arXiv subjects

C. Scarlata

Publications and source records attributed to C. Scarlata.

At least 37 records · Page 2Linked to original sources

arXiv2025

Euclid Quick Data Release (Q1): From spectrograms to spectra: the SIR spectroscopic Processing Function

The Euclid space mission aims to investigate the nature of dark energy and dark matter by mapping the large-scale structure of the Universe. A key component of Euclid's observational strategy is slitless spectroscopy, conducted using the Near Infrared Spectrometer and Photometer (NISP). This technique enables the acquisition of large-scale spectroscopic data without the need for targeted apertures, allowing precise redshift measurements for millions of galaxies. These data are essential for Euclid's core science objectives, including the study of cosmic acceleration and the evolution of galaxy clustering, as well as enabling many non-cosmological investigations. This study presents the SIR processing function (PF), which is responsible for processing slitless spectroscopic data. The objective is to generate science-grade fully-calibrated one-dimensional spectra, ensuring high-quality spectroscopic data. The processing function relies on a source catalogue generated from photometric data, effectively corrects detector effects, subtracts cross-contaminations, minimizes self-contamination, calibrates wavelength and flux, and produces reliable spectra for later scientific use. The first Quick Data Release (Q1) of Euclid's spectroscopic data provides approximately three million validated spectra for sources observed in the red-grism mode from a selected portion of the Euclid Wide Survey. We find that wavelength accuracy and measured resolving power are within requirements, thanks to the excellent optical quality of the instrument. The SIR PF represents a significant step in processing slitless spectroscopic data for the Euclid mission. As the survey progresses, continued refinements and additional features will enhance its capabilities, supporting high-precision cosmological and astrophysical measurements.

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arXiv2024

Euclid: Searches for strong gravitational lenses using convolutional neural nets in Early Release Observations of the Perseus field

The Euclid Wide Survey (EWS) is predicted to find approximately 170 000 galaxy-galaxy strong lenses from its lifetime observation of 14 000 deg^2 of the sky. Detecting this many lenses by visual inspection with professional astronomers and citizen scientists alone is infeasible. Machine learning algorithms, particularly convolutional neural networks (CNNs), have been used as an automated method of detecting strong lenses, and have proven fruitful in finding galaxy-galaxy strong lens candidates. We identify the major challenge to be the automatic detection of galaxy-galaxy strong lenses while simultaneously maintaining a low false positive rate. One aim of this research is to have a quantified starting point on the achieved purity and completeness with our current version of CNN-based detection pipelines for the VIS images of EWS. We select all sources with VIS IE < 23 mag from the Euclid Early Release Observation imaging of the Perseus field. We apply a range of CNN architectures to detect strong lenses in these cutouts. All our networks perform extremely well on simulated data sets and their respective validation sets. However, when applied to real Euclid imaging, the highest lens purity is just 11%. Among all our networks, the false positives are typically identifiable by human volunteers as, for example, spiral galaxies, multiple sources, and artefacts, implying that improvements are still possible, perhaps via a second, more interpretable lens selection filtering stage. There is currently no alternative to human classification of CNN-selected lens candidates. Given the expected 10^5 lensing systems in Euclid, this implies 10^6 objects for human classification, which while very large is not in principle intractable and not without precedent.

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arXiv2024

The Lyman Alpha Reference Sample. XVI. Global 21cm HI properties of Lyman-$α$ emitting galaxies

The Lyman-$α$ (Lya) line of hydrogen is a well-known tracer of galaxies at high-z. However, the connection between Lya observables and galaxy properties has not fully been established, limiting the use of the line to probe the physics of galaxies. Here, we derive global neutral hydrogen gas (HI) properties of nearby Lya-emitting galaxies to assess the impact of HI on the Lya output of galaxies. We observed 21cm line emission using the VLA in D-array configuration (~55" resolution, ~38 kpc) for 37 star-forming galaxies with available Lya imaging from the Lyman Alpha Reference Samples (LARS and eLARS). We detect 21cm emission for 33/37 galaxies observed. We find no significant correlation of global HI properties with Lya luminosity, escape fraction or equivalent width derived with HST photometry. Additionally, both Lya-emitters and weak or non-emitters are distributed evenly along the HI parameter space of optically-selected z=0 galaxies. Around 74% of the sample is undergoing galaxy interaction, this fraction is higher for Lya-emitters (83% for galaxies with EW$\geq$20Å) than for non or weak emitters (70%). Nevertheless, galaxies identified as interacting have Lya and HI properties statistically consistent with those of non-interacting galaxies. Our results show that global HI properties (on scales > 30kpc) have little direct impact on the Lya output from galaxies. Instead, HI likely regulates Lya emission on small scales: statistical comparisons of Lya and high angular resolution 21cm observations are required to fully assess the role of HI in Lya radiative transfer. While our study indicates that galaxy mergers could play a role in the emission of Lya photons in the local universe, especially for galaxies with high HI fractions, the line-of-sight through which a system is observed ultimately determines Lya observables.

