NGC 5774 & 5775

A Bridge Too Far?

For 6-inch or larger telescopes

This pair of apparently interacting galaxies make for a wonderful view, particularly in larger telescopes. NGC 5774 (Uppsala 9576, MCG 1-38-13, PGC 53231) is a face-on spiral galaxy. It is listed as 12.8 magnitude, subtends 3.2' x 2.5' and has a mean surface brightness of 23.8 mag/arc-sec2.

NGC 5775 (Uppsala 9579, MCG 1-38-14, PGC 53247) is nearly identical, but seen edge-on. It is listed as 12.3 magnitude, subtends 3.8' x 1.1' and has a mean surface brightness of 22.9 mag/arc-sec2, making it the brighter and easier target of the two.

Both galaxies lie at the same distance; about 70 million light years. Observations of hydrogen gas (HI) indicate apparent bridges of matter between the two galaxies, which may be in the early stages of merging. These galaxies are part of a small group which includes the nearby IC 1067, IC 1068 and NGC 5770.

This color image was created by combining red and blue second generation DSS images. NGC 5774 is on the lower left; NGC 5775 is on the right. North is down and east is to the right.
In scopes less than 16 inches the edge-on galaxy NGC 5775 is the more obvious. In 6 to 8-inch scopes seeing the face-on NGC 5774 may be a challenge. Dark skies are a must. look for the bright core.

This is the view of the field in a 6-inch at 50x.
I read of this pair recently in the AmAstro list archives. In 1999 Rich Jakiel posted an observation of a luminous bridge connecting the galaxies. Using a 24-inch f/4.5 telescope at 305x he and others observed a "broad, very low contrast arc looping along the northeastern perimeter of the pair."

Inspired, I observed this pair twice with my 18-inch Dob in May 2000. Here are my notes from May 24:

This galaxy forms a pair with NGC 5775. NGC 5774 appears as a round ball with a brighter core, extending out about 25%.

NGC 5774 is a nice edge-on spiral with a small, bright center. The NE edge is considerably sharper than the SW, probably indicating a dark lane.

I thought I could see a very faint, fairly wide haze that extends outward from NGC 5774 to the NE, arcing toward its neighbor. It appears to go through a nearby star. I wasn't able to make this "bridge" out all the way to the other galaxy.

On May 26:
This night was better than the last. Again I had the impression of a bridge, but this time I knew exactly where to look. This time the bridge impression seemed to stretch to the end of the edge-on galaxy.

I was led to wonder if this bridge may actually be an optical illusion; the eye may be stretching the nebulosity to engulf the nearby star or even detecting the galaxy superimposed on a faint star halo (these halos were not strongly visible this night but they were there). The other end of the bridge could simply be the long extension of the end of the edge-on galaxy.

NGC 5775 had an interesting appearance in the 4.8mm with a 2X barlow (851x). I could see what appeared as faint stars embedded near the center. The core appeared much less obvious.

Above is the blue image from the DSS processed to show the apparent bridges between the two galaxies.
It seems to defy credibility to claim that a feature can be observed in an 18-inch scope that is only just visible on the POSS using extreme image processing techniques! Nevertheless, given my own observations and that of Rich Jakiel I feel that on balance we really did see this feature. Why this feature doesn't show up better on the POSS remains a mystery to me.

I would be very interested in hearing other reports of these galaxies.
 

Millennium Star Atlas Vol II Chart 742
Sky Atlas 2000 Chart 14
Uranometria 2000 Vol I&II Chart 243
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