Abstract
Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (M * ∼ 1011 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 ΣSFR ∼ 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] λλ3726,3729, Hβ, [O iii] λλ4959,5007, Hα, [N ii] λλ6549,6585, and [S ii] λλ6716,6731) and absorption (Mg ii λλ2796,2803, and Fe ii λ2586) lines that allow us to investigate the kinematics of the cool gas phase (T ∼ 104 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.
Highlights
Starburst galaxies represent a fundamental phase in galaxy evolution, as they are widely considered to be the transition stage between star-forming galaxies and massive, passively evolving ellipticals (e.g., Cimatti et al 2008)
The high signal-to-noise ratio (S/N) of the spectra employed in this study provides the unique opportunity of being able to measure the kinematics of [O II], [O III], Hβ and Hα emission lines independently
The nebular emission lines are fit separately, their line profile decompositions in narrow and broad components agree in 10/14 galaxies
Summary
Starburst galaxies represent a fundamental phase in galaxy evolution, as they are widely considered to be the transition stage between star-forming galaxies and massive, passively evolving ellipticals (e.g., Cimatti et al 2008). The starburst activity and subsequent black hole feedback can cause gas depletion and removal through powerful outflows (Sanders et al 1988; Silk & Rees 1998), leading to a passively evolving system (Kormendy & Sanders 1992; Springel et al 2005; Hopkins et al 2008).
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