| 1. |
- Cook, D. O., et al.
(författare)
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Star cluster catalogues for the LEGUS dwarf galaxies
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 484:4, s. 4897-4919
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Tidskriftsartikel (refereegranskat)abstract
- We present the star cluster catalogues for 17 dwarf and irregular galaxies in the HST Treasury Program 'Legacy ExtraGalactic UV Survey' (LEGUS). Cluster identification and photometry in this sub-sample are similar to that of the entire LEGUS sample, but special methods were developed to provide robust catalogues with accurate fluxes due to low cluster statistics. The colours and ages are largely consistent for two widely used aperture corrections, but a significant fraction of the clusters are more compact than the average training cluster. However, the ensemble luminosity, mass, and age distributions are consistent suggesting that the systematics between the two methods are less than the random errors. When compared with the clusters from previous dwarf galaxy samples, we find that the LEGUS catalogues are more complete and provide more accurate total fluxes. Combining all clusters into a composite dwarf galaxy, we find that the luminosity and mass functions can be described by a power law with the canonical index of -2 independent of age and global SFR binning. The age distribution declines as a power law, with an index of approximate to -0.80 +/- 0.15, independent of cluster mass and global SFR binning. This decline of clusters is dominated by cluster disruption since the combined star formation histories and integrated-light SFRs are both approximately constant over the last few hundred Myr. Finally, we find little evidence for an upper-mass cut-off (< 2 sigma) in the composite cluster mass function, and can rule out a truncation mass below approximate to 10(4.5)M(circle dot) but cannot rule out the existence of a truncation at higher masses.
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| 2. |
- Cignoni, M., et al.
(författare)
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Star Formation Histories of the LEGUS Dwarf Galaxies. III. The Nonbursty Nature of 23 Star-forming Dwarf Galaxies
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 887:2
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Tidskriftsartikel (refereegranskat)abstract
- We derive the recent star formation histories (SFHs) of 23 active dwarf galaxies using Hubble Space Telescope observations from the Legacy Extragalactic UV Survey. We apply a color-magnitude diagram (CMD) fitting technique using two independent sets of stellar models, PARSEC-COLIBRI and MIST. Despite the nonnegligible recent activity, none of the 23 star-forming dwarfs show enhancements in the last 100 Myr larger than three times the 100 Myr average. The unweighted mean of the individual SFHs in the last 100 Myr is also consistent with a rather constant activity, irrespective of the atomic gas fraction. We confirm previous results that for dwarf galaxies, the CMD-based average star formation rates (SFRs) are generally higher than the FUV-based SFRs. For half of the sample, the 60 Myr average CMD-based SFR is more than two times the FUV SFR. In contrast, we find remarkable agreement between the 10 Myr average CMD-based SFR and the H alpha-based SFR. Finally, using core helium-burning stars of intermediate mass, we study the pattern of star formation spatial progression over the past 60 Myr and speculate on the possible triggers and connections of the star formation activity with the environment in which these galaxies live. Approximately half of our galaxies show spatial progression of star formation in the last 60 Myr and/or very recent diffuse and off-center activity compared to RGB stars.
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| 3. |
- Sacchi, E., et al.
(författare)
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Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 878:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of the flocculent spiral galaxy NGC 7793, part of the Sculptor group. By analyzing the resolved stellar populations of the galaxy, located at a distance of similar to 3.7 Mpc, we infer for the first time its radial star formation history (SFH) from Hubble Space Telescope photometry, thanks to both archival and new data from the Legacy ExtraGalactic UV Survey. We determine an average star formation rate (SFR) for the galaxy portion covered by our F555W and F814W data of 0.23 +/- 0.02 M(circle dot)yr(-1) over the whole Hubble time, corresponding to a total stellar mass of (3.09 +/- 0.33) x 10(9) M-circle dot, in agreement with previous determinations. Thanks to the new data extending to the F336W band, we are able to analyze the youngest stellar populations with a higher time resolution. Most importantly, we recover the resolved SFH in different radial regions of the galaxy; this shows an indication of a growing trend of the present-to-past SFR ratio, increasing from internal to more external regions, supporting previous findings of the inside-out growth of the galaxy.
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