The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in char... more The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. We analyze the Near Infrared Spectrograph ERO spectra of three z ∼ 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 ] ≈ 6.9–8.3, 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 g...
We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hour treasury pro... more We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hour treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web is a contiguous 0.54 deg 2 NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5σ point source depths ranging ∼27.5-28.2 magnitudes. In parallel, we will obtain 0.19 deg 2 of MIRI imaging in one filter (F770W). COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization (6 < ∼ z < ∼ 11) and map reionization's spatial distribution, environments, and drivers on scales sufficiently large to mitigate cosmic variance, (2) to identify hundreds of rare quiescent galaxies at z > 4 and place constraints on the formation of the Universe's most massive galaxies (M > 10 10 M), and (3) directly measure the evolution of the stellar mass to halo mass relation using weak gravitational lensing out to z ∼ 2.5 and measure its variance with galaxies' star formation histories and morphologies. In addition, we anticipate COSMOS-Web's legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool sub-dwarf stars in the Galactic halo, and possibly the identification of z > 10 pair-instability supernovae. In this paper we provide an overview of the survey's key measurements, specifications, goals, and prospects for new discovery.
American Astronomical Society Meeting Abstracts #235, 2020
We present our measurements of the H α, [O III], and [O II] luminosity functions as part of the L... more We present our measurements of the H α, [O III], and [O II] 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 [O III]-, and 5367 z = 1.59 [O II]-selected emission line galaxies in a 3 deg 2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10 −18 erg s −1 cm −2 and comoving volumes of (1−7) × 10 5 Mpc 3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour-colour selections. We measure the observed luminosity functions for each sample and find best fits of φ = 10 −3.16 +0.09 −0.09 Mpc −3 and L = 10 41.72 +0.09 −0.09 erg s −1 for H α, φ = 10 −2.16 +0.10 −0.12 Mpc −3 and L = 10 41.38 +0.07 −0.06 erg s −1 for [O III], and φ = 10 −1.97 +0.07 −0.07 Mpc −3 and L = 10 41.66 +0.03 −0.03 erg s −1 for [O II], with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright >10 42 erg s −1 [O III] emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming A Hα = 1 mag. We also design our own empirical restframe g − r calibration using SDSS DR12 data, test it against our z = 0.47 H α emitters with zCOSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGNcorrected star formation rate densities (SFRDs) are measured as log 10 ρ SFR /(M yr −1 Mpc −3) = −1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for H α, [O III], and [O II], respectively. We find our [O III] and [O II] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the H α sample traces ∼70 per cent of the total z = 0.47 SFRD.
Green Peas (GP) are a class of low-redshift galaxies with extreme emission lines. They are consid... more Green Peas (GP) are a class of low-redshift galaxies with extreme emission lines. They are considered to be the best analogs of high-redshift Lyman-alpha galaxies as well as strongest known Lyman continuum leakers. In addition, they also contain other high ionization emission lines such as HeII and [NeIII], that indicate the presence of a hard ionizing source. With a quest to determine the extent to which these emission lines are powered by star-formation and/or accretion due to active galactic nuclei, we have searched for AGN in GPs based on mid-infrared colors and variability from WISE. We found that the AGN candidates selected by each of these methods can be quite different, although some overlap exists. Through this work, we highlight the importance of employing variability as a diagnostic in selecting AGN candidates that can be optically-hidden, obscured and/or low-luminosity AGN. In the near future, the Roman Space Telescope will produce one of the largest datasets of galaxies...
We report spectroscopic confirmations of 15 Lyα galaxies at z ∼ 7, implying a spectroscopic confi... more We report spectroscopic confirmations of 15 Lyα galaxies at z ∼ 7, implying a spectroscopic confirmation rate of ∼80% on candidates selected from the Lyα Galaxies in the Epoch of Reionization (LAGER), which is the largest (24 deg2) survey aimed at finding Lyα emitters (LAEs) at z ∼ 7 and uses deep narrowband imaging from the Dark Energy Camera at CTIO. LAEs at high redshifts are sensitive probes of cosmic reionization, and narrowband 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 Lyα emission in 15 candidates. Three of these in COSMOS have matching confirmations from a previous spectroscopic follow-up and are part of the overdense region, LAGER-z7OD1. Two other candidates that were not detected with LRIS have prior spectroscopic confirmations from Magellan....
We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding mod... more We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 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 × 106 Mpc3 is double that of the next largest z ∼ 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 Lyα emitter (LAEs) candidates, characterize our survey’s completeness and reliability, and compute Lyα LFs. The best-fit Schechter LF 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 Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent ...
