arXiv subjects

Sangeeta Malhotra

Publications and source records attributed to Sangeeta Malhotra.

At least 37 records · Page 2Linked to original sources

arXiv2023

Constraints on the Epoch of Reionization with Roman Space Telescope and the Void Probability Function of Lyman-Alpha Emitters

We use large simulations of Lyman-Alpha Emitters with different fractions of ionized intergalactic medium to quantify the clustering of Ly$α$ emitters as measured by the Void Probability function (VPF), and how it evolves under different ionization scenarios. We quantify how well we might be able to distinguish between these scenarios with a deep spectroscopic survey using the future Nancy Grace Roman Space Telescope. Since Roman will be able to carry out blind spectroscopic surveys of Ly$α$ emitters continuously between $7 3-4σ$ at several redshifts between $7 5-8σ$) across the epoch of reionization, and would yield a detailed history of the reionization of the IGM and its effect on Lyman-$α$ Emitter clustering.

astro-ph.CO↗

arXiv2022

Semi-analytic forecasts for Roman -- the beginning of a new era of deep-wide galaxy surveys

The Nancy Grace Roman Space Telescope, NASA's next flagship observatory, will redefine deep-field galaxy survey with a field of view two orders of magnitude larger than Hubble and an angular resolution of matching quality. These future deep-wide galaxy surveys necessitate new simulations to forecast their scientific output and to optimise survey strategies. In this work, we present five realizations of 2-deg^2 lightcones, containing a total of >25 million simulated galaxies with -16 < MUV < -25 spanning z ~ 0 to 10. This dataset enables a new set of experiments with the impacts of survey size on the derived galaxy formation and cosmological constraints. The intrinsic and observable galaxy properties are predicted using a well-established, physics-based semi-analytic modelling approach. We provide forecasts for number density, cosmic SFR, field-to-field variance, and angular two-point correlation functions, and demonstrate how the future wide-field surveys will be able to improve these measurements relative to current generation surveys. We also present a comparison between these lightcones and others that have been constructed with empirical models. The mock lightcones are designed to facilitate the exploration of multi-instrument synergies and connecting with current generation instruments and legacy surveys. In addition to Roman, we also provide photometry for a number of other instruments on upcoming facilities, including Euclid and Rubin, as well as the instruments that are part of many legacy surveys. Full object catalogues and data tables for the results presented in this work are made available through a web-based, interactive portal https://www.simonsfoundation.org/semi-analytic-forecasts.

astro-ph.GA↗

arXiv2022

Probing Patchy Reionization with the Void Probability Function of Lyman-$α$ Emitters

We probe what constraints for the global ionized hydrogen fraction the Void Probability Function (VPF) clustering can give for the Lyman-Alpha Galaxies in the Epoch of Reionization (LAGER) narrowband survey as a function of area. Neutral hydrogen acts like a fog for Lyman-alpha emission, and measuring the drop in the luminosity function of Lyman-$α$ emitters (LAEs) has been used to constrain the ionization fraction in narrowband surveys. However, the clustering of LAEs is independent from the luminosity function's inherent evolution, and can offer additional constraints for reionization under different models. The VPF measures how likely a given circle is to be empty. It is a volume-averaged clustering statistic that traces the behavior of higher order correlations, and its simplicity offers helpful frameworks for planning surveys. Using the \citet{Jensen2014} simulations of LAEs within various amount of ionized intergalactic medium, we predict the behavior of the VPF in one (301x150.5x30 Mpc$^3$), four (5.44$\times 10^6$ Mpc$^3$), or eight (1.1$\times 10^7$ Mpc$^3$) fields of LAGER imaging. We examine the VPF at 5 and 13 arcminutes, corresponding to the minimum scale implied by the LAE density and the separation of the 2D VPF from random, and the maximum scale from the 8-field 15.5 deg$^2$ LAGER area. We find that even a single DECam field of LAGER (2-3 deg$^2$) could discriminate between mostly neutral vs. ionized. Additionally, we find four fields allows the distinction between 30, 50, and 95 percent ionized; and that eight fields could even distinguish between 30, 50, 73, and 95 percent ionized.

