A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: The Group Catalog

With a large, unique spectroscopic survey in the fields of 28 galaxy-scale strong gravitational lenses, we identify groups of galaxies in the 26 adequately-sampled fields. Using a group finding algorithm, we find 210 groups with at least five member galaxies; the median number of members is eight. Our sample spans redshifts of 0.04 $\le z_{grp} \le$ 0.76 with a median of 0.31, including 174 groups with $0.1 < z_{grp} < 0.6$. Groups have radial velocity dispersions of 60 $\le \sigma_{grp} \le$ 1200 km s$^{-1}$ with a median of 350 km s$^{-1}$. We also discover a supergroup in field B0712+472 at $z =$ 0.29 consisting of three main groups. We recover groups similar to $\sim$ 85% of those previously reported in these fields within our redshift range of sensitivity and find 187 new groups with at least five members. The properties of our group catalog, specifically 1) the distribution of $\sigma_{grp}$, 2) the fraction of all sample galaxies that are group members, and 3) the fraction of groups with significant substructure, are consistent with those for other catalogs. The distribution of group virial masses agrees well with theoretical expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434, B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716, MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723) are members of groups with at least five galaxies, and one more (B0712+472) belongs to an additional, visually identified group candidate. There are groups not associated with the lens that still are likely to affect the lens model; in six of 25 (24%) fields (excluding the supergroup), there is at least one massive ($\sigma_{grp} \ge$ 500 km s$^{-1}$) group or group candidate projected within 2$^{\prime}$ of the lens.Comment: 87 pages, 8 figures, a version of this was published in Ap

A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: Implications for H0H_0

Strong gravitational lensing provides an independent measurement of the Hubble parameter ($H_0$). One remaining systematic is a bias from the additional mass due to a galaxy group at the lens redshift or along the sightline. We quantify this bias for more than 20 strong lenses that have well-sampled sightline mass distributions, focusing on the convergence $\kappa$ and shear $\gamma$. In 23% of these fields, a lens group contributes a $\ge$1% convergence bias; in 57%, there is a similarly significant line-of-sight group. For the nine time delay lens systems, $H_0$ is overestimated by 11$^{+3}_{-2}$% on average when groups are ignored. In 67% of fields with total $\kappa \ge$ 0.01, line-of-sight groups contribute $\gtrsim 2\times$ more convergence than do lens groups, indicating that the lens group is not the only important mass. Lens environment affects the ratio of four (quad) to two (double) image systems; all seven quads have lens groups while only three of 10 doubles do, and the highest convergences due to lens groups are in quads. We calibrate the $\gamma$-$\kappa$ relation: $\log(\kappa_{\rm{tot}}) = (1.94 \pm 0.34) \log(\gamma_{\rm{tot}}) + (1.31 \pm 0.49)$ with a rms scatter of 0.34 dex. Shear, which, unlike convergence, can be measured directly from lensed images, can be a poor predictor of $\kappa$; for 19% of our fields, $\kappa$ is $\gtrsim 2\gamma$. Thus, accurate cosmology using strong gravitational lenses requires precise measurement and correction for all significant structures in each lens field.Comment: 34 pages, 11 figures, accepted for publication in Ap

A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE

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 rest-frame equivalent width of EW0=21+-4 A and is extended with V_FWHM=360+90-70 km/s. The source is perhaps the brightest and most massive z~8 Lyman break galaxy in the full CANDELS and BoRG/HIPPIES surveys, having assembled already 10^(9.9+-0.2) M_sol of stars at only 650 Myr after the Big Bang. The spectroscopic redshift measurement sets a new redshift record for galaxies. This enables reliable constraints on the stellar mass, star-formation rate, formation epoch, as well as combined [OIII]+Hbeta line equivalent widths. The redshift confirms that the IRAC [4.5] photometry is very likely dominated by line emission with EW0(OIII+Hbeta)= 720-150+180 A. This detection thus adds to the evidence that extreme rest-frame optical emission lines are a ubiquitous feature of early galaxies promising very efficient spectroscopic follow-up in the future with infrared spectroscopy using JWST and, later, ELTs.Comment: 6 pages, 4 figures, small updates to match ApJL accepted versio

