J/MNRAS/448/2687 Blue diffuse dwarf galaxies spectroscopic data (James+, 2015)
Uncovering blue diffuse dwarf galaxies.
James B.L., Koposov S., Stark D.P., Belokurov V., Pettini M.,
Olszewski E.W.
<Mon. Not. R. Astron. Soc., 448, 2687-2703 (2015)>
=2015MNRAS.448.2687J 2015MNRAS.448.2687J (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, spectra ; Spectroscopy
Keywords: galaxies: abundances - galaxies: dwarf - galaxies: evolution -
galaxies: irregular - galaxies: star formation
Abstract:
Extremely metal poor (XMP) galaxies are known to be very rare, despite
the large numbers of low-mass galaxies predicted by the local galaxy
luminosity function. This paper presents a subsample of galaxies that
were selected via a morphology-based search on Sloan Digital Sky
Survey images with the aim of finding these elusive XMP galaxies. By
using the recently discovered XMP galaxy, Leo P, as a guide, we
obtained a collection of faint, blue systems, each with isolated H II
regions embedded in a diffuse continuum, that have remained optically
undetected until now. Here we show the first results from optical
spectroscopic follow-up observations of 12 of ∼100 of these blue
diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen
abundances were obtained via the direct method for eight galaxies, and
found to be in the range 7.45<12+log(O/H)<8.0, with two galaxies being
classified as XMPs. All BDDs were found to currently have a young
star-forming population (<10 Myr) and relatively high ionization
parameters of their H II regions. Despite their low luminosities
(-11≲MB≲-18) and low surface brightnesses (∼23-25 mag/arcsec2),
the galaxies were found to be actively star forming, with current star
formation rates between 0.0003 and 0.078 M☉/yr. From our current
subsample, BDD galaxies appear to be a population of non-quiescent
dwarf irregular galaxies, or the diffuse counterparts to blue compact
galaxies and as such may bridge the gap between these two populations.
Our search algorithm demonstrates that morphology-based searches are
successful in uncovering more diffuse metal-poor star-forming galaxies,
which traditional emission-line-based searches overlook.
Description:
For this paper we used the data from SDSS Data Release 9 (DR9; Ahn et al.
2012, Cat. V/139). The SDSS catalogues were queried from local SQL data
base. The spatial queries to the data base were handled using Q3C
(Koposov & Bartunov 2006ASPC..351..735K 2006ASPC..351..735K). Spectroscopic observations were
obtained for each galaxy with the MMT Blue-Channel Spectrograph on the
nights of 2014 January 27-28, and objects were chosen on account of
their visibility during these nights. Observations were made using the
medium-resolution grating (300 grooves/mm), giving a spatial scale along
the slit of 0.6 arcsec/pixel, a spectral range of 3500-8000 Å, and
a spectral resolution of ∼7 Å [full width at half-maximum (FWHM)].
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
galaxy.dat 60 2 BDDs galaxies sample
tablea1.dat 141 128 Spectroscopic line fluxes and dereddened line
intensities as measured from the spectra shown
in Fig. 2.
--------------------------------------------------------------------------------
See also:
V/139 : The SDSS Photometric Catalog, Release 9
(Adelman-McCarthy+, 2012)
J/A+A/546/A122 : SDSS extremely metal-poor emission-line galaxies
(Izotov+, 2012)
J/A+A/558/A18 : HI spectra of extremely metal-poor (XMP) galaxies
(Filho+, 2013)
J/ApJ/819/110 : Extremely metal-poor (XMP) galaxies in SDSS. II.
