About the Objects

The Leo Triplet is named after the three prominent spiral galaxies located in the constellation Leo, the lion, visible in this one and a half degree field of view. Even though all three galaxies are spirals, they look very different primarily because of their orientations; they are tilted at very different angles with respect to Earth. NGC 3628, also known as the Hamburger Galaxy, is on the right side of the picture, and is perhaps the best known of the three due to the prominent dust lanes running through the disk of the galaxy. A less well known feature is the tidal tail extending up to the top of this image. This tail consists of stars and gas that have been stripped out of NGC 3628 by a close gravitational interaction, perhaps with M66 on the top left of the image. When galaxies interact, the parts of the galaxies that are close to each other will experience different gravitational forces than the parts of the galaxies that are far apart. This difference in force, combined with the rotation of the galaxies and direction of travel, can distort spiral arms and strip material out of one or more of the interacting galaxies. NGC 3628's tidal tail extends nearly 300,000 light years, and you can also see the distortion in the spiral arms of M66. 

The three main galaxies in this image lie at a distance of approximately 35 million years, though there are many more distant galaxies lurking in the background of the field of view. The single most distant object I was able to identify in the picture is a Quasar cataloged as SDSSJ112006.5+135559.1 located a bit to the right of NGC 3628. You can find it in the annotated image provided if you look carefully, though it's just a tiny black dot. The z=4.06 value corresponds to a loopback time of 11.6 billion years ago (assuming H0 of 74, Omega-matter 0.27, and Omega-lambda 0.73, flat universe). It has an apparent magnitude of 21.9.

About the Image

The data were captured using NINA and all processing up to L/RGB merging were performed in PixInsight. Color and luminance combination was performed in Photoshop as were soft light local contrast enhancement and saturation adjustment. Processing steps included:

- Calibration using darks, flat-darks, and flats
- Registration of frames that had been dithered to reduce the effects of pattern noise
- Cosmetic correction (statistical removal of hot pixels typically caused by cosmic rays and   radioactive iodine in camera/telescope glass)
- Subframe selector to cull bad data
- Normalized Scale Gradient to weight frames based on SNR and to match and simplify gradients
- Integration with error rejection (averaging the frames together to improve SNR and dynamic range)
- Noise reduction using TGV Denoise and MMT (technique described in detail by Jon Rista on his web page)
- Very slight deconvolution to recover some of the micro-contrast lost in noise reduction
- Stretching
- HDRMT to lower peak brightness in the galaxies in an effort to avoid washed out colors
- RGB combination
- Soft light contrast adjustment on the luminance frame in Photoshop to improve visibility of details in the galaxy cores
- Crop from 3:2 aspect ratio to 4:3