A New Era for Cosmological Surveys

Walter et al. present the rationale for and the observational description of the ALMA SPECtroscopic Survey (ASPECS) in the Hubble Space Telescope Ultra-Deep Field (UDF), the cosmological deep field that has the deepest multi-wavelength data available. The goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift (z > 0.5) galaxies. The ~1 arcminute region covered within the UDF was chosen to overlap with the deepest HST imaging. The observations are full frequency scans in ALMA band 3 (84–115 GHz) and band 6 (212–272 GHz) at approximately uniform line sensitivity (L_CO ~ 2 × 10⁹ K km s⁻¹ pc²), and continuum noise levels. The molecular surveys cover the different CO rotational transitions, with essentially full redshift coverage. The [C II] emission line is also covered at redshifts 6.0 < z < 8.0, A customized algorithm identifies line candidates in the molecular line scans and quantifies the ability to recover artificial sources from these data. The most likely line identification is constrained based on whether multiple CO lines are detected, and whether optical spectroscopic redshifts and optical counterparts exist. Ten (Eleven) CO line candidates are found in the 3 mm (1 mm) band, and their statistical analysis shows that < 4 of these in each band are likely spurious. Less than one-third of the total CO flux in the low-J CO line candidates are from sources unassociated with an optical / near-infrared counterpart. The data described in this paper are the basis for multiple dedicated studies presented in subsequent papers.

Image: The FWHM of the primary beam (areal coverage) of the 3 mm (orange) and 1 mm (cyan) ALMA observations, overlaid on a three-color HST image from the XDF survey (Illingworth et al. 2013). The circles show the ALMA primary beam of each pointing at the central frequencies of the two scans.

Science Team: Fabian Walter (MPIfA, Caltech, NRAO), Roberto Decarli (MPIfA), Manuel Aravena (Diego Portales), Chris Carilli (NRAO, Cambridge), Rychard Bouwens (Leiden), Elisabete da Cunha (Swinburne, Australian National Univ.), Emanuele Daddi (CEA Saclay), R. J. Ivison (ESO, Edinburgh), Dominik Riechers (Cornell), Ian Smail (Durham)), Mark Swinbank (Durham), Axel Weiss (MPIfR), Timo Anguita (Andres Bello, Millennium Inst.), Roberto Assef (Diego Portales), Roland Bacon (Lyon), Franz Bauer (Católica , Millennium Inst., Space Science Inst.), Eric F. Bell (Michigan), Frank Bertoldi (Argelander), Scott Chapman (Dalhousie), Luis Colina (CSIC), Paulo C. Cortes (JAO, NRAO), Pierre Cox (Arizona), Mark Dickinson (Arizona), David Elbaz (CEA Saclay), Jorge Gónzalez-López (Católica), Edo Ibar (Valparaiso), Hanae Inami (Lyon), Leopoldo Infante (Católica), Jacqueline Hodge (Leiden), Alex Karim (Argenlander), Olivier Le Fevre (CNRS), Benjamin Magnelli (Argelandre), Roberto Neri (IRAM), Pascal Oesch (Yale), Kazuaki Ota (Cambridge, Kavli), Gergö Popping (ESO), Hans-Walter Rix (MPIfA), Mark Sargent (Sussex), Kartik Sheth (NASA HQ), Arjen van der Wel (MPIfA), Paul van der Werf (Leiden), and Jeff Wagg (SKA)

Publication: The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Survey Description, 2016 Astrophysical Journal, 833, 67.