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arXiv2024

Emission-line galaxies at $z\sim1$ from near-IR HST Slitless Spectroscopy: metallicities, star formation rates and redshift confirmations from VLT/FORS2 spectroscopy

We follow up emission line galaxies identified through the near-infrared slitless HST/WFC3 WISP survey with VLT/FORS2 optical spectroscopy. Over 4 WISP fields, we targetted 85 of 138 line emission objects at $0.4<z<2$ identified in WFC3 spectroscopy. Half the galaxies are fainter than $H_{AB}=24$mag, and would not have been included in many well-known surveys based on broad-band magnitude selection. We confirm 95% of the initial WFC3 grism redshifts in the 38 cases where we detect lines in FORS2 spectroscopy. However, for targets which exhibited a single emission line in WFC3, up to 65% at $z<1.28$ did not have expected emission lines detected in FORS2 and hence may be spurious (although this false-detection rate improves to 33% using the latest public WISP emission line catalogue). From the Balmer decrement the extinction of the WISP galaxies is consistent with $A($H$α)=1$mag. From SED fits to multi-band photometry including Spitzer $3.6μ$m, we find a median stellar mass of $\log_{10}(M/M_{\odot})=8.94$. Our emission-line-selected galaxies tend to lie above the star-forming main sequence (i.e. higher specific star formation rates). Using [OIII], [OII] and H$β$ lines to derive gas-phase metallicities, we find typically sub-solar metallicities, decreasing with redshift. Our WISP galaxies lie below the $z=0$ mass-metallicity relation, and galaxies with higher star formation rates tend to have lower metallicity. Finally, we find a strong increase with redshift of the H$α$ rest-frame equivalent width in this emission-line selected sample, with higher $EW_0$ galaxies having larger [OIII]/H$β$ and O32 ratios on average, suggesting lower metallicity or higher ionisation parameter in these extreme emission line galaxies.

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arXiv2024

Euclid preparation. The Cosmic Dawn Survey (DAWN) of the Euclid Deep and Auxiliary Fields

Euclid will provide deep NIR imaging to $\sim$26.5 AB magnitude over $\sim$59 deg$^2$ in its deep and auxiliary fields. The Cosmic DAWN survey complements the deep Euclid data with matched depth multiwavelength imaging and spectroscopy in the UV--IR to provide consistently processed Euclid selected photometric catalogs, accurate photometric redshifts, and measurements of galaxy properties to a redshift of $z\sim 10$. In this paper, we present an overview of the survey, including the footprints of the survey fields, the existing and planned observations, and the primary science goals for the combined data set.

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arXiv2024

CLASSY X: Highlighting Differences Between Partial Covering and Semi-Analytic Modeling in the Estimate of Galactic Outflow Properties

Feedback driven massive outflows play a crucial role in galaxy evolution by regulating star formation and influencing the dynamics of surrounding media. Extracting outflow properties from spectral lines is a notoriously difficult process for a number of reasons, including the possibility that a substantial fraction of the outflow is carried by dense gas in a very narrow range in velocity. This gas can hide in spectra with insufficient resolution. Empirically motivated analysis based on the Apparent Optical Depth method, commonly used in the literature, neglects the contribution of this gas, and may therefore underestimate the true gas column density. More complex semi-analytical line transfer (e.g., SALT) models, on the other hand, allow for the presence of this gas by modeling the radial density and velocity of the outflows as power laws. Here we compare the two approaches to quantify the uncertainties in the inferences of outflow properties based on 1-D "down-the-barrel" using the UV spectra of the CLASSY galaxy sample. We find that empirical modeling may significantly underestimate the column densities relative to SALT analysis, particularly in the optically thick regime. We use simulations to show that the main reason for this discrepancy is the presence of large amount of dense material at low velocities, which can be hidden by the finite spectral resolution of the data. The SALT models in turn could over-estimate the column densities if the assumed power laws of the density profiles strong are not a property of actual outflows.

