The Ultraviolet Deep Imaging Survey of Galaxies in the Bootes Void. I. Catalog, Color–Magnitude Relations, and Star Formation

Abstract

We present a deep far and near-ultraviolet (FUV and NUV) wide-field imaging survey of galaxies in the Bootes void using the Ultraviolet Imaging Telescope on board AstroSat. Our data reach 5σ limiting magnitudes for point sources at 23.0 and 24.0 AB mag in the FUV and NUV, respectively. We report a total of six star-forming galaxies residing in the Bootes void alongside the full catalog, and of these, three are newly detected in our FUV observation. Our void galaxy sample spans a range of UV colors (−0.35 mag ≤ FUV−NUV ≤ 0.68 mag) and absolute magnitudes (−14.16 mag ≤ M NUV ≤ −18.65 mag). In addition, Sloan Digital Sky Survey and Two Micron All Sky Survey archival data are being used to study UV, optical, and infrared color–magnitude relations for our galaxies in the void. We investigate the nature of bimodal color distribution, morphologies, and star formation of the void galaxies. Most of the galaxies in our sample are fainter and less massive than L* galaxies, with M r > −20 mag. Our analysis reveals a dominant fraction of bluer galaxies over the red ones in the void region probed. The internal and Galactic extinction corrected FUV star formation rates (SFRs) in our void galaxy catalog varies in a large range of 0.05–51.01 M ⊙ yr−1, with a median of 3.96 M ⊙ yr−1. We find a weak effect of the environment on the SFRs of galaxies. Implications of our findings are discussed.

Central Star Formation in Early-type Galaxy I Zw 81 in the Bootes Void

“…The observation was made simultaneously in UVIT F154W and N242W filters. The details of the observation and data reduction are mentioned in Pandey et al (2021). Complementary archival imaging data of the galaxy in optical and infrared wave bands were collected from the following surveys: Sloan Digital Sky Survey Data Release 12 (SDSS DR12, Alam et al 2015), Canada France Hawaii Telescope (CFHT, Boulade et al 1998), Two Micron All-sky survey (2MASS, Skrutskie et al 2006) and Wide-field Infrared Survey (WISE, Wright et al 2010).…”

“…The low-density environment of the void affects some of the properties of the void galaxies, e.g., these galaxies possess higher specific star formation rates (sSFRs) than their counterparts in the dense environment (Grogin & Geller 1999). Generally, void galaxies are star-forming lowmass systems with late-type morphology (Cruzen et al 2002;Rojas et al 2004;Kreckel et al 2012;Pandey et al 2021). A fraction of them is found to be passive, early-type, interacting, or with active nuclei at the center (Constantin et al 2008;Beygu et al 2017).…”

“…Therefore, the entire process of galaxy quenching is complex and demands further study. Pandey et al (2021) studied the properties of star-forming void galaxies based on deep ultraviolet (UV) survey in the Bootes void using the Ultraviolet Imaging Telescope (UVIT). In this work, I Zw 81 was identified as the most massive galaxy detected in the observation with strong UV emission.…”

“….90 (Pandey et al 2021), I Zw 81 stands among the massive galaxies detected in isolated environments. The galaxy has been previously reported in various observational surveys of the Bootes void (Lipovetsky et al 1988;Cruzen et al 2002), and is known to host a Seyfert 2 AGN (Lipovetsky et al 1988).…”

“…These results portray that regardless of the global environment, mass quenching mechanisms active in massive galaxies are capable of shutting down ongoing star formation in a galaxy. However, the photometric properties of the galaxy in focus, I Zw 81, show blue colors on the UV and optical color-magnitude diagrams along with strong far-UV (FUV) and near-UV (NUV) emission (Pandey et al 2021), which make the galaxy interesting to study.…”