Publications (26)31.53 Total impact
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Article: Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
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ABSTRACT: We present a study of the prevalence, strength, and kinematics of ultraviolet FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected from the DEEP2 survey. We find FeII* emission in composite spectra assembled on the basis of different galaxy properties, indicating that FeII* emission is prevalent at z = 1. In these composites, FeII* emission is observed at roughly the systemic velocity. At z = 1, we find that the strength of FeII* emission is most strongly modulated by dust attenuation, and is additionally correlated with redshift, star-formation rate, and [OII] equivalent width, such that systems at higher redshifts with lower dust levels, lower star-formation rates, and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII emission in at least 15% of the individual spectra and we find that objects showing stronger MgII emission have higher specific star-formation rates, smaller [OII] linewidths, larger [OII] equivalent widths, lower dust attenuations, and lower stellar masses than the sample as a whole. MgII emission strength exhibits the strongest correlation with specific star-formation rate, although we find evidence that dust attenuation and stellar mass also play roles in the regulation of MgII emission. Future integral field unit observations of the spatial extent of FeII* and MgII emission in galaxies with high specific star-formation rates, low dust attenuations, and low stellar masses will be important for probing the morphology of circumgalactic gas.02/2013; -
Article: The Properties and Prevalence of Galactic Outflows at z = 1 in the Extended Groth Strip
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ABSTRACT: We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging, we examine galaxies on a per-object basis in order to understand both the prevalence of galactic winds at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, span the interval [-217, +155] km/s. We find that ~40% (10%) of the sample exhibits blueshifted FeII lines at the 1-sigma (3-sigma) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines, and show that MgII frequently traces higher velocity gas than FeII. Quantitative morphological parameters derived from the HST imaging suggest that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly-inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. Using star-formation rates calculated from GALEX data, and areas estimated from HST imaging, we detect a ~3-sigma correlation between outflow velocity and star-formation rate surface density, but only a weak (~1-sigma) trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory.05/2012; -
Article: Constraints on the assembly and dynamics of galaxies. II. Properties of kiloparsec-scale clumps in rest-frame optical emission of z ~ 2 star-forming galaxies
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ABSTRACT: We study the properties of luminous stellar clumps identified in deep, high resolution HST/NIC2 F160W imaging at 1.6um of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ~5000A emission, with median of about 2%; the total contribution of clump light ranges from 10%-25%. The median intrinsic clump size and stellar mass are ~1kpc and log(Mstar[Msun])~9, in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation via gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with ACS/F814W imaging available for one source, and AO-assisted SINFONI Halpha data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Halpha-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material towards the central regions. From constraints on a bulge-like component at radii <1-3kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the build-up of stellar bulges and the role of clumps in this process.04/2011; -
Article: Narrowband imaging of Escaping Lyman-Continuum Emission in the SSA22 Field
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ABSTRACT: We present the results of an ultradeep, narrowband imaging survey for Lyman-continuum (LyC) emission at z~3 in the SSA22a field. We employ a custom narrowband filter centered at 3640A (NB3640), which probes the LyC region for galaxies at z>3.06. We also analyze new and archival NB4980 imaging tuned to the wavelength of the Lya emission line at z=3.09, and archival broadband B, V, and R images of the non-ionizing UV continuum. Our NB3640 images contain 26 z>3.06 Lyman Break Galaxies (LBGs) as well as a set of 130 Lya emitters (LAEs), identified by their excess NB4980 flux relative to the BV continuum. Six LBGs and 28 LAEs are detected in the NB3640 image. LBGs appear to span a range of NB3640-R colors, while LAEs appear bimodal in their NB3640-R properties. We estimate average UV to LyC flux density ratios, corrected for foreground contamination