Near-IR photometry of disk galaxies: Search for nuclear isophotal twist and double bars

¹ DEMIRM, Observatoire de Paris, 61 Avenue de l'Observatoire, 75 014 Paris, France
² Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague 4, Czech Republic
³ ESA secondment, Space Telescope Science Institute, Baltimore, MD 21218, U.S.A.

Send offprint request to: B. Jungwiert

Received: 16 December 1996
Accepted: 21 January 1997

Abstract

We present a near-IR, mainly H band, photometry of 72 nearby ( Mpc) disk galaxies. The main goal of the survey was to search for isophotal twist inside their nuclear regions. As the twist can be due in some cases to projection effects, rather than resulting from a dynamical phenomenon, we deproject – under the simplifying assumption of a 2D geometry – all galaxies whose disk position angle and inclination are known, the latter not exceeding . We show the ellipticity, position angle and surface brightness radial profiles, and discuss how a projection of 2D and 3D bars can distort the isophotes, give an illusion of a non-existing double bar or mask a real one. We report 15 new double-barred galaxies and confirm 2 detected previously. We identify 14 additional twists not known before and we also find nuclear triaxial structures in three SA galaxies. The frequency of Seyferts among galaxies with nuclear bars or twists is high. Since these observations are part of a larger survey, the interpretation of the results will be given in a future paper, as soon as the number of objects grows enough to permit meaningful statistics. As a secondary product, we publish structural parameters (length and axis ratio) of large-scale bars in order to extend still scarce data on bars in the near-IR.