NGC 5907, the Splinter Galaxy

NGC 5907Click image for full size version

June 15, 2018

This spring gem is the Splinter Galaxy, NGC 5907. Through a large telescope, it looks to me like a toothpick. The photo brings out much more detail, including a bright core and a prominent dark dust lane. The Splinter Galaxy is about 50 million light years away and is made up mostly of white dwarf stars — small, dense stars nearing the end of their lives. They eventually lose all their heat and ability to fuse elements, and get cold and dark, like a cinder.

Many other galaxies share the field with NGC 5907, some of which are highlighted in an annotated image taken in 2018.

Tekkies:
Acquisition, focusing, and control of Paramount MX mount with N.I.N.A., TheSkyX and PHD2. Focus with Optec DirectSync motor and controller. Equipment control with PrimaLuce Labs Eagle 3 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Average transparency and seeing. Data acquired June 4-7, 2021 in a nearly moonless sky.

Luminance: Sky-Watcher Esprit 150 f/7 refractor and QHY600M camera with Optolong UV/IR filter
Chrominance: Takahashi FSQ-106 ED IV @ f/5 and QHY367C Pro one-shot colour camera with Optolong UV/IR filter

51x10m Lum = 8hr30m
110x5m chrominance = 9hr10m
Total: 17hr40m
 
Image scale 0.72 arcsec per pixel (based on Luminance)
 

Data Reduction and Initial Processing
Preprocessing: The WeightedBatchPreProcessing script was used to create a Luminance master frame from the mono camera and an RGB master frame from the one-shot colour camera. DrizzleIntegration (1x CFA Drizzle) was applied to the RGB set. The RGB master was registered to the Luminance master using StarAlignment.

Gradient Removal: DBE was applied to both masters using Subtraction.

Colour
Colour Balancing:  Colour was balanced with ColorCalibration.

Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the background areas, using an internal mask to protect bright structures. Layer settings for threshold and strength: Layer 1: 5.0 0.85, 2 iterations; Layer 2: 3.5, 0.75, 2 iterations.

Stretching:  HistogramTransformation was applied to make a pleasing, bright image, with background set to an intensity of approximately 0.10.

Lightness
Deconvolution:  A star mask was made from the Luminance master to use as a Local Deringing Support Image. A copy of the image was stretched to use as a range mask. Deconvolution was applied (100 iterations, regularized Richardson-Lucy, external PSF made using the PSFImage script; Global dark deringing = 0.03).

Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise in the background areas, using an internal mask to protect bright stars. Layer settings for threshold and strength: Layer 1: 3.0 0.85, 1 iterations; Layer 2: 2.0, 0.75, 2 iterations.

Stretching:  HistogramTransformation was applied to make a pleasing, bright image, with background set to an intensity of approximately 0.10.

Combining Lightness and Colour Images
LRGB Combination: The lightness image was applied to the RGB image using LRGBCombination with default settings.

Additional Processing

Nonlinear Noise Reduction: TGVDenoise was used in L*a*b* mode to reduce noise with a mask used to target the background areas and protect the stars and galaxy (max. 1,000 iterations and convergence selected for both lightness and chrominance). 

Contrast Enhancement: LocalHistogramEqualization was applied twice using an inverted star mask to protect the stars, first with a scale of 20 (max contrast 1.5, strength 0.25, 1 iteration), followed by a scale of 40 (max contrast 1.5, strength 0.35, 1 iteration).

Sharpening: MultiscaleLinearTransform was used to sharpen Layers 2 and 3 with strengths of 0.08and 0.03, respectively. A mask was used to protect background and stars and limit sharpening to the brighter galaxy features.

Final Steps: Background, galaxy and star brightness, contrast, and colour saturation were adjusted in several iterations using CurvesTransformation with masks as required. MorphologicalTransformation was used in Morphological Selection mode (Strength 0.5; Selection 0.11) through a star mask to shrink the brightest stars. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving in jpg format.