SALT-RSS Multiobject Spectroscopic Data Reduction to Reveal Physical Properties of [Oii]-emitting Galaxies from HETDEX and ODIN IOP 05/06/2024 10537032 10.3847/2515-5172/ad4645 Research Notes of the AAS 2515-5172 8 5 George V KharchilavaEric GawiserDanisbel HerreraNicole FirestoneRobin CiardulloCaryl GronwallKyoung-Soo LeeVandana RamakrishnanFrancisco ValdesYujin Yang Abstract

Line flux ratios from [Oii] doublets can probe electron densities in the interstellar medium of galaxies. We employ the Southern African Large Telescope’s (SALT) Robert Stobie Spectrograph (RSS), which provides sufficient resolution (R∼3000) to split the [Oii] doublets, to target galaxies from Hobby-Eberly Telescope Dark Energy Experiment and One-hundred-deg2DECam Imaging in Narrowbands with emission line fluxes of at least 2×10−16ergcm−2s−1. Reduction is carried out using RSSMOSPipeline to reduce SALT-RSS data through wavelength calibration. Despite SALT-RSS being known for its difficulty to flux calibrate, we present spectra that have been flux calibrated using alignment stars with Sloan Digital Sky Survey spectra as standards. We combine multiple spectroscopic settings to obtain full 2D spectra across a wavelength range of 3500–9500Å. A 1D spectrum can then be extracted to calculate flux ratios and line widths, revealing important physical properties of these bright [Oii]-emitters.

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INTRODUCTION 30

Nebular emission lines allow researchers to probe the characteristics of emission-line galaxies such as electron den-31 sities, ionization parameters, dust reddening, velocity dispersion, metallicities, and star formation rates. Before these 32 measurements can be made, proper reduction must be carried out so we can measure fluxes and observed wavelengths 33 of emission lines found from our targets of interest. We investigate [O II]-emitters at redshift z < 0.4 using the South-34 ern African Large Telescope's (SALT) Robert Stobie Spectrograph (RSS). Previously, our program only performed 35 reduction up to wavelength calibration, as absolute flux calibration is often thought to be impossible on This paper describes a novel approach to flux calibrating an instrument such as SALT-RSS, followed by an additional 37 routine that seeks to combine multiple spectroscopic settings on a single non-linear wavelength axis. created sensitivity function is subjected to polynomial regression before applying to the science images, removing chip 75 gaps and systematics.

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The final step before 1D spectral extraction involves reprojecting all the data onto a single non-linear wavelength 77 axis covering the full 3500 Å to 9500 Å range. We use an exponential fit that maintains resolution in the green and 78 blue gratings while intentionally oversampling in the red grating. This is done because the intrinsic resolution of the 79 red grating is much lower, and we expect the [O II] doublets to be present in the green and blue gratings. Once 82 The results yield a roughly 25% accuracy in [O II] line fluxes when compared to HETDEX for two targets measured, 83 including the target in Figure 1. We seek to maintain and improve this accuracy with upcoming developments to 84 the pipeline after several more masks are reduced. One of these developments includes putting the SDSS alignment 85 stars in slits the same size as our science slits instead of boxes.This should further improve the accuracy of our flux 86 calibration routine by better representing slit losses and by minimizing the chances of star saturation. Currently, a 1D 87 extraction routine is being adapted from RSSMOSPipeline's 1D extraction module, which needs to be restructured 88 to work with flux calibrated and reprojected data (accounting for spatially varying emission lines across the entire 89 wavelength coverage). There are currently several masks that can be reduced, and we plan more observations to be 90 carried out in upcoming semesters. 91 6. ACKNOWLEDGEMENTS 92 We would like to thank the Department of Physics & Astronomy at Rutgers University, SALT support staff, and collaborators from ODIN for their support. We also acknowledge support from NSF grants AST-2206222 and AST-2206705, as well as NASA Astrophysics Data Analysis Program grant 80NSSC22K0487. 93 94 95 This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-2233066 to NF. NF would also like to thank the LSST-DA Data Science Fellowship Program, which is funded by LSST Discovery Alliance, NSF Cybertraining Grant 1829740, the Brinson Foundation, and the Moore Foundation; her participation in this program has benefited this work. 96 97 98 99

reprojected, the data is written as a new 2D spectroscopic image in a fits file.