We present the first results of the K-band Multi-Object Spectrometer (KMOS) Lens-Amplified Spectroscopic Survey, a new ESO Very Large Telescope large program, doing multi-object integral field ...spectroscopy of galaxies gravitationally lensed behind seven galaxy clusters selected from the Hubble Space Telescope (HST) Grism Lens-Amplified Survey from Space. Using the power of the cluster magnification, we are able to reveal the kinematic structure of 25 galaxies at , in four cluster fields, with stellar masses . This sample includes five sources at with lower stellar masses than in any previous kinematic integral field unit (IFU) surveys. Our sample displays a diversity in kinematic structure over this mass and redshift range. The majority of our kinematically resolved sample is rotationally supported, but with a lower ratio of rotational velocity to velocity dispersion than in the local universe, indicating the fraction of dynamically hot disks changes with cosmic time. We find that no galaxies with stellar mass in our sample display regular ordered rotation. Using the enhanced spatial resolution from lensing, we resolve a lower number of dispersion-dominated systems compared to field surveys, competitive with findings from surveys using adaptive optics. We find that the KMOS IFUs recover emission line flux from HST grism-selected objects more faithfully than slit spectrographs. With artificial slits, we estimate that slit spectrographs miss, on average, 60% of the total flux of emission lines, which decreases rapidly if the emission line is spatially offset from the continuum.
ABSTRACT We present a Bayesian framework to account for the magnification bias from both strong and weak gravitational lensing in estimates of high-redshift galaxy luminosity functions (LFs). We ...illustrate our method by estimating the z ∼ 8 UV LF using a sample of 97 Y-band dropouts (Lyman break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the literature. We find the LF is well described by a Schechter function with characteristic magnitude of , faint-end slope of , and number density of . These parameters are consistent within the uncertainties with those inferred from the same sample without accounting for the magnification bias, demonstrating that the effect is small for current surveys at z ∼ 8, and cannot account for the apparent overdensity of bright galaxies compared to a Schechter function found recently by Bowler et al. and Finkelstein et al. We estimate that the probability of finding a strongly lensed z ∼ 8 source in our sample is in the range ∼3-15% depending on limiting magnitude. We identify one strongly lensed candidate and three cases of intermediate lensing in BoRG (estimated magnification > 1.4) in addition to the previously known candidate group-scale strong lens. Using a range of theoretical LFs we conclude that magnification bias will dominate wide field surveys-such as those planned for the Euclid and WFIRST missions-especially at z > 10. Magnification bias will need to be accounted for in order to derive accurate estimates of high-redshift LFs in these surveys and to distinguish between galaxy formation models.
We present 3D-HST, a near-infrared spectroscopic Treasury program with the Hubble Space Telescope for studying the physical processes that shape galaxies in the distant universe. 3D-HST provides ...rest-frame optical spectra for a sample of ~7000 galaxies at 1 < z < 3.5, the epoch when ~60% of all star formation took place, the number density of quasars peaked, the first galaxies stopped forming stars, and the structural regularity that we see in galaxies today must have emerged. 3D-HST will cover three quarters (625 arcmin super(2)) of the CANDELS Treasury survey area with two orbits of primary WFC3/G141 grism coverage and two to four orbits with the ACS/G800L grism in parallel. In the IR, these exposure times yield a continuum signal-to-noise ratio of ~5 per resolution element at H sub(140) ~ 23.1 and a 5sigma emission-line sensitivity of ~5 x 10- super(17) erg s super(-1) cm super(2) for typical objects, improving by a factor of ~2 for compact sources in images with low sky background levels. The WFC3/G141 spectra provide continuous wavelength coverage from 1.1 to 1.6 mu m at a spatial resolution of ~0."13, which, combined with their depth, makes them a unique resource for studying galaxy evolution. We present an overview of the preliminary reduction and analysis of the grism observations, including emission-line and redshift measurements from combined fits to the extracted grism spectra and photometry from ancillary multi-wavelength catalogs. The present analysis yields redshift estimates with a precision of sigma(z)= 0.0034(1 + z), or sigma(v) approx = 1000 km s super(-1). We illustrate how the generalized nature of the survey yields near-infrared spectra of remarkable quality for many different types of objects, including a quasar at z = 4.7, quiescent galaxies at z ~ 2, and the most distant T-type brown dwarf star known. The combination of the CANDELS and 3D-HST surveys will provide the definitive imaging and spectroscopic data set for studies of the 1 < z < 3.5 universe until the launch of the James Webb Space Telescope.
