Determining attenuation laws down to the Lyman break in z~0.3 galaxies
Star formation is the fundamental process transforming baryonic matter in the Universe, and governing the cycling of gas in-and-out of galaxies. Tracing accurately star formation is of critical importance to discriminate between galaxy evolution models.The UV is where massive young stars emit the bulk of their energy and the wavelength of choice to track the evolution of the star formation across cosmic times. Presence of dust, however, impacts the UV emission from galaxies, by dimming and reddening it. Correcting the UV for dust attenuation is thus a crucial requirement to derive the physical parameters of galaxies. Significant variations from the widely used "starburst law" are observed from one galaxy to another, which may reflect systematic variations with stellar populations or galaxy morphology. These uncharacterized variations pose an important limitation to our ability to quantify properties of high-redshift galaxies, a regime where the starburst law is almost universally applied.In order to determine and parametrize attenuation laws in the UV down to the Lyman break we propose to perform COS FUV spectroscopy on a sample of 8 star-forming galaxies at z~0.3. While broadband data can constrain dust masses and optical depth, they cannot reliably constrain the attenuation law itself due to degeneracies between the competing effects of stellar populations and dust. The combination of COS spectra with existing broadband observations will be crucial to address this issue. This will allow us to constrain dust models and will have a broad impact on the study of galaxies from the galactic neighborhood to ultra-high redshifts.
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