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The RR Lyrae projected density distribution from the Galactic centre to the halo
Ist Teil von
Astronomy and astrophysics (Berlin), 2021-02, Vol.646, p.A45
Ort / Verlag
Heidelberg: EDP Sciences
Erscheinungsjahr
2021
Link zum Volltext
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
The projected density distribution of type ab RR Lyrae (RRab) stars was characterised from the innermost regions of the Milky Way to the halo, with the aim of placing constraints on the Galaxy’s evolution. The compiled sample (
N
RRab
= 64 850) stems from fundamental mode RR Lyrae variables identified by the VVV, OGLE, and
Gaia
surveys. The distribution is well fitted by three power laws over three radial intervals. In the innermost region (
R
< 2.2°) the distribution follows Σ
RRab[1]
∝
R
−0.94 ± 0.051
, while in the external region the distribution adheres to Σ
RRab[2]
∝
R
−1.50 ± 0.019
for 2.2° <
R
< 8.0° and Σ
RRab[3]
∝
R
−2.43 ± 0.043
for 8.0° <
R
< 30.0°. Conversely, the cumulative distribution of red clump (RC) giants exhibits a more concentrated distribution in the mean, but in the central
R
< 2.2° the RRab population is more peaked, whereas globular clusters (GCs) follow a density power law (Σ
GCs
∝
R
−1.59 ± 0.060
for
R
< 30.0°) similar to that of RRab stars, especially when considering a more metal-poor subsample ([Fe/H] < −1.1 dex). The main conclusion emerging from the analysis is that the RRab distribution favours the star cluster infall and merger scenario for creating an important fraction (> 18%) of the central Galactic region. The radii containing half of the populations (half populations radii) are
R
H RRab
= 6.8° (0.99 kpc),
R
H RC
= 4.2° (0.61 kpc), and
R
H GCs
= 11.9° (1.75 kpc) for the RRab stars, RC giants, and GCs, respectively. Finally, merely ∼1% of the stars have been actually discovered in the innermost region (
R
< 35 pc) out of the expected (based on our considerations) total number of RRab therein:
N
∼ 1562. That deficit will be substantially ameliorated with future space missions like the
Nancy Grace Roman
Space Telescope (formerly WFIRST).