Michele Cappellari

Abstract:

<jats:title>ABSTRACT</jats:title> <jats:p>We present a measurement of the supermassive black hole (SMBH) mass of the nearby lenticular galaxy NGC 383, based on Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(2-1) emission line with an angular resolution of $0.050{\,\rm arcsec}\times 0.024{\,\rm arcsec}$ ($\approx 16\times 8$ pc$^2$). These observations spatially resolve the nuclear molecular gas disc down to $\approx 41\,300$ Schwarzschild radii and the SMBH sphere of influence by a factor of $\approx 24$ radially, better than any other SMBH mass measurement using molecular gas to date. The high resolution enables us to probe material with a maximum circular velocity of $\approx 1040$ km s$^{-1}$, even higher than those of the highest resolution SMBH mass measurements using megamasers. We detect a clear Keplerian increase (from the outside in) of the line-of-sight rotation velocities, a slight offset between the gas disc kinematic (i.e. the position of the SMBH) and morphological (i.e. the centre of the molecular gas emission) centres, an asymmetry of the innermost rotation velocity peaks and evidence for a mild position angle warp and/or non-circular motions within the central $\approx 0.3\,{\rm arcsec}$. By forward modelling the mass distribution and ALMA data cube, we infer an SMBH mass of $(3.58\pm 0.19)\times 10^9$ M$_\odot$ ($1\sigma$ confidence interval), more precise (5 per cent) but consistent within $\approx 1.4\sigma$ with the previous measurement using lower resolution molecular gas data. Our measurement emphasizes the importance of high spatial resolution observations for precise SMBH mass determinations.</jats:p>

Abstract:

Early-type galaxies (ETGs) show a bimodal distribution in key structural properties like stellar specific angular momentum, kinematic morphology, shape, and nuclear surface brightness profiles. Slow rotator ETGs, mostly found in the densest regions of galaxy clusters, become common when the stellar mass exceeds a critical value of around M ∗ crit ≈2×1011 M ⊙, or more precisely when lg(R e/kpc)≳12.4−lg(M ∗/M ⊙). These galaxies have low specific angular momentum, spheroidal shapes, and stellar populations that are old, metal-rich, and α-enhanced. In contrast, fast rotator ETGs form a continuous sequence of properties with spiral galaxies. In these galaxies, the age, metallicity, and α-enhancement of the stellar population correlate best with the effective stellar velocity dispersion σ e ∝ M ∗ / R e (i.e., properties are similar for R e ∝ M ∗), or with other proxies approximating their bulge mass fraction. This sequence spans from star-forming spiral disks to quenched, passive, spheroid-dominated fast rotator ETGs. Notably, at a fixed σ e, younger galaxies show lower metallicity. The structural differences and environmental distributions of ETGs suggest two distinct formation pathways: slow rotators undergo early intense star formation followed by rapid quenching via their dark halos and supermassive black holes, and later evolve through dry mergers during hierarchical cluster assembly; fast rotators, on the other hand, develop more gradually through gas accretion and minor mergers, becoming quenched by internal feedback above a characteristic lg(σ e crit/km s−1) ≳ 2.3 (in the local Universe) or due to environmental effects.