(Almeida+, 2016)
Byte-by-byte Description of file: galaxy.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Name Object identifier (KJN) (1)
5- 23 A19 --- SDSS SDSS identifier (JHHMMSS.ss+DDMMSS.s)
25- 26 I2 h RAh Hour of Right Ascension (J2000)
28- 29 I2 min RAm Minute of Right Ascension (J2000)
31- 36 F6.3 s RAs Second of Right Ascension (J2000)
37 A1 --- DE- Sign of the Declination (J2000)
38- 39 I2 deg DEd Degree of Declination (J2000)
41- 42 I2 arcmin DEm Arcminute of Declination (J2000)
44- 48 F5.2 arcsec DEs Arcsecond of Declination (J2000)
50- 54 A5 --- Target1 Target region name in tablea1.dat (KJN.N) (2)
56- 60 A5 --- Target2 Target region name in tablea1.dat (KJN.N) (2)
--------------------------------------------------------------------------------
Note (1): For simplicity, in this paper we refer to the individual objects as
"KJX", where X is the identification number and KJ corresponds
to "Koposov-James".
Note (2): Each target was observed at its parallactic angle if it fell below an
airmass of ∼1.1 during the observation. In the cases where multiple
H II regions were clearly evident in the two-dimensional spectra,
extraction profiles were adjusted to obtain separate spectra of each
region. Such cases are denoted as "KJ X.1", "KJ X.2" etc.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Line Detected emission line
10 A1 --- n_Line [abcd] Note on line (1)
12- 18 F7.2 0.1nm lambda ? Wavelength (Å)
20 A1 --- l_SKJ1.0 [<] Limit flag on SKJ1.0
21- 26 F6.2 --- SKJ1.0 ? KJ1.0 integrated line flux (2)
28- 32 F5.2 --- e_SKJ1.0 ? Uncertainty in SKJ1.0 (2)
33 A1 --- n_SKJ1.0 [efgh] Note on SKJ1.0 (3)
35 A1 --- l_IKJ1.0 [<] Limit flag on IKJ1.0
36- 41 F6.2 --- IKJ1.0 ? IKJ1.0 dereddened line intensity (2)
43- 47 F5.2 --- e_IKJ1.0 ? Uncertainty in IKJ1.0 (2)
48 A1 --- n_IKJ1.0 [ijkl] Note on IKJ1.0 (4)
50- 55 F6.2 --- SKJ1.1 ? SKJ1.1 integrated line flux (2)
57- 61 F5.2 --- e_SKJ1.1 ? Uncertainty in SKJ1.1 (2)
62 A1 --- n_SKJ1.1 [mnop] Note on SKJ1.1 (5)
64- 69 F6.2 --- IKJ1.1 ? IKJ1.1 dereddened line intensity (2)
71- 75 F5.2 --- e_IKJ1.1 ? Uncertainty in IKJ1.1 (2)
76 A1 --- n_IKJ1.1 [qrst] Note on IKJ1.1 (6)
78 A1 --- l_SKJ3.0 [<] Limit flag on SKJ3.0
79- 84 F6.2 --- SKJ3.0 ? SKJ3.0 integrated line flux (2)
86- 91 F6.2 --- e_SKJ3.0 ? Uncertainty in SKJ3.0 (2)
92 A1 --- n_SKJ3.0 [uvwx] Note on SKJ3.0 (7)
94 A1 --- l_IKJ3.0 [<] Limit flag on IKJ3.0
95-100 F6.2 --- IKJ3.0 ? IKJ3.0 dereddened line intensity (2)
102-107 F6.2 --- e_IKJ3.0 ? Uncertainty in IKJ3.0 (2)
108-109 A2 --- n_IKJ3.0 [y z a'b'] Note on IKJ3.0 (8)
111 A1 --- l_SKJ3.1 [<] Limit flag on SKJ3.1
112-117 F6.2 --- SKJ3.1 ? SKJ3.1 integrated line flux (2)
119-123 F5.2 --- e_SKJ3.1 ? Uncertainty in SKJ3.1 (2)
124-125 A2 --- n_SKJ3.1 [c'd'e'] Note on SKJ3.1 (9)
127 A1 --- l_IKJ3.1 [<] Limit flag on IKJ3.1
128-133 F6.2 --- IKJ3.1 ? IKJ3.1 dereddened line intensity (2)
135-139 F5.2 --- e_IKJ3.1 ? Uncertainty in IKJ3.1 (2)
140-141 A2 --- n_IKJ3.1 [f'g'h'] Note on IKJ3.1 (10)
--------------------------------------------------------------------------------
Note (1): E(B-V) value for each object as follows:
-----|-------------|-------------|-------------|------------
Note | KJ1.0 | KJ1.1 | KJ3.0 | KJ3.1
-----|-------------|-------------|-------------|------------
a | 0.15±0.02 | 0.00±0.00 | 0.00±0.01 | 0.05±0.01
b | 0.18±0.02 | 0.09±0.01 | 0.15±0.02 | 0.25±0.04
c | 0.13±0.01 | 0.13±0.02 | 0.09±0.01 | 0.16±0.02
d | 0.29±0.03 | 0.00±0.00 | 0.01±0.00 | ---
Note (2): Relative to Hβ=100.
