arXiv subjects

Jonathan R. Trump

Publications and source records attributed to Jonathan R. Trump.

At least 127 records · Page 7Linked to original sources

arXiv2018

Demographics of Star-forming Galaxies since $z\sim2.5$. I. The $UVJ$ Diagram in CANDELS

This is the first in a series of papers examining the demographics of star-forming galaxies at $0.2<z<2.5$ in CANDELS. We study 9,100 galaxies from GOODS-S and UDS having published values of redshifts, masses, star-formation rates (SFRs), and dust attenuation ($A_V$) derived from UV-optical SED fitting. In agreement with previous works, we find that the $UVJ$ colors of a galaxy are closely correlated with its specific star-formation rate (SSFR) and $A_V$. We define rotated $UVJ$ coordinate axes, termed $S_\mathrm{SED}$ and $C_\mathrm{SED}$, that are parallel and perpendicular to the star-forming sequence and derive a quantitative calibration that predicts SSFR from $C_\mathrm{SED}$ with an accuracy of ~0.2 dex. SFRs from UV-optical fitting and from UV+IR values based on Spitzer/MIPS 24 $μ\mathrm{m}$ agree well overall, but systematic differences of order 0.2 dex exist at high and low redshifts. A novel plotting scheme conveys the evolution of multiple galaxy properties simultaneously, and dust growth, as well as star-formation decline and quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of transition galaxies below the star-forming main sequence is identified. These objects are located between star-forming and quiescent galaxies in $UVJ$ space and have lower $A_V$ and smaller radii than galaxies on the main sequence. Their properties are consistent with their being in transit between the two regions. The relative numbers of quenched, transition, and star-forming galaxies are given as a function of mass and redshift.

astro-ph.GA↗

arXiv2018

The Sloan Digital Sky Survey Reverberation Mapping Project: the CIV Blueshift, Its Variability, and Its Dependence Upon Quasar Properties

We use the multi-epoch spectra of 362 quasars from the Sloan Digital Sky Survey Reverberation Mapping project to investigate the dependence of the blueshift of CIV relative to MgII on quasar properties. We confirm that high-blueshift sources tend to have low CIV equivalent widths (EWs), and that the low-EW sources span a range of blueshift. Other high-ionization lines, such as HeII, also show similar blueshift properties. The ratio of the line width (measured as both the full-width at half maximum and the velocity dispersion) of CIV to that of MgII increases with blueshift. Quasar variability might enhance the connection between the CIV blueshift and quasar properties (e.g., EW). The variability of the MgII line center (i.e., the wavelength that bisects the cumulative line flux) increases with blueshift. In contrast, the CIV line center shows weaker variability at the extreme blueshifts. Quasars with the high-blueshift CIV lines tend to have less variable continuum emission, when controlling for EW, luminosity, and redshift. Our results support the scenario that high-blueshift sources tend to have large Eddington ratios.

astro-ph.GA↗

arXiv2017

The Sloan Digital Sky Survey Reverberation Mapping Project: Composite Lags at $z\lesssim 1$

We present composite broad-line region (BLR) reverberation-mapping lag measurements for \halpha, \hbeta, \HeII\,$\lambda4686$ and \MgII\ for a sample of 144, $z\lesssim 1$ quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. Using only the 32-epoch spectroscopic light curves in the first 6-month season of SDSS-RM observations, we compile correlation-function measurements for individual objects and then coadd them to allow the measurement of the average lags for our sample at mean redshifts of $0.4$ (for \halpha) and $\sim 0.65$ (for the other lines). At similar quasar luminosities and redshifts, the sample-averaged lag decreases in the order of \MgII, \halpha, \hbeta\ and \HeII. This decrease in lags is accompanied by an increase in the mean line width of the four lines, and is roughly consistent with the virialized motion for BLR gas in photoionization equilibrium. These are among the first RM measurements of stratified BLR structure at $z>0.3$. Dividing our sample by luminosity, \halpha\ shows clear evidence of increasing lags with luminosity, consistent with the expectation from the measured BLR size-luminosity relation based on \hbeta. The other three lines do not show a clear luminosity trend in their average lags due to the limited dynamic range of luminosity probed and the poor average correlation signals in the divided samples, a situation that will be improved with the incorporation of additional photometric and spectroscopic data from SDSS-RM. We discuss the utility and caveats of composite-lag measurements for large statistical quasar samples with reverberation-mapping data.

