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The Nancy Grace Roman Space Telescope is capable of delivering an unprecedented all-sky, high-spatial resolution, multi-epoch infrared map to the astronomical community. This opportunity arises in the midst of numerous ground- and space-based surveys that will provide extensive spectroscopy and imaging together covering the entire sky (such as Rubin/LSST, Euclid, UNIONS, SPHEREx, DESI, SDSS-V, GALAH, 4MOST, WEAVE, MOONS, PFS, UVEX, NEO Surveyor, etc.). Roman can uniquely provide uniform high-spatial-resolution (~0.1 arcsec) imaging over the entire sky, vastly expanding the science reach and precision of all of these near-term and future surveys. This imaging will not only enhance other surveys, but also facilitate completely new science. By imaging the full sky over two epochs, Roman can measure the proper motions for stars across the entire Milky Way, probing 100 times fainter than Gaia out to the very edge of the Galaxy. Here, we propose NANCY: a completely public, all-sky survey that will create a high-value legacy dataset benefiting innumerable ongoing and forthcoming studies of the universe. NANCY is a pure expression of Roman's potential: it images the entire sky, at high spatial resolution, in a broad infrared bandpass that collects as many photons as possible. The majority of all ongoing astronomical surveys would benefit from incorporating observations of NANCY into their analyses, whether these surveys focus on nearby stars, the Milky Way, near-field cosmology, or the broader universe., Comment: Submitted to the call for white papers for the Roman Core Community Survey (June 16th, 2023), and to the Bulletin of the AAS

A key obstacle to developing a satisfying theory of galaxy evolution is the difficulty in extending analytic descriptions of early structure formation into full nonlinearity, the regime in which galaxy growth occurs. Extant techniques, though powerful, are based on approximate numerical methods whose Monte Carlo-like nature hinders intuition building. Here, we develop a new solution to this problem and its empirical validation. We first derive closed-form analytic expectations for the evolution of fixed percentiles in the real-space cosmic density distribution, {\it averaged over representative volumes observers can track cross-sectionally\}. Using the Lagrangian forms of the fluid equations, we show that percentiles in $\delta$---the density relative to the median---should grow as $\delta(t)\propto\delta_{0}^{\alpha}\,t^{\beta}$, where $\alpha\equiv2$ and $\beta\equiv2$ for Newtonian gravity at epochs after the overdensities transitioned to nonlinear growth. We then use 9.5 sq. deg. of Carnegie-Spitzer-IMACS Redshift Survey data to map {\it galaxy\} environmental densities over $0.2

The FourStar galaxy evolution survey (ZFOURGE) is a 45 night legacy program with the FourStar near-infrared camera on Magellan and one of the most sensitive surveys to date. ZFOURGE covers a total of $400\ \mathrm{arcmin}^2$ in cosmic fields CDFS, COSMOS and UDS, overlapping CANDELS. We present photometric catalogs comprising $>70,000$ galaxies, selected from ultradeep $K_s$-band detection images ($25.5-26.5$ AB mag, $5\sigma$, total), and $>80\%$ complete to $K_s<25.3-25.9$ AB. We use 5 near-IR medium-bandwidth filters ($J_1,J_2,J_3,H_s,H_l$) as well as broad-band $K_s$ at $1.05\ - 2.16\ \mu m$ to $25-26$ AB at a seeing of $\sim0.5$". Each field has ancillary imaging in $26-40$ filters at $0.3-8\ \mu m$. We derive photometric redshifts and stellar population properties. Comparing with spectroscopic redshifts indicates a photometric redshift uncertainty $\sigma_z={0.010,0.009}$, and 0.011 in CDFS, COSMOS, and UDS. As spectroscopic samples are often biased towards bright and blue sources, we also inspect the photometric redshift differences between close pairs of galaxies, finding $\sigma_{z,pairs}= 0.01-0.02$ at $1\times15$., Comment: 39 pages, 35 figures, accepted for publication in ApJ, full data release available at http://zfourge.tamu.edu/

We present coarse but robust star formation histories (SFHs) derived from spectro-photometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494 galaxies at 0.3

We build a set of composite galaxy SEDs by de-redshifting and scaling multi-wavelength photometry from galaxies in the ZFOURGE survey, covering the CDFS, COSMOS, and UDS fields. From a sample of ~4000 K_s-band selected galaxies, we define 38 composite galaxy SEDs that yield continuous low-resolution spectra (R~45) over the rest-frame range 0.1-4 um. Additionally, we include far infrared photometry from the Spitzer Space Telescope and the Herschel Space Observatory to characterize the infrared properties of our diverse set of composite SEDs. From these composite SEDs we analyze the rest-frame UVJ colors, as well as the ratio of IR to UV light (IRX) and the UV slope ($\beta$) in the IRX$-\beta$ dust relation at 1

Since z~1, the stellar mass density locked in low mass groups and clusters has grown by a factor of ~8. Here we make the first statistical measurements of the stellar mass content of low mass X-ray groups at 0.5

