J/MNRAS/492/1791 Very young galaxies from SDSS (Mamon+, 2020)
The frequency of very young galaxies in the local Universe.
II. The view from SDSS spectra.
Mamon G.A., Trevisan M., Thuan T.X., Gallazzi A., Dave R.
<Mon. Not. R. Astron. Soc., 492, 1791-1811 (2020)>
=2020MNRAS.492.1791M 2020MNRAS.492.1791M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxy catalogs ; Spectroscopy
Keywords: methods: numerical - galaxies: dwarf - galaxies: evolution -
galaxies: statistics
Abstract:
Only a handful of galaxies in the local Universe appear to be very
young. We estimate the fraction of very young galaxies (VYGs), defined
as those with more than half their stellar masses formed within the
last Gyr. We fit non-parametric star formation histories (SFHs) to
∼280000 galaxy spectra from a flux- and volume-limited subsample of
the Main Galaxy Sample (MGS) of the SDSS, which is also complete in
mass-to-light ratio, thus properly accounting for passive galaxies of
a given mass. The VYG fractions decrease with increasing galaxy
stellar mass, from ∼50 per cent at m=108M☉ to ∼0.1 per cent
at m=1011.5M☉, with differences of up to 1dex between the
different spectral models used to estimate the SFH and on how we treat
aperture effects. But old stellar populations may hide in our VYGs
despite our conservative VYG sample built with galaxies that are
globally bluer than within the region viewed by the SDSS fibre. The
VYG fractions versus mass decrease more gradually compared to the
Tweed et al. (2018MNRAS.477.1427T 2018MNRAS.477.1427T) predictions using analytical and
semi-analytical models of galaxy formation, but agree better with the
SIMBA hydrodynamical simulation. These discrepancies highlight the
usefulness of VYGs in constraining the strong uncertainties in both
galaxy formation models and spectral modelling of galaxy SFHs. Given
the lognormal cosmic SFH, these mean VYG fractions suggest that
galaxies above 108M☉ undergo at most four major starbursts on
average.
Description:
The file tableA1.dat lists the galaxies of the SDSS Main Galaxy sample
that are part of the clean sample used for the search of very young
galaxies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 125 404931 Table of galaxies belonging to the Clean sample
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- ID Unique identifier
8- 15 F8.4 deg RAdeg Right ascension (J2000)
17- 24 F8.4 deg DEdeg Declination (J2000)
26- 30 I5 --- Plate SDSS spectroscopic plate
32- 36 I5 --- MJD SDSS modified Julian date of spectroscopic
observation
38- 42 I5 --- Fiber SDSS spectroscopic fiber
44 A1 --- C [N/Y] Flag for complete sample
46 A1 --- BG [N/Y] Flag for blue gradient
(modelcolor-fibercolor<0)
49- 51 A3 --- AGN [NTY ] Flag for Active Galactic Nucleus
(from BPT diagram)
53- 57 F5.2 [Msun] logmSV log stellar mass from STARLIGHT with
V15 SSP (3)
59- 64 F6.2 Gyr ageSV lookback time relative to observed redshift
when half the stellar mass was formed from
STARLIGHT with V15 SSP (3)
66- 70 F5.2 [Msun] logmVB log stellar mass from VESPA with BC03 SSP
(2-comp dust) (2)
72- 77 F6.2 Gyr ageVB lookback time relative to observed redshift
when half the stellar mass was formed from
VESPA with BC03 SSP (3) (1)
79- 83 F5.2 [Msun] logmVM log stellar mass from VESPA with M05 SSP
(2-comp dust) (3)
85- 90 F6.2 Gyr ageVM lookback time relative to observed redshift
when half the stellar mass was formed from
VESPA with M05 SSP (3) (1)
92- 95 F4.2 --- f0-1 fraction of final stellar mass formed
0 to 1Gyr before redshift of observation,
from STARLIGHT with V15 SSP (3)
97-100 F4.2 --- f1-6 fraction of final stellar mass formed
1 to 6.1Gyr before redshift of observation,
from STARLIGHT with V15 SSP (3)
102-106 F5.2 --- f6-14 fraction of final stellar mass formed more
than 6.1Gyr before redshift of observation,
from STARLIGHT with V15 SSP (3)
108-112 F5.2 --- f0-1c fraction of final stellar mass formed
0 to 1Gyr before redshift of observation,
from STARLIGHT with V15 SSP, accounting for
mass-loss from supernovae (3)
114-118 F5.2 --- f1-6c fraction of final stellar mass formed
1 to 6.1Gyr before redshift of observation,
from STARLIGHT with V15 SSP, accounting for
mass-loss from supernovae (3)
120-125 F6.2 --- f6-14c fraction of final stellar mass formed more
than 6.1Gyr before redshift of observation,
from STARLIGHT with V15 SSP, accounting for
mass-loss from supernovae (3)
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Note (1): The VESPA star formation histories are given in Tojeiro et al.
(20)09ApJS..185....1T), Cat. J/ApJS/185/1
Note (2): The adopted VESPA spectral models use the 2-component dust model.
Note (3): The single stellar population models (SSPs) are from Bruzual & Charlot
(2003MNRAS.344.1000B 2003MNRAS.344.1000B) [BC03] and from Maraston (2005MNRAS.362..799M 2005MNRAS.362..799M) [M05]
and Vazdekis et al. (2015MNRAS.449.1177V 2015MNRAS.449.1177V) [V15].
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Acknowledgements:
Gary Mamon, gam(at)iap.fr
References:
Tweed et al., Paper I 2018MNRAS.477.1427T 2018MNRAS.477.1427T
History:
19-Mar-2020: on-line version
05-Jun-2020: correction for logmSB and ageSB into logmSV and ageSV for
V15 SSP intead of BC03 SSP.
02-Feb-2023: Description of column "f1-6" corrected (1 to 6.1Gyr and
not 0 to 6.1Gyr as previously stated).
(End) Gary Mamon [IAP], Patricia Vannier [CDS] 13-Mar-2020