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We present analysis using a citizen science campaign to improve the cosmological measures from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the Hubble expansion rate,H(z), and angular diameter distance,D_A(z), atz= 2.4, each to percent-level accuracy. This accuracy is determined primarily from the total number of detected Lyαemitters (LAEs), the false positive rate due to noise, and the contamination due to [Oii] emitting galaxies. This paper presents the citizen science project, Dark Energy Explorers (https://www.zooniverse.org/projects/erinmc/dark-energy-explorers), with the goal of increasing the number of LAEs and decreasing the number of false positives due to noise and the [Oii] galaxies. Initial analysis shows that citizen science is an efficient and effective tool for classification most accurately done by the human eye, especially in combination with unsupervised machine learning. Three aspects from the citizen science campaign that have the most impact are (1) identifying individual problems with detections, (2) providing a clean sample with 100% visual identification above a signal-to-noise cut, and (3) providing labels for machine-learning efforts. Since the end of 2022, Dark Energy Explorers has collected over three and a half million classifications by 11,000 volunteers in over 85 different countries around the world. By incorporating the results of the Dark Energy Explorers, we expect to improve the accuracy on theD_A(z) andH(z) parameters atz= 2.″4 by 10%–30%. While the primary goal is to improve on HETDEX, Dark Energy Explorers has already proven to be a uniquely powerful tool for science advancement and increasing accessibility to science worldwide.

 

We present the Texas Euclid Survey for Lyα(TESLA), a spectroscopic survey in the 10 deg²of the Euclid North Ecliptic Pole (NEP) field. Using TESLA, we study how the physical properties of Lyαemitters (LAEs) correlate with Lyαemission to understand the escape of Lyαemission from galaxies at redshifts of 2–3.5. We present an analysis of 43 LAEs performed in the NEP field using early data from the TESLA survey. We use Subaru Hyper Suprime-Cam imaging in thegrizybands, Spitzer/IRAC channels 1 and 2 from the Hawaii 20 deg²(H20) survey, and spectra acquired by the Visible Integral-Field Replicable Unit Spectrograph (VIRUS) on the Hobby–Eberly Telescope. We perform spectral energy distribution (SED) fitting to compute the galaxy properties of 43 LAEs, and study correlations between stellar mass, star formation rate (SFR), and dust to the Lyαrest-frame equivalent width (W_Lyα). We uncover marginal (1σsignificance) correlations between stellar mass andW_Lyα, and SFR andW_Lyα, with a Spearman correlation coefficient of −0.${34}_{-.14}^{+.17}$and −0.${37}_{-.14}^{+.16}$, respectively. We show that theW_Lyαdistribution of the 43 LAEs is consistent with being drawn from an exponential distribution with an e-folding scale ofW₀= 150 Å. Once complete the TESLA survey will enable the study of ≳50,000 LAEs to explore more correlations between galaxy properties andW_Lyα. The large sample size will allow the construction of a predictive model forW_Lyαas a function of SED-derived galaxy properties, which could be used to improve Lyα-based constraints on reionization.

 

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is a large-volume spectroscopic survey without preselection of sources, searching ∼540 deg²for Lyαemitting galaxies (LAEs) at 1.9 <z< 3.5. Taking advantage of such a wide-volume survey, we perform a pilot study using early HETDEX data to search for lensed Lyαemitters (LAEs). After performing a proof of concept using a previously known lensed LAE covered by HETDEX, we perform a search for previously unknown lensed LAEs in the HETDEX spectroscopic sample. We present a catalog of 26 potential LAEs lensed by foreground, red, non-star-forming galaxies atz∼ 0.4–0.7. We estimate the magnification for each candidate system, finding 12 candidates to be within the strong lensing regime (magnificationμ> 2). Follow-up observations of these potential lensed LAEs have the potential to confirm their lensed nature and explore these distant galaxies in more detail.