Our understanding of the redshift $z>3$ galaxy population relies largely on samples selected using the popular "dropout" technique, typically consisting of UV-bright galaxies with blue colors and prominent Lyman breaks. As it is currently unknown if these galaxies are representative of the massive galaxy population, we here use the FourStar Galaxy Evolution (ZFOURGE) Survey to create a stellar mass-limited sample at $z=3-4$. Uniquely, ZFOURGE uses deep near-infrared medium-bandwidth filters to derive accurate photometric redshifts and stellar population properties. The mass-complete sample consists of 57 galaxies with log M $>10.6$, reaching below $M^{\star}$ at $z=3-4$. On average, the massive $z=3-4$ galaxies are extremely faint in the observed optical with median $R_{tot}^{AB}=27.48\pm0.41$ (restframe $M_{1700}=-18.05\pm0.37$). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about $\sim100\times$ fainter at the same mass. The massive galaxies are red ($R-Ks_{AB}=3.9\pm0.2$; restframe UV-slope $\beta=-0.2\pm0.3$) likely from dust or old stellar ages. We classify the galaxy SEDs by their restframe $U-V$ and $V-J$ colors and find a diverse population: $46^{+6+10}_{-6-17}$% of the massive galaxies are quiescent, $54^{+8+17}_{-8-10}$% are dusty star-forming galaxies, and only $14^{+3+10}_{-3-4}$% resemble luminous blue star forming Lyman break galaxies. This study clearly demonstrates an inherent diversity among massive galaxies at higher redshift than previously known. Furthermore,we uncover a reservoir of dusty star-forming galaxies with $4\times$ lower specific star-formation rates compared to submillimeter-selected starbursts at $z>3$. With $5\times$ higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts., Comment: Accepted for publication in ApJ Letters. See http://zfourge.tamu.edu for more details about ZFOURGE

We describe the Carnegie-Spitzer-IMACS (CSI) Survey, a wide-field, near-IR selected spectrophotometric redshift survey with IMACS on Magellan-Baade. CSI uses a flux-limited sample of galaxies in Spitzer IRAC 3.6micron imaging of SWIRE fields to efficiently trace the stellar mass of average galaxies to z~1.5. This paper provides an overview of the survey selection, observations, and processing of the photometry and spectrophotometry. We also describe the analysis of the data: new methods of fitting synthetic SEDs are used to derive redshifts, stellar masses, emission line luminosities, and coarse information on recent star-formation. Our unique methodology for analyzing low-dispersion spectra taken with multilayer prisms in IMACS, combined with panchromatic photometry from the ultraviolet to the IR, has yielded high quality redshifts for 43,347 galaxies in our first 5.3 sq. degs of the SWIRE XMM-LSS field. A new approach to assessing data quality is also described, and three different approaches are used to estimate our redshift errors, with robust agreement. Over the full range of 3.6micron fluxes of our selection, we find typical redshift uncertainties of sigma_z/(1+z) < 0.015. In comparisons with previously published spectroscopic redshifts we find scatters of sigma_z/(1+z) = 0.011 for galaxies at 0.7< z< 0.9, and sigma_z/(1+z) = 0.014 for galaxies at 0.9< z< 1.2. For galaxies brighter and fainter than i=23 mag, we find sigma_z/(1+z) = 0.008 and sigma_z/(1+z) = 0.022, respectively. Notably, our low-dispersion spectroscopy and analysis yields comparable redshift uncertainties and success rates for both red and blue galaxies, largely eliminating color-based systematics that can seriously bias observed dependencies of galaxy evolution on environment., Comment: Accepted for publication in the Astrophysical Journal; 27 pages and 25 figures. This version has so much additional content that it supercedes arXiv:1201.0783

We report the likely identification of a substantial population of massive M~10^11M_Sun galaxies at z~4 with suppressed star formation rates (SFRs), selected on rest-frame optical to near-IR colors from the FourStar Galaxy Evolution Survey. The observed spectral energy distributions show pronounced breaks, sampled by a set of near-IR medium-bandwidth filters, resulting in tightly constrained photometric redshifts. Fitting stellar population models suggests large Balmer/4000AA breaks, relatively old stellar populations, large stellar masses and low SFRs, with a median specific SFR of 2.9+/-1.8 x 10^-11/yr. Ultradeep Herschel/PACS 100micron, 160micron and Spitzer/MIPS 24micron data reveal no dust-obscured SFR activity for 15/19 (79%) galaxies. Two far-IR detected galaxies are obscured QSOs. Stacking the far-IR undetected galaxies yields no detection, consistent with the SED fit, indicating independently that the average specific SFR is at least 10x smaller than of typical star-forming galaxies at z~4. Assuming all far-IR undetected galaxies are indeed quiescent, the volume density is 1.8+/-0.7 x 10^-5Mpc^-3 to a limit of log10M/M_Sun>10.6, which is 10x and 80x lower than at z = 2 and z = 0.1. They comprise a remarkably high fraction (~35%) of z~4 massive galaxies, suggesting that suppression of star formation was efficient even at very high redshift. Given the average stellar age of 0.8Gyr and stellar mass of 0.8x10^11M_Sun, the galaxies likely started forming stars before z =5, with SFRs well in excess of 100M_Sun/yr, far exceeding that of similarly abundant UV-bright galaxies at z>4. This suggests that most of the star-formation in the progenitors of quiescent z~4 galaxies was obscured by dust., Comment: 8 pages, 4 figures, 1 table, accepted by ApjL

