Leo A: A Late-blooming Survivor of the Epoch of Reionization in the Local Group

By A. Cole, E. Skillman, E. Tolstoy, J. Gallagher III, A. Aparicio, A. Dolphin, C. Gallart, S. Hidalgo, A. Saha, P. Stetson and 1 more. 2007

163 citations recorded by the source corpus.

As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cosmology, we have obtained deep images of the dwarf irregular galaxy Leo A with the Advanced Camera for Surveys aboard the Hubble Space Telescope. From these images we have constructed a color-magnitude diagram (CMD) reaching apparent [absolute] magnitudes of (M475, M814) ≳ (29.0 [+4.4], 27.9 [+3.4]), the deepest ever achieved for any irregular galaxy beyond the Magellanic Clouds. We derive the star formation rate (SFR) as a function of time over the entire history of the galaxy. We find that over 90% of all the star formation that ever occurred in Leo A happened more recently than 8 Gyr ago. The CMD shows only a very small amount of star formation in the first few billion years after the big bang; a possible burst at the oldest ages cannot be claimed with high confidence. The peak SFR occurred ≈1.5-4 Gyr ago, at a level 5-10 times the current value. Our modeling indicates that Leo A has experienced very little metallicity evolution; the mean inferred metallicity is consistent with measurements of the present-day gas-phase oxygen abundance. We cannot exclude a scenario in which all of the ancient star formation occurred prior to the end of the era of reionization, but it seems unlikely that the lack of star formation prior to ≈8 Gyr ago was due to early loss or exhaustion of the in situ gas reservoir.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9b34dce7ec034ad550392b04478a4518218c47d9

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Citations in the corpus

DIRECT OXYGEN ABUNDANCES FOR LOW-LUMINOSITY LVL GALAXIES (2012, unknown): “…and GR 8 have detailed star formation histories derived from Hubble Space Telescope observations of their resolved stars which clearly show that the bulk of their star formation occurred well before the last 40 Myr (Tolstoy et al. 1998; Cole et al. 2007; Dohm-Palmer et al. 1998; Weisz et al. 2011).”
THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I. HUBBLE SPACE TELESCOPE/WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS (2014, background): “…et al. 2008), which are acquiring imaging of dwarfs without previous HST pointings and/or are increasing the CMD depths in order to fully capture the oldest MSTO for galaxies with existing HST observations (e.g., Cole et al. 2007; Monelli et al. 2010a,b; Hidalgo et al. 2011; Brown et al. 2012).”
THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME (2011, background): “A more robust analysis of the chemical enrichment of dwarf galaxies would need to include the ancient MS, measured gas phase abundances, and/or individual stellar spectra (e.g., Cole et al. 2007; Monelli et al. 2010a,b; Kirby et al. 2010).”
Dark matter cores all the way down (2015, background): “It is perhaps telling that no unambiguous reionisation feature in the star formation history of surviving dwarfs has been reported to date, despite many studies looking for one (e.g. Cole et al. 2007; Hidalgo et al. 2011; Skillman et al. 2014; Weisz et al. 2014).”
THE NATURE OF STARBURSTS. I. THE STAR FORMATION HISTORIES OF EIGHTEEN NEARBY STARBURST DWARF GALAXIES (2010, result): “This “suppression” of SF at early times is similar to the SFH reported for the dwarf galaxy Leo A (Cole et al. 2007).”