ALMA Observations of Arp 220 and Dust Continuum Measurements of High-z Galaxies

Abstract

We describe preliminary results for two ALMA projects – 1) imaging the HCN(4-3) line and H26α lines in Arp 220 and 2) measurements of the dust continuum in a sample of 120 high redshift galaxies to probe the evolution of the ISM masses. The HCN observations in Arp 220 at 1/2″ resolution provide the first high resolution imaging of the dense star forming gas in this prototypical ULIRG. The HCN is seen in two clearly delineated, counter-rotating disks. The H26α emission is the first definitive probe of the star formation rate in Arp 220, avoiding obscuration by dust and contamination by AGN luminosity contributions. In the second project, the remarkable continuum sensitivity of ALMA in Band 7 is used to measure the long wavelength Rayleigh-Jeans tail of the dust emission from a sample of 120 galaxies in COSMOS at z = 0.3 to 2.2, providing estimates for the dust masses and hence, for an assumed dust-to-gas ratio, their ISM masses. This technique will enable measurements for hundreds of galaxies at high-z with observations of typically ∼10 min per galaxy. This is in contrast to CO line imaging which typically requires a few hours per galaxy even with the sensitivity of ALMA. The derived ISM masses are also subject to uncertainties in the CO-to-H2 conversion factor.