ALMA Lensing Cluster Survey: Physical characterization of near-infrared-dark intrinsically faint ALMA sources at z=2-4

• DOI: 10.48550/arxiv.2406.09890
• Publication Date: 2024-01-01
• Authors: Tsujita, Akiyoshi; Kohno, Kotaro; Huang, Shuo; Oguri, Masamune; Tadaki, Ken-ichi; Smail, Ian; Umehata, Hideki; Gao, Zhen-Kai; Wang, Wei-Hao; Sun, Fengwu; Fujimoto, Seiji; Wang, Tao; Uematsu, Ryosuke; Espada, Daniel; Valentino, Francesco; Ao, Yiping; Bauer, Franz E.; Hatsukade, Bunyo; Egusa, Fumi; Nishimura, Yuri; Koekemoer, Anton M.; Schaerer, Daniel; Lagos, Claudia; Dessauges-Zavadsk...; Brammer, Gabriel; Caputi, Karina; Egami, Eiichi; González-López, J...; Jolly, Jean-Baptiste; Knudsen, Kirsten K.; Kokorev, Vasily; Magdis, Georgios E.; Ouchi, Masami; Toft, Sune; Wu, John F.; Zitrin, Adi
• Keywords: Astrophysics of Galaxies (astro-ph.GA); FOS: Physical sciences; Astrophysics - Astrophysics of Galaxies

23 pages, 10 figures, Submitted to ApJ<br/>We present results from Atacama Large Millimeter/submillimeter Array (ALMA) spectral line-scan observations at 3-mm and 2-mm bands of three near-infrared-dark (NIR-dark) galaxies behind two massive lensing clusters MACS J0417.5-1154 and RXC J0032.1+1808. Each of these three sources is a faint (de-lensed $S_{\text{1.2 mm}}$ $<$ 1 mJy) triply lensed system originally discovered in the ALMA Lensing Cluster Survey. We have successfully detected CO and [C I] emission lines and confirmed that their spectroscopic redshifts are $z=3.652$, 2.391, and 2.985. By utilizing a rich multi-wavelength data set, we find that the NIR-dark galaxies are located on the star formation main sequence in the intrinsic stellar mass range of log ($M_*$/$M_\odot$) = 9.8 - 10.4, which is about one order of magnitude lower than that of typical submillimeter galaxies (SMGs). These NIR-dark galaxies show a variety in gas depletion times and spatial extent of dust emission. One of the three is a normal star-forming galaxy with gas depletion time consistent with a scaling relation, and its infrared surface brightness is an order of magnitude smaller than that of typical SMGs. Since this galaxy has an elongated axis ratio of $\sim 0.17$, we argue that normal star-forming galaxies in an edge-on configuration can be heavily dust-obscured. This implies that existing deep WFC3/F160W surveys may miss a fraction of typical star-forming main-sequence galaxies due to their edge-on orientation.<br/>