The stellar and dark matter distributions in elliptical galaxies measured by stacked weak gravitational lensing

TL;DR

The paper investigates central stellar and dark matter distributions in elliptical galaxies using stacked weak lensing from the HSC-SSP survey. It employs a two-component inner profile (stellar component plus a cored dark matter component) together with an outer halo model that includes a smoothly truncated NFW central halo, satellites, and a 2-halo term, analyzing seven stellar-mass bins. The study finds evidence for central dark matter cores in two intermediate-mass bins while most bins are consistent with NFW-like centers; dark matter fractions within 5 r_e are lower than some hydrodynamical simulations, implying stronger feedback, and the derived SHMR favors higher stellar masses for a given halo mass with a bottom-heavy IMF. These results demonstrate the viability of weak-lensing stacking to constrain central density profiles, the galaxy–halo connection, and IMF in massive ellipticals, with implications for feedback processes and structure formation.

Abstract

We investigate stellar mass and central dark matter density profiles of photometric luminous red galaxies with stellar masses of $\sim10^{10}-10^{12}M_\odot$ using weak gravitational lensing measurements from the Hyper Suprime-Cam Subaru Strategic Program data obtained with the Subaru Telescope. By stacking weak lensing signals from a large number of galaxies, we obtain average tangential shear profiles down to $\sim 10\,\mathrm{kpc}/h$, which are fitted assuming a two-component model consisting of stellar and dark matter components to constrain their central dark matter distribution. We find a preference for non-zero core radii of dark matter distributions in galaxies with stellar masses of $\sim 10^{11}M_\odot$. Our results imply a stronger feedback effect than that typically predicted by current hydrodynamical simulations. In addition, we provide a new constraint on the stellar-to-halo mass relation, where both stellar and halo masses are, for the first time, directly constrained by weak gravitational lensing. Our results prefer the stellar initial mass function (IMF) that is more bottom-heavy than the Salpeter IMF.

Figures (9)

• Figure 1: Surface mass density profiles $\Delta\Sigma$ obtained from weak lensing measurements and the results of fitting the inner profiles. Different panels show results for different stellar mass bins. The green points show the observational results from stacked weak gravitational lensing. The magenta dash-dotted, the orange dashed, and the red solid lines indicate the stellar matter component, the dark matter component, and the total mass, respectively. The shaded region denotes the fitting range.
• Figure 2: Comparison of best-fit stellar masses $M_{\star,\mathrm{fit}}$ with those measured from the HSC-SSP photometric data, $M_{\star,\mathrm{in}}$. The blue points show our results and the dashed line shows $M_{\star,\mathrm{fit}}=M_{\star,\mathrm{in}}$. Points shown by the lighter color might be affected by systematic errors and therefore should be interpreted with caution (see the text for more details).
• Figure 3: The projected constraint on parameters from the inner profile fitting in the $\gamma$-$r_{\mathrm{c}}$ plane. Different panels show results for different stellar mass bins.
• Figure 4: Comparison between the dark matter density profile obtained from the inner profile fitting and the NFW profile fitted to the outer lensing profile, where the NFW profile includes additional contributions from the satellite component as well as 2-halo term (see Equation \ref{['eq:NFW']}). Different panels show results for different stellar mass bins. The orange dashed and blue solid lines indicate the dark matter distribution inferred from inner profile fitting and the NFW profile from the outer profile fitting, respectively. The magenta-shaded region denotes the inner-fitting range, and the light-blue shaded region shows the outer-fitting range.
• Figure 5: The ratio of the surface mass densities $f_{\Sigma}(r)$ defined in Equation \ref{['eq:fsigma']}. The shaded regions represent the $1\sigma$, $2\sigma$, and $3\sigma$ confidence intervals from darker to lighter colors. The vertical dashed line shows $r=5r_\mathrm{e}$. Different panels show results for different stellar mass bins.