Image analysis of extragalactic spiral structures - 1

Hello everyone!

I would like to share with you this work as an amateur astronomer.

From time to time I’ll do some practice with the DS9 tool, on extragalactic subjects and galactic nebulae which are accessible from DESI data in the optical band.

To begin with this post, I’ll share some interesting features of the global structure and the spiral structure of the “face-on” galaxies: in particular, to evaluate the core-relative flux range of the spiral.

Subject: NGC 6038
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux = 2.06669 nanomaggie
r-band core flux = 6.40407 nanomaggie
z-band core flux = 10.6730 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0036 - 2.06669 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.1065/1000/20
Spiral Flux range: 0.108 - 0.177 nanomaggie
Core-relative flux range of the spiral: 5.2% - 8.7%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0055 - 6.40407 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.11/1000/20
Spiral Flux range: 0.193 - 0.320 nanomaggie
Core-relative flux range of the spiral: 3.0% - 5.0%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0095 - 10.6730 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.105/1000/20
Spiral Flux range: 0.261 - 0.431 nanomaggie
Core-relative flux range of the spiral: 2.4% - 4.0%

Interesting events: SN1999cc (green box in the g-band spiral structure), detected from Asiago Supernova Catalogue 2008.






Subject: NGC 6195
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux = 2.57190 nanomaggie
r-band core flux = 5.14782 nanomaggie
z-band core flux = 16.0440 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.00094 - 2.57190 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.152/1000/20
Spiral Flux range: 0.0819 - 0.135 nanomaggie
Core-relative flux range of the spiral: 3.2% - 5.2%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.003 - 5.14782 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.195/1000/20
Spiral Flux range: 0.119 - 0.197 nanomaggie
Core-relative flux range of the spiral: 2.3% - 3.8%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.00012 - 16.0440 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.126/1000/20
Spiral Flux range: 0.169 - 0.282 nanomaggie
Core-relative flux range of the spiral: 1.1% - 1.8%

Interesting events: SN 1975K (magenta box in the g-band spiral structure).






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Subject: UGC 7331
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux = 3.38379 nanomaggie
r-band core flux = 8.52434 nanomaggie
z-band core flux = 17.0239 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0039 - 3.38379 nanomaggie

g-band bar structure:
Scale function: Power
ZScale parameters: 0.0317/1000/20
Spiral Flux range: 0.152 - 0.252 nanomaggie
Core-relative flux range of the bar: 4.5% - 7.5%

g-band spiral structure:
Scale function: Squared
ZScale parameters: 0.068/1000/20
Spiral Flux range: 0.029 - 0.116 nanomaggie
Core-relative flux range of the spiral: 0.86% - 3.4%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0093 - 8.52434 nanomaggie

r-band bar structure:
Scale function: Power
ZScale parameters: 0.031/1000/20
Spiral Flux range: 0.297 - 0.49 nanomaggie
Core-relative flux range of the bar: 3.5% - 5.8%

r-band spiral structure:
Scale function: Squared
ZScale parameters: 0.068/1000/20
Spiral Flux range: 0.0554 - 0.22 nanomaggie
Core-relative flux range of the spiral: 0.65% - 2.6%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.011 - 17.0239 nanomaggie

z-band bar structure:
Scale function: Power
ZScale parameters: 0.0315/1000/20
Spiral Flux range: 0.51 - 0.85 nanomaggie
Core-relative flux range of the bar: 3.0% - 5.0%

z-band spiral structure:
Scale function: Squared
ZScale parameters: 0.068/1000/20
Spiral Flux range: 0.097 - 0.39 nanomaggie
Core-relative flux range of the spiral: 0.57% - 2.3%

Interesting events: none.









Very nice spiral galaxies here. If you haven’t already, it can sometimes be quite enlightening to open these as RBG stacked cubes in ds9. Using your highest frequency band for the Blue image and lowest for the Red image, you should be able to spot a redder (older stars) core and the bluest (youngest stars) in the arms of the spiral.

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UGC 7331 - update

I tried to do an RGB image of the spiral and central bar of this galaxy, previously posted here above: with a more contrast there are many details, also the spiral is dominated by young stars. The central bar is very interesting!

