Link to annotated image
NGC 5866 is a bright lenticular galaxy located 50 million light years away in Draco. It’s one of the brightest members of the NGC 5866 Group, a small galaxy group that also includes the spiral galaxies NGC 5879 and NGC 5907 (the Splinter Galaxy). This group may be a part of a large, elongated structure that comprises the M51 Group and the M101 Group, but most sources distinguish the three groups as separate entities. The dark dust lane is unusual for a lenticular galaxy, and it’s possible that the galaxy is a spiral rather than a lenticular. Orbital velocity measurements of the globular clusters around NGC 5866 indicate that the system has an unusually low amount of dark matter.
This galaxy appears likely to be Messier 102. M102 was observed by Pierre Méchain in late March or early April 1781 and was added by Messier to the final version of his catalogue published in 1781, but without coordinates. In 1783, Méchain retracted his discovery in a letter written to J. Bernoulli and claimed that M102 was an accidental duplication of M101. However, NGC 5866 closely matches both Mechain’s description in the printed version of the Messier Catalog of 1781, and the object position given by Charles Messier in hand-written notes on his personal list of the Messier Catalogue. NGC 5866 was independently found by William Herschel in 1788.
The annotated image reveals another minor mystery associated with this field of view. Cartes du Ciel shows PGC (aka LEDA) numbers for many background galaxies in this field, but few of those have entries in NED or SIMBAD. I’m not sure why, since those entries usually match up quite well. An example is the galaxy at top, which is shown in Cartes du Ciel as mag 16.4 PGC 3386739, but there is no entry in NED or SIMBAD under that PGC designator. The catalogs only list 2MASX J15054334+5557344, a LINER-type active galactic nucleus with a redshift of 0.07. CdC shows many other PGC entries in this field that have no corresponding NED/SIMBAD entry at all. In the annotation I’ve shown the PGC numbers from CdC even where there is no corresponding entry in the catalogs.
Exposure: Total exposure time 23.5 hours, 503:59:68:74 x 2 minutes LRGB. All bin 1x1. Data collected from March to May of 2021.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated luminance around 2.4 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: Full scale. The wider field and the annotated image are at 75% of the original 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 Software: Pixinisight, Affinity Photo, Photoshop CS2
Processing Workflow by Workspace in PixInsight 1.8.8:
1. Calibration
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and reject a few frames
Weighting and registration with WBPP
2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop
Dynamic Background Extraction
3. Luminance Linear Processing
Deconvolution to Sharpen:
Dynamic PSF to create PSF image
Deconvolution, using a mask created in Photoshop to sharpen selected areas only
I made a second more aggressive version (“Dust Lane Image”) with Multiscale Linear Transform to accentuate the dust lane
4. Luminance Stretching
Histo Trans x 2
I then created two stretched luminance images, the first with Curves Trans and the second with an aggressive Masked Stretch. The latter accentuated the background galaxies.
TGV Denoise on both versions
Aggressive Multiscale Median Transform on both versions, using an inverted luminance mask, to remove lumpiness in background
5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration, using Average Spiral Galaxy white reference
6. RGB Stretching
Histo Trans
Boost color saturation with Curves
Curves Trans
TGV Denoise
Aggressive Multiscale Median Transform, using an inverted luminance mask, to remove lumpiness in background
7. Color Combination
LRGB Combinations of both the Curves and Masked Stretch luminance images with the RGB image to create a “Galaxy” and a “Background Galaxies” image
8. Background Subtraction for Both Versions
a. Create an image of the background:
1. StarNet++ to create a starless image
2. Modify the starless image in Photoshop/Affinity Photo:
a. Use the Healing Brush and CloneStamp tools to remove halos, leaving only the background
b. Select the galaxy with the Magic Wand tool and expand the selection so that the whole galaxy is selected. Then delete it, and use the Smudge tool to “push in” color and patterns from the edges into the hole left by the galaxy. Then blur that area with Gaussian Blur to avoid sharp transitions.
c. Apply a heavy Noise Reduction filter so that noise is not removed during the subtraction process.
b. Subtract the background image from the original image (using Image>Apply Image) to remove remaining messy clumps in the background (and apply an offset so that the background is pure black)
c. Layer Galaxy, Background Galaxies and Dust Lane Images together with masks, save as TIFF and move back into PI
9. Final Adjustments
Histo Trans to darken background
10. Star Reduction
I used a modified version of Adam Block’s star reduction technique:
StarNet to create a new “Starless Image”
Extract two copies of luminance from the Galaxy Image, then apply a 7-layer MLT, unchecking the residual layer, to one to create a rough star mask.
Binarize to select only the stars
MorphTrans using erosion to eliminate the smallest stars
MorphTrans using dilation to enlarge the remaining stars
Edit the mask with CloneStamp to exclude any background galaxies
Convolution to blur star edges
Pixel Math: subtract luminance image from blurred star mask so that cores are excluded from mask, and on ly halos are represented in the mask = “Halo Mask”
Apply Halo Mask to Galaxy image, then run PixelMath to use Starless Image where halos otherwise would be
11. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Save as JPG
ImageSolve
ImageAnnotation (using custom catalogs for UGC/PGC galaxies, clusters and quasars)