(abridged) DYNAMO is a multi-wavelength, spatially-resolved survey of local ($z \sim 0.1$) star-forming galaxies designed to study evolution through comparison with samples at z~2. Half of the sample has integrated H-alpha luminosities of >$10^{42}$ erg/s, the typical lower limit for resolved spectroscopy at z~2. The sample covers a range in stellar mass ($10^9$-$10^{11}$ Msun) and star-formation rate (0.2-100 Msun/yr). In this first paper of a series, we present integral-field spectroscopy of H-alpha emission for the sample of 67 galaxies. We infer gas fractions in our sample as high as ~0.8, higher than typical for local galaxies. Gas fraction correlates with stellar mass in galaxies with star-formation rates below 10 Msun/yr, as found by COLDGASS, but galaxies with higher star-formation rates have higher than expected gas fractions. There is only a weak correlation, if any, between gas fraction and gas velocity dispersion. Galaxies in the sample visually classified as disc-like are offset from the local stellar-mass Tully-Fisher relation to higher circular velocities, but this offset vanishes when both gas and stars are included in the baryonic Tully-Fisher relation. The mean gas velocity dispersion of the sample is ~50 km/s, and V/sigma ranges from 2 to 10 for most of the discs, similar to 'turbulent' galaxies at high redshift. Half of our sample show disc-like rotation, while ~20 percent show no signs of rotation. The division between rotating and non-rotating is approximately..., Comment: 28 pages, 14 figures. Additional supplementary figure will be available from the Journal website. Accepted for publication in MNRAS

Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function at 0.5 < z < 2.5. ZFOURGE provides well-constrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2um . We combine this with HST imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS), allowing for the efficient selection of both blue and red galaxies down to stellar masses ~10^9.5 Msol at z ~ 2.5. The total surveyed area is 316 arcmin^2 distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey (NMBS) to provide stronger constraints at high masses. Several studies at z<=1 have revealed a steepening of the slope at the low-mass end of the stellar mass function (SMF), leading to an upturn at masses <10^10 Msol that is not well-described by a standard single-Schechter function. We find evidence that this feature extends to at least z ~ 2, and that it can be found in both the star-forming and quiescent populations individually. The characteristic mass (M*) and slope at the lowest masses (alpha) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/Msol) ~ 10.65 and ~-1.5 respectively. The SMF of star-forming galaxies has evolved primarily in normalization, while the change in shape is relatively minor. This is not the case for quiescent galaxies: the depth of our imaging allows us to show for the first time significantly more evolution at Log(M/Msol) < 10.5 than at higher masses. We find that the total mass density (down to 10^9 Msol) in star-forming galaxies has increased by a factor of ~2.2 since z ~ 2.5, whereas in quiescent galaxies it has increased by a factor of ~12 ., Comment: 17 pages, 13 figures. Accepted for publication in the ApJ

We present a multi-wavelength photometric study of ~15,000 resolved stars in the nearby spiral galaxy M83 (NGC5236, D=4.61Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83, and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction towards each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected., Comment: 28 pages, 17 figures, 2 tables. Accepted for publication in ApJ

We present the first measurement of the evolution of the galaxy group stellar mass function (GrSMF) to redshift z>~1 and low masses (M*>10^12 Msun). Our results are based on early data from the Carnegie-Spitzer-IMACS (CSI) Survey, utilizing low-resolution spectra and broadband optical/near-IR photometry to measure redshifts for a 3.6um selected sample of 37,000 galaxies over a 5.3 deg^2 area to z~1.2. Employing a standard friends-of-friends algorithm for all galaxies more massive than log(M*/Msun)=10.5, we find a total of ~4000 groups. Correcting for spectroscopic incompleteness (including slit collisions), we build cumulative stellar mass functions for these groups in redshift bins at z>0.35, comparing to the z=0 and z>0 mass functions from various group and cluster samples. Our derived mass functions match up well with z>0.35 X-ray selected clusters, and strong evolution is evident at all masses over the past 8 Gyr. Given the already low level of star formation activity in galaxies at these masses, we therefore attribute most of the observed growth in the GrSMF to group-group and group-galaxy mergers, in accordance with qualitative notions of hierarchical structure formation. Given the factor 3-10 increase in the number density of groups and clusters with M*>10^12 Msun since z=1 and the strong anticorrelation between star formation activity and environmental density, this late-time growth in group-sized halos may therefore be an important contributor to the structural and star-formation evolution of massive galaxies over the past 8 Gyr., Comment: 6 pages, 3 figures, submitted to ApJL. This paper is based on the Carnegie-Spitzer-IMACS (CSI) Survey, described in more detail at http://csi.obs.carnegiescience.edu

We describe the Carnegie-Spitzer-IMACS (CSI) Survey, a wide-field, near-IR selected spectrophotometric redshift survey with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on Magellan-Baade. By defining a flux-limited sample of galaxies in Spitzer 3.6micron imaging of SWIRE fields, the CSI Survey efficiently traces the stellar mass of average galaxies to z~1.5. This first paper provides an overview of the survey selection, observations, processing of the photometry and spectrophotometry. We also describe the processing of the data: new methods of fitting synthetic templates of spectral energy distributions are used to derive redshifts, stellar masses, emission line luminosities, and coarse information on recent star-formation. Our unique methodology for analyzing low-dispersion spectra taken with multilayer prisms in IMACS, combined with panchromatic photometry from the ultraviolet to the IR, has yielded 37,000 high quality redshifts in our first 5.3 sq.degs of the SWIRE XMM-LSS field. We use three different approaches to estimate our redshift errors and find robust agreement. Over the full range of 3.6micron fluxes of our selection, we find typical uncertainties of sigma_z/(1+z) < 0.015. In comparisons with previously published VVDS redshifts, for example, we find a scatter of sigma_z/(1+z) = 0.012 for galaxies at 0.8< z< 1.2. For galaxies brighter and fainter than i=23 mag, we find sigma_z/(1+z) = 0.009 and sigma_z/(1+z) = 0.025, respectively. Notably, our low-dispersion spectroscopy and analysis yields comparable redshift uncertainties and success rates for both red and blue galaxies, largely eliminating color-based systematics that can seriously bias observed dependencies of galaxy evolution on environment., Comment: Submitted to the Astrophysical Journal; 19 pages and 14 figures

