A Deep Hubble and Keck Search for Definitive Identification of Lyman Continuum Emitters at z~3.1
Brian Siana, Alice E. Shapley, Kristin R. Kulas, Daniel B. Nestor, Charles C. Steidel, Harry I. Teplitz, Anahita Alavi, Thomas M. Brown, Christopher J. Conselic… 展开作者
Brian Siana, Alice E. Shapley, Kristin R. Kulas, Daniel B. Nestor, Charles C. Steidel, Harry I. Teplitz, Anahita Alavi, Thomas M. Brown, Christopher J. Conselice, Henry C. Ferguson, Mark Dickinson, Mauro Giavalisco, James W. Colbert, Carrie R. Bridge, Jonathan P. Gardner, Duilia F. de Mello
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Accepted for publication in the Astrophysical Journal. 14 pages, 5 figures
Narrow-band imaging of the rest-frame Lyman continuum (LyC) of galaxies at z~3.1 has produced a large number of candidate LyC-emitting galaxies. These samples are contaminated by galaxies at lower redshift. To better understand LyC escape, we need an uncontaminated sample of galaxies that emit strongly in the LyC. Here we present deep Hubble imaging of five bright galaxies at z~3.1 that had previously been identified as candidate LyC-emitters with ground-based images. The WFC3 F336W images probe the LyC of galaxies at z>3.06 and provide an order-of-magnitude increase in spatial resolution over ground-based imaging. The non-ionizing UV images often show multiple galaxies (or components) within ~1'' of the candidate LyC emission seen from the ground. In each case, only one of the components is emitting light in the F336W filter, which would indicate LyC escape if that component is at z>3.06. We use Keck/NIRSPEC near-IR spectroscopy to measure redshifts of these components to distinguish LyC-emitters from foreground contamination. We find that two candidates are low redshift contaminants, one candidate had a previously misidentified redshift, and the other two cannot be confirmed as LyC-emitters. The level of contamination is consistent with previous estimates. For the galaxies with z>3.06, we derive strong 1 sigma limits on the relative escape fraction between 0.07 and 0.09. We still do not have a sample of definitive LyC-emitters, and a much larger study of low luminosity galaxies is required. The combination of high resolution imaging and deep spectroscopy is critical for distinguishing LyC-emitters from foreground contaminants.
The connection between the escape fraction of ionizing radiation ($f_{esc}$) and the properties of galaxies, such as stellar mass (M*), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 z~3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multi-band photometry that places constraints on stellar population parameters. We…
We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6 mag in the Hubble Ultra Deep Field (UDF). The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the LRIS spectrometer. The Keck u-band image, totaling 9 hours of integration time, has a one sigma depth of 30.7 mag arcsec^-2, making it one of the most sensitive u-band images ever obtained. The u-band image also substantiall…
We present Keck/OSIRIS infrared IFU observations of the $z = $ 3.153 sub-DLA DLA2233+131, previously detected in absorption to a background quasar and studied with single slit spectroscopy and PMAS integral field spectroscopy (IFU). We used the Laser Guide Star Adaptive Optics (LGSAO) and OSIRIS IFU to reduce the point-spread function of the background quasar to FWHM$\sim$0.15 arcseconds and marginally resolve extended, foreground DLA emission. We detect [OIII]$λ$5007 emission with a flux F$^{[OIII]\lambda5007}$ = $(2.4\pm0.5)\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, as well as unresolved [OIII]…
We present a spectroscopic redshift measurement of a very bright Lyman break galaxy at z=7.7302+-0.0006 using Keck/MOSFIRE. The source was pre-selected photometrically in the EGS field as a robust z~8 candidate with H=25.0 mag based on optical non-detections and a very red Spitzer/IRAC [3.6]-[4.5] broad-band color driven by high equivalent width [OIII]+Hbeta line emission. The Lyalpha line is reliably detected at 6.1 sigma and shows an asymmetric profile as expected for a galaxy embedded in a relatively neutral inter-galactic medium near the Planck peak of cosmic reionization. The line has a r…
We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implyin…
