M51 bridge - the real one

[Ivan Maly]

I have been interested in this feature for some time and last night was able to see it for the first time: the real bridge in the M51 system. The members here know that the northern arm, extending in projection to the position of the companion (what you hear announced as "the bridge" on warm summer nights on the observing field), in reality passes far in front of it. The real tidal tail starts in the S on the periphery of the main component and, appearing somewhat like a continuation of the southern arm, passes to the E and behind the main component, eventually passing more or less through the companion. (According to figure 21 in Toomre and Toomre, ApJ 1972 - http://adsabs.harvard.edu/abs/1972ApJ...178..623T, also reproduced in Kanipe and Webb's Arp atlas book.)

m51 bridge.jpg

Here I stretched and marked the SDSS image (note that this is based on a JPEG - the FITS may have more in it) to show two of the segments that were visible last night (20" F/4, 13 mm Ethos, SQM 21.88). Note that the S segment is photographically distinct from the end of the arm, but not connected to the bridge (arrow) in the Toomre schematic. Visually, I had a feeling that the "elbow" area of the bridge was also enhanced (like a third segment), and that there was a continuous edge on the E side, these could be illusory, unlike the two segments that are marked. Overall the feature was very plain visually and visible immediately, when I was not actually thinking about the bridge but only wanted to have a quick look while I was in the area.

[roragi]

An interesting report Ivan, thanks for showing. A changed scope? I think I remember that I had a 16''

Roberto.

[Ivan Maly]

Thanks! Yes, busy re-observing favorites with the transportable 20 I got more than a year ago. Incidentally, I have looked at M51 a couple times since this report and the view was nowhere near that clarity. The entire galaxy looked almost painfully bright on black background on that night in March.