ABSTRACT Exploiting the slitless spectroscopy taken as part of the Grism Lens-Amplified Survey from Space (GLASS), we present an extended analysis of the spatial distribution of star formation in 76 ...galaxies in 10 clusters at . We use 85 foreground and background galaxies in the same redshift range as a field sample. The samples are well matched in stellar mass (108−1011 ) and star formation rate (0.5-50 ). We visually classify galaxies in terms of broad band morphology, H morphology, and likely physical process acting on the galaxy. Most H emitters have a spiral morphology (41% 8% in clusters, 51% 8% in the field), followed by mergers/interactions (28% 8%, 31% 7%, respectively) and early-type galaxies (remarkably as high as 29% 8% in clusters and 15% 6% in the field). A diversity of H morphologies is detected, suggesting a diversity of physical processes. In clusters, 30% 8% of the galaxies present a regular morphology, mostly consistent with star formation diffused uniformly across the stellar population (mostly in the disk component, when present). The second most common morphology (28% 8%) is asymmetric/jellyfish, consistent with ram-pressure stripping or other non-gravitational processes in 18% 8% of the cases. Ram-pressure stripping appears significantly less prominent in the field (2% 2%), where the most common morphology/mechanism appears to be consistent with minor gas-rich mergers or clump accretion. This work demonstrates that while environment-specific mechanisms affect galaxy evolution at this redshift, they are diverse and their effects are subtle. A full understanding of this complexity requires larger samples and detailed and spatially resolved physical models.
ABSTRACT
While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic reionization is poorly understood due to a lack of knowledge of their physical properties. ...We isolate a sample of 35 z ≈ 4–5 continuum-faint Lyman-α emitters from deep VLT/MUSE spectroscopy and directly measure their H α emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than −16 (≈ 0.01 L⋆), implying a median Lyman-α equivalent width of 259 Å. By combining the H α measurement with the UV magnitude, we determine the ionizing photon production efficiency, ξion, a first for such faint galaxies. The measurement of log10 (ξion Hz erg−1) = 26.28 ($^{+0.28}_{-0.40}$) is in excess of literature measurements of both continuum- and emission line-selected samples, implying a more efficient production of ionizing photons in these lower luminosity, Lyman-α-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4 × 10−4 and 0.008, with light-weighted ages less than 3 Myr.
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery ...of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
Abstract
We derive a free-form mass distribution for the unrelaxed cluster A370 (z = 0.375), using the first release of the Hubble Frontier Fields images (76 orbits) and GLASS spectroscopy. Starting ...from a reliable set of 10 multiply lensed systems, we produce a free-form lens model that identifies ≈80 multiple images. Good consistency is found between models using independent subsamples of these lensed systems, with detailed agreement for the well-resolved arcs. The mass distribution has two very similar concentrations centred on the two prominent brightest cluster galaxies (or BCGs), with mass profiles that are accurately constrained by a uniquely useful system of long radially lensed images centred on both BCGs. We show that the lensing mass profiles of these BCGs are mainly accounted for by their stellar mass profiles, with a modest contribution from dark matter within r < 100 kpc of each BCG. This conclusion may favour a cooled cluster gas origin for BCGs, rather than via mergers of normal galaxies for which dark matter should dominate over stars. Growth via merging between BCGs is, however, consistent with this finding, so that stars still dominate over dark matter. We do not observe any significant offset between the positions of the peaks of the dark matter distribution and the light distribution.
