Kinematic modeling of disk galaxies-III. The warped “Spindle” NGC 2685

GIG J�zsa, TA Oosterloo, R Morganti, U Klein…�- Astronomy &�…, 2009 - aanda.org
GIG J�zsa, TA Oosterloo, R Morganti, U Klein, T Erben
Astronomy & Astrophysics, 2009aanda.org
This is the third of a series of papers in which the structure and kinematics of disk galaxies is
studied. By employing direct tilted-ring fits to the data cube as introduced in Paper I, we
analyzed the “Spindle” galaxy NGC 2685, previously regarded as a two-ringed polar ring
galaxy. Deep HI and optical (i'-band) observations are presented. The HI observations
strongly suggest that the gaseous structure of NGC 2685 does not consist of two separate
mutually inclined regions, but forms a coherent, extremely warped disk, the appearance of�…
This is the third of a series of papers in which the structure and kinematics of disk galaxies is studied. By employing direct tilted-ring fits to the data cube as introduced in Paper�I, we analyzed the “Spindle” galaxy NGC�2685, previously regarded as a two-ringed polar ring galaxy.
Deep H�I and optical (i'-band) observations are presented. The H�I observations strongly suggest that the gaseous structure of NGC�2685 does not consist of two separate mutually inclined regions, but forms a coherent, extremely warped disk, the appearance of two rings being due to projection effects. By comparing the H�I total-intensity maps with the optical image, we demonstrate that at large radii a faint stellar disk is well aligned with the outer H�I disk. The shape of the dust lanes obscuring the NE part of the inner stellar body indicates that, also at smaller radii, NGC�2685 possesses a disk containing gas, dust, and stars in which the various constituents are aligned.
At smaller radii, this disk is kinematically decoupled from the central stellar body; hence, in the region of the bright, central stellar body, NGC�2685 appears to consist of two disks that share a common center, but have different orientation: a bright stellar lenticular body apparently devoid of dust and gas, and a heavily warped low-surface brightness disk containing stars, gas, and dust. The low-surface-brightness disk changes its orientation gradually and at large radii assumes the orientation of the central stellar S0 disk. Since, according to our analysis, the intrinsic orientation of the low-surface-brightness disk changes through 70�, the gaseous disk is coherent, and is at no radius oriented perpendicularly with respect to the central stellar body, NGC�2685 is not likely to be a classical polar-ring galaxy.
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