The weak dependence of velocity dispersion on disc fractions, mass-to-light ratio, and redshift: implications for galaxy and black hole evolution

Abstract

Velocity dispersion (σ) is a key driver for galaxy structure and evolution. We here present a comprehensive semi-empirical approach to compute σ via detailed Jeans modelling assuming both a constant and scale-dependent mass-to-light ratio M*/L. We compare with a large sample of local galaxies from MaNGA and find that both models can reproduce the Faber-Jackson (FJ) relation and the weak dependence of σ on bulge-to-total ratio B/T (for B/T ≳ 0.25). The dynamical-to-stellar mass ratio within R ≲ Re can be fully accounted for by a gradient in M*/L. We then build velocity dispersion evolutionary tracks σap[M*, z] (within an aperture) along the main progenitor dark matter haloes assigning stellar masses, effective radii and Sérsic indices via a variety of abundance matching and empirically motivated relations. We find: 1) clear evidence for downsizing in σap[M*, z] along the progenitor tracks; 2) at fixed stellar mass σ∝(1 + z)0.2 − 0.3 depending on the presence or not of a gradient in M*/L. We extract σap[M*, z] from the TNG50 hydrodynamic simulation and find very similar results to our models with constant M*/L. The increasing dark matter fraction within Re tends to flatten the σap[M*, z] along the progenitors at z ≳ 1 in constant M*/L models, while σap[M*, z] have a steeper evolution in the presence of a stellar gradient. We then show that a combination of mergers and gas accretion are likely responsible for the constant or increasing σap[M*, z] with time. Finally, our σap[M*, z] are consistent with a nearly constant and steep Mbh − σ relation at z ≲ 2, with black hole masses derived from the LX − M* relation.

Coincidence between morphology and star formation activity through cosmic time: the impact of the bulge growth

“…Bluck et al (2019Bluck et al ( , 2022 showed that central stellar velocity dispersion is the main galactic property linked to the level of sSFR, in the local universe. Marsden et al (2022) also showed that at fixed stellar mass, the stellar velocity dispersion remains constant for B/T>0.2. These recent results are in line with our findings pointing to a significant role of the bulges in the quenching process.…”

LeMMINGs. VI. Connecting nuclear activity to bulge properties of active and inactive galaxies: radio scaling relations and galaxy environment

“…Ho we ver, Ho et al ( 2009 ) measured σ using the spectra of the central regions of the galaxies typically dominated by the bulge. Furthermore, Marsden et al ( 2022 ) reported weak dependence of σ on disc component. On the other hand, we find ALGs do not deviate from the best-fitting inactive L R, core − σ relation defined by the H II + ALG subsample, but they reside almost exclusively under this relation.…”

Automated learning of gravitational mass of elliptical galaxies

“…of luminous as well as dark galactic matter -if learnt or estimated, will permit computation of the spatial distribution of dark matter in the galaxy. Ubiquity of the shape of the total gravitational mass density function continues to be questioned [1][2][3] , while agreement exists on the importance of galactic mass distribution in constraining galaxy formation [1,[4][5][6] , and evolution [7,8] . Computation of the spatial distribution of dark matter in a galaxy, will indeed need to include astronomical models of the link between luminous galactic matter, and photometric information obtained from such matter in the galaxy.…”