The M81 Group Dwarf Irregular Galaxy DDO 165. II. Connecting Recent Star Formation with ISM Structures and Kinematics

TL;DR

This study links recent star formation activity in the dwarf galaxy DDO 165 with the observed structures and dynamics of its neutral interstellar medium, demonstrating that stellar feedback can account for the formation of HI holes and high velocity gas features.

Contribution

It provides a detailed analysis connecting star formation histories with ISM structures, confirming feedback as a primary mechanism for creating HI holes in DDO 165.

Findings

Feedback energy matches the energy needed for HI holes

High velocity gas features correlate with recent star formation

Extended star formation activity can produce observed ISM structures

Abstract

We compare the stellar populations and complex neutral gas dynamics of the M81 group dIrr galaxy DDO 165 using data from the HST and the VLA. Paper I identified two kinematically distinct HI components, multiple localized high velocity gas features, and eight HI holes and shells (the largest of which spans ~2.2x1.1 kpc). Using the spatial and temporal information from the stellar populations in DDO 165, we compare the patterns of star formation over the past 500 Myr with the HI dynamics. We extract localized star formation histories within 6 of the 8 HI holes identified in Paper I, as well as 23 other regions that sample a range of stellar densities and neutral gas properties. From population synthesis modeling, we derive the energy outputs (from stellar winds and supernovae) of the stellar populations within these regions over the last 100 Myr, and compare with refined estimates of the energies required to create the HI holes. In all cases, we find that "feedback" is energetically capable of creating the observed structures in the ISM. Numerous regions with significant energy inputs from feedback lack coherent HI structures but show prominent localized high velocity gas features; this feedback signature is a natural product of temporally and spatially distributed star formation. In DDO 165, the extended period of heightened star formation activity (lasting more than 1 Gyr) is energetically capable of creating the observed holes and high velocity gas features in the neutral ISM.