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The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides deep HST F275W and F435W imaging over four CANDELS fields (GOODS-N, GOODS-S, COSMOS, and EGS). We combine this newly acquired UV imaging with existing HST imaging from CANDELS as well as existing ancillary data to obtain robust photometric redshifts and reliable estimates for galaxy physical properties for over 150,000 galaxies in the $\sim$430 arcmin$^2$ UVCANDELS area. Here, we leverage the power of the new UV photometry to not only improve the photometric redshift measurements in these fields, but also constrain the full redshift probability distribution combining multiple redshift fitting tools. Furthermore, using the full UV-to-IR photometric dataset, we measure the galaxy physical properties by fitting templates from population synthesis models with two different parameterizations (flexible and fixed-form) of the star-formation histories (SFHs). Compared to the flexible SFH parametrization, we find that the fixed-form SFHs systematically underestimate the galaxy stellar masses, both at the low- ($\lesssim10^9 M_\odot$) and high- ($\gtrsim10^{10} M_\odot$) mass end, by as much as $\sim0.5$ dex. This underestimation is primarily due the limited ability of fixed-form SFH parameterization to simultaneously capture the chaotic nature of star-formation in these galaxies., Comment: 22 pages, 6 figures; accepted to ApJS; catalogs available via MAST

Lyman-Alpha Emitting galaxies (LAEs) are typically young, low-mass, star-forming galaxies with little extinction from interstellar dust. Their low dust attenuation allows their Ly$\alpha$ emission to shine brightly in spectroscopic and photometric observations, providing an observational window into the high-redshift universe. Narrowband surveys reveal large, uniform samples of LAEs at specific redshifts that probe large scale structure and the temporal evolution of galaxy properties. The One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) utilizes three custom-made narrowband filters on the Dark Energy Camera (DECam) to discover LAEs at three equally spaced periods in cosmological history. In this paper, we introduce the hybrid-weighted double-broadband continuum estimation technique, which yields improved estimation of Ly$\alpha$ equivalent widths. Using this method, we discover 6032, 5691, and 4066 LAE candidates at $z =$ 2.4, 3.1, and 4.5 in the extended COSMOS field ($\sim$9 deg$^2$). We find that [O II] emitters are a minimal contaminant in our LAE samples, but that interloping Green Pea-like [O III] emitters are important for our redshift 4.5 sample. We introduce an innovative method for identifying [O II] and [O III] emitters via a combination of narrowband excess and galaxy colors, enabling their study as separate classes of objects. We present scaled median stacked SEDs for each galaxy sample, revealing the overall success of our selection methods. We also calculate rest-frame Ly$\alpha$ equivalent widths for our LAE samples and find that the EW distributions are best fit by exponential functions with scale lengths of $w_0$ = 53 $\pm$ 1, 65 $\pm$ 1, and 59 $\pm$ 1 Angstroms, respectively., Comment: Accepted to ApJ, 24 pages, 14 figures

UVCANDELS is a HST Cycle-26 Treasury Program awarded 164 orbits of primary ultraviolet (UV) F275W imaging and coordinated parallel optical F435W imaging in four CANDELS fields: GOODS-N, GOODS-S, EGS, and COSMOS, covering a total area of $\sim426$ arcmin$^2$. This is $\sim2.7$ times larger than the area covered by previous deep-field space UV data combined, reaching a depth of about 27 and 28 ABmag ($5\sigma$ in $0.2"$ apertures) for F275W and F435W, respectively. Along with the new photometric catalogs, we present an analysis of the rest-frame UV luminosity function (LF), relying on our UV-optimized aperture photometry method yielding a factor of $1.5\times$ increase than the H-isophot aperture photometry in the signal-to-noise ratios of galaxies in our F275W imaging. Using well tested photometric redshift measurements we identify 5810 galaxies at redshifts $0.6