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arXiv2024

Euclid. V. The Flagship galaxy mock catalogue: a comprehensive simulation for the Euclid mission

We present the Flagship galaxy mock, a simulated catalogue of billions of galaxies designed to support the scientific exploitation of the Euclid mission. Euclid is a medium-class mission of the European Space Agency optimised to determine the properties of dark matter and dark energy on the largest scales of the Universe. It probes structure formation over more than 10 billion years primarily from the combination of weak gravitational lensing and galaxy clustering data. The breath of Euclid's data will also foster a wide variety of scientific analyses. The Flagship simulation was developed to provide a realistic approximation to the galaxies that will be observed by Euclid and used in its scientific analyses. We ran a state-of-the-art N-body simulation with four trillion particles, producing a lightcone on the fly. From the dark matter particles, we produced a catalogue of 16 billion haloes in one octant of the sky in the lightcone up to redshift z=3. We then populated these haloes with mock galaxies using a halo occupation distribution and abundance matching approach, calibrating the free parameters of the galaxy mock against observed correlations and other basic galaxy properties. Modelled galaxy properties include luminosity and flux in several bands, redshifts, positions and velocities, spectral energy distributions, shapes and sizes, stellar masses, star formation rates, metallicities, emission line fluxes, and lensing properties. We selected a final sample of 3.4 billion galaxies with a magnitude cut of H_E<26, where we are complete. We have performed a comprehensive set of validation tests to check the similarity to observational data and theoretical models. In particular, our catalogue is able to closely reproduce the main characteristics of the weak lensing and galaxy clustering samples to be used in the mission's main cosmological analysis. (abridged)

astro-ph.CO↗

arXiv2024

On the universal validity of Case B recombination theory

In an ongoing search for low-mass extreme emission line galaxies, we identified a galaxy with a Ha/Hb Balmer line ratio of 2.620 +- 0.078. Ha/Hb Balmer ratios lower than the dust-free Case~B value appear relatively frequently in extreme emission line galaxies. These low values suggest that the Case~B assumption may not be valid in these objects. After ruling out the possibility that the low Ha/Hb ratio is due to systematic errors introduced by observational effects, we use constraints from the total Hb luminosity, the [OIII]/[OII] line ratio and the Balmer line equivalent widths, to suggest that the gas is optically thick to both Ha and Lya photons, and the geometry and orientation of the scattering gas causes Ha photons to be preferentially removed from the line of sight with respect to higher order Balmer series photons. Finally, we use data from the SDSS survey to show that Balmer self-absorption may be more important than previously assumed in high excitation emission line galaxies, where Lya pumping of the hydrogen excited state can be effective. If not recognized, Balmer self-absorption could lead to inaccurate estimates of galaxy physical properties. As an example, the effect of dust extinction could be over-estimated, for spherically symmetric scattering medium, or under-estimated, for a not spherically-symmetric distribution.

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arXiv2024

WFC3 Infrared Spectroscopic Parallel (WISP) Survey: Photometric and Emission Line Data Release

We present reduced images and catalogues of photometric and emission line data ($\sim$230,000 and $\sim$8,000 sources, respectively) for the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. These data are made publicly available on the Mikulski Archive for Space Telescopes (MAST) and include reduced images from various facilities: ground-based $ugri$, HST WFC3, and Spitzer IRAC (Infrared Array Camera). Coverage in at least one additional filter beyond the WFC3/IR data are available for roughly half of the fields (227 out of 483), with $\sim$20% (86) having coverage in six or more filters from $u$-band to IRAC 3.6$μ$m (0.35-3.6$μ$m). For the lower spatial resolution (and shallower) ground-based and IRAC data, we perform PSF-matched, prior-based, deconfusion photometry (i.e., forced-photometry) using the TPHOT software to optimally extract measurements or upper limits. We present the methodology and software used for the WISP emission line detection and visual inspection. The former adopts a continuous wavelet transformation that significantly reduces the number of spurious sources as candidates before the visual inspection stage. We combine both WISP catalogues and perform SED fitting on galaxies with reliable spectroscopic redshifts and multi-band photometry to measure their stellar masses. We stack WISP spectra as functions of stellar mass and redshift and measure average emission line fluxes and ratios. We find that WISP emission line sources are typically `normal' star-forming galaxies based on the Mass-Excitation diagram ([OIII]/H$β$ vs. $M_\star$; $0.74<z_\mathrm{grism}<2.31$), the galaxy main sequence (SFR vs. $M_\star$; $0.30<z_\mathrm{grism}<1.45$), $S_{32}$ ratio vs. $M_\star$ ($0.30<z_\mathrm{grism}<0.73$), and $O_{32}$ and $R_{23}$ ratios vs. $M_\star$ ($1.27<z_\mathrm{grism}<1.45$).

