J/ApJ/863/134 SDSS low-metallicity blue compact dwarf galaxies (Hsyu+, 2018)
Searching for the lowest-metallicity galaxies in the local universe.
Hsyu T., Cooke R.J., Prochaska J.X., Bolte M.
<Astrophys. J., 863, 134 (2018)>
=2018ApJ...863..134H 2018ApJ...863..134H
ADC_Keywords: Galaxies, spectra; Abundances; Redshifts; Photometry, SDSS
Keywords: galaxies: abundances ; galaxies: dwarf ; galaxies: evolution
Abstract:
We report a method of identifying candidate low-metallicity blue
compact dwarf galaxies (BCDs) from the Sloan Digital Sky Survey (SDSS)
imaging data, and present 3m Lick Observatory and 10m W.M. Keck
Observatory optical spectroscopic observations of 94 new systems that
have been discovered with this method. The candidate BCDs are selected
from Data Release 12 (DR12) of SDSS on the basis of their photometric
colors and morphologies. Using the Kast spectrometer on the 3m
telescope, we confirm that the candidate low-metallicity BCDs are
emission-line galaxies, and we make metallicity estimates using the
empirical R and S calibration methods. Follow-up observations on a
subset of the lowest-metallicity systems are made at Keck using the
Low Resolution Imaging Spectrometer, which allow for a direct
measurement of the oxygen abundance. We determine that 45 of the
reported BCDs are low-metallicity candidates with 12+log(O/H)≤7.65,
including six systems which are either confirmed or projected to be
among the lowest-metallicity galaxies known, at 1/30 of the solar
oxygen abundance, or 12+log(O/H)∼7.20.
Description:
Spectroscopic observations of 135 candidate compact dwarf galaxies
(BCDs) were made using the Kast spectrograph on the Shane 3m telescope
at Lick Observatory over 22 nights during semesters 2015B, 2016A, and
2016B. The instrument setup covers ∼3300-5500Å and ∼5800-7300Å,
with the instrument at FWHM resolutions of 6.4Å and 2.7Å, in the
blue and red, respectively.
Spectroscopic observations of 29 candidate BCDs were made using the
Low Resolution Imaging Spectrometer (LRIS) at the W.M. Keck Observatory
over a three-night program during semesters 2015B and 2016A.
The instrument setup covers ∼3200-8600Å, with the blue side
covering ∼3200-5600Å and the red side covering ∼5400-8600Å. The
blue and red channels have FWHM resolutions of 2.6Å and 3.1Å
respectively.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 86 95 Observational and measured properties of our
blue compact dwarf galaxy (BCD) sample, observed
at Lick and Keck Observatory
table2a.dat 77 2256 Measured emission line fluxes
table2b.dat 75 95 Hβ fluxes and equivalent widths
table5.dat 76 95 Derived properties of our 94 BCD sample
--------------------------------------------------------------------------------
See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/ApJS/147/29 : BRHalpha data of BCDs (Gil De Paz+, 2003)
J/ApJS/156/345 : Surface photometry of BCD galaxies (Gil de Paz+, 2005)
J/A+A/429/115 : JHK' photom. of Blue Compact Dwarf Galaxies (Noeske+, 2005)
J/A+A/434/887 : HI data of blue compact dwarf galaxies (Huchtmeier+, 2005)
J/ApJS/161/240 : High-ionization em. in metal-deficient BCDs (Thuan+, 2005)
J/AJ/142/170 : the α.40 HI source catalog (Haynes+, 2011)
J/ApJ/743/77 : Extremely metal-poor galaxies in SDSS (Morales-Luis+, 2011)
J/A+A/546/A122 : SDSS extremely metal-poor galaxies (Izotov+, 2012)
J/MNRAS/448/2687 : Blue diffuse dwarf galaxies spectrosc. data (James+, 2015)
J/ApJ/819/73 : Metallicity evolution of COSMOS BCD sample (Lian+, 2016)
J/ApJ/812/158 : Leo P RR Lyrae candidates & cumulative SFH (McQuinn+, 2015)
J/other/RAA/17.41 : LAMOST metal-poor galaxies sample (Gao+, 2017)
J/MNRAS/465/3977 : Blue diffuse dwarf galaxies (James+, 2017)
J/ApJ/847/38 : Extreme emission line galaxies at z≲0.05 (Yang+, 2017)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Target Name
