Alma Spectroscopic Survey in the Hubble Ultra Deep Field: Survey Description

Abstract

We present the rationale for and the observational description of ASPECS: the ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF), the cosmological deep field that has the deepest multi-wavelength data available. Our overarching goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift (z>0.5) galaxies. The ∼1′ region covered within the UDF was chosen to overlap with the deepest available imaging from the Hubble Space Telescope. Our ALMA observations consist of full frequency scans in band3 (84-115 GHz) and band6 (212-272 GHz) at approximately uniform line sensitivity ( ¢L CO 2 × 10 9 K km s −1 pc 2 ), and continuum noise levels of 3.8 μJy beam −1 and 12.7 μJy beam −1, respectively. The molecular surveys cover the different rotational transitions of the CO molecule, leading to essentially full redshift coverage. The [C II] emission line is also covered at redshifts < < z 6.0 8.0. We present a customized algorithm to identify line candidates in the molecular line scansand quantify our ability to recover artificial sources from our data. Based on whether multiple CO lines are detected, and whether optical spectroscopic redshifts as well as optical counterparts exist, we constrain the most likely line identification. We report 10 (11) CO line candidates in the 3 mm (1 mm) band, and our 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 that are not associated with an optical/NIR counterpart. We also present continuum maps of both the band3 and band6 observations. The data presented here form the basis of a number of dedicated studies that are presented in subsequent papers.

Dissecting the IRX–β dust attenuation relation: exploring the physical origin of observed variations in galaxies

“…An increase in the assumed dust temperature naturally increases the total infrared luminosity and IRX towards a MW IRX -β relation. Bouwens et al (2016) also concludes that the dust temperature of galaxies might increase with look-back time, based on the large number of non-detected galaxies at 3mm continuum in ASPECS (The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field, Walter et al 2016). A better photometric sampling of the Rayleigh-Jeans tail of the sub-mm SED of high-redshift galaxies is necessary and will provide valuable insights.…”

The Alma Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular Gas Reservoirs in High-Redshift Galaxies

“…Furthermore, the combination of the spectral line survey and the 1 mm continuum image allows us to compare CO-and dust-based estimates of the gas mass. In other papers of this series, we present the data set and the catalog of blindly selected CO emitters (Paper I, Walter et al 2016), we study the properties of 1.2 mm detected sources (Paper II, Aravena et al 2016a), we discuss the inferred constraints on the luminosity functions of CO (Paper III, Decarli et al 2016a), and we search for [C II] emission in z=6-8 galaxies (Paper V, Aravena et al 2016b). Paper VI (Bouwens et al 2016) places our findings in the context of the dust extinction law for > z 2 galaxies, and Paper VII (Carilli et al 2016) uses ASPECS to place first direct constraints on intensity mapping experiments.…”

High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-L* population

“…This issue is less problematic for shallower X-ray surveys, which sample AGN with brighter optical/NIR counterparts, but miss the sub-population of low-luminosity AGN. Current facilities that could be used effectively to increase the spectroscopic completeness of our sample include ALMA 13 (e.g., Walter et al 2016), the Keck observatory, 14 and VLT/MUSE. 15 The last, in particular, with 27h of integration time in the Hubble Ultra Deep Field, has already been able to obtain spectroscopic redshifts for sources below the Hubble detection limit (Bacon et al 2015).…”