Note (3): Note as follows:
e = Where F(Hβ)=3.63±0.41x10-16 erg/s/cm2;
f = Where F(Hβ)=7.06±0.72x10-16 erg/s/cm2;
g = Where F(Hβ)=24.0±2.4x10-16 erg/s/cm2;
h = Where F(Hβ)=9.11±0.92x10-16 erg/s/cm2.
Note (4): Note as follows:
i = Where I(Hβ)=6.02±0.81x10-16 erg/s/cm2;
j = Where I(Hβ)=13.0±1.7x10-16 erg/s/cm2;
k = Where I(Hβ)=37.2±4.2x10-16 erg/s/cm2;
l = Where I(Hβ)=23.4±3.5x10-16 erg/s/cm2.
Note (5): Note as follows:
m = Where F(Hβ)=20.5±2.1x10-16 erg/s/cm2;
n = Where F(Hβ)=19.2±1.9x10-16 erg/s/cm2;
o = Where F(Hβ)=15.4±1.5x10-16 erg/s/cm2;
p = Where F(Hβ)=62.3±6.2x10-16 erg/s/cm2.
Note (6): Note as follows:
q = Where I(Hβ)=20.5±2.1x10-16 erg/s/cm2;
r = Where I(Hβ)=25.5±2.7x10-16 erg/s/cm2;
s = Where I(Hβ)=24.0±2.7x10-16 erg/s/cm2;
t = Where I(Hβ)=63.1±6.3x10-16 erg/s/cm2.
Note (7): Note as follows:
u = Where F(Hβ)=36.1±5.6x10-16 erg/s/cm2;
v = Where F(Hβ)=6.74±0.68x10-16 erg/s/cm2;
w = Where F(Hβ)=4.44±0.46x10-16 erg/s/cm2;
x = Where F(Hβ)=26.7±2.7x10-16 erg/s/cm2.
Note (8): Note as follows:
y = Where I(Hβ)=36.1±5.9x10-16 erg/s/cm2;
z = Where I(Hβ)=11.1±1.3x10-16 erg/s/cm2;
aa = Where I(Hβ)=5.94±0.65x10-16 erg/s/cm2;
bb = Where I(Hβ)=27.4±2.8x10-16 erg/s/cm2.
Note (9): Note as follows:
cc = Where F(Hβ)=2.81±0.30x10-16 erg/s/cm2;
dd = Where F(Hβ)=1.43±0.19x10-16 erg/s/cm2;
ee = Where F(Hβ)=5.68±0.59x10-16 erg/s/cm2.
Note (10): Note as follows:
ff = Where I(Hβ)=3.27±0.36x10-16 erg/s/cm2;
gg = Where I(Hβ)=3.27±0.61x10-16 erg/s/cm2;
hh = Where I(Hβ)=9.51±1.15x10-16 erg/s/cm2.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 23-Nov-2017