Relating the HI Gas Structure of Spiral Disks to Passing Satellites

TL;DR

This paper develops simple scaling relations linking the gas disk's density response in spiral galaxies to passing satellites' properties, validated with simulations and observations, revealing limitations in cosmological satellite models.

Contribution

It introduces new scaling relations for galactic gas response to satellites and tests their applicability with cosmological simulations and HI observations.

Findings

Scaling relations approximate disk response for two satellites.

Small perturbations match cosmological satellite effects.

Large perturbations like in M51 are not explained by typical satellites.

Abstract

We extend the work of Chang & Chakrabarti (2011) to find simple scaling relations between the density response of the gas disk of a spiral galaxy and the pericenter distance and mass ratio of a perturbing satellite. From the analysis of results from a test particle code, we obtained a simple scaling relation for the density response due to a single satellite interacting with a galactic disk, over a wide range of satellite masses and pericenter distances. We have also explored the effects of multiple satellites on the galactic disk, focusing on cases that are commonly found in cosmological simulations. Here, we use orbits for the satellites that are drawn from cosmological simulations. For these cases, we compare our approximate scaling relations to the density response generated by satellites, and find that for two satellite interactions, our scaling relations approximately recover the response of the galactic disk. We have also examined the observed HI data in the outskirts of several spiral galaxies from the THINGS sample and compared the observed perturbations to that of cosmological simulations and our own scaling relations. While small perturbations can be excited by satellites drawn from cosmological simulations, we find that large perturbations (such as those that are seen in some THINGS galaxies like M51) are not recovered by satellites drawn from cosmological simulations that are similar to Milky Way galaxies.