J/MNRAS/465/3977 Blue diffuse dwarf galaxies (James+, 2017)
Blue diffuse dwarf galaxies: a clearer picture.
James B.L., Koposov S.E., Stark D.P., Belokurov V., Pettini M.,
Olszewski E.W., Mcquinn K.B.W.
<Mon. Not. R. Astron. Soc., 465, 3977-4015 (2017)>
=2017MNRAS.465.3977J 2017MNRAS.465.3977J (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, spectra ; Spectroscopy
Keywords: galaxies: abundances - galaxies: dwarf - galaxies: evolution -
galaxies: irregular - galaxies: star formation
Abstract:
The search for chemically unevolved galaxies remains prevalent in the
nearby Universe, mostly because these systems provide excellent
proxies for exploring in detail the physics of high-z systems. The
most promising candidates are extremely metal-poor galaxies (XMPs),
i.e. galaxies with <1/10 solar metallicity. However, due to the bright
emission-line-based search criteria traditionally used to find XMPs,
we may not be sampling the full XMP population. In 2014, we reoriented
this search using only morphological properties and uncovered a
population of ∼150 'blue diffuse dwarf (BDD) galaxies', and published
a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic
observations of a larger sample of 51 BDDs, along with their Sloan
Digital Sky Survey (SDSS) photometric properties. With our improved
statistics, we use direct-method abundances to confirm that BDDs are
chemically unevolved (7.43<12+log(O/H)<8.01), with ∼20 per cent of our
sample classified as being XMP galaxies, and find that they are
actively forming stars at rates of ∼1-33x10-2M☉/yr in HII
regions randomly embedded in a blue, low-surface-brightness continuum.
Stellar masses are calculated from population synthesis models and
estimated to be in the range log (M*/M☉)~=5-9. Unlike other
low-metallicity star-forming galaxies, BDDs are in agreement with the
mass-metallicity relation at low masses, suggesting that they are not
accreting large amounts of pristine gas relative to their stellar
mass. BDD galaxies appear to be a population of actively star-forming
dwarf irregular (dIrr) galaxies which fall within the class of
low-surface-brightness dIrr galaxies. Their ongoing star formation and
irregular morphology make them excellent analogues for galaxies in the
early Universe.
Description:
At present, our full sample consists of ∼150 BDD galaxies, of which we
have obtained optical spectroscopy for 51 galaxies, as listed in Table
1. The sample considered here includes both the 12 galaxies originally
presented in James et al.(2015, Cat. J/MNRAS/448/2687, here after J15)
and 39 new BDD candidates.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 106 51 Blue diffuse dwarfs galaxies in the current
observed sample
table2.dat 113 57 Ionic and elemental abundances for the BDD
galaxies presented in this paper, derived from
the emission-line measurements given in Table A1
table3.dat 70 57 Physical properties of the new, extended sample
of BDD galaxies
table4.dat 53 51 Photometric properties of the BDD sample
calculated from SDSS images
table5.dat 32 39 Stellar masses derived from stellar population
synthesis and SDSS colours listed in Table 4
tablea1b.dat 46 57 Hβ parameters for sources of table A1
tablea1.dat 64 1824 Spectroscopic line fluxes and de-reddened line
intensities as measured from the spectra shown
in Fig. B1
--------------------------------------------------------------------------------
See also:
J/MNRAS/448/2687 : Blue diffuse dwarf galaxies spectroscopic data (James+ 2015)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [JKB]
5- 7 I3 --- JKB [1/144] JKB identification number
9- 27 A19 --- SDSS SDSS name, JHHMMSS.ss+DDMMSS.s
29- 34 I6 --- AGC ?=- AGC identification number
37- 38 I2 h RAh Right ascension (J2000)
40- 41 I2 min RAm Right ascension (J2000)
43- 44 I2 s RAs Right ascension (J2000)
46 A1 --- DE- Declination sign (J2000)
47- 48 I2 deg DEd Declination (J2000)
50- 51 I2 arcmin DEm Declination (J2000)
53- 54 I2 arcsec DEs Declination (J2000)
56- 63 F8.6 --- z ?=- Redshift (1)
65- 67 I3 Mpc Dist ?=- Distance
68 A1 --- n_Dist [*)] Note on Dist (2)
70- 72 I3 deg PA Slit position angle of first exposure of the
MMT observations
73 A1 --- --- [,]
74- 75 I2 deg PA2 ? Slit position angle value of second exposure
of the MMT observations
78- 83 A6 s Texp Exposure time of first exposure of the
MMT observations
84 A1 --- --- [,]
85- 90 A6 s Texp2 ? Exposure time of second exposure of the
MMT observations
92-106 A15 --- Obs.Date UT date of the MMT observations
--------------------------------------------------------------------------------
Note (1): Redshifts were derived from fitting all the emission lines seen
within the spectrum and converted into distances using the Hubble flow with
respect to the CMB.
