We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and ...intergalactic baryons within the same survey volumes, focusing particularly on scales from ~50 kpc to a few Mpc. The KBSS is optimized for the redshift range z ~ 2-3, combining S/N ~100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z Asymptotically = to 2.5-2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 <, ~ z <, ~ 2.8 and with projected distances < or =, slant3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Ly alpha forest region of all 15 QSO spectra, we compiled a catalog of ~6000 individual absorbers in the redshift range of interest, with 12 < or =, slant log (N sub(H i)) < or =, slant21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that N sub(H I) and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H I absorbers within Asymptotically = to 100 physical kpc of galaxies have N sub(H I) ~3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H I absorption is found within transverse distances of <, ~ 300 kpc and within + or -300 km s super(-1) of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N sub(H I)) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N sub(H I) remain significantly elevated to transverse distances of ~2 physical Mpc from galaxies in our sample. Absorbers with N sub(H I) >10 super(14.5) cm super(-2) are tightly correlated with the positions of galaxies, while absorbers with lower N sub(H I) are correlated with galaxy positions only on >, ~Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ~100 physical kpc peculiar velocities of Delta v Asymptotically = to + or -260 km s super(-1) with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r sub(vir) of galaxies are larger by Asymptotically = to 50% than randomly chosen absorbers of the same N sub(H I), suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M sub(halo) Asymptotically = to 10 super(12) M sub(middot in circle) at z ~ 2-3.
We study the Ly alpha profiles of 36 spectroscopically detected Ly alpha -emitters (LAEs) at z ~ 2-3, using Keck MOSFIRE to measure systemic redshifts and velocity dispersions from rest-frame optical ...nebular emission lines. Thirty of the 36 Ly alpha emission lines are redshifted with respect to the systemic velocity with at least lsigma significance, and the velocity offset with respect to systemic Delta v sub(Ly) alpha is correlated with the R-band magnitude, M sub(UV), and the velocity dispersion measured from nebular emission lines with >3sigma significance: brighter galaxies with larger velocity dispersions tend to have larger values of Delta v sub(Ly) alpha . Our results are consistent with a scenario in which the Ly alpha profile is determined primarily by the properties of the gas near the systemic redshift; in such a scenario, the opacity to Ly alpha photons in lower mass galaxies may be reduced if large gaseous disks have not yet developed and if the gas is ionized by the harder spectrum of young, low metallicity stars.
Abstract
Low-mass, low-metallicity galaxies at low to moderate (
z
≲ 3) redshifts offer the best opportunity for detailed examination of the interplay between massive stars, ionizing radiation and ...gas in sources similar to those that likely reionized the universe. We present new narrowband
Hubble Space Telescope
observations of
emission and the adjacent ultraviolet (UV) continuum in the low-mass (
M
⋆
= 2 × 10
8
), low-metallicity (
Z
∼ 1/20 Z
⊙
), and highly ionized gravitationally lensed galaxy SL2S J02176−0513 at
z
= 1.844. The galaxy has strong
emission with photometric equivalent width
, at odds with the
escape fraction of 10%. However, the spectroscopic
profile suggests the presence of broad absorption underlying the emission, and the total equivalent width is consistent with the escape fraction once this underlying absorption is included. The
emission is more spatially extended than the UV continuum, and the 0.″14 spatial resolution of
HST
coupled with the magnification of gravitational lensing enables us to examine the distribution of
and the UV continuum on subkiloparsec scales. We find that the peaks of the
emission and the UV continuum are offset by 650 pc, and there is no
emission arising from the region with the strongest UV light. Our combined spectroscopic and imaging data imply a significant range in neutral hydrogen column density across the object. These observations offer indirect support for a model in which ionizing radiation escapes from galaxies through channels with low column density of neutral gas.
We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z ~ 2-3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 ...galaxies between redshifts z ~ 2.0 and 2.5 and one galaxy at z ~ 3.3 which are well detected in either H alpha or O III emission. These galaxies are generally representative of the mean stellar mass of star-forming galaxies at similar redshifts, although they tend to have star formation rate surface densities slightly higher than the mean. These observations were obtained in conjunction with the Keck laser guide star adaptive optics system, with a typical angular resolution after spatial smoothing ~015 (approximately 1 kpc at the redshift of the target sample). At most five of these 13 galaxies have spatially resolved velocity gradients consistent with rotation while the remaining galaxies have relatively featureless or irregular velocity fields. All of our galaxies show local velocity dispersions ~60-100 km s-1 , suggesting that (particularly for those galaxies with featureless velocity fields) rotation about a preferred axis may not be the dominant mechanism of physical support. While some galaxies show evidence for major mergers such evidence is unrelated to the kinematics of individual components (one of our strongest merger candidates also exhibits unambiguous rotational structure), refuting a simple bimodal disk/merger classification scheme. We discuss these data in light of complementary surveys and extant UV-IR spectroscopy and photometry, concluding that the dynamical importance of cold gas may be the primary factor governing the observed kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of mechanisms for accreting low angular momentum gas and the early formation of quasi-spheroidal systems in the young universe.
Abstract We investigate the stellar and nebular properties of nine H ii regions in the spiral galaxy M101 with far-ultraviolet (FUV; ∼900–2000 Å) and optical (∼3200–10,000 Å) spectra. We detect ...significant C iii λλ 1907,1909 nebular emission in seven regions, but O iii λ 1666 only in the lowest-metallicity region. We produce new analytic functions of the carbon ionization correction factors as a function of metallicity in order to perform a preliminary C/O abundance analysis. The FUV spectra also contain numerous stellar emission and P-Cygni features that we fit with luminosity-weighted combinations of single-burst Starburst99 and BPASS models. We find that the best-fit Starburst99 models closely match the observed very-high-ionization P-Cygni features, requiring very hot, young (≲3 Myr), metal-enriched massive stars. The youngest stellar populations are strongly correlated with broad He ii emission, nitrogen Wolf–Rayet (WR) FUV and optical spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR phase may be driving excess emission in several N P-Cygni wind features ( λ 955, λ 991, λ 1720) that bias the stellar continuum fits to higher metallicities relative to the gas-phase metallicities. Accurate characterization of these H ii regions requires additional inclusion of WR stars in the stellar population synthesis models. Our FUV spectra demonstrate that the ∼900–1200 Å FUV can provide a strong test bed for future WR atmosphere and evolution models.
