Understanding and Analysing VELOCIraptor Output

VELOCIraptor produces several different types of output files.

(with the mpi threads appending their rank to the end of the file name unless not compiled with MPI or if Parallel HDF5 is used.):

Standard files

• .properties: a file containing the bulk properties of all structures identified.

• .catalog_groups: a file containing the size of the structures (in number of particles associated) & information need to read particle information produced by velociraptor

• .catalog_particles: a file containing a list of particle IDs of those in structures. Information contained in .catalog_groups is used to parse this data.

• .catalog_particles.unbound: similar to catalog_particles but lists particles in structures but are formally unbound. Information contained in .catalog_groups is used to parse this data.

Extra files

• .catalog_parttypes: a file similar to .catalog_particles but containing a list of particle types of those in structures. Information contained in .catalog_groups is used to parse this data. Produced if multiple particle types are processed by VELOCIraptor.

• .catalog_parttypes.unbound: similar to catalog_parttypes but lists particles in structures but are formally unbound.

• .profiles : a file containing the radial profiles of groups. Produced if radial profiles are requested.

• .catalog_SOlist : a file containing the a list of particle IDs of particles found within a large Spherical region around Field halos. Produced if a list of paritcles wihtin so regions is requested.

Properties

There are a variety of properties calculated for each object found. Some are typical of all halo finders such as the mass of an object (which can be a halo, subhalo, tidal debris), along with more complex properties such as the eigenvectors and eigenvalues of the mass distribution defined by the reduced inertia tensor. The number of properties also varies with the type of run. For hydrodynamic simulations where VELOCIraptor has been compiled to use gas, star and black hole properties, such as masses, temperatures, etc are also calculated. The code will also calculate properties based on loading specific extra fields associated with particle types (this interface requires HDF5 input or on the fly invocation and outputs properties with the same name as the loaded property, see Using VELOCIraptor).

Note that if HDF5 output is produced, the properties will be in the form of data sets with specific names and each data set will have attributes describing the unit of the field in the form of Dimension_Length, Dimension_Mass, Dimension_Velocity, Dimension_Time, which indicate the index of the unit. Extra output from arbitrary input fields can also have unusual units stored in Dimension_Extra_Info as a string.

We give an almost complete list of properties and the keyword associate with the property (in ASCII and HDF5). For clarity we list properties in several tables corresponding to

• Standard Properties,

• Gas Properties,

• Star Properties,

• Black Hole Properties,

• Interloper Properties,

• Extra DM Properties,

Standard Properties

This is a list of standard properties that are always calculated unless indicated otherwise (some require an extra configuration option). Properties are calculated relative to the object’s centre, which can be either the position of the particle with the minimum potential, or centre-of-mass, or position of most bound particle.