We report Keck/ESI and VLT/UVES observations of three super-damped Lyman-alpha quasar absorbers with H I column densities log N(HI) >= 21.7 at redshifts z=2-2.5. All three absorbers show similar metallicities (-1.3 to -1.5 dex), and dust depletion of Fe, Ni, and Mn. Two of the absorbers show supersolar [S/Zn] and [Si/Zn]. We combine our results with those for other DLAs to examine trends between N(HI), metallicity, dust depletion. A larger fraction of the super-DLAs lie close to or above the line [X/H]=20.59-log N(HI) in the metallicity vs. N(HI) plot, compared to the less gas-rich DLAs, sugge…
We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-α (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g. C II λ1334 and Si II λ1260). These metal-poor DLA candidates were selected from the SDSS DR5 quasar spectroscopic database, and comprise a large new sample for probing low metallicity galaxies. Medium-resolution echellette spectra from the Keck ESI spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleo…
We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $x_{\textrm{HI}}$, at $z \sim$ 6-8 using the properties of Lyman break galaxies during the Epoch of Reionization. We use large samples of LBG candidates at $5.5 \leq z \leq 8.2$ with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-$α$ equivalent width (EW) for detections or the EW limit spectrum for nondetections to parameterize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candi…
Star-forming galaxies are the sources likely to have reionized the universe. As we cannot observe them directly due to the opacity of the intergalactic medium at $z\gtrsim5$, we study $z\sim3\text{--}5$ galaxies as proxies to place observational constraints on cosmic reionization. Using new deep \textit{Hubble Space Telescope} rest-frame UV F336W and F435W imaging (30-orbit, $\sim40$~arcmin$^2$, $\sim29\text{--}30$~mag depth at 5$σ$), we attempt to identify a sample of Lyman continuum galaxies (LCGs). These are individual sources that emit ionizing flux below the Lyman break ($<912~\textÅ$). T…
We present observations of Q1549-C25, an ~L* star-forming galaxy at z=3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence for contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V_606, J_125, and H_160 Hubble Space Telescope (HST) imaging reveals that the object consists of a single, isolated component within 1". In combination, these data indicate Q1549-C25 as a clean spectroscopic detection of LyC radiati…
Lyman-$α$ photons are resonantly scattered by neutral hydrogen, and may therefore trace both the spatial extent and the kinematics of the gas surrounding galaxies. We present new observations of the extended Ly$α$ halo of Q2343-BX418, a low mass ($M_{\star} = 5\times10^8$ M$_{\odot}$), low metallicity ($Z\approx 0.25$ Z$_{\odot}$) star-forming galaxy at $z = 2.3$. Using the Keck Cosmic Web Imager, the blue-sensitive optical integral field spectrograph recently installed on the Keck II telescope, we detect Ly$α$ in emission to a radius of 23 kpc, and measure an exponential scale length of 6 kpc…
We present a rest-UV selected sample of 32 lensed galaxies at $z\sim 2$ observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed ($-19 \le {\rm M_{\rm UV}} \le -17$) at this redshift. The fraction of dwarf galaxies identified as Ly$α$ emitters ($\rm EW \ge 20\ \overset{\lower.5em\circ}{\mathrm{A}}$) is ${\rm X_{\rm LAE}}=25^{+15}_{-10}\%$. We use the Balmer lines and UV continuum to estimate the intrinsic EW allowing us to distinguish the effects of the…
We present new observations of Lyman-$α$ (Ly$α$) Blob 1 (LAB1) in the SSA22 protocluster region ($z$ = 3.09) using the Keck Cosmic Web Imager (KCWI) and the Keck Multi-object Spectrometer for Infrared Exploration (MOSFIRE). By applying matched filtering to the KCWI datacube, we have created a narrow-band Ly$α$ image and identified several prominent features. By comparing the spatial distributions and intensities of Ly$α$ and H$β$, we find that recombination of photo-ionized HI gas followed by resonant scattering is sufficient to explain all the observed Ly$α$/H$β$ ratios. We further decode the…
We introduce a new method for determining the influence of galaxies and active galactic nuclei (AGN) on the physical state of the intergalactic medium (IGM) at high redshift and illustrate its potential via a first application to the field of the $z=6.42$ QSO J1148+5251. By correlating the spatial positions of spectroscopically-confirmed Lyman break galaxies (LBGs) with fluctuations in the Lyman alpha forest seen in the high signal-to-noise spectrum of a background QSO, we provide a statistical measure of the typical escape fraction of Lyman continuum photons close to the end of cosmic reionis…
