Galaxy formation and evolution

Abstract:

Abstract We analyse black hole scaling relations for disk-dominated galaxies, and present evidence for secularly driven galaxy-black hole co-evolution. We do this observationally by looking at “bulgeless” galaxies, where the lack of a stellar bulge suggests a quiet merger history. We first compose a sample of 2,435 disk-dominated galaxies hosting optical broad line active galactic nuclei (AGN) from DESI data, and find a $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ scaling relation of log (MBH) $= - 3.7^{+0.3}_{-0.3} + 1.00^{+0.03}_{-0.03} \log (M_*)$. From these, we identify 546 bulgeless galaxies hosting AGN, a factor of ≳ 5 larger than pre-existing samples, and find they follow the same $M_{\mathrm{BH}^{}}$-$M_{*}^{}$ relation as the general disk galaxy sample. Comparing the bulgeless galaxies to those with some bulge component, we find good agreement in the $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ relation (within 3σ), but disagreement in the $M_{\mathrm{BH}^{}}$–$M_{\mathrm{*,bulge}}^{}$ relation (at >7σ). This is the opposite of what is expected from merger-driven co-evolution, suggesting secular growth is significant in establishing observed $M_{\mathrm{BH}^{}}$–$M_{*}^{}$ scaling relations. Furthermore, in a control sample of early-type galaxies we find tentative evidence of increased AGN luminosity compared to the bulgeless sample, but no statistical difference in black hole mass. This suggests the assumed merger-dominated evolutionary history of early-type galaxies does not lead to significantly increased long-term BH growth. These results support numerous recent observational and theoretical studies which suggest secular processes fuel significant supermassive black hole growth and galaxy-black hole co-evolution.

Abstract:

Understanding how the internal kinematics of massive galaxies evolve is key to constraining the physical processes that drive their assembly. We investigate the evolution of rotational support in massive ( logM*/M⊙≥10.6 ) early-type galaxies (ETGs) over the past ∼7 Gyr. We use MUSE integral-field spectroscopic (IFS) data for 212 ETGs at intermediate redshift (0.25 < z < 0.75) from the MAGNUS sample. We compare their kinematics to a carefully matched local sample of 787 ETGs (z ≤ 0.05) from the MaNGA survey. Using the specific stellar angular momentum proxy, λR, we quantify the balance between ordered rotation and random motions. We derive intrinsic λR values by applying a uniform correction for seeing and point-spread function (PSF) effects to both samples. We find a significant evolutionary trend: The intermediate-redshift ETGs are systematically more rotationally supported than their local counterparts. The median PSF-corrected λR for the MAGNUS sample is 0.48 ± 0.05, substantially higher than the median of 0.34 ± 0.03 for the matched MaNGA sample. This corresponds to a positive slope in the λR−z relation of dλR/dz = 0.25 ± 0.04 for the combined sample. The decline in rotational support is most pronounced for the most massive ( logM*/M⊙>11.3 ) and highest-velocity-dispersion (σe ≳ 200 km s−1) galaxies. Our results provide robust evidence that massive ETGs have undergone significant kinematic evolution, losing angular momentum as they evolve towards the present day, consistent with theoretical models where processes such as dry mergers play a crucial role in shaping the dynamical state of galaxies.