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Issue A&A
Volume 390, Number 3, August II 2002
Page(s) L35 - L38
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20020961



A&A 390, L35-L38 (2002)
DOI: 10.1051/0004-6361:20020961

Letter

Origin of radially increasing stellar scaleheight in a galactic disk

C. A. Narayan and C. J. Jog

Department of Physics, Indian Institute of Science, Bangalore 560 012, India
    e-mail: cjjog@physics.iisc.ernet.in

(Received 29 April 2002 / Accepted 26 June 2002)

Abstract
For the past twenty years, it has been accepted that the vertical scaleheight of the stellar disk in spiral galaxies is constant with radius. However, there is no clear physical explanation for this in the literature. Here we calculate the vertical stellar scaleheight for a self-gravitating stellar disk including the additional gravitational force of the HI and H 2 gas and the dark matter halo. We apply our model to two edge-on galaxies, NGC 891 and NGC 4565, and find that the resulting scaleheight shows a linear increase of nearly a factor of two within the optical disk for both these galaxies. Interestingly, we show that the observed data when looked at closely, do not imply a constant scaleheight but actually support this moderate flaring in scaleheight.


Key words: galaxies: fundamental parameters -- galaxies: individual: NGC 891, NGC 4565 -- galaxies: kinematics and dynamics -- galaxies: photometry -- galaxies: spiral -- galaxies: structure

Offprint request: C. A. Narayan, chaitra@physics.iisc.ernet.in

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© ESO 2002


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