J/MNRAS/514/3294 CFIS CNN post-merger galaxies catalog (Bickley+, 2022)
Star formation characteristics of CNN-identified post-mergers in the
Ultraviolet Near Infrared Optical Northern Survey (UNIONS).
Bickley R.W., Ellison S.L., Patton D.R., Bottrell C., Gwyn S., Hudson M.J.
<Mon. Not. R. Astron. Soc. 514, 3294-3307 (2022)>
=2022MNRAS.514.3294B 2022MNRAS.514.3294B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, interacting ; Optical ; Spectroscopy ; Photometry ;
Cross identifications ; Positional data ; Redshifts ;
Stars, masses ; Star Forming Region ; Photometry, classification
Keywords: methods: statistical - techniques: image processing -
galaxies: evolution - galaxies: interactions - galaxies: peculiar
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 per cent 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) that 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, which is part of the Ultraviolet Near Infrared Optical
Northern Survey. 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 2 higher
than the control sample.
Description:
In the field of post-merger epoch in galaxy evolution, we revisit the
preparation and characteristics of the simulation-trained CNN, and
prepare CFIS images of galaxies for processing by the network
previously used by Bickley et al. 2021MNRAS.504..372B 2021MNRAS.504..372B. We next apply
the CNN to the CFIS images so prepared and validate its predictions
statistically, perform rigorous visual inspection, and present a new
sample of 699 visually confirmed post-merger galaxies.
As based sample, we merge spectroscopic SDSS-DR7 and r-band
photometric UNIONS-CFHT/CFIS DR2 witha 2-arcsec tolerance. The
resulting sample contains 168597 galaxies. After being classified by
the CNN, 2000 galaxies given high post-merger p(x) predictions were in
turn inspected by the authors, employing a purity-motivated
classification philosophy in which galaxies whose post-merger statuses
were in doubt were rejected. Around 65 per cent of the galaxies were
ultimately removed from the CNN-predicted post-merger sample with
p(x)>0.75, but 699 galaxies were unanimously confirmed as
post-mergers after visual inspection. Then, as shown the table2.dat,
we present these confirmed galaxies with their redshift, stellar mass,
SFR, r-mag and p(x) prediction values.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 101 699 The hybrid visual-CNN CFIS post-merger catalogue
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See also:
J/MNRAS/486/390 : Morphology of 16908 SDSS Stripe 82 galaxies (Bottrell+, 2019)
J/A+A/582/A21 : Merging galaxies (mis)alignments (Barrera-Ballesteros+, 2015)
J/AJ/130/1516 : MCG pairs and triples of galaxies (De Propris+, 2005)
J/ApJS/221/11 : CANDELS visual classifications for GOODS-S (Kartaltepe+,2015)
J/ApJS/210/3 : SDSS bulge, disk and total stellar mass estimates
(Mendel+, 2014)
II/294 : The SDSS Photometric Catalog, Release 7
(Adelman-McCarthy+, 2009)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
https://cas.sdss.org/dr7/en/tools/explore/ : SDSS-DR7 explore tool
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID Identification number from CFISDR2/SDSS-DR7
merge resulting of 168597 galaxies sample
(NbrID)
8- 25 I18 --- objID SDSS-DR7 unique object identifier (objID)
27- 38 F12.8 deg RAdeg Right ascension from SDSS-DR7 (J2000) (ra)
40- 50 F11.8 deg DEdeg Declination from SDSS-DR7 (J2000) (decl)
52- 59 F8.6 --- z Spectroscopic redshift from SDSS-DR7 (z_spec)
61- 68 F8.5 [Msun] logM* Median value of the total stellar mass
(totalmassmed)
70- 78 F9.6 [Msun/yr] SFR Median value of the total star forming
(totalsfrmed)
80- 82 F3.1 --- f_ID [1.0] Flag to indicate being part of the
first categorie which is CNN [p(x)>0.75] and
positive classifications by the authors
84- 90 F7.4 mag rmag The CFIS r-band Petrosian apparent magnitude
(petromag_r)
92- 101 F10.8 --- CNN The CNN post-merger classification
probability (CNNprediction)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 10-Apr-2025