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∼2 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∼0−2 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.Comment: 18 pages, 10 figures, accepted to Ap