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

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$\alpha$), ${\mathrm{\Sigma }}_{\mathrm{SFR}}$ 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 $\sigma \propto \epsilon {\mathrm{\Sigma }}_{\mathrm{SFR}}^{\alpha }$, HII regions in NGC 7331 are best fit by $\epsilon =80$ , $\alpha =0.285$.

15 pages, 6 figures, 2 tables, Accepted for publication in ApJ