Title: A Search for Molecular Gas in the Host Galaxy of FRB 121102 Show Chinese title

Title: FRB 121102宿主星系中的分子气体搜寻

Abstract: We present SMA and NOEMA observations of the host galaxy of FRB 121102 in the CO 3-2 and 1-0 transitions, respectively. We do not detect emission from either transition. We set $3\sigma$ upper limits to the CO luminosity $L_{CO} < 2.5 \times 10^7\,{\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$ for CO 3-2 and $L_{CO} < 2.3 \times 10^9\, {\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$ for CO 1-0. For Milky-Way-like star formation properties, we set a $3\sigma$ upper limit on the $H_2$ mass of $2.5 \times 10^8 \rm\ M_{\odot}$, slightly less than the predictions for the $H_2$ mass based on the star formation rate. The true constraint on the $H_2$ mass may be significantly higher, however, because of the reduction in CO luminosity that is common forlow-metallicity dwarf galaxies like the FRB host galaxy. These results demonstrate the challenge of identifying the nature of FRB progenitors through study of the host galaxy molecular gas. We also place a limit of 42 $\mu$Jy ($3\sigma$) on the continuum flux density of the persistent radio source at 97 GHz, consistent with a power-law extrapolation of the low frequency spectrum, which may arise from an AGN or other nonthermal source. Show Chinese abstract

Abstract: 我们分别利用SMA和NOEMA观测了FRB 121102宿主星系中的CO 3-2和1-0跃迁。我们未能探测到来自任一跃迁的发射。对于CO 3-2，我们得到了$3\sigma$的亮度上限$L_{CO} < 2.5 \times 10^7\,{\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$；对于CO 1-0，我们得到了$L_{CO} < 2.3 \times 10^9\, {\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$的亮度上限。对于类似银河系的恒星形成属性，我们得到了$3\sigma$的质量上限$H_2$为$2.5 \times 10^8 \rm\ M_{\odot}$，略低于基于恒星形成率对$H_2$质量的预测值。 然而，由于类似FRB宿主星系的低金属矮星系通常会减少CO辐射强度，因此对$H_2$质量的真实限制可能要高得多。 这些结果展示了通过研究宿主星系的分子气体来识别FRB前身天体性质的挑战。 我们还对97 GHz处持续射电源的连续通量密度设定了一个42 $\mu$Jy（$3\sigma$）的上限，这与低频谱的幂律外推一致，该频谱可能来源于活动星系核（AGN）或其他非热源。