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Register a new userThe mass relations between supermassive black holes and their host galaxies at 1<z<2 with HST-WFC3
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Correlations between the mass of a supermassive black hole and the properties of its host galaxy (e.g., total stellar mass (M*), luminosity (Lhost)) suggest an evolutionary connection. A powerful test of a co-evolution scenario is to measure the relations MBH-Lhost and MBH-M* at high redshift and compare with local estimates. For this purpose, we acquired HST imaging with WFC3 of 32 X-ray-selected broad-line AGN at 1.2<z<1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with other properties through the 2D model fitting. The black hole mass was determined using the broad Halpha line, detected in the near-infrared with Subaru/FMOS, which potentially minimizes systematic effects using other indicators. We find that the observed ratio of MBH to total M* is 2.7 times larger at z~1.5 than in the local universe, while the scatter is equivalent between the two epochs. A non-evolving mass ratio is consistent with the data at the 2-3 sigma confidence level when accounting for selection effects and their uncertainties. The relationship between MBH-Lhost paints a similar picture. Therefore, our results cannot distinguish whether SMBHs and their total M* and Lhost proceed in lockstep or whether the growth of the former somewhat overshoots the latter, given the uncertainties. Based on a statistical estimate of the bulge-to-total mass fraction, the ratio MBH/M* is offset from the local value by a factor of ~7 which is significant even accounting for selection effects. Taken together, these observations are consistent with a scenario in which stellar mass is subsequently transferred from an angular momentum supported component of the galaxy to the pressure supported one through secular processes or minor mergers at a faster rate than mass accretion onto the SMBH.
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We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5<z<3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGN are X-ray selected from the Chandra Deep Field South and have typical luminosities of 1E42 < L_X < 1E44 erg/s. Accreting black holes in this luminosity and redshift range account for a substantial fraction of the total space density and black hole mass growth over cosmic time; they thus represent an important mode of black hole growth in the universe. We find that the majority (~80%) of the host galaxies of these AGN have low Sersic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z~2 and z~0.05.
This work aims at studying the $M_{BH}-M_{dyn}$ relation of a sample of $2<z<7$ quasars by constraining their host galaxy masses through full kinematical modeling of the cold gas kinematics, thus avoiding all possible biases and effects introduced by the rough virial estimates usually adopted so far. For this purpose we retrieved public observations of $72$ quasar host galaxies observed in ${rm [CII]_{158mu m}}$ or ${rm CO}$ transitions with the Atacama Large Millimeter Array (ALMA). We then selected those quasars whose line emission is spatially resolved and performed a kinematic analysis on ALMA observations. We estimated the dynamical mass of the systems by modeling the gas kinematics with a rotating disc taking into account geometrical and instrumental effects. Our dynamical mass estimates, combined with $M_{BH}$ obtained from literature and our own new ${rm CIV}lambda1550$ observations, have allowed us to investigate the $ M_{BH}/M_{dyn}$ in the early Universe. Overall we obtained a sample of $10$ quasars at $zsim2-7$ in which line emission is detected with high S/N ($> 5-10$) and the gas kinematics is spatially resolved and dominated by ordered rotation. The estimated dynamical masses place $6$ out of $10$ quasars above the local relation yielding to a $M_{BH}/M_{dyn}$ ratios $sim10times$ higher than those estimated in low-$z$ galaxies. On the other hand, we found that $4$ quasars at $zsim 4-6$ have dynamical-to-BH mass ratios consistent with what is observed in early-type galaxies in the local Universe.
In the last decades several correlations between the mass of the central supermassive black hole (BH) and properties of the host galaxy - such as bulge luminosity and mass, central stellar velocity dispersion, Sersic index, spiral pitch angle etc. - have been found and point at a coevolution scenario of BH and host galaxy. In this article, I review some of these relations for inactive galaxies and discuss the findings for galaxies that host an active galactic nucleus/quasar. I present the results of our group that finds that active galaxies at $zlesssim 0.1$ do not follow the BH mass - bulge luminosity relation. Furthermore, I show near-infrared integral-field spectroscopic data that suggest that young stellar populations cause the bulge overluminosity and indicate that the host galaxy growth started first. Finally, I discuss implications for the BH-host coevolution.
One of the main challenges in using high redshift active galactic nuclei to study the correlations between the mass of the supermassive Black Hole (MBH) and the properties of their active host galaxies is instrumental resolution. Strong lensing magnification effectively increases instrumental resolution and thus helps to address this challenge. In this work, we study eight strongly lensed active galactic nuclei (AGN) with deep Hubble Space Telescope imaging, using the lens modelling code Lenstronomy to reconstruct the image of the source. Using the reconstructed brightness of the host galaxy, we infer the host galaxy stellar mass based on stellar population models. MBH are estimated from broad emission lines using standard methods. Our results are in good agreement with recent work based on non-lensed AGN, demonstrating the potential of using strongly lensed AGNs to extend the study of the correlations to higher redshifts. At the moment, the sample size of lensed AGN is small and thus they provide mostly a consistency check on systematic errors related to resolution for the non-lensed AGN. However, the number of known lensed AGN is expected to increase dramatically in the next few years, through dedicated searches in ground and space based wide field surveys, and they may become a key diagnostic of black hole and galaxy co-evolution.
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