astro-ph.GA↗

arXiv2017

CANDELS: Elevated Black Hole Growth in the Progenitors of Compact Quiescent Galaxies at z~2

We examine the fraction of massive ($M_{*}>10^{10} M_{\odot}$), compact star-forming galaxies (cSFGs) that host an active galactic nucleus (AGN) at $z\sim2$. These cSFGs are likely the direct progenitors of the compact quiescent galaxies observed at this epoch, which are the first population of passive galaxies to appear in large numbers in the early Universe. We identify cSFGs that host an AGN using a combination of Hubble WFC3 imaging and Chandra X-ray observations in four fields: the Chandra Deep Fields, the Extended Groth Strip, and the UKIDSS Ultra Deep Survey field. We find that $39.2^{+3.9}_{-3.6}$\% (65/166) of cSFGs at $1.4<z<3.0$ host an X-ray detected AGN. This fraction is 3.2 times higher than the incidence of AGN in extended star-forming galaxies with similar masses at these redshifts. This difference is significant at the $6.2σ$ level. Our results are consistent with models in which cSFGs are formed through a dissipative contraction that triggers a compact starburst and concurrent growth of the central black hole. We also discuss our findings in the context of cosmological galaxy evolution simulations that require feedback energy to rapidly quench cSFGs. We show that the AGN fraction peaks precisely where energy injection is needed to reproduce the decline in the number density of cSFGs with redshift. Our results suggest that the first abundant population of massive, quenched galaxies emerged directly following a phase of elevated supermassive black hole growth and further hints at a possible connection between AGN and the rapid quenching of star formation in these galaxies.

astro-ph.GA↗

arXiv2017

z~2: An Epoch of Disk Assembly

We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star-formation at $z\sim2$ to today. Measurements of galaxy rotation velocity $V_{rot}$, which quantify ordered motions, and gas velocity dispersion $σ_g$, which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift from $z=2.5$ to $z=0.1$, spanning 10 Gyrs. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported ($V_{rot}>σ_g$). By $z=2$, the percentage of galaxies with rotational support has declined to 50$\%$ at low stellar mass ($10^{9}-10^{10}\,M_{\odot}$) and 70$\%$ at high stellar mass ($10^{10}-10^{11}M_{\odot}$). For $V_{rot}\,>\,3\,σ_g$, the percentage drops below 35$\%$ for all masses. From $z\,=\,2$ to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend towards rotational support with time, and it is reached earlier in higher mass systems. This is mostly due to an average decline in $σ_g$ by a factor of 3 since a redshift of 2, which is independent of mass. Over the same time period, $V_{rot}$ increases by a factor of 1.5 for low mass systems, but does not evolve for high mass systems. These trends in $V_{rot}$ and $σ_g$ with time are at a fixed stellar mass and should not be interpreted as evolutionary tracks for galaxy populations. When galaxy populations are linked in time with abundance matching, not only does $σ_g$ decline with time as before, but $V_{rot}$ strongly increases with time for all galaxy masses. This enhances the evolution in $V_{rot}/σ_g$. These results indicate that $z\,=\,2$ is a period of disk assembly, during which the strong rotational support present in today's massive disk galaxies is only just beginning to emerge.

astro-ph.GA↗

arXiv2017

The physical constraints on a new LoBAL QSO at z=4.82

Very few low-ionization broad absorption line (LoBAL) QSOs have been found at high redshifts to date. One high-redshift LoBAL QSO, J0122+1216, was recently discovered at the Lijiang 2.4-m Telescope with an initial redshift determination of 4.76. Aiming to investigate its physical properties, we carried out follow-up observations in the optical and near-IR spectroscopy. Near-IR spectra from UKIRT and P200 confirms that it is a LoBAL, with a new redshift determination of $4.82\pm0.01$ based on the \mgii~ emission-line. The new \mgii~ redshift determination reveals strong blueshifts and asymmetry of the high-ionization emission lines. We estimated a black hole mass of $\sim 2.3\times 10^9 M_\odot$ and Eddington ratio of $\sim 1.0$ according to the empirical \mgii-based single-epoch relation and bolometric correction factor. It is possible that strong outflows are the result of an extreme quasar environment driven by the high Eddington ratio. A lower limit on the outflowing kinetic power ($>0.9\% L_{Edd}$) was derived from both emission and absorption lines, indicating these outflows play a significant role in the feedback process to regulate the growth of its black hole as well as host galaxy evolution.

