Alice E. Shapley

Pierre and Marie Curie University - Paris 6, Lutetia Parisorum, Île-de-France, France

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Publications (164)716.97 Total impact

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    ABSTRACT: We study the Lya profiles of 36 Lya-emitters (LAEs) at z~2-3, taking advantage of the sensitivity and efficiency of Keck MOSFIRE to measure systemic redshifts from rest-frame optical nebular emission lines. The galaxies were selected via narrowband imaging of their Lya emission, and have spectroscopic measurements of their Lya profiles from Keck LRIS. The LAE sample has a median optical magnitude R = 26.0, and ranges from R = 23 to R > 27, corresponding to rest-frame UV absolute magnitudes M_UV = -22 to M_UV > -18.2. The vast majority of Lya emission lines in this sample are redshifted with respect to the systemic velocity, and the velocity offset with respect to systemic dv_Lya is correlated with R-band magnitude, M_UV, and the velocity dispersion measured from nebular emission lines with >3 sigma significance: brighter galaxies with larger velocity dispersions tend to have larger values of dv_Lya. We also make use of a comparison sample of 122 UV-color-selected R < 25.5 galaxies at z~2, all with Lya emission and systemic redshifts measured from nebular emission lines. Using the combined LAE and comparison samples for a total of 158 individual galaxies, we find that dv_Lya is anti-correlated with the Lya equivalent width with 7 sigma significance. Our results are consistent with a scenario in which the Lya profile is determined primarily by the properties of the gas near the systemic redshift; in such a scenario, the opacity to Lya 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. [Abridged]
    08/2014;
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    ABSTRACT: We present results on the z~2.3 mass-metallicity relation (MZR) using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. We use an initial sample of 87 star-forming galaxies with spectroscopic coverage of H\beta, [OIII]\lambda 5007, H\alpha, and [NII]\lambda 6584 rest-frame optical emission lines, and estimate the gas-phase oxygen abundance based on the N2 and O3N2 strong-line indicators. We find a positive correlation between stellar mass and metallicity among individual z~2.3 galaxies using both the N2 and O3N2 indicators. We also measure the emission-line ratios and corresponding oxygen abundances for composite spectra in bins of stellar mass. Among composite spectra, we find a monotonic increase in metallicity with increasing stellar mass, offset ~0.15-0.3 dex below the local MZR. When the sample is divided at the median star-formation rate (SFR), we do not observe significant SFR dependence of the z~2.3 MZR among either individual galaxies or composite spectra. We furthermore find that z~2.3 galaxies have metallicities ~0.1 dex lower at a given stellar mass and SFR than is observed locally. This offset suggests that high-redshift galaxies do not fall on the local "fundamental metallicity relation" among stellar mass, metallicity, and SFR, and may provide evidence of a phase of galaxy growth in which the gas reservoir is built up due to inflow rates that are higher than star-formation and outflow rates. However, robust conclusions regarding the gas-phase oxygen abundances of high-redshift galaxies await a systematic reappraisal of the application of locally calibrated metallicity indicators at high redshift.
