An ALMA-HST Study of Millimeter Dust Emission and Star Clusters

TL;DR

This study combines high-resolution ALMA and HST data to analyze dust emission and star clusters in NGC 628, revealing an excess of millimeter dust emission with little correlation to cluster properties, and identifying a potential obscured supernova.

Contribution

It provides the first detailed spatial analysis of dust emission in relation to stellar clusters in NGC 628 using combined ALMA and HST data.

Findings

Detected excess millimeter dust emission in NGC 628.

Found no significant correlation between dust slope and cluster age or mass.

Discovered a bright, unidentified source possibly being a dust-obscured supernova.

Abstract

We present results from a joint ALMA-HST study of the nearby spiral galaxy NGC 628. We combine the HST LEGUS database of over 1000 stellar clusters in NGC 628 with ALMA Cycle 4 millimeter/submillimeter observations of the cold dust continuum that span ~15 square kpc including the nuclear region and western portions of the galaxy's disk. The resolution -- 1.1" or approximately 50 pc at the distance of NGC 628 -- allows us to constrain the spatial variations in the slope of the millimeter dust continuum as a function of the ages and masses of the nearby stellar clusters. Our results indicate an excess of dust emission in the millimeter assuming a typical cold dust model for a normal star-forming galaxy, but little correlation of the dust continuum slope with stellar cluster age or mass. For the depth and spatial coverage of these observations, we cannot substantiate the millimeter/submillimeter excess arising from the processing of dust grains by the local interstellar radiation field. We detect a bright unknown source in NGC 628 in ALMA bands 4 and 7 with no counterparts at other wavelengths from ancillary data. We speculate this is possibly a dust obscured supernova.