The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Continuum Number Counts, Resolved 1.2 mm Extragalactic Background, and Properties of the Faintest Dusty Star-forming Galaxies
We present an analysis of a deep (1σ = 13 μJy) cosmological 1.2 mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin^2 covered by ASPECS we detect nine sources at >3.5σ significance at 1.2 mm. Our ALMA-selected sample has a median redshift of z = 1.6 ± 0.4, with only one galaxy detected at z > 2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cutoff and similar frequencies. Most galaxies have specific star formation rates (SFRs) similar to that of main-sequence galaxies at the same epoch, and we find median values of stellar mass and SFRs of 4.0 x 10^(10)M⊙ and ~40 M⊙ yr^(-1), respectively. Using the dust emission as a tracer for the interstellar medium (ISM) mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from ~0.1 to 1.0. As noted by previous studies, these values are lower than those using CO-based ISM estimates by a factor of ~2. The 1 mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover 55% ± 4% of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover 80% ± 7% of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at z ~ 1-2, with stellar masses of (1–3) × 10^(10) M⊙. For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.
© 2016 The American Astronomical Society. Received 2016 May 6; revised 2016 September 6; accepted 2016 September 6; published 2016 December 8. We thank the anonymous referee for her/his positive feedback and useful comments. M.A. acknowledges partial support from FONDECYT through grant 1140099. F.W., I.R.S., and R.J.I. acknowledge support through ERC grants COSMIC–DAWN, DUSTYGAL, and COSMICISM, respectively. F.E.B. and L.I. acknowledge Conicyt grants Basal-CATA PFB–06/2007 and Anilo ACT1417. F.E.B. also acknowledges support from FONDECYT Regular 1141218 (FEB) and the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS). E.d.C. gratefully acknowledges the Australian Research Council as the recipient of a Future Fellowship (project FT150100079). D.R. acknowledges support from the National Science Foundation under grant number AST-1614213 to Cornell University. I.R.S. also acknowledges support from STFC (ST/L00075X/1) and a Royal Society/Wolfson Merit award. Support for R.D. and B.M. was provided by the DFG priority program 1573 "The Physics of the Interstellar Medium." A.K. and F.B. acknowledge support by the Collaborative Research Council 956, sub-project A1, funded by the Deutsche Forschungsgemeinschaft (DFG). P.I. acknowledges Conict grants Basal-CATA PFB–06/2007 and Anilo ACT1417. R.J.A. was supported by FONDECYT grant number 1151408. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00146.S and ADS/JAO.ALMA#2013.1.00718.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The 3 mm part of the ALMA project was supported by the German ARC.
Submitted - 1607.06769v2.pdf
Published - Aravena_2016_ApJ_833_68.pdf