J/ApJ/819/110 Extremely metal-poor galaxies in SDSS. II. (Sanchez Almeida+ 2016)
Search for extremely metal-poor galaxies in the Sloan Digital Sky Survey.
II. High electron temperature objects.
Sanchez Almeida J., Perez-Montero E., Morales-Luis A.B., Munoz-Tunon C.,
Garcia-Benito R., Nuza S.E., Kitaura F.S.
<Astrophys. J., 819, 110 (2016)>
=2016ApJ...819..110S 2016ApJ...819..110S (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Galaxies, spectra
Keywords: galaxies: abundances; galaxies: dwarf; galaxies: evolution;
galaxies: formation; galaxies: peculiar
Abstract:
Extremely metal-poor (XMP) galaxies are defined to have a gas-phase
metallicity smaller than a tenth of the solar value
(12+log[O/H]<7.69). They are uncommon, chemically and possibly
dynamically primitive, with physical conditions characteristic of
earlier phases of the universe. We search for new XMPs in the Sloan
Digital Sky Survey (SDSS) in a work that complements Paper I
(Morales-Luis+, 2011, J/ApJ/743/77). This time, high electron
temperature objects are selected; metals are a main coolant of the
gas, so metal-poor objects contain high-temperature gas. Using the
algorithm k-means, we classify 788677 spectra to select 1281 galaxies
that have particularly intense [OIII]λ4363 with respect to
[OIII]λ5007, which is a proxy for high electron temperature.
The metallicity of these candidates was computed using a hybrid
technique consistent with the direct method, rendering 196 XMPs. A
less restrictive noise constraint provides a larger set with 332
candidates. Both lists are provided in electronic format. The selected
XMP sample has a mean stellar mass around 108M☉, with the dust
mass ∼103M☉ for typical star-forming regions. In agreement
with previous findings, XMPs show a tendency to be tadpole-like or
cometary. Their underlying stellar continuum corresponds to a fairly
young stellar population (<1Gyr), although young and aged stellar
populations coexist at the low-metallicity starbursts. About 10% of
the XMPs show large N/O. Based on their location in constrained
cosmological numerical simulations, XMPs have a strong tendency to
appear in voids and to avoid galaxy clusters. The puzzling 2%-solar
low-metallicity threshold exhibited by XMPs remains.
Description:
First, we search for XMP candidates using the algorithm k-means
(Sanchez Almeida et al. 2010ApJ...714..487S 2010ApJ...714..487S; Ordovas-Pascual & Sanchez
Almeida 2014A&A...565A..53O 2014A&A...565A..53O). It leads to 1281 candidates. Then, we
use the SDSS-DR7 spectra of the candidates to measure their integrated
metallicity, which narrows down the list to 196 XMPs. We also include
a second list (Table 2) with 332 potential XMPs that are selected
under less restrictive noise constraints.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 196 Extremely metal poor galaxies selected in this study
table2.dat 64 332 Candidate extremely metal-poor galaxies
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/A+A/568/L8 : VUDS extreme emission line 0.2≲z≲0.9 gal. (Amorin+, 2014)
J/A+A/558/A18 : Extremely metal-poor (XMP) galaxies HI spectra (Filho+, 2013)
J/ApJ/765/140 : SDSS star forming galaxies stacked spectra (Andrews+, 2013)
J/A+A/546/A122 : SDSS XMP emission-line galaxies (Izotov+, 2012)
J/ApJS/199/26 : The 2MASS Redshift Survey (2MRS) (Huchra+, 2012)
