We use medium-resolution Keck/Echellette Spectrograph and Imager spectroscopy of bright quasars to study cool gas traced by Ca
- Award ID(s):
- 1715630
- NSF-PAR ID:
- 10376810
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 909
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 151
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract ii λλ 3934, 3969 and Nai λλ 5891, 5897 absorption in the interstellar/circumgalactic media of 21 foreground star-forming galaxies at redshifts 0.03 <z < 0.20 with stellar masses 7.4 ≤ logM */M ⊙≤ 10.6. The quasar–galaxy pairs were drawn from a unique sample of Sloan Digital Sky Survey quasar spectra with intervening nebular emission, and thus have exceptionally close impact parameters (R ⊥< 13 kpc). The strength of this line emission implies that the galaxies’ star formation rates (SFRs) span a broad range, with several lying well above the star-forming sequence. We use Voigt profile modeling to derive column densities and component velocities for each absorber, finding that column densitiesN (Caii ) > 1012.5cm−2(N (Nai ) > 1012.0cm−2) occur with an incidencef C(Caii ) = 0.63+0.10−0.11(f C(Nai ) = 0.57+0.10−0.11). We find no evidence for a dependence off Cor the rest-frame equivalent widthsW r (Caii K) orW r (Nai 5891) onR ⊥orM *. Instead,W r (Caii K) is correlated with local SFR at >3σ significance, suggesting that Caii traces star formation-driven outflows. While most of the absorbers have velocities within ±50 km s−1of the host redshift, their velocity widths (characterized by Δv 90) are universally 30–177 km s−1larger than that implied by tilted-ring modeling of the velocities of interstellar material. These kinematics must trace galactic fountain flows and demonstrate that they persist atR ⊥> 5 kpc. Finally, we assess the relationship between dust reddening andW r (Caii K) (W r (Nai 5891)), finding that 33% (24%) of the absorbers are inconsistent with the best-fit Milky WayE (B −V)-W r relations at >3σ significance. -
Abstract We present results on the properties of extreme gas outflows in massive (
M *∼ 1011M ⊙), compact, starburst (star formation rate, SFR∼ 200M ⊙yr−1) galaxies atz = 0.4–0.7 with very high star formation surface densities (ΣSFR∼ 2000M ⊙yr−1kpc−2). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies, we identify outflows with maximum velocities of 820–2860 km s−1. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T ∼ 104K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies’ star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong Mgii absorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of ∼50–2200M ⊙yr−1, assuming a fiducial outflow size of 5 kpc, and mass loading factors ofη ∼ 5 for most of the sample. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution. -
Abstract The resonantly scattered Ly
α line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyα emission in 12 relatively low-mass (M ⋆∼ 109M⊙)z ∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyα and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the Hi column density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the Hi column density in the outer halos. -
Abstract We investigate galactic winds in the HizEA galaxies, a collection of 46 late-stage galaxy mergers at
z = 0.4–0.8, with stellar masses of , star formation rates (SFRs) of 20–500M ⊙yr−1, and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mgii λ λ 2796,2803 absorption lines in optical spectra from MMT, Magellan, and Keck. We find evidence of outflows in 90% of targets, with maximum outflow velocities of 550–3200 km s−1. We combine these data with ten samples from the literature to construct scaling relations for outflow velocity versus SFR, star formation surface density (ΣSFR),M *, and SFR/M *. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of ∼2–4 in outflow velocity and an order of magnitude in SFR and ΣSFR. The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R , and ΣSFR, and weaker correlations withM *and SFR/M *. The HizEA galaxies are mild outliers on the SFR andM *scaling relations, but they connect smoothly with more typical star-forming galaxies on plots of outflow velocity versus SFR/R and ΣSFR. These results provide further evidence that the HizEA galaxies’ exceptional outflow velocities are a consequence of their extreme star formation conditions rather than hidden black hole activity, and they strengthen previous claims that ΣSFRis one of the most important properties governing the velocities of galactic winds. -
null (Ed.)ABSTRACT This paper presents a survey of Mg ii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mg ii absorption and H α emission. The projected distances span a range from d = 9 to 497 kpc, redshifts of the galaxies range from z = 0.10 to 0.48, and rest-frame absolute B-band magnitudes range from MB = −16.7 to −22.8. Our analysis shows that the rest-frame equivalent width of Mg ii, Wr(2796), depends on halo radius (Rh), B-band luminosity(LB), and stellar mass (Mstar) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, Wr(2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mg ii absorbing gas 〈κ〉 is high with 〈κ〉 ≳ 60 per cent at <40 kpc for isolated galaxies and declines rapidly to 〈κ〉 ≈ 0 at d ≳ 100 kpc. Within the gaseous radius, the incidence of Mg ii gas depends sensitively on both Mstar and the specific star formation rate inferred from H α. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mg ii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to $m_{\rm cl} \gtrsim 10^5 \, \rm M_\odot$ and cool gas accretion rate of $\sim 0.7\!-\!2 \, \mathrm{ M}_\odot \, \rm yr^{-1}$. Finally, we find no strong azimuthal dependence of Mg ii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space.more » « less