We describe the survey design and science goals for ODIN (One-hundred-deg^2 DECam Imaging in Narrowbands), a NOIRLab survey using the Dark Energy Camera (DECam) to obtain deep (AB~25.7) narrow-band images over an unprecedented area of sky. The three custom-built narrow-band filters, N419, N501, and N673, have central wavelengths of 419, 501, and 673 nm and respective full-widthat-half-maxima of 7.2, 7.4, and 9.8 nm, corresponding to Lya at z=2.4, 3.1, and 4.5 and cosmic times of 2.8, 2.1, and 1.4 Gyr, respectively. When combined with even deeper, public broad-band data from Hyper Suprime-Cam, DECam, and in the future, LSST, the ODIN narrow-band images will enable the selection of over 100,000 Lya-emitting (LAE) galaxies at these epochs. ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the deep narrow-band images enable detection of highly extended Lya blobs (LABs). Primary science goals include measuring the clustering strength and dark matter halo connection of LAEs, LABs, and protoclusters, and their respective relationship to filaments in the cosmic web. The three epochs allow the redshift evolution of these properties to be determined during the period known as Cosmic Noon, where star formation was at its peak. The two narrow-band filter wavelengths are designed to enable interloper rejection and further scientific studies by revealing [O II] and [O III] at z=0.34, Lya and He II 1640 at z=3.1, and Lyman continuum plus Lya at z=4.5. Ancillary science includes similar studies of the lower-redshift emission-line galaxy samples and investigations of nearby star-forming galaxies resolved into numerous [O III] and [S II] emitting regions., Comment: 21 pages, 8 figures, submitted to Astrophysical Journal

The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space Telescope (HST) Cycle-26 Treasury Program, allocated in total 164 orbits of primary Wide-Field Camera 3 Ultraviolet and Visible light F275W imaging with coordinated parallel Advanced Camera for Surveys F435W imaging, on four of the five premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. We introduce this survey by presenting a thorough search for galaxies at $z\gtrsim2.4$ that leak significant Lyman continuum (LyC) radiation, as well as a stringent constraint on the LyC escape fraction ($f_{\rm esc}$) from stacking the UV images of a population of star-forming galaxies with secure redshifts. Our extensive search for LyC emission and stacking analysis benefit from the catalogs of high-quality spectroscopic redshifts compiled from archival ground-based data and HST slitless spectroscopy, carefully vetted by dedicated visual inspection efforts. We report a sample of five galaxies as individual LyC leaker candidates, showing $f_{\rm esc}^{\rm rel}\gtrsim60\%$ estimated using detailed Monte Carlo analysis of intergalactic medium attenuation. We develop a robust stacking method to apply to five samples of in total 85 non-detection galaxies in the redshift range of $z\in[2.4,3.7]$. Most stacks give tight 2-$\sigma$ upper limits below $f_{\rm esc}^{\rm rel}<6\%$. A stack for a subset of 32 emission-line galaxies shows tentative LyC leakage detected at 2.9-$\sigma$, indicating $f_{\rm esc}^{\rm rel}=5.7\%$ at $z\sim2.65$, supporting the key role of such galaxies in contributing to the cosmic reionization and maintaining the UV ionization background. These new F275W and F435W imaging mosaics from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes., Comment: 33 pages, 21 figures, and 5 tables. Resubmitted after addressing the referee report

Large imaging surveys, such as the Legacy Survey of Space and Time, rely on photometric redshifts and tomographic binning for 3x2pt analyses that combine galaxy clustering and weak lensing. In this paper, we propose a method for optimizing the tomographic binning choice for the lens sample of galaxies. We divide the CosmoDC2 and Buzzard simulated galaxy catalogs into a training set and an application set, where the training set is nonrepresentative in a realistic way, and then estimate photometric redshifts for the application sets. The galaxies are sorted into redshift bins covering equal intervals of redshift or comoving distance, or with an equal number of galaxies in each bin, and we consider a generalized extension of these approaches. We find that bins of equal comoving distance produce the highest dark energy figure of merit of the initial binning choices, but that the choice of bin edges can be further optimized. We then train a neural network classifier to identify galaxies that are either highly likely to have accurate photometric redshift estimates or highly likely to be sorted into the correct redshift bin. The neural network classifier is used to remove poor redshift estimates from the sample, and the results are compared to the case when none of the sample is removed. We find that the neural network classifiers are able to improve the figure of merit by ~13% and are able to recover ~25% of the loss in the figure of merit that occurs when a nonrepresentative training sample is used., Comment: 18 pages, 14 figures

