论文标题
探索恒星形成的极端条件：深入搜索狮子座环中的分子气
Exploring extreme conditions for star formation: a deep search for molecular gas in the Leo ring
论文作者
论文摘要
我们对CO J = 1-0进行敏感搜索，并在LEO中的巨型外乳层HI环中进行J = 2-1线，以研究气体金属度接近太阳能的环境中的恒星形成过程，但物理条件与明亮的星系磁盘的典型物理条件不同。我们的目的是检查已知比例关系的有效性范围。我们使用IRAM-30M望远镜观察到靠近HI气峰的11个区域，或者发现稀疏的年轻大型恒星。对于所有尖的观测值，我们在2 km/s光谱分辨率下至少一个观察到的频率达到了1至5 mk之间的光谱噪声。我们在恒星形成区域的恒星形成区域中的两条CO j = 1-0线的狮子座环〜1，其径向速度与Halpha线的速度一致，但在星系中类似质量的病毒化的分子云中，线宽度要小得多。低信噪比，小线宽度和极低的数量密度表明，可能仍未被发现的分子云群体可能存在。使用CO线的上限，最敏感的尖头观察结果表明，分子气体质量表面密度低于在星系磁盘中建立的分子Kennicutt-Schmidt关系外推的预期。环中稀疏的恒星种群，可能形成超弥漫性矮星系，可能是在这个极端环境中短分子气体耗尽时间的结果。}
We carry out sensitive searches for the CO J=1-0 and J=2-1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas metallicities are close to solar but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations. We use the IRAM-30m telescope to observe eleven regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached a spectral noise between 1 and 5~mK for at least one observed frequencies at 2~km/s spectral resolution. We marginally detect two CO J=1-0 lines in the star forming region Clump~1 of the Leo ring, whose radial velocities are consistent with those of Halpha lines but line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths and the extremely low number densities suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt-Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.}
