#Hydro Modelling stellar winds in galactic nuclei

##Requirements The following packages are required to run the code. I have only used it with the version numbers in parentheses...

Scipy (1.8.1)

Numpy (0.14)

Astropy (0.4)

Dill (0.2.1)

##Model This code is designed to model the injection of stellar winds in a galactic nucleus. The equations solve are the 1d spherically symmetric hydro equation with source terms accouting for the injection of winds from stars and potentially also including cooling and conductivity...

The relevant equations are summarized here...

Much more detail about our model may be found in https://ui.adsabs.harvard.edu/#abs/2015MNRAS.453..775G/abstract

##Comment on different galaxy models

The code includes three different types of model galaxies differing in the way their stellar density profile are implemented

1. Galaxy.

   The stellar density is assumed to be zero. Therefore the the stars do not contribute to to the gravitational potential. However by default there is a contribution from the stellar velocity dispersion: this is given by

   Thus the only gravity is from the central black hole, whose mass is stored in the dictionary params (under params['M'])

2. NukerGalaxy.

   This assumes that stellar light profile follows a Nuker Law (Faber et al. 1997). User shold pass the name of a galaxy. Along with the name the user may also pass a dictionary of nuker galaxies (using the keyword gdata). Each entry in this dictionary should itself be a dictionary of Nuker parameters.

   If no dictionary is passed to gdata one is constructed from the file wm (this is table 1 Wang & Merritt 2004).

   The mass enclosed from the stars contributes to the gravitational potential.

3. Pow Galaxy.

   This galaxy corresponds to a broken power law density profile.

##Example running of code...

The following run was designed to reproduce the results from Quataert 2004, and also illustrates a basic example of running the code.

import galaxy

#Bounds for grid
rmin=3.8E16
rmax=3.E18

'''Init is a dictionary which contain info for initializtion of the grid: rmin is the inner boundary,
rmax is the outer boundary. length (not shown) controls the number of grid points. func_params contain parameters to be passes to the initialization function ''' 
init={'rmin':rmin, 'rmax':rmax, 'func_params':dict(rho_0=1.E-23, temp=1.E7, n=0.)}

#Initialize galaxy
gal=galaxy.Galaxy(init=init)
#Set boundary condition
gal.set_param('bdry', 'bp')
#Set molecular weight 
gal.set_param('mu', 0.5)
gal.set_param('tinterval', None)
#Output directory
gal.set_param('outdir', 'quataert')
#Turn off heating from velocity dispersion
gal.set_param('sigma_heating', False)
#Turn on isothermal evolution
gal.set_param('isot', True)
#Run for sound crossing time
gal.solve(gal.tcross)
#Turn off isothermal evolution
gal.set_param('isot', False)
#Run for another sound crossing time.
gal.solve(gal.tcross)

##Summary of galaxy properties, possible values, and defaults Note that parameters may be adjusted using the set_param method (which accepts the name of a parameter and the value you would like to change it to).

Note that in finding a solution it is often useful for numerical stability to adjust a parameter gradually: this may be done using the solve_adjust method

1. params (stores structural parameters of galaxy--the assumed structure is somewhat different for each type of galaxy). These are used to calculate potentials, stellar density profiles, etc.

Numerical parameters: 2. Re (float) -90. artificial viscosity in the velocity equation

3. Re_s (float)- 1.E20 artificial viscosity in the entropy equation (note default corresponds to essential no viscosity).

4. bdry (string or tuple) type of condition to use. Note that the user may pass in a tuple specifying the inner and outer boundary conditions separately. After updating all the physical zones: we must update the ghost zones on the boundary (there are three on each side of the grid).

   *'default': power law extrapolations (of density, velocity and entropy)

   *'ss': same as default except if the mach number is less than unity on the boundary

   *'mdot_fixed': power law extrapolations of density and entropy. Velocity is set by equating the difference in mass flux between each ghost zone and the closest physical zone and the integral of the mass source term between the ghost zone and the closest physical zone.

   *'bp':

Physics parameters

4. vw_extra (float)-1.E8 extra heating rate

5. phi_cond (float)

6. mu (float) -1. molecular weight

7. isot (bool)-False turn temperature evolution on/off.

##Grid setup ...

##Driver I have written a driver code to ease the pain of running the code. Generally the easiest way to get a model galaxy working is to use an existing model as input, this may be accomplished by using the nuker_driver_gen.py code. (nuker_driver_gen.py input).