astro-ph.CO↗

arXiv2022

Finding Peas in the Early Universe with JWST

The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at cosmic dawn. We analyze the ERO spectra of three $z \sim 8$ galaxies to determine their metallicities, gas temperatures and ionization. These galaxies offer the first opportunity to understand the physical properties of epoch-of-reionization galaxies through detailed rest-optical emission line spectroscopy. We show that these objects have metal abundances $12+\log[O/H] \approx 6.9 - 8.2$, based on both the $T_e$ method and on a recent calibration of the $R_{23}$ metallicity indicator. Since the spectra are some of the earliest science data from JWST, we compare several line ratios with values expected from robust physics, to validate our measurement procedures. We compare the abundances and emission line ratios to a nearby sample of Green Pea galaxies -- a population of nearby emission line galaxies whose UV properties resemble epoch-of-reionization galaxies, and which often have large Lyman continuum escape fractions. The JWST data show striking further similarities between these high redshift galaxies and nearby Green Peas. The $z\sim 8$ galaxies span the metallicity range covered by Green Peas. They also show the compact morphology that is typical of emission line dominated galaxies at all redshifts. Based on these similarities with Green Peas, it is likely that these are the first rest-optical spectra of galaxies that are actively driving cosmological reionization

astro-ph.GA↗

arXiv2022

Evidence for Black Holes in Green Peas from WISE colors and variability

We explore the presence of active galactic nuclei (AGN)/black holes (BH) in Green Pea galaxies (GPs), motivated by the presence of high ionization emission lines such as HeII and [NeIII] in their optical spectra. In order to identify AGN candidates, we used mid-infrared (MIR) photometric observations from the all-sky Wide-field Infrared Survey Explorer (WISE) mission for a sample of 1004 GPs. Considering only $>5σ$ detections with no contamination from neighboring sources in AllWISE, we select 31 GPs out of 134 as candidate AGN based on a stringent 3-band WISE color diagnostic. Using multi-epoch photometry in W1 and W2 bands based on time-resolved unWISE coadd images, we find two sources exhibiting variability in both the WISE bands among 112 GPs with W1$\leqslant16$ mag and no contamination from neighboring sources in unWISE. These two variable sources were selected as AGN by the WISE 3-band color diagnostic as well. Compared to variable AGN fractions observed among low-mass galaxy samples in previous studies, we find a higher fraction ($\sim1.8\%$) of MIR variable sources among GPs, which demonstrates the uniqueness and importance of studying these extreme objects. Through this work, we demonstrate that MIR diagnostics are promising tools to select AGN that may be missed by other selection techniques (including optical emission-line ratios and X-ray emission) in star-formation dominated, low-mass, low-metallicity galaxies.

astro-ph.GA↗

arXiv2022

Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid

Dark matter halos that reach the HI-cooling mass without prior star formation or external metal pollution represent potential sites for the formation of small - extremely faint - Population III galaxies at high redshifts. Gravitational lensing may in rare cases boost their fluxes to detectable levels, but to find even a small number of such objects in randomly selected regions of the sky requires very large areas to be surveyed. Because of this, a small, wide-field telescope can in principle offer better detection prospects than a large telescope with a smaller field of view. Here, we derive the minimum comoving number density required to allow gravitational lensing to lift such objects at redshift $z=5-16$ above the detection thresholds of blind surveys carried out with the James Webb space telescope (JWST), the Roman space telescope (RST) and Euclid. We find that the prospects for photometric detections of Pop III galaxies is promising, and that they are better for RST than for JWST and Euclid. However, the Pop III galaxies favoured by current simulations have number densities too low to allow spectroscopic detections based on the strength of the HeII1640 emission line in any of the considered surveys unless very high star formation efficiencies ($ε> 0.1$) are envoked. We argue that targeting individual cluster lenses instead of the wide field surveys considered in this paper results in better spectroscopic detection prospects, while for photometric detection, the wide field surveys perform considerably better.

