2018/02/19 by M. Cignoni, E. Sacchi, A. Aloisi +20 · 32 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Dwarf galaxy #Galaxies: Formation, Evolution, Phenomena #Hubble sequence #Initial mass function #Star cluster #Star formation #Stellar evolution #Stellar mass #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aab041
published in The Astrophysical Journal 856(1), 62 (IOP Publishing) · 22 pages, 17 figures, accepted for publication on ApJ
arxiv created 2018/02/19 · openalex created_date 2018/03/06 · openalex publication_date 2018/03/20 · arxiv updated 2018/04/11 · openalex updated_date 2026/08/06
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.