We present the first comprehensive release of photometric redshifts (photo-z's) from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) team. We use statistics based upon the Quantile-Quantile (Q--Q) plot to identify biases and signatures of underestimated or overestimated errors in photo-z probability density functions (PDFs) produced by six groups in the collaboration; correcting for these effects makes the resulting PDFs better match the statistical definition of a PDF. After correcting each group's PDF, we explore three methods of combining the different groups' PDFs for a given object into a consensus curve. Two of these methods are based on identifying the minimum f-divergence curve, i.e., the PDF that is closest in aggregate to the other PDFs in a set (analogous to the median of an array of numbers). We demonstrate that these techniques yield improved results using sets of spectroscopic redshifts independent of those used to optimize PDF modifications. The best photo-z PDFs and point estimates are achieved with the minimum f-divergence using the best 4 PDFs for each object (mFDa4) and the Hierarchical Bayesian (HB4) methods, respectively. The HB4 photo-z point estimates produced $\sigma_{\rm NMAD} = 0.0227/0.0189$ and $|\Delta z/(1+z)| > 0.15$ outlier fraction = 0.067/0.019 for spectroscopic and 3D-HST redshifts, respectively. Finally, we describe the structure and provide guidance for the use of the CANDELS photo-z catalogs, which are available at https://archive.stsci.edu/hlsp/candels., Comment: 35 pages, 19 figures, published in ApJ, data available at https://archive.stsci.edu/hlsp/candels

Measurements of short-timescale star formation variations (i.e., "burstiness") are integral to our understanding of star formation feedback mechanisms and the assembly of stellar populations in galaxies. We expand upon the work of Broussard et al. (2019) by introducing a new analysis of galaxy star formation burstiness that accounts for variations in the $Q_{sg}=\mathrm{E(B-V)_{stars}}/\mathrm{E(B-V)_{gas}}$ distribution, a major confounding factor. We use Balmer decrements from the MOSFIRE Deep Evolution Field (MOSDEF) survey to measure $Q_{sg}$, which we use to construct mock catalogs from the Santa Cruz Semi-Analytic Models and Mufasa cosmological hydrodynamical simulation based on 3D-HST, Fiber Multi-Object Spectrograph (FMOS)-COSMOS, and MOSDEF galaxies with H$\alpha$ detections. The results of the mock catalogs are compared against observations using the burst indicator $\eta = \log_{10}(\mathrm{SFR_{H\alpha}/SFR_{NUV}})$, with the standard deviation of the $\eta$ distribution indicating burstiness. We find decent agreement between mock and observed $\eta$ distribution shapes; however, the FMOS-COSMOS and MOSDEF mocks show a systematically low median and scatter in $\eta$ in comparison to the observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in $\eta$, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement of $0.06-0.16$ dex., Comment: 17 pages, 6 Figures, 3 Tables; Submitted to ApJ

Large simulation efforts are required to provide synthetic galaxy catalogs for ongoing and upcoming cosmology surveys. These extragalactic catalogs are being used for many diverse purposes covering a wide range of scientific topics. In order to be useful, they must offer realistically complex information about the galaxies they contain. Hence, it is critical to implement a rigorous validation procedure that ensures that the simulated galaxy properties faithfully capture observations and delivers an assessment of the level of realism attained by the catalog. We present here a suite of validation tests that have been developed by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). We discuss how the inclusion of each test is driven by the scientific targets for static ground-based dark energy science and by the availability of suitable validation data. The validation criteria that are used to assess the performance of a catalog are flexible and depend on the science goals. We illustrate the utility of this suite by showing examples for the validation of cosmoDC2, the extragalactic catalog recently released for the LSST DESC second Data Challenge., Comment: 46 pages, 33 figures

