J/ApJ/837/42 N/O ratio of dwarf galaxies from SDSS (Douglass+, 2017)
Large-scale environmental dependence of the abundance ratio of nitrogen to
oxygen in blue, star-forming galaxies fainter than L*.
Douglass K.A., Vogeley M.S.
<Astrophys. J., 837, 42-42 (2017)>
=2017ApJ...837...42D 2017ApJ...837...42D (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Galaxies, spectra ; Redshifts ; Magnitudes, absolute
Keywords: galaxies: abundances; galaxies: active; galaxies: dwarf;
galaxies: evolution; galaxies: ISM
Abstract:
We examine how the cosmic environment affects the chemical evolution
of galaxies in the universe by comparing the N/O ratio of dwarf
galaxies in voids with that of dwarf galaxies in denser regions.
Ratios of the forbidden [OIII] and [SII] transitions provide estimates
of a region's electron temperature and number density. We estimate the
abundances of oxygen and nitrogen using these temperature and density
estimates and the emission-line fluxes [OII]3727, [OIII]4959,5007, and
[NII]6548,6584 with the direct Te method. Using spectroscopic
observations from the Sloan Digital Sky Survey Data Release 7, we are
able to estimate the N/O ratio in 42 void dwarf galaxies and 89 dwarf
galaxies in denser regions. The N/O ratio for void dwarfs (Mr>-17)
is slightly lower (∼12%) than for dwarf galaxies in denser regions. We
also estimate the nitrogen and oxygen abundances of 2050 void galaxies
and 3883 galaxies in denser regions with Mr>-20. These somewhat
brighter galaxies (but still fainter than L*) also display similar
minor shifts in the N/O ratio. The shifts in the average and median
element abundance values in all absolute magnitude bins studied are in
the same direction, suggesting that the large-scale environment may
influence the chemical evolution of galaxies. We discuss possible
causes of such a large-scale environmental dependence of the chemical
evolution of galaxies, including retarded star formation and a higher
ratio of dark matter halo mass to stellar mass in void galaxies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 135 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 Catalog, Release 12 (Alam+, 2015)
J/ApJ/511/639 : Abundances in blue compact galaxies (Izotov+, 1999)
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/ApJ/765/140 : Stacked spectra of SDSS star forming galaxies (Andrews+, 2013)
J/ApJ/834/186 : Metallicity of MPA-JHU SDSS-DR7 dwarf gal. (Douglass+, 2017)
http://www.mpa-garching.mpg.de/SDSS/DR7/ : MPA-JHU DR7 release
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 [63713/2496108] KIAS-VAGC galaxy index number (1)
9 A1 --- f_Seq [e] e= extreme low-metallicity dwarf galaxy;
flag added by CDS (following table 3) (2)
11- 12 I2 h RAh Hour of Right Ascension (J2000)
14- 15 I2 min RAm Minute of Right Ascension (J2000)
17- 21 F5.2 s RAs Second of Right Ascension (J2000)
23- 23 A1 --- DE- Sign of the Declination (J2000)
24- 25 I2 deg DEd Degree of Declination (J2000)
27- 28 I2 arcmin DEm Arcminute of Declination (J2000)
30- 34 F5.2 arcsec DEs Arcsecond of Declination (J2000)
36- 41 F6.4 --- zsp [0.02/0.03] Spectroscopic redshift, SDSS DR7
43- 48 F6.2 mag rMag [-17/-16.3] Absolute r band magnitude (1)
50- 53 F4.2 [-] O/H [7/9] The 12+log(O/H) abundance (3)
55- 58 F4.2 [-] e_O/H [0.02/0.7] Uncertainty in O/H (3)
60- 63 F4.2 [-] N/H [6/7.5] The 12+log(N/H) abundance (3)
65- 68 F4.2 [-] e_N/H [0.02/0.4] Uncertainty in N/H (3)
70- 74 F5.2 [-] N/O [-2/-0.6] The log(N/O) abundance (3)
76- 79 F4.2 [-] e_N/O [0.03/0.8] Uncertainty in N/O (3)
81- 89 A9 --- Loc Location code ("Void" (42 occurrences);
"Wall" (89 occurrences) or "Uncertain") (4)
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Note (1): The Index and absolute R magnitudes are taken from the Korea Institute
for Advanced Study value-added galaxy catalog (KIAS VAGC;
Choi+ 2010JKAS...43..191C 2010JKAS...43..191C).
Note (2): This subset comprises the 21 extreme low gas-phase metallicity
(12+log(O/H)<7.6) galaxies identified in Paper I (Douglass & Vogeley
2017, J/ApJ/834/186).
While the N/H values for all these galaxies are also extremely low,
the N/O ratios span the range covered by the remainder of the dwarf
galaxy sample studied. Further study of these galaxies is recommended
to confirm the abundance values and identify any shared
characteristics.
Note (3): The flux values for all required emission lines can be found in the
MPA-JHU value-added catalog. Metallicity values are calculated using
the Direct Te method, with error estimates via a Monte Carlo method.
Note (4): 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
Reference:
Douglass & Vogeley Paper I 2017ApJ...834..186D 2017ApJ...834..186D Cat. J/ApJ/834/186
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Oct-2017