# A Very Large Array Survey of Luminous Extranuclear Star-forming Regions in Luminous Infrared Galaxies in GOALS

## TL;DR

This study uses high-resolution radio imaging to analyze extranuclear star-forming regions in luminous infrared galaxies, revealing their thermal emission properties and star formation rates, and comparing them to galaxy-wide star formation activity.

## Contribution

First high-resolution radio survey of extranuclear star-forming regions in LIRGs, providing new insights into their emission properties and star formation activity beyond galaxy nuclei.

## Key findings

- Extranuclear regions show thermal emission dominance similar to normal star-forming galaxies.
- Median star-formation rate in these regions is about 1 solar mass per year.
- Extranuclear star formation is more extreme than in local spiral galaxies.

## Abstract

We present the first results of a high-resolution Karl G. Jansky Very Large Array (VLA) imaging survey of luminous and ultra-luminous infrared galaxies (U/LIRGs) in the Great Observatories All-Sky LIRG Survey (GOALS). From the full sample of 68 galaxies, we have selected 25 LIRGs that show resolved extended emission at sufficient sensitivity to image individual regions of star-formation activity beyond the nucleus.~With wideband radio continuum observations, which sample the frequency range from $3-33$ GHz, we have made extinction-free measurements of the luminosities and spectral indicies for a total of 48 individual star-forming regions identified as having de-projected galactocentric radii ($r_{G}$) that lie outside the 13.2$\mu$m core of the galaxy.~The median $3-33$ GHz spectral index and 33 GHz thermal fraction measured for these "extranuclear" regions is $-0.51 \pm 0.13$ and $65 \pm 11\%$ respectively.~These values are consistent with measurements made on matched spatial scales in normal star-forming galaxies, and suggests that these regions are more heavily-dominated by thermal free-free emission relative to the centers of local ULIRGs.~Further, we find that the median star-formation rate derived for these regions is $\sim 1 M_{\odot}$ yr$^{-1}$, and when we place them on the sub-galactic star-forming main sequence of galaxies (SFMS), we find they are offset from their host galaxies' globally-averaged specific star-formation rates (sSFRs).~We conclude that while nuclear starburst activity drives LIRGs above the SFMS, extranuclear star-formation still proceeds in a more extreme fashion relative to what is seen in local spiral galaxies.