J/A+A/618/A156 Stellar populations of the central region of M31 (Saglia+, 2018)
The stellar populations of the central region of M31.
Saglia R., Opitsch M., Fabricius M.H., Bender R., Blana M., Gerhard O.
<Astron. Astrophys. 618, A156 (2018)>
=2018A&A...618A.156S 2018A&A...618A.156S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Populations, stellar ; Spectroscopy
Keywords: galaxies: stellar content - galaxies: bulges -
galaxies: individual: M31 - Local Group - galaxies: formation -
galaxies: structure
Abstract:
We continue the analysis of the data set of our spectroscopic
observation campaign of M31, whose ultimate goal is to provide an
understanding of the three-dimensional structure of the bulge, its
formation history, and composition in terms of a classical bulge,
boxy-peanut bulge, and bar contributions. We derive simple stellar
population (SSP) properties, such as age metallicity and alpha-element
overabundance, from the measurement of Lick/IDS absorption line
indices. We describe their two-dimensional maps taking into account
the dust distribution in M31. We found 80% of the values of our age
measurements are larger than 10Gyr. The central 100-arcsec of M31 are
dominated by the stars of the classical bulge of M31. These stars are
old (11-13Gyr), metal-rich (as high as [Z/H]∼0.35dex) at the center
with a negative gradient outward and enhanced in alpha-elements
([alpha/Fe]∼0.28±0.01dex). The bar stands out in the metallicity
map, where an almost solar value of [Z/H] (∼0.02±0.01dex) with no
gradient is observed along the bar position angle (55.7°) out to
600 arcsec from the center. In contrast, no signature of the bar is
seen in the age and [alpha/Fe] maps, which are approximately
axisymmetric, delivering a mean age and overabundance for the bar and
boxy-peanut bulge of 10-13Gyr and 0.25-0.27dex, respectively. The
boxy-peanut bulge has almost solar metallicity (-0.04±0.01dex). The
mass-to-light ratio of the three components is approximately constant
at M/LV∼4.4-4.7M☉/L☉. The disk component at larger
distances is made of a mixture of stars, as young as 3-4Gyr, with
solar metallicity and smaller M/LV (∼3±0.1M☉/L☉). We
propose a two-phase formation scenario for the inner region of M31,
where most of the stars of the classical bulge come into place
together with a proto-disk, where a bar develops and quickly
transforms it into a boxy-peanut bulge. Star formation continues in
the bulge region, producing stars younger than 10Gyr, in particular
along the bar, thereby enhancing its metallicity. The disk component
appears to build up on longer timescales.
Description:
The individual spectra from the fiber based IFU were binned following
a Voronoi binning scheme to increase the SN. The first table lists the
on-sky positions of the individual fiber spectra and the bin number
that they got added to. The second table contains Lick indices data.
The third table contains stellar population parameters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 22 45328 Coordinates of the Voronoi bins
table6.dat 66 6473 Lick indices
table7.dat 76 6473 SSP parameters
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See also:
J/MNRAS/459/2262 : Maps of dust distribution in M31 bulge (Dong+, 2016)
J/MNRAS/473/4130 : M31 center emission-line point-like sources (Martin+, 2018)
J/A+A/611/A38 : Hints for a bar in M31 kinematics and morphology
(Opitsch+, 2018)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Bin [0/6472] Number of the Voronoi bin
6- 13 F8.2 arcsec xpos Coordinate, centered on nucleus, +x points West
15- 22 F8.2 arcsec ypos Coordinate, centered on nucleus, +y points North
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Bin [0/6472] Number of the Voronoi bin
6- 10 F5.2 0.1nm Hb Lick index Hβ
12- 15 F4.2 0.1nm e_Hb Error on Hβ
17- 20 F4.2 0.1nm Mgb Lick index Mgb
22- 25 F4.2 0.1nm e_Mgb Error on Mgb
27- 30 F4.2 0.1nm Fe5015 Lick index Fe5015
32- 35 F4.2 0.1nm e_Fe5015 Error on Fe5015
37- 40 F4.2 0.1nm Fe5270 Lick index Fe5270
42- 45 F4.2 0.1nm e_Fe5270 Error on Fe5270
47- 50 F4.2 0.1nm Fe5335 Lick index Fe5335
52- 55 F4.2 0.1nm e_Fe5335 Error on Fe5335
57- 61 F5.2 0.1nm Fe5406 Lick index Fe5406
63- 66 F4.2 0.1nm e_Fe5406 Error on Fe5406
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Bin [0/6472] Number of the Voronoi bin
6- 9 F4.1 Gyr Age SSP age
11- 14 F4.1 Gyr b_Age SSP minimum Age
16- 19 F4.1 Gyr B_Age SSP maximum Age
21- 24 F4.1 Gyr Age80 SSP Age80%
26- 30 F5.2 [Sun] [Z/H] SSP [Z/H]
32- 36 F5.2 [Sun] b_[Z/H] SSP minimum [Z/H]
38- 42 F5.2 [Sun] B_[Z/H] SSP maximum [Z/H]
44- 48 F5.2 [Sun] [alpha/Fe] SSP [alpha/Fe]
50- 54 F5.2 [Sun] b_[alpha/Fe] SSP minimum [alpha/Fe]
56- 60 F5.2 [Sun] B_[alpha/Fe] SSP maximum [alpha/Fe]
62- 64 F3.1 Msun/Lsun M/LV SSP M/LV
66- 68 F3.1 Msun/Lsun b_M/LV SSP minimum M/LV
70- 72 F3.1 Msun/Lsun B_M/LV SSP maximum M/LV
74- 76 F3.1 Msun/Lsun ML/V80 SSP M/LV at Age80%
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Acknowledgements:
Roberto Saglia, saglia(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 31-Jul-2018