HST Grism-derived Forecasts for Future Galaxy Redshift Surveys

The mutually complementary Euclid and Roman galaxy redshift surveys will use Halpha- and [OIII]-selected emission line galaxies as tracers of the large scale structure at $0.9 \lesssim z \lesssim 1.9$ (Halpha) and $1.5 \lesssim z \lesssim 2.7$ ([OIII]). It is essential to have a reliable and sufficiently precise knowledge of the expected numbers of Halpha-emitting galaxies in the survey volume in order to optimize these redshift surveys for the study of dark energy. Additionally, these future samples of emission-line galaxies will, like all slitless spectroscopy surveys, be affected by a complex selection function that depends on galaxy size and luminosity, line equivalent width, and redshift errors arising from the misidentification of single emission-line galaxies. Focusing on the specifics of the Euclid survey, we combine two slitless spectroscopic WFC3-IR datasets -- 3D-HST+AGHAST and the WISP survey -- to construct a Euclid-like sample that covers an area of 0.56 deg$^2$ and includes 1277 emission line galaxies. We detect 1091 ($\sim$3270 deg$^{-2}$) Halpha+[NII]-emitting galaxies in the range $0.9\leq z \leq 1.6$ and 162 ($\sim$440 deg$^{-2}$) [OIII]$\lambda$5007-emitters over $1.5\leq z \leq 2.3$ with line fluxes $\geq 2 \times 10^{-16}$ erg s$^{-1}$ cm$^{-2}$. The median of the Halpha+[NII] equivalent width distribution is $\sim$250\r{A}, and the effective radii of the continuum and Halpha+[NII] emission are correlated with a median of $\sim$0.38" and significant scatter ($\sigma \sim$0.2"$-$0.35"). Finally, we explore the prevalence of redshift misidentification in future Euclid samples, finding potential contamination rates of $\sim$14-20% and $\sim$6% down to $2\times 10^{-16}$ and $6 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$, respectively, though with increased wavelength coverage these percentages drop to nearly zero.Comment: Accepted for publication in ApJ. 27 pages, 17 figures, 3 table

Ceers key paper. I. An early look into the first 500myr of galaxy formation with jwst

We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin2 , to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at MUV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance (surface density [arcmin−2 ]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role

Galaxy Nurseries: Crowdsourced analysis of slitless spectroscopic data

We present the results of Galaxy Nurseries project, which was designed to enable crowdsourced analysis of slitless spectroscopic data by volunteer citizen scientists using the Zooniverse online interface. The dataset was obtained by the WFC3 Infrared Spectroscopic Parallel (WISP) Survey collaboration and comprises NIR grism (G102 and G141) and direct imaging. Volunteers were instructed to evaluate indicated spectral features and decide whether it was a genuine emission line or more likely an artifact. Galaxy Nurseries was completed in only 40 days, gathering 414,360 classifications from 3003 volunteers for 27,333 putative emission lines. The results of Galaxy Nurseries demonstrate the feasibility of identifying genuine emission lines in slitless spectra by citizen scientists. Volunteer responses for each subject were aggregated to compute $f_{\mathrm{Real}}$, the fraction of volunteers who classified the corresponding emission line as "Real". To evaluate the accuracy of volunteer classifications, their aggregated responses were compared with independent assessments provided by members of the WISP Survey Science Team (WSST). Overall, there is a broad agreement between the WSST and volunteers' classifications, although we recognize that robust scientific analyses typically require samples with higher purity and completeness than raw volunteer classifications provide. Nonetheless, choosing optimal threshold values for $f_{\mathrm{Real}}$ allows a large fraction of spurious lines to be vetoed, substantially reducing the timescale for subsequent professional analysis of the remaining potential lines.Comment: Accepted for publication in Research Notes of the AA

Predicting the redshift 2 Halpha luminosity function using [OIII] emission line galaxies

Upcoming space-based surveys such as Euclid and WFIRST-AFTA plan to measure Baryonic Acoustic Oscillations (BAOs) in order to study dark energy. These surveys will use IR slitless grism spectroscopy to measure redshifts of a large number of galaxies over a significant redshift range. In this paper, we use the WFC3 Infrared Spectroscopic Parallel Survey (WISP) to estimate the expected number of Halpha (Ha) emitters observable by these future surveys. WISP is an ongoing HST slitless spectroscopic survey, covering the 0.8-1.65micron wavelength range and allowing the detection of Ha emitters up to z~1.5 and [OIII] emitters to z~2.3. We derive the Ha-[OIII] bivariate line luminosity function for WISP galaxies at z~1 using a maximum likelihood estimator that properly accounts for uncertainties in line luminosity measurement, and demonstrate how it can be used to derive the Ha luminosity function from exclusively fitting [OIII] data. Using the z~2 [OIII] line luminosity function, and assuming that the relation between Ha and [OIII] luminosity does not change significantly over the redshift range, we predict the Ha number counts at z~2 - the upper end of the redshift range of interest for the future surveys. For the redshift range 0.7<z<2, we expect ~3000 galaxies/deg^2 for a flux limit of 3x10^{-16} ergs/s/cm^2 (the proposed depth of Euclid galaxy redshift survey) and ~20,000 galaxies/deg^2 for a flux limit of ~10^{-16} ergs/s/cm^2 (the baseline depth of WFIRST galaxy redshift survey).Comment: Minor revisions to match accepted ApJ versio

