Investigating HII Regions in the Disk of NGC 7331 with the Circumgalactic H$\alpha$ Spectrograph

TL;DR

This study uses integral field spectroscopy to analyze the ionized gas kinematics and star formation properties of HII regions in NGC 7331, revealing relationships between turbulence, star formation, and feedback in the galaxy's disk.

Contribution

First detailed kinematic and luminosity analysis of HII regions in NGC 7331 using CHαS, establishing the L(Hα)-σ relationship and star formation feedback effects.

Findings

HII regions exhibit a correlation between velocity dispersion and star formation rate surface density.

Turbulent HII regions are likely driven by stellar feedback.

The L(Hα)-σ relationship is characterized by specific parameters ε=80 and α=0.285.

Abstract

We investigate the ionized gas kinematics of HII regions in the disk of NGC 7331 using integral field unit data collected with the Circumgalactic H$\alpha$ Spectrograph (CH$\alpha$S). NGC 7331 is a well-studied nearby galaxy with HII regions resolved by seeing-limited observations, making it ideally suited for this work. The galaxy disk features vigorous star formation, especially in the central ring of starburst activity. We present a catalog of 136 HII regions detected in the SIRTF Nearby Galaxies Survey (SINGS) H$\alpha$ image. Using this refined catalog, we perform aperture photometry on the SINGS narrowband H$\alpha$ images of NGC 7331, extracting the H$\alpha$ luminosity L(H$\alpha$) of these regions. We present corresponding measurements of the average line-of-sight ionized gas velocity dispersion $\sigma$ in these HII regions with CH$\alpha$S. High-resolution velocity and dispersion maps of the galactic disk are produced from the CH$\alpha$S spectral imaging, selecting spaxels with high signal to noise in order to measure velocity dispersions as low as 12 km s$^{-1}$. Our measurements of the L(H$\alpha$), $\rm \Sigma_{SFR}$ and $\sigma$ in NGC 7331 are consistent with spatially resolved observations of HII regions in large surveys of nearby galaxies. We explore the L(H$\alpha$)$- \sigma$ relationship, identifying turbulent HII regions with nonthermal dispersions likely driven by stellar feedback. The dispersion is correlated with the star formation rate surface density, and using the relation $\rm \sigma \propto \epsilon \Sigma_{SFR}^{\alpha}$, HII regions in NGC 7331 are best fit by $\epsilon = 80$ , $\alpha =0.285$.