Name	Comments
ID and Type information
ID	Halo ID. ID = index of halo + 1 + TEMPORALHALOIDVAL * Snapshot_value, giving a temporally unique halo id that can be quickly parsed for an index and a snapshot number.
ID_mbp	Particle ID of the most bound particle in the group.
hostHaloID	ID of the host field halo. If an object is a field halo, this is -1.
Structuretype	Structure types contain information on how the object was found and at what level in the subhalo hierarchy. Field halos are 10. Substructures identified using the local velocity field are type 10+10=20, substructures identified using cores are type 10+5=15. For structures found at level 2 (ie: subhalos within subhalos), the type offset is 20, and so on.
numSubStruct	Number of substructures. Subhalos can have subsubhalos.
Mass and radius properties: All properties are in output units.
npart	Number of particles belonging exclusively to the object.
Mass_tot	Total mass of particles belonging exclusively to the object,
	\(M_{\rm tot}\).
Mass_FOF	Total mass of particles in the FOF, \(M_{\rm FOF}\). Is zero for substructure.
Mass_200mean	Overdensity mass defined by mean matter density, \(M_{200\rho_m}\). For field halos, if inclusive masses are desired, this is based on the particles in the FOF. If full spherical overdensity masses are desired, then includes all particles (whether they belong to the object, the background or another object) within a spherical region. For subhalos, this is based on particles belonging exclusively to the object.
Mass_200crit	Overdensity mass defined by critical density, \(M_{200\rho_c}\). Behaviour like Mass_200mean.
Mass_BN98	Overdensity mass defined by mean matter density and \(\Delta(z)\) given by Bryan & Norman (1998), \(M_{\Delta(z)\rho_c}\). Behaviour like Mass_200mean.
Mvir	User defined virial mass, \(M_{\rm vir}\). Behaviour like Mass_200mean.
R_size	Maximum distance of particles belonging exclusively to the object and the object’s centre.
R_200mean	Radius related to overdensity mass Mass_200mean.
R_200crit	〃
R_BN98	〃
Rvir	〃
R_HalfMass	Half mass radius based on the Mass_tot.
R_HalfMass_200mean	Half mass radius based on the Mass_200mean.
R_HalfMass_200crit	〃
R_HalfMass_BN98	〃
Angular Momentum in Spherical Overdensity: Calculate if extra halo properties are requested by setting the config option ` **Extensive_halo_properties_output=1** `Also calculates inclusive spherical overdensity and also exclusive to halo as _exclusive.
Lx_200c	\(x\) component of the total angular momentum all the mass within \(R_{200\rho_c}\).
Ly_200c	〃
Lz_200c	〃
Lx_200m	\(x\) component of the total angular momentum all the mass within \(R_{200\rho_m}\).
Ly_200m	〃
Lz_200m	〃
Lx_BN98	\(x\) component of the total angular momentum all the mass within \(R_{BN98}\).
Ly_BN98	〃
Lz_BN98	〃
Position and Velocity: All properties are in output units. Objects have positions periodically wrapped.
Xc	\(x\) coordinate of centre-of-mass.
Yc	〃
Zc	〃
Xcmbp	\(x\) coordinate of most bound particle.
Ycmbp	〃
Zcmbp	〃
Xcminpot	\(x\) coordinate of the minimum potential.
Ycminpot	〃
Zcminpot	〃
VXc	\(v_x\) velocity of centre-of-mass.
VYc	〃
VZc	〃
VXcmbp	\(v_x\) velocity of most bound particle.
VYcmbp	〃
VZcmbp	〃
VXcminpot	\(v_x\) velocity of the particle with the minimum potential.
VYcminpot	〃
VZcminpot	〃
Velocity and Angular Momentum: All properties are in output units.
Vmax	Maximum circular velocity based on particles belonging exclusively to the object, where circular velocities are defined by \(V_{\rm circ}^2=GM/R\).
Rmax	Radius of maximum circular velocity.
sigV	Velocity dispersion based on the velocity dispersion tensor \(\sigma_v=|\Sigma|^{1/6}\), where \(\Sigma\) is the velocity dispersion tensor.
veldisp_xx	The \(x,x\) component of the velocity dispersion tensor.
veldisp_xy	〃
veldisp_xz	〃
veldisp_yx	〃
veldisp_yy	〃
veldisp_yz	〃
veldisp_zx	〃
veldisp_zy	〃
veldisp_zz	〃
Lx	\(x\) component of the total angular momentum about the object’s centre and centre-of-mass-velocity using particles belonging exclusively to the object.
Ly	〃
Lz	〃
lambda_B	Bullock et al (2001) like spin parameter \(\lambda_B\) using total angular momentum and the spherical overdensity mass, \(\lambda_B=\frac{J}{\sqrt{2}MVR}\).
