NGC 4565, The Needle Galaxy

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July 20, 2023

NGC 4565, The Needle Galaxy, lies about 30-50 million light years from Earth in the constellation Coma Berenices.  It has a diameter of about 100,000 light years, similar to that of our own Milky Way galaxy.  Its length appears about half the Moon’s width in images, and somewhat less through the eyepiece. Although it is classified as a barred spiral galaxy, the central bar isn’t visible in this image, because the galaxy is edge-on to our line of sight.  However, the bar’s presence is evident from Spitzer Space Telescope data.  Several other galaxies also appear in this field.  The most prominent is NGC 4562 at lower right. There are dozens of faint galaxies in the field, marked in the annotated image.  The faintest of the marked galaxies, PGC3096164, has a blue magnitude of +21. There are also many unmarked galaxies, including many off the lower right tip of NGC 4565.

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 (2021) and 4 (2023) Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Average transparency and seeing. Data acquired May 12-17, 2023 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

53x5m Lum = 4hr25m
67x5m chrominance = 5hr35m
Total: 10hr00m
 
Image scale 0.72 arcsec per pixel (based on Luminance)
 
Finder Chart and Annotated Image: 
  
 
 
Data Reduction and Linear Processing

Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, local normalization and integration of all frames.

Alignment of Master Frames: DrizzleIntegration was applied to the OSC frames (within WeightedBatchPreProcessing), and the result was aligned to the Luminance master with StarAlignment. This yielded aligned Lum and Colour masters.

Gradient Removal: DynamicBackgroundExtraction was applied to both masters.

Colour Calibration:  ColorCalibration was used to calibrate the OSC master.

Deconvolution: BlurXterminator was used on the Luminance master with a custom psf FWHM determined with the PSFImage script, and star sharpening set to 0.10 with “Correct First” selected. The same settings were used with Automatic PSF on the Color image.

Linear Noise Reduction: NoiseXterminator was applied to each image with settings Amount=0.9 and Detail=0.15

Stretching:  HistogramTransformation was applied to each image to make a pleasing yet bright image. Approximate background level after stretch was 0.10

Nonlinear Processing
Luminance addition: LRGBCombination was applied to replace the lightness of the Colour image with the Luminance master.

Star Removal:  StarXterminator was used to remove the stars, with Unscreen selected

Nonlinear Noise Reduction: NoiseXterminator was used to reduce noise in the background areas of the image with settings Amount=0.9 and Detail=0.2 

Contrast Enhancement: Using a mask to select the galaxies, LocalHistogramEqualization was applied twice.  A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 40, strength 0.35; scale 100, strength 0.25).

Sharpening: The same mask was used with MultiscaleMedianTransform to sharpen Layers 1 – 5 with strengths of 0.03, 0.05, 0.07, 0.06, and 0.03, respectively. 

Star Restoration: PixelMath expression combine(starless, stars, op_screen())  was used to combine the starless and stars-only images created with StarXterminator.

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 image was annotated with the AnnotateImage script. The finder chart was made using the FindingChart process.