J/MNRAS/495/2720 Stellar populations in green valley galaxies (Angthopo+, 2020)
A detailed look at the stellar populations in green valley galaxies.
Angthopo J., Ferreras I., Silk J.
<Mon. Not. R. Astron. Soc., 495, 2720-2737 (2020)>
=2020MNRAS.495.2720A 2020MNRAS.495.2720A (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Velocity dispersion ; Spectra, optical
Keywords: galaxies: evolution - galaxies: formation - galaxies: interactions -
galaxies: stellar content
Abstract:
The green valley (GV) represents an important transitional state from
actively star-forming galaxies to passively evolving systems. Its
traditional definition, based on colour, rests on a number of
assumptions that can be subjected to non-trivial systematics. In
Angthopo, Ferreras & Silk (2019MNRAS.488L..99A 2019MNRAS.488L..99A), we proposed a new
definition of the GV based on the 4000Å break strength. In this
paper, we explore in detail the properties of the underlying stellar
populations by use of ∼230 thousand high-quality spectra from the
Sloan Digital Sky Survey (SDSS), contrasting our results with a
traditional approach via dust-corrected colours. We explore
high-quality stacked SDSS spectra, and find a population trend that
suggests a substantial difference between low- and high-mass galaxies,
with the former featuring younger populations with star formation
quenching, and the latter showing older (post-quenching) populations
that include rejuvenation events. Subtle but measurable differences
are found between a colour-based approach and our definition,
especially as our selection of GV galaxies produces a cleaner
'stratification' of the GV, with more homogeneous population
properties within sections of the GV. Our definition based on 4000Å
break strength gives a clean representation of the transition to
quiescence, easily measurable in the upcoming and future spectroscopic
surveys.
Description:
This paper continues the work presented in Angthopo, Ferreras & Silk
(2019MNRAS.488L..99A 2019MNRAS.488L..99A), based on a sample of spectroscopic data from
the classic Sloan Digital Sky Survey (SDSS, York et al.
2000AJ....120.1579Y 2000AJ....120.1579Y). We select the sample and retrieve the spectra
from Data Release 14 (Abolfathi et al. 2018ApJS..235...42A 2018ApJS..235...42A). SDSS is a
full-sky survey that includes spectroscopic observations of galaxies
with Petrosian r-band magnitude in the range 14.5<rAB<17.7. Our
selection criteria identify targets with relatively high
signal-to-noise ratio, SNmedian,r>10. We stack the spectra within
carefully defined regions on the plane that defines Green Valley (GV)
galaxies.
Our GV is defined on a plane spanned by a stellar population parameter
(i.e. either the 4000Å break strength or a more standard broad-band
colour) along with velocity dispersion (σ), as measured in the
SDSS fibre. σ is preferred with respect to stellar mass, as it
is directly measurable in good-quality spectra, being free of the
systematics associated with stellar mass estimates. Furthermore,
velocity dispersion is the observable that more strongly correlates
with stellar population properties (see e.g. Bernardi et al.
2003AJ....125.1882B 2003AJ....125.1882B; Ferreras et al. 2019MNRAS.489..608F 2019MNRAS.489..608F). The use of
spectra with the imposed threshold in S/N guarantees a robust estimate
of σ.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 79 18 Number of SDSS galaxy spectra in the upper and
lower sections of the green valley, following
the definition of GV based on the 4000Å
break strength
tabled1.dat 45 205918 Probabilities of BC, GV, or RS membership
assigned to each galaxy from the SDSS set
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See also:
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Crit Selection criteria (1)
7- 13 A7 km/s vdisp Velocity dispersion interval
15- 18 I4 --- NLGV Number of galaxy spectra in the lower section
of green valley
20- 23 F4.1 % fSFLGV Fraction of galaxies in the LGV classified as
star-forming (2)
25- 27 F3.1 % e_fSFLGV Error on fSFLGV
29- 32 F4.1 % fQLGV Fraction of galaxies in the LGV classified as
quiescent (2)
34- 37 F4.1 % e_fQLGV Error on fQLGV
39- 42 F4.1 % fAGNLGV Fraction of galaxies in the LGV classified as
AGN (2)
44- 46 F3.1 % e_fAGNLGV Error on fAGNLGV
48- 51 I4 --- NUGV Number of galaxy spectra in the upper section
of green valley
53- 56 F4.1 % fSFUGV Fraction of galaxies in the UGV classified as
star-forming (2)
58- 60 F3.1 % e_fSFUGV Error on fSFUGV
62- 65 F4.1 % fQUGV Fraction of galaxies in the UGV classified as
quiescent (2)
67- 70 F4.1 % e_fQUGV Error on fQUGV
72- 75 F4.1 % fAGNUGV Fraction of galaxies in the UGV classified as
AGN (2)
77- 79 F3.1 % e_fAGNUGV Error on fAGNUGV
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Note (1): We show three selection criteria, from top to bottom, the 4000Å
break strength (adopted in this paper), the uncorrected (g-r) colour
evaluated at a fiducial redshift of z=0.1, and the dust-corrected
colour, all measured within the SDSS spectroscopic fibre.
Note (2): The sample is split according to nebular activity, following the BPT
standard classification (Baldwin et al. 1981PASP...93....5B 1981PASP...93....5B). This
enabled us to split the sample into unclassified/quiescent (BPT=-1),
star-forming (BPT=1,2), composite (BPT=3), Seyfert (BPT=4), and LINER
(BPT=5) galaxies. We do not consider here those spectra classified as
composite (BPT=3), for a cleaner classification of the three regions.
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Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Plate SDSS plate spectral identifier
6- 10 I5 d MJD SDSS Modified Julian Date spectral identifier
12- 14 I3 --- Fiber SDSS Fiber spectral identifier
16- 20 F5.3 --- Dn4000 Break strength at 4000Å (1)
22- 26 F5.1 km/s vdisp Velocity dispersion (1)
28- 32 F5.3 --- PBC Probability of belonging to the Blue Cloud
34- 39 F6.3 --- PGV Probability of belonging to the Green Valley
41- 45 F5.3 --- PRS Probability of belonging to the Red Sequence
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Note (1): Measured within the 3arcsec diameter fibres of the spectrograph
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 15-Jun-2023