We discuss the rest-frame optical emission line spectra of a large (~50) sample of z=3.1 Lyman alpha emitters (LAEs) whose physical properties suggest such sources are promising analogs of galaxies in the reionization era. Reliable Lyman continuum escape fractions have now been determined for a large sample of such LAEs from the Lyman Continuum Escape Survey (LACES) undertaken via deep HST imaging in the SSA22 survey area reported in Fletcher et al. (2019). Using new measures of [OII] emission secured from Keck MOSFIRE spectra we re-examine, for a larger sample, earlier claims that Lyman conti…
We present new Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet (far-UV) spectroscopy and Keck Echellete optical spectroscopy of 11 ultraluminous infrared galaxies (ULIRGs), a rare population of local galaxies experiencing massive gas inflows, extreme starbursts, and prominent outflows. We detect H Lyman alpha emission from 8 ULIRGs and the companion to IRAS09583+4714. In contrast to the P Cygni profiles often seen in galaxy spectra, the H Lyman alpha profiles exhibit prominent, blueshifted emission out to Doppler shifts exceeding -1000 km/s in three HII-dominated and two AGN…
We present results of a deep spectroscopic survey designed to quantify the statistics of the escape of ionizing photons from star-forming galaxies at z~3. We measure the ratio of ionizing to non-ionizing UV flux density <f900/f1500>_obs, where f900 is the mean flux density evaluated over the range [880,910] A. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high-S/N composite spectra formed from sub-samples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise valu…
We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyman alpha emitting source at z=6.1292, HSC J142331.71-001809.1, which was discovered by the SHELLQS program from imaging data of the Subaru Hyper Suprime-Cam (HSC) survey. This source is one of five objects that show unresolved (<230 km s-1) and prominent (>10^44 erg s-1) Lyman alpha emission lines at absolute 1450 angstrom continuum magnitudes of M1450~-22 mag. Its rest-frame Lyman alpha equivalent width (EW) is 370+/-30 angstrom. In the 2 hour Keck/MOSFIRE spectrum in Y band, the high-ionization CIV 1548,1550 doublet emiss…
Using a sample of galaxies at $z\approx 3$ with detected Lyman Continuum (LyC) leakage in the SSA22 field, we attempt to verify a proposed indirect method for identifying cases with high LyC escape fraction $f_\mathrm{esc}$ based on measurements of the H$β$ equivalent width (EW) and the $β$ slope of the UV continuum. To this end, we present Keck/MOSFIRE H$β$ emission line flux measurements of LyC galaxies (LCGs) at spectroscopic redshifts $z_{\mathrm{spec}} \sim 3.3$, Lyman break galaxies (LBGs) at photometric redshifts $z_{\mathrm{phot}} = 2.7$--$3.7$, and Ly$α$ emitters at $z_{\mathrm{phot}}…
We use the wealth of deep archival optical spectroscopy on the GOODS-South field from Keck, the VLT, and other facilities to select candidate high-redshift Lyman continuum (LyC) leakers in the Hubble Deep UV Legacy Survey (HDUV) dataset. We select sources at $2.35 < z < 3.05$, where the HST/WFC3 F275W filter probes only the redshifted LyC. We find five moderately F275W-bright sources (four detected at $\gtrsim3σ$ significance) in this redshift range. However, two of these show evidence in their optical spectra for contamination by foreground galaxies along the line-of-sight. We then perform an…
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our new MOSFIRE observations confirm that Lyman-alpha is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1, confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at z=7.477, verifying a tentative detection presented in an earlier study. The ubiquity of Lyman-alpha in this sample is puzzling given that the IGM …
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized re…
[Abridged] We investigate the physical properties of a Lyman continuum emitter candidate at $z=3.212$ with photometric coverage from $U$ to MIPS 24$μ$m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with $S/N>5$. Non-zero Ly$α$ flux at the systemic redshift and high Lyman-$α$ escape fraction suggest a low HI column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The [OIII]$λ\lambda4959,5007+\mathrm{H}β…
