五百米口径球面Radio Telescope揭示的z $\sim$ 0.05恒星形成星系的原子气体
The atomic gas of star-forming galaxies at z$\sim$0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope
摘要：
我们报告了在500米口径球面射电望远镜（FAST）调试阶段对4个z $\sim$ 0.05恒星形成星系进行的新的HI观测。FAST是世界上最大的单碟望远镜，拥有500米口径和19束接收器。利用FAST提供的前所未有的灵敏度，我们的目标是研究原子气体，通过HI 21厘米发射线，在低$z$恒星形成星系从瓦尔帕莱索ALMA/APEX线发射调查（VALES）项目。与以前的ALMA CO（$J=1-0$）观测一起，HI数据提供了测量气体质量和动力学的关键信息。作为一个试点HI调查，我们瞄准了四个本地恒星形成星系在$z\sim0.05$。特别是，其中一个已经在HI中被Arecibo Legacy Fast ALFA调查（ALCAFA）检测到，允许仔细比较。我们使用一个ON-OFF的观测方法，使我们能够达到0.7mJy/束的均方根在1.7km/s的速度分辨率内只有20分钟的目标积分时间。我们展示了FAST 19束接收器的巨大能力，推动了银河系外源HI发射线的可探测性。FAST探测到的HI谱线与ALTAFA的结果一致。我们的观测与以前的多波长数据的背景下，揭示这些低$z$星系的物理性质。我们发现CO（$J=1-0$）和HI的发射谱线轮廓是相似的。由HI数据估算的动力学质量比由CO观测得到的动力学质量和重子质量高一个数量级，这意味着由HI动力学探测的质量主要由暗物质晕决定。在一种情况下，一个目标显示过量的CO（$J=1-0$）在线中心，这可以解释为一个增强的CO（$J=1-0$）的排放所引起的核星暴显示高速色散。
英文摘要：
We report new HI observations of four z$\sim$0.05 star-forming galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). FAST is the largest single-dish telescope with a 500 meter aperture and a 19-Beam receiver. Exploiting the unprecedented sensitivity provided by FAST, we aim to study the atomic gas, via the HI 21cm emission line, in low-$z$ star-forming galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES) project. Together with previous ALMA CO($J=1-0$) observations, the HI data provides crucial information to measure the gas mass and dynamics. As a pilot HI survey, we targeted four local star-forming galaxies at $z\sim0.05$. In particular, one of them has already been detected in HI by the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing a careful comparison. We use an ON-OFF observing approach that allowed us to reach an rms of 0.7mJy/beam at a 1.7km/s velocity resolution within only 20 minutes ON-target integration time. We demonstrate the great capabilities of the FAST 19-beam receiver for pushing the detectability of the HI emission line of extra-galactic sources. The HI emission line detected by FAST shows good consistency with the previous ALFALFA results. Our observations are put in context with previous multi-wavelength data to reveal the physical properties of these low-$z$ galaxies. We find that the CO($J=1-0$) and HI emission line profiles are similar. The dynamical mass estimated from the HI data is an order of magnitude higher than the baryon mass and the dynamical mass derived from the CO observations, implying that the mass probed by dynamics of HI is dominated by the dark matter halo. In one case, a target shows an excess of CO($J=1-0$) in the line centre, which can be explained by an enhanced CO($J=1-0$) emission induced by a nuclear starburst showing high velocity dispersion.
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