and intergalactic medium absorption, finding <F_{UV}/F_{LyC}>^{LBG} = 11.3^{+10.3}_{-5.4}, which implies a LBG LyC escape fraction f_{esc}^{LyC} ~ 0.1, and <F_{UV}/F_{LyC}>^{LAE} = 2.2^{+0.9}_{-0.6}. The strikingly blue LAE flux density ratios defy interpretation in terms of standard stellar population models. Assuming <F_{UV}/F_{LyC}>^{LBG} applies down to L=0.1L*, we estimate a galaxy contribution to the intergalactic hydrogen ionization rate that is consistent with independent estimates based on the Lya forest opacity at z~3. If we assume that <F_{UV}/F_{LyC}>^{LAE} holds at the faintest luminosities, the galaxy contribution significantly exceeds that inferred from the Lya forest. Further follow-up study of these faint LAEs is crucial, given the potentially important contribution similar objects make to the process of reionization. (Abridged)02/2011; -
Article: Diffuse Lyman Alpha Emitting Halos: A Generic Property of High Redshift Star Forming Galaxies
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ABSTRACT: Using a sample of 92 UV continuum-selected, spectroscopically identified galaxies with = 2.65, all of which have been imaged in the Ly-a line with extremely deep narrow-band imaging, we examine galaxy Ly-a emission profiles to very faint surface brightness limits. The galaxies are representative of spectroscopic samples of LBGs at similar redshifts in terms of apparent magnitude, UV luminosity, inferred extinction, and star formation rate, and were selected without regard to Ly-a emission properties. We use extremely deep stacks of UV continuum and Ly-a emission line images to show that all sub-samples exhibit diffuse Ly-a emission to radii of at least 10" (80 physical kpc), including galaxies whose spectra exhibit Ly-a in net absorption. The intensity scaling, but not the surface brightness distribution, is strongly correlated with the emission observed in the central ~1". The characteristic scale length for Ly-a line emission exceeds that of the UV continuum light for the same galaxies by factors of at least 5-10, regardless of the spectral morphology of Ly-a. Including the extended Ly-a halos increases the total Ly-a flux [and rest equivalent width W_0(Lya)] by an average factor of 5. We argue that most, if not all, of the observed Ly-a emission in the diffuse halos originates in the galaxy H II regions and is scattered in our direction by H I gas in the galaxy's circum-galactic medium (CGM). We show that whether or not a galaxy is classified as a giant "Lyman-a Blob" (LAB) depends sensitively on the Ly-a surface brightness threshold reached by an observation. Accounting for diffuse Ly-a halos, all LBGs would be LABs if surveys were routinely sensitive to 10 times lower surface brightness thresholds; also, essentially all LBGs would qualify as LAEs (W_0(Lya) > 20 A).01/2011; -
Article: Constraints on the Assembly and Dynamics of Galaxies: I. Detailed Rest-frame Optical Morphologies on Kiloparsec-scale of z ~ 2 Star-forming Galaxies
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ABSTRACT: We present deep and high-resolution HST/NIC2 F160W imaging at 1.6micron of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n<1), with median effective radii of ~5kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), Multiplicity (Psi), and M_20 coefficients. The strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Halpha emission reveal no significant differences, suggesting similar global distributions of the on-going star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z~2 galaxy types indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z~2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Psi and M_20. The combined NIC2 and SINFONI dataset yields insights of unprecedented detail into the nature of mass accretion at high redshift. [Abridged]11/2010; -
Article: Excess AGN Activity in the z=2.30 Protocluster in HS 1700+64
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ABSTRACT: We present the results of spectroscopic, narrow-band and X-ray observations of a z=2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of BX/MD galaxies, which are selected to be at z~2.2-2.7 by their rest-frame ultraviolet colours, we find that there are 5 protocluster AGN which have been identified by characteristic emission-lines in their optical/near-IR spectra; this represents an enhancement over the field significant at ~98.5 per cent confidence. Using a ~200 ks Chandra/ACIS-I observation of this field we detect a total of 161 X-ray point sources to a Poissonian false-probability limit of 4x10^{-6} and identify 8 of these with BX/MD galaxies. Two of these are spectroscopically confirmed protocluster members and are also classified as emission-line AGN. When compared to a similarly selected field sample the analysis indicates this is also evidence for an enhancement of X-ray selected BX/MD AGN over the field, significant at ~99 per cent confidence. Deep Lya narrow-band