Astrid Data Structure

PIG_{id}: Particle data within each halo(=group=FoFgroup), organized by halos

• FoFGroup
  • Group of particles linked by Friend-of-friend algorithm and contains information of particles within each halo
  • Data can be read by pig.open('FoFGroup/{feature}')[:]

  • Detailed data structure:

    Feature	Size	Unit	Description
    GroupID	[Nhalo, 6]	None	ID of the FoF halo to which this particle belongs.−1 is particle does not belongto a halo. Could be different from snapshot to snapshot.
    LengthByType	[Nhalo, 6]	None	The number of particles of each type within halo ‘ID’ E.g. pig.open('FoFGroup/LengthByType')[:][5][0] is the number of gas(type 0) particles in the 5th halo Useful for acquiring particle info within the data
    OffsetByType	[Nhalo, 6]	None	=cumsum(LengthByType,axis=0)
    MassByType	[Nhalo, 6]	1e10Msun/h	Total mass of a particular species
    Mass	[Nhalo, 6]	1e10Msun/h	Total mass of the halo
    Firstpos	[Nhalo, 3]	ckpc/h	The position of particle with minID.
    MassCenterPosition	[Nhalo, 3]	ckpc/h	(x,y,z) coordinate of the halo center of mass
    MassCenterVelocity	[Nhalo, 3]	(1/a)km/s	(vx,vy,vz) -> the mass-weighted velocity
    Imom	[Nhalo, 3]	unit	Moment of inertia (for rotation), relative to the COM
    StarFormationRate	[Nhalo,1]	(1e10 Msun)/(980 Myr)	The rate at which star particles are born
    BlackholeAccretionRate	[Nhalo,1]	(1e10 Msun)/(980 Myr)	The rate at which BHs accrete mass Accretion (=increase in mass by swallowing gas) rate of all BHs within the halo
    BlackholeMass	[Nhalo,1]	1e10 Msun/h	Total mass of all BHs linked to this halo
    MinID	[Nhalo,1]	None	Minimum ID/li>

• Features shared by all particle types
  • These are the features shared by Gas, DM, Star and BH particles
  • They will be summarized here and not repeated in the particle-specific descriptions.

  • Detailed data structure:

    Feature	Size	Unit	Description
    ID	[Npart,1]	None	64-bit unique IDs of each particle.
    GroupID	[Npart,1]	None	The ID of the FoF group the particle belongs to at this snapshot
    Mass	[Npart,1]	1e10 Msun/h	Mass of each particle
    Position	[Npart,3]	ckpc/h	Position of each particle in internal units relative to the lower-left corner of the box.
    Velocity	[Npart,3]	(1/a)(km/s)	(vx,vy,vz) velocity of each particle.
    Density	[Npart,1]	(1e10 Msun/h)/(ckpc/h)3	The density of the particle in internal units.
    Potential	[Npart,1]	(km/s)2/a	Gravitational potential experienced by this particle.

• Gas Particle (Type 0) Specific Data
  • These are the features specific to the gas particles (some also shared by Stars and BHs)
  • Most features are [Ngas,1] or [Ngas,3] arrays, where Ngas=sum(LengthByType[:,0]) is the number of gas particles associated with halos

  • Detailed data structure:

    Feature	Size	Unit	Description
    Internal Energy	[Ngas,1]	(km/s)2	The internal energy (energy per unit mass) in internal units. Use to calculate gas temperature
    Entropy	[Ngas,1]	[km/s]2/((1e10 Msun/h)/(kpc/h)3)(gamma-1)	Entropy of each gas particle
    Pressure	[Ngas,1]	[km/s]2*((1e10 Msun/h)/(kpc/h)3)*a	Pressure of gas particle
    EgyWtDensity	[Ngas,1]	(1e10 Msun/h)/(ckpc/h)3	Entropy-weighted density of each gas particle
    ElectronAbundance	[Ngas,1]	unitless	The number density of free electrons per hydrogen atom. Defined so that the maximum for fully ionized primordial gas is ∼1.15.
    SmoothingLength	[Ngas,1]	ckpc/h	The SPH smoothing length of the gas particle.
    Generation	[Ngas,1]	unitless	For gas particles, the number of stars spawned by the gas particle.
    H2Fraction	[Ngas,1]	unitless	Ionization fraction by mass.
    Metallicity	[Ngas,1]	unitless	Mass fraction of elements beyond H and He.
    NeutralHydrogenFraction	[Ngas,1]	unitless	The neutral hydrogen fraction, derived from the cooling rate network.
    StarFormationRate	[Ngas,1]	Msun/yr(different from FOF)	The star formation rate for particles on the star-forming equation of state.

• DM Particle (Type 1) Specific Data
  • All features are already described in the shared features.

  • Data structure:

    • GroupID
    • Mass
    • Position
    • Velocity
    • Potential
    • ID
    • Generation
• Star Particle (Type 4) Specific Data

  • Data structure:

    • These are the features specific to Star particles.
    • Some features are shared with gas particles.

    • Detailed data structure:

      Feature	Size	Unit	Description
      StarFormationTime	[Nstar,1]	unitless	The scale factor at which thestar or black hole particle was formed.
      Metallicity	[Nstar,1]	unitless	Mass fraction of elements beyond H and He.
      Generation	[Nstar,1]	unitless	The number of Star particles spawned by the gas particle before this one.

  • BH Particle (Type 5) Specific Data

    • Data structure:

      • These are the features specific to BH particles.
      • Some features are shared with gas particles.

      • Detailed data structure:

        Feature	Size	Unit	Description
        BlackholeAccretionRate	[Nbh,1]	(1e10Msun)/(980 Myr)	The mass accretion rate of the blackhole.
        Mass	[Nbh,1]	1e10 Msun/h	Dynamical mass of the blackhole, used for force calculations.
        BlackholeMass	[Nbh,1]	1e10 Msun/h	The accretion mass of the blackhole. This may differ from the dynamical mass.
        BlackholeProgenitors	[Nbh,1]	unitless	The number of seed black holes that merged into this one.
        BlackholeLastMergerID	[Nbh,1]	unitless	ID of the blackhole last swallowed by this one.
        BlackholePressure	[Nbh,1]	[km/s]2*((1e10 Msun/h)/(kpc/h)3)*a	Pressure at the location of BH particle
        BlackholeMinPotPos	[Nbh,3]	ckpc/h	The position of the particle nearest the potential minimum of the halo the last time this black hole was active.
        BlackholeGasVel	[Nbh,3]	(1/a)(km/s)	Velocity of the surrounding gas within the SPH kernel.
        BlackholeMinPotVel	[Nbh,3]	(1/a)(km/s)	The velocity of the particle nearest thepotential minimum of the halo the last time this black hole was active.
        Generation	[Nbh,1]	unitless	The number of BH particles spawned by the gas particle before this one

    UML