We report the first results from the Z-FOURGE survey: the discovery of a candidate galaxy cluster at z = 2.2 consisting of two compact overdensities with red galaxies detected at >20{\sigma} above the mean surface density. The discovery was made possible by a new deep (Ks < 24.8 AB 5{\sigma}) Magellan/FourStar near-IR imaging survey with 5 custom medium-bandwidth filters. The filters pinpoint the location of the Balmer/4000\AA\ break in evolved stellar populations at 1.5 < z < 3.5, yielding significantly more accurate photometric redshifts than possible with broadband imaging alone. The overdensities are within 1' of each other in the COSMOS field and appear to be embedded in a larger structure that contains at least one additional overdensity (\sim10{\sigma}). Considering the global properties of the overdensities, the z = 2.2 system appears to be the most distant example of a galaxy cluster with a population of red galaxies. A comparison to a large {\Lambda}CDM simulation suggests that the system may consist of merging subclusters, with properties in between those of z > 2 protoclusters with more diffuse distributions of blue galaxies and the lower-redshift galaxy clusters with prominent red sequences. The structure is completely absent in public optical catalogs in COSMOS and only weakly visible in a shallower near-IR survey. The discovery showcases the potential of deep near-IR surveys with medium-band filters to advance the understanding of environment and galaxy evolution at z > 1.5., Comment: final version accepted by ApJL, see http://z-fourge.strw.leidenuniv.nl for more details

We present an analysis of the size growth seen in early-type galaxies over 10 Gyr of cosmic time. Our analysis is based on a homogeneous synthesis of published data from 17 spectroscopic surveys observed at similar spatial resolution, augmented by new measurements for galaxies in the Gemini Deep Deep Survey. In total, our sample contains structural data for 465 galaxies (mainly early-type) in the redshift range 0.2

Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136., Comment: 15 pages, 12 figures. Accepted for publication in The Astrophysical Journal

This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at $z\sim1.5-8$, and to study Type Ia SNe beyond $z>1.5$. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of \sim800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper., Comment: 39 pages, 25 figures

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z>1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8. The survey covers approximately 800 arcmin^2 and is divided into two parts. The CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125 arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (EGS, COSMOS, and UDS) and covers the full area to a 5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper., Comment: Submitted to Astrophysical Journal Supplement Series; Revised version, subsequent to referee report

We use new WFC3 observations of the nearby grand design spiral galaxy M83 to develop two independent methods for estimating the ages of young star clusters. The first method uses the physical extent and morphology of Halpha emission to estimate the ages of clusters younger than tau ~10 Myr. It is based on the simple premise that the gas in very young (tau < few Myr) clusters is largely coincident with the cluster stars, is in a small, ring-like structure surrounding the stars in slightly older clusters (e.g., tau ~5 Myr), and is in a larger ring-like bubble for still older clusters (i.e., ~5-10 Myr). The second method is based on an observed relation between pixel-to-pixel flux variations within clusters and their ages. This method relies on the fact that the brightest individual stars in a cluster are most prominent at ages around 10 Myr, and fall below the detection limit (i.e., M_V < -3.5) for ages older than about 100 Myr. These two methods are the basis for a new morphological classification system which can be used to estimate the ages of star clusters based on their appearance. We compare previous age estimates of clusters in M83 determined from fitting UBVI Halpha measurements using predictions from stellar evolutionary models with our new morphological categories and find good agreement at the ~95% level. The scatter within categories is ~0.1 dex in log tau for young clusters (<10 Myr) and ~0.5 dex for older (>10 Myr) clusters. A by-product of this study is the identification of 22 "single-star" HII regions in M83, with central stars having ages ~4 Myr., Comment: 33 pages, 10 figures, 3 tables; published in March ApJ

We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 \degA)/H{\beta} vs. [S II](6716 \deg A+6731 \deg A)/H{\alpha} with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (0.2" x 0.2") basis and compare it with several photo- and shock-ionization models. For the photo-ionized gas, we observe a gradual increase of the log([O III]/H{\beta}) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photo-ionized from the shock-ionized component of the gas. We find that the shock-ionized H{\alpha} emission ranges from ~2% to about 15-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is an horizontal distribution around log([O III]/H{\beta}) ~ 0. This feature is well fit by a shock-ionization model with 2.0 Z\odot metallicity and shock velocities in the range of 250 km/s to 350 km/s. A low velocity shock component, < 200 km/s, is also detected, and is spatially located at the boundary between the outer ring and the spiral arm. The low velocity shock component can be due to : 1) supernova remnants located nearby, 2) dynamical interaction between the outer ring and the spiral arm, 3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83., Comment: Accepted for publication in ApJ. aastex preprint 12pt, 21 pages, 13 figures