Krot	Measure of rotational support about the angular momentum axis \(\kappa_{\rm rot}=\frac{\sum_i 1/2 m_i j_{z,i}r_i}{\sum_i T_i}\), where the first sum is over the motion of particles along the angular momentum axis and the second sum is over kinetic energies (see Sales et al (2010)).
Morphology: All properties are in output units.
cNFW	Calculated assuming an NFW profile (Navarro, Frenk, & White 1997) following Prada et al, (2012a) where we solve \(\frac{V_{\rm max}^2}{GM_\Delta/R_\Delta}-\frac{0.216c}{\ln(1+c)-c/(1+c)}=0.\)
cNFW_200crit	Calculated assuming an NFW profile (Navarro, Frenk, & White 1997) using the half mass radius relative to the overdensity radius :math:``muequiv R_{1/2}/R_Delta` where here uses the 200crit overdensity mass to solve \(\ln(1+\mu c)-\mu c/(1+\mu c) - 1/2[\ln(1+c)-c/(1+c)] =0.\)
cNFW_200mean	〃
cNFW_BN98	〃
q	We calculate the shape using the reduced inertia tensor (Dubinski et al, 1991; Allgood et al, 2006), \(\tilde{I}_{j,k}=\sum\limits_n \frac{m_n x^\prime_{j,n} x^\prime_{k,n}}{(r^\prime_{n})^2}\) where the sum is over particles exclusively belonging to the object and, \((r^\prime_n)^2=(x^\prime_n)^2+(y^\prime_n/q)^2+(z^\prime_n/s)^2\) is the ellipsoidal distance between the halo’s centre and the \(n_{\rm th}\) particle, primed coordinates are in the eigenvector frame of the reduced inertia tensor and \(q\) & \(s\) are the semi-major and minor axis ratios respectively. Thus \(q\) is the semi-major axis ratio. In eigenvector frame, x axis is major, y is semi-major, and z minor.
s	Minor axis ratio.
eig_xx	Eigenvectors of morphology.
eig_xy	〃
eig_xz	〃
eig_yx	〃
eig_yy	〃
eig_yz	〃
eig_zx	〃
eig_zy	〃
eig_zz	〃
Energy: All properties are in output units.
Ekin	The total kinetic energy, \(\sum T_i\).
Epot	The total gravitational potential energy \(1/2\sum W_i\), where 1/2 comes from double counting.
Efrac	The fraction of particles that are formally bound (i.e., have \(W_i+T_i<0\)).
Quantities within \(R(V_{\rm max})\): Properties based on particles within \(r\leq R(V_{\rm max})\).
RVmax_sigV	Dispersion, like sigV for \(r\leq R(V_{\rm max})\).
RVmax_veldisp_xx	Dispersion tensor, like veldisp_xx for \(r\leq R(V_{\rm max})\).
RVmax_veldisp_xy	〃
RVmax_veldisp_xz	〃
RVmax_veldisp_yx	〃
RVmax_veldisp_yy	〃
RVmax_veldisp_yz	〃
RVmax_veldisp_zx	〃
RVmax_veldisp_zy	〃
RVmax_veldisp_zz	〃
RVmax_lambda_B	Spin parameter, like lambda_B for \(r\leq R(V_{\rm max})\).
RVmax_Lx	Total angular momentum, like Lx for \(r\leq R(V_{\rm max})\).
RVmax_Ly	〃
RVmax_Lz	〃
RVmax_q	Semi-major axis ratio, like q for \(r\leq R(V_{\rm max})\).
RVmax_s	Minor axisratio, like s for \(r\leq R(V_{\rm max})\).
RVmax_eig_xx	Eigenvectors of morphology, like eig_xx for \(r\leq R(V_{\rm max})\).
RVmax_eig_xy	〃
RVmax_eig_xz	〃
RVmax_eig_yx	〃
RVmax_eig_yy	〃
RVmax_eig_yz	〃
RVmax_eig_zx	〃
RVmax_eig_zy	〃
RVmax_eig_zz	〃
Additional Spherical Overdensity Mass/radius: If extra spherical overdensity values are requested via Overdensity_values_in_critical_density config option, code calculates masses/radii/angular momentum following a naming convention of SO_property_rhocrivalue_rhocrit where rhocritvalue is the overdensity value in units of the critical density, e.g., SO_mass_100_rhocrit. The code will also calculate quantities based on particle type: gas, star, interloper, following SO_property_parttype_rhocrivalue_rhocrit
mass	Mass enclosing a average density of the associated SO value.
Lx	Angular momentum of enclosed mass in x-direction
Ly	〃 in y-direction
Lz	〃 in z-direction
Aperture quantities: If aperture quantities are requested code calculates a variety of properties within spherical aperture in pkpc. Naming convention is Aperture_quantity_radiusvalue_kpc, or for a specific particle type Aperture_quantity_parttype_radiusvalue_kpc, e.g. Aperture_mass_10_kpc. Particle types where individual quantities are calculated: gas, star, bh, interloper. We list the property names here.
mass	Total mass in aperture.
npart	Total number of particles.
rhalfmass	Radius enclosing half the mass within the aperture.
veldisp	Velocity disperion
Projected aperture quantities: Similar to aperture quantitites but for 3 different projections based on particles within a projected radius in pkpc. Naming convention is Projected_aperture_i_quantity_radiusvalue_kpc, where i is from 0, 1, 2 for a x,y,z projection.
mass	Total mass in aperture.
rhalfmass	Radius enclosing half the mass within the aperture.

