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Sink particles

The block named &SINK_PARAMS contains the parameters related to the sink particle implementation, which can be used for

star formation (most recently Bleuler & Teyssier 2015)
supermassive black hole evolution and AGN feedback (most recently Biernacki, Teyssier and Bleuler 2017)

Overview of parameters

Variable name	Fortran type	Default value	Description
`smbh`	`boolean`	`.false.`	Controls if sink behaves as a star or SMBH
`agn`	`boolean`	`.false.`	Controls if SMBH sink produces feedback
`create_sinks`	`boolean`	`.false.`	Specifies if sinks are formed with clump finder
`nsinkmax`	`integer`	`2000`	Maximum number of sinks allowed to form
`mass_sink_direct_force`	`float`	`-1`	Mass in Msun above which sinks are treated with direct N-body solver
`ir_cloud`	`integer`	`4`	Radius of cloud region in unit of grid spacing
`ir_cloud_massive`	`integer`	`3`	Radius of massive cloud region in unit of grid spacing
`sink_soft`	`integer`	`2`	Gravitational softening length in dx at levelmax for "direct force" sinks
`n_sink`	`float`	`.false.`	Sink (as a star) formation density threshold in H/cc
`rho_sink`	`float`	`.false.`	Sink (as a star) formation density threshold in g/cc
`d_sink`	`float`	`.false.`	Sink (as a star) formation density threshold in code units
`clump_core`	`boolean`	`.false.`	Trims the clump (for sinks as stars only)
`mass_sink_seed`	`float`	`0.0`	Dynamical mass of sink seed in Msun
`mass_smbh_seed`	`float`	`0.0`	Accretion mass of sink seed in Msun, if 0, then dynamical and accretion masses are equivalent
`mass_halo_AGN`	`float`	`1e10`	Mass of a halo in which AGN sinks are seeded
`mass_clump_AGN`	`float`	`1e10`	Mass of a clump in which AGN sinks are seeded
`accretion_scheme`	`string`	`none`	Accretion scheme: none, bondi
`eddington_limit`	`boolean`	`.false.`	Controls if accretion rate should be limited by Eddington rate
`acc_sink_boost`	`float`	`1`	Value of boost factor in Bondi velocity (-1 to depend on density)
`boost_threshold_density`	`float`	`0.1`	Threshold density for boosting, typically the same as n_star; in H/cc
`bondi_use_vrel`	`boolean`	`.false.`	Excludes relative velocity between gas and sink from the accretion calculations
`mass_merger_vel_check_AGN`	`float`	`-1`	Mass above which the check for two sinks' binding energy is applied, in Msun
`merging_timescale`	`float`	`-1`	Time during which sinks are considered for merging (non-SMBH only)
`verbose_AGN`	`boolean`	`.false.`	Controls verbosity of AGN in the log file
`AGN_fbk_mode_switch_threshold`	`float`	`0.1`	Controls the AGN feedback switching
`AGN_fbk_frac_ener`	`float`	`1.0`	Controls what fraction of energy goes into thermal feedback
`T2_min`	`float`	`1e7`	Minimum temperature to which AGN blast should heat the gas in K
`T2_AGN`	`float`	`1e12`	Temperature of AGN blasts in K - feedback efficiency
`AGN_fbk_frac_mom`	`float`	`1.0`	Controls what fraction of energy goes into kinetic feedback
`epsilon_kin`	`float`	`1.0`	Kinetic feedback coupling efficiency
`kin_mass_loading`	`float`	`100.`	Kinetic feedback mass loading
`cone_opening`	`float`	`180.`	Opening angle of the cone through which momentum feedback proceeds

Example set of parameters for cosmological simulations with AGN feedback

The example listed below by no means can fit everyone's needs, but can serve as a minimum starting example.

#!fortran
&SINK_PARAMS
! General switches
smbh=.true.                 ! turns sinks into SMBH
agn=.true.                  ! enables AGN feedback
create_sinks=.true.         ! enables formation of new sink particles
mass_sink_direct_force=1.0  ! minimum mass of sink to treat it with direct solver, in M_sun

! Seeding masses
mass_sink_seed=1.0d6        ! dynamical mass of sink particle
mass_smbh_seed=1.0d6        ! accretion mass of sink particle
mass_halo_AGN=5.d10         ! minimum mass of PHEW halo in which a sink is seeded
mass_clump_AGN=1.d9         ! minimum mass of PHEW clump in which a sink is seeded

! Accretion
accretion_scheme='bondi'    ! selects Bondi accretion as accretion mode
eddington_limit=.true.      ! enables Eddington limit on accretion
acc_sink_boost=-1           ! boosts accretion according to Booth&Schaye 2009
boost_threshold_density=0.1 ! threshold density for boosting, typically the same as n_star; in H/cc
bondi_use_vrel=.false.      ! excludes relative velocity between gas and sink from the accretion calculations 

! Merging
mass_merger_vel_check=1e8   ! sum of sinks' masses for which velocities are checked upon merging to determine if the system is bound

! Feedback
T2_min=0                    ! if feedback can heat the gas to this temperature then deposit it; here deposits at every fine step
T2_AGN=0.15d12              ! thermal feedback efficiency
AGN_fbk_frac_ener=1.0       ! controls what fraction of energy goes into thermal feedback, here 100%
AGN_fbk_frac_mom=0.0        ! controls what fraction of energy goes into momentum feedback, here 0%
AGN_fbk_mode_switch_threshold=1d-2 ! switches between thermal (above) and momentum modes for this ratio of Bondi-to-Eddington
epsilon_kin=1.              ! momentum feedback efficiency
kin_mass_loading=100.       ! mass loading factor of momentum feedback
cone_opening=90.            ! opening angle of the cone in which momentum feedback is deposited (180. means full sphere)
/

Notes:

if agn=.false. all feedback settings are disregarded
in order to seed the sink both mass_halo_AGN and mass_clump_AGN have to be satisfied (as well as condition of only one sink per halo and minimum density of the halo - at least star forming)
currently the only other accretion mode besides bondi is none; please feel free to add more
to not boost accretion, set acc_sink_boost=0.0
it is highly advised to use T2_min=0.0 in order to have all feedback modes on the finest timestep
if chi_switch=0.0, then the initial values of AGN_fbk_frac_* will be used throughout the simulation