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arXiv 2107.09769astro-ph.GA
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$z\approx 2-3$中质量恒星形成星系的分子气体收支和特征

Molecular gas budget and characterization of intermediate-mass star-forming galaxies at $z\approx 2-3$

M. Solimano, J. González-López, L. F. Barrientos, M. Aravena, S. López, N. Tejos, K. Sharon, H. Dahle, M. Bayliss, C. Ledoux, J. R. Rigby, M. Gladders

摘要:

恒星质量低于$10^{10}\,M_\odot$的恒星形成星系(SFG)构成了$z>2$星系群的大部分。这些星系中冷气体的性质只能在非常深的ALMA观测中或通过瞄准强透镜星系来探测。在这里,我们报告的试点调查的结果,使用阿塔卡马紧凑阵列(ACA)的分子气体在最强烈的放大星系选择为巨大的弧在光学数据。在休息帧紫外线波长的选择,确保来源是经常恒星形成星系,没有强烈的尘埃星暴活动的先验迹象。我们进行了第4和第7波段的观测,以探测来自$z\approx2-3$的四个强透镜系统的中$J$ CO、[CI]和热连续谱作为分子气体示踪剂:我们的目标是SGAS J1226651.3+215220(A和B)、SGAS J003341.5+024217和朝阳弧。然后将测得的分子质量投影到源平面上,并使用从高分辨率HST观测中开发的详细透镜模型。利用多波长光度法,通过SED拟合得到恒星的内禀质量和恒星形成速率。只有在一个源中,三种示踪剂被稳健地检测到,而在其他源中,它们要么未被检测到,要么仅被连续检测到。隐含的分子气体质量范围从检测源中的$4\times 10^{9}\,M_\odot$到最大放大源中的上限$\lesssim 10^9\,M_\odot$。推断的气体分数和气体耗尽的时间尺度被发现躺在约0.5至1.0德克斯低于所建立的标度关系的基础上以前的研究unlensed大质量星系。我们的研究结果表明,中低质量星系的冷气含量不应该从更大质量的高$z$星系的趋势中推断出来。(摘要摘要)

英文摘要:

Star-forming galaxies (SFGs) with stellar masses below $10^{10}\,M_\odot$ make up the bulk of the galaxy population at $z>2$. The properties of the cold gas in these galaxies can only be probed in very deep ALMA observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array (ACA) of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame UV wavelengths ensures that sources are regular star forming galaxies, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid-$J$ CO, [C I] and thermal continuum as molecular gas tracers from four strongly lensed systems at $z\approx2-3$: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass is then projected onto the source plane with detailed lens models developed from high resolution HST observations. Multiwavelength photometry is then used to obtain the intrinsic stellar mass and star formation rate via SED fitting. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from $4\times 10^{9}\,M_\odot$ in the detected source to an upper limit of $\lesssim 10^9\,M_\odot$ in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5 to 1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high-$z$ galaxies. (Abridged abstract)

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