Spatially Extended Low Ionization Emission Regions (LIERs) at z∼0.9z\sim0.9

We present spatially resolved emission diagnostics for eight $z\sim0.9$ galaxies that demonstrate extended low ionization emission-line regions (LIERs) over kpc scales. Eight candidates are selected based on their spatial extent and emission line fluxes from slitless spectroscopic observations with the HST/WFC3 G141 and G800L grisms in the well-studied GOODS survey fields. Five of the candidates (62.5%) are matched to X-ray counterparts in the \textit{Chandra X-Ray Observatory} Deep Fields. We modify the traditional Baldwin-Philips-Terlevich (BPT) emission line diagnostic diagram to use [SII]/(H$\alpha$+[NII]) instead of [NII]/H$\alpha$ to overcome the blending of [NII] and H$\alpha$+[NII] in the low resolution slitless grism spectra. We construct emission line ratio maps and place the individual pixels in the modified BPT. The extended LINER-like emission present in all of our candidates, coupled with X-Ray properties consistent with star-forming galaxies and weak [OIII]$\lambda$5007\AA\ detections, is inconsistent with purely nuclear sources (LINERs) driven by active galactic nuclei. While recent ground-based integral field unit spectroscopic surveys have revealed significant evidence for diffuse LINER-like emission in galaxies within the local universe $(z\sim0.04)$, this work provides the first evidence for the non-AGN origin of LINER-like emission out to high redshifts.Comment: 11 pages, 1 table, 6 figures, accepted for publication in the Astrophysics Journal (ApJ

The Most Luminous z~9-10 Galaxy Candidates yet Found: The Luminosity Function, Cosmic Star-Formation Rate, and the First Mass Density Estimate at 500 Myr

[abridged] We present the discovery of four surprisingly bright (H_160 ~ 26 - 27 mag AB) galaxy candidates at z~9-10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z~10 galaxy candidates that are known, just ~500 Myr after the Big Bang. Two similarly bright sources are also detected in a systematic re-analysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5-6.2sigma in the very deep Spitzer/IRAC 4.5 micron data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z=10.2+-0.4) is robustly detected also at 3.6 micron (6.9sigma), revealing a flat UV spectral energy distribution with a slope beta=-2.0+-0.2, consistent with demonstrated trends with luminosity at high redshift. The abundance of such luminous candidates suggests that the luminosity function evolves more significantly in phi_* than in L_* at z>~8 with a higher number density of bright sources than previously expected. Despite the discovery of these luminous candidates, the cosmic star formation rate density for galaxies with SFR >0.7 M_sun/yr shows an order-of-magnitude increase in only 170 Myr from z ~ 10 to z ~ 8, consistent with previous results. Based on the IRAC detections, we derive galaxy stellar masses at z~10, finding that these luminous objects are typically 10^9 M_sun. The cosmic stellar mass density at z~10 is log10 rho_* = 4.7^+0.5_-0.8 M_sun Mpc^-3 for galaxies brighter than M_UV~-18. The remarkable brightness, and hence luminosity, of these z~9-10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature, demonstrates the value of additional search fields covering a wider area to understand star-formation in the very early universe, and highlights the opportunities for JWST to map the buildup of galaxies at redshifts much earlier than z~10.Comment: 20 pages, 12 figures, changed to match resubmitted version to Ap

A Spectroscopic Study of the Environments of Gravitational Lens Galaxies

(Abridged) We present the first results from our spectroscopic survey of the environments of strong gravitational lenses. The lens galaxy belongs to a poor group of galaxies in six of the eight systems in our sample. We discover three new groups associated with the lens galaxies of BRI 0952-0115 (five members), MG 1654+1346 (seven members), and B2114+022 (five members). We more than double the number of members for another three previously known groups around the lenses MG 0751+2716 (13 total members), PG 1115+080 (13 total members), and B1422+231 (16 total members). We determine the kinematics of the six groups, including their mean velocities, velocity dispersions, and projected spatial centroids. The velocity dispersions of the groups range from 110 +170, -80 to 470 +100, -90 km/s. In at least three of the lenses -- MG0751, PG1115, and B1422 -- the group environment significantly affects the lens potential. These lenses happen to be the quadruply-imaged ones in our sample, which suggests a connection between image configuration and environment. The lens galaxy is the brightest member in fewer than half of the groups. Our survey also allows us to assess for the first time whether mass structures along the line of sight are important for lensing. We first show that, in principle, the lens potential may be affected by line-of-sight structures over a wide range of spatial and redshift offsets from the lens. We then quantify real line-of-sight effects using our survey and find that at least four of the eight lens fields have substantial interloping structures close in projection to the lens, and at least one of those structures (in the field of MG0751) significantly affects the lens potential.Comment: Accepted for publication in the Astrophysical Journal. Figure 6 posted as a JPEG image. Requires emulateapj.st