imaging reveals that a total of 4/123 Lya emitters (LAEs) are found to be associated with X-ray sources, with two of these confirmed protocluster members and one highly likely member. We do not find a significant enhancement of AGN activity in this LAE sample over that of the field (result significant at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD and LAE samples are found to be 6.9_{-4.4}^{+9.2} and 2.9_{-1.6}^{+2.9} per cent, respectively, for protocluster AGN with L_{2-10 keV}>4.6x10^{43} erg s^{-1} at z=2.30. These findings are similar to results from the z=3.09 protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both suggest AGN activity is favoured in dense environments at z>2. Comment: 8 pages, 2 figures. Accepted for publication in MNRAS.05/2010; -
Article: The Structure and Kinematics of the Circum-Galactic Medium from Far-UV Spectra of z~2-3 Galaxies
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ABSTRACT: We present new results on the kinematics and spatial distribution of metal-enriched gas within 125 kpc (physical) of Lyman Break galaxies at redshifts z~2-3. In particular, we demonstrate how rest-UV galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. After recalibrating the measurement of galaxy systemic redshifts from their UV spectra, we investigate the kinematics of galaxy-scale outflows via the strong interstellar (IS) absorption and Lya emission lines (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1-15 arcsec) angular pairs of z~2-3 LBGs in which the spectra background galaxies probe the circumgalactic gas surrrounding those in the foreground. The close pairs, together with spectra of the foreground galaxies themselves, sample galactocentric impact parameters b=0-125 kpc (physical) at =2.2. The ensemble provides a spatial map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Lya emission lines, as well as the observed variation of absorption line strength (of HI, CII, CIV, SiII, SiIV) versus galactocentric impact parameter. We discuss the results of the observations in the context of "cold accretion", in which cool gas accretes via filamentary streams directly onto the central regions of galaxies. At present, we find little observational support for cool infalling material, whereas evidence supporting the large-scale effects of outflows is strong. Reconciling theory and observation on the subject of gas flows into and out of forming galaxies seems necessary. Comment: To appear in ApJ; minor revisions to match journal version; added 1 figure, several references, and a subsection discussing the inferred rate of gas outflow into the IGM03/2010; -
Article: The SINS Survey: SINFONI Integral Field Spectroscopy of z ~ 2 Star-forming Galaxies
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ABSTRACT: We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical nebular emission line, mainly Hα, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z ~ 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the "SINS Hα sample," consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the Hα and [N II] emission lines. Only 30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS Hα sample covers a reasonable representation of massive M 1010 M ☉star-forming galaxies at z 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values 3 × 1010 M ☉, 70 M ☉ yr–1, and 3 Gyr–1. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The Hα morphologies tend to be irregular and/or clumpy. About one-third of the SINS Hα sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Hα luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates.The Astrophysical Journal 11/2009; 706(2):1364. · 6.02 Impact Factor -
Article: SINFONI Integral Field Spectroscopy of z ~ 2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution
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ABSTRACT: We present ~05 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ~ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r1/2 ≈ 4 h kpc, and line emission is detected over 20 h kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s-1 over ~10 h kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii 10 h kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of vc ~ 180 ± 90 km s-1 and dynamical masses from ~0.5 to 25 × 1010 h M☉ within r1/2. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average vc at 10 h kpc, the virial mass of the typical halo of a galaxy in our sample is 1011.7±0.5 h M☉. Kinematic modeling of the three best cases implies a ratio of vc to local velocity dispersion vc/σ ~ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr.The Astrophysical Journal 12/2008; 645(2):1062. · 6.02 Impact Factor -
Article: Deep Mid-Infrared Observations of Lyman Break Galaxies
