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1. The Circumgalactic Hα Spectrograph (CHαS). I. Design, Engineering, and Early Commissioning

   https://doi.org/10.3847/1538-4357/ac9d9c  

   Melso, Nicole ; Schiminovich, David ; Smiley, Brian ; Ong, Hwei Ru ; Santiago, Bárbara Cruvinel ; Sitaram, Meghna ; Aleman, Ignacio Cevallos ; Graber, Sarah ; Murillo, Marisa ; Rosenthal, Marni ; et al ( December 2022 , The Astrophysical Journal)

   The Circumgalactic HαSpectrograph (CHαS) is a ground-based optical integral field spectrograph designed to detect ultrafaint extended emission from diffuse ionized gas in the nearby universe. CHαS is particularly well suited for making direct detections of tenuous Hαemission from the circumgalactic medium (CGM) surrounding low-redshift galaxies. It efficiently maps large regions of the CGM in a single exposure, targeting nearby galaxies (d< 35 Mpc) where the CGM is expected to fill the field of view. We are commissioning CHαS as a facility instrument at MDM Observatory. CHαS is deployed in the focal plane of the Hiltner 2.4 m telescope, utilizing nearly all of the telescope’s unvignetted focal plane (10′–15′) to conduct wide-field spectroscopic imaging. The catadioptric design provides excellent wide-field imaging performance. CHαS is a pupil-imaging spectrograph employing a microlens array to divide the field of view into >60,000 spectra. CHαS achieves an angular resolution of [1.3–2.6] arcseconds and a resolving power ofR= [10,000–20,000]. Accordingly, the spectrograph can resolve structure on the scale of 1–5 kpc (at 10 Mpc) and measure velocities down to 15–30 km s⁻¹. CHαS intentionally operates over a narrow (30 Å) bandpass; however, it is configured to adjust the central wavelength and target a broad rangemore »of optical emission lines individually. A high–diffraction efficiency volume phase holographic grating ensures high throughput across configurations. CHαS maintains a high grasp and moderate spectral resolution, providing an ideal combination for mapping discrete, ultralow–surface brightness emission on the order of a few milli-Rayleigh.

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2. The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections*

   https://doi.org/10.3847/1538-4357/ac2e03  

   Gebhardt, Karl ; Mentuch Cooper, Erin ; Ciardullo, Robin ; Acquaviva, Viviana ; Bender, Ralf ; Bowman, William P. ; Castanheira, Barbara G. ; Dalton, Gavin ; Davis, Dustin ; de Jong, Roelof S. ; et al ( December 2021 , The Astrophysical Journal)

   We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyαemitting galaxies between 1.88 <z< 3.52, in a 540 deg²area encompassing a comoving volume of 10.9 Gpc³. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.
3. A Search for Lensed Lyα Emitters within the Early HETDEX Data Set

   https://doi.org/10.3847/1538-4357/ac9186  

   Laseter, Isaac H. ; Finkelstein, Steven L. ; Bagley, Micaela J. ; Davis, Dustin M. ; Gebhardt, Karl ; Gronwall, Caryl ; Ciardullo, Robin ; Zeimann, Gregory R. ; Cooper, Erin Mentuch ; Farrow, Daniel ( November 2022 , The Astrophysical Journal)

   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.
4. Prime Focus Spectrograph (PFS) for the Subaru Telescope: its start of the last development phase

   https://doi.org/10.1117/12.2628152  

   Tamura, Naoyuki ; Moritani, Yuki ; Yabe, Kiyoto ; Ishizuka, Yuki ; Kamata, Yukiko ; Allaoui, Ali ; Arai, Akira ; Arnouts, Stéphane ; Barkhouser, Robert H. ; Barette, Rudy ; et al ( August 2022 , Proceedings of the SPIE)

   Evans, Christopher J. ; Bryant, Julia J. ; Motohara, Kentaro (Ed.)

   PFS (Prime Focus Spectrograph), a next generation facility instrument on the Subaru telescope, is now being tested on the telescope. The instrument is equipped with very wide (1.3 degrees in diameter) field of view on the Subaru's prime focus, high multiplexity by 2394 reconfigurable fibers, and wide waveband spectrograph that covers from 380nm to 1260nm simultaneously in one exposure. Currently engineering observations are ongoing with Prime Focus Instrument (PFI), Metrology Camera System (MCS), the first spectrpgraph module (SM1) with visible cameras and the first fiber cable providing optical link between PFI and SM1. Among the rest of the hardware, the second fiber cable has been already installed on the telescope and in the dome building since April 2022, and the two others were also delivered in June 2022. The integration and test of next SMs including near-infrared cameras are ongoing for timely deliveries. The progress in the software development is also worth noting. The instrument control software delivered with the subsystems is being well integrated with its system-level layer, the telescope system, observation planning software and associated databases. The data reduction pipelines are also rapidly progressing especially since sky spectra started being taken in early 2021 using Subaru Nigh Skymore »Spectrograph (SuNSS), and more recently using PFI during the engineering observations. In parallel to these instrumentation activities, the PFS science team in the collaboration is timely formulating a plan of large-sky survey observation to be proposed and conducted as a Subaru Strategic Program (SSP) from 2024. In this article, we report these recent progresses, ongoing developments and future perspectives of the PFS instrumentation.« less
5. On the Triggering of Extreme Starburst Events in Low-metallicity Galaxies: A Deep Search for Companions of Green Peas

   https://doi.org/10.3847/1538-4357/ac97ef  

   Laufman, Lauren ; Scarlata, Claudia ; Hayes, Matthew ; Skillman, Evan ( November 2022 , The Astrophysical Journal)

   Green pea galaxies are starbursting, low-mass galaxies that are good analogues to star-forming galaxies in the early universe. We perform a survey of 23 green peas using the Multi Unit Spectroscopic Explorer (MUSE) Integral Field Unit spectrograph on the Very Large Telescope to search for companion galaxies. The survey reaches an average point-source depth of ∼10⁻¹⁸erg cm⁻²s⁻¹for emission lines. The MUSE field of view allows us to probe a 1 × 1 arcmin²field around these galaxies and to search their surroundings for faint companions that could have interacted with them and induced their starburst episodes. We search for companions using a variety of methods including template matching to emission- and absorption-line spectra. When restricting the search to the same physical area (R= 78 kpc) for all galaxies, we find that the fraction of green pea galaxies with companions is${0.11}_{-0.05}^{+0.07}$. We define a control sample of star-forming galaxies with the same stellar masses and redshifts as the green peas, but consistent with the star formation main sequence. We find that green pea galaxies are as likely to have companions as the control sample; for which the fraction of objects with companions is${0.08}_{-0.03}^{+0.05}$. Given thatmore »we do not find statistical evidence for an elevated companion fraction in the green peas in this study, we argue that the “companions” are likely unrelated to the bursts in these galaxies.

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