ABSTRACT We measure C iii 1907, C iii 1909 emission lines in 11 gravitationally lensed star-forming galaxies at z ∼ 1.6-3, finding much lower equivalent widths than previously reported for fainter ...lensed galaxies. While it is not yet clear what causes some galaxies to be strong C iii emitters, C iii emission is not a universal property of distant star-forming galaxies. We also examine C iii emission in 46 star-forming galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS on HST and IUE. Twenty percent of these local galaxies show strong C iii emission, with equivalent widths < −5 . Three nearby galaxies show C iii emission equivalent widths as large as the most extreme emitters yet observed in the distant universe; all three are Wolf-Rayet galaxies. At all redshifts, strong C iii emission may pick out low-metallicity galaxies experiencing intense bursts of star formation. Such local C iii emitters may shed light on the conditions of star formation in certain extreme high-redshift galaxies.
We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts . The resulting new composite spans , with a peak signal-to-noise ratio (S/N) of ...103 per spectral resolution element (∼100 km s−1). It is the highest S/N, highest spectral resolution composite spectrum of z ∼ 2-3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at and , suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. As such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least −2000 km s−1. We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at . We publicly release our composite spectra.
We present the results of a Chandra X-ray survey of the eight most massive galaxy clusters at z > 1.2 in the South Pole Telescope 2500 deg2 survey. We combine this sample with previously published ...Chandra observations of 49 massive X-ray-selected clusters at 0 < z < 0.1 and 90 Sunyaev-Zel'dovich-selected clusters at 0.25 < z < 1.2 to constrain the evolution of the intracluster medium (ICM) over the past ∼10 Gyr. We find that the bulk of the ICM has evolved self-similarly over the full redshift range probed here, with the ICM density at scaling like . In the centers of clusters ( ), we find significant deviations from self-similarity ( ), consistent with no redshift dependence. When we isolate clusters with overdense cores (i.e., cool cores), we find that the average overdensity profile has not evolved with redshift-that is, cool cores have not changed in size, density, or total mass over the past ∼9-10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self-similarly evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to .
We introduce Project MegaSaura: the Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MegaSaura comprises medium-resolution, rest-frame ultraviolet spectroscopy of N = 15 ...bright gravitationally lensed galaxies at redshifts of 1.68 < z < 3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range 3200 < λo < 8280 ; the average spectral resolving power is R = 3300. The median spectrum has a signal-to-noise ratio (S/N) = 21 per resolution element at 5000 . As such, the MegaSaura spectra have superior S/N and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MegaSaura spectra to the astronomical community through a data release.
We present new, deep observations of the Phoenix cluster from Chandra, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order-of-magnitude improvement in depth ...and/or angular resolution over previous observations at X-ray, optical, and radio wavelengths. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling models. In particular, the entropy profile is well fit by a single power law at all radii, with no evidence for excess entropy in the core. In the inner ∼10 kpc, the cooling time is shorter than any other known cluster by an order of magnitude, while the ratio of the cooling time to freefall time (tcool/tff) approaches unity, signaling that the intracluster medium is unable to resist multiphase condensation on kpc scales. The bulk of the cooling in the inner ∼20 kpc is confined to a low-entropy filament extending northward from the central galaxy, with tcool/tff ∼ 1 over the length of the filament. In this filament, we find evidence for ∼1010 M in cool (∼104 K) gas (as traced by the O iiλλ3726,3729 doublet), which is coincident with the low-entropy filament and absorbing soft X-rays. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets. These data support a picture in which active galactic nucleus feedback is promoting the formation of a multiphase medium via uplift of low-entropy gas, either via ordered or chaotic (turbulent) motions.
For lensed galaxy SGAS J111020.0+645950.8 at redshift z = 2.481, which is magnified by a factor of 28 8, we analyze the morphology of star formation, as traced by rest-frame ultraviolet emission, in ...both the highly magnified source plane and simulations of how this galaxy would appear without lensing magnification. Were this galaxy not lensed, but rather drawn from a Hubble Space Telescope deep field, we would conclude that almost all its star formation arises from an exponential disk (Sérsic index of 1.0 0.4) with an effective radius of measured from two-dimensional fitting to F606W using Galfit, and measured by fitting a radial profile to F606W elliptical isophotes. At the normal spatial resolution of the deep fields, there is no sign of clumpy star formation within SGAS J111020.0+645950.8. However, the enhanced spatial resolution enabled by gravitational lensing tells a very different story; much of the star formation arises in two dozen clumps with sizes of r = 30-50 pc spread across the 7 kpc length of the galaxy. The color and spatial distribution of the diffuse component suggests that still-smaller clumps are unresolved. Despite this clumpy, messy morphology, the radial profile is still well-characterized by an exponential profile. In this lensed galaxy, stars are forming in complexes with sizes well below 100 pc; such sizes are wholly unexplored by surveys of galaxy evolution at .