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ABSTRACT: As part of the in-orbit checkout activities for the Spitzer Space Telescope, the Infrared Array Camera (IRAC) team carried out a deep observation (average integration time ~8 hr) of a field surrounding the bright QSO HS 1700+6416. This field contains several hundred z ~ 3 Lyman break galaxy (LBG) candidates, and we report here on their mid-infrared properties, including the IRAC detection rate, flux densities, and colors, and the results of fitting population synthesis models to the optical, near-infrared, and IRAC magnitudes. The results of the model fitting show that previous optical/near-infrared studies of LBGs were not missing large, hidden old stellar populations. The LBG candidates' properties are consistent with those of massive star-forming galaxies at z ~ 3. Other IRAC sources in the same field have similar properties, so IRAC selection may prove to be a promising method of finding additional high-redshift galaxies.The Astrophysical Journal Supplement Series 12/2008; 154(1):97. · 13.46 Impact Factor -
Article: Submillimeter Galaxies at z ~ 2: Evidence for Major Mergers and Constraints on Lifetimes, IMF, and CO-H2 Conversion Factor
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ABSTRACT: We report subarcsecond resolution IRAM PdBI millimeter CO interferometry of four z ~ 2 submillimeter galaxies (SMGs), and sensitive CO(3-2) flux limits toward three z ~ 2 UV/optically selected star-forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of ~500 km s−1 across ≤0.2'' (1.6 kpc) diameter regions, suggesting that the star-forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived "maximum" star-forming events in highly dissipative mergers of gas-rich galaxies. The resulting high-mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion timescales and stellar ages, we estimate that the SMG phase duration is about 100 Myr. Our analysis of SMGs and optically/UV selected high-redshift star-forming galaxies supports a "universal" Chabrier IMF as being valid over the star-forming history of these galaxies. We find that the 12CO luminosity to total gas mass conversion factors at z ~ 2-3 are probably similar to those assumed at z ~ 0. The implied gas fractions in our sample galaxies range from 20% to 50%.The Astrophysical Journal 12/2008; 680(1):246. · 6.02 Impact Factor -
Article: The SINS Survey: Rotation Curves and Dynamical Evolution of Distant Galaxies with SINFONI
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ABSTRACT: It has become clear in recent years that about half of the stellar mass in galaxies was put in place by redshift z ~ 1, when the Universe was 40% of its current age. However, the details of how the mass was assembled and what physical processes were involved at early stages of galaxy evolution remain unclear. Progress has been hampered by the lack of detailed spatially-resolved studies of galaxies beyond z ~ 1. This has now become possible with SINFONI, the adaptive optics-assisted near-infrared integral field spectrometer at the VLT. Here we report on our SINFONI observations of massive star-forming galaxies at z ~ 2-3. The data enabled us to investigate their morphologies and kinematics on typical spatial scales of 4-5 kpc. The most surprising outcome is that a majority of these galaxies appear to be large, rotating, and often gas-rich discs. Even more compelling evidence is provided by the exceptionally detailed SINFONI data of a z ~ 2 galaxy observed with adaptive optics, resulting in a spatial resolution of 1.2 kpc, and of a highly magnified z ~ 3 galaxy for which the gravitational lensing of a foreground galaxy cluster acts as a microscope, revealing the dynamics on scales as small as 200 pc.The Messenger. 08/2006; 125:11. -
Article: The Connection Between Galaxies and Intergalactic Absorption Lines at Redshift 2<z<3
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ABSTRACT: Absorption-line spectroscopy of 23 background QSOs and numerous background galaxies has let us measure the spatial distribution of metals and neutral hydrogen around 1044 UV-selected galaxies at redshifts 1.8<z<3.3. The typical galaxy is surrounded to radii r~40 proper kpc by gas that has a large velocity spread (dv>260 km/s) and produces very strong absorption lines (N_CIV >> 10^14 cm^-2) in the spectra of background objects. Absorption with an average column density of N_CIV ~ 10^14 cm^-2 extends to 80 kpc, a radius large enough to imply that most strong intergalactic CIV absorption is associated with star-forming galaxies like those in our sample. We find that the galaxy-CIV cross-correlation length increases with CIV column density and is similar to the galaxy-galaxy length (r_0 ~ 4 h^-1 Mpc) for N_CIV > 10^12.5 cm^-2. Distortions in the redshift-space galaxy-CIV correlation function on small scales may imply that some of the CIV systems have large peculiar velocities. Four of the five detected OVI absorption systems in our sample lie within 400 proper kpc of a known galaxy. Strong Lyman-a absorption is produced by the intergalactic gas within 1 h^-1 comoving Mpc of most galaxies, but for a significant minority (~1/3) the absorption is weak or absent. We were unable to identify any statistically significant differences between galaxies with weak nearby HI absorption and the rest, although galaxies with weak absorption may have higher star-formation rates. Galaxies near intergalactic CIV systems appear to reside in relatively dense environments and to have distinctive spectral energy distributions that are characterized by blue colors and young ages. (abridged)06/2005; -