We report spectroscopic confirmations of 15 Lyman-alpha galaxies at $z\sim7$, implying a spectroscopic confirmation rate of $\sim$80% on candidates selected from LAGER (Lyman-Alpha Galaxies in the Epoch of Reionization), which is the largest (24 deg$^2$) survey aimed at finding Lyman-alpha emitters (LAEs) at $z\sim7$ using deep narrow-band imaging from DECam at CTIO. LAEs at high-redshifts are sensitive probes of cosmic reionization and narrow-band imaging is a robust and effective method for selecting a large number of LAEs. In this work, we present results from the spectroscopic follow-up of…
Recent evidence suggests that high-redshift Ly-alpha emitting galaxies (LAEs) with logL(Ly-alpha) > 43.5 erg/s, referred to as ultraluminous LAEs (ULLAEs), may show less evolution than lower-luminosity LAEs in the redshift range z=5.7-6.6. Here we explore the redshift evolution of the velocity widths of the Ly-alpha emission lines in LAEs over this redshift interval. We use new wide-field, narrowband observations from Subaru/Hyper Suprime-Cam to provide a sample of 24 z=6.6 and 12 z=5.7 LAEs with log L(Ly-alpha) > 43 erg/s, all of which have follow-up spectroscopy from Keck/DEIMOS. Combining w…
Several decades of observations and discoveries have shown that high-redshift AGN and massive galaxies are often surrounded by giant Lyman-alpha nebulae extending in some cases up to 500 kpc in size. In this review, I discuss the properties of the such nebulae discovered at z>2 and their connection with gas flows in and around the galaxies and their halos. In particular, I show how current observations are used to constrain the physical properties and origin of the emitting gas in terms of the Lyman-alpha photon production processes and kinematical signatures. These studies suggest that recomb…
We present the first results of our pilot study of 8 photometrically selected Lyman continuum (LyC) emitting galaxy candidates from the COSMOS field and focus on their optical emission line ratios. Observations were performed in the H and K bands using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) instrument at the Keck Observatory, targeting the [OII], H$β$, and [OIII] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [OIII]/[OII] ratios (O32), with an average ratio for our sample of 2.…
We measured metallicities for 33 z=3.4-4.2 absorption line systems drawn from a sample of H I-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of H I column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, fin…
Observations of reionization-era analogs at $z\sim3$ are a powerful tool for constraining reionization. Rest-ultraviolet observations are particularly useful, in which both direct and indirect tracers of ionizing-photon production and escape can be observed. We analyse a sample of 124 $z\sim3$ galaxies from the Keck Lyman Continuum Spectroscopic Survey, with sensitive spectroscopic measurements of the Lyman continuum (LyC) region. We present a method of removing foreground contamination from our sample using high-resolution, multiband Hubble Space Telescope imaging. We re-measure the global pr…
We report the detection of Ly$α$ emission at $\sim9538$Å in the Keck/DEIMOS and \HST WFC3 G102 grism data from a triply-imaged galaxy at $z=6.846\pm0.001$ behind galaxy cluster MACS J2129.4$-$0741. Combining the emission line wavelength with broadband photometry, line ratio upper limits, and lens modeling, we rule out the scenario that this emission line is \oii at $z=1.57$. After accounting for magnification, we calculate the weighted average of the intrinsic Ly$α$ luminosity to be $\sim1.3\times10^{42}~\mathrm{erg}~\mathrm{s}^{-1}$ and Ly$α$ equivalent width to be $74\pm15$Å. Its intrinsic U…
Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-$α$ forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck-I telescope. Over an observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we used 240 galaxies and quasars at $2.17<z<3.00$, with a mean comoving …
We report on a search for ultraluminous Lyman alpha emitting galaxies (LAEs) at z=6.6 using the NB921 filter on Hyper Suprime-Cam on the Subaru telescope. We searched a 30 degree squared area around the North Ecliptic Pole, which we observed in broadband g', r', i', z', and y' and narrowband NB816 and NB921, for sources with NB921 < 23.5 and z' - NB921 > 1.3. This corresponds to a selection of log L(Ly-alpha) > 43.5 erg/s. We followed up seven candidate LAEs (out of thirteen) with the Keck DEIMOS spectrograph and confirmed five z=6.6 LAEs, one z=6.6 AGN with a broad Ly-alpha line and a strong …
