Ionized and Cold Gas Components in Low Surface Brightness Galaxy AGC 102004

Abstract

We present the integral field spectroscopic observations of ionized gas (H α and [N II ]) using the PCWI, along with deep CO(2–1) observations by the ${}^{\unicode{x02035}}{\bar{{\rm{U}}}}^{\unicode{x02035}}\bar{{\rm{u}}}$ receiver on JCMT for AGC 102004. The velocity field of H α shows an anomalous distribution in the northwestern (NW) disk. The H α spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous H α in the NW disk. The Gaussian fit center of H α emission is offset by +24.2 km s ^−1 from the systemic velocity obtained from the H i emission. We derive the gas-phase metallicity, 12+log(O/H), using [N II ] λ 6583/H α ratio as a proxy. The mean value of 12+log(O/H) is 8.30 ± 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 nondetection 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 × 10 ^7 M _⊙ with X _CO = 3.02 × 10 ^20 cm ^−2 (K km s ^−1 ) ^−1 . The ${M}_{{{\rm{H}}}_{2}}$ / M ${}_{{\rm{H}}\,{\rm{I}}}^{{\rm{corr}}}$ of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

Keywords

• Low surface brightness galaxies
• Galaxy mergers
• Molecular gas
• Metallicity