astro-ph.GA↗

arXiv2022

LAGER Ly$α$ Luminosity Function at $z\sim7$, Implications for Reionization

We present a new measurement of the Ly$α$ luminosity function at redshift $z=6.9$, finding moderate evolution from $z=5.7$ that is consistent with a fully or largely ionized $z\sim7$ intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of $6.1\times10^{6}$ Mpc$^{3}$ is double that of the next largest $z\sim 7$ survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify $N=95$ new $z=6.9$ Ly$α$ emitters (LAEs); characterize our survey's completeness and reliability; and compute Ly$α$ luminosity functions. The best-fit Schechter luminosity function parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Ly$α$ luminosity density declines at the same rate as the UV continuum LF from $z=5.7$ to $z=6.9$. This is consistent with an intergalactic medium that was fully ionized as early as redshift $z\sim 7$, or with a volume-averaged neutral hydrogen fraction of $x_{HI} < 0.33$ at $1σ$.

astro-ph.GA↗

arXiv2021

New spectroscopic confirmations of Lyman-$α$ emitters at z $\sim$ 7 from the LAGER survey

We report spectroscopic confirmations of 15 Lyman-alpha galaxies at $z\sim7$, implying a spectroscopic confirmation rate of $\sim$80% on candidates selected from LAGER (Lyman-Alpha Galaxies in the Epoch of Reionization), which is the largest (24 deg$^2$) survey aimed at finding Lyman-alpha emitters (LAEs) at $z\sim7$ using deep narrow-band imaging from DECam at CTIO. LAEs at high-redshifts are sensitive probes of cosmic reionization and narrow-band imaging is a robust and effective method for selecting a large number of LAEs. In this work, we present results from the spectroscopic follow-up of LAE candidates in two LAGER fields, COSMOS and WIDE-12, using observations from Keck/LRIS. We report the successful detection of Ly$α$ emission in 15 candidates (11 in COSMOS and 4 in WIDE-12 fields). Three of these in COSMOS have matching confirmations from a previous LAGER spectroscopic follow-up and are part of the overdense region, LAGER-$z7$OD1. Additionally, two candidates that were not detected in the LRIS observations have prior spectroscopic confirmations from Magellan. Including these, we obtain a spectroscopic confirmation success rate of $\sim$$80$% for LAGER LAE candidates. Apart from Ly$α$, we do not detect any other UV nebular lines in our LRIS spectra; however, we estimate a 2$σ$ upper limit for the ratio of NV/Ly$α$, $f_{NV}/f_{Lyα} \lesssim 0.27$, which implies that ionizing emission from these sources is mostly dominated by star formation. Including confirmations from this work, a total of 33 LAE sources from LAGER are now spectroscopically confirmed. LAGER has more than doubled the sample of spectroscopically confirmed LAE sources at $z\sim7$.

astro-ph.GA↗

arXiv2021

The Compact UV Size of Green Pea Galaxies As Local Analogs of High-redshift Ly$α$-Emitters