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arXiv2024

Euclid: Testing photometric selection of emission-line galaxy targets

Multi-object spectroscopic galaxy surveys typically make use of photometric and colour criteria to select targets. Conversely, the Euclid NISP slitless spectrograph will record spectra for every source over its field of view. Slitless spectroscopy has the advantage of avoiding defining a priori a galaxy sample, but at the price of making the selection function harder to quantify. The Euclid Wide Survey aims at building robust statistical samples of emission-line galaxies with fluxes in the Halpha-NII complex brighter than 2e-16 erg/s/cm^2 and within 0.9<z<1.8. At faint fluxes, we expect significant contamination by wrongly measured redshifts, either due to emission-line misidentification or noise fluctuations, with the consequence of reducing the purity of the final samples. This can be significantly improved by exploiting Euclid photometric information to identify emission-line galaxies over the redshifts of interest. To this goal, we compare and quantify the performance of six machine-learning classification algorithms. We consider the case when only Euclid photometric and morphological measurements are used and when these are supplemented by ground-based photometric data. We train and test the classifiers on two mock galaxy samples, the EL-COSMOS and Euclid Flagship2 catalogues. Dense neural networks and support vector classifiers obtain the best performance, with comparable results in terms of the adopted metrics. When training on Euclid photometry alone, these can remove 87% of the sources that are fainter than the nominal flux limit or lie outside the range 0.9<z<1.8, a figure that increases to 97% when ground-based photometry is included. These results show how by using the photometric information available to Euclid it will be possible to efficiently identify and discard spurious interlopers, allowing us to build robust spectroscopic samples for cosmological investigations.

astro-ph.CO↗

arXiv2024

Euclid preparation. Optical emission-line predictions of intermediate-z galaxy populations in GAEA for the Euclid Deep and Wide Surveys

In anticipation of the Euclid Wide and Deep Surveys, we present optical emission-line predictions at intermediate redshifts from 0.4 to 2.5. Our approach combines a mock light cone from the GAEA semi-analytic model to self-consistently model nebular emission from HII regions, narrow-line regions of active galactic nuclei (AGN), and evolved stellar populations. Our analysis focuses on seven optical emission lines: H$α$, H$β$, [SII]$λλ6717, 6731$, [NII]$λ6584$, [OI]$λ6300$, [OIII]$λ5007$, and [OII]$λλ3727, 3729$. We find that Euclid will predominantly observe massive, star-forming, and metal-rich line-emitters. Interstellar dust, modelled using a Calzetti law with mass-dependent scaling, may decrease observable percentages by a further 20-30% with respect to our underlying emission-line populations from GAEA. We predict Euclid to observe around 30-70% of H$α$-, [NII]-, [SII]-, and [OIII]-emitting galaxies at redshift below 1 and under 10% at higher redshift. Observability of H$β$-, [OII]-, and [OI]- emission is limited to below 5%. For the Euclid-observable sample, we find that BPT diagrams can effectively distinguish between different galaxy types up to around redshift 1.8, attributed to the bias toward metal-rich systems. Moreover, we show that the relationships of H$α$ and [OIII]+H$β$ to the star-formation rate, and the [OIII]-AGN luminosity relation, exhibit minimal changes with increasing redshift. Based on line ratios [NII]/H$α$, [NII]/[OII], and [NII]/[SII], we further propose novel z-invariant tracers for the black hole accretion rate-to-star formation rate ratio. Lastly, we find that commonly used metallicity estimators display gradual shifts in normalisations with increasing redshift, while maintaining the overall shape of local calibrations. This is in tentative agreement with recent JWST data.

