J/ApJ/834/9 Spectroscopy obs. of LeoA, Aqr & Sgr dwarf gal. (Kirby+, 2017)
Chemistry and kinematics of the late-forming dwarf irregular galaxies Leo A, Aquarius, and Sagittarius DIG. Kirby E.N., Rizzi L., Held E.V., Cohen J.G., Cole A.A., Manning E.M., Skillman E.D., Weisz D.R. <Astrophys. J., 834, 9-9 (2017)> =2017ApJ...834....9K (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Radial velocities ; Galaxies, nearby ; Spectroscopy ; Photometry, VRI Keywords: galaxies: abundances; galaxies: dwarf; Local Group; stars: abundances; galaxies: individual: (Leo A, DDO 210, Sgr dIG) Abstract: We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and the Sagittarius dwarf irregular galaxy. The three galaxies-but especially Leo A and Aquarius-share in common delayed star formation histories (SFHs) relative to many other isolated dwarf galaxies. The stars in all three galaxies are supported by dispersion. We found no evidence of stellar velocity structure, even for Aquarius, which has rotating HI gas. The velocity dispersions indicate that all three galaxies are dark-matter-dominated, with dark-to-baryonic mass ratios ranging from 4.4-0.8+1.0 (SagDIG) to 9.6-1.8+2.5 (Aquarius). Leo A and SagDIG have lower stellar metallicities than Aquarius, and they also have higher gas fractions, both of which would be expected if Aquarius were further along in its chemical evolution. The metallicity distribution of Leo A is inconsistent with a closed or leaky box model of chemical evolution, suggesting that the galaxy was pre-enriched or acquired external gas during star formation. The metallicities of stars increased steadily for all three galaxies, but possibly at different rates. The [α/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended SFHs than Sculptor, consistent with photometrically derived SFHs. Overall, the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies, including dwarf spheroidal galaxies. Description: Kirby+ (2014, J/MNRAS/439/1015) already published some Keck/DEIMOS spectroscopy of stars in Leo A and Aquarius. We obtained additional DEIMOS spectra of individual stars in those galaxies, as well as Sagittarius dwarf irregular galaxy (SagDIG). We observed the three galaxies with DEIMOS over several nights in 2013 and 2014. We set the central wavelength to 7800Å with a resolving power of R∼7000. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 94 320 Radial velocities and membership table3.dat 101 179 Chemical abundances table4.dat 265 3 Galaxy properties
See also: J/MNRAS/455/2163 : BI LCs of DDO210 pulsating variables (Ordonez+, 2016) J/ApJS/216/10 : DUSTiNGS. I. The Good Source Catalog (Boyer+, 2015) J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015) J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015) J/A+A/572/A42 : SagDIG carbon and oxygen stars (Momany+, 2014) J/ApJS/214/19 : Suprime-Cam wide-field photometry of Leo A (Stonkute+, 2014) J/A+A/570/A78 : Deep VI photometry of Sgr dIrr (Beccari+, 2014) J/ApJ/790/73 : RGB iron & alpha abundances in M31 satellites (Vargas+, 2014) J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014) J/MNRAS/444/1812 : M54 and Sgr dSph red giants abundances (Mucciarelli+, 2014) J/MNRAS/439/1015 : Velocities of red giants in 7 LG dwarf gal. (Kirby+, 2014) J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013) J/AJ/146/46 : Star Formation Rate in nearby galaxies (Karachentsev+, 