We study the dependence of Ly$α$ escape from galaxies on UV continuum size and luminosity using a sample of 40 Green Pea (GP) galaxies, which are the best local analogs of high-redshift Ly$α$-emitters (LAEs). We use the Cosmic Origins Spectrograph near-ultraviolet images from the \textit{Hubble Space Telescope} to measure the UV size and luminosity with $0.047''$ spatial resolution. Like most galaxies the GPs show a log-normal size distribution. They also show a positive correlation between size and UV-continuum luminosity. The slope of the size-continuum luminosity relation for GPs is consistent with those of continuum-selected star-forming galaxies at low and high redshifts. A distinctive feature of GPs is a very compact typical radius of 0.33 kpc with a population spread (1$σ$) of 0.19 kpc. The peak of the size distribution and the intercept of the size-luminosity relation of GPs are noticeably smaller than those of continuum-selected star-forming galaxies at similar redshifts. There are statistically significant anti-correlations found between the circularized half-light radius ($r_{\rm cir,50}$), the Ly$α$ equivalent width (EW(Ly$α$)), and the Ly$α$ escape faction ($f^{Lyα}_{esc}$), suggesting that small UV-continuum radii are crucial for Ly$α$ emission. GPs and high-redshift LAEs have similar sizes, once spatial resolution effects are properly considered. Our results show that a compact/small size is crucial for escape of Ly$α$ photons, and that Ly$α$-emitters show constant characteristic size independent of their redshift.

astro-ph.GA↗

arXiv2021

The Metal Abundances across Cosmic Time ($\mathcal{MACT}$) Survey. III -- The relationship between stellar mass and star formation rate in extremely low-mass galaxies

Extragalactic studies have demonstrated there is a moderately tight ($\approx$0.3 dex) relationship between galaxy stellar mass ($M_{\star}$) and star formation rate (SFR) that holds for star-forming galaxies at $M_{\star} \sim 3 \times 10^8$-10$^{11}~M_{\odot}$, i.e., the "star formation main sequence." However, it has yet to be determined whether such a relationship extends to even lower mass galaxies, particularly at intermediate or higher redshifts. We present new results using observations for 714 narrowband H$α$-selected galaxies with stellar masses between $10^6$ and $10^{10}~M_{\odot}$ (average of $10^{8.2}~M_{\odot}$) at $z \approx$ 0.07-0.5. These galaxies have sensitive UV to near-infrared photometric measurements and optical spectroscopy. The latter allows us to correct our H$α$ SFRs for dust attenuation using Balmer decrements. Our study reveals: (1) for low-SFR galaxies, our H$α$ SFRs systematically underpredict compared to FUV measurements, consistent with other studies; (2) at a given stellar mass ($\approx $10$ ^{8}~M_{\odot}$), log(specific SFR) evolves as $ A \log(1+z) $ with $ A = 5.26 \pm 0.75 $, and on average, specific SFR increases with decreasing stellar mass; (3) the SFR-$M_{\star}$ relation holds for galaxies down to $\sim$10$^6~M_{\odot}$ ($\sim$1.5 dex below previous studies), and over lookback times of up to 5 Gyr, follows a redshift-dependent relation of $\log{({\rm SFR})} \propto α\log(M_{\star}/M_{\odot}) + βz$ with $α= 0.60 \pm 0.01$ and $β= 1.86 \pm 0.07$; and (4) the observed dispersion in the SFR-$M_{\star}$ relation at low stellar masses is $\approx$0.3 dex. Accounting for survey selection effects using simulated galaxies, we estimate the true dispersion is $\approx$0.5 dex.

astro-ph.GA↗

arXiv2021

Correlations between H$α$ Equivalent Width and Galaxy Properties at $z = 0.47$: Physical or Selection-driven?

The H$α$ equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic star-formation activity. Previous assessments show that EW strongly anti-correlates with stellar mass as $M^{-0.25}$ similar to the sSFR -- stellar mass relation. However, such a correlation may be driven/formed by selection effects. In this study, we investigate how H$α$ EWs correlate with galaxy properties and how selection biases could alter such correlations using a $z = 0.47$ narrowband-selected sample of 1572 H$α$ emitters from the Ly$α$ Galaxies in the Epoch of Reionization (LAGER) survey. The sample covers 3 deg$^2$ of COSMOS and $1.1\times10^5$ cMpc$^3$. We assume an intrinsic EW distribution to form mock samples of H$α$ emitters (HAEs) and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find EW intrinsically correlates with stellar mass as $W_0 \propto M^{-0.16\pm0.03}$ and decreases by a factor of $\sim 3$ from $10^{7}$ to $10^{10}$ M$_\odot$. We find low-mass HAEs to be $\sim 320$ times more likely to have rest-frame EW$ > 200$Åcompared to high-mass HAEs. Combining the intrinsic EW -- stellar mass correlation with an observed SMF correctly reproduces the observed H$α$ LF, while not correcting for selection effects underestimates the number of bright HAEs. This suggests that the intrinsic EW -- stellar mass correlation is physically significant and reproduces three statistical distributions of galaxy populations (LF, SMF, EW distribution). At lower masses, we find there are more high-EW outliers compared to high masses, even after taking into account selection effects. Our results suggest that high sSFR outliers indicative of bursty SF activity are intrinsically more prevalent in low-mass HAEs and not a byproduct of selection effects.

