CaltechAUTHORS
Published March 20, 2018 | Version Published + Accepted Version
Journal Article Open

Star Formation Histories of the LEGUS Dwarf Galaxies. I. Recent History of NGC 1705, NGC 4449, and Holmberg II

Creators

  • 1. ROR icon University of Pisa
  • 2. ROR icon INFN Sezione di Pisa
  • 3. ROR icon University of Bologna
  • 4. ROR icon Space Telescope Science Institute
  • 5. ROR icon University of Massachusetts Amherst
  • 6. ROR icon California Institute of Technology
  • 7. ROR icon Stockholm University
  • 8. ROR icon University of Wyoming
  • 9. ROR icon IBM Research - Thomas J. Watson Research Center
  • 10. ROR icon University of Wisconsin–Madison
  • 11. ROR icon Heidelberg University
  • 12. ROR icon Max Planck Institute for Astronomy
  • 13. ROR icon Lowell Observatory
  • 14. ROR icon University of Virginia
  • 15. ROR icon Johns Hopkins University

Abstract

We use Hubble Space Telescope observations from the Legacy Extragalactic UV Survey to reconstruct the recent star formation histories (SFHs) of three actively star-forming dwarf galaxies, NGC 4449, Holmberg II, and NGC 1705, from their UV color–magnitude diagrams (CMDs). We apply a CMD fitting technique using two independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the uncertainties related to stellar evolution modeling. Irrespective of the adopted stellar models, all three dwarfs are found to have had almost constant star formation rates (SFRs) in the last 100–200 Myr, with modest enhancements (a factor of ~2) above the 100 Myr averaged SFR. Significant differences among the three dwarfs are found in terms of the overall SFR, the timing of the most recent peak, and the SFR/area. The initial mass function of NGC 1705 and Holmberg II is consistent with a Salpeter slope down to ≈5 M ⊙, whereas it is slightly flatter, s = −2.0, in NGC 4449. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. They also share the drawback that all synthetic diagrams predict a clear separation in color between the upper main-sequence and helium-burning stars, which is not apparent in the data. Since neither differential reddening, which is significant in NGC 4449, nor unresolved binaries appear to be sufficient to fill the gap, we suggest this calls for a revision of both sets of stellar evolutionary tracks.

Additional Information

© 2018. The American Astronomical Society. Received 2017 October 2; revised 2018 February 1; accepted 2018 February 14; published 2018 March 26. We warmly thank Kristy McQuinn for helpful discussions and suggestions. M.C. and M.T. acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. D.A.G. kindly acknowledges financial support by the German Research Foundation (DFG) through programme GO 1659/3-2. B.G.E. acknowledges support from NASA grant HST-GO-13364.14-A.

Attached Files

Published - Cignoni_2018_ApJ_856_62.pdf

Accepted Version - 1802.06792

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Cignoni_2018_ApJ_856_62.pdf

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Additional details

Additional titles

Alternative title
Star Formation Histories of the LEGUS Dwarf Galaxies (I): recent History of NGC1705, NGC4449 and Holmberg II

Identifiers

Eprint ID
85769
Resolver ID
CaltechAUTHORS:20180411-150615795

Related works

Describes
https://arxiv.org/abs/1802.06792 (URL)

Funding

Istituto Nazionale di Astrofisica (INAF)
1.05.01.88.04
Deutsche Forschungsgemeinschaft (DFG)
GO 1659/3-2
NASA
HST-GO-13364.14-A
NASA
NAS 5-26555

Dates

Created
2018-04-11
Created from EPrint's datestamp field
Updated
2021-11-15
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Infrared Processing and Analysis Center (IPAC)