    08/2014;
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    ABSTRACT: We present initial results of a large near-IR spectroscopic survey covering the 15 fields of the Keck Baryonic Structure Survey (KBSS) using the recently-commissioned MOSFIRE instrument on the Keck 1 10m telescope. We focus on 179 galaxies with redshifts 2.0 < z < 2.6, most of which have high-quality MOSFIRE spectra in both H and K-band atmospheric windows, allowing sensitive measurements of [OIII]4960,5008, H-beta, [NII]6585, and H-alpha emission lines. We show unambiguously that the locus of z~2.3 galaxies in the "BPT" nebular diagnostic diagram exhibits an almost entirely disjoint, yet similarly tight, relationship between the line ratios [NII]/Halpha and [OIII]/Hbeta as compared to local galaxies. We argue that the offset of the z~2.3 BPT locus relative to that at z~0 is caused primarily by higher excitation (driven by both higher ionization parameter and harder stellar ionizing radiation field) than applies to most local galaxies. Also unlike nearby counterparts, a z~2.3 galaxy's position along the BPT locus is surprisingly insensitive to gas-phase O/H. The observed emission line ratios are most easily reproduced by models in which the stellar ionizing radiation field has Teff=50000-60000 K, gas-phase O/H in the range 0.2 < Z/Zsun < 1.0, and gas-phase N/O close to solar. Such high sustained Teff are not easily produced by standard population synthesis models, but are expected if massive binaries and/or rapid stellar rotation are important for the evolution of main sequence O-stars in typical high-redshift galaxies. We assess the applicability of commonly-used strong line indices for estimating gas-phase metallicities of high redshift galaxies, as well as their likely systematic biases. The empirical correlation between M* and inferred metallicity (the "MZR") at z~2.3 is as tight as for local galaxy samples, but is offset to lower metallicity (at all M*) by ~0.35 dex (abridged)
    05/2014;
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    ABSTRACT: The MOSFIRE Deep Evolution Field (MOSDEF) survey is using the MOSFIRE instrument on the Keck I telescope to obtain more than 1700 rest-frame optical spectra of galaxies from redshift 1.5 to 3.6 over four years. We are using the first 200 spectra to investigate the prevalence of outflows measured in emission in broad components of the nebular emission lines. We create stacks of galaxies based on properties such as star formation rate, stellar mass, and star formation rate surface density (controlling for the presence of AGNs) in order to study how outflow strength depends on these factors. Additionally, we will stack spectra by redshift to understand how outflows change over time. We will present the results of two component (narrow and broad) fits to the nebular emission and compare to theoretical predictions of outflow efficiency.
    01/2014;
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    ABSTRACT: We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ~6-7 Msol/yr) galaxy at z=1.433, magnified by a factor of 11.5 by the gravitational lensing produced by a massive foreground galaxy at z=0.741. We analysed the integrated physical properties of the HII regions of CSWA 20 using temperature- and density-sensitive emission lines. We find the abundance of oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the Sun. The unusually low C/O ratio may be an indication of a particularly rapid timescale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from HII regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ~2 uncertainty of each method. The interstellar medium of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the interstellar medium (ISM) with speeds of up 750 km/s, similar to the values measured in other high-z galaxies sustaining much higher rates of star formation.
    11/2013; 440(2).
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    ABSTRACT: We report the detection of ubiquitous powerful nuclear outflows in massive (> 10^11 Msun) z~2 star-forming galaxies (SFGs), which are plausibly driven by an Active Galactic Nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics (AO) assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Halpha and forbidden [NII] and [SII] line emission, with typical velocity FWHM ~ 1500 km/s, [NII]/Halpha ratio ~ 0.6, and intrinsic extent of 2 - 3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~ 60 Msun/yr and mass loading of ~ 3. At larger radii, a weaker broad component is detected but with lower FWHM ~ 485 km/s and [NII]/Halpha ~ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles, and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial to confirm the importance and energetics of the nuclear outflow phenomenon, and its connection to AGN activity and bulge growth.
    11/2013;
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    ABSTRACT: We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the Hα line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the "Plateau de Bure high-z, blue-sequence survey" (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a "mixed" extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlogΣstar form/dlogΣmol gas, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 ± 0.1.
    The Astrophysical Journal 07/2013; 773(1):68. · 6.73 Impact Factor
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    ABSTRACT: We present Keck/MOSFIRE observations of the role of environment in the formation of galaxies at z~2. Using K-band spectroscopy of H-alpha and [N II] emission lines, we have analyzed the metallicities of galaxies within and around a z=2.3 protocluster discovered in the HS1700+643 field. Our main sample consists of 23 protocluster and 20 field galaxies with estimates of stellar masses and gas-phase metallicities based on the N2 strong-line metallicity indicator. With these data we have examined the mass-metallicity relation (MZR) with respect to environment at z~2. We find that field galaxies follow the well-established trend between stellar mass and metallicity, such that more massive galaxies have larger metallicities. The protocluster galaxies, however, do not exhibit a dependence of metallicity on mass, with the low-mass protocluster galaxies showing an enhancement in metallicity compared to field galaxies spanning the same mass range. A comparison with galaxy formation models suggests that the mass-dependent environmental trend we observed can be qualitatively explained in the context of the recycling of "momentum-driven" galaxy wind material. Accordingly, winds are recycled on a shorter timescale in denser environments, leading to an enhancement in metallicity at fixed mass for all but the most massive galaxies. Future hydrodynamical simulations of z~2 overdensities matching the one in the HS1700 field will be crucial for understanding the origin of the observed environmental trend in detail.
