## GNU Astronomy Utilities

#### 9.1.3.1 CosmicCalculator input options

The inputs to CosmicCalculator can be specified with the following options:

-z FLT
--redshift=FLT

The redshift of interest. There are two other ways that you can specify the target redshift: 1) Spectral lines and their observed wavelengths, see --obsline. 2) Velocity, see --velocity. Hence this option cannot be called with --obsline or --velocity.

-y FLT
--velocity=FLT

Input velocity in km/s. The given value will be converted to redshift internally, and used in any subsequent calculation. This option is thus an alternative to --redshift or --obsline, it cannot be used with them. The conversion will be done with the more general and accurate relativistic equation of $$1+z=\sqrt{(c+v)/(c-v)}$$, not the simplified $$z\approx v/c$$.

-H FLT
--H0=FLT

Current expansion rate (in km sec$$^{-1}$$ Mpc$$^{-1}$$).

-l FLT
--olambda=FLT

Cosmological constant density divided by the critical density in the current Universe ($$\Omega_{\Lambda,0}$$).

-m FLT
--omatter=FLT

Matter (including massive neutrinos) density divided by the critical density in the current Universe ($$\Omega_{m,0}$$).

-r FLT

Radiation density divided by the critical density in the current Universe ($$\Omega_{r,0}$$).

-O STR/FLT,FLT
--obsline=STR/FLT,FLT

Find the redshift to use in next steps based on the rest-frame and observed wavelengths of a line. This option is thus an alternative to --redshift or --velocity, it cannot be used with them.

The first argument identifies the line. It can be one of the standard names, or any rest-frame wavelength in Angstroms. The second argument is the observed wavelength of that line. For example, --obsline=Ly-alpha,6000 is the same as --obsline=1215.64,6000. Wavelengths are assumed to be in Angstroms by default (other units can be selected with --lineunit, see CosmicCalculator spectral line calculations).

The list of pre-defined names for the lines in Gnuastro’s database is available by running

\$ astcosmiccal --listlines