J/MNRAS/497/4587 Redshifts and fluxes for emission-line galaxies (Karim+, 2020)
Validation of emission-line galaxies target selection algorithms for the Dark
Energy Spectroscopic Instrument using the MMT Binospec.
Karim T., Lee J.H., Eisenstein D.J., Burtin E., Moustakas J., Raichoor A.,
Yeche C.
<Mon. Not. R. Astron. Soc., 497, 4587-4601 (2020)>
=2020MNRAS.497.4587K 2020MNRAS.497.4587K (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Photometry, ugriz ; Redshifts ; Spectroscopy ;
Optical ; Infrared
Keywords: methods: observational - catalogues - cosmology: observations
Abstract:
The forthcoming Dark Energy Spectroscopic Instrument (DESI) experiment
plans to measure the effects of dark energy on the expansion of the
Universe and create a 3D map of the Universe using galaxies up to
z∼1.6 and QSOs up to z∼3.5.In order to create this map, DESI will
obtain spectroscopic redshifts of over 30 million objects; among them,
a majority are [OII] emitting star-forming galaxies known as
emission-line galaxies (ELGs). These ELG targets will be pre-selected
by drawing a selection region on the g-r versus r-z colour-colour
plot, where high-redshift ELGs form a separate locus from the lower
redshift ELGs and interlopers. In this paper, we study the efficiency
of three ELG target selection algorithms - the Final Design Report
(FDR) cut based on the DEEP2 photometry, Number Density Modelling
(NDM) and Random Forest - to determine how the combination of these
three algorithms can be best used to yield a simple selection boundary
that will be best suited to meet DESI's science goals. To do this, we
selected 17 small patches in the DESI footprint where we run the three
target selection algorithms to pre-select ELGs based on their
photometry. We observed the pre-selected ELGs using the MMT Binospec,
which is similar in functionality to the DESI instrument, to obtain
their spectroscopic redshifts and fluxes of 1054 ELGs. By analysing
the redshift and fluxing distribution of these galaxies, we find that
although NDM performed the best, simple changes in the FDR definition
would also yield sufficient performance.
Description:
In this paper, we study the efficiency and performance of three ELGs
target selection algorithms - Final Design Report (FDR), Number
Density Modelling (NDM), and Random Forest (RF) - with the help of the
MMT Binospec for the forthcoming DESI experiment. We determined
redshift and flux of 1054 emission-line galaxies (ELGs).
We chose to use the Binospec (Fabricant et al. 2019PASP..131g5004F 2019PASP..131g5004F) at
MMT, a slitmask instrument, to conduct our pilot survey because its
wavelength coverage and resolutions are similar to that of DESI,
ranging between 2000 and 5500 over a wavelength range from 360 to
980nm. Specifically, we opted to use two 600 lines/mm grating modes
covering the wavelength ranges 4500-6960 and 7255-9750Å with
resolutions 2740 and 4360 respectively. Hereafter, we call the bluer
grating mode 'blue mask' and the redder grating mode 'red mask'. All
of the ELGs were observed with both blue and red masks.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 91 1054 Redshift catalogue of 1054 ELGs from this paper
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.9 deg RAdeg Right ascension (J2000)
15- 26 F12.9 deg DEdeg Declination (J2000)
28- 38 F11.8 mag gmag g-band magnitude corrected for the Milky
Way extinction (1)
40- 50 F11.8 mag rmag r-band magnitude corrected for the Milky
Way extinction (1)
52- 62 F11.8 mag zmag z-band magnitude corrected for the Milky
Way extinction (1)
64- 74 F11.9 --- z Spectroscopic redshift in barycentric
frame
76- 87 F12.9 10-20W/m2 Flux ? Final flux (2)
89 A1 --- confblue Confidence in the blue mask (3)
91 A1 --- confred Confidence in the red mask (3)
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Note (1): The filter magnitudes are quoted from the DR8 catalogue of the Legacy
Surveys
Note (2): The variation of flux calibrations vectors are up to 20 percent so the
fluxes are considered to have an uncertainty of 20 percent (see
Section 5.3 of the article)
Note (3): The confidence numbers refer to the visual confidence we attributed
to the emission-line galaxies (ELGs); blue and red masks refer to the
fact that each of the ELGs were observed twice, once in blue and once
in red gratings and as a result, each ELGs was visually inspected up
to two times
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 27-Jul-2023