Radial Distributions of Surface Mass Density and Mass-to-Luminosity Ratio in Spiral Galaxies

TL;DR

This study analyzes the radial distribution of surface mass density and mass-to-luminosity ratios in spiral galaxies using rotation curves, revealing how dark matter dominates at larger radii and providing data for galaxy formation models.

Contribution

It introduces a method to derive radial profiles of surface mass density and mass-to-luminosity ratios in spiral galaxies directly from rotation curves and photometric data.

Findings

ML peaks or plateaus at galaxy centers and decreases outward.

ML increases steeply beyond 2h, indicating dark matter dominance.

Profiles are compiled into an archival atlas for further research.

Abstract

We present radial profiles of the surface mass density (SMD) in spiral galaxies directly calculated using rotation curves (RC) on two approximations of flat-disk (SMD-F) and spherical mass distribution (SMD-S). The SMDs are combined with surface brightness (SB) using photometric data to derive radial variations of the mass-to-luminosity ratio (ML). It is found that ML has generally a central peak or a plateau, and decreases to a local minimum at $R\sim 0.1-0.2 h$, where $R$ is the radius and $h$ is the scale radius of optical disk. The ML ratio, then, increases rapidly till $\sim 0.5h$, and is followed by gradual rise till $\sim 2h$, remaining at around ML$\sim 2$ in w1 band (infrared $\lambda$ 3.4 $\mu$m) and $\sim 10\ [M_\odot L_\odot^{-1}]$ in r-band ($\lambda$6200-7500 A). Beyond this radius, ML steeply increases toward the observed edges at $R\sim 5h$, attaining values as high as ML$\sim 20$ in w1 and $\sim 10^2\ [M_\odot L_\odot^{-1}]$ in r-band, indicative of dominant dark matter. The general properties of the ML distributions will be useful to constrain cosmological formation models of spiral galaxies. The radial profiles of the RC, SMD, and ML are available in pdf/eps figures and machine-readable tables as an archival atlas at URL http://www.ioa.s.u-tokyo.ac.jp/$\sim$sofue/smd2018/ and as the supplementary data on PASJ home page.