DJp.2.13 — A project to unveil the population of Low-Mass Star-Forming Galaxies of the Universe

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Aug 10th at 6:00 PM until 6:00 PM

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Author(s): Jesus Gallego4, Lucía Rodriguez-Muñoz4, Laurence Tresse2, Camilla Pacifici5, Stéphane Charlot1, Armando Gil de Paz4, Carlos Gomez-Guijarro4, Víctor Villar4, Guillermo Barro3

Institution(s): 1. Institut Astrophysique de Paris, 2. Laboratoire d'Astrophysique de Marseille, 3. Lick Observatory, 4. Universidad Complutense Madrid, 5. Yonsei University

Dwarf galaxies play a key role in galaxy formation and evolution: (1) hierarchical models predict that low-mass systems merged to form massive galaxies (building block paradigm; Dekel & Silk 1986); (2) dwarf systems might have been responsible for the reionization of the Universe (Wyithe & Loeb 2006); (3) theoretical models are particularly sensitive to the density of low-mass systems at diferent redshifts (Mamon et al. 2011), being one of the key science cases for the future E-ELT (Evans et al. 2013). While the history of low-mass dark matter halos is relatively well understood, the formation history of dwarf galaxies is still poorly reproduced by the models due to the distinct evolution of baryonic and dark matter.
We present constraints on the star formation histories (SFHs) of a sample of low-mass Star-Forming Galaxies (LMSFGs; 7.3 < log M∗/Mo < 8.0, at 0.3 < zspec < 0.9) selected by photometric stellar mass and apparent magnitude. The SFHs were obtained through the analysis of their spectral energy distributions using a novel approach (Pacifici et al. 2012) that (1) consistently combines photometric (HST and ground-based multi-broadband) and spectroscopic (equivalent widths of emission lines from VLT and GTC spectroscopy) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time.
The median SFH of our LMSFGs appears to form 90% of the median stellar mass inferred for the sample in the ∼0.5–1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for dwarf SFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for a slightly more massive secondary sample 8.0 < log M∗/Mo < 9.1).
This is a pilot study for future surveys on dwarf galaxies at high redshift.