Link to Redshift Chart
At the center of this collection of galaxies, which is located about 400 million light years away near the west border of the spring constellation Bootes, is the 69th entry in Paul Hickson’s 1982 catalog of compact galaxy groups. Officially, Hickson 69 includes only the distorted edge-on spiral galaxy UGC 8842 and its four small companions, but the redshift chart indicates that almost all of the bright galaxies in this field of view are located at the same distance. Their redshifts range from 0.029 to 0.031, making this tight group of 18 galaxies only about 25 million light years across. The outlier is the elliptical galaxy IC 4348, at upper left, and five companions, including the edge-on spiral PGC 1731550, which have redshifts that place them about 100 million light years beyond the larger group. Given the distances and the location in Bootes, I'm guessing this all of these galaxies are part of the CfA2 Great Wall, or the even larger Hercules-Corona Borealis Great Wall which, assuming it's real, is the largest structure in the universe.
Beyond these groups are the usual assortment of apparently random background galaxies, and then the galaxy cluster SPD 2011 32376, located about 1.8 billion light years way. After that lie the quasars, at distances of up to 11 billion light years (z = 2.6).
Although this is a fairly photogenic group, this appears to be the first deep image of it.
Exposure: Total exposure time about 11.5 hours, 209 x 2 minutes luminance, 45:45:44 x 2 minutes R:G:B. All bin 1x1. Data collected in May and June 2021.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated luminance 2.8 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.9 arcsecs/pixel (75% of full scale).
Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.2 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.18212 (SX Windows Drivers 15.26.50.450 [i.e., version 1.2.2] also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon Type IIi 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 4.2
Guide SW: PHD 2.6.11, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.6 SP1
Platesolving: ASTAP, 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, Photoshop CS2
Standard Processing Workflow by Workspace in PixInsight 1.8.9:
1. Processing
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and manually reject a few frames
Weighting, registration and integration with WBPP
RGB Combination for RGB frames
Dynamic Background Extraction on luminance and RGB images
ImageSolve RGB, then run Spectrophotometric Color Calibration, using Average Spiral Galaxy white reference
BlurXterminator using Correct Only on luminance and RGB
BlurXterminator on luminance and RGB
NoiseXterminator on luminance and RGB
DynamicCrop on RGB and luminance
2. Luminance Stretching
Histo Trans x 3
Curves Trans
Final Curves Trans
3. RGB Stretching
Create a saturation mask: apply ScreenTransferFunction to Histo Trans, then apply to the stretched luminance/narrowband image(s). Enlarge the mask with MorphologicalTransformation. Blur the mask slightly with Convolution.
Histo Trans x 2
Curves Trans to boost saturation, using the saturation mask to prevent spurious background colors from being boosted
Curves Trans to brighten
4. Color Blending
LRGB Combine
5. Background Subtraction (Artificial Flat)
Broadband images captured with my (non-Edge) C11 usually have circular artifacts left over from flat calibration, because it’s basically impossible to create accurate flats when the mirror shifts while capturing light frames. To remove these artifacts, I create and subtract an artificial flat, which is simply an image of the messy background, with all stars and imaging targets removed.
a. Create an image of the background by removing stars with StarXterminator
b. Clean this image up in Photoshop, removing the target(s) and any leftover stars
c. Blur this background image slightly (otherwise in the next step you’ll remove all the noise, creating an unnatural-looking noiseless image)
d. Back in PI use PixelMath to subtract the background image from the main image (adding a pedestal, to avoiding having a pure black background).
6. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Rescale as desired
ImageSolve
Create annotated images with the AnnotateImage script, using some custom databases to extract quasar redshifts and galaxy clusters
Save final image, annotated image
