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 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 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 2012ApJ...758..124H), And VII (Ho et al. 2014, 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 80 9 Observed Properties of M31 Satellite Sample
table2.dat 69 817 Iron and Alpha Abundance Results
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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
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Bytes Format Units Label Explanations
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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)
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Note (1): Absolute magnitude sources :
And X = Brasseur et al. 2011ApJ...729...23B 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 2013ApJ...768...50T;
And II = Ho et al. 2012ApJ...758..124H 2012ApJ...758..124H;
NGC 147,185 = Geha et al. 2012ApJ...757...85G 2012ApJ...757...85G;
M32 = Howley et al. 2013ApJ...765...65H 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 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.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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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)
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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.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Mar-2017