Further Evidence for Gas Streams in Barred Spirals: NGC 4027 and NGC 7741.
Abstract
67, 113, 270,1962) of large-scale departures from circular motions in NGC 4631, a late-type barred spiral of the Magellanic-type seen edgewise. In order to place the interpretation of the rotation curve and the reality of gas streaming in bars beyond doubt it was necessary to find typical SB (s)d and SB (s)m systems meeting the following conditions: (a) the inclination angle is such that the spiral structure is immediately in evidence (i ~ 600), but not so small that departures from circular motion will have negligible line-of-sight components, and (b) the bar is in the plane of vision, i.e.,is along the minor axis of the projected image, so that the rotational velocity will have no component on the line of sight and any line shift observed will directly reflect departures from circular motions. Two systems meeting these rather strict requirements, NGC 4027 and 7741, have been found; they were observed recently with the prime-focus spectrograph of the 82-inch telescope at McDonald Observatory. Measurements of the N6563 (Ha) and X6584 EN ~~J emission lines in spectrograms taken with the slit placed along the bars are presented; in both galaxies the lines are conspicuously inclined and the geometric relationships are such the tilt corresponds to stream velocities of the order of +50 to 100 km/sec directed along the bar and away from the center. This direct evidence supports the results previously derived from the analysis of NGC 4631.
- Publication:
-
The Astronomical Journal
- Pub Date:
- June 1963
- DOI:
- 10.1086/108958
- Bibcode:
- 1963AJ.....68..278D