2013) J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013) J/ApJ/768/172 : Kinematic analysis of red giant in M31 dSphs (Collins+, 2013) J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012) J/ApJ/756/74 : 2MASS view of Sgr dSph. VII. Kinematics (Frinchaboy+, 2012) J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012) J/ApJ/752/45 : SPLASH: Stellar spectrosc. of M31 satellites (Tollerud+, 2012) J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010) J/ApJ/711/361 : Local Group dE galaxies. II. (Geha+, 2010) J/ApJ/708/1290 : A 2MASS view of the Sgr dSph. VI. (Chou+, 2010) J/ApJ/706/599 : Hα and UV SFR in the local volume (Lee+, 2009) J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009) J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007) J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004) J/AJ/123/3154 : RV light curves of variable stars in Leo A (Dolphin+, 2002) J/AJ/119/777 : BVRI photometry of Sagittarius DIG (Lee+, 2000) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Gal Dwarf galaxy abbreviation (1) 10- 25 A16 --- Name Object name (G1) 27- 28 I2 h RAh Hour of Right Ascension (J2000) 30- 31 I2 min RAm Minute of Right Ascension (J2000) 33- 37 F5.2 s RAs Second of Right Ascension (J2000) 39 A1 --- DE- Sign of the Declination (J2000) 40- 41 I2 deg DEd Degree of Declination (J2000) 43- 44 I2 arcmin DEm Arcminute of Declination (J2000) 46- 49 F4.1 arcsec DEs Arcsecond of Declination (J2000) 51- 55 F5.2 mag Imag0 [17.5/23.8] Extinction-corrected I band Vega magnitude (2) 57- 61 F5.2 mag (V-I)0 [-0.6/3.6] Reddening-corrected (V-I) Vega color index (2) 63 I1 --- N [1/3] Number of masks for this target 65- 67 I3 0.1nm-1 S/N [1/109] Signal-to-noise ratio (3) 69- 74 F6.1 km/s HRV [-291/211]? Heliocentric radial velocity 76- 79 F4.1 km/s e_HRV [1/35]? Error on HRV 81 A1 --- Mm [NY] Membership in dwarf galaxy 83- 94 A12 --- f_Mm ? Reason(s) for non-membership (4)
Note (1): Galaxy abbreviation as follows: LeoA = Leo A; 168 sources Aquarius = Aquarius Dwarf Galaxy; 58 sources SagDIG = Sagittarius dIG ; 94 sources Note (2): For Leo A, we used the V and I Subaru/Suprime-Cam catalog of Stonkute+ (2014, J/ApJS/214/19). For Aquarius, we used the catalog of McConnachie+ (2006MNRAS.373..715M), who observed the galaxy with Suprime-Cam in the V and I filters. For SagDIG, we used two different photometry catalogs. We combined Momany+ (2002A&A...384..393M) photometry from the ESO Multimode Instrument at the ESO New Technology Telescope (NTT) with Momany+ (2014, J/A+A/572/A42) photometry from the HST/Advanced Camera for Surveys (ACS). The NTT photometry was obtained in V and I filters, and we converted the ACS F475W, F606W, and F814W magnitudes into V and I with the transformation equations of Saha+ (2011PASP..123..481S). All magnitudes were corrected for extinction with the Schlegel+ (1998ApJ...500..525S) dust maps. Note (3): To convert to S/N per pixel, multiply by 0.57. Note (4): Reason for non-membership flag as follows: galaxy = Spectrum indicates that the object is a galaxy (25 sources), not an individual star. TiO = TiO bands present in spectrum (not necessarily an indicator of membership). CN = Spectrum shows strong CN features (not an indicator of membership). v = Non-member by radial velocity. CMD = Non-member by location in CMD. Na = Non-member by presence of strong NaI 8190 doublet.