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J1044+0353 is considered a local analog of the young galaxies that ionized the intergalactic medium at high redshift due to its low mass, low metallicity, high specific star formation rate, and strong high-ionization emission lines. We use integral field spectroscopy to trace the propagation of the starburst across this small galaxy using Balmer emission- and absorption-line equivalent widths and find a poststarburst population (∼15–20 Myr) roughly 1 kpc east of the much younger, compact starburst (∼3–4 Myr). Using the direct electron temperature method to map the O/H abundance ratio, we find similar metallicities (1–3σ) between the starburst and poststarburst regions but with a significant dispersion of about 0.3 dex within the latter. We also map the Doppler shift and width of the strong emission lines. Over scales several times the size of the galaxy, we discover a velocity gradient parallel to the galaxy’s minor axis. The steepest gradients (∼30 km s⁻¹kpc⁻¹) appear to emanate from the oldest stellar association. We identify the velocity gradient as an outflow viewed edge on based on the increased line width and skew in a biconical region. We discuss how this outflow and the gas inflow necessary to trigger the starburst affect the chemical evolution of J1044+0353. We conclude that the stellar associations driving the galactic outflow are spatially offset from the youngest association, and a chemical evolution model with a metal-enriched wind requires a more realistic inflow rate than a homogeneous chemical evolution model.

 

Lyαline profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Lyαline profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Lyαemission profile in the bottom of a damped, Lyαabsorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Lyαabsorption and the Lyαemission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Lyαexchange between high-N_Hiand low-N_Hipaths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Lyαpeak separation and the [Oiii]/[Oii] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Lyαpeak separation decreases. We combine measurements of Lyαpeak separation and Lyαred peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Lyαtrough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Lyαpeak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Lyαphotons outside the spectroscopic aperture reshapes Lyαprofiles because the distances to these compact starbursts span a large range.

 

Galaxy formation and evolution are regulated by the feedback from galactic winds. Absorption lines provide the most widely available probe of winds. However, since most data only provide information integrated along the line of sight, they do not directly constrain the radial structure of the outflows. In this paper, we present a method to directly measure the gas electron density in outflows (n_e), which in turn yields estimates of outflow cloud properties (e.g., density, volume filling factor, and sizes/masses). We also estimate the distance (r_n) from the starburst at which the observed densities are found. We focus on 22 local star-forming galaxies primarily from the COS Legacy Archive Spectroscopic SurveY (CLASSY). In half of them, we detect absorption lines from fine-structure excited transitions of Siii(i.e., Siii*). We determinen_efrom relative column densities of Siiiand Siii*, given Siii* originates from collisional excitation by free electrons. We find that the derivedn_ecorrelates well with the galaxy’s star formation rate per unit area. From photoionization models or assuming the outflow is in pressure equilibrium with the wind fluid, we getr_n∼ 1–2r_*or ∼5r_*, respectively, wherer_*is the starburst radius. Based on comparisons to theoretical models of multiphase outflows, nearly all of the outflows have cloud sizes large enough for the clouds to survive their interaction with the hot wind fluid. Most of these measurements are the first ever for galactic winds detected in absorption lines and, thus, will provide important constraints for future models of galactic winds.

 

Galactic winds are a crucial player in galaxy formation and evolution, but observations of them have proven extraordinarily difficult to interpret, leaving large uncertainties even in basic quantities such as mass outflow rates. Here we present an analysis of the wind of the nearby dwarf starburst galaxy M82 using a semi-analytic model that is able to take advantage of the full three-dimensional information present in position–position–velocity data cubes measured in the H i 21-cm line, the CO J = 2 → 1 line, and the Hα line. Our best-fitting model produces position-dependent spectra in good agreement with the observations, and shows that the total wind mass flux in the atomic and molecular phases is ≈10 M⊙ yr−1 (corresponding to a mass loading factor of ≈2–3), with less than a factor of 2 uncertainty; the mass flux in the warm ionized phase is more poorly constrained, and may be comparable to or smaller than this. At least over the few kpc off the plane for which we trace the outflow, it appears to be a wind escaping the galaxy, rather than a fountain that falls back. Our fits require that clouds of cool gas entrained into the wind expand only modestly, suggesting they are confined by magnetic fields, radiative cooling, or a combination of both. Finally, we demonstrate that attempts to model the wind using simplifying assumptions such as instantaneous acceleration and a constant terminal wind speed can yield significantly erroneous results.

 

The circumgalactic medium (CGM) plays a vital role in the formation and evolution of galaxies, acting as a lifeline between galaxies and the surrounding intergalactic medium. In this study, we leverage a unique sample of quasar pairs to investigate the properties of the CGM with absorption line tomography. We present a new sample of medium-resolution Keck/ESI, Magellan/MagE, and VLT/XSHOOTER spectra of 29 quasar pairs at redshift 2 <z< 3. We supplement the sample with additional spectra of 32 pairs from the literature, creating a catalog of 61 quasar pairs with angular separations between 1.″7 and 132.″9 and projected physical separations (r_⊥) between 14 kpc and 887 kpc. We construct a catalog of 906 metal-line absorption doublets of Civ(λλ1548, 1550) with equivalent widths ranging from 6 m Å ≤W_r,1550≤ 2053 m Å. The best-fit linear model to the log-space equivalent width frequency distribution ($\log f(W_r)=m\log (W_r)+b$) of the sample yields coefficients ofm= −1.44 ± 0.16 andb= −0.43 ± 0.16. To constrain the projected extent of Civ, we calculate the transverse autocorrelation function. The flattening of the autocorrelation function at lowr_⊥provides a lower limit for the coherence length of the metal enriched CGM—on the order of 200h⁻¹comoving kpc. This physical size constraint allows us to refine our understanding of the metals in the CGM, where the extent of Civin the CGM depends on gas flows, feedback, timescale of metal injection and mixing, and the mass of the host galaxies.

