J/ApJ/743/77 Extremely metal-poor (XMP) galaxies in SDSS (Morales-Luis+, 2011)
Systematic search for extremely metal-poor galaxies in the Sloan Digital Sky
Survey.
Morales-Luis A.B., Sanchez Almeida J., Aguerri J.A.L., Munoz-Tunon C.
<Astrophys. J., 743, 77 (2011)>
=2011ApJ...743...77M 2011ApJ...743...77M
ADC_Keywords: Abundances ; Galaxies, spectra ; Photometry, SDSS ; Redshifts
Keywords: galaxies: abundances - galaxies: formation - galaxies: starburst -
galaxies: statistics - methods: data analysis
Abstract:
We carry out a systematic search for extremely metal-poor (XMP)
galaxies in the spectroscopic sample of Sloan Digital Sky Survey
(SDSS) data release 7 (DR7). The XMP candidates are found by
classifying all the galaxies according to the form of their spectra in
a region 80Å wide around Hα. Due to the data size, the method
requires an automatic classification algorithm. We use k-means. Our
systematic search renders 32 galaxies having negligible [NII] lines,
as expected in XMP galaxy spectra. Twenty-one of them have been
previously identified as XMP galaxies in the literature - the
remaining 11 are new. This was established after a thorough
bibliographic search that yielded only some 130 galaxies known to have
an oxygen metallicity 10 times smaller than the Sun (explicitly, with
12+log(O/H)≤7.65). XMP galaxies are rare; they represent 0.01% of the
galaxies with emission lines in SDSS/DR7. Although the final
metallicity estimate of all candidates remains pending, strong-line
empirical calibrations indicate a metallicity about one-tenth solar,
with the oxygen metallicity of the 21 known targets being
12+log(O/H)∼7.61±0.19. Since the SDSS catalog is limited in apparent
magnitude, we have been able to estimate the volume number density of
XMP galaxies in the local universe, which turns out to be
(1.32±0.23)x10-4Mpc-3. The XMP galaxies constitute 0.1% of the
galaxies in the local volume, or ∼0.2% considering only emission-line
galaxies. All but four of our candidates are blue compact dwarf
galaxies, and 24 of them have either cometary shape or are formed by
chained knots.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 32 XMP candidates found by classifying all SDSS/DR7
galaxies according to their spectra around Hα
table2.dat 111 129 XMP targets found in the literature
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/A+A/546/A122 : SDSS XMP emission-line galaxies (Izotov+, 2012)
J/ApJ/695/259 : Massive metal-poor galaxies from SDSS (Peeples+, 2009)
J/ApJ/662/15 : Abundances in extragalactic HII regions (Izotov+, 2007)
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/ApJS/161/240 : High-ionization emission in metal-deficient BCD (Thuan+, 2005)
J/ApJ/602/200 : HII regions abundances in BCD galaxies (Izotov+, 2004)
J/A+A/421/539 : VLT spectroscopy of Tol 1214-277 + Tol 65 (Izotov+, 2004)
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- 2 I2 --- Seq Running sequence number
4 A1 --- f_Seq [k] k: known XMP galaxies (the rest are new)
6- 9 A4 --- --- [SDSS]
11- 29 A19 --- SDSS SDSS-DR7 name (JHHMMSS.ss+DDMMSS.s) (1)
31- 34 F4.1 mag gmag SDSS-DR7 g-band magnitude
36- 40 F5.3 --- z SDSS-DR7 redshift
42- 45 F4.2 --- (O/H) Oxygen abundance from SDSS: 12+log(O/H) (2)
47- 50 F4.2 --- (O/H)l ? Oxygen abundance: 12+log(O/H) (3)
52- 69 I18 --- SpObjID SDSS-DR7 unique spectrum identification
71- 87 A17 --- Comm Comment (sketch of galaxy shape)
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Note (1): SDSS J015809.39+000637.2 is a misprint for SDSS J015809.39-000637.2;
corrected at CDS.
Note (2): Using the calibration by Pettini & Pagel (2004MNRAS.348L..59P 2004MNRAS.348L..59P),
given in our Equation (4).
Note (3): From the literature as listed in Table 2.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Galaxy name
16 A1 --- f_Name [k] k: galaxies also identified in this
work (Table 1)
18- 19 I2 h RAh Hour of right ascension (J2000)
21- 22 I2 min RAm Minute of right ascension (J2000)
24- 25 I2 s RAs Second of right ascension (J2000)
27 A1 --- DE- Sign of declination (J2000)
28- 29 I2 deg DEd Degree of declination (J2000)
31- 32 I2 arcmin DEm Arcminute of declination (J2000)
34- 35 I2 arcsec DEs Arcsecond of declination (J2000)
37- 40 F4.1 mag gmag ? SDSS-DR7 g-band magnitude
42- 59 I18 --- SpObjID ? SDSS-DR7 unique spectrum identification
61- 64 F4.2 --- (O/H) Oxygen abundance: 12+log(O/H)
66- 90 A25 --- Auth Author's name reference for the oxygen
abundance (1)
92-110 A19 --- BibCode Bibcode for the oxygen abundance
111 A1 --- f_BibCode [*] *: not explained in the paper
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Note (1): KO = the galaxy belongs to the compilation by Kunth & Ostlin
2000A&ARv..10....1K 2000A&ARv..10....1K
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 03-May-2013