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
`check_energies`	`boolean`	`.true.`	when flagging clumps for sink formation, check whether their gravitational energy is dominant
`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, threshold
`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
`nlevelmax_sink`	`integer`	`0`	Allow sinks to form on a level that is lower than what is set by nlevelmax. This is useful in zoom simulations where nlevelmax is set to a high value but in the first phase refinement is limited to only a few levels. nlevelmax_sink should be set to the maximum allowed refinement level.
`cloud_pts_check`	`boolean`	`.false.`	Useful when there is a large number of sinks (>1000) with a large number of cores. When true: optimizes the creation of cloud particles.

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

Sink particles

Contents

Sink particles#

Overview of parameters#

Example set of parameters for cosmological simulations with AGN feedback#