直接成像阻尼Ly-alpha星系在z>2。III：z~2.7中性气藏的恒星形成率
Directly imaging damped Ly-alpha galaxies at z>2. III: The star formation rates of neutral gas reservoirs at z~2.7
摘要：
我们目前的调查结果，旨在探讨恒星形成的32阻尼Ly-alpha系统（DLAs）在z~2.7的属性。利用消除亮背景类星体眩光的“双DLA”技术，我们直接测量了DLA及其邻近星系的静止坐标系FUV通量。在吸收气体的位置，我们对DLAs的未被遮蔽的恒星形成率（SFR）进行了严格的限制，即2 σ极限为<0.09-0.27 M/yr，对应于SFR表面密度<10^（-2.6）-10 ^（-1.5）M/yr/kpc ^[2]。这些限制的恒星形成规律，金属富集，和DLAs的冷却速率的影响进行了研究。通过研究碰撞参量的分布作为SFR的函数检测到这些DLA周围的所有星系，我们把新的直接约束的DLA主机的UV光度函数的亮端。我们发现<13% of the hosts have SFR>在碰撞参量b <（SFR/（M/yr））^（0.8）+6 kpc时，2 M/yr，与目前已确认的DLA星系样品不同。我们的观测结果也不支持这样一种情况，即大多数DLA来自距离20 < b < 100 kpc的明亮LBG。这些新的发现证实了这样一种观点，即DLAs并不来自与吸收体重合的高度恒星形成系统，而是表明DLAs与微弱的、可能孤立的恒星形成星系有关。这种情况下的潜在缺点和未来的进一步调查的策略进行了讨论。
英文摘要：
We present results from a survey designed to probe the star formation properties of 32 damped Ly-alpha systems (DLAs) at z~2.7. By using the "double-DLA" technique that eliminates the glare of the bright background quasars, we directly measure the rest-frame FUV flux from DLAs and their neighbouring galaxies. At the position of the absorbing gas, we place stringent constraints on the unobscured star formation rates (SFRs) of DLAs to 2-sigma limits of <0.09-0.27 M/yr, corresponding to SFR surface densities <10^(-2.6)-10^(-1.5) M/yr/kpc^2. The implications of these limits for the star formation law, metal enrichment, and cooling rates of DLAs are examined. By studying the distribution of impact parameters as a function of SFRs for all the galaxies detected around these DLAs, we place new direct constraints on the bright end of the UV luminosity function of DLA hosts. We find that <13% of the hosts have SFR>2 M/yr at impact parameters b < (SFR/(M/yr))^(0.8)+6 kpc, differently from current samples of confirmed DLA galaxies. Our observations also disfavor a scenario in which the majority of DLAs arise from bright LBGs at distances 20 < b < 100 kpc. These new findings corroborate a picture in which DLAs do not originate from highly star forming systems that are coincident with the absorbers, and instead suggest that DLAs are associated with faint, possibly isolated, star-forming galaxies. Potential shortcomings of this scenario and future strategies for further investigation are discussed.
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