{"id":828,"date":"2020-01-23T02:59:54","date_gmt":"2020-01-23T02:59:54","guid":{"rendered":"http:\/\/itziararetxaga.net\/?p=828"},"modified":"2020-01-29T20:18:55","modified_gmt":"2020-01-29T20:18:55","slug":"the-redshift-and-star-formation-mode-of-aztec2-a-pair-of-massive-galaxies-at-z-4-63","status":"publish","type":"post","link":"http:\/\/www.itziararetxaga.net\/es\/2020\/01\/the-redshift-and-star-formation-mode-of-aztec2-a-pair-of-massive-galaxies-at-z-4-63\/","title":{"rendered":"The redshift and star formation mode of AzTEC2: a pair of massive galaxies at z = 4.63"},"content":{"rendered":"

Jim\u00e9nez-Andrade, E. F.<\/a>; Zavala, J. A.<\/a>; \u00a0Magnelli, B.<\/a>; Casey, C. M.<\/a>; \u00a0Liu, D.<\/a>; Romano-D\u00edaz, E.<\/a>; \u00a0Schinnerer, E.<\/a>; Harrington, K.<\/a>; Aretxaga, I.<\/a>; Karim, A.<\/a>; Staguhn, J.<\/a>; Burnham, A. D.<\/a>; Monta\u00f1a, A.<\/a>; Smol\u010di\u0107, V.<\/a>; Yun, M.<\/a>; Bertoldi, F.<\/a>; Hughes, D.<\/a><\/p>\n

Accepted for publication in Astrophysical Journal (arXiv: 2001.06997<\/a>)<\/p>\n

We combine observations from the Atacama Large Millimeter\/submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) to assess the redshift and to study the star formation conditions in AzTEC2: one of the brightest sub-millimeter galaxies (SMGs) in the COSMOS field (S1.1mm<\/sub> = 10.5 \u00b1 1.4 mJy). Our high-resolution observations confirm that AzTEC2 splits into two components (namely AzTEC2-A and AzTEC2-B) for which we detect [C II] and 12<\/sup>CO(5\u21924) line emission, implying a redshift of 4.626\u00b10.001 (4.633\u00b10.001) for AzTEC2-A (AzTEC2-B) and ruling out previous associations with a galaxy at z \u223c 1. We use the 12<\/sup>CO(5\u21924) line emission and adopt typical SMG-like gas excitation conditions to estimate the molecular gas mass, which is Mgas(\u03b1CO<\/sub>\/2.5) =2.1 \u00b1 0.4 \u00d7 1011<\/sup> M\fsun for AzTEC2-A, and a factor four lower for AzTEC2-B. With the infrared-derived star formation rate of AzTEC2-A (1920\u00b1100 Msun\f yr\u22121<\/sup>) and AzTEC2-B (710\u00b135 M\fsun yr\u22121<\/sup>), they both will consume their current gas reservoir within (30\u2212200) Myr. We find evidence of a rotation-dominated [C II] disk in AzTEC2-A, with a de-projected rotational velocity of vrot<\/sub>(i = 39\u25e6) = 660 \u00b1 130 km s\u22121<\/sup>, velocity dispersion 100 km s\u22121<\/sup>, and dynamical mass of Mdyn<\/sub>(i = 39\u25e6) = 2.6+1.2\u22120.9 \u00d7 1011<\/sup> Msun\f. We propose that an elevated gas accretion rate from the cosmic web might be the main driver of the intense levels of star formation in AzTEC2-A, which might be further enhanced by gravitational torques induced by its minor companion (AzTEC2-B). These results strengthen the picture whereby the population of single-dish selected SMGs is rather heterogeneous, including a population of pairs of massive, highly-active galaxies in a pre-coalescence phase.<\/p>\n

\"AzTEC2\"
Multi-wavelength view towards the AzTEC2 source. Left panel: AzTEC\/JCMT 1.1mm (white Scott et al. 2008), ALMA Band 7\/887um (green; this study) and VLA Band S\/10 cm (blue; Smolcic et al. 2017) contours overlaid on top the HST\/ACS F814W image. All contour levels are above three times the noise r.m.s. The zoomed-in image (right panel) shows two foreground sources: a massive elliptical galaxy at z = 0.34 and a SFG at z = 1.12. ALMA and VLA imaging at sub-arcsec resolution reveal two optically-undetected components at z ~ 4.63, labeled as AzTEC2-A and AzTEC2-B.<\/figcaption><\/figure>\n