J/ApJS/208/7 Sodium excess objects. I. SDSS-DR7 (Jeong+, 2013)
On the nature of sodium excess objects.
I. Data and observed trends.
Jeong H., Yi S.K., Kyeong J., Sarzi M., Sung E.-C., Oh K.
<Astrophys. J. Suppl. Ser., 208, 7 (2013)>
=2013ApJS..208....7J 2013ApJS..208....7J
ADC_Keywords: Abundances ; Galaxies, spectra ; Photometry, SDSS ; Morphology ;
Redshifts
Keywords: catalogs - galaxies: abundances -
galaxies: elliptical and lenticular, cD - galaxies: evolution -
galaxies: spiral - galaxies: stellar content
Abstract:
Several studies have reported the presence of sodium excess objects
having neutral atomic absorption lines at 5895Å (Na.D) and 8190Å
that are deeper than expected based on stellar population models that
match the stellar continuum. The origin of these lines is therefore
hotly debated. van Dokkum & Conroy (2010Natur.468..940V 2010Natur.468..940V) proposed that
low-mass stars (≲0.3M☉) are more prevalent in massive
early-type galaxies, which may lead to a strong Na I 8190 line
strength. It is necessary to test this prediction, however, against
other prominent optical line indices such as Na.D, Mg b, and Fe 5270,
which can be measured with a significantly higher signal-to-noise
ratio than Na I 8190. We identified a new sample of roughly 1000 Na.D
excess objects (NEOs; ∼8% of galaxies in the sample) based on Na.D
line strength in the redshift range 0.00≤z≤0.08 from the Sloan
Digital Sky Survey (SDSS) DR7 through detailed analysis of galaxy
spectra. We explore the properties of these new objects here. The
novelty of this work is that the galaxies were carefully identified
through direct visual inspection of SDSS images, and we systematically
compared the properties of NEOs and those of a control sample of
galaxies with normal Na.D line strengths. We note that the majority of
galaxies with high velocity dispersions (σe>250km/s) show Na.D
excesses.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 114 963 A sample of the catalog of Na.D excess objects
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/A+A/445/79 : Nearby early-type gal. with ionized gas. II. (Annibali+, 2006)
J/A+A/433/497 : Nearby early-type gal. with ionized gas. I. (Rampazzo+, 2005)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 18 I18 --- ObjID SDSS-DR7 object identifier (58NNNNNNNNNNNNNNNN)
20- 21 I2 h RAh Hour of Right Ascension (J2000)
23- 24 I2 min RAm Minute of Right Ascension (J2000)
26- 30 F5.2 s RAs Second of Right Ascension (J2000)
32 A1 --- DE- Sign of the Declination (J2000)
33- 34 I2 deg DEd Degree of Declination (J2000)
36- 37 I2 arcmin DEm Arcminute of Declination (J2000)
39- 42 F4.1 arcsec DEs Arcsecond of Declination (J2000)
44- 49 F6.4 --- z [0.007/0.0721] SDSS-DR7 spectroscopic redshift
51- 56 F6.2 mag rMag [-23.7/-20.7] SDSS absolute r band magnitude
58- 61 F4.2 mag u-r [1.27/6.89] SDSS (u-r) color index
63- 66 F4.2 --- fNaD [0.5/4.22] NaD excess index (1)
68- 72 F5.2 0.1nm NaD [2.9/10.8] Observed NaD line strength; in Å (2)
74- 78 F5.2 --- fMgb [-0.57/1.26] Mgb excess index
80- 83 F4.2 0.1nm Mgb [0.6/5.6] Observed Mgb line strength; in Å (2)
85- 89 F5.2 --- fFe [-0.75/1.75] Fe5270 excess index
91- 94 F4.2 0.1nm Fe [0.4/5.5] Obs. Fe5270 line strength; in Å (2)
96-100 F5.2 --- fHb [-1.72/0.23] Hβ excess index
102-106 F5.2 0.1nm Hb [-2.4/5] Obs. Hβ line strength; in Å (2)
108-111 A4 --- Morph Morphology (3)
113-114 A2 --- Class BPT class; emission line classification (4)
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Note (1): To investigate the nature of NEOs (Na excess objects), we
selected Na.D excess candidates in the redshift range 0.00≤z≤0.08
from SDSS DR7 by adopting a new index, fNaD. This index quantifies the
Na.D excess by comparing the observed spectrum with the best-fit model
spectrum. Roughly 8% (1603/20571, fNaD≥0.5) of galaxies in the sample
were classified as NEOs.
Note (2): Observed line strength from OSSY (Oh et al. 2011ApJS..195...13O 2011ApJS..195...13O)
catalog.
Note (3): Morphology code as:
oETG = ordinary early-type NEO (Na-Excess Object);
pETG = peculiar early-type NEO;
oLTG = ordinary late-type NEO;
pLTG = peculiar late-type NEO.
Note (4): BPT class is determined on the basis of the Baldwin, Phillips
and Terlevich (1981PASP...93....5B 1981PASP...93....5B) excitation diagram (see Fig.9):
SF = Star-forming;
Co = Composite;
Se = Seyfert;
LI = Liner;
NE = object that do not have A/N>3 in the four main lines.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 30-Sep-2013