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. =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^-2^M_{sun}_/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_{sun}_)~=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 H{beta} 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{deg} 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 H{alpha} luminosity for HII region 19- 23 F5.2 10+31W e_LHa rms uncertainty on LHa 25- 29 F5.2 10-2Msun/yr SFRHa H{alpha} 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 H{alpha} luminosity (entire galaxy) 43- 47 F5.2 10+31W e_LHatot ? rms uncertainty on LHatot 49- 53 F5.2 10-2Msun/yr SFRHatot ?=- Total H{alpha} 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(H{alpha}) and EW(H{beta}) 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 H{beta} line flux (in 10^-16^erg/s/cm^2^) 18- 21 F4.2 10-19W/m2 e_FHb rms uncertainty on FHb 24- 29 F6.2 10-19W/m2 IntHb H{beta} line intensity (in 10^-16^erg/s/cm^2^) 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 H{beta}=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 H{beta}=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