INFORMATION ON THE MILKY WAY FROM THE TWO MICRON ALL SKY SURVEY WHOLE SKY STAR COUNT: THE STRUCTURE PARAMETERS

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/50875

Title:	INFORMATION ON THE MILKY WAY FROM THE TWO MICRON ALL SKY SURVEY WHOLE SKY STAR COUNT: THE STRUCTURE PARAMETERS
Authors:	Chang,CK;Ko,CM;Peng,TH
Contributors:	天文研究所
Keywords:	GALACTIC MODEL PARAMETERS;PHOTOMETRIC SPACE DENSITIES;LUMINOSITY FUNCTION;FAINT STARS;THICK DISC;METALLICITY DISTRIBUTION;TRIANGULUM-ANDROMEDA;STELLAR POPULATIONS;HIGH-LATITUDES;DWARF GALAXY
Date:	2011
Issue Date:	2012-03-27 18:11:55 (UTC+8)
Publisher:	國立中央大學
Abstract:	The K(s)-band differential star count of the Two Micron All Sky Survey (2MASS) is used to derive the global structure parameters of the smooth components of the Milky Way. To avoid complication introduced by other fine structures and significant extinction near and at the Galactic plane, we only consider Galactic latitude vertical bar b vertical bar > 30 degrees data. The star count data are fitted with a three-component model: double exponential thin disk and thick disk, and a power-law decay oblate halo. Using maximum likelihood, the best-fit local density of the thin disk is n(0) = 0.030 +/- 0.002 stars pc(-3). The best-fit scale height and length of the thin disk are H(z1) = 360 +/- 10 pc and H(r1) = 3.7 +/- 1.0 kpc, and those of the thick disk are H(z2) = 1020 +/- 30 pc and H(r2) = 5.0 +/- 1.0 kpc, the local thick-to-thin disk density ratio is f(2) = 7% +/- 1%. The best-fit axis ratio, power-law index, and local density ratio of the oblate halo are kappa = 0.55 +/- 0.15, p = 2.6 +/- 0.6, and f(h) = 0.20% +/- 0.10%, respectively. Moreover, we find some degeneracy among the key parameters (e.g., n(0), H(z1), f(2), and H(z2)). Any pair of these parameters are anti-correlated to each other. The 2MASS data can be well fitted by several possible combinations of these parameters. This is probably the reason why there is a wide range of values for the structure parameters in literature similar to this study. Since only medium and high Galactic latitude data are analyzed, the fitting is insensitive to the scale lengths of the disks.
Relation:	ASTROPHYSICAL JOURNAL
Appears in Collections:	[Graduate Institute of Astronomy] journal & Dissertation

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