Hickson 44 Compact Galaxy Group
Click image for full size version
January 23, 2025
This group of galaxies is known as Hickson 44 (the 44th entry in Hickson’s catalogue of compact galaxy groups). It lies in the constellation Leo, sitting on the lion’s shoulder. The cluster lies at a distance of about 80-100 million light years. The largest galaxy, near centre, is NGC 3190. The S-shaped galaxy is NGC 3187. Near lower left is NGC 3185, and elliptical galaxy NGC 3193 is the fuzzy object at upper right in this image. These four galaxies are interacting gravitationally with each other, and becoming distorted in the process. Several other galaxies appear as faint smudges and are identified in an annotated image. To give a sense of scale for this image, NGC 3190 is about 75,000 light years across.
I’ve previously posted images of this region in April 2015 and January 2017, but the 2025 image above reveals more detail, and has better colour and control of noise.
Tekkies:
Acquisition, focusing, and control of Paramount MX mount and other equipment with N.I.N.A. and TheSkyX. Guiding with PHD2. Primalucelab low-profile 2″ Essato focuser and ARCO rotator. Equipment control with Primalucelab Eagle 4 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Data acquired under average transparency and seeing March 7 – March 13, 2024.
Celestron 14″ EDGE HD telescope at f/11 (3,912 mm focal length) and QHY600M camera binned 2×2 with Optolong filters.
79 x 1m Red = 1hr 19m
90 x 1m Green = 1hr 30m
86 x 1m Blue = 1hr 26m
Total: 4hr 215m
Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, integration and Drizzle integration of all frames (1x drizzle, 0.9 Drop Shrink).
RGB and SynthL masters: A master RGB image was made from the Red, Green and Blue Drizzled masters using ChannelCombination in RGB mode. A synthetic luminance (SynthL) master was made from the R-G-B masters using ImageIntegration with weighting by SNR.
Gradient Removal: DynamicBackgroundExtraction was applied to the SynthL and RGB masters.
Colour Calibration: BlurXterminator was applied to the RGB master with Correct Only selected, followed by SpectrophotometricColorCalibration.
Deconvolution: BlurXterminator was applied to the RGB and SynthL masters with Automatic psf , star sharpening set to 0.5, and non-stellar set to 0.9.
Linear Noise Reduction: NoiseXterminator was applied to the RGB and SynthL masters with settings Amount=0.9 and Detail=0.25.
Stretching: HistogramTransformation was applied to make a pleasing image from the RGB and SynthL masters. Approximate background level after stretch was 0.1 for SynthL and 0.08 for RGB.
Nonlinear Processing
Combining RGB and SynthL: LRGBCombination was used to replace the lightness channel of the RGB image with SynthL.
Star Removal: StarXterminator was used to remove the stars from the master, with default settings, except Large Overlap was selected. The stars-only image was retained.
Nonlinear Noise Reduction: NoiseXterminator was used to reduce noise in the background areas of the SynthRGB master with Amount=0.9 and Detail=0.15.
Re-stretch: HistogramTransformation was used to boost contrast by moving the dark point to the toe of the histogram and slightly decreasing the mid-point slider.
Blemish Repair: CloneStamp was used to correct a few small defects in the starless image.
Contrast Enhancement: LocalHistogramEqualization was applied twice using a mask to select only the galaxies. A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 50, strength 0.25; scale 140, strength 0.2).
Sharpening: MultiscaleMedianTransform was applied. (Layers 2 – 4 with strengths of 0.07, 0.07, and 0.05, respectively), using a mask to select only the galaxies.
Contrast, Brightness and Colour: Galaxy brightness, contrast, and saturation were adjusted in several iterations using CurvesTransformation with masks as required.
Stars-only steps: The CIE L* channel (i.e. the lightness channel) was extracted from the stars-only image and then applied to the star image as a mask. CurvesTransformation’s Saturation slider was used to boost colour in the stars.
Star Restoration: The PixelMath expression combine(starless, stars, op_screen()) was used to combine the starless starless image with the stars-only image. The StarReduction script was applied with small star protection enabled (Tranfer method, strength 0.35) to slightly reduce the larger stars.
Final Steps: Background, galaxy, and star brightness, contrast, and saturation were adjusted in several iterations using CurvesTransformation with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. The finder chart was made using the FindingChart process. The annotated image was made with the AnnotateImage script.
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