Journal Article

Bulge–disc decompositions and structural bimodality of Ursa Major cluster spiral galaxies

Michael McDonald, Stéphane Courteau and R. Brent Tully

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 2, pages 628-640
Published in print February 2009 | ISSN: 0035-8711
Published online February 2009 | e-ISSN: 1365-2966 | DOI:
Bulge–disc decompositions and structural bimodality of Ursa Major cluster spiral galaxies

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We present bulge and disc (B/D) decompositions of existing K′ surface brightness profiles for 65 Ursa Major (UMa) cluster spiral galaxies. This improves upon the disc-only fits of Tully et al. The 1996 disc fits were used by Tully & Verheijen for their discovery of the bimodality of structural parameters in the UMa cluster galaxies. It is shown that our new one-dimensional B/D decompositions yield disc structural parameters that differ only slightly from the basic fits of Tully et al. and evidence for structural bimodality of UMa galaxies is maintained. Our B/D software for the decomposition of one-dimensional surface brightness profiles of galaxies uses a non-linear minimization scheme to recover the best-fitting Sérsic bulge and the exponential disc while accounting for the possible presence of a compact nucleus and spiral arms and for the effects of seeing and disc truncations. In agreement with Tully & Verheijen, we find that the distribution of near-infrared disc central surface brightnesses is bimodal with an F-test confidence of 80 per cent. There is also strong evidence for a local minimum in the luminosity function at . A connection between the brightness bimodality and a dynamical bimodality, based on new H i linewidths, is identified. The B/D parameters are presented in Table 1.

Table 1

B/D parameters.

(1) PGC(2) T(3) KT(4) b/a(5) B/T(6) C28(7) (8) (9) (10) (11) (12) (13) (14) 34971Sm11.220.310.002.9721.4731.8120.4738.3217.9835202Sd11.360.980.052.3020.9419.2021.5330.9920.778.560.3017.4235676SBc7.830.580.031.9319.8173.6519.3776.9717.445.870.6014.7735711SBa8.640.560.032.7818.7932.2218.4835.5117.523.750.4014.3135999SBb9.130.330.002.9118.8324.6217.9429.0615.4436136SBcd10.770.370.002.4420.0120.5619.0523.3221.9236343Scd11.

Notes. Column (1) PGC number, (2) morphology from the NED, (3) total K′ magnitude, (4) ratio of the minor-to-major axis diameters, (5) ratio of the B/T luminosity, (6) Galaxy concentration, defined as C28= 5 log (r80/r20), where r20 and r80 are radii enclosing 20 and 80 per cent of the total light, respectively, (7) effective surface brightness, defined as the surface brightness at the galaxy half-light radius, (8) effective radius within which half of the total galaxy light is enclosed, (9) effective surface brightness of the disc, (10) half-light radius of the disc, (11) effective surface brightness of the bulge, (12) half-light radius of the bulge, (13) the Sérsic parameter for the bulge and (14) surface brightness of the galaxy nucleus.

Keywords: galaxies: clusters: general; galaxies: evolution; galaxies: formation; galaxies: luminosity function, mass function; galaxies: statistics; galaxies: structure

Journal Article.  7630 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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