The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: a new look at the star-forming medium throughout cosmic time

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) is a survey of gas and dust in the Hubble Ultra Deep Field, arguably the best studied extragalactic field in the sky. The survey capitalizes on the unparalleled sensitivity of the Atacama Large Millimeter/sub-millimeter Array (ALMA) to disclose the properties of the star-forming medium in galaxies through cosmic times. The data set consists of three main parts:

1) The ASPECS Pilot consisted of two 20 hr projects (PIs: Walter and Aravena) scanning the 3mm and 1.2mm transparent windows of the atmosphere (84-115 GHz and 212-272 GHz), respectively. This project covers an area of about 1 square arcmin and led to 7 publications (see here).

2) The ASPECS Large Program (LP) builds on the success of the ASPECS Pilot. This 150 hr endeavor is the first ALMA Large Program approved for extragalactic studies (PIs: Walter, Aravena, Carilli). It adopts the same observing strategy of the ASPECS Pilot, but expanded over a larger area (about 4.6 square arcmin) at uniform sensitivity. The mosaic encompasses most of the Hubble eXtremely Deep Field (XDF). The 3mm part of the project led to 4 submitted publications. The 1.2mm part of the project has been completed. Data processing and analysis are on-going (Spring 2019).

3) The Wide ASPECS survey focuses on a subset of the frequency settings at 3mm used in the ASPECS Pilot and ASPECS LP. It completes the `wedding cake' approach of ASPECS by covering a wide area (52 square arcmin, following the CANDELS footpring) at shallower sensitivity. Data analysis is on-going (Spring 2019).

The ASPECS data unveil reservoirs of molecular gas in galaxies up to z~4. This is the medium where stars form, and therefore it is the most intimately connected with the formation and evolution of galaxies. The ASPECS data also provide the most sensitive image of the sky at 1.2mm available to date, thus disclosing the emission of dust, which is heated up by the star formation.