astro-ph.GA↗

arXiv2016

The Sloan Digital Sky Survey Reverberation Mapping Project: Velocity Shifts of Quasar Emission Lines

Quasar emission lines are often shifted from the systemic velocity due to various dynamical and radiative processes in the line-emitting region. The level of these velocity shifts depends both on the line species and on quasar properties. We study velocity shifts for the line peaks of various narrow and broad quasar emission lines relative to systemic using a sample of 849 quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. The coadded (from 32 epochs) spectra of individual quasars have sufficient signal-to-noise ratio (SNR) to measure stellar absorption lines to provide reliable systemic velocity estimates, as well as weak narrow emission lines. The sample also covers a large dynamic range in quasar luminosity (~2 dex), allowing us to explore potential luminosity dependence of the velocity shifts. We derive average line peak velocity shifts as a function of quasar luminosity for different lines, and quantify their intrinsic scatter. We further quantify how well the peak velocity can be measured for various lines as a function of continuum SNR, and demonstrate there is no systematic bias in the line peak measurements when the spectral quality is degraded to as low as SNR~3 per SDSS pixel. Based on the observed line shifts, we provide empirical guidelines on redshift estimation from [OII]3728, [OIII]5008, [NeV]3426, MgII, CIII], HeII1640, broad Hbeta, CIV, and SiIV, which are calibrated to provide unbiased systemic redshifts in the mean, but with increasing intrinsic uncertainties of 46, 56, 119, 205, 233, 242, 400, 415, and 477 km/s, in addition to the measurement uncertainties. These more realistic redshift uncertainties are generally much larger than the formal uncertainties reported by the redshift pipelines for spectroscopic quasar surveys, and demonstrate the infeasibility of measuring quasar redshifts to better than ~200 km/s with only broad lines.

astro-ph.GA↗

arXiv2016

The Bursty Star Formation Histories of Low-mass Galaxies at $0.4<z<1$ Revealed by Star Formation Rates Measured from H$β$ and FUV

We investigate the burstiness of star formation histories (SFHs) of galaxies at $0.4<z<1$ by using the ratio of star formation rates (SFRs) measured from H$β$ and FUV (1500 Å) (H$β$--to--FUV ratio). Our sample contains 164 galaxies down to stellar mass (M*) of $10^{8.5} M_\odot$ in the CANDELS GOODS-N region, where Team Keck Redshift Survey DEIMOS spectroscopy and HST/WFC3 F275W images from CANDELS and Hubble Deep UV Legacy Survey are available. When the {\it ratio} of H$β$- and FUV-derived SFRs is measured, dust extinction correction is negligible (except for very dusty galaxies) with the Calzetti attenuation curve. The H$β$--to--FUV ratio of our sample increases with M* and SFR. The median ratio is $\sim$0.7 at M*$\sim10^{8.5} M_\odot$ (or SFR$\sim 0.5 M_\odot/yr$) and increases to $\sim$1 at M*$\sim10^{10} M_\odot$ (or SFR $\sim 10 M_\odot/yr$). At M*$<10^{9.5} M_\odot$, our median H$β$--to--FUV ratio is lower than that of local galaxies at the same M*, implying a redshift evolution. Bursty SFH on a timescale of a few tens of megayears on galactic scales provides a plausible explanation of our results, and the importance of the burstiness increases as M* decreases. Due to sample selection effects, our H$β$--to--FUV ratio may be an upper limit of the true value of a complete sample, which strengthens our conclusions. Other models, e.g., non-universal initial mass function or stochastic star formation on star cluster scales, are unable to plausibly explain our results.

