Source structure and molecular gas properties from high-resolution CO imaging of SPT-selected dusty star-forming galaxies

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of high-J CO lines ($J_{\mathrm{up}}=6$, 7, 8) and associated dust continuum towards five strongly lensed, dusty, star-forming galaxies (DSFGs) at redshift $z=2.7$-5.7. These galaxies, discovered in the South Pole Telescope survey, are observed at $0.2^{\prime \prime }$-$0.4^{\prime \prime }$ resolution with ALMA. Our high-resolution imaging coupled with the lensing magnification provides a measurement of the structure and kinematics of molecular gas in the background galaxies with spatial resolutions down to kiloparsec scales. We derive visibility-based lens models for each galaxy, accurately reproducing observations of four of the galaxies. Of these four targets, three show clear velocity gradients, of which two are likely rotating disks. We find that the reconstructed region of CO emission is less concentrated than the region emitting dust continuum even for the moderate-excitation CO lines, similar to what has been seen in the literature for lower-excitation transitions. We find that the lensing magnification of a given source can vary by 20-50% across the line profile, between the continuum and line, and between different CO transitions. We apply Large Velocity Gradient (LVG) modeling using apparent and intrinsic line ratios between lower-J and high-J CO lines. Ignoring these magnification variations can bias the estimate of physical properties of interstellar medium of the galaxies. The magnitude of the bias varies from galaxy to galaxy and is not necessarily predictable without high resolution observations.

19 pages, 12 figures, accepted by ApJ

References in corpus (13)

• The Detection of a Population of Submillimeter-Bright, Strongly-Lensed Galaxies
• Intense Star Formation within Resolved Compact Regions in a Galaxy at z=2.3
• Galaxy growth in a massive halo in the first billion years of cosmic history
• The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the sub-millimeter number counts
• The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
• ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~ 7
• The Herschel-ATLAS: a sample of 500μm-selected lensed galaxies over 600 square degrees
• The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
• Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z~2-4 as probed by multi-J CO lines
• The JCMT Nearby Galaxies Legacy Survey I. Star Forming Molecular Gas in Virgo Cluster Spiral Galaxies
• A spatially resolved study of cold dust, molecular gas, HII regions, and stars in the $z=2.12$ submillimeter galaxy ALESS67.1
• Size bias and differential lensing of strongly lensed, dusty galaxies identified in wide-field surveys
• A complete distribution of redshifts for sub-millimetre galaxies in the SCUBA-2 Cosmology Legacy Survey UDS field