SCUBA-2-COSMOS 場中最亮次毫米星系的 ALMA 光譜巡測 (AS2COSPEC)：z=2-5 極亮和超亮紅外星系的物理特性

Abstract

我們呈現了 18 個完整樣本 850 微米選定最亮的瀰塵恆星形成星系 (DSFGs)，也稱為次毫米星系 (SMGs) 的物理特性。該樣本是在 COSMOS 場進行的 ALMA 第三波段光譜巡測 (AS2COSPEC) 的一部分，其中 17 個透過 CO 或 [CI](1-0) 發射線的光譜紅移在 z=2-5。我們使用樣本的 X射線到無線電波光度進行光譜能量分佈 (SED) 建模，並推斷出它們的物理特性。總的來說，我們發現紅外光度中位數為 L_IR=(9.9+/-1.2)x10^12 L_sun，恆星質量中位數為 M_star=(1.2+/-0.8)x10^11 M_sun，塵埃質量中位數為 M_dust=(3.5+/-0.5)x10^9 M_sun，以及分子氣體質量中位數為 M_gas=(α_CO/0.8)(1.2+/-0.1)x10^11 M_sun，這表明它們是這個時期質量最大、富含星際介質 (ISM) 且恆星形成最活躍的系統之一。有趣的是，儘管 SMGs 中的恆星形成活動非常活躍，但它們的分子氣體比例和耗盡時間與質量較小、活躍較低、位處相似時期星系的比例相似，這表明共同的恆星形成物理機制。我們也確定樣本 SMGs 的塵埃發射率指數中位數為 β=2.1+/-0.1 和有效塵埃溫度中位數為 T_eff=29+/-2 K。通過將我們的結果與其他 DSFG 樣本的結果相結合，我們發現在固定紅外光度下相對較低的 T_eff 結果可以透過我們 850 微米通量限制的選擇來理解。我們還發現 β 與紅移和紅外光度均不相關，這表明亮紅外星系的塵埃顆粒成分在不同宇宙時期可能是相似的。最後，我們完整而統一的巡測使我們能夠對分子氣體和塵埃質量函數的最大端加以限制。

We report physical properties of a complete sample of 18 brightest 850μm selected dusty star-forming galaxies (DSFGs), also known as submillimeter galaxies (SMGs). This sample is part of an ALMA band 3 spectroscopic survey (AS2COSPEC) conducted in the COSMOS field, and spectroscopic redshifts are measured in 17 of them at z=2-5 via CO or [CI](1-0) emission lines. We perform spectral energy distribution (SED) modeling using X-ray-to-radio photometry of the sample sources and deduce their physical properties. Overall, we find a median infrared luminosity of L_IR=(9.9+/-1.2)x10^12 L_sun, a median stellar mass of M_star=(1.2+/-0.8)x10^11 M_sun, a median dust mass of M_dust=(3.5+/-0.5)x10^9 M_sun, and a median molecular gas mass of M_gas=(α_CO/0.8)(1.2+/-0.1)x10^11 M_sun, suggesting that they are one of the most massive, ISM-enriched, and actively star-forming systems at this epoch. Intriguingly, despite the intense star formation activity in SMGs, their molecular gas fraction and depletion time are scaled similarly as less massive and less active galaxies at similar epochs, suggesting common physical mechanisms governing their star formation. We also determine a median dust emissivity index of β=2.1+/-0.1 and an effective dust temperature T_eff=29+/-2 K for our sample SMGs. By combining our results with those from other DSFG samples, we find that the relatively lower T_eff at fixed infrared luminosity can be understood by our 850μm flux-limited selection. We also find that β does not correlate with redshift nor infrared luminosity, indicating that the dust grain compositions could be similar across different cosmic times for infrared luminous galaxies. Finally, our complete and uniform survey enables us to put constraints on the most massive end of the molecular gas and dust mass functions.