 

We report an active galactic nucleus (AGN) with an extremely high equivalent width (EW), EW_{Lyα+N V,rest}≳921Å, in the rest frame, atz∼ 2.24 in the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX), as a representative case of the high-EW AGN population. The continuum level is a nondetection in the HETDEX spectrum; thus the measured EW is a lower limit. The source is detected with significant emission lines (>7σ) at Lyα+ Nvλ1241, Civλ1549, and a moderate emission line (∼4σ) at Heiiλ1640 within the wavelength coverage of HETDEX (3500–5500 Å). Ther-band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit ofr= 25.12 at 5σ. The Lyαemission line spans a clearly resolved region of ∼10″ (85 kpc) in diameter. The Lyαline profile is strongly double peaked. The spectral decomposed blue gas and red gas Lyαemission are separated by ∼1.″2 (10.1 kpc) with a line-of-sight velocity offset of ∼1100 km s⁻¹. This source is probably an obscured AGN with powerful winds.

 

We present the results of a stellar population analysis of 72 Lyα-emitting galaxies (LAEs) in GOODS-N at 1.9 <z< 3.5 spectroscopically identified by the Hobby−Eberly Telescope Dark Energy Experiment (HETDEX). We provide a method for connecting emission-line detections from the blind spectroscopic survey to imaging counterparts, a crucial tool needed as HETDEX builds a massive database of ∼1 million Lyαdetections. Using photometric data spanning as many as 11 filters covering 0.4 <λ(μm) < 4.5 from the Hubble Space Telescope and Spitzer Space Telescope, we study the objects’ global properties and explore which properties impact the strength of Lyαemission. We measure a median stellar mass of${0.8}_{-0.5}^{+2.9}\times {10}^9{M}_{\odot }$and conclude that the physical properties of HETDEX spectroscopically selected LAEs are comparable to LAEs selected by previous deep narrowband studies. We find that stellar mass and star formation rate correlate strongly with the Lyαequivalent width. We then use a known sample ofz> 7 LAEs to perform a protostudy of predicting Lyαemission from galaxies in the epoch of reionization, finding agreement at the 1σlevel between prediction and observation for the majority of strong emitters.

 

We present the first active galactic nuclei (AGN) catalog of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between 2017 January and 2020 June. HETDEX is an ongoing spectroscopic survey (3500–5500 Å) with no target preselection based on magnitudes, colors or morphologies, enabling us to select AGN based solely on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the Lyαand Civλ1549 line pair, or with a single broad emission line with FWHM > 1000 km s⁻¹. Each source is further confirmed by visual inspections. This catalog contains 5322 AGN, covering an effective sky coverage of 30.61 deg². A total of 3733 of these AGN have secure redshifts, and we provide redshift estimates for the remaining 1589 single broad-line AGN with no crossmatched spectral redshifts from the Sloan Digital Sky Survey Data Release 14 of QSOs. The redshift range of the AGN catalog is 0.25 <z< 4.32, with a median ofz= 2.1. The bolometric luminosity range is 10⁹–10¹⁴L_☉with a median of 10¹²L_☉. The medianr-band magnitude of our AGN catalog is 21.6 mag, with 34% havingr> 22.5, and 2.6% reaching the detection limit atr∼ 26 mag of the deepest imaging surveys we searched. We also provide a composite spectrum of the AGN sample covering 700–4400 Å.

 

We investigate the stellar mass–black hole mass (${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$) relation with type 1 active galactic nuclei (AGNs) down to${\mathit{}}_{\mathrm{BH}}={10}^7{M}_{\odot }$, corresponding to a ≃ −21 absolute magnitude in rest-frame ultraviolet, atz= 2–2.5. Exploiting the deep and large-area spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGNs with${\mathit{}}_{\mathrm{BH}}$ranging from 10⁷–10¹⁰M_⊙that are measured with single-epoch virial method using Civemission lines detected in the HETDEX spectra.${\mathit{}}_{*}$of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, the Wide-field Infrared Survey Explorer, and ground-based 4–8 m class telescopes byCIGALEspectral energy distribution (SED) fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially resolved host galaxies with the James Webb Space Telescope/NIRCam CEERS data. We obtain the${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation covering the unexplored low-mass ranges of${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$, and conduct forward modeling to fully account for the selection biases and observational uncertainties. The intrinsic${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation atz∼ 2 has a moderate positive offset of 0.52 ± 0.14 dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$. Our${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation is inconsistent with the${\mathit{}}_{\mathrm{BH}}$suppression at the low-${\mathit{}}_{*}$regime predicted by recent hydrodynamic simulations at a 98% confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations.

