arXiv 1102.10192011-02-04astro-ph.CO

z~3-5星系质量-金属丰度关系的探讨

Exploring the Galaxy Mass-Metallicity Relation at z~3-5

Tanmoy Laskar, Edo Berger, Ranga-Ram Chary

备注：: 7 pages, 10 figures. Submitted to ApJ
DOI：: 10.1088/0004-637X/739/1/1

摘要：

长持续时间的伽马射线暴（GRB）由于其极端的亮度和与大质量恒星的联系，为研究高红移恒星形成星系提供了首要工具。本文利用伽玛暴研究了z~3-5处的星系恒星质量-金属丰度（M*-Z）关系。我们使用ISM金属丰度的LGRB主机来自余辉吸收光谱（Z~0.01-1太阳），结合主机星系恒星质量确定从深斯皮策3.6微米观测20 GRB主机。我们探测到约1/4的恒星I波段星等在-21.5到-22.5 AB等之间，并根据叠加分析对剩余的恒星设定了M > -19等的限制。利用这些观测结果，我们给出了长伽玛暴主天体在z>3时的第一静止坐标系光度分布，发现它与长伽玛暴主天体在z~1时的光度分布相似。与相同红移的莱曼破裂星系相比，伽玛暴的宿主通常更暗，但样本太小，无法排除整体相似的光度函数。另一方面，在z~3-4处，GRB宿主似乎比莱曼α发射体的种群更明亮。利用简单恒星星族（年龄在7000万年到200万年之间）的质光比的保守范围，我们推断了宿主恒星的质量，并给出了z~3-5（~ 3.5）处的质量-金属丰度测量结果<z>。我们发现，所检测到的伽玛射线暴主机，与M*~ 2 e10太阳质量，显示了广泛的金属丰度，但平均金属丰度在这个质量尺度，Z~0.1太阳，低于测量z<3。结合未检测到的M*<3e 9太阳质量和Z<0.03太阳质量的宿主的叠加，我们发现了在z~3.5处存在M*-Z关系的证据，并且这种关系从z~2开始持续演化为系统性的低金属丰度。

英文摘要：

Long-duration gamma-ray bursts (GRBs) provide a premier tool for studying high-redshift star-forming galaxies thanks to their extreme brightness and association with massive stars. Here we use GRBs to study the galaxy stellar mass-metallicity (M*-Z) relation at z~3-5, where conventional direct metallicity measurements are extremely challenging. We use the ISM metallicities of LGRB hosts derived from afterglow absorption spectroscopy (Z~0.01-1 solar), in conjunction with host galaxy stellar masses determined from deep Spitzer 3.6 micron observations of 20 GRB hosts. We detect about 1/4 of the hosts with I-band magnitudes ~ -21.5 to -22.5 AB mag, and place a limit of M > -19 mag on the remaining hosts from a stacking analysis. Using these observations, we present the first rest-frame optical luminosity distribution of long GRB hosts at z>3 and find that it is similar to the distribution of long GRB hosts at z~1. In comparison to Lyman-break galaxies at the same redshift, GRB hosts are generally fainter, but the sample is too small to rule out an overall similar luminosity function. On the other hand, the GRB hosts appear to be more luminous than the population of Lyman-alpha emitters at z~3-4. Using a conservative range of mass-to-light ratios for simple stellar populations (with ages of 70 Myr to ~2 Gyr), we infer the host stellar masses and present mass-metallicity measurements at z~3-5 (<z> ~ 3.5). We find that the detected GRB hosts, with M*~2e10 solar masses, display a wide range of metallicities, but that the mean metallicity at this mass scale, Z~0.1 solar, is lower than measurements at z<3. Combined with stacking of the non-detected hosts with M*< 3e9 solar masses and Z<0.03 solar, we find evidence for the existence of an M*-Z relation at z~3.5 and continued evolution of this relation to systematically lower metallicities from z~2.

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