Submitted to ApJ Preprint typeset using LATEX style emulateapj v. 08/22/09 EVIDENCE FOR UBIQUITOUS COLLIMATED GALACTIC-SCALE OUTFLOWS ALONG THE STAR-FORMING SEQUENCE AT Z ∼ 0.5 (original) (raw)
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The Astrophysical Journal, 2014
We present an analysis of the Mg II λλ2796, 2803 and Fe II λλ2586, 2600 absorption line profiles in individual spectra of 105 galaxies at 0.3 < z < 1.4. The galaxies, drawn from redshift surveys of the GOODS fields and the Extended Groth Strip, fully sample the range in star formation rates (SFRs) occupied by the star-forming sequence with stellar masses log M * /M ⊙ 9.5 at 0.3 < z < 0.7. Using the Doppler shifts of the Mg II and Fe II absorption lines as tracers of cool gas kinematics, we detect large-scale winds in 66 ± 5% of the galaxies. High-resolution Hubble Space Telescope/Advanced Camera for Surveys imaging and our spectral analysis indicate that the outflow detection rate depends primarily on galaxy orientation: winds are detected in ∼ 89% of galaxies having inclinations (i) < 30 • (face-on), while the wind detection rate is only ∼ 45% in objects having i > 50 • (edge-on). Combined with the comparatively weak dependence of the wind detection rate on intrinsic galaxy properties (including SFR surface density), this suggests that biconical outflows are ubiquitous in normal, starforming galaxies at z ∼ 0.5, with over half of the sample having full wind cone opening angles of ∼ 100 • . We find that the wind velocity is correlated with host galaxy M * at 3.4σ significance, while the equivalent width (EW) of the flow is correlated with host galaxy SFR at 3.5σ significance, suggesting that hosts with higher SFR may launch more material into outflows and/or generate a larger velocity spread for the absorbing clouds. The large (> 1Å) Mg II outflow EWs typical of this sample are rare in the context of Mg II absorption studies along QSO sightlines probing the extended halos of foreground galaxies, implying that this wind material is not often detected at impact parameters > 10 kpc. Assuming that the gas is launched into dark matter halos with simple, isothermal density profiles, the wind velocities measured for the bulk of the cool material (∼ 200 − 400 km s −1 ) are sufficient to enable escape from the halo potentials only for the lowest-M * systems in the sample. However, the highest-velocity gas in the outflows typically carries sufficient energy to reach distances of 50 kpc, and may therefore be a viable source of cool material for the massive circumgalactic medium observed around bright galaxies at z ∼ 0.
THE PERSISTENCE OF COOL GALACTIC WINDS IN HIGH STELLAR MASS GALAXIES BETWEEN z ∼ 1.4 AND ∼1
The Astrophysical Journal, 2010
We present an analysis of the Mg II λλ2796, 2803 and Fe II λλ2586, 2600 absorption line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field, has a range in stellar mass (M * ) comparable to that of the sample at z ∼ 1.4 analyzed in a similar manner by Weiner et al. (2009, W09), but extends to lower redshifts and has specific star formation rates which are lower by ∼ 0.6 dex. We identify outflows of cool gas from the Doppler shift of the Mg II absorption lines and find that the equivalent width (EW) of absorption due to outflowing gas increases on average with M * and star formation rate (SFR). We attribute the large EWs measured in spectra of the more massive, higher-SFR galaxies to optically thick absorbing clouds having large velocity widths. The outflows have hydrogen column densities N (H) 10 19.3 cm −2 , and extend to velocities of ∼ 500 km s −1 . While galaxies with SFR > 10 M ⊙ yr −1 host strong outflows in both this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log M * /M ⊙ 10.5) galaxies at lower redshifts. Using a simple galaxy evolution model which assumes exponentially declining SFRs, we infer that strong outflows persist in galaxies with log M * /M ⊙ > 10.5 as they age between z = 1.4 and z ∼ 1, presumably because of their high absolute SFRs. Finally, using high resolution HST/ACS imaging in tandem with our spectral analysis, we find evidence for a weak trend (at 1σ significance) of increasing outflow absorption strength with increasing galaxy SFR surface density.
