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Strong Halpha Emitters (HAEs) dominate the z~4 Lyman-break galaxy population.We have identified local analogs of these HAEs using the Sloan Digital SkySurvey (SDSS). At z<0.4, only 0.04% of galaxies are classified as HAEs withHalpha equivalent widths (>500A) comparable to that of z~4 HAEs. Local HAEshave lower stellar mass and lower ultraviolet (UV) luminosity than z~4 HAEs,yet the Halpha-to-UV luminosity ratio as well as their specific star-formationrate is consistent with that of z~4 HAEs indicating that they are scaled downversions of high-z star-forming galaxies. Compared to the previously studiedlocal analogs of z~2 Lyman break galaxies selected using rest-frame UV, localHAEs show similar UV luminosity surface density, weaker Dn(4000) breaks, lowermetallicity and lower stellar mass. This supports the idea that local HAEs areless evolved galaxies than the traditional Lyman break analogs. We are not ableto constrain if the star-formation history in local HAEs is powered by mergersor by cosmological cold flow accretion. However, in the stacked spectrum, localHAEs show a strong HeII4686 emission line suggesting a population of young(<10Myr), hot, massive stars similar to that seen in some Wolf-Rayet galaxies.Low [NII]/[OIII] line flux ratios imply that local HAEs are inconsistent withbeing systems that host bright AGN. Instead, it is highly likely that localHAEs are galaxies with an elevated ionization parameter, either due to a highelectron density or large escape fraction of hydrogen ionizing photons as inthe case for Wolf-Rayet galaxies.

Dissection of Halpha Emitters : Low-z Analogs of z>4 Star-Forming Galaxies