J/MNRAS/486/1377 Photometric SFR using machine learning (Delli Veneri+, 2019)
Star formation rates for photometric samples of galaxies using
machine learning methods.
Delli Veneri M., Cavuoti S., Brescia M., Longo G., Riccio G.
<Mon. Not. R. Astron. Soc. 486, 1377-1391 (2019)>
=2019MNRAS.486.1377D 2019MNRAS.486.1377D (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry ; Redshifts
Keywords: methods: data analysis - techniques: photometric - catalogues -
galaxies: distances and redshifts - galaxies: photometry
Abstract:
Star formation rates (SFRs) are crucial to constrain theories of
galaxy formation and evolution. SFRs are usually estimated via
spectroscopic observations requiring large amounts of telescope time.
We explore an alternative approach based on the photometric estimation
of global SFRs for large samples of galaxies, by using methods such as
automatic parameter space optimisation, and supervised machine
learning models. We demonstrate that, with such approach, accurate
multiband photometry allows to estimate reliable SFRs. We also
investigate how the use of photometric rather than spectroscopic
redshifts, affects the accuracy of derived global SFRs. Finally, we
provide a publicly available catalogue of SFRs for more than 27
million galaxies extracted from the Sloan Digital Sky Survey Data
Release 7. The catalogue will be made available through the Vizier
facility.
Description:
This catalogue contains SFRs for 27,513,324 galaxies of the SDSS-DR7.
To produce the catalogue, we started by querying the Galaxy View4 of
the SDSS-DR7 for all the needed photometric features of galaxies with
a "good" photometry (see PhotoFlags) and containing no Missing Values.
We then applied the magnitudes cuts of our knowledge base (in order to
keep the photometric features within the ranges of our knowledge base)
and cross-matched the resulted data set with the photoz catalogue
derived by Brescia et al. (2014b), in order to use them as a quality
flag. The final catalogue contains the following columns:
Identifiers: dr9objid, objid, ra, dec, i.e. respectively, the object
identifier in the SDSS DR9 and DR7 and their ascension and declination
coordinates;
Quality flags: photoz and Quality_Flag, i.e. the photometric redshifts
measured by Brescia et al. (2014b) and the associated flag. The
Quality_Flag can assume three values 1, 2, and 3; 1 stands for the
best photo-z accuracy, 2 and 3 for decreasing accuracy;
SFR: It is computed by the MLPQNA model with the 32 best features
selected by the PHILAB method (excluding redshifts).
In order to select only SFRs with high-quality (i.e. only select
sources inside the training set parameter space constrains), the user
should impose photoz=0.33 and Quality_Flag=1. This is due by
considering that in our knowledge base there are only objects with
spectroscopic redshift less than 0.33, thus we are able to predict
SFRs only for objects within such redshift range. These constraints
will select ∼6.6 million objects. Since we do not have any
spectroscopic redshifts for the catalogue objects, we must use
photometric redshifts (where available) to perform these cuts.
Nevertheless using photometric redshifts instead of spectroscopic ones
may introduce some contamination in the catalogue, i.e. a source may
be inside the photoz=0.33 cut when in reality it has a spectroscopic
redshift higher than 0.33. To estimate the number of such
contaminants, we verify that among the 871 784 objects with
photoz=0.33 and a spectroscopic redshift only ∼1.33 per cent resulted
to have a true redshift higher that 0.33.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 80 27513324 SFR Catalogue
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See also:
J/A+A/568/A126 : SDSS-DR9 photometric redshifts (Brescia+, 2014)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- dr9objID SDSS-DR9 objID
21- 38 I18 --- objID SDSS-DR7 objID
40- 49 E10.6 deg RAdeg [] Right Ascension (J2000)
51- 60 E10.6 deg DEdeg Declination (J2000)
62- 69 E8.6 --- photoz Photometric redshift measured by
Brescia et al. (2014, Cat. J/A+A/568/A126)
71 I1 --- Qual [0/3] Quality Flag from Brescia et al.
(2014, Cat. J/A+A/568/A126) (1)
73- 80 F8.4 [yr-1] SSFR Photometric Star Specific Formation Rates,
in -log((Mass/Msun)*(1/yr)) unit
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Note (1): Quality flag as follows:
1 = high accuracy
2 = lower accuracy (medium)
3 = lower accuracy (low)
0 = none
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Acknowledgements:
Michele Delli Veneri, micheledelliveneri(at)gmail.com
(End) Michele Delli Veneri [INAF-OACN, Italy] Patricia Vannier [CDS] 23-May-2019