Sizing Up Ly Alpha and Lyman Break Galaxies

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Malhotra, Sangeeta
Rhoads, James E.
Finkelstein, Steven L.
Hathi, Nimish
Nilsson, Kim
McLinden, Emily
Pirzkal, Norbert

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We measure the sizes for a sample of 174 Ly alpha-selected galaxies with broadband imaging with the Hubble Space Telescope. Over the redshift range 2.25 < z < 6, Ly alpha-selected galaxies have a characteristic, constant, small size in rest-frame ultraviolet (UV) light. Coupled with a characteristic star Formation intensity (i.e., UV luminosity per unit area), this can explain their non-evolving ultraviolet continuum luminosity function. This is in contrast to Lyman break galaxies (LBGs) over the same redshift range, which have been previously shown to increase in linear size as H(z) (1). The compact physical size seems to be a critical determining factor in whether a galaxy will show Ly alpha emission or not. The L-* of LBGs and its evolution with redshift can be derived from a simple model where the star Formation intensity has an upper limit set by feedback processes, independent of redshift. The increase in L-* of LBGs is mainly driven by the increase in linear size over redshifts for z = 2-7. Since Ly alpha galaxies do not grow in linear size, they do not show an increase in L-*.



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Malhotra, Sangeeta, James E. Rhoads, Steven L. Finkelstein, Nimish Hathi, Kim Nilsson, Emily McLinden, and Norbert Pirzkal. "Sizing up Ly? and Lyman Break Galaxies." The Astrophysical Journal Letters, Vol. 750, No. 2 (May, 2012): L36.