| cosgrow {celestial} | R Documentation |
Cosmological growth and evolution calculations
Description
These functions allow various properties of the expansion of the Universe to be calculated: e.g. OmegaM/OmegaL/OmegaR/OmegaK for ay redshift, growth rate and growth factor, sigma8, and RhoCrit and RhoMean. They use curvature correctly, calculated internally using the relation OmegaM+OmegaL+OmegaR+OmegaK=1, but by default they assume a flat Universe where only OmegaM needs to be specified and OmegaR=0 (so no radiation pressure at any epoch).
Usage
cosgrow(z=1, H0=100, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0 = -1, wprime = 0,
Sigma8=0.8, fSigma8=FALSE, Dist='Co',
Mass='Msun', ref)
cosgrowz(z = 1)
cosgrowa(z = 1)
cosgrowH(z=1, H0=100, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
ref)
cosgrowCoVel(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1,
wprime=0, ref)
cosgrowPecVel(z=1, zob=1)
cosgrowOmegaM(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowOmegaL(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowOmegaR(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowOmegaK(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowDecelq(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowEoSwDE(z=1, w0=-1, wprime=0)
cosgrowRhoDE(z=1,w0=-1, wprime=0, rhoDE=1)
cosgrowFactor(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0, ref)
cosgrowRate(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
Sigma8=0.8, fSigma8=FALSE, ref)
cosgrowSigma8(z=1, OmegaM=0.3,OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
Sigma8=0.8, ref)
cosgrowFactorApprox(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
ref)
cosgrowRateApprox(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
Sigma8=0.8, fSigma8=FALSE, ref)
cosgrowSigma8Approx(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1, wprime=0,
Sigma8=0.8, ref)
cosgrowRhoCrit(z=1, H0=100, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1,
wprime=0, Dist='Co', Mass='Msun', ref)
cosgrowRhoMean(z=1, H0=100, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, w0=-1,
wprime=0, Dist='Co', Mass='Msun', ref)
cosgrowDeltaVir(z=1, OmegaM=0.3, OmegaL=1-OmegaM-OmegaR, OmegaR=0, ref)
Arguments
z |
Cosmological redshift, where z must be > -1 (can be a vector). |
zob |
Observed redshift, where z must be > -1 (can be a vector). Essentially a combination of the cosmological redshift z and the peculiar velocity of the objects with respect to this. |
H0 |
Hubble constant as defined at z=0 (default is H0=100 (km/s)/Mpc). |
OmegaM |
Omega matter (default is 0.3). |
OmegaL |
Omega Lambda (default is for a flat Universe with OmegaL = 1-OmegaM-OmegaR = 0.7). |
OmegaR |
Omega Radiation (default is 0, but ~OmegaM/3400 is typical). |
w0 |
The value of dark energy equation of state at z=0. |
wprime |
The evolution term that governs how the dark energy equation of state evolves with redshift. |
rhoDE |
The z=0 reference energy density for dark energy. |
Sigma8 |
The value of Sigma8 to use if fsigma8=TRUE (by default this is a reasonable 0.8 for simplicity). |
fSigma8 |
Logical to express whether the growth rate of structure calculated by cosgrow, cosgrowRate or cosgrowRateApprox is given as f*Sigma8 (TRUE) or simply f (FALSE). This is useful for redshift space distortion comparisons (RSD), since RSD strictly measures f*Sigma8. |
Dist |
Determines the distance type, i.e. whether the Rho critical energy or mean mass densities are calculated with respect to angular / physical distances (Ang), with respect to comoving distances (Co) or with respect to physical metres (m). |
Mass |
Determines the mass type, i.e. whether Rho critical energy or mean mass densities are calculated with respect to solar masses (Msun) or with respect to kilograms (kg). |
ref |
The name of a reference cosmology to use, one of 137 / 737 / Planck / Planck13 / Planck15 / Planck18 / WMAP / WMAP9 / WMAP7 / WMAP5 / WMAP3 / WMAP1 / Millennium / GiggleZ. Planck = Planck18 and WMAP = WMAP9. The usage is case insensitive, so wmap9 is an allowed input. See |
Details
The above functions are heavily based on the equations in Hamilton A.J.S., 2001, MNRAS 322 419 and Lahav O., et al., 1991, MNRAS, 251, 136.
Negative value of z> -1 are allowed, which produces future predictions based on present day cosmology.
The approximation routines are generally accurate to sub 1 percent, and since they do not involve numerical integration they are substantially faster when computing large grids of numbers, i.e. they are recommended for plots, since the accuracy is sub the line width.
