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H α morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters

Hannon, Stephen and Lee, Janice C. and Whitmore, B. C. and Chandar, R. and Adamo, A. and Mobasher, B. and Aloisi, A. and Calzetti, D. and Cignoni, M. and Cook, D. O. and Dale, D. and Deger, S. and Della Bruna, L. and Elmegreen, D. M. and Gouliermis, D. A. and Grasha, K. and Grebel, E. K. and Herrero, A. and Hunter, D. A. and Johnson, K. E. and Kennicutt, R. and Kim, H. and Sacchi, E. and Smith, L. and Thilker, D. and Turner, J. and Walterbos, R. A. M. and Wofford, A. (2019) H α morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters. Monthly Notices of the Royal Astronomical Society, 490 (4). pp. 4648-4665. ISSN 0035-8711. doi:10.1093/mnras/stz2820.

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The morphology of H II regions around young star clusters provides insight into the time-scales and physical processes that clear a cluster’s natal gas. We study ∼700 young clusters (≤10 Myr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H α morphology (concentrated, partially exposed, no-emission) and whether they have neighbouring clusters (which could affect the clearing time-scales). Through visual inspection of the HST images, and analysis of ages, reddenings, and stellar masses from spectral energy distributions fitting, together with the (U− B), (V − I) colours, we find (1) the median ages indicate a progression from concentrated (∼3 Myr), to partially exposed (∼4 Myr), to no H α emission (>5 Myr), consistent with the expected temporal evolution of H II regions and previous results. However, (2) similarities in the age distributions for clusters with concentrated and partially exposed H α morphologies imply a short time-scale for gas clearing (≲1 Myr). Also, (3) our cluster sample’s median mass is ∼1000 M⊙, and a significant fraction (∼20 per cent⁠) contain one or more bright red sources (presumably supergiants), which can mimic reddening effects. Finally, (4) the median E(B − V) values for clusters with concentrated H α and those without H α emission appear to be more similar than expected (∼0.18 versus ∼0.14, respectively), but when accounting for stochastic effects, clusters without H α emission are less reddened. To mitigate stochastic effects, we experiment with synthesizing more massive clusters by stacking fluxes of clusters within each H α morphological class. Composite isolated clusters also reveal a colour and age progression for H α morphological classes, consistent with analysis of the individual clusters.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hannon, Stephen0000-0001-9628-8958
Lee, Janice C.0000-0002-2278-9407
Whitmore, B. C.0000-0002-3784-7032
Adamo, A.0000-0002-8192-8091
Aloisi, A.0000-0003-4137-882X
Calzetti, D.0000-0002-5189-8004
Cignoni, M.0000-0001-6291-6813
Cook, D. O.0000-0002-6877-7655
Dale, D.0000-0002-5782-9093
Deger, S.0000-0003-1943-723X
Elmegreen, D. M.0000-0002-1392-3520
Gouliermis, D. A.0000-0002-2763-0075
Grasha, K.0000-0002-3247-5321
Grebel, E. K.0000-0002-1891-3794
Herrero, A.0000-0001-8768-2179
Hunter, D. A.0000-0002-3322-9798
Johnson, K. E.0000-0001-8348-2671
Kennicutt, R.0000-0001-5448-1821
Sacchi, E.0000-0001-5618-0109
Smith, L.0000-0002-0806-168X
Thilker, D.0000-0002-8528-7340
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 October 3. Received 2019 September 14; in original form 2019 June 3. Published: 12 October 2019. Based on observations with the NASA/ESA/CSA Hubble Space Telescope that were retrieved from MAST at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. The observations were obtained through HST programmes #13364 and #13773. Support for these programmes was provided through a grant from the STScI under NASA contract NAS5-26555.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Space Telescope Science InstituteUNSPECIFIED
Subject Keywords:ISM: H II regions – ISM: evolution – galaxies: star clusters – galaxies: ISM
Issue or Number:4
Record Number:CaltechAUTHORS:20200110-093456510
Persistent URL:
Official Citation:Stephen Hannon, Janice C Lee, B C Whitmore, R Chandar, A Adamo, B Mobasher, A Aloisi, D Calzetti, M Cignoni, D O Cook, D Dale, S Deger, L Della Bruna, D M Elmegreen, D A Gouliermis, K Grasha, E K Grebel, A Herrero, D A Hunter, K E Johnson, R Kennicutt, H Kim, E Sacchi, L Smith, D Thilker, J Turner, R A M Walterbos, A Wofford, H α morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters, Monthly Notices of the Royal Astronomical Society, Volume 490, Issue 4, December 2019, Pages 4648–4665,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100624
Deposited By: Tony Diaz
Deposited On:10 Jan 2020 19:20
Last Modified:16 Nov 2021 17:55

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