NGC 4565, The Needle Galaxy

NGC 4565Click image for full size version

March 8, 2020

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, its presence is evident from Spitzer Space Telescope data.  Several other galaxies also appear in this field.  The most prominent is NGC 4562 at upper 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, guiding and control of Paramount MX mount with TheSkyX. Focus with Optec DirectSync motor and controller. Automation with CCDCommander. Equipment control with PrimaLuce Labs Eagle 3 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Minimal moonlight, above average transparency and average or better seeing. Data acquired February 21-March 1, 2020.

Luminance: Sky-Watcher Esprit 150 f/7 refractor and QHY 16200-A camera with Optolong UV/IR filter
Chrominance: Takahashi FSQ-106 ED IV @ f/3.6 and QHY367C one-shot colour camera with Optolong L-Pro filter

Luminance:      58 x 10m = 580m
Chrominance:  244 x 3m  = 732m
Total: 21hr52m
 
Image scale 1.15 arcsec per pixel (based on Luminance)

Data Reduction and Processing
Preprocessing: The WeightedBatchPreProcessing script was used to create a Luminance master frame (from the mono camera) and a RGB master frame (from the one-shot colour camera).

Gradient Removal: DBE was applied to L and RGB masters using Subtraction to remove the minimal gradient that remained after integration.

Colour
Channel Registration:  To improve channel registration, the colour channels of the RGB master were extracted and aligned with StarAlignment, using Thin Plate Splines with Distortion Correction and the green channel as the reference frame. The registered colour channels were recombined with ChannelCombination.

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; Layer 3: 3.0, 0.5, 1 iteration; Layer 4: 1.0, 0.25, 1 iteration.

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

Lightness
Deconvolution:  StarMask was applied with default settings to produce a Local Deringing Support Image. A clone of the image was stretched to use as a deconvolution mask. Deconvolution was applied (100 iterations, regularized Richardson-Lucy, external PSF made using PSFImage script with about 50 stars).

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, 1 iterations; Layer 3: 1.0, 0.5, 1 iteration.

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

Recombining Lightness and Colour Images

Registration of L and RGB: DynamicAlignment was used to register the RGB master to the L master.

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 (max. 1000 iterations and convergence selected for both lightness and chrominance). 

Sharpening:  The galaxy was sharpened with a pass of MultiscaleLinearTransform (bias +0.1 on 2nd and 3rd layers) followed by UnsharpMask (Standard Deviation of 1.0, amount 0.6, Dark Deringing 0.05)

Final Steps: Galaxy, background and star brightness, contrast, and colour 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.