We use near-infrared data obtained with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through use of a combination of narrow and medium band filters spanning the J and H bands, and which are particularly sensitive to the presence of the 1.3-1.5{\mu}m H2O molecular band - unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and for BDs. This photometric method provides effective temperatures for BDs to an accuracy of {\pm}350K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperature between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered towards the luminous core of NGC 3603. However, if these are located at the distance of the cluster, they are far too luminous to be normal BDs. We argue that it is unlikely that these objects are either artifacts of our dataset, normal field BDs/M-type giants or extra-galactic contaminants and, therefore, might represent a new class of stars having the effective temperatures of BDs but with luminosities of more massive stars. We explore the interesting scenario in which these objects would be normal stars that have recently tidally ingested a Hot Jupiter, the remnants of which are providing a short-lived extended photosphere to the central star. In this case, we would expect them to show the signature of fast rotation., Comment: 26 Pages, 8 Figures, Accepted for publication on ApJ

In this paper we present the coordinates of 67 55' x 55' patches of sky which have the rare combination of both high stellar surface density (>0.5 arcmin^{-2} with 13

(Abridged) We present a spatially-resolved near-UV/optical study of NGC 4150, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. Previous studies of this early-type galaxy (ETG) indicate that it has a large reservoir of molecular gas, exhibits a kinematically decoupled core (likely indication of recent merging) and strong, central H_B absorption (indicative of young stars). The core of NGC 4150 shows ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of near-UV/optical colours that are similar to those of nearby E+A (post-starburst) galaxies. We parametrise the properties of the recent star formation (age, mass fraction, metallicity and internal dust content) in the NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar models. The typical age of the recent star formation (RSF) is around 0.9 Gyrs, consistent with the similarity of the near-UV colours to post-starburst systems, while the morphological structure of the young component supports the proposed merger scenario. The RSF metallicity, representative of the metallicity of the gas fuelling star formation, is around 0.3 - 0.5 Zsun. Assuming that this galaxy is a merger and that the gas is sourced mainly from the infalling companion, these metallicities plausibly indicate the gas-phase metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM relation suggests (crudely) that the mass of the accreted system is around 3x10^8 Msun, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF mass fractions indicates that the RSF contributes about 2-3 percent of the stellar mass. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of ETGs at late epochs., Comment: 28 pages, 2 tables, accepted for publication in ApJ

We report the first results from the Hubble Infrared Pure Parallel Imaging Extragalactic Survey, which utilizes the pure parallel orbits of the Hubble Space Telescope to do deep imaging along a large number of random sightlines. To date, our analysis includes 26 widely separated fields observed by the Wide Field Camera 3, which amounts to 122.8 sq.arcmin in total area. We have found three bright Y098-dropouts, which are candidate galaxies at z >~ 7.4. One of these objects shows an indication of peculiar variability and its nature is uncertain. The other two objects are among the brightest candidate galaxies at these redshifts known to date L>2L*. Such very luminous objects could be the progenitors of the high-mass Lyman break galaxis (LBGs) observed at lower redshifts (up to z~5). While our sample is still limited in size, it is much less subject to the uncertainty caused by "cosmic variance" than other samples because it is derived using fields along many random sightlines. We find that the existence of the brightest candidate at z~7.4 is not well explained by the current luminosity function (LF) estimates at z~8. However, its inferred surface density could be explained by the prediction from the LFs at z~7 if it belongs to the high-redshift tail of the galaxy population at z~7., Comment: ApJL in press (accepted Dec. 27, 2010); minor corrections and one figure added to address referee's comments

High spatial and spectral resolution observations of star formation and kinematics in early galaxies have shown that two-thirds are massive rotating disk galaxies with the remainder being less massive non-rotating objects. The line of sight averaged velocity dispersions are typically five times higher than in today's disk galaxies. This has suggested that gravitationally-unstable, gas-rich disks in the early Universe are fuelled by cold, dense accreting gas flowing along cosmic filaments and penetrating hot galactic gas halos. However these accreting flows have not been observed, and cosmic accretion cannot power the observed level of turbulence. Here we report on a new sample of rare high-velocity-dispersion disk galaxies we have discovered in the nearby Universe where cold accretion is unlikely to drive their high star-formation rates. We find that the velocity dispersion is most fundamentally correlated with their star-formation rates, and not their mass nor gas fraction, which leads to a new picture where star formation itself is the energetic driver of galaxy disk turbulence at all cosmic epochs., Comment: 9 pages, 2 figures, Supplimentary Info available at: http://pulsar.swin.edu.au/~agreen/nature/sigma_mean_arXiv.pdf. Accepted for publication in Nature

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts., Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figures

Early release science observations of the cluster NGC3603 with the WFC3 on the refurbished HST allow us to study its recent star formation history. Our analysis focuses on stars with Halpha excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Halpha excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate., Comment: 10 pages, 8 figures, accepted for publication in The Astrophysical Journal

We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early Release Science (ERS) observations in the Great Observatories Origins Deep Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter. Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50 square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and 0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma}) for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies. In this paper, we describe: a) the scientific rationale, and the data taking plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the procedure of generating object catalogs across the 10 different ERS filters, and the specific star-galaxy separation techniques used; and c) the reliability and completeness of the object catalogs from the WFC3 ERS mosaics. The excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26 mag from the UV to the near-IR, respectively., Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.26