    The Astrophysical Journal 06/2013; 774(2). · 6.73 Impact Factor
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    ABSTRACT: We present results from a survey for z~2.85 Lyman-Continuum (LyC) emission in the HS1549+1933 field and place constraints on the amount of ionizing radiation escaping from star-forming galaxies. Using a custom narrowband filter (NB3420) tuned to wavelengths just below the Lyman limit at z>=2.82, we probe the LyC spectral region of 49 Lyman break galaxies (LBGs) and 91 Lya-emitters (LAEs) spectroscopically confirmed at z>=2.82. Four LBGs and seven LAEs are detected in NB3420. Using V-band data probing the rest-frame non-ionizing UV, we observe that many NB3420-detected galaxies exhibit spatial offsets between their LyC and non-ionizing UV emission and are characterized by extremely blue NB3420-V colors, corresponding to low ratios of non-ionizing to ionizing radiation (F_UV/F_LyC) that are in tension with current stellar population synthesis models. We measure average values of F_UV/F_LyC for our LBG and LAE samples, correcting for foreground galaxy contamination and HI absorption in the IGM. We find (F_UV/F_LyC)_corr^LBG=82 +/- 45 and (F_UV/F_LyC)_corr^LAE=7.4 +/- 3.6. These flux-density ratios correspond respectively to relative LyC escape fractions of f_esc,rel^LBG=5-8% and f_esc,rel^LAE=18-49%, absolute LyC escape fractions of f_esc^LBG=1-2% and f_esc^LAE=5-15%, and a comoving LyC emissivity from star-forming galaxies of 8.8-15.0 x 10^24 ergs/s/Hz/Mpc^3. In order to study the differential properties of galaxies with and without LyC detections, we analyze narrowband Lya imaging and rest-frame near-infrared imaging, finding that while LAEs with LyC detections have lower Lya equivalent widths on average, there is no substantial difference in the rest-frame near-infrared colors of LBGs or LAEs with and without LyC detections. These preliminary results are consistent with an orientation-dependent model where LyC emission escapes through cleared paths in a patchy ISM.
    The Astrophysical Journal 06/2013; · 6.73 Impact Factor
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    ABSTRACT: We present new high-precision measurements of the opacity of the intergalactic and circumgalactic medium (IGM, CGM) at =2.4. Using Voigt profile fits to the full Lyman alpha and Lyman beta forests in 15 high-resolution high-S/N spectra of hyperluminous QSOs, we make the first statistically robust measurement of the frequency of absorbers with HI column densities 14 < log(NHI) < 17.2. We also present the first measurements of the frequency distribution of HI absorbers in the volume surrounding high-z galaxies (the CGM, 300 pkpc), finding that the incidence of absorbers in the CGM is much higher than in the IGM. In agreement with Rudie et al. (2012), we find that there are fractionally more high-NHI absorbers than low-NHI absorbers in the CGM compared to the IGM, leading to a shallower power law fit to the CGM frequency distribution. We use these new measurements to calculate the total opacity of the IGM and CGM to hydrogen-ionizing photons, finding significantly higher opacity than most previous studies, especially from absorbers with log(NHI) < 17.2. Reproducing the opacity measured in our data as well as the incidence of absorbers with log(NHI) > 17.2 requires a broken power law parameterization of the frequency distribution with a break near log(NHI) ~ 15. We compute new estimates of the mean free path (mfp) to hydrogen-ionizing photons at z=2.4, finding mfp = 147 +- 15 Mpc when considering only IGM opacity. If instead, we consider photons emanating from a high-z star-forming galaxy and account for the local excess opacity due to the surrounding CGM of the galaxy itself, the mean free path is reduced to mfp = 121 +- 15 Mpc. These mfp measurements are smaller than recent estimates and should inform future studies of the metagalactic UV background and of ionizing sources at z~2-3.