Note (2): Note on Distance as follows:
) = denote those which are uncertain due to peculiar velocities
(see the text for details)
* = for objects that are within 20° of the Virgo cluster and will
therefore have an additional uncertainty due to the Virgo flow.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- JKB JKB identification number
7- 12 F6.1 cm-3 Ne Electron density, Ne([OII],[SII])
14- 19 F6.1 cm-3 E_Ne Error on Ne (upper value)
22- 27 F6.1 cm-3 e_Ne Error on Ne (lower value)
30 A1 --- l_Te[OIII] Limit flag on Te[OIII]
31- 35 I5 K Te[OIII] Electron temperature from [OIII]
37- 40 I4 K e_Te[OIII] ? rms uncertainty on Te[OIII]
42 A1 --- l_Te[OII] Limit flag on Te[OII]
43- 47 I5 K Te[OII] Electron temperature from [OII]
49- 54 F6.1 K e_Te[OII] ? rms uncertainty on Te[OII]
56 A1 --- l_O+/H+ Limit flag on O+/H+
57- 61 F5.2 10-5 O+/H+ O+/H+ line ratio
63- 66 F4.2 10-5 e_O+/H+ ? rms uncertainty on O+/H+
68 A1 --- l_O2+/H+ Limit flag on O2+/H+
69- 73 F5.2 10-5 O2+/H+ O2+/H+ line ratio
75- 78 F4.2 10-5 e_O2+/H+ ? rms uncertainty on O2+/H+
80 A1 --- l_12+log(O/H) Limit flag on 12+log(O/H)
81- 84 F4.2 --- 12+log(O/H) Abundance 12+log(O/H)
86- 89 F4.2 --- e_12+log(O/H) ? rms uncertainty on 12+log(O/H)
91 A1 --- l_log(N/O) Limit flag on log(N/O)
92- 96 F5.2 [-] log(N/O) ?=- Abundance log(N/O)
98-101 F4.2 [-] e_log(N/O) ? rms uncertainty on log(N/O)
103 A1 --- l_[O/H] Limit flag on [O/H]
104-108 F5.2 [-] [O/H] Abundance [O/H]
110-113 F4.2 [-] e_[O/H] ? rms uncertainty on [O/H]
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [JKB]
5- 9 A5 --- JKB JKB identification number
10 A1 --- n_JKB [*] * for objects with uncertain
distances, i.e. D<20Mpc
12- 17 F6.2 10+31W LHa Hα luminosity for HII region
19- 23 F5.2 10+31W e_LHa rms uncertainty on LHa
25- 29 F5.2 10-2Msun/yr SFRHa Hα star formation rate for
HII region
31- 34 F4.2 10-2Msun/yr e_SFRHa rms uncertainty on SFRHa
36- 41 F6.2 10+31W LHatot ?=- Total Hα luminosity
(entire galaxy)
43- 47 F5.2 10+31W e_LHatot ? rms uncertainty on LHatot
49- 53 F5.2 10-2Msun/yr SFRHatot ?=- Total Hα star formation rate
(entire galaxy)
55- 58 F4.2 10-2Msun/yr e_SFRHatot ? rms uncertainty on SFRHatot
60 A1 --- l_Age Limit flag on Age
61- 65 F5.2 Myr Age Age, determined from EW(Hα) and
EW(Hβ)
67- 70 F4.2 Myr e_Age ? rms uncertainty on Age
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [JKB]
5- 7 I3 --- JKB JKB identification number
8 A1 --- n_JKB [*] Note on JKB (1)
10 A1 --- f_JKB [a] a for Known to be a single HII region
within M 81
12- 16 F5.2 mag gmag SDSS g magnitude
18- 22 F5.2 mag u-g ?=- SDSS u-g colour index
24- 28 F5.2 mag g-r SDSS g-r colour index
30- 34 F5.2 mag r-i SDSS r-i colour index
36- 40 F5.2 mag i-z SDSS i-z colour index
42- 47 F6.2 mag bMAG ?=- Absolute B magnitude (2)
49- 53 F5.2 mag/arcsec+2 SuBrV Surface brightness in V band
--------------------------------------------------------------------------------
Note (1): Note as follows:
* = objects with uncertain distances, i.e. D<20Mpc, and consequential
photometric uncertainties of >1mag
Note (2): Objects without bMAG values are those for which spectroscopic
redshifts could not be measured.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- JKB
5- 7 I3 --- JKB JKB identification number
8 A1 --- n_JKB [*] * for object with uncertain distances,
i.e. D<20Mpc
10 A1 --- f_JKB [a] a for Known to be a single HII region
within M 81
12- 15 F4.2 [Msun] logM* Stellar mass
17- 20 F4.2 [Msun] e_logM* rms uncertainty on logM*
22- 27 F6.2 [yr-1] logSSFR Specific star formation rate derived from M*
and total SFRs listed in Table 3
29- 32 F4.2 [yr-1] e_logSSFR rms uncertainty on logSSFR
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [JKB]
5- 9 A5 --- JKB JKB identification number
12- 16 F5.2 10-19W/m2 FHb Hβ line flux (in 10-16erg/s/cm2)
18- 21 F4.2 10-19W/m2 e_FHb rms uncertainty on FHb
24- 29 F6.2 10-19W/m2 IntHb Hβ line intensity (in 10-16erg/s/cm2)
31- 35 F5.2 10-19W/m2 e_IntHb rms uncertainty on IntHb
38- 41 F4.2 mag E(B-V) Color excess
43- 46 F4.2 mag e_E(B-V) rms uncertainty on E(B-V)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [JKB]
5- 10 A6 --- JKB JKB identification number
12- 31 A20 --- El Element
33 A1 --- l_Flux Limit flag on Flux
34- 39 F6.2 --- Flux ?=- Line flux relative to Hβ=100
41- 46 F6.2 --- e_Flux ? rms uncertainty on Flux
51 A1 --- l_Int Limit flag on Int
52- 57 F6.2 --- Int ?=- De-reddened line intensity relative
to Hβ=100
59- 64 F6.2 --- e_Int ? rms uncertainty on Int
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 08-Apr-2019