J/ApJ/864/144 N/O and Ne/O ratios of SDSS dwarf galaxies (Douglass+, 2018)
Influence of the void environment on chemical abundances in dwarf galaxies and
implications for connecting star formation and halo mass.
Douglass K.A., Vogeley M.S., Cen R.
<Astrophys. J., 864, 144 (2018)>
=2018ApJ...864..144D 2018ApJ...864..144D
ADC_Keywords: Abundances; Galaxies, spectra; Redshifts; Optical
Keywords: galaxies: abundances ; galaxies: dwarf ; galaxies: evolution
Abstract:
We study how the void environment affects the chemical evolution of
galaxies in the universe by comparing the oxygen and nitrogen
abundances of dwarf galaxies in voids with dwarf galaxies in denser
regions. Using spectroscopic observations from the Sloan Digital Sky
Survey Data Release 7, we estimate the oxygen, nitrogen, and neon
abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser
regions. We use the Direct Te method for calculating the gas-phase
chemical abundances in the dwarf galaxies because it is best suited
for low-metallicity, low-mass (dwarf) galaxies. A substitute for the
[OII]λ3727 doublet is developed, permitting oxygen abundance
estimates of SDSS dwarf galaxies at all redshifts with the Direct Te
method. We find that void dwarf galaxies have about the same oxygen
abundance and Ne/O ratio as dwarf galaxies in denser environments.
However, we find that void dwarf galaxies have slightly higher neon
(∼10%) abundances than dwarf galaxies in denser environments. The
opposite trend is seen in both the nitrogen abundance and N/O ratio:
void dwarf galaxies have slightly lower nitrogen abundances (∼5%) and
lower N/O ratios (∼7%) than dwarf galaxies in denser regions.
Therefore, we conclude that the void environment has a slight
influence on dwarf galaxy chemical evolution. Our mass-N/O
relationship shows that the secondary production of nitrogen commences
at a lower stellar mass in void dwarf star-forming galaxies than in
dwarf star-forming galaxies in denser environments. We also find that
star-forming void dwarf galaxies have higher HI masses than the
star-forming dwarf galaxies in denser regions. Our star-forming dwarf
galaxy sample demonstrates a strong anti-correlation between the sSFR
and N/O ratio, providing evidence that oxygen is produced in
higher-mass stars than those which synthesize nitrogen. The lower N/O
ratios and smaller stellar mass for secondary nitrogen production seen
in void dwarf galaxies may indicate both delayed star formation as
predicted by ΛCDM cosmology and a dependence of cosmic
downsizing on the large-scale environment. A shift toward slightly
higher oxygen abundances and higher HI masses in void dwarf galaxies
could be evidence of larger ratios of dark matter halo mass to stellar
mass in voids compared with denser regions.
Description:
We look to expand on the work by Douglass & Vogeley (2017, J/ApJ/834/186
and 2017, J/ApJ/837/42) by substantially increasing their sample size
of dwarf galaxies.
We use emission-line flux data from the MPA-JHU value-added catalog,
which is based on the SDSS DR7 sample of galaxies; as described at
http://www.sdss.org/dr12/spectro/galaxy_mpajhu/ and in Tremonti+
(2004ApJ...613..898T 2004ApJ...613..898T).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 101 1717 Analyzed dwarf galaxies
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/AJ/118/2561 : Survey of gal. within prominent nearby voids (Grogin+, 1999)
J/ApJ/511/639 : Abundances in blue compact galaxies (Izotov+, 1999)
J/AJ/119/32 : Survey of galaxies within nearby voids. II (Grogin+, 2000)
J/MNRAS/330/75 : Chemical abundances in UV-selected galaxies (Contini+, 2002)
J/A+A/448/955 : Abundances of emission galaxies in SDSS-DR3 (Izotov+, 2006)
J/ApJ/636/214 : HII regions in dwarf irregular galaxies (van Zee+, 2006)
J/AJ/144/16 : Optical & HI properties of galaxies in voids (Kreckel+, 2012)
J/ApJ/765/140 : Stacked spectra of SDSS star forming galaxies (Andrews+, 2013)
J/ApJ/819/110 : Extremely metal-poor gal. in SDSS. II. (Sanchez Almeida+ 2016)
J/ApJ/834/186 : Metallicity of MPA-JHU SDSS-DR7 dwarf gal. (Douglass+, 2017)
J/ApJ/837/42 : N/O ratio of dwarf galaxies from SDSS (Douglass+, 2017)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- Seq [40726/3011653] KIAS-VAGC galaxy index number
9- 10 I2 h RAh [7/17] Hour of Right Ascension (J2000)
12- 13 I2 min RAm Minute of Right Ascension (J2000)
15- 19 F5.2 s RAs Second of Right Ascension (J2000)
21- 21 A1 --- DE- Sign of the Declination (J2000)
22- 23 I2 deg DEd Degree of Declination (J2000)
25- 26 I2 arcmin DEm Arcminute of Declination (J2000)
28- 32 F5.2 arcsec DEs Arcsecond of Declination (J2000)
34- 39 F6.4 --- z [0.0001/0.03] Spectroscopic redshift
41- 44 F4.2 [-] log(O/H) [7.1/9.3] The 12+log(O/H) abundance (1)
46- 49 F4.2 [-] e_log(O/H) [0.02/0.6] Uncertainty in log(O/H) (1)
51- 54 F4.2 [-] log(N/H) [5.1/7.7] The 12+log(N/H) abundance (1)
56- 59 F4.2 [-] e_log(N/H) [0/0.5] Uncertainty in log(N/H) (1)
61- 64 F4.2 [-] log(Ne/H) [5.1/8.3] The 12+log(Ne/H) abundance (1)
66- 69 F4.2 [-] e_log(Ne/H) [0.01/0.8] Uncertainty in log(Ne/H) (1)
71- 75 F5.2 [-] log(N/O) [-3.9/-0.3] log N/O abundance ratio (1)
77- 80 F4.2 [-] e_log(N/O) [0.02/0.6] Uncertainty in log(N/O) (1)
82- 86 F5.2 [-] log(Ne/O) [-2.4/-0.4] log Ne/O abundance ratio (1)
88- 91 F4.2 [-] e_log(Ne/O) [0.02/0.9] Uncertainty in log(Ne/O) (1)
93-101 A9 --- Loc Location (2)
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Note (1): Abundance values are calculated using the direct Te method
described in Izotov+ (2006, J/A+A/448/955) and the O+ approximation
defined in Section 2.2, with error estimates via a Monte Carlo method.
Note (2): The void catalog of Pan+ (2012MNRAS.421..926P 2012MNRAS.421..926P) is used
to classify the galaxies as either Void or Wall. If a galaxy is
located too close to the boundary of the SDSS survey to identify
whether or not it is inside a void, it is labeled as Uncertain.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Aug-2019