Emission from the Ionized Gaseous Halos of Low Redshift Galaxies and Their Neighbors

TL;DR

This study analyzes ionized gas emission in the halos of low-redshift galaxies using SDSS data, revealing an inflection point at 50 kpc likely due to correlated halos, and compares observations with simplified theoretical models.

Contribution

It extends previous work by identifying the radial emission inflection and testing a simplified model of gaseous halos against observational data.

Findings

Radial emission inflection at ~50 kpc linked to correlated halos

Simplified models reproduce the inflection's location and amplitude

Gaseous halo properties relate more to galaxy morphology than stellar mass

Abstract

Using a sample of nearly half a million galaxies, intersected by over 8 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we extend our previous study of the recombination radiation emitted by the gaseous halos of nearby galaxies. We identify an inflection in the radial profile of the H$\alpha$+N[{\small II}] radial emission profile at a projected radius of $\sim 50$ kpc and suggest that beyond this radius the emission from ionized gas in spatially correlated halos dominates the profile. We confirm that this is a viable hypothesis using results from a highly simplified theoretical treatment in which the dark matter halo distribution from cosmological simulations is straightforwardly populated with gas. Whether we fit the fraction of halo gas in a cooler (T $= 12,000$ K), smooth ($c = 1$) component (0.26 for galaxies with M$_* = 10^{10.88}$ M$_\odot$ and 0.34 for those with M$_* = 10^{10.18}$ M$_\odot$) or take independent values of this fraction from published hydrodynamical simulations (0.19 and 0.38, respectively), this model successfully reproduces the radial location and amplitude of the observed inflection. We also observe that the physical nature of the gaseous halo connects to primary galaxy morphology beyond any relationship to the galaxy's stellar mass and star formation rate. We explore whether the model reproduces behavior related to the central galaxy's stellar mass, star formation rate, and morphology. We find that it is unsuccessful in reproducing the observations at this level of detail and discuss various shortcomings of our simple model that may be responsible.