J/ApJ/743/77 : Paper I. XMP galaxies in SDSS (Morales-Luis+, 2011)
J/AJ/142/170 : ALFALFA survey: the α.40 HI sources (Haynes+, 2011
J/MNRAS/398/451 : PopStar I: Evolutionary synthesis models (Molla+, 2009)
J/A+A/448/955 : Abundances of emission galaxies in SDSS-DR3 (Izotov+, 2006)
J/ApJS/161/240 : High-ionization emission in metal-poor BCDs (Thuan+, 2005)
J/ApJS/153/429 : SDSS strong emission line HII galaxies (Kniazev+, 2004)
J/ApJS/147/29 : BRHalpha data of blue compact dwarf gal. (Gil De Paz+, 2003)
J/A+AS/91/285 : HII galaxies spectrophotometric catalogue (Terlevich+, 1991)
http://wwwmpa.mpa-garching.mpg.de/SDSS/DR7/ : MPA-JHU DR7 release
http://www.sdss.org/surveys/eboss/ : eBOSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Running index number; sorted according to
growing RA
5- 22 A18 --- ID Source identifier (JHHMMSS.s+DDMMSS.s)
24- 27 F4.2 [-] logO/H [7/7.7] Log Oxygen abundance; 12+log(O/H) (G1)
29- 32 F4.2 [-] e_logO/H [0.07/0.5] Uncertainty in logO/H
34- 38 F5.2 [-] logN/O [-1.7/-0.8]?=-9.99 Log Nitrogen to Oxygen
abundance ratio (G1)
40- 43 F4.2 [-] e_logN/O [0.1/0.4]?=0 Uncertainty in logN/O
45- 49 F5.2 [-] logU [-2.9/-1.5] Log ionization parameter (G2)
51- 54 F4.2 [-] e_logU [0/0.5] Uncertainty in logU
56- 59 F4.2 --- CHb [0/0.8] Extinction coefficient in H beta
61- 64 F4.2 --- e_CHb [0.01/1.3] Uncertainty in CHb
66- 66 I1 --- Match [0/7]? Galaxy match code (1)
68- 71 F4.2 [-] logO/H-DM [7.3/7.7]?=9.99 Direct method log Oxygen
abundance; 12+log(O/H) (2)
73- 76 F4.2 [-] e_logO/H-DM [0.02/0.2]?=0 Uncertainty in logO/H-DM
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Note (1): Match code as follows:
1 = Table 1 in Paper I (Morales-Luis+, 2011, J/ApJ/743/77);
2 = Table 2 in Paper I (Morales-Luis+, 2011, J/ApJ/743/77);
3 = Tables 1 & 2 in Paper I (Morales-Luis+, 2011, J/ApJ/743/77);
4 = Izotov et al. (2012, J/A+A/546/A122);
5 = Table 1 in Paper I & Izotov et al. (2012, J/A+A/546/A122);
6 = Table 2 in Paper I & Izotov et al. (2012, J/A+A/546/A122);
7 = Table 1 & 2 in Paper I, & Izotov et al. (2012, J/A+A/546/A122);
0 = no match.
Note (2): Using the direct method (Section 3.3).
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Running index number; sorted according to
growing RA
5- 22 A18 --- ID Source identifier (JHHMMSS.s+DDMMSS.s)
24- 27 F4.2 [-] logO/H [6.9/7.7] Log Oxygen abundance; 12+log(O/H) (G1)
29- 32 F4.2 [-] e_logO/H [0.07/0.6] Uncertainty in logO/H
34- 38 F5.2 [-] logN/O [-1.8/-0.8]?=-9.99 Log Nitrogen to Oxygen
abundance ratio (G1)
40- 43 F4.2 [-] e_logN/O [0.1/0.5]?=0 Uncertainty in logN/O
45- 49 F5.2 [-] logU [-3.1/-1.5] Log ionization parameter (G2)
51- 54 F4.2 [-] e_logU [0/0.6] Uncertainty in logU
56- 59 F4.2 --- CHb [0/0.8] Extinction coefficient in H beta
61- 64 F4.2 --- e_CHb [0.01/1.3] Uncertainty in CHb
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Global notes:
Note (G1): Using HCM (code HII-CHI-mistry; Perez-Montero 2014MNRAS.441.2663P 2014MNRAS.441.2663P);
see Section 3.2.
Note (G2): e.g., Stasinska et al. (2012EAS....54....3S 2012EAS....54....3S).
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History:
From electronic version of the journal
References:
Morales-Luis et al. Paper I. 2011ApJ...743...77M 2011ApJ...743...77M Cat. J/ApJ/743/77
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-May-2016