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

Creators: Turner, J. A.; Dale, D. A.; Adamo, A.; Calzetti, D.; Grasha, K.; Grebel, E. K.; Johnson, K. E.; Lee, J. C.; Smith, L. J.; Yoon, I.

Abstract

We present results from a joint ALMA/HST study of the nearby spiral galaxy NGC 628. We combine the Hubble Space Telescope (HST) Legacy ExtraGalactic UV Survey (LEGUS) database of over 1000 stellar clusters in NGC 628 with ALMA Cycle 4 mm/submillimeter observations of the cold dust continuum that span ~15 kpc² 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.

Additional Information

© 2019 The American Astronomical Society. Received 2019 June 10; revised 2019 August 27; accepted 2019 August 28; published 2019 October 16. We thank the referee for the helpful recommendations. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00650.S, ADS/JAO.ALMA#2013.1.00532.S, and ADS/JAO.ALMA#2016.1.01435.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank Eric Murphy and Laurie Rousseau-Nepton for valuable discussions. A.A. acknowledges the support of the Swedish Research Council, Vetenskapsrådet, and the Swedish National Space Agency (SNSA). J.A.T. was supported by the Wyoming NASA Space Grant Consortium. These observations are associated with program # 13364, the support for which was provided by NASA through a grant from the Space Telescope Science Institute (STScI). Based on observations obtained with the NASA/ESA Hubble Space Telescope, at STScI, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. This research is partially support by by NSF grants 1716335 (PI: K. Johnson) by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Facilities: ALMA - Atacama Large Millimeter Array, HST (ACS - , UVIS). - Software: APLpy (Robitaille & Bressert 2012), Astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018), CASA (McMullin et al. 2007), NumPy (van der Walt et al. 2011), SExtractor (Bertin & Arnouts 1996).

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