We present a measurement of the intrinsic space density of intermediate-redshift (
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Abstract z ∼ 0.5), massive (M *∼ 1011M ⊙), compact (R e ∼ 100 pc) starburst (ΣSFR∼ 1000M ⊙yr−1kpc−1) galaxies with tidal features indicative of them having undergone recent major mergers. A subset of them host kiloparsec-scale, > 1000 km s−1outflows and have little indication of AGN activity, suggesting that extreme star formation can be a primary driver of large-scale feedback. The aim for this paper is to calculate their space density so we can place them in a better cosmological context. We do this by empirically modeling the stellar populations of massive, compact starburst galaxies. We determine the average timescale on which galaxies that have recently undergone an extreme nuclear starburst would be targeted and included in our spectroscopically selected sample. We find that massive, compact starburst galaxies targeted by our criteria would be selectable for Myr and have an intrinsic space density . This space density is broadly consistent with ourz ∼ 0.5 compact starbursts being the most extremely compact and star-forming low-redshift analogs of the compact star-forming galaxies in the early universe, as well as them being the progenitors to a fraction of intermediate-redshift, post-starburst, and compact quiescent galaxies. -
Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (
M *∼ 1011M ⊙), compact starburst galaxies atz = 0.4–0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean ΣSFR∼ 2000M ⊙yr−1kpc−2) and powerful galactic outflows (maximum speedsv 98∼ 1000–3000 km s−1). Our unique data set includes an ensemble of both emission ([Oii] λλ 3726,3729, Hβ , [Oiii] λλ 4959,5007, Hα , [Nii] λλ 6549,6585, and [Sii] λλ 6716,6731) and absorption (Mgii λλ 2796,2803, and Feii λ 2586) lines that allow us to investigate the kinematics of the cool gas phase (T ∼ 104K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (mediann e ∼ 530 cm−3), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [Sii] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.