Gas Properties

This is a list of gas properties that are calculated if code is compiled with USE_GAS. Some require an extra configuration option. Also, Spherical overdensity masses + angular momentum, aperture properties, projected aperture properties are calculated for gas particles along along with some extra gas only properties.

Name	Comments
Gas quantities: Bulk properties of gas particles/tracers when compiled to process gas properties. Properties unique to gas are T_gas and SFR_gas.
n_gas	Number of gas particles.
M_gas	Total gas mass \(M_{\rm gas}\).
M_gas_Rvmax	Gas mass within \(R(V_{\rm max})\).
M_gas_30kpc	Gas mass within 30 pkpc.
M_gas_500c	Gas mass within a spherical overdensity of \(500\rho_c\).
Xc_gas	\(x\) coordinate of centre-of-mass of gas particles relative to Xc.
Yc_gas	〃
Zc_gas	〃
VXc_gas	\(x\) coordinate of centre-of-mass velocity of gas particles relative to VXc.
VYc_gas	〃
VZc_gas	〃
Efrac_gas	Like Efrac but for gas particles only.
R_HalfMass_gas	Like R_HalfMass but for gas particles only.
veldisp_xx_gas	Like veldisp_xx but for gas particles only and relative to the centre-of-mass.
veldisp_xy_gas	〃
veldisp_xz_gas	〃
veldisp_yx_gas	〃
veldisp_yy_gas	〃
veldisp_yz_gas	〃
veldisp_zx_gas	〃
veldisp_zy_gas	〃
veldisp_zz_gas	〃
Lx_gas	Like Lx but for gas particles only and relative to the centre-of-mass.
Ly_gas	〃
Lz_gas	〃
q_gas	Like q but for gas particles only and relative to the centre-of-mass.
s_gas	Like s but for gas particles only and relative to the centre-of-mass.
eig_xx_gas	Like eig_xx but for gas particles only and relative to the centre-of-mass.
eig_xy_gas	〃
eig_xz_gas	〃
eig_yx_gas	〃
eig_yy_gas	〃
eig_yz_gas	〃
eig_zx_gas	〃
eig_zy_gas	〃
eig_zz_gas	〃
Krot_gas	Like Krot but for gas particles only and relative to the halo’s centre.
T_gas	Average temperature of gas.
Zmet_gas	Average metallicity of gas.
SFR_gas	Total star formation rate of gas.
Star Forming (sf)/Non Star Forming (nsf) Gas quantities: Similar to gas properties but split by sf/nsf gas. For brevity, we list only quantities unique to sf, as the nsf gas is similar but with _nsf naming convention. Only calculated if USE_GAS and USE_STAR flags on.
M_gas_sf	Total gas mass \(M_{\rm gas}\).
R_HalfMass_gas_sf	Half mass radii.
sigV_gas_sf	Velocity dispersion of the gas.
Lx_gas_sf	Like Lx_gas but for star forming gas.
Ly_gas_sf	〃
Lz_gas_sf	〃
Krot_gas_sf	Like Krot_gas but for star forming gas
T_gas_sf	Average temperature of star forming gas.
Zmet_gas_sf	Average metallicity of star forming gas.
Aperture quantities: If aperture quantities are requested code calculates a variety of properties within spherical aperture in pkpc. Naming convention is Aperture_quantity_gas_radiusvalue_kpc. We list the additional properties calculated for gas here (which are in addition to mass,rhalfmass, etc).
Zmet	Average gas metallicity in aperture.
SFR	Total star formation rate of gas in aperture.
Projected aperture quantities: Similar to aperture quantitites but for 3 different projections based on particles within a projected radius in pkpc. Naming convention is Projected_aperture_i_quantity_gas_radiusvalue_kpc, where i is from 0, 1, 2 for a x,y,z projection. We list the additional properties calculated for gas here (which are in addition to mass,rhalfmass, etc).
Zmet	Average gas metallicity in projected aperture.
SFR	Total star formation rate of gas in projected aperture.

