Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628

Creators: Adamo, A.; Cook, D. O.; Martin, C.; Lee, J. C.

Abstract

We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes ~-2 and a truncation of a few times 10^5 M⊙. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find mass-independent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (≤10^4 M⊙) clusters, suggesting that a mass-dependent component is necessary to fully describe the YSC disruption process in NGC 628.

Additional Information

© 2017 The American Astronomical Society. Received 2017 February 14; revised 2017 April 28; accepted 2017 April 30; published 2017 June 5. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. We are thankful to the anonymous referee for comments and suggestions that have improved the manuscript. A.A. thanks Nate Bastian for sharing the codes used to make the density contours of the color–color diagrams and the maximum-likelihood analysis. Mark Gieles and Nate Bastian are thanked for comments on an early draft of the manuscript. A.A. acknowledges partial support from the Swedish Royal Academy. G.A. acknowledges support from the Science and Technology Facilities Council (ST/L00075X/1 and ST/M503472/1). C.D. acknowledges funding from the FP7 ERC starting grant LOCALSTAR (no. 280104). M.F. acknowledges support by the Science and Technology Facilities Council (grant number ST/L00075X/1). D.A.G. kindly acknowledges financial support by the German Research Foundation (DFG) through program GO 1659/3-2. A.H. thanks the Spanish MINECO for grant AYA2015-68012-c2-1. These observations are associated with program # 13364. Support for program # 13364 was provided by NASA through a grant from the Space Telescope Science Institute. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Facility: HST (WFC3, ACS).

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