Limits on Lyman-alpha Luminous Protogalaxies

Abstract

The bulk of the energy released from protogalaxies, defined here as young ellipticals and bulges undergoing their first major bursts of star formation at large redshifts, is from the nuclear burning in massive stars. This may amount to ~ 10^(61) erg per an average (L_*) galaxy, which is at least an order of magnitude higher than the amount of binding energy released in the protogalactic collapse; an active nucleus, if present, could contribute a comparable amount of energy. If released over a period of ~ 10^8 -10^9 years, this corresponds to protogalaxy (hereafter PG) luminosities of ~ 10^(11) -10^(12) L_☉. For unobscured protogalaxies, a few percent of this energy is expected to emerge in the form of recombination lines, primarily Lyɑ. Star formation rate of 100 M_☉/yr would power a restframe Lyɑ line luminosity of ~ 10^(44) erg/s. At the redshifts of interest, for a range of standard cosmologies, the luminosity distances are ~ 10^(29) - 10^(30) cm, and thus the expected observable Lyɑ line fluxes from unobscured PGs are ~ 10^(-16±1) erg/cm^2 /s, which is detectable with present-day technology. Thus, most PG searches to date employed the Lyn line as the observable signature of young galaxies powered by star formation. More details can be found in our recent reviews and references therein.

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