We report spectroscopic confirmations of 15 Lyman-alpha galaxies at z ∼ 7, implying a spectroscop... more We report spectroscopic confirmations of 15 Lyman-alpha galaxies at z ∼ 7, implying a spectroscopic confirmation rate of ∼80% on candidates selected from LAGER (Lyman-Alpha Galaxies in the Epoch of Reionization), which is the largest (24 deg) survey aimed at finding Lyman-alpha emitters (LAEs) at z ∼ 7 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 Lyα 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-z7OD1. Additionally, two candidates that were not detected in the LRI...
We explore the presence of active galactic nuclei (AGN)/black hole (BH) in Green Pea galaxies (GP... more We explore the presence of active galactic nuclei (AGN)/black hole (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 516 GPs. We select 58 GPs as candidate AGN based on a stringent 3-band WISE color diagnostic. Using multi-epoch photometry of W1 and W2 bands from the WISE/NEOWISE-R observations, we find 38 GPs showing significant variability in both the WISE bands. Four of these were selected as AGN by the WISE 3-band color diagnostic as well. Interestingly, we find a high fraction of MIR variable sources among GPs which demonstrates the uniqueness and importance of studying these extreme objects. Through this work, we demonstrate that photometric variability is a promising tool to select AGN that may be missed by other...
We present a new measurement of the Lyα luminosity function at redshift z = 6.9, finding moderate... more We present a new measurement of the Lyα luminosity function at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 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 × 10 Mpc is double that of the next largest z ∼ 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 Lyα emitters (LAEs); characterize our survey’s completeness and reliability; and compute Lyα 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 Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to z = 6.9...
chorus/, respectively. The spectroscopic datasets and the datasets generated or analysed during t... more chorus/, respectively. The spectroscopic datasets and the datasets generated or analysed during this study are available from the corresponding author upon reasonable request. The LAE catalog for LAGER-z7OD1 used in this study has been published in the Supplementary Information. Code Availability Statement Codes used in this study are not publicly released yet but are available from the corresponding author on reasonable request.
Monthly Notices of the Royal Astronomical Society, 2021
The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) a... more The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying resul...
Monthly Notices of the Royal Astronomical Society, 2020
We present our measurements of the H α, [O iii], and [O ii] luminosity functions as part of the L... more We present our measurements of the H α, [O iii], and [O ii] 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 [O iii]-, and 5367 z = 1.59 [O ii]-selected emission line galaxies in a 3 deg2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10−18 erg s−1 cm−2 and comoving volumes of (1−7) × 105 Mpc3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour–colour selections. We measure the observed luminosity functions for each sample and find best fits of $\phi ^\star = 10^{-3.16^{+0.09}_{-0.09}}$ Mpc−3 and $L^\star = 10^{41.72^{+0.09}_{-0.09}}$ erg s−1 for H α, $\phi ^\star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc−3 and $L^\star = 10^{41.38^{+0.07}_{-0.06}}$ erg s−1 for [O iii], and $\phi ^\star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc−3 and $L^\st...
We have used the Arecibo Telescope and the Green Bank Telescope (GBT) to carry out a deep search ... more We have used the Arecibo Telescope and the Green Bank Telescope (GBT) to carry out a deep search for Hi 21 cm emission from a large sample of “Green Pea” galaxies, yielding 19 detections, and 21 upper limits on the Hi mass. We obtain Hi masses of M Hi ≈ (4–300) × 108 M ⊙ for the detections, with a median Hi mass of ≈ 2.6 × 109 M ⊙; for the non-detections, the median 3σ upper limit on the Hi mass is ≈ 5.5 × 108 M ⊙. These are the first estimates of the atomic gas content of Green Pea galaxies. We find that the Hi-to-stellar mass ratio in Green Peas is consistent with trends identified in star-forming galaxies in the local universe. However, the median Hi depletion timescale in Green Peas is ≈0.6 Gyr, an order of magnitude lower than that obtained in local star-forming galaxies. This implies that Green Peas consume their atomic gas on very short timescales. A significant fraction of the Green Peas of our sample lie ≳0.6 dex (2σ) above the local M Hi –M B relation, suggesting recent ga...
We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) f... more We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an Hα selected sample at z ∼ 0.62 from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new Hα 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 ∼1.5 deg 2. A total of 241 Hα emitters were selected based on robust selection criteria using spectro-photometric redshifts and broadband color-color classification. Given that dust extinction is a dominant uncertainty in the estimation of LF and SFRD, we explore the effect of different dust correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, A Hα = 1 mag, a luminosity-dependent correction, and a stellar-mass dependent correction. The resulting Hα 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 Hα 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 SFR = 10 −1.39 M yr −1 Mpc −3 (constant dust correction), ρ SFR = 10 −1.47 M yr −1 Mpc −3 (luminosity-dependent dust correction), and ρ SFR = 10 −1.49 M 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 Hα surveys.