astro-ph.GA↗

arXiv2021

A Lyman-α protocluster at redshift 6.9

Protoclusters, the progenitors of the most massive structures in the Universe, have been identified at redshifts of up to 6.6. Besides exploring early structure formation, searching for protoclusters at even higher redshifts is particularly useful to probe the reionization. Here we report the discovery of the protocluster LAGER-z7OD1 at a redshift of 6.93, when the Universe was only 770 million years old and could be experiencing rapid evolution of the neutral hydrogen fraction in the intergalactic medium. The protocluster is identified by an overdensity of 6 times the average galaxy density, and with 21 narrowband selected Lyman-$α$ galaxies, among which 16 have been spectroscopically confirmed. At redshifts similar to or above this record, smaller protogroups with fewer members have been reported. LAGER-z7OD1 shows an elongated shape and consists of two subprotoclusters, which would have merged into one massive cluster with a present-day mass of $3.7 \times 10^{15}$ solar masses. The total volume of the ionized bubbles generated by its member galaxies is found to be comparable to the volume of the protocluster itself, indicating that we are witnessing the merging of the individual bubbles and that the intergalactic medium within the protocluster is almost fully ionized. LAGER-z7OD1 thus provides a unique natural laboratory to investigate the reionization process.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2020

Void Probability Function of Simulated Surveys of high-redshift Lyman-Alpha Emitters

We calculate the void probability function (VPF) in simulations of Lyman-$α$ emitters (LAEs) across a wide redshift range ($z=3.1,\ 4.5,\ 5.7,\ 6.6$). The VPF measures the zero-point correlation function (i.e. places devoid of galaxies) and naturally connects to higher order correlation functions while being computationally simple to calculate. We explore the Poissonian and systematic errors on the VPF, specify its accuracy as a function of average source density and the volume probed, and provide the appropriate size scales to measure the VPF. At small radii the accuracy of the VPF is limited by galaxy density, while at large radii the VPF is limited by the number of independent volumes probed. We also offer guidelines for understanding and quantifying the error in the VPF. We approximate the error in the VPF by using independent sub-volumes of the catalogs, after finding that jackknife statistics underestimate the uncertainty. We use the VPF to probe the strength of higher order correlation functions by measuring and examining the hierarchical scaling between the correlation functions using count-in-cells. The negative binomial model (NBM) has been shown to best describe the scaling between the two point correlation function and VPF for low-redshift galaxy observations. We further test the fit of the NBM by directly deriving the volume averaged two-point correlation function from the VPF and vice versa. We find the NBM best describes the $z=3.1, 4.5, 5.7$ simulated LAEs, with a 1$σ$ deviation from the model in the $z=6.6$ catalog. This suggests that LAEs show higher order clustering terms similar to those of normal low redshift galaxies.

astro-ph.GA↗

arXiv2020

The Importance Of Star Formation Intensity In LYα Escape From Green Pea Galaxies And Lyman Break Galaxy Analogs

