J/ApJ/883/128 alpha & Fe abundances in the giant stellar stream (Gilbert+, 2019)
Elemental abundances in M31: first alpha and iron abundance measurements in
M31's giant stellar stream.
Gilbert K.M., Kirby E.N., Escala I., Wojno J., Kalirai J.S., Guhathakurta P.
<Astrophys. J., 883, 128 (2019)>
=2019ApJ...883..128G 2019ApJ...883..128G
ADC_Keywords: Abundances; Spectra, optical; Stars, giant; Radial velocities;
Galaxies, nearby
Keywords: galaxies: halos ; galaxies: individual (M31) ; stars: abundances ;
stars: kinematics and dynamics ; techniques: spectroscopic
Abstract:
We present the first measurements of [Fe/H] and [α/Fe]
abundances, obtained using spectral synthesis modeling, for red giant
branch stars in M31's giant stellar stream (GSS). The spectroscopic
observations, obtained at a projected distance of 17kpc from M31's
center, yielded 61 stars with [Fe/H] measurements, including 21 stars
with [α/Fe] measurements, from 112 targets identified as M31
stars. The [Fe/H] measurements confirm the expectation from
photometric metallicity estimates that stars in this region of M31's
halo are relatively metal rich compared to stars in the Milky Way's
inner halo: more than half the stars in the field, including those not
associated with kinematically identified substructure, have [Fe/H]
abundances >-1.0. The stars in this field are α-enhanced at
lower metallicities, while [α/Fe] decreases with increasing
[Fe/H] above metallicities of [Fe/H]≳-0.9. Three kinematical
components have been previously identified in this field: the GSS, a
second kinematically cold feature of unknown origin, and M31's
kinematically hot halo. We compare probabilistic [Fe/H] and
[α/Fe] distribution functions for each of the components. The
GSS and the second kinematically cold feature have very similar
abundance distributions, while the halo component is more metal poor.
Although the current sample sizes are small, a comparison of the
abundances of stars in the GSS field with abundances of M31 halo and
dSph stars from the literature indicate that the progenitor of the
stream was likely more massive, and experienced a higher efficiency of
star formation, than M31's existing dSphs or the dEs NGC147 and NGC185.
Description:
The field analyzed here is located on M31's giant stellar stream (GSS)
at a mean projected distance from M31's center of 17kpc (Figure 1). We
observed this field with the DEep Imaging Multi-Object Spectrograph
(DEIMOS) Spectrograph on the Keck II 10m telescope on 2017 Oct 22, for
a total integration time of 6.4hr in 0.7"-0.9" seeing.
Targets were chosen using a catalog (Kalirai+ 2006ApJ...641..268K 2006ApJ...641..268K)
derived from g' and i' band imaging obtained with the MegaCam
instrument on the 3.6m Canada-France-Hawaii Telescope (CFHT).
The final M31 data set presented here contains only stars that are
more than three times as likely to be M31 RGB stars than foreground MW
stars. See Section 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 78 61 Parameters of stars with abundance measurements
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See also:
II/183 : UBVRI Photometric Standards (Landolt 1992)
J/MNRAS/327/918 : CaII in extragalactic red giants (Tolstoy+, 2001)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/663/960 : Radial velocities of Leo I stars (Sohn+, 2007)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/MNRAS/390/1437 : Stellar streams in Andromeda (M31) (Chapman+, 2008)
J/ApJ/682/1217 : Abundances in red giants in 7 GCs (Kirby+, 2008)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/A+A/480/379 : Abundances of 59 red giants in LMC (Pompeia+, 2008)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/AJ/137/272 : Space velocities orbits in the MW halo (Roederer+ 2009)
J/ApJ/719/931 : Chemical evolution of the UMi dSph (Cohen+, 2010)
J/AN/331/474 : Abundances of metal-poor stars (Frebel, 2010)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/A+A/544/A73 : BVI photometry of Fornax dSph galaxy (de Boer+, 2012)
J/ApJ/761/33 : Chemical data of 89 stars in the LMC disk (Lapenna+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/752/45 : SPLASH: Stellar sp. of M31 satellites (Tollerud+, 2012)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/A+A/560/A44 : Abundances of LMC bar & disk stars (Van der Swaelmen+, 2013)
J/ApJ/790/73 : Abundances of RGBs in M31 satellites (Vargas+, 2014)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/MNRAS/455/199 : CaII triplet in red giant spectra (Da Costa, 2016)
J/A+A/605/A46 : Sgr dSph nucleus stars chemical abund. (Mucciarelli+, 2017)
J/ApJ/846/145 : PHAT. XIX. Formation history of M31 disk (Williams+, 2017)
J/ApJ/868/55 : M31 halo. II. PAndAS (McConnachie+, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- Name [2070316/2075349] Object identifier
9- 10 I2 h RAh [0] Hour of Right Ascension (J2000)
12- 13 I2 min RAm [43] Minute of Right Ascension (J2000)
15- 19 F5.2 s RAs [25.7/53.1] Second of Right Ascension (J2000)
21 A1 --- DE- [+] Sign of the Declination (J2000)
22- 23 I2 deg DEd [39/40] Degree of Declination (J2000)
25- 26 I2 arcmin DEm Arcminute of Declination (J2000)
28- 31 F4.1 arcsec DEs Arcsecond of Declination (J2000)
33- 37 F5.2 0.1nm-1 SN [5.6/21.5] Signal-to-Noise
39- 44 F6.1 km/s HRV [-597.1/-207.4] Heliocentric radial velocity
46- 49 I4 K Teff [3774/4966] Effective temperature
51- 52 I2 K e_Teff [18/87] Uncertainty in Teff
54- 57 F4.2 [cm/s2] log(g) [0.5/1.5] log surface gravity
59- 63 F5.2 [Sun] [Fe/H] [-2.13/-0.03] Metallicity (1)
65- 68 F4.2 [Sun] e_[Fe/H] [0.1/0.4] Uncertainty in [Fe/H]
70- 73 F4.2 [Sun] [a/Fe] [0.09/0.8]? log α to Fe number
abundance (1)
75- 78 F4.2 [Sun] e_[a/Fe] [0.18/0.4]? Uncertainty in [a/Fe]
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Note (1): Measurements of [Fe/H] and [a/Fe] included here pass all quality
criteria discussed in Section 3. Stars with evidence of TiO in their
spectra have been excluded from the final sample of abundances.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Mar-2021