arXiv 0809.17722008-09-10astro-ph

HI和大多数缺金属星系中的恒星形成

HI and star formation in the most metal-deficient galaxies

Ekta, Jayaram N. Chengalur, S. A. Pustilnik

备注：: 11 pages, 11 figures. Accepted for publication in MNRAS
DOI：: 10.1111/j.1365-2966.2008.13928.x

摘要：

我们提出了三个巨型米波射电望远镜（GMRT）的观测（即，DDO 68，SDSS J2104-0035和UGC 772）是已知的六个最缺乏金属的活跃恒星形成星系。虽然对于这些星系是否正在经历恒星形成的第一阶段还存在争议，但它们是“年轻”的，因为它们的ISM在化学上是未进化的。在这方面，它们是早期宇宙中最接近年轻星系的等价物。我们观察到的这三个星系都有不规则的HI形态和运动学，我们将其解释为与邻近星系的潮汐相互作用，或者最近合并的后果。六个最缺乏金属的星系中剩下的三个也被认为具有高度干扰的HI分布，并且正在相互作用。这很有趣，因为这些星系仅仅是根据它们的金属丰度而不是任何特定的相互作用迹象来选择的。在这个意义上（即，它们的气体还没有时间进入一个规则的圆盘），人们可以把这些极度缺乏金属（XMD）的星系看作是“X”。目前的恒星形成事件很可能是由相互作用/合并引发的。也有可能是潮汐相互作用导致了与外盘贫金属气体的混合增强，从而导致中心恒星形成区的气相金属丰度较低。我们还发现，在一般情况下，这些星系不显示高HI柱密度和当前的恒星形成区域之间的一一对应关系。然而，在某种程度上，人们可以定义一个阈值密度，它的值（~10^{21}个原子cm^{-2}）类似于具有更高金属丰度的星系。

英文摘要：

We present Giant Metrewave Radio Telescope (GMRT) observations for three (viz., DDO 68, SDSS J2104-0035 and UGC 772) of the six most metal-deficient actively star-forming galaxies known. Although there is a debate as to whether these galaxies are undergoing their first episode of star formation or not, they are `young' in the sense that their ISM is chemically unevolved. In this regard, they are the nearest equivalents of young galaxies in the early Universe. All three galaxies, that we have observed, have irregular HI morphologies and kinematics, which we interpret as either due to tidal interaction with neighbouring galaxies, or the consequences of a recent merger. The remaining three of the six most metal-deficient galaxies are also known to have highly disturbed HI distributions and are interacting. It is interesting because these galaxies were chosen solely on the basis of their metallicity and not for any particular signs of interaction. In this sense (i.e., their gas has not yet had time to settle into a regular disc), one could regard these extremely metal deficient (XMD) galaxies as `young'. The current star formation episode is likely to have been triggered by interaction/merger. It is also possible that the tidal interaction has lead to enhanced mixing with metal-poor gas in outer disc, and hence to a low gas-phase metallicity in the central star-forming regions. We also find that in general these galaxies do not show a one-to-one correspondence between regions of high HI column density and regions with current star formation. However, to the extent that one can define a threshold density, its value (~10^{21} atoms cm^{-2}) is similar to that in galaxies with much higher metallicity.

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