Coma Galaxy Cluster
May 22, 2017
The Coma Galaxy Cluster lies in Coma Berenices. The galaxy cluster is mainly in the centre of the image, and hundreds of galaxies are visible (you can see the annotated image but it may not help much since there are so many). There are at leas 1,000 galaxies in this cluster, with an average distance of about 330 million light years. The two large elliptical galaxies in the centre are NGC4874 and NGC4889. They are both very large galaxies, and are referred to as “supergiant elliptical galaxies.”
Moravian G3-16200 EC camera (on loan from O’Telescope), Optolong R, G and B filters, Takahashi FSQ-106 ED IV at f/3.6, Paramount MX. Acquisition with the SkyX unguided. Focused with FocusMax. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. No moon, average transparency and seeing.
31x5m R, 29x5m G and 30m B, unbinned frames (total=7hr30m).
Creation and cleanup: The BatchPreProcessing script was used to perform calibration, cosmetic correction and registration of all frames. DrizzleIntegration was used to make the channel masters. The R, G and B masters were cropped and processed separately with DBE, and then combined to make an RGB image which was processed with ColorCalibration.
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the RGB image. Layer settings for threshold and strength: Layer 1: 5, 1.0 Layer 2: 3.5, 0.84 Layer 3: 2.5, 0.71 Layer 4: 1.0, 0.55 Layer 5: 1.5, 0.28 Layer 6: 1.0, 0.16.
Stretching: HistogramTransformation was applied to the RGB image to make a pleasing, bright image.
Creation and cleanup of SynthL: The linear R, G and B masters were combined using the ImageIntegration tool (average, additive with scaling, noise evaluation, iterative K-sigma / biweight midvariance, no pixel rejection).
Deconvolution: A star mask was made to use as a local deringing support image. A copy of the image was stretched to use as a range mask. Deconvolution was applied (80 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 25 stars).
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the background areas of the synthL file. Layer settings for threshold and strength: Layer 1: 5, 1.0 Layer 2: 3.5, 0.84 Layer 3: 2.5, 0.71 Layer 4: 1.0, 0.55 Layer 5: 1.5, 0.28 Layer 6: 1.0, 0.16.
Stretching: HistogramTransformation was applied to the SynthL to make a pleasing, bright image.
Noise Reduction and Re-Stretch: TGVDenoise was applied in L*a*b* mode with 300 iterations with a range mask used to protect high signal areas. This was followed by a HistogramTransformation to raise the black point (but with no clipping).
Combining SynthL with RGB:
The processed SynthL was applied to the RGB image using LRGBCombine.
Final Steps: Background, galaxy and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required.
Image scale is about 1.6 arcsec per pixel for this camera / telescope / combination and Drizzle integration.