UBIQUITOUS OUTFLOWS IN DEEP2 SPECTRA OF STAR-FORMING GALAXIES AT z = 1.4
The Astrophysical Journal, 2009
Galactic winds are a prime suspect for the metal enrichment of the intergalactic medium and may have a strong influence on the chemical evolution of galaxies and the nature of QSO absorption line systems. We use a sample of 1406 galaxy spectra at z ∼ 1.4 from the DEEP2 redshift survey to show that blueshifted Mg II λ λ 2796, 2803Å absorption is ubiquitous in starforming galaxies at this epoch. This is the first detection of frequent outflowing galactic winds at z ∼ 1. The presence and depth of absorption are independent of AGN spectral signatures or galaxy morphology; major mergers are not a prerequisite for driving a galactic wind from massive galaxies. Outflows are found in coadded spectra of galaxies spanning a range of 30× in stellar mass and 10× in star formation rate (SFR), calibrated from K-band and from MIPS IR fluxes. The outflows have column densities of order N H ∼ 10 20 cm −2 and characteristic velocities of ∼ 300 − 500 km/sec, with absorption seen out to 1000 km/sec in the most massive, highest SFR galaxies. The velocities suggest that the outflowing gas can escape into the IGM and that massive galaxies can produce cosmologically and chemically significant outflows. Both the Mg II equivalent width and the outflow velocity are larger for galaxies of higher stellar mass and SFR, with V wind ∼ SFR 0.3 , similar to the scaling in low redshift IR-luminous galaxies. The high frequency of outflows in the star-forming galaxy population at z ∼ 1 indicates that galactic winds occur in the progenitors of massive spirals as well as those of ellipticals. The increase of outflow velocity with mass and SFR constrains theoretical models of galaxy evolution that include feedback from galactic winds, and may favor momentum-driven models for the wind physics.
The Astronomical …, 2010
We analyze star forming galaxies drawn from SDSS DR7 to show how the interstellar medium (ISM) Na I λλ5890, 5896 (Na D) absorption lines depend on galaxy physical properties, and to look for evidence of galactic winds. We combine the spectra of galaxies with similar geometry/physical parameters to create composite spectra with signal-to-noise ∼ 300. The stellar continuum is modeled using stellar population synthesis models, and the continuum-normalized spectrum is fit with two Na I absorption components. We find that: (1) ISM Na D absorption lines with equivalent widths EW > 0.8 Å are only prevalent in disk galaxies with specific properties -large extinction (A V ), high star formation rates (SFR), high star formation rate per unit area (Σ SFR ), or high stellar mass (M * ).
2013
We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5 h −1 70 kpc. The background galaxy spectrum reveals strong Fe II, Mg II, Mg I, and Ca II absorption at the redshift of the foreground galaxy, with a Mg II λ2796 rest equivalent width of 3.93 ± 0.08 ˚A, indicative of a velocity width exceeding 400 km s−1. Because the background galaxy is large (> 4 h −1 70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M∗/M ⊙ = 11.15 ±0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak AGN. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude the absorbing gas wa...
GALAXIES PROBING GALAXIES: COOL HALO GAS FROM A z = 0.47 POST-STARBURST GALAXY
The Astrophysical Journal, 2010
We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5 h −1 70 kpc. The background galaxy spectrum reveals strong Fe II, Mg II, Mg I, and Ca II absorption at the redshift of the foreground galaxy, with a Mg II λ2796 rest equivalent width of 3.93 ± 0.08Å, indicative of a velocity width exceeding 400 km s −1. Because the background galaxy is large (> 4 h −1 70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M * /M ⊙ = 11.15 ± 0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak AGN. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude the absorbing gas was most likely ejected or tidally stripped from the interstellar medium of the host galaxy or its progenitors during the past starburst event. Adopting the latter interpretation, these results place one of only a few constraints on the radial extent of cool gas driven or stripped from a galaxy in the distant Universe. Future studies with integral field unit spectroscopy of spatially extended background galaxies will provide multiple sightlines through foreground absorbers and permit analysis of the morphology and kinematics of the gas surrounding galaxies with a diverse set of properties and environments.
Absorption‐Line Probes of Gas and Dust in Galactic Superwinds
The Astrophysical Journal Supplement Series, 2000
We have obtained moderate resolution (R = a few thousand) spectra of the NaIλλ5890,5896 (NaD) absorption-line in a sample of 32 far-IR-bright starburst galaxies. In 18 cases, the NaD line in the nucleus is produced primarily by interstellar gas, while cool stars contribute significantly in the others. In 12 of the 18 "interstellar-dominated" cases the NaD line is blueshifted by over 100 km s −1 relative to the galaxy systemic velocity (the "outflow sources"), while no case shows a net redshift of more than 100 km s −1 . The absorption-line profiles in these outflow sources span the range from near the galaxy systemic velocity to a maximum blueshift of ∼ 400 to 600 km s −1 . The outflow sources are galaxies systematically viewed more nearly face-on than the others. We therefore argue that the absorbing material consists of ambient interstellar material that has been entrained and accelerated along the minor axis of the galaxy by a hot starburst-driven superwind. The NaD lines are optically-thick, but indirect arguments imply total Hydrogen column densities of N H ∼ few ×10 21 cm −2 . This implies that the superwind is expelling matter at a rate comparable to the star-formation rate. This outflowing material is evidently very dusty: we find a strong correlation between the depth of the NaD profile and the line-of-sight reddening. Typical implied values are E(B − V ) = 0.3 to 1 over regions several-to-ten kpc in size. We briefly consider some of the potential implications of these observations. The estimated terminal velocities of superwinds inferred from the present data and extant X-ray data are typically 400 to 800 km s −1 , are independent of the galaxy rotation speed, and are comparable to (substantially exceed) the escape velocities for L * (dwarf) galaxies. The resulting selective loss of metals from shallower potential wells can establish the mass-metallicity relation in spheroids, produce the observed metallicity in the intra-cluster medium, and enrich a general IGM to of-order 10 −1 solar metallicity. If the outflowing dust grains can survive their journey into the IGM, their effect on observations of cosmologically-distant objects would be significant.
