Modeling Nearly Spherical Pure-Bulge Galaxies with Stellar Mass-to-Light Ratio Gradient under $Λ$CDM and MOND Paradigms: I. Methodology, Dynamical Stellar Mass and Fundamental Mass Plane [GA]

We carry out spherical Jeans modeling of nearly round pure-bulge galaxies selected from the ATLAS$^{\rm 3D}$ (A3D) sample, with the goal of investigating astrophysical problems including dark matter, modified gravity, galactic structure and velocity dispersion (VD) anisotropy. Our analysis allows for gradients in the stellar mass-to-light ratio ($M_\star/L$) and uses a generalized Osipkov-Merritt model for the VD anisotropy. We produce Monte Carlo sets of models based on the stellar VD profiles under both the LCDM and the MOND paradigms. For the case of the LCDM paradigm we use empirical properties of dark halos from the literature.
Here we describe the galaxy data, the empirical inputs, and the modeling procedures of obtaining the Monte Carlo sets. We then present the projected dynamical stellar mass, $M_{\rm \star e}$, within the effective radius $R_{\rm e}$, and the fundamental mass plane (FMP) as a function of gradient strength $K$ defined so that the van Dokkum et al gradient corresponds to $K=1$. We find the scaling of the $K$-dependent mass with respect to the A3D reported mass as: $\log_{10} [M_{\rm \star e}(K)/M_{\rm \star e}^{\rm A3D}] = a’ + b’ K$ with $a’=-0.019\pm 0.012$ and $b’=-0.18\pm 0.02$ (LCDM), or $a’=-0.023\pm 0.014$ and $b’=-0.23\pm 0.03$ (MOND), for $0\le K < 1.5$. The derived FMP has coefficients consistent with the virial expectation and only the zero point scales with $K$. The median value of $K$ from the Monte Carlo sets for the A3D galaxies is $\langle K\rangle =0.53^{+0.05}_{-0.04}$.
We perform a similar analysis of the much larger SDSS DR7 spectroscopic sample. In this case, we use the additional requirement that the VD slope be similar to that in the A3D galaxies. Our analysis of the SDSS galaxies suggests a positive correlation of $K$ with stellar mass with the degree of correlation depending on $\langle K\rangle$. (abridged)

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K. Chae, M. Bernardi and R. Sheth
Tue, 3 Apr 18
29/57

Comments: 44 pages, 20 figures, submitted to ApJ