The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in char... more The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. We analyze the Near Infrared Spectrograph ERO spectra of three z ∼ 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 ] ≈ 6.9–8.3, 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 g...
We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hour treasury pro... more We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hour treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web is a contiguous 0.54 deg 2 NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5σ point source depths ranging ∼27.5-28.2 magnitudes. In parallel, we will obtain 0.19 deg 2 of MIRI imaging in one filter (F770W). COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization (6 < ∼ z < ∼ 11) and map reionization's spatial distribution, environments, and drivers on scales sufficiently large to mitigate cosmic variance, (2) to identify hundreds of rare quiescent galaxies at z > 4 and place constraints on the formation of the Universe's most massive galaxies (M > 10 10 M), and (3) directly measure the evolution of the stellar mass to halo mass relation using weak gravitational lensing out to z ∼ 2.5 and measure its variance with galaxies' star formation histories and morphologies. In addition, we anticipate COSMOS-Web's legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool sub-dwarf stars in the Galactic halo, and possibly the identification of z > 10 pair-instability supernovae. In this paper we provide an overview of the survey's key measurements, specifications, goals, and prospects for new discovery.
American Astronomical Society Meeting Abstracts #235, 2020
We present our measurements of the H α, [O III], and [O II] luminosity functions as part of the L... more We present our measurements of the H α, [O III], and [O II] 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 [O III]-, and 5367 z = 1.59 [O II]-selected emission line galaxies in a 3 deg 2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10 −18 erg s −1 cm −2 and comoving volumes of (1−7) × 10 5 Mpc 3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour-colour selections. We measure the observed luminosity functions for each sample and find best fits of φ = 10 −3.16 +0.09 −0.09 Mpc −3 and L = 10 41.72 +0.09 −0.09 erg s −1 for H α, φ = 10 −2.16 +0.10 −0.12 Mpc −3 and L = 10 41.38 +0.07 −0.06 erg s −1 for [O III], and φ = 10 −1.97 +0.07 −0.07 Mpc −3 and L = 10 41.66 +0.03 −0.03 erg s −1 for [O II], with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright >10 42 erg s −1 [O III] emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming A Hα = 1 mag. We also design our own empirical restframe g − r calibration using SDSS DR12 data, test it against our z = 0.47 H α emitters with zCOSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGNcorrected star formation rate densities (SFRDs) are measured as log 10 ρ SFR /(M yr −1 Mpc −3) = −1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for H α, [O III], and [O II], respectively. We find our [O III] and [O II] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the H α sample traces ∼70 per cent of the total z = 0.47 SFRD.
Green Peas (GP) are a class of low-redshift galaxies with extreme emission lines. They are consid... more Green Peas (GP) are a class of low-redshift galaxies with extreme emission lines. They are considered to be the best analogs of high-redshift Lyman-alpha galaxies as well as strongest known Lyman continuum leakers. In addition, they also contain other high ionization emission lines such as HeII and [NeIII], that indicate the presence of a hard ionizing source. With a quest to determine the extent to which these emission lines are powered by star-formation and/or accretion due to active galactic nuclei, we have searched for AGN in GPs based on mid-infrared colors and variability from WISE. We found that the AGN candidates selected by each of these methods can be quite different, although some overlap exists. Through this work, we highlight the importance of employing variability as a diagnostic in selecting AGN candidates that can be optically-hidden, obscured and/or low-luminosity AGN. In the near future, the Roman Space Telescope will produce one of the largest datasets of galaxies...
We report spectroscopic confirmations of 15 Lyα galaxies at z ∼ 7, implying a spectroscopic confi... more We report spectroscopic confirmations of 15 Lyα galaxies at z ∼ 7, implying a spectroscopic confirmation rate of ∼80% on candidates selected from the Lyα Galaxies in the Epoch of Reionization (LAGER), which is the largest (24 deg2) survey aimed at finding Lyα emitters (LAEs) at z ∼ 7 and uses deep narrowband imaging from the Dark Energy Camera at CTIO. LAEs at high redshifts are sensitive probes of cosmic reionization, and narrowband 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 Lyα emission in 15 candidates. Three of these in COSMOS have matching confirmations from a previous spectroscopic follow-up and are part of the overdense region, LAGER-z7OD1. Two other candidates that were not detected with LRIS have prior spectroscopic confirmations from Magellan....
We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding mod... more We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 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 × 106 Mpc3 is double that of the next largest z ∼ 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 Lyα emitter (LAEs) candidates, characterize our survey’s completeness and reliability, and compute Lyα LFs. The best-fit Schechter LF 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 Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent ...