We present infrared, optical, and X-ray data of 48 X-ray bright, optically dull AGNs in the COSMOS field. These objects exhibit the X-ray luminosity of an active galactic nucleus (AGN) but lack broad and narrow emission lines in their optical spectrum. We show that despite the lack of optical emission lines, most of these optically dull AGNs are not well-described by a typical passive red galaxy spectrum: instead they exhibit weak but significant blue emission like an unobscured AGN. Photometric observations over several years additionally show significant variability in the blue emission of four optically dull AGNs. The nature of the blue and infrared emission suggest that the optically inactive appearance of these AGNs cannot be caused by obscuration intrinsic to the AGNs. Instead, up to ~70% of optically dull AGNs are diluted by their hosts, with bright or simply edge-on hosts lying preferentially within the spectroscopic aperture. The remaining ~30% of optically dull AGNs have anomalously high f_x/f_o ratios and are intrinsically weak, not obscured, in the optical. These optically dull AGNs are best described as a weakly accreting AGN with a truncated accretion disk from a radiatively inefficient accretion flow., Comment: 12 pages, 10 figures. Accepted for publication in the ApJ

We present black hole masses and accretion rates for 182 Type 1 AGN in COSMOS. We estimate masses using the scaling relations for the broad Hb, MgII, and CIV emission lines in the redshift ranges 0.16

We present optical spectroscopy for an X-ray and optical flux-limited sample of 677 XMM-Newton selected targets covering the 2 deg^2 COSMOS field, with a yield of 485 high-confidence redshifts. The majority of the spectra were obtained over three seasons (2005-2007) with the IMACS instrument on the Magellan (Baade) telescope. We also include in the sample previously published Sloan Digital Sky Survey spectra and supplemental observations with MMT/Hectospec. We detail the observations and classification analyses. The survey is 90% complete to flux limits of f_{0.5-10 keV}>8 x 10^-16 erg cm^-2 s^-1 and i_AB+<22, where over 90% of targets have high-confidence redshifts. Making simple corrections for incompleteness due to redshift and spectral type allows for a description of the complete population to $i_AB+<23. The corrected sample includes 57% broad emission line (Type 1, unobscured) AGN at 0.133 x 10^42 erg s^-1) to z<1, of both optically obscured and unobscured types. We find statistically significant evidence that the obscured to unobscured AGN ratio at z<1 increases with redshift and decreases with luminosity., Comment: Accepted for publication in the ApJ. 31 pages, 17 figures. Table 2 is available on request

We report the discovery of a giant Lya emitter (LAE) with a Spitzer/IRAC counterpart near the reionization epoch at z=6.595. The giant LAE is found from the extensive 1 deg^2 Subaru narrow-band survey for z=6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrow-band object with L(Lya) = 3.9+/-0.2 x 10^43 erg/s in our survey volume of 10^6 Mpc^3, but also a spatially extended Lya nebula with the largest isophotal area whose major axis is at least ~3''. This object is more likely to be a large Lya nebula with a size of >~17 kpc than to be a strongly-lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is v(FWHM)=251+/-21 km/s, and that the line-center velocity changes by ~60 km/s in a 10-kpc range. The stellar mass and star-formation rate are estimated to be 0.9-5.0 x 10^10 Mo and >34 Mo/yr, respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of inter-galactic medium., Comment: 13 pages, 9 figures, 2 tables. ApJ, in press

The FourStar infrared camera is a 1.0-2.5 micron (JHKs) near infrared camera for the Magellan Baade 6.5m telescope at Las Campanas Observatory (Chile). It is being built by Carnegie Observatories and the Instrument Development Group at Johns Hopkins and is scheduled for completion in 2009. The instrument uses four Teledyne HAWAII-2RG arrays that produce a 10.9 x 10.9 arcmin field of view. The outstanding seeing at the Las Campanas site coupled with FourStar's high sensitivity and large field of view will enable many new survey and targeted science programs., Comment: 10 pages, 10 figures. To appear in to appear in "Ground-based and Airborne Instrumentation for Astronomy II" SPIE conference Proc. 7014, Marseille, 23-28 June 2008

We present the results of NICMOS imaging of a sample of 16 high mass passively evolving galaxies with 1.31 Gyr. Our rest-frame R-band images show that most of these objects have compact regular morphologies which follow the classical R^1/4 law. These galaxies scatter along a tight sequence in the Kormendy relation. Around one-third of the massive red objects are extraordinarily compact, with effective radii under one kiloparsec. Our NICMOS observations allow the detection of such systems more robustly than is possible with optical (rest-frame UV) data, and while similar systems have been seen at z>2, this is the first time such systems have been detected in a rest-frame optical survey at 1.3, Comment: Accepted version (to appear in ApJ)

We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z \~ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range., Comment: 31 pages, 18 figures (6 pages with 4 figures added to appendix), Accepted by Astrophysical Journal

We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place., Comment: 4 pages, 2 figures, Invited talk at IAU Symposium 235, Prague, August 2006

We present spectroscopic redshifts for the first 466 X-ray and radio-selected AGN targets in the 2 deg^2 COSMOS field. Spectra were obtained with the IMACS instrument on the Magellan (Baade) telescope, using the nod-and-shuffle technique. We identify a variety of Type 1 and Type 2 AGN, as well as red galaxies with no emission lines. Our redshift yield is 72% down to i_AB=24, although the yield is >90% for i_AB<22. We expect the completeness to increase as the survey continues. When our survey is complete and additional redshifts from the zCOSMOS project are included, we anticipate ~1100 AGN with redshifts over the entire COSMOS field. Our redshift survey is consistent with an obscured AGN population that peaks at z~0.7, although further work is necessary to disentangle the selection effects., Comment: 19 pages, 14 figures. Accepted to ApJS special COSMOS issue. The full electronic version of Table 2 can be found at http://shaihulud.as.arizona.edu/~jtrump/tab2.txt

