arXiv subjects

Steven L. Finkelstein

Publications and source records attributed to Steven L. Finkelstein.

At least 235 records · Page 13Linked to original sources

arXiv2021

The Shape and Scatter of The Galaxy Main Sequence for Massive Galaxies at Cosmic Noon

We present the main sequence for all galaxies and star-forming galaxies for a sample of 28,469 massive ($M_\star \ge 10^{11}$M$_\odot$) galaxies at cosmic noon ($1.5 < z < 3.0$), uniformly selected from a 17.5 deg$^2$ area (0.33 Gpc$^3$ comoving volume at these redshifts). Our large sample allows for a novel approach to investigating the galaxy main sequence that has not been accessible to previous studies. We measure the main sequence in small mass bins in the SFR-M$_{\star}$ plane without assuming a functional form for the main sequence. With a large sample of galaxies in each mass bin, we isolate star-forming galaxies by locating the transition between the star-forming and green valley populations in the SFR-M$_{\star}$ plane. This approach eliminates the need for arbitrarily defined fixed cutoffs when isolating the star-forming galaxy population, which often biases measurements of the scatter around the star-forming galaxy main sequence. We find that the main sequence for all galaxies becomes increasingly flat towards present day at the high-mass end, while the star-forming galaxy main sequence does not. We attribute this difference to the increasing fraction of the collective green valley and quiescent galaxy population from $z=3.0$ to $z=1.5$. Additionally, we measure the total scatter around the star-forming galaxy main sequence and find that it is $\sim0.5-1.0$ dex with little evolution as a function of mass or redshift. We discuss the implications that these results have for pinpointing the physical processes driving massive galaxy evolution.

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arXiv2021

The NEWFIRM HETDEX Survey: Photometric Catalog and a Conservative Sample of Massive Quiescent Galaxies at z=3-5 over 17.5 deg^2 in the SHELA Field

We present the results of a deep K_s-band (2.1 um) imaging survey of the Spitzer/HETDEX Exploratory Large Area (SHELA) field using the NEWFIRM near-infrared (NIR) camera on the KPNO Mayall 4-m telescope. This NEWFIRM HETDEX Survey (NHS) reaches a 5-sigma depth of 22.4 AB mag (2"-diameter apertures corrected to total), is ~50% and 90% complete at K~22.65 and K~22.15, respectively, and covers 22 deg^2 of the 24 deg^2 SHELA Spitzer/ IRAC footprint (within ``Stripe 82' of the Sloan Digital Sky Survey). We present a K_s-band-selected catalog which includes deep ugriz imaging from the Dark Energy Camera and 3.6 and 4.5 um imaging from Spitzer/IRAC, with forced-photometry of 1.7 million sources across 17.5 deg^2. The large area and moderate depth of this catalog enables the study of the most massive galaxies at high redshift, and minimizes uncertainties associated with counting statistics and cosmic variance. As a demonstration, we derive stellar masses (M*) and star-formation rates (SFRs) for candidate galaxies at 3 < z < 5, and select a conservative sample of nine candidate massive (M* > 10^11 Msol) quiescent galaxies, which have measured SFRs significantly below the main-sequence at this redshift. Five are ultra-massive with M* > 10^12, though uncertainties in IRAC blending, gravitational lensing, or AGN emission could result in true masses which are lower. Simulations predict that these galaxies should be extremely rare, thus we discuss what physical processes in models could be altered to allow the formation of such massive quiescent galaxies at such early times.

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arXiv2021

The HETDEX Survey: The Ly$α$ Escape Fraction from 3D-HST Emission Line Galaxies at $z \sim 2$

We measure the Ly$α$ escape fraction of 935 [OIII]-emitting galaxies between $1.9 < z < 2.35$ by comparing stacked spectra from the Hubble Space Telescope/WFC3's near-IR grism to corresponding stacks from the Hobby Eberly Telescope Dark Energy Experiment's Internal Data Release 2. By measuring the stacks' H$β$ to Ly$α$ ratios, we determine the Ly$α$ escape fraction as a function of stellar mass, star formation rate, internal reddening, size, and [OIII]/H$β$ ratio. We show that the escape fraction of Ly$α$ correlates with a number of parameters, such as galaxy size, star formation rate, and nebular excitation. However, we also demonstrate that most of these relations are indirect, and the primary variables that control the escape of Ly$α$ are likely stellar mass and internal extinction. Overall, the escape of Ly$α$ declines from $\gtrsim 18\%$ in galaxies with $\log M/M_{\odot} \lesssim 9$ to $\lesssim 1\%$ for systems with $\log M/M_{\odot} \gtrsim 10$, with the sample's mean escape fraction being $6.0^{+0.6\%}_{-0.5\%}$.

