NGC 4725 is a large intermediate barred spiral galaxy, presenting to us at a 46 degree angle, located near another large galaxy (not in the frame); the tidal forces from the gravitational interactions between these massive galaxies has resulted in NGC 4725 being distorted. NGC 4725 is estimated to be about 40 million light years away from us; at that distance, it is well over 100,000 light years in diameter (similar in size to our Milky Way, itself a large galaxy).

The smaller galaxy below and to the left of NGC 4725 is NGC 4712, which is five times as far away from us as NGC 4725; it is just in the same line-of-sight, but not related to NGC 4725 in any way.

Two distinctive features of NGC 3628 (in addition to its odd shape) are (i) the ring structure surrounding the central bar, in which much star formation is occurring (the pinkish regions are particularly large, intense star-forming regions), and (ii) the fact that it seems only to have a single spiral arm.

As usual in a deep-sky image, there are a lot of small (meaning distant) galaxies in the uncropped versions of the image (look for the oblong and/or fuzzy "stars").

Technical Information:

Ha:L:R:G:B: 440:1150:195:180:240 (a total of almost 37 hours of light-frame exposure time); luminance was a blend of 30-minute images and 10-minute images through the luminance filter; red and green exposures were all 15-minute exposures; blue all 20-minute exposures. The red channel has the Ha data (an integration of twenty-two 20-minute images) woven into it. After discovering that my mirror looked like it had been on the wrong end of a mudslide, I cleaned it and re-took the luminance images (and did not use any of the earlier luminance data).

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.

Processing: All images calibrated (darks, bias and sky flats), aligned and combined in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, deconvolution, multiscale linear transform, HDR multiscale transform, Ha blending, and noise reduction) done in Pixinsight; some cleanup finish work was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights in March, April and May of 2022. Image posted June 30, 2022.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally very good; luminance images varied in FWHM from 1.7 to 2.2 arcseconds.

CCD Chip temperature: -25C

Copyright 2022 Mark de Regt

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