J/MNRAS/431/2034 SED of K+A galaxies from UV to mid-IR (Melnick+, 2013)
The spectral energy distributions of K+A galaxies from the UV to the mid-IR:
stellar populations, star formation and hot dust.
Melnick J., De Propris R.
<Mon. Not. R. Astron. Soc., 431, 2034-2049 (2013)>
=2013MNRAS.431.2034M 2013MNRAS.431.2034M
ADC_Keywords: Galaxies, photometry ; Energy distributions
Keywords: galaxies: abundances - galaxies: evolution - galaxies: formation -
galaxies: interactions - galaxies: stellar content
Abstract:
We present spectrum synthesis fits to 808 K+A galaxies selected from
the Sloan Digital Sky Survey (SDSS) and population synthesis of their
spectral energy distributions, extending from the far-UV (0.15µm)
to the mid-IR (22µm), based on the results of STARLIGHT code
fitting to the SDSS spectra. Our modelling shows that K+A galaxies
have undergone a large starburst, involving a median 50% of
their present stellar masses, superposed over an older stellar
population. The metal abundance of the intermediate-age stars shows
that star formation did not take place in pristine gas, but was part
of a dramatic increase in the star formation rates for originally
gas-rich objects. We find no evidence for ongoing QSO activity in the
UV, which is well modelled by the emission of intermediate-age stars.
We use K+A galaxies as local counterparts of high-redshift objects to
test for the presence of thermally pulsing asymptotic giant branch
(TP-AGB) stars in similarly aged populations and find no excess in the
infrared due to emission from such stars, arguing that more distant
galaxies are indeed old and massive at their redshift. All of our
galaxies show significant excesses in the mid-IR compared to the light
from their stars. We fit this ad hoc with a 300K blackbody. Possible
sources include TP-AGB stars, obscured young star clusters and hidden
AGNs, heating a significant dust component.
Description:
In this framework, the class of objects known as "K+A galaxies" is
particularly interesting. These appear to be galaxies whose spectrum
shows signs of a recent (within 0.2-2Gyr) episode of star formation,
producing a strong Balmer series due to A stars, superposed over an
old stellar population (dominated by K giants) typical of spheroids
and early-type spirals. Nevertheless, there is no strong [OII] or Half
emission indicating that star formation is currently not taking place.
In many cases, the starburst appears to have comprised a significant
fraction (20-60%) of the galaxy mass. K+A galaxies therefore are
observed in a short-lived phase as they transit from the blue cloud
to the red sequence and thus provide the opportunity to obtain unique
insights into the processes leading to the morphological and
spectrophotometric transformation of galaxies.
We used a sample of 811 K+A galaxies selected from the SDSS as
described by Nielsen et al. (2012ApJ...761L..16N 2012ApJ...761L..16N). This is an
expansion of the K+A sample used by Goto (2007MNRAS.381..187G 2007MNRAS.381..187G) and
drawn from the seventh data release of the SDSS (Abazajian et al.
2009ApJS..182..543A 2009ApJS..182..543A). Briefly, only objects classified as galaxies
with a spectroscopic S/N>10 per pixel are considered. The selection
criteria of K+A galaxies are equivalent widths of Hα>-3.0Å,
Hδ>5.0Å and [OII]>-2.5Å where emission lines are negative.
Galaxies with redshift 0.35<z<0.37 have been excluded due to
contamination by the 5577Å atmospheric feature.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 117 808 Spectral energy distributions
table3.dat 105 808 STARLIGHT populations for K+A galaxies
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/808] Sequential number
5- 24 A20 --- SDSS SDSS name (HHMMSS.sss+DDMMSS.ss)
26- 32 F7.2 10-19W/m2/nm FUV ?=0 GALEX FUV flux (1)
34- 40 F7.2 10-19W/m2/nm NUV ?=0 GALEX NUV flux (1)
42- 47 F6.2 10-19W/m2/nm Fu' ?=0 SDSS u' flux (1)
49- 54 F6.2 10-19W/m2/nm Fg' ?=0 SDSS g' flux (1)
56- 61 F6.2 10-19W/m2/nm Fr' ?=0 SDSS r' flux (1)
63- 68 F6.2 10-19W/m2/nm Fi' ?=0 SDSS i' flux (1)
70- 75 F6.2 10-19W/m2/nm Fz ?=0 SDSS z flux (1)
77- 82 F6.2 10-19W/m2/nm FJ ?=0 2MASS or UKIDSS J flux (1)
84- 89 F6.2 10-19W/m2/nm FH ?=0 2MASS or UKIDSS H flux (1)
91- 95 F5.2 10-19W/m2/nm FKs ?=0 2MASS or UKIDSS Ks flux (1)
97-101 F5.2 10-19W/m2/nm F3.4um ?=0 WISE 3.4um flux (1)
103-106 F4.2 10-19W/m2/nm F4.6um ?=0 WISE 4.6um flux (1)
108-111 F4.2 10-19W/m2/nm F12um ?=0 WISE 12um flux (1)
113-117 F5.2 10-19W/m2/nm F22um ?=0 WISE 22um flux (1)
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Note (1): 0.00 stands for upper limits. Fluxes in 10-17erg/s/cm2/Å.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/808] Sequential number
5- 24 A20 --- SDSS SDSS name (HHMMSS.sss+DDMMSS.ss)
26- 31 F6.4 --- z Redshift (from SDSS-DR7)
33- 37 F5.1 GMsun Mass Mass (in 109M☉)
39- 43 F5.2 mag AVint Internal absorption
45- 48 F4.2 mag AVmw Milky Way absorption
50- 54 F5.1 --- [NII]/Ha Abundance ratio [NII](6584Å)/Hα
56- 59 F4.1 0.1nm EWHa Hα Equivalent width of Hα
61- 64 F4.1 0.1nm EW[OIII] Equivalent width of [OIII](5007Å)
66- 69 F4.1 0.1nm EW[OII] Equivalent width of [OII](3727-29Å)
71- 74 F4.1 % Y [0/100] Fraction of Young population stars (1)
76- 79 F4.1 % I.p [0/100] Fraction of Intermediate Age
population, metal poor stars (1)
81- 84 F4.1 % I.0 [0/100] Fraction of Intermediate Age
population, solar metallicity stars (1)
86- 90 F5.1 % I.r [0/100] Fraction of Intermediate Age
population, metal rich stars (1)
92- 95 F4.1 % O.p [0/100] Fraction of Old population,
metal poor stars (1)
97-100 F4.1 % O.0 [0/100] Fraction of Old population,
solar metallicity stars (1)
102-105 F4.1 % O.r [0/100] Fraction of Old population,
metal rich stars (1)
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Note (1): Age and metallicity bins used to display the results of the SSP
(simple stellar population) model fits.
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Bins STARLIGHT Maraston-mix
BC03+Chabrier rhb+Kroupa
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Age t (Gyr)
Young t< 0.1 t< 0.1
Intermediate 0.25≤t≤4.25 0.3≤t≤4.25
Old t> 4.25 t> 4.25
Metallicity Z
Metal poor Z≤0.008 Z≤0.01
Solar Z =0.02 Z =0.02
Metal rich Z =0.05 Z =(0.04+0.07)/2
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 11-Jun-2014