A Mixture of LBG Overdensities in the Fields of Three 6<z<76 < z < 7 Quasars: Implications for the Robustness of Photometric Selection

The most luminous quasars at $z > 6$ are suspected to be both highly clustered and reside in the most massive dark matter halos in the early Universe, making them prime targets to search for galaxy overdensities and/or protoclusters. We search for Lyman-break dropout-selected galaxies using HST WFC3/ACS broadband imaging in the fields of three $6 < z < 7$ quasars, as well as their simultaneously observed coordinated-parallel fields, and constrain their photometric redshifts using EAZY. One field, J0305-3150, shows a volume density 10$\times$ higher than the blank-field UV luminosity function (UVLF) at M$_{UV} < -20$, with tentative evidence of a 3$\sigma$ overdensity in its parallel field located 15 cMpc away. Another field, J2054-0005, shows an angular overdensity within 500 ckpc from the quasar but still consistent with UVLF predictions within 3$\sigma$, while the last field, J2348-3054, shows no enhancement. We discuss methods for reducing uncertainty in overdensity measurements when using photometric selection and show that we can robustly select LBGs consistent with being physically associated with the quasar, corroborated by existing JWST/NIRCam WFSS data in the J0305 field. Even accounting for incompleteness, the overdensities in J0305 and J2054 are higher for brighter galaxies at short angular separations, suggesting preferential enhancement of more massive galaxies in the immediate vicinity of the quasar. Finally, we compare the LBG population with previously-identified [CII] and mm-continuum companions; the LBG overdensities are not accompanied by an enhanced number of dusty galaxies, suggesting that the overdense quasar fields are not in the bursty star-forming phase sometimes seen in high-redshift protoclusters.Comment: 22 pages (main text), 12 figures, 10 tables, 2 appendices. Final version after addressing referee report, accepted to ApJ May 202

Lyman Continuum Escape Fraction from Low-mass Starbursts at z = 1.3

We present a new constraint on the Lyman continuum (LyC) escape fraction at . We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys Solar Blind Channel on the Hubble Space Telescope, targeting 11 star-forming galaxies at 1.2 190 Å, low stellar mass (M⋆ 3) in the individual galaxies or in the stack in the far-UV images. We place 3σ limits on the relative escape fraction of individual galaxies to be f_(esc,rel) < [0.10-0.22] and a stacked 3σ limit of f_(esc,rel) < 0.07. Measuring various galaxy properties, including stellar mass, dust attenuation, and star formation rate, we show that our measured values fall within the broad range of values covered by the confirmed LyC emitters from the literature. In particular, we compare the distribution of Hα and [O III] EWs of confirmed LyC emitters and non-detections, including the galaxies in this study. Finally, we discuss if a dichotomy seen in the distribution of Hα EWs can perhaps distinguish the LyC emitters from the non-detections

HST Grism-derived Forecasts for Future Galaxy Redshift Surveys

The mutually complementary Euclid and Roman galaxy redshift surveys will use Hα- and [O III]-selected emission-line galaxies (ELGs) as tracers of the large-scale structure at 0.9 ≾ z ≾ 1.9 (Hα) and 1.5 ≾ z ≾ 2.7 ([O III]). It is essential to have a reliable and sufficiently precise knowledge of the expected numbers of Hα-emitting galaxies in the survey volume in order to optimize these redshift surveys for the study of dark energy. Additionally, these future samples of ELGs will, like all slitless spectroscopy surveys, be affected by a complex selection function that depends on galaxy size and luminosity, line equivalent width (EW), and redshift errors arising from the misidentification of single ELGs. Focusing on the specifics of the Euclid survey, we combine two slitless spectroscopic WFC3-IR data sets—3D-HST+AGHAST and the WFC3 Infrared Spectroscopic Parallel survey—to construct a Euclid-like sample that covers an area of 0.56 deg² and includes 1277 ELGs. We detect 1091 (~3270 deg⁻²) Hα+[N II]-emitting galaxies in the range 0.9 ≤ z ≤ 1.6 and 162 (~440 deg⁻²) [O III] λ5007 emitters over 1.5 ≤ z ≤ 2.3 with line fluxes ≥2 × 10⁻¹⁶ erg s⁻¹ cm⁻². The median of the Hα+[N II] EW distribution is ~250 Å, and the effective radii of the continuum and Hα+[N II] emission are correlated with a median of ~0.”38 and significant scatter (σ ~ 0.”2–0.”35). Finally, we explore the prevalence of redshift misidentification in future Euclid samples, finding potential contamination rates of ~14%–20% and ~6% down to 2 × 10⁻¹⁶ erg s⁻¹ cm−2 and 6 × 10⁻¹⁷ erg s⁻¹ cm⁻², respectively, although with increased wavelength coverage these percentages drop to nearly zero