引力透镜星系SMM J163554 .2+661225的帕邢α辐射
Paschen-alpha Emission in the Gravitationally Lensed Galaxy SMM J163554.2+661225
摘要：
我们报告的检测帕邢α发射线的z=2.515星系SMM J163554.2+661225使用斯皮策光谱。SMM J163554.2+661225是一个亚毫米选择的红外（IR）发光星系，维持着很高的恒星形成率（SFR），没有来自光学或红外光谱的活动星系核证据，也没有X射线发射。这个星系被Abell 2218星系团引力透镜化，使得它可以被斯皮策光谱仪观测到。对由H-α和Pa-α谱线推导出的星云消光进行校正后，尘埃校正后的光度为L（Pa-α）=（2.57+/-0.43）x 10^43 erg s^-1，这对应于电离率Q =（1.6+/-0.3）x 10^55 photons s^-1。假设初始质量函数类似萨尔彼得，瞬时SFR是每年171+/-28太阳质量。使用70、450和850微米数据得到的总红外光度为L（IR）=（5-10）x 10^11太阳光度，并对引力透镜进行了校正。这对应于SFR=90-180太阳质量/年，其中上限与帕邢α光度的结果一致。虽然L（8微米）/ L（Pa-α）的比值与在本地星系和恒星形成区观察到的外推关系一致，但相对于具有可比帕邢-α光度的本地星系，静止框架24微米光度显着较低。因此，SMM J163554.2+661225可能缺乏较温暖的尘埃成分（T ~ 70 K），这与深埋的恒星形成有关，与具有可比SFR的本地星系形成对比。相反，星暴与恒星形成的本星系一致，其本征光度L（IR）~ 10^10太阳光度，但“放大”了10-100倍。
英文摘要：
We report the detection of the Paschen-alpha emission line in the z=2.515 galaxy SMM J163554.2+661225 using Spitzer spectroscopy. SMM J163554.2+661225 is a sub-millimeter-selected infrared (IR)-luminous galaxy maintaining a high star-formation rate (SFR), with no evidence of an AGN from optical or infrared spectroscopy, nor X-ray emission. This galaxy is lensed gravitationally by the cluster Abell 2218, making it accessible to Spitzer spectroscopy. Correcting for nebular extinction derived from the H-alpha and Pa-alpha lines, the dust-corrected luminosity is L(Pa-alpha) = (2.57+/-0.43) x 10^43 erg s^-1, which corresponds to an ionization rate, Q = (1.6+/-0.3) x 10^55 photons s^-1. The instantaneous SFR is 171+/-28 solar masses per year, assuming a Salpeter-like initial mass function. The total IR luminosity derived using 70, 450, and 850 micron data is L(IR) = (5-10) x 10^11 solar luminosities, corrected for gravitational lensing. This corresponds to a SFR=90-180 solar masses per year, where the upper range is consistent with that derived from the Paschen-alpha luminosity. While the L(8 micron) / L(Pa-alpha) ratio is consistent with the extrapolated relation observed in local galaxies and star-forming regions, the rest-frame 24 micron luminosity is significantly lower with respect to local galaxies of comparable Paschen-alpha luminosity. Thus, SMM J163554.2+661225 arguably lacks a warmer dust component (T ~ 70 K), which is associated with deeply embedded star formation, and which contrasts with local galaxies with comparable SFRs. Rather, the starburst is consistent with star-forming local galaxies with intrinsic luminosities, L(IR) ~ 10^10 solar luminosities, but "scaled-up" by a factor of 10-100.
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