astro-ph.GA↗

arXiv2016

Kinematic Downsizing at z~2

We present results from a survey of the internal kinematics of 49 star-forming galaxies at z$\,\sim\,$2 in the CANDELS fields with the Keck/MOSFIRE spectrograph (SIGMA, Survey in the near-Infrared of Galaxies with Multiple position Angles). Kinematics (rotation velocity $V_{rot}$ and integrated gas velocity dispersion $σ_g$) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z$\,\sim\,$2, massive star-forming galaxies ($\log\,M_*/M_{\odot}\gtrsim10.2$) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of $V_{rot}/σ_g$ which are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low mass galaxies ($\log\,M_*/M_{\odot}\lesssim10.2$) at this epoch are still in the early stages of disk assembly: their kinematics are often supported by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of $V_{rot}$. This "kinematic downsizing" implies that the process(es) responsible for disrupting disks at z$\,\sim\,$2 have a stronger effect and/or are more active in low mass systems. In conclusion, we find that the period of rapid stellar mass growth at z$\,\sim\,$2 is coincident with the nascent assembly of low mass disks and the assembly and settling of high mass disks.

astro-ph.GA↗

arXiv2016

Disentangling AGN and Star Formation Activity at High Redshift Using Hubble Space Telescope Grism Spectroscopy

Differentiating between active galactic nuclei (AGN) activity and star formation in z ~ 2 galaxies is difficult because traditional methods, such as line ratio diagnostics, change with redshift while multi-wavelength methods (X-ray, radio, IR) are sensitive to only the brightest AGN. We have developed a new method for spatially resolving emission lines in HST/WFC3 G141 grism spectra and quantifying AGN activity through the spatial gradient of the [O III]/H$β$ line ratio. Through detailed simulations, we show that our novel line-ratio gradient approach identifies ~ sim 40% more low-mass and obscured AGN than obtained by classical methods. Based on our simulations, we developed a relationship that maps stellar mass, star formation rate, and measured [O III]/H$β$ gradient to AGN Eddington ratio. We apply our technique to previously studied stacked samples of galaxies at z ~2 and find that our results are consistent with these studies. Using this gradient method will also be able to inform other galaxy evolution science, such as inside-out quenching and metallicity gradients, and will be widely applicable to future spatially resolved JWST data.

astro-ph.GA↗

arXiv2016

Stellar Mass--Gas-phase Metallicity Relation at $0.5\leq z\leq0.7$: A Power Law with Increasing Scatter toward the Low-mass Regime

We present the stellar mass ($M_{*}$)--gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts ($0.5\leq z\leq0.7$) for 1381 field galaxies collected from deep spectroscopic surveys. The star formation rate (SFR) and color at a given $M_{*}$ of this magnitude-limited ($R\lesssim24$ AB) sample are representative of normal star-forming galaxies. For masses below $10^9 M_\odot$, our sample of 237 galaxies is $\sim$10 times larger than those in previous studies beyond the local universe. This huge gain in sample size enables superior constraints on the MZR and its scatter in the low-mass regime. We find a power-law MZR at $10^{8} M_\odot < M_{*} < 10^{11} M_\odot$: ${12+log(O/H) = (5.83\pm0.19) + (0.30\pm0.02)log(M_{*}/M_\odot)}$. Our MZR shows good agreement with others measured at similar redshifts in the literature in the intermediate and massive regimes, but is shallower than the extrapolation of the MZRs of others to masses below $10^{9} M_\odot$. The SFR dependence of the MZR in our sample is weaker than that found for local galaxies (known as the Fundamental Metallicity Relation). Compared to a variety of theoretical models, the slope of our MZR for low-mass galaxies agrees well with predictions incorporating supernova energy-driven winds. Being robust against currently uncertain metallicity calibrations, the scatter of the MZR serves as a powerful diagnostic of the stochastic history of gas accretion, gas recycling, and star formation of low-mass galaxies. Our major result is that the scatter of our MZR increases as $M_{*}$ decreases. Our result implies that either the scatter of the baryonic accretion rate or the scatter of the $M_{*}$--$M_{halo}$ relation increases as $M_{*}$ decreases. Moreover, our measures of scatter at $z=0.7$ appears consistent with that found for local galaxies.

astro-ph.GA↗

arXiv2015

The Sloan Digital Sky Survey Reverberation Mapping Project: First Broad-line Hbeta and MgII Lags at z>~0.3 from six-Month Spectroscopy

