# SDSS--IV MaNGA : The Inner Density Slopes of nearby galaxies

## TL;DR

This study measures the total density slopes within the effective radius of over 2000 nearby galaxies, revealing a nearly constant slope for high-velocity dispersion galaxies and shallower slopes for dwarfs, with implications for dark matter halos.

## Contribution

It provides the first large sample analysis of density slopes across a wide range of galaxy masses using MaNGA data, highlighting the variation with velocity dispersion and galaxy environment.

## Key findings

- High-mass galaxies ($\sigma_v>100$ km/s) have an average density slope of 2.24.
- Dwarf galaxies ($M_*<10^{10} M_ ext{sun}$) tend to have slopes shallower than 1.
- Simulations predict shallower slopes for massive galaxies compared to observations.

## Abstract

We derive the mass weighted total density slopes within the effective (half-light) radius, $\gamma'$, for more than 2000 nearby galaxies from the SDSS-IV MaNGA survey using Jeans-anisotropic-models applied to IFU observations. Our galaxies span a wide range of the stellar mass ($10^9$ $M_{\rm \odot}< M_* < 10^{12}$ M$_{\odot}$) and the velocity dispersion (30 km/s $< \sigma_v <$ 300 km/s). We find that for galaxies with velocity dispersion $\sigma_v>100$ km/s, the density slope has a mean value $\langle \gamma^{\prime} \rangle = 2.24$ and a dispersion $\sigma_{\gamma}=0.22$, almost independent of velocity dispersion. A clear turn over in the $\gamma'-\sigma_v$ relation is present at $\sigma\sim 100$ km/s, below which the density slope decreases rapidly with $\sigma_v$. Our analysis shows that a large fraction of dwarf galaxies (below $M_* = 10^{10}$ M$_{\odot}$) have total density slopes shallower than 1, which implies that they may reside in cold dark matter halos with shallow density slopes. We compare our results with that of galaxies in hydrodynamical simulations of EAGLE, Illustris and IllustrisTNG projects, and find all simulations predict shallower density slopes for massive galaxies with high $\sigma_v$. Finally, we explore the dependence of $\gamma'$ on the positions of galaxies in halos, namely centrals vs. satellites, and find that for the same velocity dispersion, the amplitude of $\gamma'$ is higher for satellite galaxies by about 0.1.