Cosmic (hydrogen) reionization marks one of the major phase transitions of the universe at redshift z >= 6. During this epoch, hydrogen atoms in the intergalactic medium (IGM) were ionized by Lyman continuum (LyC) photons. However, it remains challenging to identify the major sources of the LyC photons responsible for reionization. In particular, individual contributions of quasars (or active galactic nuclei, AGNs) and galaxies are still under debate. Here we construct the far-ultraviolet (far-UV) luminosity function for type 1 quasars at z >= 6 that spans 10 magnitudes (-19 < M_UV < -29), con…
We present new observations of the field containing the z=3.786 protocluster, PC217.96+32.3. We confirm that it is one of the largest and most overdense high-redshift structures known. Such structures are rare even in the largest cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image a 1.2x0.6 deg area (~150x75 comoving Mpc) surrounding the protocluster's core and discovered 165 candidate Lyman Alpha emitting galaxies (LAEs) and 788 candidate Lyman Break galaxies (LBGs). There are at least 2 overdense regions traced by the LAEs, the largest of which shows an areal overd…
The observed deficit of strongly Lyman-alpha emitting galaxies at z>6.5 is attributed to either increasing neutral hydrogen in the intergalactic medium (IGM) and/or to the evolving galaxy properties. To investigate this, we have performed very deep near-IR spectroscopy of z>7 galaxies using MOSFIRE on the Keck-I Telescope. We measure the Lyman-alpha fraction at z~8 (combined photometric redshift peak at z=7.7) using two methods. First, we derived NLyα/Ntot directly using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al. 2012) t…
We present the luminosity function (LF) for ultraluminous Ly$α$ emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with logL(Ly$α$) > 43.5 erg s$^{-1}$. We select our main sample using the g', r', i', z', and NB921 observations of a wide-area (30 deg$^2$) Hyper Suprime-Cam survey of the North Ecliptic Pole (NEP) field. We select candidates with g', r', i' > 26, NB921 $\leq$ 23.5, and NB921 - z' $\leq$ 1.3. Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an AGN at z = 6.6, two [OIII]$λ$50…
We present the results from a VLT/SINFONI and Keck/NIRSPEC near-infrared spectroscopic survey of 16 Lyman-alpha emitters (LAEs) at $z$ = 2.1 - 2.5 in the COSMOS and GOODS-N fields discovered from the HETDEX Pilot Survey. We detect rest-frame optical nebular lines (H$α$ and/or [OIII]$λ$5007) for 10 of the LAEs and measure physical properties, including the star formation rate (SFR), gas-phase metallicity, gas-mass fraction, and Ly$α$ velocity offset. We find that LAEs may lie below the mass-metallicity relation for continuum-selected star-forming galaxies at the same redshift. The LAEs all show…
We present chemical abundance measurements for 47 damped Lyman-alpha systems (DLAs), 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. HI column densities of the DLAs are measured with Voigt profile fits to the Lyman-alpha profiles, and we find an increased number of false DLA identifications with SDSS at z>4 due to the increased density of the Lyman-alpha forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous …
We perform joint modeling of the composite rest-frame far-UV (FUV) and optical spectra of redshift 1.85<z<3.49 star-forming galaxies to deduce key properties of the massive stars, ionized ISM, and neutral ISM, with the aim of investigating the principal factors affecting the production and escape of Ly-alpha (Lya) photons. Our sample consists of 136 galaxies with deep Keck/LRIS and MOSFIRE spectra covering, respectively, Ly-beta through CIII] 1907, 1909; and [OII], [NeIII], H-beta, [OIII], H-alpha, [NII], and [SII]. Spectral and photoionization modeling indicate that the galaxies are uniformly…
Connecting CGM enrichment with Lyman alpha emitters at 2.9 < z < 6.7
Swinburne University of Technology（斯威本科技大学）；University of Geneva（日内瓦大学）；INAF-Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；IFPU-Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）
Using new Keck DEIMOS spectroscopy, we examine the origin of the steep number counts of ultra-faint emission-line galaxies recently reported by Dressler et al. (2011). We confirm six Lyman Alpha emitters (LAEs), three of which have significant asymmetric line profiles with prominent wings extending 300-400 km/s redward of the peak emission. With these six LAEs, we revise our previous estimate of the number of faint LAEs in the Dressler et al. survey. Combining these data with the density of bright LAEs in the Cosmic Origins Survey and Subaru Deep Field provides the best constraints to date on …
