sedFitThin {cosmoFns} | R Documentation |

Function takes Herschel-SPIRE photometry and fits optically-thin greybody function for a single-component temperature and galaxy luminosity. Function generates nsamp realizations of observed flux densities with standard deviations for error analysis.

```
sedFitThin(s, e = s*0.2, z = 2.5, nsamp = 100, alpha = 2, beta = 1.5,
wl= c(250, 350, 500), sc.start = 1.e-6, T.start = 50)
```

`s` |
Vector of observed-frame flux densities [Jy] |

`e` |
Vector of standard deviation of observed-frame flux density [Jy] |

`z` |
Galaxy redshift |

`nsamp` |
Number of realizations for Monte-Carlo calculation |

`alpha` |
Index of power-law for short-wavelength extension |

`beta` |
Dust emissivity power law |

`wl` |
Vector of observed-frame wavelengths corresponding to |

`sc.start` |
Initial guess for fit luminosity density scaling factor |

`T.start` |
Initial guess for dust temperature [K] |

Conversion from observed to rest frame is from equation (24) in Hogg 2000. Dust temperature and 8-1000 micron luminosity derivation is described in Blain, Barnard & Chapman 2003. Galaxy SEDs typically fall off more slowly than greybody on the Wien side; see plot generated by examples below to visualize power-law extension suggested by Blain et al. 2003.

List of class `sedfit`

with elements:

`td` |
Mean of dust temperature distribution |

`e.td` |
Standard deviation of dust temperature distribution |

`lum.gb` |
Mean of greybody luminosity distribution |

`e.lum.gb` |
Standard deviation of greybody luminosity distribution |

`lum.gbpl` |
Mean of greybody-power law luminosity distribution |

`e.lum.gbpl` |
Standard deviation of greybody-power law luminosity distribution |

`scaleFactor` |
Conversion between observed frame flux density and rest frame luminosity density |

`success` |
Fraction of fit attempts that converged |

`results` |
Matrix with |

Fit will sometimes crash on numerical derivative and throw an error. In
this case the routine will halt without producing results. The more
usual lack of convergence is reported as a warning, and the
corresponding results will be `NA`

in the output matrix.

A. Harris

Hogg 2000, astro-ph 9905116v4; Blain, Barnard & Chapman 2003, MNRAS 338, 733.

```
s <- c(0.242, 0.293, 0.231)
e <- c(0.037, 0.045, 0.036)
z <- 2.41
beta <- 1.5
alpha <- 2
X <- sedFitThin(s=s, e=e, z=z, alpha=alpha, beta=beta, nsamp=100)
str(X)
## Make a plot
# greybody in blue, power-law extension in red dashed line
# functions
# optically thin greybody
otGreybody <- function(nu, T, beta, sc=1) {
# nu in GHz, T in K, beta and sc unitless
sc*nu^(3+beta)/(exp(0.04801449*nu/T) - 1)
}
# high frequency tail
hfTail <- function(nu, alpha) nu^-alpha
#
# setups for 8-1000 microns:
nu.low <- 3e5/1000
nu.high <- 3e5/8
l.nue <- s*X$scaleFactor
#
# greybody
nue.sweep <- seq(nu.low, nu.high, len=350)
pred <- otGreybody(nue.sweep, X$results[1,1], beta=beta,
X$results[1,4])
ylim <- range(pred, l.nue)
par(fig=c(0,1,0.2,1), mgp=c(1.8, 0.6, 0))
plot(3e5/nue.sweep, pred, t='l', ylim=ylim, log='xy', col=4,
xlab='Rest frame wavelength [microns]',
ylab=expression(paste('Luminosity density [ ', L[sun],
' ', Hz^-1, ']')))
# power law
nue.sweep <- seq(X$results[1,5], nu.high, len=100)
val.t <- otGreybody(nu=X$results[1,5], T=X$results[1,1], beta=beta,
sc=X$results[1,4])
lines(3e5/nue.sweep, val.t*hfTail(nue.sweep/X$results[1,5], alpha=alpha),
col=2, lwd=1, lty=2)
# data
wl <- c(250, 350, 500)
nue <- 3e5/wl*(1+z)
points(3e5/nue, l.nue, pch=16, col=3)
```

[Package *cosmoFns* version 1.1-1 Index]