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J/ApJ/790/73  Iron and alpha abundance of RGBs in M31 satellites (Vargas+, 2014)

The distribution of alpha elements in Andromeda dwarf galaxies. Vargas L.C., Geha M.C., Tollerud E.J. <Astrophys. J., 790, 73 (2014)> =2014ApJ...790...73V (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Magnitudes ; Velocity dispersion ; Abundances, [Fe/H] Keywords: galaxies: abundances - galaxies: dwarf - galaxies: evolution - galaxies: individual: M31 - Local Group Abstract: We present alpha to iron abundance ratios for 226 individual red giant branch stars in nine dwarf galaxies of the Andromeda (M31) satellite system. The abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample of alpha abundance ratios measured in the M31 satellite system. The dwarf galaxies in our sample exhibit a variety of alpha abundance ratios, with the average values in each galaxy ranging from approximately solar ([α/Fe] ∼ + 0.0) to alpha-enhanced ([α/Fe] ∼ + 0.5). These variations do not show a correlation with internal kinematics, environment, or stellar density. We confirm radial gradients in the iron abundance of two galaxies out of the five with sufficient data (NGC 185 and And II). There is only tentative evidence for an alpha abundance radial gradient in NGC 185. We homogeneously compare our results to the Milky Way classical dwarf spheroidals, finding evidence for wider variation in average alpha abundance. In the absence of chemical abundances for the M31 stellar halo, we compare to the Milky Way stellar halo. A stellar halo comprised of disrupted M31 satellites is too metal-rich and inconsistent with the Milky Way halo alpha abundance distribution even if considering only satellites with predominantly old stellar populations. The M31 satellite population provides a second system in which to study chemical abundances of dwarf galaxies and reveals a wider variety of abundance patterns than the Milky Way. Description: We measure metallicities and alpha abundances for a large sample of stars in nine dwarf satellites of M31. The sample consists of RGB stellar spectra taken with Keck/DEIMOS (Faber et al., 2003SPIE.4841.1657F) during multiple runs. We include data for NGC 147, NGC 185 (Geha et al. 2010, J/ApJ/711/361), And II (Ho et al. 2012ApJ...758..124H), And VII (Ho et al. 2014, arXiv:1405.4424), and new observations for And V and And X (described in Section 2.3). The remaining spectra were drawn from the Spectroscopic and Photometric Landscape of Andromeda's stellar Halo (SPLASH) project, in particular the data set presented by Tollerud et al. (2012, J/ApJ/752/45). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 80 9 Observed Properties of M31 Satellite Sample table2.dat 69 817 Iron and Alpha Abundance Results
See also: J/ApJ/711/361 : Local Group dE galaxies. II. (Geha+, 2010) J/AJ/144/4 : Properties of dwarf galaxies in the Local Group (McConnachie+, 2012) J/ApJ/752/45 : SPLASH: Stellar spectroscopy of M31 satellites (Tollerud+, 2012) J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 7 A7 --- UFD Name of M31 Satellite Galaxy 9- 13 F5.1 mag VMag V band absolute magnitude (1) 15- 17 F3.1 mag e_VMag Error in VMag 19- 22 F4.1 km/s sigmalos LOS velocity dispersion (2) 24- 26 F3.1 km/s e_sigmalos Error in sigmalos 28- 31 F4.1 km/s Vrms Quadrature sum of dispersion and rotation velocity (3) 33- 35 F3.1 km/s e_Vrms Error in Vrms 37- 40 F4.1 mag/arcsec2 muV Surface brightness in V band (4) 42- 44 F3.1 mag/arcsec2 e_muV Error in muV 46- 48 F3.1 arcmin r1/2 Half-light radius (4) 50- 52 F3.1 arcmin e_r1/2 Error in r1/2 54- 59 F6.2 deg PA Position angle (4) 61- 64 F4.2 --- epsilon Ellipticity (4) 66- 69 F4.1 mag (m-M)0 Distance modulus (5) 71- 73 F3.1 mag e_(m-M)0 Error in (m-M)0 75- 76 I2 --- N[alpha/Fe] Number of measurements of [alpha/Fe] (6) 78- 80 I3 --- N[Fe/H] Number of measurements of [Fe/H] (7)
Note (1): Absolute magnitude sources : And X = Brasseur et al. 2011ApJ...729...23B; And I, III, V, VII = Tollerud et al. 2012, J/ApJ/752/45; And II, NGC 147, NGC 185, M32 = McConnachie 2012, J/AJ/144/4, and references there in. Note (2): Velocity dispersion sources: And I, III, V, VII, X = Tollerud et al. 2013ApJ...768...50T; And II = Ho et al. 2012ApJ...758..124H; NGC 147,185 = Geha et al. 2012ApJ...757...85G; M32 = Howley et al. 2013ApJ...765...65H. Note (3): Non-zero rotation velocities taken from same sources as velocity dispersions. Note (4): From compilation by McConnachie (2012, J/AJ/144/4). Note (5): Distance moduli sources : Conn et al. (2012, J/ApJ/758/11), except And VII (Tollerud et al. 2012, J/ApJ/752/45), And X (Brasseur et al. 2011ApJ...729...23B), M32 (McConnachie 2012, J/AJ/144/4). Note (6): Excluding [Fe/H] > -0.5 stars (see discussion in Section 3.2). All measurements are from S/N ≥ 15 Å-1. Note (7): Used for computing metallicity radial gradients. All measurements are from S/N ≥ 8 Å-1.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 7 A7 --- UFD Name of M31 Satellite Galaxy 10- 11 I2 h RAh Hour of Right Ascension (J2000) 13- 14 I2 min RAm Minute of Right Ascension (J2000) 16- 20 F5.2 s RAs Second of Right Ascension (J2000) 22 A1 --- DE- Sign of the Declination (J2000) 23- 24 I2 deg DEd Degree of Declination (J2000) 26- 27 I2 arcmin DEm Arcminute of Declination (J2000) 29- 32 F4.1 arcsec DEs Arcsecond of Declination (J2000) 35- 39 F5.2 [Sun] [Fe/H] Iron abundance relative to the Sun 42- 45 F4.2 [Sun] e_[Fe/H] Uncertainty in [Fe/H] 48- 52 F5.2 [Sun] [a/Fe] ? Alpha-to-iron abundance ratio 55- 58 F4.2 [Sun] E_[a/Fe] ? Upper limit uncertainty in [a/Fe] 61- 64 F4.2 [Sun] e_[a/Fe] ? Lower limit uncertainty in [a/Fe] 66- 69 A4 --- --- Flag (1)
Note (1): Flag as follows : u = Lower limit uncertainty in [a/Fe] is outside of our grid, thus we set e_[a/Fe] = [a/Fe]-min([a/Fe]_grid) = [a/Fe]-(-0.8). mr = [Fe/H] > -0.5 star, so [a/Fe] is corrected based on extrapolation in Figure 2. f = Only [Fe/H] is available for this star.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Mar-2017
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