RGB spiral structure:
Scale function: Squared
ZScale parameters: 0.068/1000/20
R = z, G = r, B = g

RGB bar structure:
Scale function: Power
ZScale parameters: 0.0315/1000/20
R = z, G = r, B = g


Subject: UGC 9968
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux = 1.10352 nanomaggie
r-band core flux = 2.99521 nanomaggie
z-band core flux = 6.16214 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0046 - 1.10352 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.38/1000/20
Spiral Flux range: 0.049 - 0.079 nanomaggie
Core-relative flux range of the spiral: 4.4% - 7.2%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.009 - 2.99521 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.38/1000/20
Spiral Flux range: 0.102 - 0.165 nanomaggie
Core-relative flux range of the spiral: 3.4% - 5.5%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.017 - 6.16214 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.38/1000/20
Spiral Flux range: 0.199 - 0.281 nanomaggie
Core-relative flux range of the spiral: 3.2% - 4.6%

RGB spiral structure:
Scale function: Power
ZScale parameters: 0.38/1000/20
R = z, G = r, B = g

Interesting events: none







NGC 6038 - update

Gradual fading from red stars, close to the core, toward younger stars along the spirals.

RGB spiral structure:
Scale function: Squared
ZScale parameters: 0.11/1000/20
R = z, G = r, B = g

Subject: UGC 9757
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux = 1.1175 nanomaggie
r-band core flux = 2.88628 nanomaggie
z-band core flux = 6.14588 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0039 - 1.1175 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.036/1000/20
Spiral Flux range: 0.104 - 0.172 nanomaggie
Core-relative flux range of the spiral: 9.3% - 15.4%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.008 - 2.88628 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.04/1000/20
Spiral Flux range: 0.173 - 0.286 nanomaggie
Core-relative flux range of the spiral: 6.0% - 9.9%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.014 - 6.14588 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.04/1000/20
Spiral Flux range: 0.281 - 0.463 nanomaggie
Core-relative flux range of the spiral: 4.6% - 7.5%

RGB spiral structure:
Scale function: Squared
ZScale parameters: 0.04/1000/20
R = z, G = r, B = g

Interesting events: SN 2009ai (magenta box in the g-band spiral structure)







Subject: UGC 8050
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux (peak) = 0.863522 nanomaggie
r-band core flux (peak) = 2.4196 nanomaggie
z-band core flux (peak) = 5.42595 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0058 - 0.863522 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.01/1000/20
Spiral Flux range: 0.072 - 0.131 nanomaggie
Core-relative flux range of the spiral: 8.3% - 15.2%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0089 - 2.4196 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.052/1000/20
Spiral Flux range: 0.149 - 0.247 nanomaggie
Core-relative flux range of the spiral: 6.2% - 10.2%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.012 - 5.42595 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.028/1000/20
Spiral Flux range: 0.201 - 0.336 nanomaggie
Core-relative flux range of the spiral: 3.7% - 6.2%

RGB spiral structure:
Scale function: Squared
ZScale parameters: 0.025/1000/20
Colormap Parameters: contrast = 1.85; bias = 0.5
R = z, G = r, B = g

Interesting events: SN 2008ay (magenta box in the g-band spiral structure).







Subject: UGC 6322
Frame: coadded FITS from DESI Legacy Imaging Surveys + cutout to exclude sources brighter than the core.
Image Settings: zoommed 2x + Gaussian Filter (radius = 3 pixel with sigma = 1.5, to reduce the residual noise).
LUT = gist-ncar (color look-up table implemented with DS9).

g-band core flux (peak) = 1.56786 nanomaggie
r-band core flux (peak) = 4.10172 nanomaggie
z-band core flux (peak) = 8.14541 nanomaggie

g-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0015 - 1.56786 nanomaggie

g-band spiral structure:
Scale function: Power
ZScale parameters: 0.085/1000/20
Spiral Flux range: 0.02 - 0.036 nanomaggie
Core-relative flux range of the spiral: 1.3% - 2.3%

r-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.0057 - 4.10172 nanomaggie

r-band spiral structure:
Scale function: Power
ZScale parameters: 0.11/1000/20
Spiral Flux range: 0.036 - 0.061 nanomaggie
Core-relative flux range of the spiral: 0.88% - 1.5%

z-band global structure:
Scale function: Log
ZScale parameters: 0.01/1000/20
Flux range: 0.015 - 8.14541 nanomaggie

z-band spiral structure:
Scale function: Power
ZScale parameters: 0.11/1000/20
Spiral Flux range: 0.052 - 0.098 nanomaggie
Core-relative flux range of the spiral: 0.64% - 1.2%

RGB spiral structure:
Scale function: Squared
ZScale parameters: 0.06/1000/20
Colormap Parameters: contrast = 1.35; bias = 0.5
R = z, G = r, B = g

Interesting events: SN 1971A (magenta box in the g-band spiral structure)