Star formation characteristics of CNN-identified post-mergers in the Ultraviolet Near Infrared Optical Northern Survey (UNIONS)

Abstract

The importance of the post-merger epoch in galaxy evolution has been well-documented, but post-mergers are notoriously difficult to identify. While the features induced by mergers can sometimes be distinctive, they are frequently missed by visual inspection. In addition, visual classification efforts are highly inefficient because of the inherent rarity of post-mergers (~1% in the low-redshift Universe), and non-parametric statistical merger selection methods do not account for the diversity of post-mergers or the environments in which they appear. To address these issues, we deploy a convolutional neural network (CNN) which has been trained and evaluated on realistic mock observations of simulated galaxies from the IllustrisTNG simulations, to galaxy images from the Canada France Imaging Survey (CFIS), which is part of the Ultraviolet Near Infrared Optical Northern Survey (UNIONS). We present the characteristics of the galaxies with the highest CNN-predicted post-merger certainties, as well as a visually confirmed subset of 699 post-mergers. We find that post-mergers with high CNN merger probabilities (p(x)>0.8) have an average star formation rate that is 0.1 dex higher than a mass- and redshift-matched control sample. The SFR enhancement is even greater in the visually confirmed post-merger sample, a factor of two higher than the control sample.

14 pages, 9 figures, visually confirmed post-merger catalog available via MNRAS

References in corpus (27)

• The Gaia mission
• Galaxy Pairs in the Sloan Digital Sky Survey I: Star Formation, AGN Fraction, and the Luminosity/Mass-Metallicity Relation
• Galaxy Merger Morphologies and Time-Scales from Simulations of Equal-Mass Gas-Rich Disc Mergers
• SKIRT: an Advanced Dust Radiative Transfer Code with a User-Friendly Architecture
• A fitting formula for the merger timescale of galaxies in hierarchical clustering
• Galaxy pairs in the Sloan Digital Sky Survey - IX: Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer
• The Redshift Evolution of Wet, Dry, and Mixed Galaxy Mergers from Close Galaxy Pairs in the DEEP2 Galaxy Redshift Survey
• MegaPipe: the MegaCam image stacking pipeline at the Canadian Astronomical Data Centre
• A definitive merger-AGN connection at z~0 with CFIS: mergers have an excess of AGN and AGN hosts are more frequently disturbed
• Morphology and star formation in IllustrisTNG: the build-up of spheroids and discs
• Star Formation in Close Pairs Selected from the Sloan Digital Sky Survey
• On the possible environmental effect in distributing heavy elements beyond individual gaseous halos
• Interacting galaxies on FIRE-2: The connection between enhanced star formation and interstellar gas content
• Deep learning predictions of galaxy merger stage and the importance of observational realism
• From Starburst to Quiescence: Testing AGN feedback in Rapidly Quenching Post-Starburst Galaxies
• Galaxy Zoo: Quantitative Visual Morphological Classifications for 48,000 galaxies from CANDELS
• Galaxy And Mass Assembly (GAMA): Refining the Local Galaxy Merger Rate using Morphological Information
• Galaxy Merger Rates up to z $\sim$ 3 using a Bayesian Deep Learning Model $-$ A Major-Merger classifier using IllustrisTNG Simulation data
• Identifying Galaxy Mergers in Observations and Simulations with Deep Learning
• Convolutional neural network identification of galaxy post-mergers in UNIONS using IllustrisTNG
• Interacting galaxies in the IllustrisTNG simulations -- II: Star formation in the post-merger stage
• Galaxy mergers moulding the circum-galactic medium - I. The impact of a major merger
• Simulating the COSMOS: The fraction of merging galaxies at high redshift
• Bulge plus disc and Sérsic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the $ugriz$ structural measurements
• Interacting galaxies in the IllustrisTNG simulations -- III: (the rarity of) quenching in post-merger galaxies
• The combined and respective roles of imaging and stellar kinematics in identifying galaxy merger remnants
• Robustness of deep learning algorithms in astronomy -- galaxy morphology studies

Cited by in corpus (17)

• Galaxy mergers can rapidly shut down star formation
• IllustrisTNG in the HSC-SSP: image data release and the major role of mini mergers as drivers of asymmetry and star formation
• The merger fraction of post-starburst galaxies in UNIONS
• Interacting galaxies in the IllustrisTNG simulations -- IV: Enhanced Supermassive Black Hole Accretion Rates in Post-Merger Galaxies
• The ALMaQUEST Survey X: What powers merger induced star formation?
• Post-Starburst Properties of Post-Merger Galaxies
• AGN in post-mergers from the Ultraviolet Near Infrared Optical Northern Survey
• The interconnection between galaxy mergers, AGN activity and rapid quenching of star formation in simulated post-merger galaxies
• The SAMI Galaxy Survey: Using Tidal Streams and Shells to Trace the Dynamical Evolution of Massive Galaxies
• Galaxy merger challenge: A comparison study between machine learning-based detection methods
• Effect of low-mass galaxy interactions on their star formation
• SDSS-IV MaNGA: Unveiling Galaxy Interaction by Merger Stages with Machine Learning
• Determining the time before or after a galaxy merger event
• Dwarf-Dwarf interactions and their influence on star formation : Insights from post-merger galaxies
• Galaxies OBserved as Low-luminosity Identified Nebulae (GOBLIN): a catalog of 43,000 high-probability dwarf galaxy candidates in the UNIONS survey
• The major merger-active galactic nucleus connection up to the cosmic noon
• Dynamically close galaxy pairs from the unWISE survey: Testing the merger-AGN-star formation connection