The IR Compactness of Dusty Galaxies Set Star-formation and Dust Properties at z~0-2

TL;DR

This study investigates the relationship between infrared surface densities and dust properties in dusty galaxies at redshifts around 0 to 2, revealing that high IR surface densities correlate with increased star-formation efficiency and changes in dust characteristics.

Contribution

It provides new insights into dust and star-formation physics in high-redshift galaxies using high-resolution ALMA data and mid-IR spectroscopy, highlighting similarities and differences across cosmic time.

Findings

High IR surface densities are linked to increased star-formation efficiency.

PAH/IR luminosity ratios decline at high IR surface densities, indicating dust condition changes.

High-z galaxies exhibit similar dust properties to local luminous IR galaxies despite different evolutionary stages.

Abstract

Surface densities of gas, dust and stars provide a window into the physics of star-formation that, until the advent of high-resolution far-infrared/sub-millimeter observations, has been historically difficult to assess amongst dusty galaxies. To study the link between infrared (IR) surface densities and dust properties, we leverage the Atacama Large Millimetre/Submillimetre Array (ALMA) archive to measure the extent of cold dust emission in 15 $z\sim2$ IR selected galaxies selected on the basis of having available mid-IR spectroscopy from Spitzer. We use the mid-IR spectra to constrain the relative balance between dust heating from star-formation and active galactic nuclei (AGN), and to measure emission from Polycylic Aromatic Hydrocarbons (PAHs) -- small dust grains that play a key role in the photoelectric heating of gas. In general, we find that dust-obscured star-formation at high IR surface densities exhibits similar properties at low- and high-redshift, namely: local luminous IR galaxies have comparable PAH luminosity to total dust mass ratios as high-$z$ galaxies, and star-formation at $z\sim0-2$ is more efficient at high IR surface densities despite the fact that our sample of high$-z$ galaxies are closer to the main-sequence than local luminous IR galaxies. High star-formation efficiencies are coincident with a decline in the PAH/IR luminosity ratio reminiscent of the deficit observed in far-infrared fine-structure lines. Changes in the gas and dust conditions arising from high star-formation surface densities might help drive the star-formation efficiency up. This could help explain high efficiencies needed to reconcile star-formation and gas volume densities in dusty galaxies at cosmic noon.