Galactic Winds in Low-Mass Galaxies
Proceedings of the International Astronomical Union, 2018
Mass-loss via stellar-feedback driven outflows is predicted to play a critical role in the baryon cycle of low-mass galaxies. However, observational constraints on warm winds are limited as outflows are transient, intrinsically low-surface brightness events and, thus, difficult to detect. Here, we search for outflows in a sample of eleven nearby starburst dwarf galaxies which are strong candidates for outflows. Despite deep H? imaging on galaxies, only a fraction of the sample show evidence of winds. The spatial extent of all detected ionized gas is limited and would still be considered part of the ISM by simulations. These new observations indicate that the physical extent of warm phase outflows is modest and most of the mass will be recycled to the galaxy. The sample is part of the panchromatic STARBurst IRegular Dwarf Survey (STARBIRDS) designed to characterize the starburst phenomenon and its impact on the evolution of low-mass galaxies.
Supernovae and Agn Driven Galactic Outflows
The Astrophysical Journal, 2013
We present analytical solutions for winds from galaxies with NFW dark matter halo. We consider winds driven by energy and mass injection from multiple supernovae (SNe), as well as momentum injection due to radiation from a central black hole. We find that the wind dynamics depends on three velocity scales: (a) v ⋆ ∼ (Ė/2Ṁ) 1/2 describes the effect of starburst activity, withĖ,Ṁ as energy and mass injection rate in a central region of radius R; (b) v • ∼ (GM • /2R) 1/2 for the effect of a central black hole of mass M • on gas at distance R and (c) v s = (GM h /2Cr s) 1/2 which is closely related to the circular speed (v c) for NFW halo, with r s as the halo scale radius and C is a function of halo concentration parameter. Our generalized formalism, in which we treat both energy and momentum injection from starbursts and radiation from central active galactic nucleus (AGN), allows us to estimate the wind terminal speed to be (4v 2 ⋆ + 6(Γ − 1)v 2 • − 4v 2 s) 1/2 , where Γ is the ratio of force due to radiation pressure to gravity of the central black hole. Our dynamical model also predicts the following: (a) winds from quiescent star forming galaxies cannot escape from 10 11.5 ≤ M h ≤ 10 12.5 M ⊙ galaxies, (b) circumgalactic gas at large distances from galaxies should be present for galaxies in this mass range, (c) for an escaping wind, the wind speed in low to intermediate mass galaxies is ∼ 400-1000 km/s, consistent with observed X-ray temperatures; (d) winds from massive galaxies with AGN at Eddington limit have speeds 1000 km/s. We also find that the ratio [2v 2 ⋆ − (1 − Γ)v 2 • ]/v 2 c dictates the amount of gas lost through winds. Used in conjunction with an appropriate relation between M • and M h , and an appropriate opacity of dust grains in infrared (K band), this ratio has the attractive property of being minimum at a certain halo mass scale (M h ∼ 10 12-12.5 M ⊙) that signifies the cross-over of AGN domination in outflow properties from starburst activity at lower masses. We find that stellar mass for massive galaxies scales as M ⋆ ∝ M 0.26 h , and for low mass galaxies, M ⋆ ∝ M 5/3 h .
The large-scale distribution of cool gas around luminous red galaxies
Monthly Notices of the Royal Astronomical Society, 2014
We present a measurement of the correlation function between luminous red galaxies and cool gas traced by Mg II λλ2796, 2803 absorption, on scales ranging from about 30 kpc to 20 Mpc. The measurement is based on cross-correlating the positions of about one million red galaxies at z ∼ 0.5 and the flux decrements induced in the spectra of about 10 5 background quasars from the Sloan Digital Sky Survey. We find that: (i) This galaxy-gas correlation reveals a change of slope on scales of about 1 Mpc, consistent with the expected transition from a dark matter halo dominated environment to a regime where clustering is dominated by halo-halo correlations. Assuming that, on average, the distribution of Mg II gas follows that of dark matter up to a gas-to-mass ratio, we find the standard halo model to provide an accurate description of the gas distribution over three orders of magnitude in scale. Within this framework we estimate the average host halo mass of luminous red galaxies to be about 10 13.5 M , in agreement with other methods. We also find the Mg II gas-to-mass ratio around LRGs to be consistent with the cosmic value estimated on Mpc scales. Combining our galaxygas correlation and the galaxy-mass correlation function from galaxy-galaxy lensing analyses we can directly measure the Mg II gas-to-mass ratio as a function of scale and reach the same conclusion.