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

Journal Article · Thu Jun 01 00:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA719E· OSTI ID:22872668

Ryon, J. E.; Gallagher, J. S. ^[1]; Smith, L. J. ^[2]; Adamo, A.; Messa, M. ^[3]; Calzetti, D.; Grasha, K. ^[4]; Bright, S. N.; Cignoni, M.; Ubeda, L. ^[5]; Cook, D. O.; Dale, D. A. ^[6]; Elmegreen, B. E. ^[7]; Fumagalli, M. ^[8]; Gouliermis, D. A. ^[9]; Grebel, E. K. ^[10]; Kim, H. ^[11]; Thilker, D. ^[12]

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1. University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States)
2. European Space Agency/Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)
3. Dept. of Astronomy, The Oskar Klein Centre, Stockholm University, Stockholm (Sweden)
4. Dept. of Astronomy, University of Massachusetts—Amherst, Amherst, MA 01003 (United States)
5. Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)
6. Dept. of Physics and Astronomy, University of Wyoming, Laramie, WY (United States)
7. IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY (United States)
8. Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Durham University, Durham (United Kingdom)
9. Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)
10. Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12–14, D-69120 Heidelberg (Germany)
11. Gemini Observatory, Casilla 603, La Serena (Chile)
12. Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)

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{sup 3} M{sub ⊙} 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.

• OSTI ID: 22872668
• Journal Information: Astrophysical Journal, Vol. 841, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CONCENTRATION RATIO
DISTANCE
DISTRIBUTION
GALAXIES
MASS TRANSFER
RELAXATION
ROCHE EQUIPOTENTIALS
SPACE
STAR CLUSTERS
STAR EVOLUTION
STELLAR WINDS
TELESCOPES
TWO-BODY PROBLEM
TWO-DIMENSIONAL CALCULATIONS