The Host Galaxies of Active Galactic Nuclei with Direct Black Hole Mass Measurements

TL;DR

The study leverages high-resolution HST imaging and advanced 2D decompositions to measure host-galaxy properties for 44 AGNs with direct $M_{ m BH}$ measurements, establishing that active and quiescent galaxies share the same $M_{ m BH}$-host scaling relations and extending them to lower masses in spiral hosts. It demonstrates that $M_{ m BH}$ correlates tightly with spheroid luminosity ($L_{ m sph}$) rather than total host luminosity, with many hosts hosting pseudo-bulges, implying secular growth plays a key role. The analysis of BLR inclination reveals no clear alignment with the host disk, but a robust link to the BLR opening angle and a strong alignment with the accretion-disk/jet inclinations, consistent with a coherently oriented inner AGN engine. Overall, the results provide a precise nearby benchmark for black hole–galaxy co-evolution across cosmic time and support the universality of SMBH scaling relations across activity states and morphologies.

Abstract

Reverberation mapping (RM) determines the mass of black holes (BH) in active galactic nuclei (AGNs) by resolving the BH gravitational sphere of influence in the time domain. Recent RM campaigns yielded direct BH masses through dynamical modeling for a sample of 32 objects, spanning a wide range of AGN luminosities and BH masses. In addition, accurate BH masses have been determined by spatially resolving the broad-line region with GRAVITY for a handful of AGNs. Here, we present a detailed analysis of Hubble Space Telescope images using surface-brightness profile fitting with state-of-the-art programs. We derive AGN luminosity and host-galaxy properties, such as radii and luminosities for spheroid, disk, and bar (if present). The spheroid effective radii were used to measure stellar velocity dispersion from integral-field spectroscopy. Since the BH masses of our sample do not depend on any assumption of the virial factor needed in single-epoch spectroscopic mass estimates, we can show that the resulting scaling relations between the mass of the supermassive BHs and their host galaxies match those of quiescent galaxies, naturally extending to lower masses in these (predominantly) spiral galaxies. We find that the inner AGN orientation, as traced by the broad-line region inclination angle, is uncorrelated with the host-galaxy disk. Our sample has the most direct and accurate MBH measurements of any AGN sample and provides a fundamental local benchmark for studies of the evolution of massive black holes and their host galaxies across cosmic time.

Figures (12)

• Figure 1: $M_{\rm BH}$--Spheroid Luminosity Relation. In the left panel, the relation between $M_{\rm BH}$ and spheroid luminosity in the $I$-band is shown, in the right panel, the same but in the $V$-band. Grey data points are quiescent galaxies Kormendy_Ho:2013; colored data points are our sample (classical bulges in yellow, pseudo-bulges in blue). The fitted relation is shown as a shaded gray stripe corresponding to the 68% (1-sigma) confidence interval of the linear regression. Since our sample consists of local AGNs with directly measured $M_{\rm BH}$ through dynamical modeling which is free of assumptions of the virial factor, we can show that AGNs follow the same scaling relations as those of quiescent galaxies.
• Figure 2: Left:BLR Inclination vs. Host Inclination. Comparison between inclination of the BLR, based on CARAMEL and GRAVITY modeling, and host-galaxy disk inclination, for our sample of 34 RM AGNs (classical bulges in yellow, pseudo-bulges in blue). There is no correlation between the inclination of the central AGN and the large-scale host-galaxy disk; if at all, there is an indication of a weak anti-correlation (Pearson correlation coefficient of $-0.16$). Right:BLR Inclination vs. BLR Opening Angle. Similar to the left panel, but now comparing inclination and opening angle of the BLR, based on CARAMEL and GRAVITY modeling. Both parameters are correlated (Pearson correlation coefficient of 0.71). The fitted relation is shown as a shaded gray stripe corresponding to the 68% (1-sigma) confidence interval of the linear regression. The correlation is driven by the absence of double-peaked lines in the sample. In other words, in modeling the data, the opening angle of the BLR cannot be much smaller than the inclination angle, while still reproducing the observed single-peaked lines.
• Figure 3: BLR Inclination vs. Accretion Disk/Jet Inclination. Comparison between inclination of the BLR, based on CARAMEL modeling and accretion disk inclination Du:2025 or radio-jet inclination (compiled in this paper). Both parameters are correlated (Pearson correlation coefficient of 0.9). The fitted relation is shown as a shaded gray stripe corresponding to the 68% (1-sigma) confidence interval of the linear regression. (The 1:1 dotted line is shown for comparison only.)
• Figure 4: Surface-Photometry Fits. From left to right: observed HST image ("data", including scale bar of 5 arcseconds and North-East directions); best-fit galight/lenstronomy model ("model"); PSF-subtracted image ("data—point source"); residual image after subtraction of best-fit model from data, divided by the noise level ("normalized residual"); and surface-brightness profile (data = black circles, model = red line, PSF = blue line, spheroid = yellow line; if present: disk = purple line, bar = orange line). The surface-brightness profile is shown for illustration only, as the fits were performed on the 2D image. Surface-brightness values are given in the plane of the sky (total light within circular aperture; the x-axis is based on a circularized radius). Note that all images are displayed as observed with HST (see Table \ref{['tab:hst']}) and fitted by lenstronomy. Each row of images corresponds to one object (as labeled on the y-axis of the leftmost panel).
• Figure 5: Figure \ref{['fig:lenstronomy1']} continued.