NGC 5746 & NGC 5740 – Barred Spiral Galaxies

NGC 5746 and NGC 5740

Click image for full size version

May 18, 2020

NGC 5746 and NGC 5740NGC 5746, at upper right of centre, is a barred-spiral galaxy in Virgo, about 95 million light years distant. The top of the central bulge seems to show a double hump. This galaxy is considered to be similar to NGC 4565, which is also seen nearly edge-on.

At lower left of centre is barred-spiral galaxy NGC 5740, seen nearly face-on. It is considerably closer than NGC 5746, lying 46 to 68 million light years from Earth. Some of the many other galaxies in the field are marked on the annotated image. Click the image to see it full size.

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. No moon, average or better transparency, and average seeing. Data acquired April 2 – May 16, 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:      60 x 10m = 600m
Chrominance:  193x 3m  = 579m
Total: 19hr39m
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 Drizzled RGB master frame (from the one-shot colour camera). MURE Denoise script was applied to L. 

Gradient Removal: DBE was applied to L and RGB masters using Subtraction.

Channel Registration:  To improve colour channel registration, the colour channels of the RGB master were extracted with ChannelExtraction 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.

Deconvolution:  StarMask was applied with default settings to produce a Local Deringing Support Image. A clone of the image was stretched  with HistogramTransformation and Curves in order to use it as a deconvolution mask. Deconvolution was applied (100 iterations, regularized Richardson-Lucy, external PSF made using PSFImage script with about 30 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 0.7, 1 iterations; Layer 2: 2.0, 0.5, 1 iteration.

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

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 (max. 1,000 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), hyperbolic Large-scale Transfer Function with strength of 0.73.

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.