J/ApJ/889/177 RGB abundances in the disk, stream & halo of M31 (Escala+, 2020)
Elemental abundances in M31: a comparative analysis of alpha and iron element
abundances in the the outer disk, giant stellar stream, and inner halo of M31.
Escala I., Gilbert K.M., Kirby E.N., Wojno J., Cunningham E.C.,
Guhathakurta P.
<Astrophys. J., 889, 177 (2020)>
=2020ApJ...889..177E 2020ApJ...889..177E
ADC_Keywords: Galaxies, nearby; Abundances; Stars, giant; Radial velocities;
Stars, halo
Keywords: Andromeda galaxy ; Stellar abundances ; Galaxy stellar halos ;
Local Group ; Galaxy stellar disks ; Galaxy formation
Abstract:
We measured [Fe/H] and [α/Fe] using spectral synthesis of
low-resolution stellar spectroscopy for 70 individual red-giant-branch
stars across four fields spanning the outer disk, Giant Stellar
Stream (GSS), and inner halo of M31. Fields at M31-centric projected
distances of 23kpc in the halo, 12kpc in the halo, 22kpc in the GSS,
and 26kpc in the outer disk are α-enhanced, with
<[α/Fe]≥0.43, 0.50, 0.41, and 0.58, respectively.
The 23 and 12kpc halo fields are relatively metal-poor, with
<[Fe/H]≥-1.54 and -1.30, whereas the 22kpc GSS and 26kpc outer disk
fields are relatively metal-rich with <[Fe/H]≥-0.84 and -0.92,
respectively. For fields with substructure, we separated the stellar
populations into kinematically hot stellar halo components and
kinematically cold components. We did not find any evidence of a
radial [α/Fe] gradient along the high surface brightness core of
the GSS between ∼17 and 22kpc. However, we found tentative suggestions
of a negative radial [α/Fe] gradient in the stellar halo, which
may indicate that different progenitor(s) or formation mechanisms
contributed to the build up of the inner versus outer halo.
Additionally, the [α/Fe] distribution of the metal-rich
([Fe/H]>-1.5), smooth inner stellar halo (rproj≲26kpc) is
inconsistent with having formed from the disruption of a progenitor(s)
similar to present-day M31 satellite galaxies. The 26kpc outer disk
is most likely associated with the extended disk of M31, where its
high α-enhancement provides support for an episode of rapid star
formation in M31's disk possibly induced by a major merger.
Description:
Deep M31 observations for the 12kpc Halo, 22kpc Giant Stellar Stream
and 26kpc Disk fields, on 2014 Sep 29, 30 and Oct 1 on two separate
slitmasks for each field, were made for a total of 6.5, 5.5, and
5.9hr, respectively, with the Keck/DEIMOS at a central wavelength of
7200Å. The spectral resolution is approximately ∼2.8Å FWHM.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 85 129 Stellar parameters and elemental abundances of
individual M31 RGB stars
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/433/185 : Abundance analysis of 102 F and G dwarfs (Bensby+, 2005)
J/MNRAS/367/1329 : Elemental abundances for 176 stars (Reddy+, 2006)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters (Kirby+, 2008)
J/ApJS/184/152 : Deep optical photometry in M31 (Brown+, 2009)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/AJ/137/272 : Space velocities orbits in the Milky Way halo (Roederer+ 2009)
J/ApJ/714/663 : Stellar density map of the Milky Way (de Jong+, 2010)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/ApJ/735/L46 : Spectroscopy of 64 K red giants (Bensby+, 2011)
J/ApJ/743/19 : Photometry of variable star cand. in M31 (Clementini+, 2011)
J/ApJ/753/64 : Detailed abundances for 97 metal-poor stars (Ishigaki+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/771/67 : Abundances for 97 metal-poor stars. II. (Ishigaki+, 2013)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/A+A/572/A33 : Abundances from Gaia-ESO Survey (Mikolaitis+, 2014)
J/ApJ/790/73 : Iron & alpha abund. of RGBs in M31 satellites (Vargas+, 2014)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/A+A/577/A81 : Deep SDSS Optical Spectroscopy. II. (Fernandez-Alvar+, 2015)
J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015)
J/MNRAS/455/199 : CaII triplet in red giant spectra (Da Costa, 2016)
J/ApJ/819/135 : Lithium-rich giants in globular clusters (Kirby+, 2016)
J/ApJ/846/145 : PHAT. XIX. Formation history of M31 disk (Williams+, 2017)
J/ApJ/859/L8 : Properties of TriAnd stars (Hayes+, 2018)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
J/ApJ/868/55 : Structure of M31 halo. II. PAndAS (McConnachie+, 2018)
J/ApJ/883/128 : alpha & Fe abund. in the giant stellar stream (Gilbert+, 2019)
J/AJ/159/46 : Abundances of 416 stars in 5 dSphs of M31 (Kirby+, 2020)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Field Field (1)
8- 14 I7 --- ID [2493/3000724] Object Name
16- 17 I2 h RAh [0] Hour of Right Ascension (J2000)
19- 20 I2 min RAm [43/50] Minute of Right Ascension (J2000)
22- 26 F5.2 s RAs Second of Right Ascension (J2000)
28- 28 A1 --- DE- [+] Sign of the Declination (J2000)
29- 30 I2 deg DEd [39/42] Degree of Declination (J2000)
32- 33 I2 arcmin DEm Arcminute of Declination (J2000)
35- 38 F4.1 arcsec DEs Arcsecond of Declination (J2000)
40- 45 F6.1 km/s HRV [-552/-102] Heliocentric Radial Velocity
47- 48 I2 0.1nm-1 SN [4/32] Signal-to-noise ratio per Angstrom
50- 53 I4 K Teff [3569/5257] Stellar surface temperature
55- 58 I4 K e_Teff [2/2399] Uncertainty in Teff (2)
60- 63 F4.2 [cm/s2] logg [0.39/1.85] log of stellar surface gravity
65- 69 F5.2 [-] [Fe/H] [-3.52/-0.02] Metallicity
71- 74 F4.2 [-] e_[Fe/H] [0.13/0.32] Uncertainty in [Fe/H] (2)
76- 80 F5.2 [-] [a/Fe] [-0.6/1.2]? α metal abundance
82- 85 F4.2 [-] e_[a/Fe] [0.17/0.5]? Uncertainty [a/Fe] (2)
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Note (1): Field as follows:
H = 12kpc Halo field (44 occurrences);
S = 22kpc Giant Stellar Stream (GSS) field (31 occurrences);
D = 26kpc Disk field (35 occurrences);
f130_2 = 23kpc Halo field published by Escala+ (2019ApJ...878...42E 2019ApJ...878...42E)
Note (2): The errors presented for Teff represent only the random component
of the total uncertainty. However, the errors for [Fe/H] and [a/Fe]
include systematic components that account for errors propagated by
inaccuracies in Teff (Escala+ 2019ApJ...878...42E 2019ApJ...878...42E).
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History:
From electronic version of the journal
References:
Escala et al. rproj=23kpc 2019ApJ...878...42E 2019ApJ...878...42E
Gilbert et al. rproj=17kpc 2019ApJ...883..128G 2019ApJ...883..128G Cat. J/ApJ/883/128
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Jul-2021