    The Astrophysical Journal 04/2013; 769(2). · 6.73 Impact Factor
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    ABSTRACT: Mapping Mg II resonance emission scattered by galactic winds offers a means to determine the spatial extent and density of the warm outflow. Using Keck/LRIS spectroscopy, we have resolved scattered Mg II emission to the east of 32016857, a star-forming galaxy at z =0.9392 with an outflow. The Mg II emission from this galaxy exhibits a P-Cygni profile, extends further than both the continuum and [O II] emission along the eastern side of the slit, and has a constant Doppler shift along the slit which does not follow the velocity gradient of the nebular [O II] emission. Using the Sobolev approximation, we derive the density of Mg+ ions at a radius of 12 to 18 kpc in the outflow. We model the ionization correction and find that much of the outflowing Mg is in Mg++. We estimate that the total mass flux could be as large as 330 - 500 solar masses per year, with the largest uncertainties coming from the depletion of Mg onto grains and the clumpiness of the warm outflow. We show that confining the warm clouds with a hot wind reduces the estimated mass flux of the warm outflow and indicates amass-loading factor near unity in the warm phase alone. Based on the high blue luminosities that distinguish 32016857 and TKRS 4389, described by Rubin et al. 2011, from other galaxies with P-Cygni emission, we suggest that, as sensitivity to diffuse emission improves, scattering halos may prove to be a generic property of star-forming galaxies at intermediate redshifts.
    The Astrophysical Journal 04/2013; 770(1). · 6.73 Impact Factor
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    ABSTRACT: We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z ~ 1.2 and 2.2, with log(M *(M ☉)) ≥ 10.4 and log(SFR(M ☉/yr)) ≥ 1.5. Including a correction for the incomplete coverage of the M*-SFR plane, and adopting a "Galactic" value for the CO-H2 conversion factor, we infer average gas fractions of ~0.33 at z ~ 1.2 and ~0.47 at z ~ 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z ~ 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a ~0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z ~ 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M *, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z ~ 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
    The Astrophysical Journal 04/2013; 768(1):74. · 6.73 Impact Factor
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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.
    The Astrophysical Journal 02/2013; 774(1). · 6.73 Impact Factor
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    ABSTRACT: Galaxy clusters constitute the most massive gravitationally bound structures in the universe. Galaxies found in the central, densest region of clusters at z < 1 are typically early- type galaxies with low star-formation rates (SFRs), while more active, late-type galaxies are preferentially located in the sparser edges of the cluster field. These trends demonstrate how environment plays a key role in the evolution of galaxies. Here we describe recent results from the newly commissioned MOSFIRE instrument at Keck Observatory on two protoclusters found in the HS 1700+643 (z = 2.30) and the SSA22a (z = 3.09) fields. Protoclusters at z > 2 are still in the process of forming and have not yet virialized, making them perfect for studying the “seeds” of the environmental trends that are seen locally. We have measured the rest-frame optical lines Hα, [N II], [S II]λλ6717,6732, [O III]λλ4959,5007, and Hβ for Q1700 and [O III]λλ4959,5007, Hβ , and [O II]λ3727 for SSA22a. This dataset has made possible a differential comparison of numerous physical properties (e.g. gas-phase metallicity, velocity dispersion, and electron density) for protocluster and “field” galaxies at roughly the same redshift. Based on our results, we present new findings on how environment affects the formation and evolution of galaxies at these early epochs.
