EXTREME EMISSION-LINE GALAXIES IN CANDELS: BROADBAND-SELECTED, STARBURSTING DWARF GALAXIES ATz> 1

We identify an abundant population of extreme emission-line galaxies (EELGs) at redshift z ∼ 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey imaging from Hubble Space Telescope /Wide Field Camera 3 ( HST /WFC3). Sixty-nine EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broadband magnitudes. Supported by spectroscopic confirmation of strong [O iii ] emission lines—with rest-frame equivalent widths ∼1000 Å—in the four candidates that have HST /WFC3 grism observations, we conclude that these objects are galaxies with ∼10 8 M ☉ in stellar mass, undergoing an enormous starburst phase with of only ∼15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the comoving number density (3.7 × 10 −4 Mpc −3 ) can produce in ∼4 Gyr much of the stellar mass density that is presently contained in 10 8 –10 9 M ☉ dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z > 1.