The ALMA Spectroscopic Survey in the HUDF: Deep 1.2 mm Continuum Number Counts

We present the results from the 1.2 mm continuum image obtained as part of the Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field. The 1.2 mm continuum image has a size of 2.9 (4.2) arcmin2 within a primary beam response of 50% (10%) and an rms value of $9.3\,\mu \mathrm{Jy}\,{\mathrm{beam}}^{-1}$. We detect 35 sources at high significance (Fidelity ≥0.5); 32 have well-characterized near-infrared Hubble Space Telescope counterparts. We estimate the 1.2 mm number counts to flux levels of $\lt 30\,\mu \mathrm{Jy}$ in two different ways: we first use the detected sources to constrain the number counts and find a significant flattening of the counts below S ν ~ 0.1 mJy. In a second approach, we constrain the number counts using a probability of deflection statistics (P(D)) analysis. For this latter approach, we describe new methods to accurately measure the noise in interferometric imaging (employing jackknifing in the cube and in the visibility plane). This independent measurement confirms the flattening of the number counts. Our analysis of the differential number counts shows that we are detecting ~93% (~100% if we include the lower fidelity detections) of the total continuum dust emission associated with galaxies in the Hubble Ultra Deep Field. The ancillary data allow us to study the dependence of the 1.2 mm number counts on redshift (z = 0−4), galaxy dust mass (${M}_{\mathrm{dust}}={10}^{7}\mbox{--}{10}^{9}{M}_{\odot }$), stellar mass (${M}_{* }={10}^{9}\mbox{--}{10}^{12}{M}_{\odot }$), and star formation rate ($\mathrm{SFR}=1-1000\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$). In an accompanying paper we show that the number counts are crucial to constrain galaxy evolution models and the understanding of star-forming galaxies at high redshift.M.N. and F.W. acknowledge support from ERC Advanced grant 740246 (Cosmic Gas). D.R. acknowledges support from the National Science Foundation under grant no. AST-1614213 and from the Alexander von Humboldt Foundation through a Humboldt Research Fellowship for Experienced Researchers. R.J.A. was supported by FONDECYT grant number 1191124. I.R.S. acknowledges support from STFC (ST/P000541/1). B.M. acknowledge support from the Collaborative Research Centre 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG)—project ID 184018867. We acknowledge support from CONICYT grants CATA-Basal AFB-170002 (FEB); FONDECYT Regular 1190818 (FEB); Chile’s Ministry of Economy, Development, and Tourism’s Millennium Science. Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS (FEB). Este trabajo cont ó con el apoyo de CONICYT + PCI + INSTITUTO MAX PLANCK DE ASTRONOMIA MPG190030 (M.A.)