The Rest-Frame Submillimeter Spectrum of High Redshift, Dusty, Star-Forming Galaxies from the SPT-SZ Survey

TL;DR

This study presents an average rest-frame submillimeter spectrum of 78 high-redshift dusty star-forming galaxies from the SPT-SZ survey, revealing molecular line features and ISM properties across a broad redshift range.

Contribution

It provides the first comprehensive average spectrum of a large sample of high-redshift DSFGs, including molecular line detections and analysis of ISM characteristics related to galaxy properties.

Findings

Detection of multiple molecular lines including CO, [CI], H2O, and others.

Variation in molecular line emission with dust temperature.

Insights into the ISM conditions of high-redshift star-forming galaxies.

Abstract

We present the average rest-frame spectrum of the final catalog of dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope SZ survey (SPT-SZ) and measured with Band 3 of the Atacama Large Millimeter/submillimeter Array (ALMA). This work builds on the previous average rest-frame spectrum, given in Spilker et al. (2014) for the first 22 sources, and is comprised of a total of 78 sources, normalized by their respective apparent dust masses. The spectrum spans $1.9$$<$z$<$$6.9$ and covers rest-frame frequencies of 240$-$800 GHz. Combining this data with low-J CO observations from the Australia Telescope Compact Array (ATCA), we detect multiple bright line features from $^{12}$CO, $[$CI$]$, and H$_2$O, as well as fainter molecular transitions from $^{13}$CO, HCN, HCO$^+$, HNC, CN, H$_2$O$^+$, and CH. We use these detections, along with limits from other molecules, to characterize the typical properties of the interstellar medium (ISM) for these high redshift DSFGs. We are able to divide the large sample into subsets in order to explore how the average spectrum changes with various galaxy properties, such as effective dust temperature. We find that systems with hotter dust temperatures exhibit differences in the bright $^{12}$CO emission lines, and contain either warmer and more excited dense gas tracers, or larger dense gas reservoirs. These observations will serve as a reference point to studies of the ISM in distant luminous DSFGs (L$_{\mathrm{IR}}$$>$$10^{12}$L$_\odot$), and will inform studies of chemical evolution before the peak epoch of star formation at $z=2-3$.