Arp 239 is the catalog number for these two interacting galaxies. The larger of the two is also cataloged as NGC 4490, a barred spiral galaxy; the smaller is NGC 4485. The odd shape is the result of gravitational interactions between the two; the pink regions are regions of intense star formation, a common result of significant gravitational interaction between galaxies. The two galaxies probably are in the extended process of spiraling toward a merger, having recently (in cosmic terms; millions of years ago) made a close pass, and are now separating, before being pulled together again. A result of this is that NGC 4490 retains very little of its spiral structure (NGC 4485 still shows some spiral structure, even in this image) Arp 269 is thought to be about 25 million light years from us; at that distance, NGC 4490 has a diameter of about 53,000 light years (almost half of that of our Milky Way galaxy). The dominant blue color is from the energetic, young stars being formed at a high rate.

It is interesting to note the bridge of stars between the two galaxies, which includes a lot of gas and some pink star-forming regions. This bridge is about 25,000 light years long, and likely is the result either of the smaller galaxy passing through the larger galaxy in the recent past, or coming so close that the greater gravity of the larger galaxy is stealing matter from the smaller galaxy.

As usual, there are a lot of background galaxies in the uncropped versions of this photo.

The entire field of the uncropped version is about the same width as a full moon.

Technical Information:

(HaL)(HaR)GB: 460:600:195:180:195 (a total of over 27 hours of exposures); luminance layer consists of a blend of 36 fifteen-minute images through a luminance filter, 20 three-minute images throught the luminance filter, and 23 twenty-minute images through an Ha filter; R channel is a blend of 13 fifteen-minute images taken through a red filter, and the Ha data; G consists of 12 fifteen-minute images taken through a green filter, while B is the combination of 13 twenty-minute images taken through a blue filter.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 with internal filter wheel (SBIG filter set), guided by an SBIG AO-X/STX Guider, 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, Noise XTerminator and Blur XTerminator, gradient removal; blending in the Ha data) done in Pixinsight; some finish work (LRGB combination, contrast and saturation adjustment) was done in Photoshop CC.

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

Date: Images taken on many nights in April and May of 2024. Image posted October 30, 2024.

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

Seeing: Generally good; but lost a lot of data to bad weather conditions

CCD Chip temperature: -25C

Copyright 2024 Mark de Regt

Hit Counter