Michele Cappellari

Abstract:

We present a new measurement of the dark and luminous matter distribution of massive elliptical galaxies, and their evolution with redshift, by combining strong lensing and dynamical observables. Our sample of 56 lens galaxies covers a redshift range of . By combining new Hubble Space Telescope imaging with previously observed velocity dispersion and line-of-sight measurements, we decompose the luminous matter profile from the dark matter profile and perform a Bayesian hierarchical analysis to constrain the population-level properties of both profiles. We find that the inner slope of the dark matter density profile (‘cusp’; ) is consistent ( with intrinsic scatter) with a standard Navarro–Frenk–White (NFW; ) at . Additionally, we find an appreciable evolution with redshift () resulting in a shallower slope (of tension from NFW) at redshifts . This is in excellent agreement with previous population-level observational studies, as well as with predictions from hydrodynamical simulations such as IllustrisTNG. We also find the stellar mass-to-light ratio at the population level is consistent with that of a Salpeter initial mass function, a small stellar mass-to-light gradient [, with ], and isotropic stellar orbits. Our averaged total mass density profile is consistent with a power-law profile within 0.25 to 4 Einstein radii (), with an internal mass-sheet transformation parameter consistent with no mass sheet. Our findings confirm the validity of the standard mass models used for time-delay cosmography.

Abstract:

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially resolved observations (∼100 pc resolution) of warm ionized-gas emission lines (Hβ, [O iii], [N ii], H, and [S ii]) from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope and cold molecular gas [12CO(2-1) or 12CO(3-2)] from the Atacama Large Millimeter/submillimeter Array to study the SF properties of eight ETGs and bulges. We use the ionized-gas emission lines to classify the ionization mechanisms and demonstrate a complete absence of regions dominated by SF ionization in these ETGs and bulges, despite abundant cold molecular gas. The ionization classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and H -derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF regulation mechanism for at least half of our sample galaxies.