Name	Comments
Extra Gas Properties: If extra gas fields are loaded by listing them using Gas_internal_property_names Gas_chemistry_names and/or Gas_chemistry_production_names. The are associated input options related to the input index calclation type done and output units. The output will have the following naming convention: nameoffield_index_#_calculation_units_gas e.g.`, AlphaElements_index_0_average_unitless_gas. Also requires that code is compiled with the USE_GAS flag As an example we show the fields if Gas_internal_property_names=Pressure,MetalMassFractionFromSNIa, Gas_internal_property_index=0,1, Gas_internal_property_output_units=kPa,unitless, Gas_internal_property_calculation_type=max,average,
Pressure_index_0_max_kPa_gas	maximum pressure of gas in object.
MetalMassFractionFromSNIa_index_1_average_unitless_gas	average of this field.
One can also specify aperture_total and aperture_average as functions if aperture quantities are calcualed. The output will have a simlar naming convention to above but with Aperture_ at the start and ending with the aperture aperture itself #_kpc` for each aperture listed.

Star Properties

This is a list of stellar properties that are calculated if code is compiled with USE_STAR. Some require an extra configuration option.

Name	Comments
Star quantities: Bulk stellar properties when compiled to process star properties. Similar to gas properties but has _star instead of _ gas. For brevity, we list only quantities unique to star particles.
tage_star | Average stellar age.
Aperture quantities: If aperture quantities are requested code calculates a variety of properties within spherical aperture in pkpc. Naming convention is Aperture_quantity_star_radiusvalue_kpc. We list the additional properties calculated for star here (which are in addition to mass,rhalfmass, etc).
Zmet	Average stellar metallicity in aperture.
Projected aperture quantities: Similar to aperture quantitites but for 3 different projections based on particles within a projected radius in pkpc. Naming convention is Projected_aperture_i_quantity_star_radiusvalue_kpc, where i is from 0, 1, 2 for a x,y,z projection. We list the additional properties calculated for gas here (which are in addition to mass,rhalfmass, etc).
Zmet	Average stellar metallicity in projected aperture.
Extra Star Properties: Like the extra gas properties but calculated if ` Star_internal_property_names Star_chemistry_names `and/or Star_chemistry_production_names. Naming convention is the same but ends with _star Also requires that code is compiled with the USE_STAR flag

Black Hole Properties

This is a list of black hole properties that are calculated if code is compiled with USE_BH. Some require an extra configuration option.

Name	Comments
Black hole quantities: Bulk properties of black hole particles when compiled to process black hole properties.
n_bh	Number of black hole particles.
Mass_bh	Total mass of black hole particles.
Extra Black hole Properties: Like the extra gas properties but calculated if ` BH_internal_property_names BH_chemistry_names `and/or BH_chemistry_production_names. Naming convention is simialr save ends with _bh Also requires that code is compiled with the USE_BH flag

Interloper Properties

This is a list of interloper DM properties that are calculated if code is compiled with ZOOM_SIM. These properties are based on low resolution particles and can be used to gauge the level of contamination

Name	Comments
Interloper particles: If analysing multi-resolution simulations, low resolution particles are often treated as contaminants. These are bulk properties of low resolution contaminant particles.
n_interloper	Number of low resolution, interloper particles.
Mass_interloper	Total mass of low resolution, interloper particles.

Extra DM Properties

This is a list of Extra DM properties that are calculated if code is compiled with USE_EXTRADM. These properties are useful if running on standard dark matter.

Name	Comments
Extra DM Properties: Like the extra gas properties but calculated if ` Extra_DM_internal_property_names `has fields specified. Useful for nonstandard dark matter runs, such as annihilating or interacting dark matter. Naming convention is nameoffield_extra_dm Also requires that code is compiled with the USE_EXTRADM flag