[gnuastro-commits] master a2e1c98: Watkins et al 2015 added in tutorial to show reality of detection

[Mohammad Akhlaghi]

branch: master
commit a2e1c9880bc8bd05977ab2fba52da832b6e206a1
Author: Mohammad Akhlaghi <address@hidden>
Commit: Mohammad Akhlaghi <address@hidden>

    Watkins et al 2015 added in tutorial to show reality of detection
    
    In Aaron Watkins' 2015 paper, deep images show the outer wings of M51 at
    much higher signal to noise ratios that are visible to the eye in noise. To
    further help convince people on the reality of this detection, it is cited
    after the detection step and before measuring the surface brightness limit
    in the tutorial.
    
    Some other parts of the text in the tutorial were also edited for easier
    reading.
    
    This was suggested by Ignacio Trujillo.
---
 doc/announce-acknowledge.txt |  1 +
 doc/gnuastro.texi            | 36 +++++++++++++++++++-----------------
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/doc/announce-acknowledge.txt b/doc/announce-acknowledge.txt
index 6d507b9..815b582 100644
--- a/doc/announce-acknowledge.txt
+++ b/doc/announce-acknowledge.txt
@@ -4,3 +4,4 @@ Pierre-Alain Duc
 Gaspar Galaz
 Mamta Pommier
 Michael Stein
+Ignacio Trujillo
diff --git a/doc/gnuastro.texi b/doc/gnuastro.texi
index 7fcfa34..a22694a 100644
--- a/doc/gnuastro.texi
+++ b/doc/gnuastro.texi
@@ -4261,21 +4261,22 @@ more than 20 times) than the standard deviation (final 
extension). So we
 can stop configuring NoiseChisel at this point in the tutorial. We leave
 further configuration for a more accurate detection to you as an exercise.
 
-At first sight, this extent may seem too far deep into the noise. Ofcourse,
-there is no way you can visually see extended signal that is has a 0.05
-signal-to-noise ratio. Therefore, if the statistical argument above to
-justify this extent hasn't convinced you, see this amateur astronomer's 12
-hour deep image of this system (and the much wider area around it):
address@hidden://i.redd.it/address@hidden image is taken from
-this Reddit discussion:
+In this shallow image, this extent may seem too far deep into the noise for
+visual confirmation. Therefore, if the statistical argument above, to
+justify the reality of this extented structure, hasn't convinced you, see
+the deep images of this system in @url{https://arxiv.org/abs/1501.04599,
+Watkins et al. [2015]}, or a 12 hour deep image of this system (with a
+12-inch telescope): @url{https://i.redd.it/address@hidden
+image is taken from this Reddit discussion:
 
@url{https://www.reddit.com/r/Astronomy/comments/9d6x0q/12_hours_of_exposure_on_the_whirlpool_galaxy/}}.
 
-Let's see how deeply/successfully we carved out M51 and NGC 5195's tail
-from the noise. For this measurement, we'll need to estimate the average
-flux on the outer edges of the detection. Fortunately all this can be done
-with a few simple commands (and no higher-level language mini-environments)
-using @ref{Arithmetic} and @ref{MakeCatalog}. First, let's give a separate
-label to all the connected pixels of NoiseChisel's detection map:
+Now that we know this detection is real, let's measure how deep we carved
+the signal out of noise. For this measurement, we'll need to estimate the
+average flux on the outer edges of the detection. Fortunately all this can
+be done with a few simple commands (and no higher-level language
+mini-environments) using @ref{Arithmetic} and @ref{MakeCatalog}. First,
+let's give a separate label to all the connected pixels of NoiseChisel's
+detection map:
 
 @example
 $ astarithmetic r_detected.fits 2 connected-components -hDETECTIONS \
@@ -4356,11 +4357,12 @@ The outer wings where therefore non-parametrically 
detected until
 @mymath{\rm{S/N}\approx0.05}!
 
 @cindex Surface brightness
-This is very good, but how much is this in standard units of surface
-brightness, or magnitudes per square arcseconds? To find out, we'll first
-need to calculate how many pixels of this image are in one
+This is very good! But the signal-to-noise ratio is a relative measurement.
+Let's also measure the depth of our detection in absolute surface
+brighntess units; or magnitudes per square arcseconds. To find out, we'll
+first need to calculate how many pixels of this image are in one
 arcsecond-squared. Fortunately the world coordinate system (or WCS) meta
-data of Gnuastro's output FITS files (and in particular @code{CDELT}
+data of Gnuastro's output FITS files (in particular the @code{CDELT}
 keywords) give us this information.
 
 @example