This paper presents the results of the Rubin Observatory Dark Energy Science Collaboration (DESC) 3x2pt tomography challenge, which served as a first step toward optimizing the tomographic binning strategy for the main DESC analysis. The task of choosing an optimal tomographic binning scheme for a photometric survey is made particularly delicate in the context of a metacalibrated lensing catalogue, as only the photometry from the bands included in the metacalibration process (usually riz and potentially g) can be used in sample definition. The goal of the challenge was to collect and compare bin assignment strategies under various metrics of a standard 3x2pt cosmology analysis in a highly idealized setting to establish a baseline for realistically complex follow-up studies; in this preliminary study, we used two sets of cosmological simulations of galaxy redshifts and photometry under a simple noise model neglecting photometric outliers and variation in observing conditions, and contributed algorithms were provided with a representative and complete training set. We review and evaluate the entries to the challenge, finding that even from this limited photometry information, multiple algorithms can separate tomographic bins reasonably well, reaching figures-of-merit scores close to the attainable maximum. We further find that adding the g band to riz photometry improves metric performance by ~15% and that the optimal bin assignment strategy depends strongly on the science case: which figure-of-merit is to be optimized, and which observables (clustering, lensing, or both) are included., Comment: 30 pages (incl. 12 in appendix), 12 figures. Version accepted for publication in the Open Journal of Astrophysics

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will produce several billion photometric redshifts (photo-$z$'s), enabling cosmological analyses to select a subset of galaxies with the most accurate photo-$z$. We perform initial redshift fits on Subaru Strategic Program galaxies with deep $grizy$ photometry using Trees for Photo-Z (TPZ) before applying a custom neural network classifier (NNC) tuned to select galaxies with $(z_\mathrm{phot} - z_\mathrm{spec})/(1+z_\mathrm{spec}) < 0.10$. We consider four cases of training and test sets ranging from an idealized case to using data augmentation to increase the representation of dim galaxies in the training set. Selections made using the NNC yield significant further improvements in outlier fraction and photo-$z$ scatter ($\sigma_z$) over those made with typical photo-$z$ uncertainties. As an example, when selecting the best third of the galaxy sample, the NNC achieves a 35% improvement in outlier rate and a 23% improvement in $\sigma_z$ compared to using uncertainties from TPZ. For cosmology and galaxy evolution studies, this method can be tuned to retain a particular sample size or to achieve a desired photo-$z$ accuracy; our results show that it is possible to retain more than a third of an LSST-like galaxy sample while reducing $\sigma_z$ by a factor of two compared to the full sample, with one-fifth as many photo-$z$ outliers. For surveys like LSST that are not limited by shot noise, this method enables a larger number of tomographic redshift bins and hence a significant increase in the total signal-to-noise of galaxy angular power spectra., Comment: 17 pages, 13 figures; Accepted to ApJ August 2021

Star Formation Histories (SFHs) reveal physical processes that influence how galaxies form their stellar mass. We compare the SFHs of a sample of 36 nearby (D $\leq$ 4 Mpc) dwarf galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST), inferred from the Color Magnitude Diagrams (CMDs) of individually resolved stars in these galaxies, with those reconstructed by broad-band Spectral Energy Distribution (SED) fitting using the Dense Basis SED fitting code. When comparing individual SFHs, we introduce metrics for evaluating SFH reconstruction techniques. For both the SED and CMD methods, the median normalized SFH of galaxies in the sample shows a period of quiescence at lookback times of 3-6 Gyr followed by rejuvenated star formation over the past 3 Gyr that remains active until the present day. To determine if these represent special epochs of star formation in the D $\leq$ 4 Mpc portion of the Local Volume, we break this ANGST dwarf galaxy sample into subsets based on specific star formation rate and spatial location. Modulo offsets between the methods of about 1 Gyr, all subsets show significant decreases and increases in their median normalized SFHs at the same epochs, and the majority of the individual galaxy SFHs are consistent with these trends. These results motivate further study of potential synchronized star formation quiescence and rejuvenation in the Local Volume as well as development of a hybrid method of SFH reconstruction that combines CMDs and SEDs, which have complementary systematics., Comment: Accepted for publication in ApJ, 25 pages, 18 figures, 3 tables