    01/2013;
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    ABSTRACT: We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in normal star forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular gas - star formation relation for the z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M*, gas fractions correlate strongly with the specific star formation rate. The variation of specific star formation rate between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
    11/2012;
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    ABSTRACT: We use stellar population synthesis modeling to analyze the host-galaxy properties of a sample of 33 UV-selected, narrow-lined active galactic nuclei (AGNs) at z {approx} 2-3. In order to quantify the contribution of AGN emission to host galaxy broadband spectral energy distributions (SEDs), we use the subsample of 11 AGNs with photometric coverage spanning from rest-frame UV through near-IR wavelengths. Modeling the SEDs of these objects with a linear combination of stellar population and AGN templates, we infer the effect of the AGN on derived stellar population parameters. We also estimate the typical bias in derived stellar populations for AGNs lacking rest-frame near-IR wavelength coverage, and develop a method for inferring the true host-galaxy properties. We compare AGN host-galaxy properties to those of a sample of UV-selected, star-forming non-AGNs in the same redshift range, including a subsample carefully matched in stellar mass. Although the AGNs have higher masses and star-formation rates than the full non-active sample, their stellar population properties are consistent with those of the mass-selected sample, suggesting that the presence of an AGN is not connected with the cessation of star formation activity in star-forming galaxies at z {approx} 2-3. We suggest that a correlation between M {sub BH} and galaxy stellar mass is already in place at this epoch. Assuming a roughly constant Eddington ratio for AGNs at all stellar masses, we are unable to detect the AGNs in low-mass galaxies because they are simply too faint.
    The Astrophysical Journal 11/2012; 760(1). · 6.73 Impact Factor
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    ABSTRACT: We investigate the contribution of star-forming galaxies to the ionizing background at z~3, building on previous work based on narrowband (NB3640) imaging in the SSA22a field. We use new Keck/LRIS spectra of Lyman break galaxies (LBGs) and narrowband-selected Lya emitters (LAEs) to measure redshifts for 16 LBGs and 87 LAEs at z>3.055, such that our NB3640 imaging probes the Lyman-continuum (LyC) region. When we include the existing set of spectroscopically-confirmed LBGs, our total sample with z>3.055 consists of 41 LBGs and 91 LAEs, of which nine LBGs and 20 LAEs are detected in our NB3640 image. With our combined imaging and spectroscopic data sets, we critically investigate the origin of NB3640 emission for detected LBGs and LAEs. We remove from our samples 3 LBGs and 3 LAEs with spectroscopic evidence of contamination of their NB3640 flux by foreground galaxies, and statistically model the effects of additional, unidentified foreground contaminants. The resulting contamination and LyC-detection rates, respectively, are 62 +/-13% and 8 +/-3% for our LBG sample, and 47 +/-10% and 12 +/-2% for our LAE sample. The corresponding ratios of non-ionizing UV to LyC flux-density, corrected for intergalactic medium (IGM) attenuation, are 18.0 +34.8/-7.4 for LBGs, and 3.7 +2.5/-1.1 for LAEs. We use these ratios to estimate the total contribution of star-forming galaxies to the ionizing background and the hydrogen photoionization rate in the IGM, finding values larger than, but consistent with, those measured in the Lya forest. Finally, the measured UV to LyC flux-density ratios imply model-dependent LyC escape fractions of f_{esc}^{LyC} ~ 5-7% for our LBG sample and f_{esc}^{LyC} ~ 10-30% for our fainter LAE sample.
    The Astrophysical Journal 10/2012; 765(1). · 6.73 Impact Factor
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    ABSTRACT: Although grand-design spiral galaxies are relatively common in the local Universe, only one has been spectroscopically confirmed to lie at redshift z > 2 (HDFX 28; z = 2.011); and it may prove to be a major merger that simply resembles a spiral in projection. The rarity of spirals has been explained as a result of disks being dynamically 'hot' at z > 2 (refs 2-5), which may instead favour the formation of commonly observed clumpy structures. Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe. At z < 2, the velocity dispersion of disks decreases, and spiral galaxies are more numerous by z ≈ 1 (refs 7, 13-15). Here we report observations of the grand-design spiral galaxy Q2343-BX442 at z = 2.18. Spectroscopy of ionized gas shows that the disk is dynamically hot, implying an uncertain origin for the spiral structure. The kinematics of the galaxy are consistent with a thick disk undergoing a minor merger, which can drive the formation of short-lived spiral structure. A duty cycle of <100 Myr for such tidally induced spiral structure in a hot massive disk is consistent with its rarity.