A Tentative Detection of an Emission Line at 1.6 μm for the z ~ 12 Candidate UDFj-39546284

We present deep WFC3 grism observations of the candidate z \~{} 12 galaxy UDFj-39546284 in the Hubble Space Telescope (HST) Ultra Deep Field (UDF), by combining spectroscopic data from the 3D-HST and CANDELS surveys. The total exposure time is 40.5 ks and the spectrum covers 1.10 {\lt} {$λ$} {\lt} 1.65 {$μ$}m. We search for faint emission lines by cross-correlating the two-dimensional G141 spectrum with the observed H $_{160}$ morphology, a technique that is unique to slitless spectroscopy at HST resolution. We find a 2.7{$σ$} detection of an emission line at 1.599 {$μ$}m{\mdash}just redward of the JH $_{140}$ filter{\mdash}with flux 3.5 {\plusmn} 1.3 {\times} 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$. Assuming that the line is real, it contributes 110\% {\plusmn} 40\% of the observed H $_{160}$ flux and has an observed equivalent width {\gt}7300 Å. If the line is confirmed, it could be Ly{$α$} at z = 12.12. However, a more plausible interpretation, given current results, could be a lower redshift feature such as [O III]{$λ$}4959,5007 at z = 2.19. We find two other 3D-HST [O III] emitters within 1000 km s$^{-1}$ of that redshift in the GOODS-South field. Additional support for this interpretation comes from the discovery of a bright ''[O III] blob'' with a secure G141 grism redshift of z = 1.605. This object has a strikingly large observed equivalent width of nearly 9000 Å that results in similar ''dropout'' colors as UDFj-39546284. Based on observations made with the NASA/ESA Hubble Space Telescope, programs GO-12099, 12177, and 12547, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.Large scale structure and cosmolog

Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS

We determine the intrinsic, 3-dimensional shape distribution of star-forming galaxies at 0<z<2.5, as inferred from their observed projected axis ratios. In the present-day universe star-forming galaxies of all masses 1e9 - 1e11 Msol are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M* > 1e10 Msol) disks are the most common geometric shape at all z < 2. Lower-mass galaxies at z>1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 1e9 Msol (1e10 Msol) are a mix of roughly equal numbers of elongated and disk galaxies at z~1 (z~2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z~1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks.Comment: Published in ApJ Letter

Galaxy Merger Fractions in Two Clusters at Z ∼ 2 Using the Hubble Space Telescope

We measure the fraction of galaxy-galaxy mergers in two clusters at z ,F∼ ,F2 using imaging and grism observations from the Hubble Space Telescope. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the Spitzer Space Telescope, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high-resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the z ,F∼ ,F1.6 cluster (IRC0222A) and G141 for the z ,F∼ ,F2 cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of in IRC0222A and in IRC0222B. In comparison, we measure a merger fraction of for field galaxies at z ,F∼ ,F2. Our study indicates that the galaxy-galaxy merger fraction in clusters at z ,F∼ ,F2 is enhanced compared to the field population, but note that more cluster measurements at this epoch are needed to confirm our findings

The Effect of Environment on Shear in Strong Gravitational Lenses

Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of gamma = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six 4-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is gamma = 0.05 (ranging from 0.01 to 0.14), indicating that line-of-sight contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the line of sight, particularly those bright (I < 21.5) galaxies projected within 5' of the lens.Comment: Accepted for publication in The Astrophysical Journal; 28 pages, 9 figures, 5 table