CaltechAUTHORS
Published December 2019 | Version Published + Accepted Version
Journal Article Open

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

Creators

  • 1. ROR icon University of California, Berkeley
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon Infrared Processing and Analysis Center
  • 4. ROR icon Space Telescope Science Institute
  • 5. ROR icon University of Toledo
  • 6. ROR icon Stockholm University
  • 7. ROR icon University of Massachusetts Amherst
  • 8. ROR icon University of Pisa
  • 9. ROR icon University of Wyoming
  • 10. ROR icon Vassar College
  • 11. ROR icon Heidelberg University
  • 12. ROR icon Max Planck Institute for Astronomy
  • 13. ROR icon Instituto de Astrofísica de Canarias
  • 14. ROR icon University of La Laguna
  • 15. ROR icon Lowell Observatory
  • 16. ROR icon University of Virginia
  • 17. ROR icon University of Cambridge
  • 18. ROR icon University of Arizona
  • 19. ROR icon Johns Hopkins University
  • 20. ROR icon New Mexico State University
  • 21. ROR icon National Autonomous University of Mexico

Abstract

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.

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 (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_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.

Attached Files

Published - stz2820.pdf

Accepted Version - 1910.02983.pdf

Files

1910.02983.pdf

Files (15.5 MB)

Name Size
md5:c4fc45d12f49cdc1560de942515d606b
5.6 MB Preview Download
md5:29a6cc2bcaa1069a91afa120002ee0e4
9.9 MB Preview Download

Additional details

Identifiers

Eprint ID
100624
Resolver ID
CaltechAUTHORS:20200110-093456510

Related works

Describes
https://arxiv.org/abs/1910.02983 (URL)

Funding

NASA
NAS5-26555
NASA
13364
NASA
13773
Space Telescope Science Institute

Dates

Created
2020-01-10
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Infrared Processing and Analysis Center (IPAC)