Satellite galaxy velocity dispersions in the SDSS and modified gravity models

TL;DR

This paper uses SDSS galaxy data to compare gravitational models by analyzing satellite galaxy velocity dispersions, incorporating interloper effects to assess the viability of different gravity theories.

Contribution

It introduces a method that accounts for interlopers in velocity dispersion analysis, enabling comparison of gravity models without needing to isolate true satellite galaxies.

Findings

Interloper contamination prevents exclusion of several gravity theories.

Incorporating interlopers allows better modeling of galaxy velocity data.

Current SDSS data is insufficient to definitively test modified gravity models.

Abstract

The Sloan Digital Sky Survey (SDSS) provides data on several hundred thousand galaxies. Precise location of these galaxies in the sky, along with information about their luminosities and line-of-sight (Doppler) velocities allows one to construct a three-dimensional map of their location and estimate their line-of-sight velocity dispersion. This information, in principle, allows one to test dynamical gravity models, specifically models of satellite galaxy velocity dispersions near massive hosts. A key difficulty is the separation of true satellites from interlopers. We sidestep this problem by not attempting to derive satellite galaxy velocity dispersions from the data, but instead incorporate an interloper background into the mathematical models and compare the result to the actual data. We find that due to the presence of interlopers, it is not possible to exclude several gravitational theories on the basis of the SDSS data.