Article: The Spatial Clustering of Star-forming Galaxies at Redshifts 1.4<z<3.5
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ABSTRACT: We analyzed the spatial distribution of 28500 photometrically selected galaxies with AB magnitude 23.5<R<25.5 and redshift 1.4<z<3.5 in 21 fields with a total area of 0.81 square degrees. The galaxies were divided into three subsamples, with mean redshifts z=1.7, 2.2, 2.9, according to the UGR selection criteria of Adelberger et al. (2004) and Steidel et al. (2003). Combining the galaxies' measured angular clustering with redshift distributions inferred from 1600 spectroscopic redshifts, we find comoving correlation lengths at the three redshifts of r_0 = 4.5+-0.6, 4.2+-0.5, and 4.0+-0.6 h^-1 Mpc, respectively, and infer a roughly constant correlation function slope of gamma=1.6+-0.1. We derive similar numbers from the 1600 object spectroscopic sample itself with a new statistic, K, that is insensitive to many possible systematics. Galaxies that are bright in R (lambda_rest ~ 1500-2500A) cluster more strongly than fainter galaxies at z=2.9 and z=2.2 but not, apparently, at z=1.7. Comparison to a numerical simulation that is consistent with recent WMAP observations suggests that galaxies in our samples are associated with dark matter halos of mass ~ 10^12, and that a small fraction of the halos contain more than one galaxy that satisfies our selection criteria. Adding recent observations of galaxy clustering at z~0 and z~1 to the simulation results, we conclude that the typical object in our samples will evolve into an elliptical galaxy by redshift z=0 and will already have an early-type spectrum by redshift z=1. We comment briefly on the implied relationship between galaxies in our survey and those selected with other techniques. (slightly abridged) Comment: 17 pages, accepted for publication in the ApJ10/2004; -
Article: Evidence for Solar Metallicities in Massive Star-forming Galaxies at z>~2
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ABSTRACT: We present results of near-IR spectroscopic measurements of 7 star-forming galaxies at 2.1<z<2.5. Drawn from a large spectroscopic survey of galaxies photometrically pre-selected by their U_nGR colors to lie at z~2, these galaxies were chosen for their bright rest-frame optical luminosities (K_s<=20.0). Most strikingly, the majority of the sample of 7 galaxies exhibit [NII]/Ha nebular emission line ratios indicative of at least solar HII region metallicities, at a lookback time of 10.5 Gyr. The broadband colors of the K_s-bright sample indicate that most have been forming stars for more than a Gyr at z~2, and have already formed stellar masses in excess of 10^11 Msun. The descendants of these galaxies in the local universe are most likely metal-rich and massive spiral and elliptical galaxies, while plausible progenitors for them can be found among the population of z~3 Lyman Break Galaxies. While the K_s-bright z~2 galaxies appear to be highly evolved systems, their large Ha luminosities and uncorrected Ha star-formation rates of 24-60 Msun/yr indicate that active star formation is still ongoing. The luminous UV-selected objects presented here comprise more than half of the high-redshift (z>1.5) tails of current K-band-selected samples such as the K20 and Gemini Deep Deep surveys. Comment: 15 pages including 5 figures. Accepted for publication in ApJ05/2004; -
Article: A Survey of Star-Forming Galaxies in the z=1.4-2.5 `Redshift Desert': Overview
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ABSTRACT: We present the first results of a large-scale survey, using the UV/blue sensitive LRIS-B spectrograph on the Keck I telescope, of galaxies in the redshift interval 1.4<z<2.5, often called the `redshift desert' because of historical difficulties in spectroscopically identifying galaxies in that range. We introduce two samples of star forming galaxies, `BX' galaxies at =2.20+/-0.32 and `BM' galaxies at =1.70+/-0.34; currently we have spectroscopically confirmed 749 of the former and 114 of the latter. We also present initial results of deep near-IR photometry and spectroscopy, from which we show that z~2 galaxies are significantly redder in their optical/IR colors compared to similarly UV-selected galaxies at z~3, but that the characteristics of their galaxy-scale outflows are quite similar. We illustrate by example the information which can be deduced on the stellar populations, metallicities, and kinematics of `redshift desert' galaxies from easily accessible rest-frame far-UV and rest-frame optical spectra. Far from being hostile to observations, the universe at z~2 is uniquely suited to providing information on the astrophysics of star-forming galaxies and the intergalactic medium, and the relationship between the two [abridged].02/2004; -