11 A1 --- m_Name Multiple component ID on Name
13- 14 I2 h RAh Hour of Right Ascension (J2000)
16- 17 I2 min RAm Minute of Right Ascension (J2000)
19- 23 F5.2 s RAs Second of Right Ascension (J2000)
25 A1 --- DE- Sign of the Declination (J2000)
26- 27 I2 deg DEd Degree of Declination (J2000)
29- 30 I2 arcmin DEm Arcminute of Declination (J2000)
32- 36 F5.2 arcsec DEs Arcsecond of Declination (J2000)
38- 47 A10 --- Obs Observation description; Telescope+Inst (1)
49- 54 F6.4 --- z [0.001/0.06] Spectroscopic redshift
56- 60 F5.1 Mpc Dist [7.2/240] Luminosity distance assuming
a Planck cosmology
62- 66 F5.2 mag gmag [16.5/22.9] The SDSS-DR12 g band AB magnitude
68- 71 F4.2 mag e_gmag [0/0.2] Uncertainty in gmag
73- 76 F4.2 mag u-g [0.2/1.4] The (u-g) color index
78- 81 F4.2 [Sun] logO [6.4/8.7] Oxygen abundance; 12+log(O/H) (2)
83- 86 F4.2 [Sun] e_logO [0/0.4] Uncertainty in logO
--------------------------------------------------------------------------------
Note (1): The asterisk (*) in this column indicates that observations were made
first using Lick+Kast, with follow-up made using Keck+LRIS. For such
systems, the derived values reported here are measurements from the
Keck+LRIS observations.
Note (2): All metallicity estimates for systems observed on Shane+Kast are
determined using the R and S calibration methods, with the reported
metallicity being the average of the R and S methods. All BCDs
observed using Keck+LRIS have direct metallicity calculations,
except for J0743+4807, J0812+4836, J0834+5905. In these cases, we
do not significantly detect the [OIII]4363Å line and adopt an
upper limit to the [OIII]4363Å emission line flux equivalent to
3 times the error in the measured line flux at that wavelength. This
results in a lower limit on their metallicities.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2a.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Target name
11 A1 --- m_Name Multiple component ID on Name
24- 42 A19 --- Line Line identifier
44- 52 A9 0.1nm lambda Wavelength(s) for Line
57- 64 F8.6 --- FLine [0/2510]? Emission line flux; corrected for the
underlying stellar absorption and internal
reddening, relative to Hβ
71- 77 F7.5 --- e_FLine [0.0001/355]? Uncertainty in Value
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Target name
11 A1 --- m_Name Multiple component ID on Name
14- 20 F7.2 10+17mW/m2 FHb ? Hβ flux, F(Hβ);
in 10e-17erg/s/cm2 units
26- 30 F5.2 10+17mW/m2 e_FHb ? FHb uncertainty
35- 47 F13.9 0.1nm EWHb ? Hβ equivalent width in Angstoms
50- 58 F9.5 0.1nm e_EWHb ? EWHb uncertainty
62- 66 F5.3 --- cHb ? Hβ reddening corrections, c(Hβ)
72- 75 F4.2 0.1nm EWHa ? Hα equivalent width in Angstroms
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Target name
11 A1 --- m_Name Multiple component ID on Name
13- 17 F5.1 Mpc Dist [7.2/240]? Luminosity distance
19- 23 F5.1 Mpc DM00 [8.6/236.6]? Distance corrected for the
local velocity field using
Mould+ (2000ApJ...529..786M 2000ApJ...529..786M)
25- 30 F6.2 mag BMag [-17.5/-10]? Absolute B band magnitude (1)
32- 38 F7.4 [10+32W] LHa [0.04/57.4]? Hα luminosity;
in 1e+39erg/s units (2)
40- 45 F6.4 [10+32W] e_LHa [0.001/2]? Uncertainty in LHa
47- 54 F8.4 Msun/yr SFR [0.19/252]? Star Formation Rate (2)
56- 61 F6.4 Msun/yr e_SFR [0.007/8.3]? Uncertainty in SFR
63- 69 F7.3 Msun M* [0.02/213.5]? Stellar mass (2)
71- 76 F6.3 Msun e_M* [0.01/28]? Uncertainty in M*
--------------------------------------------------------------------------------
Note (1): Calculated from the empirical ugri-UBVRc transformations presented
in Cook+ (2014MNRAS.445..890C 2014MNRAS.445..890C).
Note (2): Calculations discussed in Section 4.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Aug-2019