Deviations from the Infrared-Radio Correlation in Massive, Ultra-compact Starburst Galaxies

Abstract

Feedback through energetic outflows has emerged as a key physical process responsible for transforming star-forming galaxies into the quiescent systems observed in the local universe. To explore this process, this paper focuses on a sample of massive and compact merger remnant galaxies hosting high-velocity gaseous outflows ($|v|\gtrsim 10^3$ km s${}^{-1}$), found at intermediate redshift ($z\sim 0.6$). From their mid-infrared emission and compact morphologies, these galaxies are estimated to have exceptionally large star formation rate (SFR) surface densities (${\Sigma }_{SFR}\sim 10^3$ ${\mathrm{M}}_{\odot }$ yr${}^{-1}$ kpc${}^{-2}$), approaching the Eddington limit for radiation pressure on dust grains. This suggests that star formation feedback may be driving the observed outflows. However, these SFR estimates suffer from significant uncertainties. We therefore sought an independent tracer of star formation to probe the compact starburst activity in these systems. In this paper, we present SFR estimates calculated using 1.5 GHz continuum Jansky Very Large Array observations for 19 of these galaxies. We also present updated infrared (IR) SFRs calculated from WISE survey data. We estimate SFRs from the IR to be larger than those from the radio for 16 out of 19 galaxies by a median factor of 2.5. We find that this deviation is maximized for the most compact galaxies hosting the youngest stellar populations, suggesting that compact starbursts deviate from the IR-radio correlation. We suggest that this deviation stems either from free-free absorption of synchrotron emission, a difference in the timescale over which each indicator traces star formation, or exceptionally hot IR-emitting dust in these ultra-dense galaxies.

arXiv comment15 pages, 9 figures, 2 tables; accepted for publication in ApJ

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• Compact Starburst Galaxies with Fast Outflows: Central Escape Velocities and Stellar Mass Surface Densities from Multi-band Hubble Space Telescope Imaging
• Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows
• Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows
• The Ionization and Dynamics of the Makani Galactic Wind
• The Space Density of Intermediate Redshift, Extremely Compact, Massive Starburst Galaxies