Barred Spiral Galaxy in Ursa Major

Link to annotated image

M 109 is a barred spiral galaxy located 88 million light-years away. It has a morphological classification of SB(rs)bc, which indicates that it has a weak inner ring (rs), and moderate to loosely wound arm structure (bc). These characteristics mean that it's very similar to our own galaxy. M 109 is the brightest member of a group of 50 or so galaxies known as the M 109 or Ursa Major North Group, centered about 55 million light years away, that forms a small part of the Virgo Cluster. The annotated image shows that most of the brighter small galaxies in the image are companions of M 109. It also reveals two background galaxy clusters, one of which ([SPD2011] 28884) appears quite dense, and many quasars. The small galaxy near the bottom of the frame may be a dwarf elliptical companion of M 109, but there’s also a high redshift galaxy (WISEA J115721.23+531333.7) cataloged at this position, so it may be an odd quasar.


Exposure: Total exposure time about 18.3 hours, 440:41:34:34 x 2 minutes LRGB. All bin 1x1. Data collected February to April 2020.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.4 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% of full scale)

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon Type IIe LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.1.0.457
Guide SW: PHD 2.6.7, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2

Processing Workflow by Workspace in PixInsight 1.8.8:

1. Calibration
BatchPreProcessing with flats and bias, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
Subframe Selector for luminance to confirm selections and weight by FWHM and SNR
StarAlign to register frames

2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop

3. Luminance Linear Processing
Dynamic Background Extraction
Deconvolution with PSF on luminance frame, using a mask created manually in Photoshop so that only the regions I wanted were sharpened.

4. Luminance Stretching
Histo Trans x 2
Curves Trans
(No further noise reduction required)
TGV Denoise
(I made a second, less stretched version to use as a luminance star image)
Slight Local Histogram Equalization to bring out contrast in spiral arms

5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration, using G2V white reference

6. RGB Stretching
Histo Trans
Masked Stretch
Curves
Desaturate background with Curves, using an inverted Range Mask
(I made a second version using masked stretch only, to use for color in the luminance star image)

7. Color Combination
LRGB Combination of luminance and RGB images to create a “Galaxy” image
Using masks created in Photoshop, slightly boost yellow in core and blue in spiral arms with Curves
LRGB Combination of luminance and RGB stars images to create a “Stars” image

8. Star Reduction
StarNet to remove stars in the Galaxy image. I used the StarNet image in Photoshop so that I removed only the large and medium-sized stars from the Galaxy image:
a. Layer StarNet image over Galaxy image
b. Select>Color Range to select only the larger stars in the Galaxy image
c. Adjust the selection size with Select>Expand/Contract
d. Create a mask from the selection, and slightly blur it with Gaussian Blur
e. Use the mask to mask in the StarNet image, and thus erase the larger stars.
f. Sharpen remaining small stars with slight Unsharp Mask
g. Layer the Stars image on top, set it as Lighten layer (a similar result can be had in PI using the PixelMath max command), which brings the reduced stars in to replace the larger stars that were removed from the Galaxy image
h. Repair comatic halos: On medium-sized stars, Filter>Radial Blur, then sharpen slightly with Unsharp Mask.

An artificial flat, created in Photoshop, was used to flatten the background, which was essential due to numerous bright rays from nearby Phecda (second magnitude Gamma Ursae Majoris).

Save as TIFF and move back into PI

9. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Resample to 50% of scale
Save as JPG
ImageSolve
ImageAnnotation (using custom catalogs for galaxy clusters and quasars)