Exploring star formation in dwarf galaxies at Z1
Master Thesis
2014
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University of Cape Town
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Abstract
This dissertation presents the first H α measurements of star formation rates (SFRs) for dwarf galaxies at z~1 (when the Universe was approximately half its current age) using the Hubble Space Telescope (HST).We target a sample derived from the Redshift One LDSS3 Emission Line Survey (ROLES), which used [OII]3727 as a tracer of star formation to target very low stellar masses (M~10 8:5M) at this epoch. In this dissertation, we study these low mass ROLES galaxies using near-infrared slitless spectroscopy from HST. We target and measure the luminosity of the H α emission line. Even though H_ is a more direct SFR indicator, H α derived SFRs still need to be corrected for dust which is normally done using Balmer decrement measurements that are not available for our spectra. We find that using SED-fitted dust estimates, in the V-band, underestimates the extinction in high mass galaxies, in agreement with a recent result obtained by Price et al. (2013). We instead derive an empirical mass-dependent dust correction to take into account the extra extinction needed in high mass galaxies. We compare our dust corrected H α SFRs to the [OII] SFRs from ROLES. The [OII] SFRs were calculated using a mass-dependent empirical correction derived for galaxies in the Local Universe (Gilbank et al. 2010a). We find that the empirically corrected [OII] SFRs agree quite well with our dust corrected H α SFRs, having a slope of 1.6±0.7. This confirms that the mass-dependent empirical correction to [OII] works at z~1. We study the H α SSFR-mass relation for galaxies. We confirm previous results that at similar redshifts, low mass galaxies form their stars later and on longer timescales than high mass galaxies. However, our study probes down to lower limiting SFRs and lower stellar masses than any other previous studies, placing tighter constraints on galaxy evolution at this epoch.
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Reference:
Ramraj, R. 2014. Exploring star formation in dwarf galaxies at Z1. University of Cape Town.