Reverberation mapping (RM) measurements of broad-line region (BLR) lags in z>0.3 quasars are important for directly measuring black hole masses in these distant objects, but so far there have been limited attempts and success given the practical difficulties of RM in this regime. Here we report preliminary results of 15 BLR lag measurements from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, a dedicated RM program with multi-object spectroscopy designed for RM over a wide redshift range. The lags are based on the 2014 spectroscopic light curves alone (32 epochs over 6 months) and focus on the Hbeta and MgII broad lines in the 100 lowest-redshift (z<0.8) quasars included in SDSS-RM; they represent a small subset of the lags that SDSS-RM (including 849 quasars to z~4.5) is expected to deliver. The reported preliminary lag measurements are for intermediate-luminosity quasars at 0.3<~z<0.8, including 9 Hbeta lags and 6 MgII lags, for the first time extending RM results to this redshift-luminosity regime and providing direct quasar black hole mass estimates over ~ half of cosmic time. The MgII lags also increase the number of known MgII lags by several-fold, and start to explore the utility of MgII for RM at high redshift. The location of these new lags at higher redshifts on the observed BLR size-luminosity relationship is statistically consistent with previous Hbeta results at z<0.3. However, an independent constraint on the relationship slope at z>0.3 is not yet possible due to the limitations in our current sample. Our results demonstrate the general feasibility and potential of multi-object RM for z>0.3 quasars.

astro-ph.GA↗

arXiv2015

HST Emission Line Galaxies at z ~ 2: Comparing Physical Properties of Lyman Alpha and Optical Emission Line Selected Galaxies

We compare the physical and morphological properties of z ~ 2 Lyman-alpha emitting galaxies (LAEs) identified in the HETDEX Pilot Survey and narrow band studies with those of z ~ 2 optical emission line galaxies (oELGs) identified via HST WFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same range in stellar mass (7.5 < logM < 10.5), size (0.5 < R < 3.0 kpc), and star-formation rate (~1 < SFR < 100). Remarkably, a comparison of the most commonly used physical and morphological parameters -- stellar mass, half-light radius, UV slope, star formation rate, ellipticity, nearest neighbor distance, star formation surface density, specific star formation rate, [O III] luminosity, and [O III] equivalent width -- reveals no statistically significant differences between the populations. This suggests that the processes and conditions which regulate the escape of Ly-alpha from a z ~ 2 star-forming galaxy do not depend on these quantities. In particular, the lack of dependence on the UV slope suggests that Ly-alpha emission is not being significantly modulated by diffuse dust in the interstellar medium. We develop a simple model of Ly-alpha emission that connects LAEs to all high-redshift star forming galaxies where the escape of Ly-alpha depends on the sightline through the galaxy. Using this model, we find that mean solid angle for Ly-alpha escape is 2.4+/-0.8 steradians; this value is consistent with those calculated from other studies.

astro-ph.GA↗

arXiv2015

Astronomy Job Crisis

Astronomers in CANDELS outline changes for the academic system to promote a smooth transition for junior scientists from academia to industry.

astro-ph.IM↗

arXiv2015

Young, Star-forming Galaxies and their local Counterparts: the Evolving Relationship of Mass-SFR-Metallicity since z ~ 2.1

We explore the evolution of the Stellar Mass-Star Formation Rate-Metallicity Relation using a set of 256 COSMOS and GOODS galaxies in the redshift range 1.90 < z < 2.35. We present the galaxies' rest-frame optical emission-line fluxes derived from IR-grism spectroscopy with the Hubble Space Telescope and combine these data with star formation rates and stellar masses obtained from deep, multi-wavelength (rest-frame UV to IR) photometry. We then compare these measurements to those for a local sample of galaxies carefully matched in stellar mass (7.5 < log(M*/Msol) < 10.5) and star formation rate (-0.5 < log(SFR) < 2.5 in Msol yr^-1). We find that the distribution of z ~ 2.1 galaxies in stellar mass-SFR-metallicity space is clearly different from that derived for our sample of similarly bright (L_H\b{eta} > 3 . 10^40 ergs s^-1) local galaxies, and this offset cannot be explained by simple systematic offsets in the derived quantities. At stellar masses above ~10^9 Msol and star formation rates above ~10 Msol yr^-1, the z ~ 2.1 galaxies have higher oxygen abundances than their local counterparts, while the opposite is true for lower-mass, lower-SFR systems.