We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe ...Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on dark-energy density, rho sub(DE)(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat LAMBDACDM universe, we find ohm sub(Lambda) = 0.729 + or - 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant dark-energy equation-of-state parameter w = -1.013 super(+0.068) sub(-0.073) (68% CL). Curvature is constrained to ~0.7% in the owCDM model and to 2% in a model in which dark energy is allowed to vary with parameters w sub(0) and w sub(a). Further tightening the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.
We report first results from an ongoing monitoring campaign to measure time delays between the six images of the quasar SDSS J2222+2745, gravitationally lensed by a galaxy cluster. The time delay ...between A and B, the two most highly magnified images, is measured to be tau sub(AB) - 47.7 + or - 6.0 days (95% confidence interval), consistent with previous model predictions for this lens system. The strong intrinsic variability of the quasar also allows us to derive a time delay value of tau sub(CA) = 722 + or - 24 days between image C and A, in spite of modest overlap between their light curves in the current data set. Image C, which is predicted to lead all the other lensed quasar images, has undergone a sharp, monotonic flux increase of 60%-75% during 2014. A corresponding brightening is firmly predicted to occur in images A and B during 2016. The amplitude of this rise indicates that time delays involving all six known images in this system, including those of the demagnified central images D-F, will be obtainable from further ground-based monitoring of this system during the next few years.
The second Red-sequence Cluster Survey (RCS-2) is a ~1000 deg2, multi-color imaging survey using the square-degree imager, MegaCam, on the Canada-France-Hawaii Telescope. It is designed to detect ...clusters of galaxies over the redshift range 0.1 z 1. The primary aim is to build a statistically complete, large (~104) sample of clusters, covering a sufficiently long redshift baseline to be able to place constraints on cosmological parameters via the evolution of the cluster mass function. Other main science goals include building a large sample of high surface brightness, strongly gravitationally lensed arcs associated with these clusters, and an unprecedented sample of several tens of thousands of galaxy clusters and groups, spanning a large range of halo mass, with which to study the properties and evolution of their member galaxies. This paper describes the design of the survey and the methodology for acquiring, reducing, and calibrating the data for the production of high-precision photometric catalogs. We describe the method for calibrating our griz imaging data using the colors of the stellar locus and overlapping Two Micron All Sky Survey photometry. This yields an absolute accuracy of <0.03 mag on any color and 0.05 mag in the r-band magnitude, verified with respect to the Sloan Digital Sky Survey (SDSS). Our astrometric calibration is accurate to 03 from comparison with SDSS positions. RCS-2 reaches average 5 Delta *s point-source limiting magnitudes of griz = 24.4, 24.3, 23.7, 22.8, approximately 1-2 mag deeper than the SDSS. Due to the queue-scheduled nature of the observations, the data are highly uniform and taken in excellent seeing, mostly FWHM 07 in the r band. In addition to the main science goals just described, these data form the basis for a number of other planned and ongoing projects (including the WiggleZ survey), making RCS-2 an important next-generation imaging survey.
ABSTRACT
We present spatially resolved Echelle spectroscopy of an intervening Mg ii–Fe ii–Mg i absorption-line system detected at zabs = 0.73379 towards the giant gravitational arc PSZ1 ...G311.65–18.48. The absorbing gas is associated with an inclined disc-like star-forming galaxy, whose major axis is aligned with the two arc-segments reported here. We probe in absorption the galaxy’s extended disc continuously, at ≈3 kpc sampling, from its inner region out to 15× the optical radius. We detect strong ($W_0^{2796}\gt 0.3$Å) coherent absorption along 13 independent positions at impact parameters D = 0–29 kpc on one side of the galaxy, and no absorption at D = 28–57 kpc on the opposite side (all de-lensed distances at zabs). We show that (1) the gas distribution is anisotropic; (2) $W_0^{2796}$, $W_0^{2600}$, $W_0^{2852}$, and the ratio $W_0^{2600}\!/W_0^{2796}$, all anticorrelate with D; (3) the $W_0^{2796}$–D relation is not cuspy and exhibits significantly less scatter than the quasar-absorber statistics; (4) the absorbing gas is co-rotating with the galaxy out to D ≲ 20 kpc, resembling a ‘flat’ rotation curve, but at D ≳ 20 kpc velocities decline below the expectations from a 3D disc-model extrapolated from the nebular O ii emission. These signatures constitute unambiguous evidence for rotating extra-planar diffuse gas, possibly also undergoing enriched accretion at its edge. Arguably, we are witnessing some of the long-sought processes of the baryon cycle in a single distant galaxy expected to be representative of such phenomena.
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