bugGNU Astronomy Utilities - Bugs: bug #65254, Non-flat cases of angular diameter...

 
 

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bug #65254: Non-flat cases of angular diameter distance

Submitter:  Boud Roukema <boud>
Submitted:  Sun 04 Feb 2024 04:26:25 PM UTC
   
 
Category:  CosmicCalculator Severity:  3 - Normal
Item Group:  Output not reasonable Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open

Sun 04 Feb 2024 04:26:25 PM UTC, original submission:  

PROBLEM: Gnuastro 0.22.1-bc3d calculates the comoving one-radian arclength (= the "areal radius" = the "proper motion distance"), and the corresponding physical-units one-radian arclength that is usually called the "angular diameter distance", and other parameters deriving from this, on the assumption that the FLRW model is flat. This is incorrect for non-flat models. This implies that:

  • --angulardiamdist
  • --luminositydist
  • --arcsectandist
  • --distancemodulus

are all wrong in the non-flat cases. This error was mentioned earlier in bug #65195 [1].)

TASK: Introduce a function equivalent to cosm_get_pm_dist in cosmdist 0.3.12 (GPL-2+) [2] to calculate the comoving one-radian arclength based on the radial comoving distance (currently called 'proper_distance' in gnuastro, which is acceptable) and the cosmology curvature parameter. Then functions such as gal_cosmology_angular_distance will need to be corrected.

CHECK:
These checks are for cosmdist 0.3.12 and gnuastro 0.22.1-bc3d, showing that only the flat case (olambda+omatter+oradiation = 1) for astcosmiccal is currently correct; the non-flat cases are wrong.

Comoving tangential one-radian arclength:

$ for OmLam0 in 0.0 0.1 0.8 0.9; do echo 9 | ./cosmdist --tangential -r 0 -m 0.9 -l ${OmLam0} ; done
6219.73
6105.05
4981.32
4758.45
$ for OmLam0 in 0.0 0.1 0.8 0.9; do ./bin/cosmiccal/astcosmiccal --arcsectandist --oradiation=0.0 --omatter=0.9 --olambda=${OmLam0} --H0=70 --redshift=9 --quiet; done |awk '{print $1*3600*180/3.141593/1000.0 *(1.0+9.0)}' # convert 1 arcsec to 1 radian; convert physical to comoving units
6019.57
6105.05
6851.35
6986.83


Angular diameter distance:

$ for OmLam0 in 0.0 0.1 0.8 0.9; do echo 9 | ./cosmdist --angular-diameter -r 0 -m 0.9 -l ${OmLam0} ; done
621.97
610.51
498.13
475.85
$ for OmLam0 in 0.0 0.1 0.8 0.9; do ./bin/cosmiccal/astcosmiccal --angulardiamdist --oradiation=0.0 --omatter=0.9 --olambda=${OmLam0} --H0=70 --redshift=9 --quiet; done
601.956856
610.505315
685.134960
698.682594


Luminosity distance:

$ for OmLam0 in 0.0 0.1 0.8 0.9; do echo 9 | ./cosmdist --luminosity -r 0 -m 0.9 -l ${OmLam0} ; done
62197.34
61050.53
49813.16
47584.52
$ for OmLam0 in 0.0 0.1 0.8 0.9; do ./bin/cosmiccal/astcosmiccal --luminositydist --oradiation=0.0 --omatter=0.9 --olambda=${OmLam0} --H0=70 --redshift=9 --quiet; done
60195.685626
61050.531477
68513.496031
69868.259418


[1] https://savannah.gnu.org/bugs/?65195

[2] https://codeberg.org/boud/cosmdist/src/branch/main/lib/get_pm_dist.c


Boud Roukema <boud>
Group Member

 

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    Follows 1 latest change.

    Date Changed by Updated Field Previous Value => Replaced by
    2024-02-04 boud CategoryNone CosmicCalculator

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