Article: Rest-Frame Ultraviolet Spectra of z~3 Lyman Break Galaxies
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ABSTRACT: We present the results of a systematic study of the rest-frame UV spectroscopic properties of Lyman Break Galaxies (LBGs). The database of almost 1000 LBG spectra proves useful for constructing high S/N composite spectra. The composite spectrum of the entire sample reveals a wealth of features attributable to hot stars, HII regions, dust, and outflowing neutral and ionized gas. By grouping the database according to galaxy parameters such as Lyman-alpha equivalent width, UV spectral slope, and interstellar kinematics, we isolate some of the major trends in LBG spectra which are least compromised by selection effects. We find that LBGs with stronger Lyman-alpha emission have bluer UV continua, weaker low-ionization interstellar absorption lines, smaller kinematic offsets between Lyman-alpha and the interstellar absorption lines, and lower star-formation rates. There is a decoupling between the dependence of low- and high-ionization outflow features on other spectral properties. Most of the above trends can be explained in terms of the properties of the large-scale outflows seen in LBGs. According to this scenario, the appearance of LBG spectra is determined by a combination of the covering fraction of outflowing neutral gas which contains dust, and the range of velocities over which this gas is absorbing. Higher sensitivity and spectral resolution observations are still required for a full understanding of the covering fraction and velocity dispersion of the outflowing neutral gas in LBGs, and its relationship to the escape fraction of Lyman continuum radiation in galaxies at z~3. Comment: 28 pages including 17 figures. Accepted for publication in ApJ01/2003; -
Article: Galaxies and Intergalactic Matter at Redshift z~3: Overview
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ABSTRACT: We present the first results from a survey of the relative spatial distributions of galaxies, intergalactic neutral hydrogen, and intergalactic metals at high redshift. We obtained high-resolution spectra of 8 bright QSOs at 3.1<z<4.1 and spectroscopic redshifts for 431 Lyman-break galaxies (LBGs) at slightly lower redshifts. Comparing the locations of galaxies to the absorption lines in the QSO spectra shows that the intergalactic medium contains less neutral hydrogen than the global average within r<0.5h^-1 comoving Mpc of LBGs and more than average at slightly larger distances 1<r<5 h^-1 comoving Mpc. The intergalactic medium within the largest overdensities at z~3, which will presumably evolve into the intracluster medium by z~0, is rich in neutral hydrogen and CIV. The lack of HI absorption at small distances from LBGs appears unlikely to be produced solely by the Lyman continuum radiation they emit; it may show that the galaxies' supernovae-driven winds maintain their measured outflow velocities of ~600 km/s for a few hundred million years and drive away nearby intergalactic gas. We present correlation functions of galaxies with Lyman-alpha forest flux decrements, with CIV systems, and with other galaxies. We describe the association of galaxies with damped Lyman-a systems and with intergalactic HeII opacity. A strong observed correlation of galaxies with intergalactic metals supports the idea that Lyman-break galaxies' winds have enriched their surroundings. Comment: 32 pages including 26 figures. To appear in ApJ10/2002; -
Article: Physical Conditions in Lyman Break Galaxies Derived From Rest-Frame UV Spectra
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ABSTRACT: We present the results of detailed studies of the astrophysical conditions in z~3 Lyman Break Galaxies (LBGs), placing particular emphasis on what is learned from LBG rest frame UV spectra. By drawing from our database of ~1000 spectra, and constructing higher S/N composite spectra from galaxies grouped according to properties such as luminosity, extinction, morphology, and environment, we can show how the rest-frame UV spectroscopic properties systematically depend on other galaxy properties. Such information is crucial to understanding the detailed nature of LBGs, and their impact on the surrounding IGM.01/2002;
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2009–2011
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University of California, Los Angeles
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Los Angeles, CA, USA
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University of California, Berkeley
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