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Effective Radii of Young, Massive Star Clusters in Two LEGUS Galaxies

Ryon, J. E. and Gallagher, J. S. and Smith, L. J. and Adamo, A. and Calzetti, D. and Bright, S. N. and Cignoni, M. and Cook, D. O. and Dale, D. A. and Elmegreen, B. E. and Fumagalli, M. and Gouliermis, D. A. and Grasha, K. and Grebel, E. K. and Kim, H. and Messa, M. and Thilker, D. and Ubeda, L. (2017) Effective Radii of Young, Massive Star Clusters in Two LEGUS Galaxies. Astrophysical Journal, 841 (2). Art. No. 92. ISSN 1538-4357.

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We present a study of the effective (half-light) radii and other structural properties of a systematically selected sample of young, massive star clusters (≥5 × 10^3 M⊙ and ≤200 Myr) in two nearby spiral galaxies, NGC 628 and NGC 1313. We use Hubble Space Telescope (HST) WFC3/UVIS and archival ACS/WFC data obtained by the Legacy Extragalactic UV Survey (LEGUS), an HST Treasury Program. We measure effective radii with GALFIT, a two-dimensional image-fitting package, and with a new technique to estimate effective radii from the concentration index of observed clusters. The distribution of effective radii from both techniques spans ~0.5–10 pc and peaks at 2–3 pc for both galaxies. We find slight positive correlations between effective radius and cluster age in both galaxies, but no significant relationship between effective radius and galactocentric distance. Clusters in NGC 1313 display a mild increase in effective radius with cluster mass, but the trend disappears when the sample is divided into age bins. We show that the vast majority of the clusters in both galaxies are much older than their dynamical times, suggesting they are gravitationally bound objects. We find that about half of the clusters in NGC 628 are underfilling their Roche lobes, based on their Jacobi radii. Our results suggest that the young, massive clusters in NGC 628 and NGC 1313 are expanding, due to stellar mass loss or two-body relaxation, and are not significantly influenced by the tidal fields of their host galaxies.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Adamo, A.0000-0002-8192-8091
Calzetti, D.0000-0002-5189-8004
Cook, D. O.0000-0002-6877-7655
Dale, D. A.0000-0002-5782-9093
Additional Information:© 2017 The American Astronomical Society. Received 2017 February 25; revised 2017 April 28; accepted 2017 April 30; published 2017 May 30. 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. These observations are associated with program #13364. These observations are associated with program # 13364. Support for program # 13364 was provided by NASA through a grant from the Space Telescope Science Institute. D.A.G. kindly acknowledges financial support by the German Research Foundation (DFG) through grant GO1659/3-2. M.F. acknowledges support by the Science and Technology Facilities Council (grant number ST/L00075X/1). Facility: HST - Hubble Space Telescope satellite (ACS/WFC, WFC3/UVIS). Software: SourceExtractor (Bertin & Arnouts 1996), Yggdrasil (Zackrisson et al. 2011), Starburst99 (Leitherer et al. 1999), GALFIT (Peng et al. 2002, 2010), IRAF, scipy, baolab (Larsen 1999).
Funding AgencyGrant Number
NASANAS 5-26555
Deutsche Forschungsgemeinschaft (DFG)GO1659/3-2
Science and Technology Facilities Council (STFC)ST/L00075X/1
Subject Keywords:galaxies: general – galaxies: individual (NGC 628, NGC 1313) – galaxies: star clusters: general
Issue or Number:2
Record Number:CaltechAUTHORS:20170531-104615329
Persistent URL:
Official Citation:J. E. Ryon et al 2017 ApJ 841 92
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77855
Deposited By: Tony Diaz
Deposited On:31 May 2017 18:10
Last Modified:03 Oct 2019 18:02

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