Spatially resolved stellar-to-total dynamical mass relation: Radial variations, gradients and profiles of galaxy stellar populations

Abstract

Although galaxy evolution is governed by the interplay between baryonic physics and dark matter halo assembly, how halo properties shape observed galaxies remains unclear. With current challenges in measuring halo properties, the stellar-to-total dynamical mass relation is introduced as an alternative metric sensitive to the dark matter content within galaxies. We explore how spatially resolved stellar population properties vary across this relation using optical IFS data and photometry from 265 CALIFA galaxies. Spatially resolved ages and metallicities, [M/H], are derived using a Bayesian framework fed with a library of model spectra based on stochastic star formation and metallicity histories and dust attenuation. We study these properties in terms of both stellar and total dynamical mass, with the latter being enclosed mass within three effective radii from Jeans dynamical modeling. We find that ages and [M/H] measured at different annuli depend on both stellar and total mass, yet showing distinct radial trends. While the dependence of age on total mass is more prominent in the outskirts, that of [M/H] is significant in the inner parts. This behavior is reflected in the stellar population profiles and gradients, more strongly for age and connected to morphology. Intermediate-mass early-types have higher stellar-to-total mass ratios and flatter age profiles with older ages, and steep negative [M/H] profiles, whereas later-types have lower stellar-to-total mass ratios, negative age profiles with younger ages and shallower negative [M/H] profiles. Moreover, at fixed stellar mass galaxies have more negative age gradients and shallower [M/H] ones as total mass increases. Our results show that total dynamical mass is linked to systematic variations in stellar populations and radial gradients at fixed stellar mass, suggesting a relevant role of dark matter halos in shaping galaxy properties

Figures (11)

• Figure 1: Stellar-to-total dynamical mass relation for our CALIFA galaxies in terms of stellar population properties measured at different annul. Each column corresponds to a different annulus with increasing galactocentric distance from left to right (see text). Galaxies are shown as circles colored-coded by median ages (upper rows) and metallicities (bottom rows) measured within their corresponding annuli. Partial correlation coefficient strengths are shown in the bottom right corner (solid black or green lines) between the stellar population parameters and $M_{\star}$ (vertical) and $M_{tot}$ (horizontal). Black (green) lines correspond to statistically (not) significant partial correlation coefficients. Grey solid lines have a length which corresponds to a correlation coefficient of 0.6 for reference. The direction of maximal increase of the stellar population parameters (see text) is indicated as a blue solid line when both partial correlation coefficients are significant, while red if at least one of the two is not significant
• Figure 2: Stellar population gradients across the stellar-to-total dynamical mass relation. Galaxies are shown as circles colored-coded by age gradient, $\nabla \log \rm Age$, (upper panels), and metallicity gradient, $\nabla \rm [M/H]$, (lower panels). Inner gradient (left panels), outer gradient (middle panels) and the global gradient (right panels). Partial correlation coefficient strengths are shown in the bottom right corner (solid black or green lines) between the $\nabla \log \rm Age$ / $\nabla \rm [M/H]$ and $M_{\star}$ (vertical) and $M_{tot}$ (horizontal). Black (green) lines correspond to statistically (not) significant partial correlation coefficients. Grey solid lines have a length which corresponds to a correlation coefficient of 0.6 for reference. The direction of maximal increase of the stellar population parameters (see text) is indicated as a blue solid line when both partial correlation coefficients are significant, while red if at least one of the two is not significant.
• Figure 3: Mean stellar-to-total dynamical mass relation for CALIFA. Galaxies are divided according to the position of the mean STDMR (black solid line). Galaxies above the mean relation are shown with red, and while the ones below with blue circles.
• Figure 4: Scaling relations between age/[M/H] and stellar mass for galaxies with different positions with respect to the mean STDMR. Scaling relations with age are shown in the upper panels and the ones with [M/H] in the bottom ones. Ages ([M/H]) are measured within the inner ($r/R_e \leq 1$) and within outer regions ($1 <r/R_e \leq 1.5$) of the galaxies (left and right panels respectively). For individual galaxies, median ages ([M/H]) (computed within the corresponding annuli) are plotted as a function of stellar mass color-coded with their vertical offset with respect to the mean STDMR (in the STDMR plane). Median ages ([M/H]) of the galaxies above and below the STDMR (see Fig. \ref{['fig:meanTDMR_class']}) are indicated with solid lines, red for galaxies above the mean STDMR and blue for the ones below.
• Figure 5: Scaling relations between age/[M/H] and total mass for galaxies at different radial annuli, with different positions with respect to the mean STDMR. Scaling relations with age are shown in the upper panels, and the ones with [M/H] in the bottom ones. Ages ([M/H]) are measured within the inner ($r/R_e \leq 1$) and within outer regions ($1 <r/R_e \leq 1.5$) of the galaxies (left and right panels respectively). For individual galaxies, median ages ([M/H]) (computed within the corresponding annuli) are plotted as a function of total mass color-coded with their vertical offset with respect to the mean STDMR (in the STDMR plane). Median ages ([M/H]) of the galaxies above and below the STDMR are indicated with solid lines, red for galaxies above the mean STDMR and blue for the ones below (see Fig. \ref{['fig:meanTDMR_class']}). To guide the eye, a halo mass conversion is reported in the upper axis (see text).