We present the results of a spectroscopic survey with LRIS-B on Keck of more than 280 star-forming galaxies and AGNs at redshifts 1.4 z 3.0 in the GOODS-N field. Candidates are selected by their U ...sub(n)GR colors using the "BM/BX" criteria to target redshift 1.4 z 2.5 galaxies and the LBG criteria to target redshift z 6 3 galaxies; combined these samples account for 625%-30% of the R and K sub(s) band counts to R = 25.5 and K sub(s)(AB) = 24.4, respectively. The 212 BM/BX galaxies and 74 LBGs constitute the largest spectroscopic sample of galaxies at z > 1.4 in GOODS-N. Extensive multiwavelength data allow us to investigate the stellar populations, stellar masses, bolometric luminosities (L sub(bol)), and extinction of z 6 2 galaxies. Deep Chandra and Spitzer data indicate that the sample includes galaxies with a wide range in L sub(bol) ( 10 super(10) to >10 super(12) L sub( )) and 4 orders of magnitude in dust obscuration (L sub(bol)/L sub(UV)). The sample includes galaxies with a large dynamic range in evolutionary state, from very young galaxies (ages 650 Myr) with small stellar masses (M* 10 super(9) M sub( )) to evolved galaxies with stellar masses comparable to the most massive galaxies at these redshifts (M* > 10 super(11) M sub( )). Spitzer data indicate that the optical sample includes some fraction of the obscured AGN population at high redshifts: at least 3 of 11 AGNs in the z > 1.4 sample are undetected in the deep X-ray data but exhibit power-law SEDs longward of 62 km (rest frame) indicative of obscured AGNs. The results of our survey indicate that rest-frame UV selection and spectroscopy presently constitute the most timewise efficient method of culling large samples of high-redshift galaxies with a wide range in intrinsic properties, and the data presented here will add significantly to the multiwavelength legacy of GOODS.
Abstract
We investigate the connection between galactic outflows and star formation using two independent data sets covering a sample of 22 galaxies between 1 ≲
z
≲ 1.5. The Hubble Space Telescope ...WFC3/G141 grism provides low spectral resolution, high spatial resolution spectroscopy yielding H
α
emission-line maps from which we measure the spatial extent and strength of star formation. In the rest-frame near-UV, Keck/DEIMOS observes Fe
ii
and Mg
ii
interstellar absorption lines, which provide constraints on the intensity and velocity of the outflows. We compare outflow properties from individual and composite spectra with the star formation rate (SFR) and SFR surface density (Σ
SFR
), as well as the stellar mass and specific SFR (sSFR). The Fe
ii
and Mg
ii
equivalent widths (EWs) increase with both SFR and Σ
SFR
at ≳3
σ
significance, while the composite spectra show larger Fe
ii
EWs and outflow velocities in galaxies with higher SFR, Σ
SFR
, and sSFR. Absorption-line profiles of the composite spectra further indicate that the differences between subsamples are driven by outflows rather than the interstellar medium. While these results are consistent with those of previous studies, the use of H
α
images makes them the most direct test of the relationship between star formation and outflows at
z
> 1 to date. Future facilities such as the James Webb Space Telescope and the upcoming Extremely Large Telescopes will extend these direct, H
α
-based studies to lower masses and SFRs, probing galactic feedback across orders of magnitude in galaxy properties and augmenting the correlations we find here.
Abstract
Detailed analyses of high-redshift galaxies are challenging because these galaxies are faint, but this difficulty can be overcome with gravitational lensing, in which the magnification of ...the flux enables spectroscopy with a high signal-to-noise ratio (S/N). We present the rest-frame ultraviolet (UV) Keck Echellette Spectrograph and Imager (ESI) spectrum of the newly discovered
z
= 2.79 lensed galaxy SDSS J1059+4251. With an observed magnitude F814W = 18.8 and a magnification factor
μ
= 31 ± 3, J1059+4251 is both highly magnified and intrinsically luminous, about two magnitudes brighter than
M
UV
*
at
z
∼ 2–3. With a stellar mass
M
*
= (3.22 ± 0.20) × 10
10
M
⊙
, star formation rate SFR = 50 ± 7 M
⊙
yr
−1
, and stellar metallicity
Z
*
≃ 0.15–0.5
Z
⊙
, J1059+4251 is typical of bright star-forming galaxies at similar redshifts. Thanks to the high S/N and the spectral resolution of the ESI spectrum, we are able to separate the interstellar and stellar features and derive properties that would be inaccessible without the aid of the lensing. We find evidence of a gas outflow with speeds up to −1000 km s
−1
, and of an inflow that is probably due to accreting material seen along a favorable line of sight. We measure relative elemental abundances from the interstellar absorption lines and find that
α
-capture elements are overabundant compared to iron-peak elements, suggestive of rapid star formation. However, this trend may also be affected by dust depletion. Thanks to the high data quality, our results represent a reliable step forward in the characterization of typical galaxies at early cosmic epochs.
The detection of photons sufficiently energetic to ionize neutral hydrogen, coming from a compact, star-forming galaxy, offers clues to how the first generation of galaxies may have reionized ...hydrogen gas in the early Universe. See Letter p.178
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