GMRT CAT$z$1-COSMOS巡天：COSMOS天区中$z\approx1$处恒星形成星系的HI 21厘米发射
The GMRT CAT$z$1-COSMOS Survey: HI 21 cm emission from star-forming galaxies at $z\approx1$ in the COSMOS field
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中文总结 AI 辅助
通过GMRT对COSMOS天区216小时观测，叠加8,122个恒星形成星系的HI 21厘米信号，以4.2σ显著性测得平均HI质量，证实z<1处恒星形成率下降源于原子气体吸积不足。
中文摘要 AI 辅助
我们报告了升级后的巨米波射电望远镜（GMRT）Band-4 $550-850$ MHz对COSMOS天区的216小时观测，使用7个GMRT指向覆盖了$2.4$平方度的面积，其中中心指向的源上时间为67小时，其余六个指向共分配89小时。我们在90千秒差距的空间分辨率下，对8,122个具有精确光谱红移且位于其红移HI 21厘米频率处GMRT主波束半功率宽度内的恒星形成星系的HI 21厘米发射信号进行了叠加。我们在$4.2\sigma$显著性水平上探测到这8,122个星系的叠加HI 21厘米信号，获得平均HI质量为$\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$。这是第二个在$z\approx1$处测得平均HI含量的星系群；另一个是DEEP2天区中的蓝色恒星形成星系。我们还通过叠加GMRT 680 MHz连续谱图像，探测到这8,122个星系的中值1.4 GHz射电连续谱发射信号，获得加权中值恒星形成率（SFR）为${8.90\pm0.92}~M_\odot$ yr$^{-1}$。我们测量了COSMOS中$\langle{z}\rangle=1.081$处恒星形成星系的特征HI-恒星质量比为$\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$，以及特征HI消耗时标为$\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr，两者均与之前在$z\approx1$处蓝色恒星形成DEEP2星系的测量结果一致。我们的结果支持来自DEEP2巡天的证据，即观测到的$z<1$处SFR密度下降是由于星系际介质中原子气体吸积不足，无法补充恒星形成过程中消耗的气体储备。
英文摘要
We report a 216-hr upgraded Giant Metrewave Radio Telescope (GMRT) Band-4 $550-850$ MHz observation of the COSMOS field, using 7 GMRT pointings to cover an area of $2.4$ sq. deg., with on-source times of $67$ hrs in the central pointing, and $89$ hrs distributed across the other six pointings. We stacked, at a spatial resolution of 90 kpc, the HI 21 cm emission signals from 8,122 star-forming galaxies with accurate spectroscopic redshifts and lying within the FWHM of the GMRT primary beam at their redshifted HI 21 cm frequencies. We detect the stacked HI 21 cm signal from the 8,122 galaxies at $4.2σ$ significance, obtaining an average HI mass of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle=(15.5\pm3.7)\times10^9 \textrm{M}_\odot$. This is only the second galaxy population at $z\approx1$ with a measurement of the average HI content; the other being the blue star-forming galaxies in the DEEP2 fields. We also detected the median 1.4 GHz radio continuum emission signal from the 8,122 galaxies by stacking the GMRT 680 MHz continuum images, obtaining a weighted-median star-formation rate (SFR) of ${8.90\pm0.92}~M_\odot$ yr$^{-1}$. We measure a characteristic HI-to-stellar mass ratio of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\langle{M_\star}\rangle=(1.15\pm0.27)$ and a characteristic HI depletion timescale of $\langle{M_{\scriptsize{\textrm{HI}}}}\rangle/\textrm{SFR}=(1.74\pm0.45)$ Gyr for star-forming galaxies at $\langle{z}\rangle=1.081$ in COSMOS, both consistent with earlier measurements for the blue, star-forming DEEP2 galaxies at $z\approx1$. Our results support the evidence from the DEEP2 survey that the observed decline in the SFR density at $z<1$ is due to insufficient accretion of atomic gas from the intergalactic medium to replenish the gas reservoir consumed in the process of star-formation.
发表机构
- Inter-University Centre for Astronomy and Astrophysics（天文与天体物理大学间中心）
- National Centre for Radio Astrophysics, Tata Institute of Fundamental Research（塔塔基础研究所国家射电天文学中心）
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