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哈勃超深场中的ALMA光谱观测:紫外选择z=2-10星系的红外过量作为紫外连续斜率和恒星质量的函数

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and Stellar Mass

Rychard Bouwens, Manuel Aravena, Roberto Decarli, Fabian Walter, Elisabete da Cunha, Ivo Labbe, Franz Bauer, Frank Bertoldi, Chris Carilli, Scott Chapman, Emanu… 展开作者

Rychard Bouwens, Manuel Aravena, Roberto Decarli, Fabian Walter, Elisabete da Cunha, Ivo Labbe, Franz Bauer, Frank Bertoldi, Chris Carilli, Scott Chapman, Emanuele Daddi, Jacqueline Hodge, Rob Ivison, Alex Karim, Olivier Le Fevre, Benjamin Magnelli, Kazuaki Ota, Dominik Riechers, Ian Smail, Paul van der Werf, Axel Weiss, Pierre Cox, David Elbaz, Jorge Gonzalez-Lopez, Leopoldo Infante, Pascal Oesch, Jeff Wagg, Steve Wilkins

摘要:

我们利用哈勃超深场中1弧分^[2]区域的1.2毫米深度连续观测数据(12.7微焦耳/光束RMS),对红移范围z=2-10(在整个范围内,在1 σ下,约为2-3 Msol/yr)的330个莱曼破裂星系中被尘埃笼罩的恒星形成过程进行了探测。考虑到ASPECS的深度和面积,将Meurerz ~0 IRX-beta关系外推到z>~2(假设Td ~35 K),我们预计可以探测到35个星系。然而,在ASPECS中,在z>~2处仅发现6个试探性检测,在>3sigma处仅发现3个。根据恒星质量、紫外光度和紫外连续谱斜率对z=2-10的星系进行细分,并将结果叠加,我们只在质量最大(>10^9.75 Msol)的子样本中发现了一个显著的检测,红外过量(IRX= L_{IR} / L_{UV})与以前的z~2结果一致。然而,我们从我们大量选择的sub-L*(<10^9.75 Msol)星系中测量到的红外过量在z=2-3和z=4-10时分别为0.11(-0.42)(+0.32)和0.14(-0.14)(+0.15),甚至低于SMC IRX-β关系(95%置信度)。这些结果表明恒星质量对预测z>~2星系的红外光度具有重要意义。我们还发现,IRX-恒星质量关系的演变依赖于尘埃温度的演变。如果尘埃温度随红移单调增加(as(1+z)^0.32),使得在z>=4时T_d~44-50 K,那么目前的结果表明,这种关系在z~6时几乎没有演化。我们使用这些结果来重新审视最近的估计z>~3 SFR密度。一个不太明显的含义是在解释z~5星系中看到的高Halpha EWs:我们的结果意味着恒星形成星系产生莱曼连续谱光子的效率是传统模型中的两倍(每单位紫外光度)。恒星形成的星系可以使宇宙膨胀,即使逃逸分数<10%。

英文摘要:

We make use of deep 1.2mm-continuum observations (12.7microJy/beam RMS) of a 1 arcmin^2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star formation from 330 Lyman-break galaxies spanning the redshift range z=2-10 (to ~2-3 Msol/yr at 1sigma over the entire range). Given the depth and area of ASPECS, we would expect to tentatively detect 35 galaxies extrapolating the Meurer z~0 IRX-beta relation to z>~2 (assuming T_d~35 K). However, only 6 tentative detections are found at z>~2 in ASPECS, with just three at >3sigma. Subdividing z=2-10 galaxies according to stellar mass, UV luminosity, and UV-continuum slope and stacking the results, we only find a significant detection in the most massive (>10^9.75 Msol) subsample, with an infrared excess (IRX=L_{IR}/L_{UV}) consistent with previous z~2 results. However, the infrared excess we measure from our large selection of sub-L* (<10^9.75 Msol) galaxies is 0.11(-0.42)(+0.32) and 0.14(-0.14)(+0.15) at z=2-3 and z=4-10, respectively, lying below even an SMC IRX-beta relation (95% confidence). These results demonstrate the relevance of stellar mass for predicting the IR luminosity of z>~2 galaxies. We furthermore find that the evolution of the IRX-stellar mass relationship depends on the evolution of the dust temperature. If the dust temperature increases monotonically with redshift (as (1+z)^0.32) such that T_d~44-50 K at z>=4, current results are suggestive of little evolution in this relationship to z~6. We use these results to revisit recent estimates of the z>~3 SFR density. One less obvious implication is in interpreting the high Halpha EWs seen in z~5 galaxies: our results imply that star-forming galaxies produce Lyman-continuum photons at twice the efficiency (per unit UV luminosity) as implied in conventional models. Star-forming galaxies can then reionize the Universe, even if the escape fraction is <10%.

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