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arXiv2021

The Stars of the HETDEX Survey. I. Radial Velocities and Metal-Poor Stars from Low-Resolution Stellar Spectra

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution ($R\sim750$) spectra of Lyman-Alpha Emitters. In its search for these galaxies, HETDEX will also observe a few 10$^{5}$ stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between $10 < G < 22$ spread across the HETDEX footprint at relatively high ($b\sim60^\circ$) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for $\sim$42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1$σ$ precision of 28.0 km/s and bias of 3.5 km/s with respect to the LAMOST surveys and 1$σ$ precision of 27.5 km/s and bias of 14.0 km/s compared to the SEGUE survey. Since these RVs are for faint ($G\geq16$) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (t-SNE), we also demonstrate that the HETDEX spectra can be used to determine a star's T${\rm{eff}}$, and log g and its [Fe/H]. With the t-SNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] $< -1$~dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys.

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arXiv2020

Texas Spectroscopic Search for Ly$α$ Emission at the End of Reionization III. the Ly$α$ Equivalent-width Distribution and Ionized Structures at $z > 7$

Ly$α$ emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Ly$α$ emission at $z>7$ using a comprehensive Keck/MOSFIRE near-infrared spectroscopic dataset, as part of the Texas Spectroscopic Search for Ly$α$ Emission at the End of Reionization Survey. We analyze data from 10 nights of MOSFIRE observations which together target 72 high-$z$ candidate galaxies in the GOODS-N field, all with deep exposure times of 4.5-19 hr. Utilizing an improved automated emission-line search, we report 10 Ly$α$ emission lines detected ($>$4$σ$) at $z>7$, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Ly$α$ emitters ($>$50Å), and additional tentative Ly$α$ emission lines detected at 3 - 4$σ$ from five additional galaxies. We constrain the Ly$α$ EW distribution at $z\sim7.6$, finding a significant drop from $z\lesssim6$, suggesting an increasing fraction of neutral hydrogen (HI) in the IGM in this epoch. We estimate the Ly$α$ transmission through the IGM ($=$EW$_{z\sim\text{7.6}}$/EW$_{z\sim\text{2-6}}$), and infer an IGM HI fraction ($X_{\text{HI}}$) of $49^{+19}_{-19}\%$ at $z\sim7.6$, which is lower in modest tension ($>$1$σ$) with recent measurements at $z \sim$ 7.6. The spatial distribution of the detected Ly$α$ emitters implies the presence of a potential highly ionized region at $z\sim7.55$ which hosts four Ly$α$ emitters within a $\sim$ 40 cMpc spatial separation. The prominence of this ionized region in our dataset could explain our lower inferred value of $X_{\text{HI}}$, though our analysis is also sensitive to the chosen reference Ly$α$ EW distribution values and reionization models.

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arXiv2020

JWST/MIRI Simulated Imaging: Insights into Obscured Star-Formation and AGN for Distant Galaxies in Deep Surveys

The JWST MIRI instrument will revolutionize extragalactic astronomy with unprecedented sensitivity and angular resolution in mid-IR. Here, we assess the potential of MIRI photometry to constrain galaxy properties in the Cosmic Evolution Early Release Science (CEERS) survey. We derive estimated MIRI fluxes from the spectral energy distributions (SEDs) of real sources that fall in a planned MIRI pointing. We also obtain MIRI fluxes for hypothetical AGN-galaxy mixed models varying the AGN fractional contribution to the total IR luminosity ($\rm frac_{AGN}$). Based on these model fluxes, we simulate CEERS imaging (3.6-hour exposure) in 6 bands from F770W to F2100W using MIRISIM, and reduce these data using JWST PIPELINE. We perform PSF-matched photometry with TPHOT, and fit the source SEDs with X-CIGALE, simultaneously modeling photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both redshift and $\rm frac_{AGN}$ is generally improved by factors of $\gtrsim 2$ for all sources at $z\lesssim 3$. Notably, for pure-galaxy inputs ($\rm frac_{AGN}=0$), the accuracy of $\rm frac_{AGN}$ is improved by $\sim 100$ times thanks to MIRI. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical $L_{\rm X}$-$L_{\rm 6μm}$ relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy $\approx 0.3$ dex). Our work demonstrates that MIRI will be able to place strong constraints on the mid-IR luminosities from star formation and AGN, and thereby facilitate studies of the galaxy/AGN co-evolution.