    Nature 07/2012; 487(7407):338-40. · 38.60 Impact Factor
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    ABSTRACT: We analyze rest-frame optical morphologies and gas-phase kinematics as traced by rest-frame far-UV and optical spectra for a sample of 204 star forming galaxies in the redshift range z ~ 2-3 drawn from the Keck Baryonic Structure Survey (KBSS). We find that spectroscopic properties and gas-phase kinematics are closely linked to morphology: compact galaxies with semi-major axis radii r <~ 2 kpc are substantially more likely than their larger counterparts to exhibit LyA in emission. Although LyA emission strength varies widely within galaxies of a given morphological type, all but one of 19 galaxies with LyA equivalent width W_LyA > 20 Angstroms have compact and/or multiple-component morphologies with r <= 2.5 kpc. The velocity structure of absorption lines in the galactic continuum spectra also varies as a function of morphology. Galaxies of all morphological types drive similarly strong outflows (as traced by the blue wing of interstellar absorption line features), but the outflows of larger galaxies are less highly ionized and exhibit larger optical depth at the systemic redshift that may correspond to a decreasing efficiency of feedback in evacuating gas from the galaxy. This v ~ 0 km/s gas is responsible both for shifting the mean absorption line redshift and attenuating W_LyA (via a longer resonant scattering path) in galaxies with larger rest-optical half light radii. In contrast to galaxies at lower redshifts, there is no evidence for a correlation between outflow velocity and inclination, suggesting that outflows from these puffy and irregular systems may be poorly collimated. (Abbrev.)
    The Astrophysical Journal 06/2012; 759(1). · 6.73 Impact Factor
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    ABSTRACT: We present Keck/LRIS spectra of over 200 galaxies with well-determined redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet, low-ionization absorption lines with previously measured masses, luminosities, colors, and star formation rates to describe the demographics and properties of galactic flows. Among star-forming galaxies with blue colors, we find a net blueshift of the FeII absorption greater than 200 km/s (100 km/s) towards 2.5% (20%) of the galaxies. The fraction of blueshifted spectra does not vary significantly with stellar mass, color, or luminosity but does decline at specific star formation rates less than roughly 0.8 Gyr^{-1}. The insensitivity of the blueshifted fraction to galaxy properties requires collimated outflows at these redshifts, while the decline in outflow fraction with increasing blueshift might reflect the angular dependence of the outflow velocity. The low detection rate of infalling gas, 3 to 6% of the spectra, suggests an origin in (enriched) streams favorably aligned with our sightline. We find 4 of these 9 infalling streams have projected velocities commensurate with the kinematics of an extended disk or satellite galaxy. The strength of the MgII absorption increases with stellar mass, B-band luminosity, and U-B color, trends arising from a combination of more interstellar absorption at the systemic velocity and less emission filling in more massive galaxies. Our results provides a new quantitative understanding of gas flows between galaxies and the circumgalactic medium over a critical period in galaxy evolution.
    The Astrophysical Journal 06/2012; 760(2). · 6.73 Impact Factor

Publication Stats

7k Citations
716.97 Total Impact Points

Institutions

  • 2013
    • Pierre and Marie Curie University - Paris 6
      • Institut d'astrophysique de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2008–2013
    • University of California, Los Angeles
      • • Department of Physics and Astronomy
      • • Division of Astronomy & Astrophysics
      Los Angeles, California, United States
  • 2012
    • University of Toronto
      • Dunlap Institute for Astronomy and Astrophysics
      Toronto, Ontario, Canada
    • University of Western Australia
      • International Centre for Radio Astronomy Research (ICRAR)
      Perth City, Western Australia, Australia
  • 2001–2012
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
  • 2010
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
    • University of Southern California
      Los Angeles, California, United States
  • 2006–2008
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2005–2008
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, CA, United States