Spitzer 24 Micron Observations of Optical/Near-Infrared-Selected Extremely Red Galaxies: Evidence for Assembly of Massive Galaxies at z ∼ 1-2?
Spitzer 24 Micron Observations of Optical/Near-Infrared-Selected Extremely Red Galaxies: Evidence for Assembly of Massive Galaxies at z ∼ 1-2?
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DOI：
10.1086/422917
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发表时间：
2004-09
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通讯作者：
Lin Yan;P. Choi;D. Fadda;F. Marleau;B. Soifer;M. Im;L. Armus;D. Frayer;L. Storrie-Lombardi;D. Thompson;H. Teplitz;G. Helou;P. Appleton;Scott C. Chapman;F. Fan;I. Heinrichsen;M. Lacy;D. Shupe;G. Squires;J. Surace;Gillian Wilson
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作者：
Lin Yan;P. Choi;D. Fadda;F. Marleau;B. Soifer;M. Im;L. Armus;D. Frayer;L. Storrie-Lombardi;D. Thompson;H. Teplitz;G. Helou;P. Appleton;Scott C. Chapman;F. Fan;I. Heinrichsen;M. Lacy;D. Shupe;G. Squires;J. Surace;Gillian Wilson
我们使用斯皮策太空望远镜的 24 μm 数据，对 (R - Ks) ≥ 5.3 星等且 Ks < 20.2 星等的极红星系样本中的尘埃源比例进行了直接测量。结合斯皮策初探勘测 (FLS) ELAIS N1 中约 64 arcmin2 区域内的深 24 μm Ks 和 R 波段数据，我们发现我们的极红物体 (ERO) 样本中 50% ± 6% 的可测量 24 μm 通量高于 40 μJy 的 3 σ 通量限制。该通量极限对应于 z ∼ 1 处 12 M⊙ yr-1 的恒星形成率 (SFR)，比之前的任何长波长测量都灵敏得多。 24 μm 检测到的 ERO 具有 24 μm/2.2 μm 和 24 μm/0.7 μm 通量比，与 z ≥ 1 时的红外发光、尘埃源一致，并且其红色数量级太红，无法用任何红移处的红外静止螺旋或纯老恒星群来解释。其中一些 24 μm 检测到的 ERO 可能是活跃的星系核；然而，根据深度 X 射线观测和光谱分析，整个 ERO 样本中的比例可能很小，为 10%-20%。 FLS 场中类似选择的 ERO 样本的 Keck 光谱表明 ELAIS N1 中的大多数 ERO 可能位于 z ∼ 1。24 μm 检测到的 ERO 样本的平均 24 μm 通量 (167 μJy) 大致对应于 z ∼ 1 处的 3 × 1010 L⊙ 的静止帧 12 μm 光度 νLν(12 μm)。的 根据IRAS νLν(12 μm)和红外光度LIR(8-1000 μm)之间的相关性，我们推断24 μm探测到的ERO在z = 1.0和1.5时分别为3×1011和1×1012 L⊙，与局地发光红外星系(LIRGs)和超发光红外星系相似。 （ULIRG）。相应的恒星形成率大约为 50-170 M⊙ yr-1。如果根据本地 LIRG 和 ULIRG 推断，该星暴阶段的时间尺度约为 108 年，则这些 24 μm 检测到的 ERO 的质量下限为 5 × 109 至 2 × 1010 M⊙。一些星暴 ERO 在 z ∼ 1-2 时期正处于剧烈转变过程中，成为大质量早期型星系，这似乎是合理的。
We carried out direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) ≥ 5.3 mag and Ks < 20.2 mag, using 24 μm data from the Spitzer Space Telescope. Combining deep 24 μm Ks- and R-band data over an area of ∼64 arcmin2 in ELAIS N1 of the Spitzer First Look Survey (FLS), we find that 50% ± 6% of our extremely red object (ERO) sample have measurable 24 μm flux above the 3 σ flux limit of 40 μJy. This flux limit corresponds to a star formation rate (SFR) of 12 M⊙ yr-1 at z ∼ 1, much more sensitive than any previous long-wavelength measurement. The 24 μm-detected EROs have 24 μm/2.2 μm and 24 μm/0.7 μm flux ratios consistent with infrared luminous, dusty sources at z ≥ 1, and are an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Some of these 24 μm-detected EROs could be active galactic nuclei; however, the fraction among the whole ERO sample is probably small, 10%-20%, as suggested by deep X-ray observations as well as optical spectroscopy. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z ∼ 1. The mean 24 μm flux (167 μJy) of the 24 μm-detected ERO sample roughly corresponds to the rest-frame 12 μm luminosity, νLν(12 μm), of 3 × 1010 L⊙ at z ∼ 1. Using the correlation between IRAS νLν(12 μm) and infrared luminosity LIR(8-1000 μm), we infer that the of the 24 μm-detected EROs is 3 × 1011 and 1 × 1012 L⊙ at z = 1.0 and 1.5, respectively, similar to that of local luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies (ULIRGs). The corresponding SFR would be roughly 50-170 M⊙ yr-1. If the timescale of this starbursting phase is on the order of 108 yr as inferred for the local LIRGs and ULIRGs, the lower limit on the masses of these 24 μm-detected EROs is 5 × 109 to 2 × 1010 M⊙. It is plausible that some of the starburst EROs are in the midst of a violent transformation to become massive early type galaxies at the epoch of z ∼ 1-2.