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arXiv2022

The Origin of the Observed Lyman alpha EW Distribution of Dwarf Galaxies at z~2

We present a rest-UV selected sample of 32 lensed galaxies at $z\sim 2$ observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed ($-19 \le {\rm M_{\rm UV}} \le -17$) at this redshift. The fraction of dwarf galaxies identified as Ly$α$ emitters ($\rm EW \ge 20\ \overset{\lower.5em\circ}{\mathrm{A}}$) is ${\rm X_{\rm LAE}}=25^{+15}_{-10}\%$. We use the Balmer lines and UV continuum to estimate the intrinsic EW allowing us to distinguish the effects of the ionizing spectra and Ly$α$ escape fraction on the observed EW distribution. Fainter galaxies ($\rm M_{\rm UV} > -19$) show larger intrinsic EWs and escape fractions than brighter galaxies. Only galaxies with intrinsic EWs greater than 40$\ \overset{\lower.5em\circ}{\mathrm{A}}$ have escape fractions larger than 0.05. We find an anti-correlation between the escape fraction and $\rm A_V$ as well as UV spectral slope. The volumetric escape fraction of our sample is $f_{\rm esc}^{\rm Lyα} = 4.59^{+2.0}_{-1.4}\%$ in agreement with measurements found elsewhere in the literature. About half of the total integrated Ly$α$ luminosity density comes from galaxies with ${\rm EW}_{\rm obs}>20\ \overset{\lower.5em\circ}{\mathrm{A}}$.

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arXiv2022

Early results from GLASS-JWST. X: Rest-frame UV-optical properties of galaxies at 7 < z < 9

We present the first James Webb Space Telescope/NIRCam-led determination of $7 9.5$. Their star formation main sequence is consistent with predictions from simulations. Lastly, we introduce an analytical framework to constrain main-sequence evolution at $z>7$ based on galaxy ages and basic assumptions, through which we find results consistent with expectations from cosmological simulations. While this work only gives a glimpse of the properties of typical galaxies that are thought to drive the reionization of the universe, it clearly shows the potential of JWST to unveil unprecedented details on galaxy formation in the first billion years.

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arXiv2022

Early results from GLASS-JWST. XI: Stellar masses and mass-to-light ratio of z>7 galaxies

We exploit James Webb Space Telescope (JWST) NIRCam observations from the GLASS-JWST-Early Release Science program to investigate galaxy stellar masses at z>7. We first show that JWST observations reduce the uncertainties on the stellar mass by a factor of at least 5-10, when compared with the highest quality data sets available to date. We then study the UV mass-to-light ratio, finding that galaxies exhibit a two orders of magnitude range of M/L_UV values for a given luminosity, indicative of a broad variety of physical conditions and star formation histories. As a consequence, previous estimates of the cosmic star stellar mass density - based on an average correlation between UV luminosity and stellar mass - can be biased by as much as a factor of ~6. Our first exploration demonstrates that JWST represents a new era in our understanding of stellar masses at z>7, and therefore of the growth of galaxies prior to cosmic reionization.

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arXiv2022

Early results from GLASS-JWST. VII: evidence for lensed, gravitationally bound proto-globular clusters at z=4 in the Hubble Frontier Field A2744

We investigate the blue and optical rest-frame sizes (lambda~2300A-4000A) of three compact star-forming regions in a galaxy at z=4 strongly lensed (x30, x45, x100) by the Hubble Frontier Field galaxy cluster A2744 using GLASS-ERS JWST/NIRISS imaging at 1.15um, 1.50mu and 2.0mu with PSF < 0.1". In particular, the Balmer break is probed in detail for all multiply-imaged sources of the system. With ages of a few tens of Myr, stellar masses in the range (0.7-4.0) x 10^6 Msun and optical/ultraviolet effective radii spanning the interval 3 < R_eff < 20 pc, such objects are currently the highest redshift (spectroscopically-confirmed) gravitationally-bound young massive star clusters (YMCs), with stellar mass surface densities resembling those of local globular clusters. Optical (4000A, JWST-based) and ultraviolet (1600A, HST-based) sizes are fully compatible. The contribution to the ultraviolet underlying continuum emission (1600A) is ~30%, which decreases by a factor of two in the optical for two of the YMCs (~4000A rest-frame), reflecting the young ages (<30 Myr) inferred from the SED fitting and supported by the presence of high-ionization lines secured with VLT/MUSE. Such bursty forming regions enhance the sSFR of the galaxy, which is ~10 Gyr^-1. This galaxy would be among the extreme analogs observed in the local Universe having high star formation rate surface density and high occurrence of massive stellar clusters in formation.

