OH Megamasers in HI Surveys: Forecasts and a Machine Learning Approach to Separating Disks from Mergers

Abstract

OH megamasers (OHMs) are rare, luminous masers found in gas-rich major galaxy mergers. In untargeted neutral hydrogen ($\mathrm{HI}$) emission-line surveys, spectroscopic redshifts are necessary to differentiate the ${\lambda }_{\text{rest}}=18$ cm masing lines produced by OHMs from $\mathrm{HI}$ 21 cm lines. Next generation $\mathrm{HI}$ surveys will detect an unprecedented number of galaxies, most of which will not have spectroscopic redshifts. We present predictions for the numbers of OHMs that will be detected and the potential "contamination" they will impose on $\mathrm{HI}$ surveys. We examine Looking at the Distant Universe with the MeerKAT Array (LADUMA), a single-pointing deep-field survey reaching redshift $z_{\mathrm{HI}}=1.45$, as well as potential future surveys with the Square Kilometre Array (SKA) that would observe large portions of the sky out to redshift $z_{\mathrm{HI}}=1.37$. We predict that LADUMA will potentially double the number of known OHMs, creating an expected contamination of 1.0% of the survey's $\mathrm{HI}$ sample. Future SKA $\mathrm{HI}$ surveys are expected to see up to 7.2% OH contamination. To mitigate this contamination, we present methods to distinguish $\mathrm{HI}$ and OHM host populations without spectroscopic redshifts using near- to mid-IR photometry and a k-Nearest Neighbors algorithm. Using our methods, nearly 99% of OHMs out to redshift $z_{\mathrm{OH}}\sim 1.0$ can be correctly identified. At redshifts out to $z_{\mathrm{OH}}\sim 2.0$, 97% of OHMs can be identified. The discovery of these high-redshift OHMs will be valuable for understanding the connection between extreme star formation and galaxy evolution.

arXiv comment14 pages, 11 figures, accepted for publication in ApJ

References in corpus (30)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• A simple model to interpret the ultraviolet, optical and infrared emission from galaxies
• Mid-Infrared Selection of Active Galaxies
• The merger rate of galaxies in the Illustris Simulation: a comparison with observations and semi-empirical models
• The Major and Minor Galaxy Merger Rates at z < 1.5
• The PRIsm MUlti-Object Survey (PRIMUS) I: Survey Overview and Characteristics
• An Atlas of Galaxy Spectral Energy Distributions from the Ultraviolet to the Mid-Infrared
• Observational constraints on the merger history of galaxies since $z\approx 6$: Probabilistic galaxy pair counts in the CANDELS fields
• Predictions for ASKAP Neutral Hydrogen Surveys
• A Search for OH Megamasers at z > 0.1. III. The Complete Survey
• Highest Redshift Image of Neutral Hydrogen in Emission: A CHILES Detection of a Starbursting Galaxy at z=0.376
• A consistent measure of the merger histories of massive galaxies using close-pair statistics I: Major mergers at $z<3.5$
• A Virtual Sky with Extragalactic HI and CO Lines for the SKA and ALMA
• Extragalactic Zeeman Detections in OH Megamasers
• Galaxy Merger Rates up to z $\sim$ 3 using a Bayesian Deep Learning Model $-$ A Major-Merger classifier using IllustrisTNG Simulation data
• Major Merging History in CANDELS. I. Evolution of the Incidence of Massive Galaxy-Galaxy Pairs from z=3 to z~0
• A Pilot for a VLA HI Deep Field
• 4MOST Consortium Survey 7: Wide-Area VISTA Extragalactic Survey (WAVES)
• EMERGE: Empirical predictions of galaxy merger rates since $z\sim 6$
• The OH Megamaser Luminosity Function
• The Effect of 53 micron IR Radiation on 18 cm OH Megamaser Emission
• A Dense Gas Trigger for OH Megamasers
• The Role of Magnetic Fields in Starburst Galaxies as Revealed by OH Megamasers
• Identifying OH Imposters in the ALFALFA Neutral Hydrogen Survey
• Apertif view of the OH Megamaser IRAS 10597+5926: OH 18 cm satellite lines in wide-area HI surveys

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• LADUMA: Discovery of a luminous OH megamaser at $z>0.5$
• Radio properties of the OH megamaser galaxy IIZw 096
• A serendipitous discovery of HI-rich galaxy groups with MeerKAT
• FAST Ultra-Deep Survey (FUDS): Data Release for FUDS0
• Radio continuum and OH line emission of high-z OH megamaser galaxies
• FASHI: A search for extragalactic OH megamasers with FAST
• A Comprehensive Multiwavelength Study of the OH Megamaser galaxy IRAS 09320+6134
• Testing OH Megamaser Identification Methods in HI Surveys: Updated Source-Flagging Algorithms and New Detections in ALFALFA