We present the largest search to date for Y-band dropout galaxies (z ~ 8 Lyman break galaxies, LBGs) based on 350 arcmin super(2) of Hubble Space Telescope observations in the V, Y, J, and H bands ...from the Brightest of Reionizing Galaxies (BoRG) survey. We introduce a new Bayesian formalism for estimating the galaxy luminosity function, which does not require binning (and thus smearing) of the data and includes a likelihood based on the formally correct binomial distribution as opposed to the often-used approximate Poisson distribution. We demonstrate the utility of the new method on a sample of 97 Y-band dropouts that combines the bright BoRG galaxies with the fainter sources published in Bouwens et al. from the Hubble Ultra Deep Field and Early Release Science programs. The data are consistent with a substantial fraction of neutral hydrogen at z > 7, in agreement with recent suggestions based on deep spectroscopy of z ~ 8 LBGs.
Abstract
We present the first estimate of the Ly α luminosity function using blind spectroscopy from the Multi Unit Spectroscopic Explorer, MUSE, in the Hubble Deep Field-South. Using automatic ...source-detection software, we assemble a homogeneously detected sample of 59 Ly α emitters covering a flux range of −18.0 < log10 (F) < −16.3 (erg s−1 cm−2), corresponding to luminosities of 41.4 < log10 (L) < 42.8 (erg s−1). As recent studies have shown, Ly α fluxes can be underestimated by a factor of 2 or more via traditional methods, and so we undertake a careful assessment of each object's Ly α flux using a curve-of-growth analysis to account for extended emission. We describe our self-consistent method for determining the completeness of the sample, and present an estimate of the global Ly α luminosity function between redshifts 2.91 < z < 6.64 using the 1/V
max estimator. We find that the luminosity function is higher than many number densities reported in the literature by a factor of 2–3, although our result is consistent at the 1σ level with most of these studies. Our observed luminosity function is also in good agreement with predictions from semi-analytic models, and shows no evidence for strong evolution between the high- and low-redshift halves of the data. We demonstrate that one's approach to Ly α flux estimation does alter the observed luminosity function, and caution that accurate flux assessments will be crucial in measurements of the faint-end slope. This is a pilot study for the Ly α luminosity function in the MUSE deep-fields, to be built on with data from the Hubble Ultra Deep Field that will increase the size of our sample by almost a factor of 10.
We present a new and simple technique for selecting extensive, complete, and pure quasar samples, based on their intrinsic variability. We parameterize the single-band variability by a power-law ...model for the light-curve structure function, with amplitude A and power-law index {gamma}. We show that quasars can be efficiently separated from other non-variable and variable sources by the location of the individual sources in the A-{gamma} plane. We use {approx}60 epochs of imaging data, taken over {approx}5 years, from the SDSS stripe 82 (S82) survey, where extensive spectroscopy provides a reference sample of quasars, to demonstrate the power of variability as a quasar classifier in multi-epoch surveys. For UV-excess selected objects, variability performs just as well as the standard SDSS color selection, identifying quasars with a completeness of 90% and a purity of 95%. In the redshift range 2.5 < z < 3, where color selection is known to be problematic, variability can select quasars with a completeness of 90% and a purity of 96%. This is a factor of 5-10 times more pure than existing color selection of quasars in this redshift range. Selecting objects from a broad griz color box without u-band information, variability selection in S82 can afford completeness and purity of 92%, despite a factor of 30 more contaminants than quasars in the color-selected feeder sample. This confirms that the fraction of quasars hidden in the 'stellar locus' of color space is small. To test variability selection in the context of Pan-STARRS 1 (PS1) we created mock PS1 data by down-sampling the S82 data to just six epochs over 3 years. Even with this much sparser time sampling, variability is an encouragingly efficient classifier. For instance, a 92% pure and 44% complete quasar candidate sample is attainable from the above griz-selected catalog. Finally, we show that the presented A-{gamma} technique, besides selecting clean and pure samples of quasars (which are stochastically varying objects), is also efficient at selecting (periodic) variable objects such as RR Lyrae.
PDF
