A Semi-Analytical Line Transfer (SALT) Model III: Galactic Inflows

TL;DR

This paper introduces a semi-analytical model for interpreting ultraviolet spectra of galactic inflows, revealing that medium-resolution observations can effectively identify inflowing gas through inverse P-Cygni profiles.

Contribution

The study extends the SALT model to simulate inflowing gas spectra, exploring various scenarios and highlighting the importance of medium-resolution spectroscopy for detecting galactic inflows.

Findings

Inflows can produce spectral features that mimic ISM signatures in low-resolution spectra.

Medium-resolution spectroscopy can resolve inverse P-Cygni profiles indicative of inflows.

Galactic inflows are likely undercounted due to spectral resolution limitations.

Abstract

We present calculations of ultraviolet spectra resulting from the scattering of photons by gas in-falling onto an isotropically emitting source of radiation. The model is based on an adaptation of the semi-analytical line transfer (SALT) code of Scarlata & Panagia (2015), and designed to interpret the inverse P-Cygni profiles observed in the spectra of partially ionized galactic inflows. In addition to presenting the model, we explore the parameter space of the inflowing SALT model and recreate various physically motivated scenarios including spherical inflows, inflows with covering fractions less than unity, and galactic fountains (i.e., galactic systems with both an inflowing and outflowing component). The resulting spectra from inflowing gas show spectral features that could be misinterpreted as ISM features in low resolution spectroscopy ($\sigma \approx 120$ $\rm{km }$ $\rm{s}^{-1}$), suggesting that the total number of galactic systems with inflows is undercounted. Our models suggest that observations at medium resolution ($R = 6000$ or $\sigma \approx 50$ $\rm{km }$ $\rm{s}^{-1}$) that can be obtained with 8m-class telescopes will be able to resolve the characteristic inverse P Cygni profiles necessary to identify inflows.