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arXiv2020

CLEAR: The Gas-Phase Metallicity Gradients of Star-Forming Galaxies at 0.6 < z < 2.6

We report on the gas-phase metallicity gradients of a sample of 264 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12-orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lya Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies (84%) in this sample are consistent with a zero or slightly positive metallicity gradient across the full mass range probed (8.5 < log M_*/M_sun < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass---consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider---including star-formation rates, sizes, star-formation rate surface densities, and star-formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.

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arXiv2020

Investigating The Growing Population of Massive Quiescent Galaxies at Cosmic Noon

We explore the buildup of quiescent galaxies using a sample of 28,469 massive ($M_\star \ge 10^{11}$M$_\odot$) galaxies at redshifts $1.5<z<3.0$, drawn from a 17.5 deg$^2$ area (0.33 Gpc$^3$ comoving volume at these redshifts). This allows for a robust study of the quiescent fraction as a function of mass at $1.5<z<3.0$ with a sample $\sim$40 times larger at log($M_{\star}$/$\rm M_{\odot}$)$\ge11.5$ than previous studies. We derive the quiescent fraction using three methods: specific star-formation rate, distance from the main sequence, and UVJ color-color selection. All three methods give similar values at $1.5<z<2.0$, however the results differ by up to a factor of two at $2.0<z<3.0$. At redshifts $1.5 < z < 3.0$ the quiescent fraction increases as a function of stellar mass. By $z=2$, only 3.3 Gyr after the Big Bang, the universe has quenched $\sim$25% of $M_\star = 10^{11}$M$_\odot$ galaxies and $\sim$45% of $M_\star = 10^{12}$M$_\odot$ galaxies. We discuss physical mechanisms across a range of epochs and environments that could explain our results. We compare our results with predictions from hydrodynamical simulations SIMBA and IllustrisTNG and semi-analytic models (SAMs) SAG, SAGE, and Galacticus. The quiescent fraction from IllustrisTNG is higher than our empirical result by a factor of $2-5$, while those from SIMBA and the three SAMs are lower by a factor of $1.5-10$ at $1.5<z<3.0$.

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arXiv2020

Cosmological 3D HI Gas Map with HETDEX Ly$α$ Emitters and eBOSS QSOs at $z=2$: IGM-Galaxy/QSO Connection and a $\sim$ 40-Mpc Scale Giant HII Bubble Candidate

We present cosmological ($30-400$ Mpc) distributions of neutral hydrogen (HI) in the inter-galactic medium (IGM) traced by Ly$α$ Emitters (LAEs) and QSOs at $z=2.1-2.5$, selected with the data of the on-going Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the eBOSS survey. We investigate spatial correlations of LAEs and QSOs with HI tomography maps reconstructed from HI Ly$α$ forest absorption in the spectra of background galaxies and QSOs obtained by the CLAMATO survey and this study, respectively. In the cosmological volume far from QSOs, we find that LAEs reside in regions of strong HI absorption, i.e. HI rich, which is consistent with results of previous galaxy-background QSO pair studies. Moreover, there is an anisotropy in the HI-distribution plot of transverse and line-of-sight distances; on average the HI absorption peak is blueshifted by $\sim 200$ km s$^{-1}$ from the LAE Ly$α$ redshift, reproducing the known average velocity offset between the Ly$α$ emission redshift and the galaxy systemic redshift. We have identified a $\sim$ 40-Mpc scale volume of HI underdensity that is a candidate for a giant HII bubble, where six QSOs and an LAE overdensity exist at $\left < z \right > =2.16$. The coincidence of the QSO and LAE overdensities with the HI underdensity indicates that the ionizing photon radiation of the QSOs has created a highly ionized volume of multiple proximity zones in a matter overdensity. Our results suggest an evolutionary picture where HI gas in an overdensity of galaxies becomes highly photoionized when QSOs emerge in the galaxies.

