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Abstract High-velocity outflows are ubiquitous in compact, massive (M*∼ 1011M⊙),z∼ 0.5 galaxies with extreme star formation surface densities (ΣSFR∼ 2000M⊙yr−1kpc−2). We have previously detected and characterized these outflows using Mgiiabsorption lines. To probe their full extent, we present Keck/KCWI integral field spectroscopy of the [Oii] and Mgiiemission nebulae surrounding all of the 12 galaxies in this study. We find that [Oii] is more effective than Mgiiin tracing low surface brightness, extended emission in these galaxies. The [Oii] nebulae are spatially extended beyond the stars, with radial extentR90between 10 and 40 kpc. The nebulae exhibit nongravitational motions, indicating galactic outflows with maximum blueshifted velocities ranging from −335 to −1920 km s−1. The outflow kinematics correlate with the bursty star formation histories of these galaxies. Galaxies with the most recent bursts of star formation (within the last <3 Myr) exhibit the highest central velocity dispersions (σ≳ 400 km s−1), while the oldest bursts have the lowest-velocity outflows. Many galaxies exhibit both high-velocity cores and more extended, slower-moving gas indicative of multiple outflow episodes. The slower, larger outflows occurred earlier and have decelerated as they propagate into the circumgalactic medium and mix on timescales ≳50 Myr.
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Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows
Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive ( M * ∼ 10 11 M ⊙ ), compact starburst galaxies at z = 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 Σ SFR ∼ 2000 M ⊙ yr −1 kpc −2 ) and powerful galactic outflows (maximum speeds v 98 ∼ 1000–3000 km s −1 ). Our unique data set includes an ensemble of both emission ([O ii] λλ 3726,3729, H β , [O iii] λλ 4959,5007, H α , [N ii] λλ 6549,6585, and [S ii] λλ 6716,6731) and absorption (Mg ii λλ 2796,2803, and Fe ii λ 2586) lines that allow us to investigate the kinematics of the cool gas phase ( T ∼ 10 4 K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n 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 [S ii] 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.
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- PAR ID:
- 10346179
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 923
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac2fa4