astro-ph.GA↗

arXiv2015

The Dust Attenuation Curve versus Stellar Mass for Emission Line Galaxies at z ~ 2

We derive the mean wavelength dependence of stellar attenuation in a sample of 239 high redshift (1.90 < z < 2.35) galaxies selected via Hubble Space Telescope (HST) WFC3 IR grism observations of their rest-frame optical emission lines. Our analysis indicates that the average reddening law follows a form similar to that derived by Calzetti et al. for local starburst galaxies. However, over the mass range 7.2 < log M/Msolar < 10.2, the slope of the attenuation law in the UV is shallower than that seen locally, and the UV slope steepens as the mass increases. These trends are in qualitative agreement with Kriek & Conroy, who found that the wavelength dependence of attenuation varies with galaxy spectral type. However, we find no evidence of an extinction "bump" at 2175 A in any of the three stellar mass bins, or in the sample as a whole. We quantify the relation between the attenuation curve and stellar mass and discuss its implications.

astro-ph.GA↗

arXiv2015

The Team Keck Redshift Survey 2: MOSFIRE Spectroscopy of the GOODS-North Field

We present the Team Keck Redshift Survey 2 (TKRS2), a near-infrared spectral observing program targeting selected galaxies within the CANDELS subsection of the GOODS-North Field. The TKRS2 program exploits the unique capabilities of MOSFIRE, an infrared multi-object spectrometer which entered service on the Keck I telescope in 2012 and contributes substantially to the study of galaxy spectral features at redshifts inaccessible to optical spectrographs. The TKRS2 project targets 97 galaxies drawn from samples that include z~2 emission-line galaxies with features observable in the JHK bands as well as lower-redshift targets with features in the Y band. We present a detailed measurement of MOSFIRE's sensitivity as a function of wavelength, including the effects of telluric features across the YJHK filters. The largest utility of our survey is in providing rest-frame-optical emission lines for z>1 galaxies, and we demonstrate that the ratios of strong, optical emission lines of z~2 galaxies suggest the presence of either higher N/O abundances than are found in z~0 galaxies or low-metallicity gas ionized by an active galactic nucleus. We have released all TKRS2 data products into the public domain to allow researchers access to representative raw and reduced MOSFIRE spectra.

astro-ph.GA↗

arXiv2015

Are Compton-Thick AGN the Missing Link Between Mergers and Black Hole Growth?

We examine the host morphologies of heavily obscured active galactic nuclei (AGN) at $z\sim1$ to test whether obscured supermassive black hole growth at this epoch is preferentially linked to galaxy mergers. Our sample consists of 154 obscured AGN with $N_{\rm H}>10^{23.5}$ cm$^{-2}$ and $z<1.5$. Using visual classifications, we compare the morphologies of these AGN to control samples of moderately obscured ($10^{22}$ cm$^{-2}$ $<N_{\rm H}< 10^{23.5}$ cm$^{-2}$) and unobscured ($N_{\rm H}<10^{22}$ cm$^{-2}$) AGN. These control AGN are matched in redshift and intrinsic X-ray luminosity to our heavily obscured AGN. We find that heavily obscured AGN at z~1 are twice as likely to be hosted by late-type galaxies relative to unobscured AGN ($65.3^{+4.1}_{-4.6}\%$ vs $34.5^{+2.9}_{-2.7}\%$) and three times as likely to exhibit merger or interaction signatures ($21.5^{+4.2}_{-3.3}\%$ vs $7.8^{+1.9}_{-1.3}\%$). The increased merger fraction is significant at the 3.8$σ$ level. We also find that the incidence of point-like morphologies is inversely proportional to obscuration. If we exclude all point sources and consider only extended hosts, we find the correlation between merger fraction and obscuration is still evident, however at a reduced statistical significance ($2.5σ$). The fact that we observe a different disk/spheroid fraction versus obscuration indicates that viewing angle cannot be the only thing differentiating our three AGN samples, as a simple unification model would suggest. The increased fraction of disturbed morphologies with obscuration supports an evolutionary scenario, in which Compton-thick AGN are a distinct phase of obscured SMBH growth following a merger/interaction event. Our findings also suggest that some of the merger-triggered SMBH growth predicted by recent AGN fueling models may be hidden among the heavily obscured, Compton-thick population.

astro-ph.GA↗