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Gal Dwarf galaxy abbreviation 10- 23 A14 --- Name Object name (G1) 27- 30 I4 K Teff [3984/4987] Effective temperature 32- 35 F4.2 [cm/s2] log(g) [0.4/1.7] Surface gravity 37- 41 F5.2 [Sun] [Fe/H] [-2.7/-0.5] Iron abundance relative to Sun 43- 46 F4.2 [Sun] e_[Fe/H] [0.1/0.5] Uncertainty in [Fe/H] 48- 52 F5.2 [Sun] [Mg/Fe] [-0/1.2]? Magnesium-to-iron ratio relative to Sun 54- 57 F4.2 [Sun] e_[Mg/Fe] [0.2/0.5]? Uncertainty in [Mg/Fe] 59- 63 F5.2 [Sun] [Si/Fe] [-0.7/1.2]? Silicon-to-iron ratio relative to Sun 65- 68 F4.2 [Sun] e_[Si/Fe] [0.2/0.5]? Uncertainty in [Si/Fe] 70- 74 F5.2 [Sun] [Ca/Fe] [-0.8/1.1]? Calcium-to-iron ratio relative to Sun 76- 79 F4.2 [Sun] e_[Ca/Fe] [0.1/0.5]? Uncertainty in [Ca/Fe] 81- 85 F5.2 [Sun] [Ti/Fe] [-0.8/1.1]? Titanium-to-iron ratio relative to Sun 87- 90 F4.2 [Sun] e_[Ti/Fe] [0.1/0.5]? Uncertainty in [Ti/Fe] 92- 96 F5.2 [Sun] [a/Fe] [-0.8/1.2]? Alpha-to-iron ratio relative to Sun 98-101 F4.2 [Sun] e_[a/Fe] [0.1/0.5]? Uncertainty in [a/Fe]
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 8 A8 --- Gal Galaxy name 10- 13 I4 kpc Dist [827/1047] Distance 15- 16 I2 kpc e_Dist [11/53] Dist uncertainty 18 I1 --- r_Dist [1/3] Distance reference (1) 20- 22 F3.1 10+6Lsun LV [1.7/6.6] Luminosity 24- 26 F3.1 10+6Lsun e_LV [0.2/1.4] LV uncertainty 28 I1 --- r_LV [4/6] LV reference (1) 30- 33 F4.2 arcmin rh [0.9/2.2] Half-light radius in arcmin 35- 38 F4.2 arcmin e_rh [0.03/0.2] rh uncertainty 40 I1 --- r_rh [4/6] rh reference (1) 42- 44 I3 pc rhpc [277/517] Half-light radius in parsec 46- 47 I2 pc e_rhpc [16/29] rhpc uncertainty 49 I1 --- r_rhpc [4/6] rhpc reference (1) 51- 53 F3.1 10+6Msun M* [1.5/3.3] Stellar mass 55- 57 F3.1 10+6Msun e_M* [0.2/0.7] M* uncertainty 59 I1 --- r_M*  Stellar mass reference (1) 61- 63 F3.1 10-5Msun/yr SFRHa [0/9.3] Hα star formation rate 65- 68 A4 --- r_SFRHa SFRHa reference(s) (1) 70- 72 F3.1 10-4Msun/yr SFRUV [0/7.2] UV star formation rate 74- 75 I2 --- r_SFRUV [8/11] SFRUV reference (1) 77- 79 F3.1 10+6Msun M(HI) [2.2/8.3] HI gas mass 81- 83 F3.1 10+6Msun e_M(HI) [0.3/1.2] M(HI) uncertainty 85- 86 I2 --- r_M(HI)  M(HI) reference (1) 88- 93 F6.1 km/s V(HI) [-140.3/23.7] HI velocity 95- 96 I2 --- r_V(HI)  V(HI) reference (1) 98-100 F3.1 km/s sigHI [6.2/8.2] HI velocity dispersion 102-103 I2 --- r_sigHI  sigHI reference (1) 105-107 I3 --- Nm [25/127] Number of members 109-114 F6.1 km/s HRV [-142/27] Heliocentric velocity 116-118 F3.1 km/s e_HRV [0.9/2] Negative uncertainty on HRV 120-122 F3.1 km/s E_HRV [1/2] Positive uncertainty on HRV 124-128 F5.1 km/s Vgsr [-30.7/6.2] GSR velocity 130-132 F3.1 km/s sigma [7.8/9.4] Velocity dispersion 134-136 F3.1 km/s e_sigma [0.6/1.1] Negative uncertainty on sigma 138-140 F3.1 km/s E_sigma [0.8/1.8] Positive uncertainty on sigma 142-144 F3.1 10+7Msun M1/2 [1.8/4] Mass within the half-light radius (2) 146-148 F3.1 10+7Msun e_M1/2 [0.3/0.4] Negative uncertainty on M1/2 150-152 F3.1 10+7Msun E_M1/2 [0.4/0.4] Positive uncertainty on M1/2 154-155 I2 Msun/Lsun M/L [10/21] Mass-to-light ratio within the half-light radius 157 I1 Msun/Lsun e_M/L [3/4] Negative uncertainty on M/L 159 I1 Msun/Lsun E_M/L [3/6] Positive uncertainty on M/L 161-163 F3.1 --- Mt/Mb [4.4/9.6] Total (dynamical) mass divided by baryonic mass (3) 165-167 F3.1 --- e_Mt/Mb [0.8/1.8] Negative uncertainty on Mt/Mb 169-171 F3.1 --- E_Mt/Mb [1/2.5] Positive uncertainty on Mt/Mb 173-177 F5.2 [-] [Fe/H] [-1.9/-1.5] Average [Fe/H] 179-182 F4.2 [-] e_[Fe/H] [0.06/0.09] Positive uncertainty on [Fe/H] 184-187 F4.2 [-] E_[Fe/H] [0.06/0.2] Negative uncertainty on [Fe/H] 189-191 F3.1 10-2 peffL [2.4/5.5] Effective yield (leaky box); in 10-2Z☉, see equation 3 193-195 F3.1 10-2 e_peffL [0.4/1.1] Negative uncertainty on peffL 197-199 F3.1 10-2 E_peffL [0.4/1.2] Positive uncertainty on peffL 201-203 F3.1 10-2 peffP [2.4/5.3] Effective yield (pre-enriched); in 10-2Z☉, see equation 4 205-207 F3.1 10-2 e_peffP [0.3/1.2] Negative uncertainty on peffP 209-211 F3.1 10-2 E_peffP [0.4/1.4] Positive uncertainty on peffP 213 A1 --- l_[Fe/H]0 Upper limit flag on [Fe/H]0 214-218 F5.2 [-] [Fe/H]0 Initial metallicity of the gas for the pre-enriched model 220-223 F4.2 [-] e_[Fe/H]0 [0.12]? [Fe/H]0 negative uncertainty 225-228 F4.2 [-] E_[Fe/H]0 [0.1]? [Fe/H]0 positive uncertainty 229 A1 --- f_[Fe/H]0 [d] d: Upper limit with 95% confidence 231-235 F5.2 --- dlnPP [-1.8/12.2] ΔlnP value for the pre-enriched model (4) 237-239 F3.1 10-2 peffA [2.1/4.4] Effective yield (accretion); in 10-2Z☉, see equations 5 & 6 241-243 F3.1 10-2 e_peffA [0.3/0.7] Negative uncertainty on peffA 245-247 F3.1 10-2 E_peffA [0.3/0.8] Positive uncertainty on peffA 249-251 F3.1 --- M [2.3/7.1] Accretion parameter M (5) 253-255 F3.1 --- e_M [0.9/3.8] Negative uncertainty on M 257-259 F3.1 --- E_M [1.9/6.2] Positive uncertainty on M 261-265 F5.2 --- dlnPA [-1.2/11.1] ΔlnP value for the accretion model (4)
Note (1): Reference as follows: 1 = Tammann et al. (2011A&A...531A.134T). 2 = Cole et al. (2014ApJ...795...54C). 3 = Momany et al. (2005A&A...439..111M). LV and rh based on surface brightness profiles from: 4 = de Vaucouleurs et al. (1991, VII/155), 5 = McConnachie et al. (2006MNRAS.373..715M), and 6 = Lee & Kim (2000, J/AJ/119/777). Both values are updated for the distances adopted here. LV is corrected for extinction based on Schlafly & Finkbeiner (2011ApJ...737..103S). 7 = Based on stellar mass-to-light ratios from Woo+ (2008MNRAS.390.1453W). 8 = Karachentsev & Kaisina (2013, J/AJ/146/46). 9 = van Zee (2000AJ....119.2757V). 10 = Hunter & Elmegreen (2004, J/AJ/128/2170). 11 = Hunter et al. (2010AJ....139..447H). 12 = Measured from the HI maps of Hunter et al. (2012, J/AJ/144/134). HI masses updated for the distances adopted here. The uncertainty in M(HI) incorporates error on the 21cm flux--assumed to be 11%--and uncertainty in distance. Note (2): Mass within the half-light radius, calculated as M1/2=4G-1σv2rh (Wolf+ 2010MNRAS.406.1220W). Note (3): Total (dynamical) mass divided by baryonic mass (Mb=M*+M(HI)) within the half-light radius. The calculation assumes that half of the stellar mass and half of the gas mass is located within the half-light radius. Note (4): Logarithm of the strength with which the pre-enriched or accretion model is favored over the leaky box model. Negative values of ΔlnP indicate that the model is disfavored. Note (5): In the accretion model (Lenden-Bell, 1975VA.....19..299L; see also Kirby+, 2011ApJ...727...78K), M is the ratio of the final mass to the initial gas mass. See equations 5 and 6.
Global notes: Note (G1): Sources in LeoA are from Stonkute+, 2014, J/ApJS/214/19; Sources in Aquarius come from Kirby+, 2013, J/ApJ/779/102; <[KCG2013] Aqr NNNN> in Simbad and Sources in SagDIG come from Momany+, 2014, J/A+A/572/A42.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-May-2017
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