Although low-mass star-forming galaxies are the leading candidates of the reionisation process, we cannot conclusively rule out high-mass star-forming galaxies as candidates. While most simulations indicate the former is the best candidate some models suggest that at z > 6 massive, UV-bright galaxies - "oligarchs" - account for at least 80% of the ionising budget. To test this hypothesis we target massive (log10 (M*[Msol]) > 10), UV-bright (MUV ~ -22) Lya emitters at z > 7 in archival data, observed with similar resolution spectrographs (VLT/X-shooter and Keck/MOSFIRE). To increase the reliabi…
While the Lyman-$α$ ($\mathrm{Ly}α$) emission line serves as an important tool in the study of galaxies at $z\lesssim 6$, finding Ly$α$ emitters (LAE) at significantly higher redshifts has been more challenging, probably because of the increasing neutrality of the intergalactic medium above $z\sim6$. Galaxies with extremely high rest-frame Ly$α$ equivalent widths, EW(Ly$α$) $\gtrsim 150$ Å, at $z>6$ are good candidates for Ly$α$ follow-up observations, and can stand out in multiband imaging surveys because of their unusual colors. We have conducted a photometric search for such objects in the …
We study the stellar population properties of the IRAC-detected $6 \lesssim z \lesssim 10$ galaxy candidates from the Spitzer UltRa Faint SUrvey Program (SURFS UP). Using the Lyman Break selection technique, we find a total of 16 new galaxy candidates at $6 \lesssim z \lesssim 10$ with $S/N \geq 3$ in at least one of the IRAC $3.6μ$m and $4.5μ$m bands. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of $\sim 1.2$--$5.5$. We find that the IRAC-detected $6 \lesssim z \lesssim 10$ sample is likely not a h…
The redshift-dependent fraction of color-selected galaxies revealing Lyman alpha emission has become the most valuable constraint on the evolving neutrality of the early intergalactic medium. However, in addition to resonant scattering by neutral gas, the visibility of Lyman alpha is also dependent on the intrinsic properties of the host galaxy, including its stellar population, dust content and the nature of outflowing gas. Taking advantage of significant progress we have made in determining the line emitting properties of $z \simeq 4-6$ galaxies, we propose an improved method, based on using…
We present results of a spectroscopic search for Lyman-alpha emitters (LAEs) in the Cl1604 supercluster field using the extensive spectroscopic Keck/DEIMOS database taken as part of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. A total of 12 slitmasks were observed and inspected in the Cl1604 field, spanning a survey volume of 1.365x10^4 co-moving Mpc^3. We find a total of 17 high redshift (4.39 < z < 5.67) LAE candidates down to a limiting flux of 1.9x10^(-18) ergs/s/cm (~0.1L* at z~5), 13 of which we classify as high quality. The resulting LAE number den…
We report the discovery of Lyman-alpha emission (Ly$α$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 Å which we a…
We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z~3.2-3.7 using MOSFIRE on the Keck 1 telescope. Strong rest-frame optical [O III] and Hbeta emission lines were detected in 18 LBGs. The median flux ratio of [O III]5007 to Hbeta is 5.1+/-0.5, a factor of 5-10x higher than in local galaxies with similar stellar masses. The observed Hbeta luminosities are in good agreement with expectations from the estimated star-formation rates, and none of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei…
Deep narrow-band surveys have revealed a large population of faint Lyman-alpha (Lya) emitters (LAEs) in the distant Universe, but relatively little is known about the most luminous sources ($L_{Lyα}>10^{42.7}$ erg/s; $L_{Lyα}>L^*_{Lyα}$). Here we present the spectroscopic follow-up of 21 luminous LAEs at z~2-3 found with panoramic narrow-band surveys over five independent extragalactic fields (~4x10$^6$ Mpc$^{3}$ surveyed at z~2.2 and z~3.1). We use WHT/ISIS, Keck/DEIMOS and VLT/X-SHOOTER to study these sources using high ionisation UV lines. Luminous LAEs at z~2-3 have blue UV slopes ($β=-2.0…
Faint Lyman-$α$ (Ly$α$) emitters become increasingly rarer towards the re-ionisation epoch (z~6-7). However, observations from a very large (~5deg$^2$) Ly$α$ survey at z=6.6 (Matthee et al. 2015) show that this is not the case for the most luminous emitters. Here we present follow-up observations of the two most luminous z~6.6 Ly$α$ candidates in the COSMOS field: `MASOSA' and `CR7'. We used X-SHOOTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. We find redshifts of z=6.541 and z=6.604 for MASOSA and CR7, respectively. MASOSA has a strong detection …
