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  1. Abstract

    Supernova (SN) 2023ixf was discovered on 2023 May 19. The host galaxy, M101, was observed by the Hobby–Eberly Telescope Dark Energy Experiment collaboration over the period 2020 April 30–2020 July 10, using the Visible Integral-field Replicable Unit Spectrograph (3470 ≲λ≲ 5540 Å) on the 10 m Hobby–Eberly Telescope. The fiber filling factor within ±30″ of SN 2023ixf is 80% with a spatial resolution of 1″. Ther< 5.″5 surroundings are 100% covered. This allows us to analyze the spatially resolved preexplosion local environments of SN 2023ixf with nebular emission lines. The two-dimensional maps of the extinction and the star formation rate (SFR) surface density (ΣSFR) show weak increasing trends in the radial distributions within ther< 5.″5 regions, suggesting lower values of extinction and SFR in the vicinity of the progenitor of SN 2023ixf. The median extinction and that of the surface density of SFR withinr< 3″ areE(BV) = 0.06 ± 0.14, andΣSFR=105.44±0.66Myr1arcsec2.There is no significant change in extinction before and after the explosion. The gas metallicity does not change significantly with the separation from SN 2023ixf. The metal-rich branch of theR23calculations indicates that the gas metallicity around SN 2023ixf is similar to the solar metallicity (∼Z). The archival deep images from the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) show a clear detection of the progenitor of SN 2023ixf in thezband at 22.778 ± 0.063 mag, but nondetections in the remaining four bands of CFHTLS (u,g,r,i). The results suggest a massive progenitor of ≈22M.

     
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  2. Abstract

    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,DA(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 theDA(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.

     
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  3. 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. 
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  4. Abstract

    We investigate the stellar mass–black hole mass (*BH) relation with type 1 active galactic nuclei (AGNs) down toBH=107M, 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 withBHranging from 107–1010Mthat are measured with single-epoch virial method using Civemission lines detected in the HETDEX spectra.*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*BHrelation covering the unexplored low-mass ranges ofBH107108M, and conduct forward modeling to fully account for the selection biases and observational uncertainties. The intrinsic*BHrelation 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 ofBH107108M. Our*BHrelation is inconsistent with theBHsuppression at the low-*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.

     
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  5. Abstract

    We have extracted 636 spectra taken at the positions of 583 transient sources from the third data release of the Hobby–Eberly Telescope Dark Energy eXperiment (HETDEX). The transients were discovered by the Zwicky Transient Facility (ZTF) during 2018–2022. The HETDEX spectra provide a potential means to obtain classifications for a large number of objects found by photometric surveys for free. We attempt to explore and classify the spectra by utilizing several template-matching techniques. We have identified two transient sources, ZTF20aatpoos = AT 2020fiz and ZTF19abdkelq, as supernova (SN) candidates. We classify AT 2020fiz as a Type IIP SN observed ∼10 days after explosion, and we propose ZTF19abdkelq as a likely Type Ia SN caught ∼40 days after maximum light. ZTF photometry of these two sources are consistent with their classifications as SNe. Beside these two objects, we have confirmed several ZTF transients as variable active galactic nuclei based on their spectral appearance, and determined the host galaxy types of several other ZTF transients.

     
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  6. Abstract

    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.

     
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  7. Abstract

    We describe the ensemble properties of the 1.9 <z< 3.5 Lyman alpha emitters (LAEs) found in the HETDEX survey’s first public data release, HETDEX Public Source Catalog 1. Stacking the low-resolution (R∼ 800) spectra greatly increases the signal-to-noise ratio (S/N), revealing spectral features otherwise hidden by noise, and we show that the stacked spectrum is representative of an average member of the set. The flux-limited, LyαS/N restricted stack of 50,000 HETDEX LAEs shows the ensemble biweightaveragez∼ 2.6 LAE to be a blue (UV continuum slope ∼ −2.4 andE(B – V)< 0.1), moderately bright (MUV∼ −19.7) star-forming galaxy with strong Lyαemission (logLLyα∼ 42.8 andWλ(Lyα) ∼ 114 Å), and potentially significant leakage of ionizing radiation. The rest-frame UV light is dominated by a young, metal-poor stellar population with an average age of 5–15 Myr and metallicity of 0.2–0.3Z.

     
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  8. Abstract

    We report an active galactic nucleus (AGN) with an extremely high equivalent width (EW), EWLyα+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.

     
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  9. Abstract

    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 ∼1042.3to 1045.9erg s−1. Our LyαLF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest atLLyα=1043.4erg 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 luminosityM1450*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 (M1450*) increases, and the turnover density (Φ*) decreases with increasing redshift.

     
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  10. Abstract

    We present extended Lyαemission out to 800 kpc of 1034 [Oiii]-selected galaxies at redshifts 1.9 <z< 2.35 using the Hobby–Eberly Telescope Dark Energy Experiment. The locations and redshifts of the galaxies are taken from the 3D-HST survey. The median-stacked surface brightness profile of the Lyαemission of the [Oiii]-selected galaxies agrees well with that of 968 bright Lyα-emitting galaxies (LAEs) atr> 40 kpc from the galaxy centers. The surface brightness in the inner parts (r< 10 kpc) around the [Oiii]-selected galaxies, however, is 10 times fainter than that of the LAEs. Our results are consistent with the notion that photons dominating the outer regions of the Lyαhalos are not produced in the central galaxies but originate outside of them.

     
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