We analyze the clustering of galaxies in the first public data release of the HSC Subaru Strategic Program. Despite the relatively small footprints of the observed fields, the data are an excellent proxy for the deep photometric datasets that will be acquired by LSST, and are therefore an ideal test bed for the analysis methods being implemented by the LSST DESC. We select a magnitude limited sample with $i<24.5$ and analyze it in four redshift bins covering $0.15\lesssim z \lesssim1.5$. We carry out a Fourier-space analysis of the two-point clustering of this sample, including all auto- and cross-correlations. We demonstrate the use of map-level deprojection methods to account for fluctuations in the galaxy number density caused by observational systematics. Through an HOD analysis, we place constraints on the characteristic halo masses of this sample, finding a good fit up to scales $k_{\rm max}=1\,{\rm Mpc}^{-1}$, including both auto- and cross-correlations. Our results show monotonically decreasing average halo masses, which can be interpreted in terms of the drop-out of red galaxies at high redshifts for a flux-limited sample. In terms of photometric redshift systematics, we show that additional care is needed in order to marginalize over uncertainties in the redshift distribution in galaxy clustering, and that these uncertainties can be constrained by including cross-correlations. We are able to make a $\sim3\sigma$ detection of lensing magnification in the HSC data. Our results are stable to variations in $\sigma_8$ and $\Omega_c$ and we find constraints that agree well with measurements from Planck and low-redshift probes. Finally, we use our pipeline to study the clustering of galaxies as a function of limiting flux, and provide a simple fitting function for the linear galaxy bias for magnitude limited samples as a function of limiting magnitude and redshift. [abridged], Comment: 65 pages, 30 figures, 5 tables, to be submitted to JCAP

One of the key questions in understanding the formation and evolution of galaxies is how starbursts affect the assembly of stellar populations in galaxies over time. We define a burst indicator ($\eta$), which compares a galaxy's star formation rates on short ($\sim10$ Myr) and long ($\sim100$ Myr) timescales. To estimate $\eta$, we apply the detailed time-luminosity relationship for H$\alpha$ and near-ultraviolet emission to simulated star formation histories (SFHs) from semi-analytic models and the Mufasa hydrodynamical cosmological simulations. The average of $\eta$ is not a good indicator of star formation stochasticity (burstiness); indeed, we show that this average should be close to zero unless the population has an average SFH which is rising or falling rapidly. Instead, the width of the $\eta$ distribution characterizes the burstiness of a galaxy population's recent star formation. We find this width to be robust to variations in stellar initial mass function and metallicity. We apply realistic noise and selection effects to the models to generate mock HST and JWST galaxy catalogs and compare these catalogs with 3D-HST observations of 956 galaxies at $0.65

We investigate the properties of galaxies as they shut off star formation over the 4 billion years surrounding peak cosmic star formation. To do this we categorize $\sim7000$ galaxies from $1

Using deep multi-wavelength photometry of galaxies from ZFOURGE, we group galaxies at $2.56$. Many of the EELGs also exhibit Lyman-$\alpha$ emission. Additionally, we find that many of these sources are clustered in an overdensity in the Chandra Deep Field South, with five spectroscopically confirmed members at $z=3.474 \pm 0.004$. The spatial distribution and photometric redshifts of the ZFOURGE population further confirm the overdensity highlighted by the EELGs., Comment: Accepted for publication in ApJL. 8 pages, 4 figures

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 a strong and weak gravitational lens model of the galaxy cluster MACSJ0416.1-2403, constrained using spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) and Hubble Frontier Fields (HFF) imaging data. We search for emission lines in known multiply imaged sources in the GLASS spectra, obtaining secure spectroscopic redshifts of 31 multiple images belonging to 16 distinct source galaxies. The GLASS spectra provide the first spectroscopic measurements for 6 of the source galaxies. The weak lensing signal is acquired from 884 galaxies in the F606W HFF image. By combining the weak lensing constraints with 15 multiple image systems with spectroscopic redshifts and 9 multiple image systems with photometric redshifts, we reconstruct the gravitational potential of the cluster on an adaptive grid. The resulting total mass density map is compared with a stellar mass density map obtained from the deep Spitzer Frontier Fields imaging data to study the relative distribution of stellar and total mass in the cluster. We find that the projected stellar mass to total mass ratio, $f_{\star}$, varies considerably with the stellar surface mass density. The mean projected stellar mass to total mass ratio is $\langle f_{\star} \rangle= 0.009 \pm 0.003 $ (stat.), but with a systematic error as large as $0.004-0.005$, dominated by the choice of the IMF. We find agreement with several recent measurements of $f_{\star}$ in massive cluster environments. The lensing maps of convergence, shear, and magnification are made available to the broader community in the standard HFF format., Comment: 48 pages, 45 figures

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