Value
cosgrow |
Returns a data.frame (even if only 1 redshift if requested) with the following parameters evaluated at the respective redshift/s: |
| z | Requested redshift |
| a | Universe expansion factor, as given by a=1/(1+z) |
| H | Hubble expansion rate in units of (km/s)/Mpc |
| CoVel | Cosmological recession velocity in units of km/s |
| OmegaM | Omega Matter |
| OmegaL | Omega Lambda |
| OmegaR | Omega Radiation |
| OmegaK | Omega K(c)urvature |
| Decelq | Traditional deceleration parameter q |
| Factor | Exact growth factor (g, see cosgrowFactor below for details) |
| Rate | Exact growth rate (f or f*Sigma8, see cosgrowRate below for details) |
| Sigma8 | Power spectrum fluctuation amplitude on the scale 8 Mpc/z |
| RhoCrit | Critical energy density of the Universe at z, where \rho_{crit}=(3.H(z)^2)/(8.\pi.G), in units of M_{\odot}/Mpc^3 |
| RhoMean | Mean mass density of the Universe at z, where \rho_{mean}=\rho_{crit}.\Omega_{M}(z), in units of M_{\odot}/Mpc^3 |
The outputs of the standalone functions are:
cosgrowz |
Returns the input redshift (only included for clarity). |
cosgrowa |
Returns the Universe expansion factor, as given by a=1/(1+z). |
cosgrowH |
Returns the value of the Hubble expansion rate at z, in units of km/s/Mpc. |
cosgrowCoVel |
Returns the value of the cosmological recession velocity of the object in units of km/s. |
cosgrowPecVel |
Returns the value of the peculiar velocity of the object in units of km/s. |
cosgrowOmegaM |
Returns the value of Omega Matter at z. |
cosgrowOmegaL |
Returns the value of Omega Lambda at z. |
cosgrowOmegaR |
Returns the value of Omega Radiation at z. |
cosgrowOmegaK |
Returns the value of Omega K(c)urvature at z. |
cosgrowDecelq |
Returns the traditional deceleration parameter q, given by q=OmegaM/2+Omegar-OmegaL. |
cosgrowEoSwDE |
Returns w for the dark energy equation of state, where |
cosgrowRhoDE |
Returns the energy density for dark energy, given by |
cosgrowFactor |
Returns the exact value of the growth factor (typically referred to as 'g' in the astronomy literature), at z. This is defined such that it equals 1 at z=Inf and is less than 1 at lower z. |
cosgrowRate |
Returns either the true (typically referred to as 'f' in the astronomy literature) or RSD type (f*Sigma8) value of the growth rate of structure, at z. This is defined such that it equals 1 at z=Inf and is less than 1 at lower z. |
cosgrowSigma8 |
Returns the power spectrum fluctuation amplitude on the scale 8 Mpc/z at z, and is unitless. |
cosgrowFactorApprox |
Returns the approximate value of the growth factor (typically referred to as 'g' in the astronomy literature), at z. This is defined such that it equals 1 at z=Inf and is less than 1 at lower z. |
cosgrowRateApprox |
Returns either the approximate true (typically referred to as 'f' in the astronomy literature) or approximate RSD type (f*Sigma8) value of the growth rate of structure, at z. This is defined such that it equals 1 at z=Inf and is less than 1 at lower z. |
cosgrowSigma8Approx |
Returns the approximate power spectrum fluctuation amplitude on the scale 8 Mpc/z at z, and is unitless. |
cosgrowRhoCrit |
Returns the critical energy density of the Universe at z, where |
cosgrowRhoMean |
Returns the mean mass density of the Universe at z, where |
cosgrowDeltaVir |
Returns the delta-critical virial radius overdensity criterion for a range of flat Universes with varying OmegaM. Taken from Eqn. 6 of Bryan & Norman (1998). |
Note
The difference between RhoCrit and RhoMean at z=0 is simply RhoMean=RhoCrit*OmegaM. Corrected for 1/(1+z)^3 RhoMean stays constant with redshift (as it should- to first order we do not gain or lose mass within a comoving volume).
The growth rate and growth factor does not make use of OmegaR in the cosgrow function, hence OmegaR cannot be provided in the individual functions. This is because correctly accounting for the effect of radiation pressure before the surface of last scattering (z~1100) on the growth rate of structure is highly complex, and beyond the scope of this package. In the case of cosgrow, even if OmegaR is specified it is, in effect, set to zero when making growth factor and rate calculations.
The evolution of the dark matter equation of state (w) is parameterised as described in Wright (2006).
It is important to remember that H is in physical units for both the numerator and denominator (i.e. 'proper' at a given redshift, so the units are km/s / pMpc). To ask the question "is the Universe accelerating?" is to really ask "is the expansion factor accelerating?". This requires the denominator to be in comoving units (so rescaling for proper distances today) and measuring the differential with time or redshift. You will only find an accelerating Universe when dividing H(z)/(1+z)! See the examples to see how we can find this location, and that it is consistent with the start of acceleration calculated from the decleration parameter (q) directly.