We have studied ultraviolet images of 40 Green Pea galaxies and 15 local Lyman Break Galaxy Analogs to understand the relation between Ly$α$ photon escape and central UV photometric properties. We measured star formation intensity (SFI, star formation rate per unit area) from the central 250 pc region ($S_{\rm 250pc}$) using COS/NUV images from the \textit{Hubble Space Telescope}. The measured $S_{\rm 250pc}$ of our sample Green Peas ranges from 2.3--46 $M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$, with a geometric mean of $15 M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$ and a standard deviation of 0.266 dex, forming a relatively narrow distribution. The Lyman Break Galaxy Analogs show a similarly narrow distribution of $S_{\rm 250pc}$ (0.271 dex), though with a larger mean of 28 $M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$. We show that while the Ly$α$ equivalent width (EW(Ly$α$)) and the Ly$α$ escape fraction ($f^{Lyα}_{esc}$) are not significantly correlated with the central SFI ($S_{\rm 250pc}$), both are positively correlated with the ratio of surface brightness to galaxy stellar mass ($S_{\rm 250pc}/M_{\rm star}$), with correlation coefficients ($p$-values) of 0.702 ($1\times 10^{-8}$) and 0.529 ($5\times 10^{-4}$) with EW(Ly$α$) and $f^{Lyα}_{esc}$, respectively. These correlations suggest a scenario where intense central star formation can drive a galactic wind in galaxies with relatively shallow gravitational potential wells, thus clearing channels for the escape of Ly$α$ photons.

astro-ph.GA↗

arXiv2020

Bubble mapping with the Square Kilometer Array -- I. Detecting galaxies with Euclid, JWST, WFIRST and ELT within ionized bubbles in the intergalactic medium at z>6

The Square Kilometer Array is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z>6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centered on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z=7-10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at redshifts z=10 or below. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z~10, due to the very small number of line-of-sight interlopers expected at similar redshifts.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2020

A large, deep 3 deg$^2$ survey of H$α$, [OIII], and [OII] emitters from LAGER: constraining luminosity functions

We present our measurements of the H$α$, [OIII], and [OII] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 $z = 0.47$ H$α$-, 3933 $z = 0.93$ [OIII]-, and 5367 $z = 1.59$ [OII]-selected emission line galaxies in a single 3 deg$^2$ CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5$σ$ depths of $8.2\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ and comoving volumes of $(1-7)\times10^{5}$ Mpc$^3$ making our survey one of the deepest narrowband surveys. We measure the observed luminosity functions and find best-fits of $ϕ^\star = 10^{-3.16\pm0.09}$ Mpc$^{-3}$ and $L^\star = 10^{41.72\pm0.09}$ erg s$^{-1}$ for H$α$, $ϕ^\star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc$^{-3}$ and $L^\star = 10^{41.38^{+0.07}_{-0.06}}$ erg s$^{-1}$ for [OIII], and $ϕ^\star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc$^{-3}$ and $L^\star = 10^{41.66\pm0.03}$ erg s$^{-1}$ for [OII], with $α$ fixed to $-1.75$, $-1.6$, and $-1.3$, respectively. An excess of bright $> 10^{42}$ erg s$^{-1}$ [OIII] emitters is observed and may be due to AGN contamination. Dust corrections are applied assuming $A_{\rm{H}α} = 1$ mag. We also design our own empirical rest-frame $g - r$ calibration using SDSS DR12 data, test it against our $z = 0.47$ H$α$ emitters with $z$COSMOS $1$D spectra, and calibrate it for $(g - r)$ between $-0.8$ and $1.3$ mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as $\log_{10}ρ_{\rm{SFR}}/(\rm{M}_\odot\ \rm{yr}^{-1}\ \rm{Mpc}^{-3}) = -1.63\pm0.04$, $-1.07\pm0.06$, and $-0.90\pm0.10$ for H$α$, [OIII], and [OII], respectively. We find our [OIII] and [OII] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multi-wavelength SFRDs, while the H$α$ sample traces $\sim 70$ percent of the total $z = 0.47$ SFRD.

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