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arXiv2020

Exploring AGN and Star Formation Activity of Massive Galaxies at Cosmic Noon

We investigate the relation between AGN and star formation (SF) activity at $0.5 < z < 3$ by analyzing 898 galaxies with X-ray luminous AGN ($L_X > 10^{44}$ erg s$^{-1}$) and a large comparison sample of $\sim 320,000$ galaxies without X-ray luminous AGN. Our samples are selected from a large (11.8 deg$^2$) area in Stripe 82 that has multi-wavelength (X-ray to far-IR) data. The enormous comoving volume ($\sim 0.3$ Gpc$^3$) at $0.5 < z < 3$ minimizes the effects of cosmic variance and captures a large number of massive galaxies ($\sim 30,000$ galaxies with $M_* > 10^{11} \ M_{\odot}$) and X-ray luminous AGN. While many galaxy studies discard AGN hosts, we fit the SED of galaxies with and without X-ray luminous AGN with Code Investigating GALaxy Emission (CIGALE) and include AGN emission templates. We find that without this inclusion, stellar masses and star formation rates (SFRs) in AGN host galaxies can be overestimated, on average, by factors of up to $\sim 5$ and $\sim 10$, respectively. The average SFR of galaxies with X-ray luminous AGN is higher by a factor of $\sim 3$ to $10$ compared to galaxies without X-ray luminous AGN at fixed stellar mass and redshift, suggesting that high SFRs and high AGN X-ray luminosities may be fueled by common mechanisms. The vast majority ($> 95 \%$) of galaxies with X-ray luminous AGN at $z=0.5-3$ do not show quenched SF: this suggests that if AGN feedback quenches SF, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity.

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arXiv2020

A Strong-Lensing Model for the WMDF JWST/GTO Very Rich Cluster Abell 1489

We present a first strong-lensing model for the galaxy cluster RM J121218.5+273255.1 ($z=0.35$; hereafter RMJ1212; also known as Abell 1489). This cluster is amongst the top 0.1\% richest clusters in the redMaPPer catalog; it is significantly detected in X-ray and through the Sunyaev-Zel'dovich effect in ROSAT and \emph{Planck} data, respectively; and its optical luminosity distribution implies a very large lens, following mass-to-light scaling relations. Based on these properties it was chosen for the Webb Medium Deep Fields (WMDF) JWST/GTO program. In preparation for this program, RMJ1212 was recently imaged with GMOS on Gemini North and in seven optical and near-infrared bands with the \emph{Hubble Space Telescope}. We use these data to map the inner mass distribution of the cluster, uncovering various sets of multiple images. We also search for high-redshift candidates in the data, as well as for transient sources. We find over a dozen high-redshift ($z\gtrsim6$) candidates based on both photometric redshift and the dropout technique. No prominent ($\gtrsim5 σ$) transients were found in the data between the two HST visits. Our lensing analysis reveals a relatively large lens with an effective Einstein radius of $θ_{E}\simeq32\pm3''$ ($z_{s}=2$), in broad agreement with the scaling-relation expectations. RMJ1212 demonstrates that powerful lensing clusters can be selected in a robust and automated way following the light-traces-mass assumption.

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arXiv2020

Semi-analytic forecasts for JWST -- IV. Implications for cosmic reionization and LyC escape fraction

Galaxies forming in low-mass halos are thought to be primarily responsible for reionizing the Universe during the first billion years after the Big Bang. Yet, these halos are extremely inefficient at forming stars in the nearby Universe. In this work, we address this apparent tension, and ask whether a physically motivated model of galaxy formation that reproduces the observed abundance of faint galaxies in the nearby Universe is also consistent with available observational constraints on the reionization history. By interfacing the Santa Cruz semi-analytic model for galaxy formation with an analytic reionization model, we constructed a computationally efficient pipeline that connects `ground-level' galaxy formation physics to `top-level' cosmological-scale observables. Based on photometric properties of the galaxy populations predicted up to $z=15$, we compute the reionization history of intergalactic hydrogen. We quantify the three degenerate quantities that influence the total ionizing photon budget, including the abundance of galaxies, the intrinsic production rate of ionizing photons, and the LyC escape fraction. We explore covariances between these quantities using a Markov chain Monte Carlo method. We find that our locally calibrated model is consistent with all currently available constraints on the reionization history, under reasonable assumptions about the LyC escape fraction. We quantify the fraction of ionizing photons contributed by galaxies of different luminosities and find that the galaxies expected to be detected in JWST NIRCam wide and deep surveys are responsible for producing $\sim 40$-$80\%$ of ionizing photons throughout the EoR. All results presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.