We describe preliminary results from an ultra-sensitive, spectroscopic emission-line survey and illustrate the challenges inherent in identifying high-redshift LyA emitters. Our multi-slit windows technique complements other types of emission-line surveys. Narrowband imaging surveys cover large areas of sky but only detect much brighter objects. Longslit spectra taken along cluster caustics yield intrinsically fainter lensed LyA emitters but probe small volumes of space. We have observed the COSMOS deep field and a field at 15h +00. To a line flux of a few times 10^-18 erg/s/cm^2, we found 150 emission-line sources (with no detectable continuum) among 4 masks. These candidates are being re-observed with broad spectral coverage to determine the line identity. To date, the interloper to LyA ratio is about 8:1. The sky positions of the LyA candidates generally do not coincide with those of foreground objects in ultra-deep r band or i' images -- consistent with the presence of a strong Lyman break., Comment: To appear in proceedings of UC Irvine May 2005 workshop on "First Light & Reionization", eds. E. Barton & A. Cooray, New Astronomy Reviews, in press. New version contains typo corrections

We present spectroscopic evidence from the Gemini Deep Deep Survey (GDDS) for a significant population of color-selected red galaxies at 1.3 < z < 2.2 whose integrated light is dominated by evolved stars. Unlike radio-selected objects, the z > 1.5 old galaxies have a sky density > 0.1 per sq. arcmin. Conservative age estimates for 20 galaxies with z > 1.3; = 1.49, give a median age of 1.2 Gyr and = 2.4. One quarter of the galaxies have inferred z_f > 4. Models restricted to abundances less than or equal to solar give median ages and z_f of 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute approximately 50% of the stellar mass density at 1 < z < 2. The derived ages and most probable star formation histories suggest a high star-formation-rate (300-500 solar masses per year) phase in the progenitor population. We argue that most of the red galaxies are not descendants of the typical z=3 Lyman break galaxies. Galaxies associated with luminous sub-mm sources have the requisite star formation rates to be the progenitor population. Our results point toward early and rapid formation for a significant fraction of present day massive galaxies., Comment: 12 pages, 2 figures, 1 table, Accepted for publication, ApJ Letters

The Gemini Deep Deep Survey (GDDS) is an ultra-deep (K<20.6 mag, I<24.5 mag) redshift survey targeting galaxies in the "redshift desert" between 1

We report spectroscopic detection of three z~6 Lyman-alpha emitting galaxies, in the vicinity of the Hubble Ultra Deep Field, from the early data of the Gemini Lyman-$\alpha$ at Reionisation Era (GLARE) project. Two objects, GLARE#3001 (z =5.79) and GLARE#3011 (z =5.94), are new detections and are fainter in $z'$ (z'_{AB} =26.37 and 27.15) than any Lyman break galaxy previously detected in Lyman-alpha. A third object, GLARE#1042 (z =5.83) has previously been detected in line emission from the ground; we report here a new spectroscopic continuum detection. Gemini/GMOS-S spectra of these objects, obtained using nod & shuffle, are presented together with a discussion of their photometric properties. All three objects were selected for spectroscopy via the i-drop Lyman Break technique, the two new detections from the GOODS v1.0 imaging data. The red i'-z' colors and high equivalent widths of these objects suggest a high-confidence z>5 Lyman-alpha identification of the emission lines. This brings the total number of known z>5 galaxies within 9 arcmin of the Hubble Ultra Deep Field to four, of which three are at the same redshift (z=5.8 within 2000 km/s suggesting the existence of a large-scale structure at this redshift., Comment: 5 pages, 2 figures. Revised to match accepted version

Magueijo and Smolin have introduced a modification of the Lorentz group for the momentum-space transformations in Doubly-Special Relativity. As presented the group is non-linear, but we show that it is a group of fraction-linear transformations in 4 dimensional real projective space. We pass to the associated 5 dimensional linear space and identify the subgroup as a conjugate of the ordinary Lorentz group, giving the conjugating matrix. Taking the dual of the 5-space, we identify a subgroup as the Lorentz transformations about a point different to the origin., Comment: 4 pages

We report the discovery of a luminous z=5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an `i-drop' from the GOODS public survey imaging with HST/ACS (object 3 in Stanway, Bunker & McMahon 2003, astro-ph/0302212). The large colour of (i'-z')_AB=1.6 indicated a spectral break consistent with the Lyman-alpha forest absorption short-ward of Lyman-alpha at z~6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08arcsec, so r_hl<0.5kpc/h_70). We have obtained a deep (5.5-hour) spectrum of this z'(AB)=24.7 galaxy with the DEIMOS optical spectrograph on Keck, and here we report the discovery of a single emission line centred on 8245Ang detected at 20sigma with a flux of f~2E-17 ergs/s/cm^2. The line is clearly resolved with detectable structure at our resolution of better than 55km/s, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman-alpha emission from a z=5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width Delta(v)_FWHM=260km/s and rest-frame equivalent width (W=20Ang) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization NV1240Ang emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34M_sun/yr/h^2_70 (Omega_M=0.3, Omega_Lambda=0.7). This is the most luminous starburst known at z>5. Our spectroscopic redshift for this object confirms the validity of the i'-drop technique of Stanway, Bunker & McMahon (2003) to select star-forming galaxies at z~6., Comment: 5 pages, accepted for publication in MNRAS (Letters). Replaced with version matching accepted paper