 

Abstract The high incidence rate of the O vi λλ 1032, 1038 absorption around low-redshift, ∼ L * star-forming galaxies has generated interest in studies of the circumgalactic medium. We use the high-resolution EAGLE cosmological simulation to analyze the circumgalactic O vi gas around z ≈ 0.3 star-forming galaxies. Motivated by the limitation that observations do not reveal where the gas lies along the line of sight, we compare the O vi measurements produced by gas within fixed distances around galaxies and by gas selected using line-of-sight velocity cuts commonly adopted by observers. We show that gas selected by a velocity cut of ±300 km s −1 or ±500 km s −1 produces a higher O vi column density, a flatter column density profile, and a higher covering fraction compared to gas within 1, 2, or 3 times the virial radius ( r vir ) of galaxies. The discrepancy increases with impact parameter and worsens for lower-mass galaxies. For example, compared to the gas within 2 r vir , identifying the gas using velocity cuts of 200–500 km s −1 increases the O vi column density by 0.2 dex (0.1 dex) at 1 r vir to over 0.75 dex (0.7 dex) at ≈ 2 r vir for galaxies with stellar masses of 10 9 –10 9.5 M ⊙ (10 10 –10 10.5 M ⊙ ). We furthermore estimate that excluding O vi outside r vir decreases the circumgalactic oxygen mass measured by Tumlinson et al. (2011) by over 50%. Our results demonstrate that gas at large line-of-sight separations but selected by conventional velocity windows has significant effects on the O vi measurements and may not be observationally distinguishable from gas near the galaxies. 

Abstract We present spatially resolved Hubble Space Telescope grism spectroscopy of 15 galaxies at z ∼ 0.8 drawn from the DEEP2 survey. We analyze H α +[N ii ], [S ii ], and [S iii ] emission on kiloparsec scales to explore which mechanisms are powering emission lines at high redshifts, testing which processes may be responsible for the well-known offset of high-redshift galaxies from the z ∼ 0 locus in the [O iii ]/H β versus [N ii ]/H α Baldwin—Phillips—Terlevich (BPT) excitation diagram. We study spatially resolved emission-line maps to examine evidence for active galactic nuclei (AGN), shocks, diffuse ionized gas (DIG), or escaping ionizing radiation, all of which may contribute to the BPT offsets observed in our sample. We do not find significant evidence of AGN in our sample and quantify that, on average, AGN would need to contribute ∼25% of the H α flux in the central resolution element in order to cause the observed BPT offsets. We find weak (2 σ ) evidence of DIG emission at low surface brightnesses, yielding an implied total DIG emission fraction of ∼20%, which is not significant enough to be the dominant emission line driver in our sample. In general we find that the observed emission is dominated by star-forming H ii regions. We discuss trends with demographic properties and the possible role of α -enhanced abundance patterns in the emission spectra of high-redshift galaxies. Our results indicate that photoionization modeling with stellar population synthesis inputs is a valid tool to explore the specific star formation properties which may cause BPT offsets, to be explored in future work. 

ABSTRACT We present the results from an analysis of deep Herschel far-infrared (far-IR) observations of the edge-on disc galaxy NGC 3079. The point spread function-cleaned Photodetector Array Camera and Spectrometer (PACS) images at 100 and 160 µm display a 25 × 25 kpc2 X-shape structure centred on the nucleus that is similar in extent and orientation to that seen in H α, X-rays, and the far-ultraviolet. One of the dusty filaments making up this structure is detected in the Spectral and Photometric Imaging Receiver 250 µm map out to ∼25 kpc from the nucleus. The match between the far-IR filaments and those detected at other wavelengths suggests that the dusty material has been lifted out of the disc by the same large-scale galactic wind that has produced the other structures in this object. A closer look at the central 10 × 10 kpc2 region provides additional support for this scenario. The dust temperatures traced by the 100–160 µm flux ratios in this region are enhanced within a biconical region centred on the active galactic nucleus, aligned along the minor axis of the galaxy, and coincident with the well-known double-lobed cm-wave radio structure and H α–X-ray nuclear superbubbles. PACS imaging spectroscopy of the inner 6 kpc region reveals broad [C ii] 158 µm emission line profiles and OH 79 µm absorption features along the minor axis of the galaxy with widths well in excess of those expected from beam smearing of the disc rotational motion. This provides compelling evidence that the cool material traced by the [C ii] and OH features directly interacts with the nuclear ionized and relativistic outflows traced by the H α, X-ray, and radio emission.