The models described here have been computed with the method outlined
in Efstathiou, Rowan-Robinson & Siebenmorgen (2000, MNRAS, 313, 734)
and Efstathiou & Rowan-Robinson (2003, MNRAS, in press).  The
calculation of the emission of small grains/PAHs is carried out with
the method of Siebenmorgen & Krugel (1992, AA, 259, 614).


low-z cirrus models
-------------------

cirrus_models.dat is an IDL saveset containing the structure 'models'.
This structure contains a grid of 1040 models. Three parameters are
varied: (1) tau is the e-folding time of the assumed exponential decay
of the star formation rate (2) Av is the visual extinction (3) chi is
the factor that controls the intensity of the starlight illuminating
the dust.  A model with chi=1 assumes the same bolometric intensity as
the ISRF in the solar neighbourhood. Note, however, that in general
the spectrum of the radiation field will be different.

 All models are calculated for an age of 12.5Gyrs. Also f=1 and t_m=3e6
are assumed.

high-z cirrus models
-------------------- 

high_z_cirrus_models.dat is an IDL saveset containing the structure
'models'.  This structure contains a grid of 672 models. Two
parameters are varied: (1) Av, the visual extinction varies from 0 to
3.1 in steps of 0.1 (2) chi, the factor that controls the intensity of
the starlight illuminating the dust varies from 1 to 21 in steps of
1. A model with chi=1 assumes the same bolometric intensity as the
ISRF in the solar neighbourhood. Note, however, that in general the
spectrum of the radiation field will be different.

 All models are calculated for an age of 0.25Gyrs. Also f=0 and t_m=0
are assumed. The star formation rate is assumed to have an e-folding
time of 6Gyrs.


Tools for calculating new models
--------------------------------

More cirrus models can be calculated with the IDL routine
cirrus_model.pro which is also included in this directory
(tar archive code.tar).

cirrus_model can be used to simulate pure cirrus emission or
a combination of cirrus and starburst (see Efstathiou &Rowan-Robinson 2003)

Example 1 (pure cirrus):
------------------------

 dt=2.e6
 time=dt*indgen(7000)
 tau=6.e9
 sfr=exp(-time/tau)
 chi=1.
 age=0.25e9 
 f=1.
 t_m=0.
 build_ssp,f,t_m,models
 cirrus_model, time, sfr, age, chi, lambda, gal_models,Av=0.5
 
Example 2 (cirrus with a molecular cloud phase for 1.e7 years):
--------------------------------------------------------------

 dt=2.e6
 time=dt*indgen(7000)
 tau=6.e9
 sfr=exp(-time/tau)
 chi=1.
 age=0.25e9 
 f=1.
 t_m=1.e7
 build_ssp,f,t_m,models
 cirrus_model, time, sfr, age, chi, lambda, gal_models,Av=0.5
 
Example 3 (cirrus with a starburst in last 3e7 years):
------------------------------------------------------

 dt=2.e6
 time=dt*indgen(7000)
 tau=6.e9
 age=0.25e9
 sfr=exp(-time/tau) 
 t_sb=age-3.e7
 sb=where(time ge t_sb)
 tau_sb=1.e7
 f_sb=1.
 sfr(sb)= sfr(sb) + f_sb*exp(-(time(sb)-t_sb)/tau_sb)
 chi=1.
 f=1.
 t_m=3.e7
 build_ssp,f,t_m,models
 cirrus_model, time, sfr, age, chi, lambda, gal_models,Av=0.5


 A description of the input, output and keywords can be found in the
body of the routine. The output is lambda and gal_models which give
the wavelength grid (in microns) and the calculated spectrum (nuF_nu)
in solar luminosities (assuming sfr is in solar masses per year and time
 is in years).