We report spectroscopic confirmations of 15 Lyman-alpha galaxies at z ∼ 7, implying a spectroscop... more We report spectroscopic confirmations of 15 Lyman-alpha galaxies at z ∼ 7, implying a spectroscopic confirmation rate of ∼80% on candidates selected from LAGER (Lyman-Alpha Galaxies in the Epoch of Reionization), which is the largest (24 deg) survey aimed at finding Lyman-alpha emitters (LAEs) at z ∼ 7 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 Lyα 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-z7OD1. Additionally, two candidates that were not detected in the LRI...
We explore the presence of active galactic nuclei (AGN)/black hole (BH) in Green Pea galaxies (GP... more We explore the presence of active galactic nuclei (AGN)/black hole (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 516 GPs. We select 58 GPs as candidate AGN based on a stringent 3-band WISE color diagnostic. Using multi-epoch photometry of W1 and W2 bands from the WISE/NEOWISE-R observations, we find 38 GPs showing significant variability in both the WISE bands. Four of these were selected as AGN by the WISE 3-band color diagnostic as well. Interestingly, we find a high fraction of MIR variable sources among GPs which demonstrates the uniqueness and importance of studying these extreme objects. Through this work, we demonstrate that photometric variability is a promising tool to select AGN that may be missed by other...
We present a new measurement of the Lyα luminosity function at redshift z = 6.9, finding moderate... more We present a new measurement of the Lyα luminosity function at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 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 × 10 Mpc is double that of the next largest z ∼ 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 Lyα emitters (LAEs); characterize our survey’s completeness and reliability; and compute Lyα 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 Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to z = 6.9...
chorus/, respectively. The spectroscopic datasets and the datasets generated or analysed during t... more chorus/, respectively. The spectroscopic datasets and the datasets generated or analysed during this study are available from the corresponding author upon reasonable request. The LAE catalog for LAGER-z7OD1 used in this study has been published in the Supplementary Information. Code Availability Statement Codes used in this study are not publicly released yet but are available from the corresponding author on reasonable request.
Monthly Notices of the Royal Astronomical Society, 2021
The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) a... more The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying resul...
Monthly Notices of the Royal Astronomical Society, 2020
We present our measurements of the H α, [O iii], and [O ii] luminosity functions as part of the L... more We present our measurements of the H α, [O iii], and [O ii] 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 [O iii]-, and 5367 z = 1.59 [O ii]-selected emission line galaxies in a 3 deg2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10−18 erg s−1 cm−2 and comoving volumes of (1−7) × 105 Mpc3 making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour–colour selections. We measure the observed luminosity functions for each sample and find best fits of $\phi ^\star = 10^{-3.16^{+0.09}_{-0.09}}$ Mpc−3 and $L^\star = 10^{41.72^{+0.09}_{-0.09}}$ erg s−1 for H α, $\phi ^\star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc−3 and $L^\star = 10^{41.38^{+0.07}_{-0.06}}$ erg s−1 for [O iii], and $\phi ^\star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc−3 and $L^\st...
We have used the Arecibo Telescope and the Green Bank Telescope (GBT) to carry out a deep search ... more We have used the Arecibo Telescope and the Green Bank Telescope (GBT) to carry out a deep search for Hi 21 cm emission from a large sample of “Green Pea” galaxies, yielding 19 detections, and 21 upper limits on the Hi mass. We obtain Hi masses of M Hi ≈ (4–300) × 108 M ⊙ for the detections, with a median Hi mass of ≈ 2.6 × 109 M ⊙; for the non-detections, the median 3σ upper limit on the Hi mass is ≈ 5.5 × 108 M ⊙. These are the first estimates of the atomic gas content of Green Pea galaxies. We find that the Hi-to-stellar mass ratio in Green Peas is consistent with trends identified in star-forming galaxies in the local universe. However, the median Hi depletion timescale in Green Peas is ≈0.6 Gyr, an order of magnitude lower than that obtained in local star-forming galaxies. This implies that Green Peas consume their atomic gas on very short timescales. A significant fraction of the Green Peas of our sample lie ≳0.6 dex (2σ) above the local M Hi –M B relation, suggesting recent ga...
We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) f... more We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an Hα selected sample at z ∼ 0.62 from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new Hα 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 ∼1.5 deg 2. A total of 241 Hα emitters were selected based on robust selection criteria using spectro-photometric redshifts and broadband color-color classification. Given that dust extinction is a dominant uncertainty in the estimation of LF and SFRD, we explore the effect of different dust correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, A Hα = 1 mag, a luminosity-dependent correction, and a stellar-mass dependent correction. The resulting Hα 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 Hα 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 SFR = 10 −1.39 M yr −1 Mpc −3 (constant dust correction), ρ SFR = 10 −1.47 M yr −1 Mpc −3 (luminosity-dependent dust correction), and ρ SFR = 10 −1.49 M 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 Hα surveys.
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Papers by Santosh Harish