Ionized and cold gas components in low surface brightness galaxy AGC 102004

Abstract

We present the integral field spectroscopic observations of ionized gas (H$\hat{I}\pm$ and [{\ion{N}{II}}]) using the PCWI, along with deep CO(2-1) observations by the ${}^{‵}{\bar{\mathrm{U}}}^{‵}\bar{\mathrm{u}}$ receiver on JCMT for AGC 102004. The velocity field of H$\hat{I}\pm$ shows an anomalous distribution in the North-Western (NW) disk. The H$\hat{I}\pm$ spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous H$\hat{I}\pm$ in the NW disk. The Gaussian fit center of H$\hat{I}\pm$ emission is offset by +24.2 km s${}^{-1}$ from the systemic velocity obtained from the HI emission. We derive the gas-phase metallicity, 12+log(O/H), using [{\ion{N}{II}}]$\hat{I}»$6583/H$\hat{I}\pm$ ratio as a proxy. The mean value of 12+log(O/H) is 8.30 $\pm$ 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2-1) emission has non-detection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s${}^{-1}$. The upper limit of molecular gas mass in AGC 102004 is 2.1 $\times$ 10${}^7$ M$\odot$ with X${}_{\mathrm{CO}}$ = 3.02$\times$10${}^{20}$ cm${}^{-2}$ (K km s${}^{-1}$)${}^{-1}$. The M${}_{{\mathrm{H}}_2}$/M${}_{\mathrm{HI}}^{\mathrm{corr}}$ of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

10 pages, 9 figures, Accepted for publication in ApJ