J/ApJ/902/51 Abundances for M31 RGB stars from Keck/DEIMOS (Escala+, 2020)
Elemental abundances in M31: properties of the inner stellar halo.
Escala I., Kirby E.N., Gilbert K.M., Wojno J., Cunningham E.C.,
Guhathakurta P.
<Astrophys. J., 902, 51 (2020)>
=2020ApJ...902...51E 2020ApJ...902...51E
ADC_Keywords: Galaxies, nearby; Abundances, [Fe/H]; Radial velocities;
Stars, giant; Spectra, optical
Keywords: Andromeda Galaxy ; Galaxy stellar halos ; Stellar abundances ;
Galaxy abundances ; Galaxy formation
Abstract:
We present measurements of [Fe/H] and [α/Fe] for 128 individual
red giant branch stars (RGB) in the stellar halo of M31, including its
Giant Stellar Stream (GSS), obtained using spectral synthesis of low-
and medium-resolution Keck/DEIMOS spectroscopy (R∼3000 and 6000,
respectively). We observed four fields in M31's stellar halo (at
projected radii of 9, 18, 23, and 31kpc), as well as two fields in the
GSS (at 33kpc). In combination with existing literature measurements,
we have increased the sample size of [Fe/H] and [α/Fe]
measurements from 101 to a total of 229 individual M31 RGB stars. From
this sample, we investigate the chemical abundance properties of M31's
inner halo, finding <[Fe/H]≥-1.08±0.04 and <[α/Fe]≥0.40±0.03.
Between 8 and 34kpc, the inner halo has a steep [Fe/H] gradient
(-0.025±0.002dex/kpc) and negligible [α/Fe] gradient, where
substructure in the inner halo is systematically more metal-rich than
the smooth component of the halo at a given projected distance.
Although the chemical abundances of the inner stellar halo are largely
inconsistent with that of present-day dwarf spheroidal (dSph)
satellite galaxies of M31, we identified 22 RGB stars kinematically
associated with the smooth component of the stellar halo that have
chemical abundance patterns similar to M31 dSphs. We discuss formation
scenarios for M31's halo, concluding that these dSph-like stars may
have been accreted from galaxies of similar stellar mass and star
formation history, or of higher stellar mass and similar star
formation efficiency.
Description:
Table 1 presents previously unpublished deep (≳5hr) observations of
six spectroscopic fields in M31. The spectral resolution of the
Keck/DEIMOS 600ZD (1200G) grating is approximately 2.8 (1.3)Å FWHM,
or R∼3000 (6500) at the CaII triplet region (λ∼8500Å).
Additional deep DEIMOS observations of M31 fields utilized in this
work were published by Escala+ (2019ApJ...878...42E 2019ApJ...878...42E ; 2020, J/ApJ/889/177)
and Gilbert+ 2019, J/ApJ/883/128
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 89 21 Deep DEIMOS observations in M31
table4.dat 84 208 Catalog of stellar parameters and abundances
--------------------------------------------------------------------------------
See also:
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/AJ/124/234 : M31 outer halo UBVRI photometry & metallicity (Reitzel+, 2002)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
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/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/ApJ/743/19 : Phot. of variable star candidates in M31 (Clementini+, 2011)
J/A+A/530/A15 : Abundances of 94 stars (Nissen+, 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/752/45 : SPLASH: Stellar spectrosc. of M31 satellites (Tollerud+, 2012)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/788/72 : Observed sample of z∼0.7 massive galaxies (Gallazzi+, 2014)
J/ApJ/790/73 : Iron & alpha abund. of RGBs in M31 satellites (Vargas+, 2014)
J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015)
J/AJ/151/144 : ASPCAP weights for 15 APOGEE chemical elements (Garcia+, 2016)
J/ApJ/825/50 : Variable stars in M31 & M33. III. YSGs & RSGs (Gordon+, 2016)
J/ApJ/852/50 : Gal. halo with APOGEE. II. Abund. (Fernandez-Alvar+, 2018)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
J/ApJ/856/15 : Stellar mass-metallicity relation. I. (Leethochawalit+, 2018)
J/ApJ/868/55 : Large-scale structure of M31 halo. II. (McConnachie+, 2018)
J/ApJ/883/128 : alpha & Fe abund. in the giant stellar stream (Gilbert+, 2019)
J/ApJ/885/100 : Star mass-metallicity relation. II. (Leethochawalit+, 2019)
J/ApJ/889/177 : RGB abund. in the disk, stream & halo of M31 (Escala+, 2020)
J/AJ/159/46 : Elemental abund. of 416 stars in 5 dSphs of M31 (Kirby+, 2020)
J/ApJ/895/78 : [Fe/H] and [α/Fe] in M31 dwarf galaxies (Wojno+, 2020)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field M31 field identifier
8- 9 I2 kpc Dist [9/33] Projected radial distance, rproj,
from the center of M31
11- 14 A4 --- Comp Kinematical component: "Halo" or "GSS"
(Giant Stellar Stream)
16- 17 I2 h RAh Hour of right ascension (J2000)
19- 20 I2 min RAm Minute of right ascension (J2000)
22- 26 F5.2 s RAs Second of right ascension (J2000)
28 A1 --- DE- Sign of declination (J2000)
29- 30 I2 deg DEd Degree of declination (J2000)
32- 33 I2 arcmin DEm Arcminute of declination (J2000)
35- 38 F4.1 arcsec DEs Arcsecond of declination (J2000)
40- 44 F5.1 deg PA [-20/178.2] Position angle (east of north)
46- 50 A5 --- Grating Grating
52- 58 A7 --- Slit Slitmask name (1)
60- 70 A11 "Y/M/D" Date Date of observation (UT)
72- 75 F4.2 arcsec Seeing [0.43/0.88] Average seeing
77- 80 F4.2 --- Airmass [1.06/1.52] Average airmass, X
82- 85 F4.2 h Exp [0.43/3.5] Exposure time per slitmask
87- 89 I3 --- Ns [67/143]? Number of stars targeted
per slitmask
--------------------------------------------------------------------------------
Note (1): Slitmasks labeled as "a," "b," etc., are identical, except that the
slits are tilted according to the parallactic angle at the approximate
time of observation for the slitmask.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field M31 field
8- 14 I7 --- [EKG2020] [1092174/8005126] Object identifier
16- 17 I2 h RAh [0] Hour of Right Ascension (J2000)
19- 20 I2 min RAm [3/51] 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 [38/41] 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 [-647.2/-142.6] Heliocentric radial velocity
47- 48 I2 10/nm-1 SN [4/56] Signal-to-noise per Angstrom
50- 53 I4 K Teff [3609/4825] Effective temperature
55- 57 I3 K e_Teff [2/162] Uncertainty in Teff
59- 62 F4.2 [cm/s2] logg [0.28/1.51] Surface gravity, log
64- 68 F5.2 [-] [Fe/H] [-3.2/-0.09] Metallicity
70- 73 F4.2 [-] e_[Fe/H] [0.1/0.4] Uncertainty in [Fe/H]
75- 79 F5.2 [-] [a/Fe] [-0.5/1.1]? α element abundance
81- 84 F4.2 [-] e_[a/Fe] [0.13/0.5]? Uncertainty in [a/Fe]
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Apr-2022