 

We present the Lyαemission line luminosity function (LF) of the active galactic nuclei (AGN) in the first release of the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX) AGN catalog. The AGN are selected either by emission line pairs characteristic of AGN or by a single broad emission line, free of any photometric preselections (magnitude/color/morphology). The sample consists of 2346 AGN spanning 1.88 <z< 3.53, covering an effective area of 30.61 deg². Approximately 2.6% of the HETDEX AGN are not detected at >5σconfidence atr∼ 26 in the deepestr-band images we have searched. The Lyαline luminosity ranges from ∼10^42.3to 10^45.9erg s⁻¹. Our LyαLF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest at$L_{\text{Ly}\mathit{\text{α}}}^{\ast }={10}^{43.4}$erg s⁻¹. We explore the evolution of the AGN LF over a broader redshift range (0.8 <z< 3); constructing the rest-frame ultraviolet (UV) LF with the 1450 Å monochromatic luminosity of the power-law component of the continuum (M₁₄₅₀) fromM₁₄₅₀∼ −18 to −27.5. We divide the sample into three redshift bins (z∼ 1.5, 2.1, and 2.6). In all three redshift bins, our UV LFs indicate that the space density of AGN is highest at the turnover luminosity$M_{1450}^{*}$with opposite slopes on the bright end and the faint end. TheM₁₄₅₀LFs in the three redshift bins can be well fit with a luminosity evolution and density evolution model: the turnover luminosity ($M_{1450}^{*}$) increases, and the turnover density (Φ*) decreases with increasing redshift.

 

Abstract The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the universe at z ∼ 2.4 to 1% precision for both H ( z ) and D A ( z ). HETDEX is in the process of mapping in excess of one million Ly α emitting (LAE) galaxies and a similar number of lower- z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly α emission from the lower- z interloping galaxies, primarily [O ii ], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Å rest-frame equivalent width cut commonly used to distinguish LAEs from lower- z [O ii ] emitting galaxies. Despite a spectral resolving power, R ∼ 800, that cannot resolve the [O ii ] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly α by [O ii ] of 1.2% and a Ly α recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements. 

Abstract We used data from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) to study the incidence of AGN in continuum-selected galaxies at z ∼ 3. From optical and infrared imaging in the 24 deg 2 Spitzer HETDEX Exploratory Large Area survey, we constructed a sample of photometric-redshift selected z ∼ 3 galaxies. We extracted HETDEX spectra at the position of 716 of these sources and used machine-learning methods to identify those which exhibited AGN-like features. The dimensionality of the spectra was reduced using an autoencoder, and the latent space was visualized through t-distributed stochastic neighbor embedding. Gaussian mixture models were employed to cluster the encoded data and a labeled data set was used to label each cluster as either AGN, stars, high-redshift galaxies, or low-redshift galaxies. Our photometric redshift (photo z ) sample was labeled with an estimated 92% overall accuracy, an AGN accuracy of 83%, and an AGN contamination of 5%. The number of identified AGN was used to measure an AGN fraction for different magnitude bins. The ultraviolet (UV) absolute magnitude where the AGN fraction reaches 50% is M UV = −23.8. When combined with results in the literature, our measurements of AGN fraction imply that the bright end of the galaxy luminosity function exhibits a power law rather than exponential decline, with a relatively shallow faint-end slope for the z ∼ 3 AGN luminosity function.