(Abridged) We present rest-frame R-band galaxy luminosity function measurements for three different redshift ranges: 0.5<=z<=0.75, 0.75<=z<=1.0, and 1.0<=z<=1.5. Our measurements are based on photometric redshifts for ~3000 H-band selected galaxies with apparent magnitudes 17<=H<=20 from the Las Campanas Infrared Survey. We show that our photometric redshifts are accurate with an RMS dispersion between the photometric and spectroscopic redshifts of \sigma_z/(1+z)~0.08. Using galaxies identified in the Hubble Deep Field South and Chandra Deep Field South regions, we find, respectively, that (7.3\pm 0.2) % and (16.7\pm 0.4)% of the H<=20 galaxies are at z>=1. We first demonstrate that the systematic uncertainty inherent in the luminosity function measurements due to uncertainties in photometric redshifts is non-negligible and therefore must be accounted for. We then develop a technique to correct for this systematic error by incorporating the redshift error functions of individual galaxies in the luminosity function analysis. The redshift error functions account for the non-gaussian characteristics of photometric redshift uncertainties. They are the products of a convolution between the corresponding redshift likelihood functions of individual galaxies and a Gaussian distribution function that characterizes template-mismatch variance. We demonstrate, based on a Monte Carlo simulation, that we are able to completely recover the bright end of the intrinsic galaxy luminosity function using this technique. Finally, we calculate the luminosity function separately for the total H-band selected sample and for a sub-sample of early-type galaxies that have a best-fit spectral type of E/S0 or Sab from the photometric redshift analysis., Comment: 42 pages and 12 figures; Accepted for publication in the Astrophysical Journal

Optical spectra of 14 emission-line galaxies representative of the 1999 NICMOS parallel grism Ha survey of McCarthy et al. are presented. Of the 14, 9 have emission lines confirming the redshifts found in the grism survey. The higher resolution of our optical spectra improves the redshift accuracy by a factor of 5. The [O II]/Ha values of our sample are found to be more than two times lower than expected from Jansen et al. This [O II]/Ha ratio discrepancy is most likely explained by additional reddening in our Ha-selected sample [on average, as much as an extra E(B-V) = 0.6], as well as to a possible stronger dependence of the [O II]/Ha ratio on galaxy luminosity than is found in local galaxies. The result is that star formation rates (SFRs) calculated from [O II]3727 emission, uncorrected for extinction, are found to be on average 4 +/- 2 times lower than the SFRs calculated from Ha emission. Classification of emission-line galaxies as starburst or Seyfert galaxies based on comparison of the ratios [O II]/Hb and [Ne III]3869/Hb is discussed. New Seyfert 1 diagnostics using the Ha line luminosity, H-band absolute magnitude, and Ha equivalent widths are also presented. One galaxy is classified as a Seyfert 1 based on its broad emission lines, implying a comoving number density for Seyfert 1s of 2.5{+5.9, -2.1} times 10^{-5} Mpc^{-3}. This commoving number density is a factor of 2.4{+5.5,-2.0} times higher than estimated by other surveys., Comment: 51 pages, 18 figures; Accepted for publication in the Astrophysical Journal; Revised version with minor changes and an additional reference which gives further support to our conclusions

We present the results of an analysis of the large scale velocity fields of the ionized gas associated with powerful radio galaxies. Long-slit spectra of 52 objects provide a sample of resolved velocities that span a wide range of redshifts, radio and emission-line luminosities. Line widths reaching 1000 km/s and resolved velocity fields with amplitudes of up 1500 km/ s are found on scales from 10 to 100 kpc in the environments of radio galaxies at redshifts larger than 0.5. The global velocities and FWHM are of comparable amplitudes in the FRII sources, while the FRI sources have FWHM values that are larger than their resolved velocity fields. We find evidence for systematically larger line widths and velocity field amplitudes at z > 0.6. Several of the largest amplitude systems contain two galaxies with small projected separations. All of the > 1000 km/s systems occur in objects at z > 0.6 and all have comparable radio and [OII] sizes. There is a weak correlation of off-nuclear line widths and velocity field with the ratio of the radio and emission-line sizes, but it is of low statistical significance and there is a very large dispersion. The change in properties at redshifts above z ~ 0.6 could reflect a difference in environments of the host galaxies, with the hosts inhabiting higher density regions with increasing redshift. The mass of ionized gas and the apparent enclosed dynamical mass are correllated and both increase steeply with redshift and/or radio power., Comment: 26 pages, 2 tables, 4 postscript figures. To appear in the May 2000 Astronomical Journal

We present ground-based images of the z=1.824 radio galaxy 3C 256 in the standard BVRIJHK filters and an interference filter centered at 8800A, a Hubble Space Telescope image in a filter dominated by Ly-alpha emission (F336W), and spectra covering rest-frame wavelengths from Ly-alpha to [O III] 5007. Together with published polarimetry observations, we use these to decompose the overall spectral energy distribution into nebular continuum emission, scattered quasar light, and stellar emission. The nebular continuum and scattered light together comprise half (one third) of the V-band (K-band) light within a 4-arcsec aperture, and are responsible for the strong alignment between the optical/near-infrared light and the radio emission. The stellar emission is dominated by a population estimated to be 100-200 Myr old (assuming a Salpeter IMF), and formed in a short burst with a peak star formation rate of 1-4x10^3 Msun/yr. The total stellar mass is estimated to be no more than 2x10^{11} Msun, which is far less than other luminous radio galaxies at similar redshifts, and suggests that 3C 256 will undergo further star formation or mergers., Comment: 35 pages including 10 figures; to appear in Nov 10 ApJ