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arXiv2020

CLEAR II: Evidence for Early Formation of the Most Compact Quiescent Galaxies at High Redshift

The origin of the correlations between mass, morphology, quenched fraction, and formation history in galaxies is difficult to define, primarily due to the uncertainties in galaxy star-formation histories. Star-formation histories are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. Here we use "non-parametric" star-formation histories and a nested sampling method to derive constraints on the formation and quenching timescales of quiescent galaxies at $0.7 $10.25, where $Σ_1$ is the stellar mass within 1~pkpc (proper kpc). Quiescent galaxies with the highest stellar-mass surface density, $\logΣ_1 / (M_\odot\ \mathrm{kpc}^{-2}) > 10.25$, } show a \textit{minimum} formation redshift: all such objects in our sample have $z_{50} > 2.9$. Quiescent galaxies with lower surface density, $\log Σ_1 / (M_\odot\ \mathrm{kpc}^{-2}) = 9.5 - 10.25$, show a range of formation epochs ($z_{50} \simeq 1.5 - 8$), implying these galaxies experienced a range of formation and assembly histories. We argue that the surface density threshold $\logΣ_1/(M_\odot\ \mathrm{kpc}^{-2})>10.25$ uniquely identifies galaxies that formed in the first few Gyr after the Big Bang, and we discuss the implications this has for galaxy formation models.

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arXiv2020

Semi-analytic forecasts for JWST -- III. Intrinsic production efficiency of Lyman-continuum radiation

The James Webb Space Telescope (JWST) is expected to enable transformational progress in studying galaxy populations in the very early Universe, during the Epoch of Reionization (EoR). A critical parameter for understanding the sources that reionized the Universe is the Lyman-continuum production efficiency, $ξ_{\rm ion}$, defined as the rate of production of ionizing photons divided by the intrinsic UV luminosity. In this work, we combine self-consistent star formation and chemical enrichment histories predicted by semi-analytic models of galaxy formation with stellar population synthesis (SPS) models to predict the expected dependence of $ξ_{\rm ion}$ on galaxy properties and cosmic epoch from $z=4-10$. We then explore the sensitivity of the production rate of ionizing photons, $\dot{N}_{\rm ion}$, to the choice of SPS model and the treatment of stellar feedback in our galaxy formation model. We compare our results to those of other simulations, constraints from empirical models, and observations. We find that adopting SPS models that include binary stars predict about a factor of two more ionizing radiation than models that only assume single stellar populations. We find that UV-faint, low-mass galaxies have values of $ξ_{\rm ion}$ about 0.25 dex higher than those of more massive galaxies, but find weak evolution with cosmic time, about 0.2 dex from $z\sim 12-4$ at fixed rest-UV luminosity. We provide predictions of $\dot{N}_{\rm ion}$ as a function of $M_{\rm h}$ and a number of other galaxy properties. All results presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.

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arXiv2020

Probing the Bright End of the Rest-Frame Ultraviolet Luminosity Function at z = 8-10 with Hubble Pure-Parallel Imaging

Looking for bright galaxies born in the early universe is fundamental to investigating the Epoch of Reionization, the era when the first stars and galaxies ionized the intergalactic medium. We utilize Hubble Space Telescope pure parallel imaging to select galaxy candidates at a time 500 to 650 million years after the Big Bang, which corresponds to redshifts z ~ 8-10. These data come from the Brightest of Reionizing Galaxies Survey (BoRG) Cycle 22 dataset, which consists of pure-parallel imaging in ~ 90 different lines of sight that sum up to an area of ~ 420 arcmin^2. This survey uses five filters and has the advantage (compared to the Cycle 21 BoRG program) of including imaging in the JH140 band, covering continuous wavelengths from the visible to near-infrared (lambda = 0.35um - 1.7um). This allows us to perform reliable selection of galaxies at z>8 using the photometric redshift technique. We use these galaxy candidates to constrain the bright end of the rest-frame ultraviolet luminosity function in this epoch. These candidates are excellent targets for follow-up observations, particularly with the James Webb Space Telescope.