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arXiv2022

Early results from GLASS-JWST. VI: Extreme rest-optical equivalent widths detected in NIRISS Wide Field Slitless Spectroscopy

Wide Field Slitless Spectroscopy (WFSS) provides a powerful tool for detecting strong line emission in star forming galaxies (SFGs) without the need for target pre-selection. As part of the GLASS-JWST-ERS program, we leverage the near-infrared wavelength capabilities of NIRISS ($1-2.2μ$m) to observe rest-optical emission lines out to $\rm{z}\sim 3.4$, to a depth and with a spatial resolution higher than ever before (H$α$ to z<2.4; [OIII]+H$β$ to z<3.4). In this letter we constrain the rest-frame [OIII]$\lambda5007$ equivalent width (EW) distribution for a sample of 76 $1<\rm{z}<3.4$ SFGs in the Abell 2744 Hubble Frontier Field and determine an abundance fraction of extreme emission line galaxies with EW$>750$A in our sample to be $12\%$. We determine a strong correlation between the measured H$β$ and [OIII]$\lambda5007$ EWs, supporting that the high [OIII]$\lambda5007$ EW objects require massive stars in young stellar populations to generate the high energy photons needed to doubly ionise oxygen. We extracted spectra for objects up to 2 mag fainter in the near-infrared than previous WFSS studies with the Hubble Space Telescope. Thus, this work clearly highlights the potential of JWST/NIRISS to provide high quality WFSS datasets in crowded cluster environments.

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arXiv2022

The Far-Ultraviolet Continuum Slope as a Lyman Continuum Escape Estimator at High-redshift

Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high-redshifts. While observations have established that reionization occurred, observational constraints on the emissivity of ionizing photons at high-redshift remains elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and archival observations, a combined sample of 89 star-forming galaxies at z~0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6$σ$ significant) inverse correlation between the continuum slope at 1550Å (defined as F$_λ\proptoλ^β$) and both the LyC escape fraction (f$_{esc}$) and f$_{esc}$ times the ionizing photon production efficiency ($ξ_{ ion}$). On average, galaxies with redder continuum slopes have smaller f$_{esc}$ than galaxies with bluer slopes due to higher dust attenuation. More than 5% (20%) of the LyC emission escapes galaxies with $β$<-2.1 (-2.6). We find strong correlations between $β$ and the gas-phase ionization ([OIII]/[OII] flux ratio; at 7.5$σ$ significance), galaxy stellar mass (at 5.9$σ$), the gas-phase metallicity (at 4.6$σ$), and the observed FUV absolute magnitude (M$_{UV}$ at 3.4$σ$). Using previous observations of $β$ at high-redshift, we estimate the evolution of f$_{esc}$ with both $z$ and M$_{UV}$. The LzLCS suggest that fainter and lower mass galaxies dominate the ionizing photon budget at higher redshift, possibly due to their rapidly evolving metal and dust content. Finally, we use our correlation between $β$ and f$_{ esc}\timesξ_{ion}$ to predict the ionizing emissivity of galaxies during the epoch of reionization. Our estimated emissivities match IGM observations, and suggest that star-forming galaxies emit sufficient LyC photons into the IGM to exceed recombinations near redshifts of 7-8.

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arXiv2022

The GLASS James Webb Space Telescope Early Release Science Program. I. Survey Design and Release Plans

The GLASS James Webb Space Telescope Early Release Science (hereafter GLASS-JWST-ERS) Program will obtain and make publicly available the deepest extragalactic data of the ERS campaign. It is primarily designed to address two key science questions, namely, "what sources ionized the universe and when?" and "how do baryons cycle through galaxies?", while also enabling a broad variety of first look scientific investigations. In primary mode, it will obtain NIRISS and NIRSpec spectroscopy of galaxies lensed by the foreground Hubble Frontier Field cluster, Abell 2744. In parallel, it will use NIRCam to observe two fields that are offset from the cluster center, where lensing magnification is negligible, and which can thus be effectively considered blank fields. In order to prepare the community for access to this unprecedented data, we describe the scientific rationale, the survey design (including target selection and observational setups), and present pre-commissioning estimates of the expected sensitivity. In addition, we describe the planned public releases of high-level data products, for use by the wider astronomical community.

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