The average SFR of galaxies with X-ray luminous AGN is higher by a factor of $sim 3$ to $10$ compared to galaxies without X-ray luminous AGN at fixed stellar mass and redshift, suggesting that high SFRs and high AGN X-ray luminosities may be fueled by common mechanisms. The vast majority ($> 95 %$) of galaxies with X-ray luminous AGN at $z=0.5-3$ do not show quenched SF: this suggests that if AGN feedback quenches SF, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity.
There exist strong evidence supporting the co-evolution of central supermassive black holes and their host galaxies. It is however still unclear what the exact role of nuclear activity, in the form of accretion onto these supermassive black holes, in this co-evolution is. We use a rich multi-wavelength dataset available for the North Ecliptic Pole field, most notably surveyed by the AKARI satellite infrared telescope to study the host galaxy properties of AGN. In particular we are interested in investigating star-formation in the host galaxies of radio-AGN and the putative radio feedback mechanism, potentially responsible for the eventual quenching of star-formation. Using both broadband SED modeling and optical spectroscopy, we simultaneously study the nu- clear and host galaxy components of our sources, as a function of their radio luminosity, bolo- metric luminosity, and radio-loudness. Here we present preliminary results concerning the AGN content of the radio sources in this field, while offering tentative evidence that jets are inefficient star-formation quenchers, except in their most powerful state.
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