We present our spectroscopic observations of the galaxy NGC 7468 performed at the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit spectrograph, the multipupil fiber spectrograph MPFS, and the scanning Fabry-Perot interferometer (IF

Shalyapina et al.:NGC7468:a galaxy with an inner polar disk

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Fig.6.(a)Rotation curves.1:the resulting curve;2:for the disk component;3:for the halo;4:our data;5:the data from Richter et al.(1990).(b)The change in the location of the dynamic axis with radius.

of the galaxy’s outer disk.The model describes the obser-vations satisfactorily,except for the region near condensa-tion“a”,where large residual velocities(∼50km s−1)are observed.We found no rotation around the major axis in the stellar velocityfield.Therefore,we conclude that the stars and the gas in the galaxy’s central region belong to different kinematic systems.

DISCUSSION

As was noted in the Introduction,the putative polar ring manifests itself in the galaxy’s images as lobes on its northern and southern sides.However,analysis of the ve-locityfield that we constructed from the IFP data and the velocityfield derived from neutral hydrogen(Taylor et al. 1994)shows no peculiar features near these lobes.The gas in these regions is involved in the rotation of the galactic disk around the minor axis.Here,there is no kinematically decoupled subsystem characteristic of polar rings,which forces us to reject the assumption that NGC7468is a galaxy with an outer polar ring.The nature of the lobes and the brightening in the south is not quite clear.If we assume,following Taylor et al.(1993),that the galaxy to the north of NGC7468is spatially close to it(according to this paper,the difference between their line-of-sight veloc-ities is73km s−1),then these may be considered as tidal structures,as may be evidenced by the deviations of the observed velocities from the circular ones in the region of the brightening(by40km s−1)and in the region of the southern lobe(by approximately20km s−1).On the other hand,these may be weakly developed spiral arms.Their appearance and the color bluer than that for the remain-ing parts of the galaxy(Cairos et al.2001b)can serve as evidence for this interpretation.

At the same time,we found a kinematically decoupled gaseous subsystem,a rotating inner disk,in the central part of NGC7468(∼1.5kpc in diameter).The angle between the galactic disk and the plane of the inner disk is 86◦.Thus,we can assert that the galaxy has an inner polar disk(possibly,a ring)rather than a bar whose presence was used to explain some of the features in the velocity field constructed from the HI data(Taylor et al.1994).

According to current views(Bournaud and Combes 2003),a polar structure in a galaxy can be formed either through accretion from a neighboring gas-rich galaxy dur-ing their close interaction or through the direct collision of galaxies,which can lead to the complete absorption of the less massive participant of the collision by the more massive galaxy.At the observed orientation of the inner disk,the position of the northern galaxy does not permit us to consider it a donor galaxy.Thus,we conclude that NGC7468collided with a low-mass gas-rich galaxy that was absorbed.As a result,a metal-poor polar gaseous disk was formed,and the observed induced star formation be-gan in the central region of the galaxy(in a ring with a radius of∼1.2kpc).The individual condensations in this ring are spaced0.5−1kpc apart.Such distances are ob-served between neighboring gas-dust clouds.The sizes of the condensations do not exceed500pc,in agreement with the sizes of stellar associations and stellar complexes.The intensity ratio of the emission lines suggests the photoion-ization mechanism of the emission in these regions.

Note also that the difference between the relative brightnesses of the condensations in the continuum and in the emission lines may be due to the age difference be-tween these star-forming regions.Condensation“c”,being relatively brighter in the continuum,may be an older stel-lar complex at a stage when the surrounding gas had al-ready been partially swept up to large distances by strong light pressure light and/or supernova explosions.

CONCLUSIONS

Below,we summarize our results.

(1)Based on the long-slit spectra near Hα,we found a kinematically decoupled gaseous subsystem in the central region rotating around the galaxy’s major axis.

(2)Our analysis of the line-of-sight velocity elds ob-tained using two-dimensional spectroscopy confirmed the existence of two kinematic subsystems of ionized gas:one of these is the gaseous disk of the galaxy,and the other is an inner disk1.5kpc in size.The angle between the planes of the disks is86◦;i.e.,the inner disk is polar.In