Flare in the Galactic stellar outer disc detected in SDSS-SEGUE data

López-Corredoira, M.; Molgó, J.
Bibliographical reference

Astronomy and Astrophysics, Volume 567, id.A106, 8 pp.

Advertised on:
7
2014
Number of authors
2
IAC number of authors
1
Citations
71
Refereed citations
68
Description
Aims: We explore the outer Galactic disc up to a Galactocentric distance of ≈30 kpc to derive its parameters and measure the magnitude of its flare. Methods: We obtained the 3D density of stars of type F8V-G5V with a colour selection from extinction-corrected photometric data of the Sloan Digital Sky Survey - Sloan Extension for Galactic Understanding and Exploration (SDSS-SEGUE) over 1400 deg2 in off-plane low Galactic latitude regions and fitted it to a model of flared thin+thick disc. Results: The best-fit parameters are a thin-disc scale length of 2.0 kpc, a thin-disc scale height at solar Galactocentric distance of 0.24 kpc, a thick-disc scale length of 2.5 kpc, and a thick-disc scale height at solar Galactocentric distance of 0.71 kpc. We derive a flaring in both discs that causes the scale height of the average disc to be multiplied with respect to the solar neighbourhood value by a factor of 3.3+2.2-1.6 at R = 15 kpc and by a factor of 12+20-7 at R = 25 kpc. Conclusions: The flare is quite prominent at large R and its presence explains the apparent depletion of in-plane stars that are often confused with a cut-off at R ≳ 15 kpc. Indeed, our Galactic disc does not present a truncation or abrupt fall-off there, but the stars are spread in off-plane regions, even at z of several kpc for R ≳ 20 kpc. Moreover, the smoothness of the observed stellar distribution also suggests that there is a continuous structure and not a combination of a Galactic disc plus some other substructure or extragalactic component: the hypothesis to interpret the Monoceros ring in terms of a tidal stream of a putative accreted dwarf galaxy is not only unnecessary because the observed flare explains the overdensity in the Monoceros ring observed in SDSS fields, but it appears to be inappropriate.
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Morphology and dynamics of the Milky Way
This project consists of two parts, each differentiated but both complementary: morphology and dynamics. Detailed study of the morphology of the Milky Way pretends to provide a data base for the stellar distribution in the most remote and heavily obscured regions of our Galaxy, through the development of semiempirical models based on the
Martín
López Corredoira