NGC 5754 - Arp 297

Object: NGC 5752-55 galaxies in Bootes, also known as Arp 297 which is classified as "Double galaxies with long filaments".

In the bright pair NGC 5752/4 we are seeing the remnants of a weak encounter, well past closest approach, which occurred about 250 million years ago. [Ref. 1] The kink in the spiral arm on the North side of NGC 5754 also marked by a bright knot in my image, is where according to a n-body simulation, the interloper galaxy NGC 5752 passed through the disk of the much larger spiral. The difference in mass between the two galaxies is estimated to be a factor of 5 to 10. From our perspective the parabolic orbit started from behind NGC5754 and from the south-west (dark green line in figure below). After doing an about turn, NGC 5752 is now headed south-west on the other side of the nucleus and is in front of NGC 5754 (bright green line). The long tidal tail extending to the west is about 275 kly long. The stars and dust in the tail are presumably material stripped out of NGC 5752 during closest approach and left behind as the pair traverse the universe. Our own galaxy is moving ~300 km/sec with respect to our local group. At a comparable velocity the length of the tail implies an interaction time of about 300 Myr, which is inline with the duration of the n-body simulation.

The northern pair of galaxies NGC 5755/53 are much further away than the brighter pair and do not seem to be interacting at this time, although the very different sizes of NGC 5755 two spiral arms of suggests a previous close encounter.

Data for the brightest 4 galaxies in the field:
NGC 5754 13.1m 2.0' x 1.8', type SB(rs)b, distance 64 Mpc (~209 Mly)
NGC 5752 14.1m 0.5' x 0.2', type unknown, distance 64 Mpc
NGC 5755 13.5m 1.3' x 1.0', type SBd, distance 134 Mpc
NGC 5753 15.0m 0.6' x 0.5', type unknown, distance 134 Mpc
Image FOV: 15.6' x 15.6' which at a distance of 64 Mpc corresponds to about 1 x 1 Mly (from an inferred 316 parsec/arcsec scale)

Calibration: 15 bias, 32 darks and 5 tshirt flats
Subimages: 12 x 600 sec (2 hrs) SD Mask combine (linear normalization). Input FWHM 3.80.4", flatness 0.050.03
Scope: C11XLT with C6.3FR, EFL=1586mm (f/5.7 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST8XME (1.17"/pixel) set to -25C oriented at 0d04' (N up, E left)
Guiding: Self-guide, exposure time 1 sec.
Acquisition and Processing: MaxIm DL/CCD v4.5
Imaged on: May 13, 2007

Processing Log:
Flatten Bgd: Complex with 148 points, still some donut artifacts visible at high stretch.
Remove Bloom: auto setting, 5 stars, very good job.
Filter: Kernel LowPass with Pixel range: 0-1975, reduce=2, feather=5.
DDP: Bgd=1938, Mid=2130, no filter
Clone used 5 brightest stars from Kernel LowPassMore filtered version
Edit Pixels around bottom of three bright stars
Crop: removed left side due to non-overlap combine
Crop: again, from offset 105,145 to square 800,800
Curves: to enhance faint extension, medium convex

Below is an image taken with the Hale 200-inch in the I band (wavelength ~ 800 nm) clearly showing the extremely long tidal tail from NGC 5752.

Reference 1: Massive Star Clusters in Ongoing Galaxy Interactions: Clues to Cluster Formation
by Keel, William C.; Borne, Kirk D. printed in The Astronomical Journal, Volume 126, Issue 3, pp. 1257-1275.