Author(s)
Aaron Robotham
References
Based on the equations in:
Bryan & Norman, 1998, ApJ, 495, 80
Davis T.M. & Lineweaver, Charles H., 2004, PASA, 21, 97
Davis T.M. & Scrimgeour M.I., 2014, MNRAS, 442, 1117
Hamilton A.J.S., 2001, MNRAS 322 419
Lahav O., et al., 1991, MNRAS, 251, 136
Peacock J.A., 1999, Cosmological Physics, Cambridge University Press
Wright E.L., 2006, PASP, 118, 1711
See Also
cosvol, cosmap, cosdist, cosref, coshalo
Examples
cosgrow(0.3)
cosgrow(0.3,ref='Planck')
cosgrowz(0.3)
cosgrowa(0.3)
cosgrowH(0.3)
cosgrowCoVel(0.3)
cosgrowPecVel(0.3,0.31)
cosgrowOmegaM(0.3)
cosgrowOmegaL(0.3)
cosgrowOmegaK(0.3)
sum(cosgrowOmegaM(0.3)+cosgrowOmegaL(0.3)+cosgrowOmegaK(0.3)) #Still 1.
cosgrowDecelq(0.3)
cosgrowEoSwDE(0.3)
cosgrowFactor(0.3)
cosgrowFactorApprox(0.3) #Approximation better than 1% for reasonable cosmologies.
cosgrowRate(0.3)
cosgrowRateApprox(0.3) #Approximation better than 1% for reasonable cosmologies.
cosgrowRhoCrit(0.3)
cosgrowRhoMean(0.3)
cosgrowRhoMean(0)-cosgrowRhoMean(2,Dist='Ang')/(1+2)^3 #Mass is conserved in co-vol
cosgrowRhoMean(0)-cosgrowRhoMean(10,Dist='Co') #Mass is conserved in co-vol
# Various recessional velocities (see Figure 2 of Davis & Lineweaver 2004):
plot(10^seq(-1,4,by=0.01), cosgrowCoVel(10^seq(-1,4,by=0.01), ref='planck')
/299792.458, type='l', log='x', xlab='z', ylab='Cosmological Recession Velocity / c')
lines(10^seq(-1,4,by=0.01), cosgrowPecVel(0,10^seq(-1,4,by=0.01))/299792.458, col='red')
lines(10^seq(-1,4,by=0.01), 10^seq(-1,4,by=0.01), col='blue')
abline(h=1,v=1.5,lty=2)
legend('topleft', legend=c('GR', 'SR', 'Approx (cz)', 'Superluminal'), lty=c(1,1,1,2),
col=c('black','red','blue','black'))
# Comparison of the various energy densities that make up the Universe for Planck 2013:
plot(cosdistUniAgeAtz(10^seq(-3,4.9,by=0.1), ref='Planck')*1e9,
cosgrowRhoCrit(10^seq(-3,4.9,by=0.1), ref='Planck', Dist='m', Mass='kg')*
cosgrowOmegaR(10^seq(-3,4.9,by=0.1), ref='Planck'), type='l',log='xy',
xlab='Years since Universe formed', ylab=expression('Energy Density'*(kg/m^3)))
lines(cosdistUniAgeAtz(10^seq(-3,4.9,by=0.1), ref='Planck')*1e9,
cosgrowRhoCrit(10^seq(-3,4.9,by=0.1), ref='Planck', Dist='m', Mass='kg')*
cosgrowOmegaM(10^seq(-3,4.9,by=0.1), ref='Planck'), col='red')
lines(cosdistUniAgeAtz(10^seq(-3,4.9,by=0.1), ref='Planck')*1e9,
cosgrowRhoCrit(10^seq(-3,4.9,by=0.1), ref='Planck', Dist='m', Mass='kg')*
cosgrowOmegaL(10^seq(-3,4.9,by=0.1), ref='Planck'), col='blue')
abline(v=cosdistUniAgeAtz(0.33,ref='Planck')*1e9,lty=2) # Matter = Vacuum
abline(v=cosdistUniAgeAtz(3391,ref='Planck')*1e9,lty=2) # Matter = Radiation
legend('topright', legend=c('Radiation Energy Density', 'Matter Energy Density',
'Vacuum Energy Density'), lty=1, col=c('black','red','blue'))
# Where's the acceleration?
plot(seq(0,2,len=1e3),cosgrowH(seq(0,2,len=1e3)),type='l',xlab='z',
ylab='H(z) / km/s / pMpc')
# There it is!
plot(seq(0,2,len=1e3),cosgrowH(seq(0,2,len=1e3))/(1+seq(0,2,len=1e3)),
type='l',xlab='z',ylab='H(z) / km/s / cMpc')
#When does it start accelerating?
accel.loc=which.min(abs(cosgrowDecelq(seq(0,2,len=1e3))))
abline(v=seq(0,2,len=1e3)[accel.loc],lty=2)