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arXiv2020

On the (Lack of) Evolution of the Stellar Mass Function of Massive Galaxies from $z$=1.5 to 0.4

We study the evolution in the number density of the highest mass galaxies over $0.4 10.3$ using a forward-modeling method that fully accounts for statistical and systematic uncertainties on stellar mass. From $z$=0.4 to 1.5 the massive end of the SMF shows minimal evolution in its shape: the characteristic mass ($M^\ast$) evolves by less than 0.1 dex ($\pm$0.05 dex); the number density of galaxies with $\log (M_\ast/M_\odot) >11$ stays roughly constant at $\log (n/\mathrm{Mpc}^{-3})$ $\simeq$ $-$3.4 ($\pm$0.05), then declines to $\log (n/\mathrm{Mpc}^{-3})$=$-$3.7 ($\pm$0.05) at $z$=1.5. We discuss the uncertainties in the SMF, which are dominated by assumptions in the star formation history and details of stellar population synthesis models for stellar mass estimations. For quiescent galaxies, the data are consistent with no (or slight) evolution ($\lesssim0.1$ dex) in the characteristic mass nor number density from $z\sim 1.5$ to the present. This implies that any mass growth (presumably through "dry" mergers) of the quiescent massive galaxy population must balance the rate of mass losses from late-stage stellar evolution and the formation of quenching galaxies from the star-forming population. We provide a limit on this mass growth from $z=1.0$ to 0.4 of $ΔM_\ast/M_\ast\leq$ 45% (i.e., $\simeq0.16$ dex) for quiescent galaxies more massive than $10^{11}$ $M_\odot$.

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arXiv2020

A comprehensive study of H$α$ emitters at $z \sim$ 0.62 in the DAWN survey: the need for deep and wide regions

We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an H$α$ selected sample at $z\sim0.62$ from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new H$α$ sample in the extended COSMOS region (compared to Coughlin et al. 2018) with the inclusion of flanking fields, resulting in a total area coverage of $\sim$1.5 deg$^2$. A total of 241 H$α$ emitters were selected based on robust selection criteria using spectro-photometric redshifts and broadband color-color classification. We explore the effect of different dust correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, A{$_{\textrm{H}α}=1$} mag, a luminosity-dependent correction, and a stellar-mass dependent correction. The resulting H$α$ LFs are well fitted using Schechter functions with best-fit parameters: L$^*=10^{42.24}$ erg s$^{-1}$, $ϕ^*=10^{-2.85}$ Mpc$^{-3}$, $α= -1.62$ for constant dust correction, L$^*=10^{42.31}$ erg s$^{-1}$, $ϕ^*=10^{-2.8}$ Mpc$^{-3}$, $α=-1.39$ for luminosity-dependent dust correction, and L$^*=10^{42.36}$ erg s$^{-1}$, $ϕ^*=10^{-2.91}$ Mpc$^{-3}$, $α= -1.48$, for stellar mass-dependent dust correction. The deep and wide nature of the DAWN survey effectively samples H$α$ emitters over a wide range of luminosities, thereby providing better constraints on both the faint and bright end of the LF. Also, the SFRD estimates $ρ_{\textrm{SFR}}=10^{-1.39}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (constant dust correction), $ρ_{\textrm{SFR}}=10^{-1.47}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (luminosity-dependent dust correction), and $ρ_{\textrm{SFR}}=10^{-1.49}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (stellar mass-dependent dust correction) are in good agreement with the evolution of SFRD across redshifts ($0 < z < 2$) seen from previous H$α$ surveys.

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arXiv2020

The Atacama Cosmology Telescope: SZ-based masses and dust emission from IR-selected cluster candidates in the SHELA survey

We examine the stacked thermal Sunyaev-Zel\text{'}dovich (SZ) signals for a sample of galaxy cluster candidates from the Spitzer-HETDEX Exploratory Large Area (SHELA) Survey, which are identified in combined optical and infrared SHELA data using the redMaPPer algorithm. We separate the clusters into three richness bins, with average photometric redshifts ranging from 0.70 to 0.80. The richest bin shows a clear temperature decrement at 148 GHz in the Atacama Cosmology Telescope data, which we attribute to the SZ effect. All richness bins show an increment at 220 GHz, which we attribute to dust emission from cluster galaxies. We correct for dust emission using stacked profiles from Herschel Stripe 82 data, and allow for synchrotron emission using stacked profiles created by binning source fluxes from NVSS data. We see dust emission in all three richness bins, but can only confidently detect the SZ decrement in the highest richness bin, finding $M_{500}$ = $8.7^{+1.7}_{-1.3} \times 10^{13} M_\odot$. Neglecting the correction for dust depresses the inferred mass by 26 percent, indicating a partial fill-in of the SZ decrement from thermal dust and synchrotron emission by the cluster member galaxies. We compare our corrected SZ masses to two redMaPPer mass--richness scaling relations and find that the SZ mass is lower than predicted by the richness. We discuss possible explanations for this discrepancy, and note that the SHELA richnesses may differ from previous richness measurements due to the inclusion of IR data in redMaPPer.

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