Journal Article

The structure of spiral galaxies — I. Near-infrared properties of bulges, discs and bars

M. S. Seigar and P. A. James

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 299, issue 3, pages 672-684
Published in print September 1998 | ISSN: 0035-8711
Published online September 1998 | e-ISSN: 1365-2966 | DOI:
The structure of spiral galaxies — I. Near-infrared properties of bulges, discs and bars

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We present data for a sample of 45 spiral galaxies over a range of Hubble types, imaged in the near-IR JK bands. Parameters are calculated describing the bulge, disc and bar K-band light distributions, and we look for correlations showing the interrelation between these components.

We find that bulge profiles are not well-fitted by the classic de Vaucouleurs profile, and that exponential or R1/2 fits are preferred. The bulge-to-disc ratio correlates only weakly with Hubble type. Many of the galaxies show central reddening of their JK colours, which we interpret as due to nuclear starbursts or dusty AGN.

We define a new method for measuring the strength of bars, which we call ‘equivalent angle’. We stress that this is better than the traditional bar—interbar contrast, as it is not subject to seeing and resolution effects.

Bars are found in 40 of the 45 galaxies, nine of which had been previously classified as unbarred. Bar strengths are found not to correlate with disc surface brightness or the presence of near neighbours, but a tendency is found for the most strongly barred galaxies to lie within a restricted, intermediate range of bulge-to-disc ratio. Bar light profiles are found to be either flat or exponentially decreasing along their long axes, with profile type not correlating strongly with Hubble type. Bar short axis profiles are significantly asymmetric, with the steeper profile being generally on the leading edge, assuming trailing arms. In the K band we find bars with higher axial ratios than have been found previously in optical studies.

Keywords: galaxies: fundamental parameters; galaxies: spiral; galaxies: structure; infrared: galaxies

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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