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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 (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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 89 135 Analyzed dwarf galaxies
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) : MPA-JHU DR7 release : SDSS home page Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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 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)
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). 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) 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.
History: From electronic version of the journal Reference: Douglass & Vogeley Paper I 2017ApJ...834..186D Cat. J/ApJ/834/186
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Oct-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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