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Group catalogs

Group catalogs contain a list of identified haloes and subhaloes, and their associated properties. They are identified at run time using the FOF and SUBFIND algorithms, respectively. Briefly, the FOF algorithm isolates groups of dark matter particles (haloes) that are closer to each other than 0.2 times the mean inter-particle distance. Other types of particles are then associated to the same group as their nearest DM particle. This subdivision is purely geometrical and does not include any physical property of the particle group. Each group is then split into physically-bound systems (subhaloes) using the SUBFIND algorithm. THESAN provides one catalog for each snapshot. The scale factor and redshift at which they are produced are listed under Group catalogs times below (click to open).

Group catalogs times ▾

Snapshot	scale factor	redshift
0	0.0476	20.00
1	0.0495	19.20
2	0.0514	18.47
3	0.0532	17.81
4	0.0550	17.19
5	0.0567	16.63
6	0.0585	16.11
7	0.0602	15.62
8	0.0618	15.17
9	0.0635	14.75
10	0.0651	14.35
11	0.0668	13.98
12	0.0684	13.63
13	0.0699	13.30
14	0.0715	12.98
15	0.0731	12.69
16	0.0746	12.41
17	0.0761	12.14
18	0.0776	11.89
19	0.0791	11.64
20	0.0806	11.41
21	0.0820	11.19
22	0.0835	10.98
23	0.0849	10.78
24	0.0863	10.59
25	0.0877	10.40
26	0.0891	10.22

Snapshot	scale factor	redshift
27	0.0905	10.05
28	0.0919	9.88
29	0.0933	9.72
30	0.0946	9.57
31	0.0960	9.42
32	0.0973	9.28
33	0.0986	9.14
34	0.0999	9.01
35	0.1013	8.88
36	0.1026	8.75
37	0.1039	8.63
38	0.1051	8.51
39	0.1064	8.40
40	0.1077	8.29
41	0.1090	8.18
42	0.1102	8.07
43	0.1115	7.97
44	0.1127	7.87
45	0.1139	7.78
46	0.1152	7.68
47	0.1164	7.59
48	0.1176	7.50
49	0.1188	7.42
50	0.1200	7.33
51	0.1212	7.25
52	0.1224	7.17
53	0.1236	7.09

Snapshot	scale factor	redshift
54	0.1248	7.01
55	0.1260	6.94
56	0.1271	6.87
57	0.1283	6.79
58	0.1295	6.72
59	0.1306	6.66
60	0.1318	6.59
61	0.1329	6.52
62	0.1341	6.46
63	0.1352	6.40
64	0.1363	6.34
65	0.1375	6.28
66	0.1386	6.22
67	0.1397	6.16
68	0.1408	6.10
69	0.1419	6.05
70	0.1430	5.99
71	0.1441	5.94
72	0.1452	5.89
73	0.1463	5.83
74	0.1474	5.78
75	0.1485	5.73
76	0.1496	5.69
77	0.1506	5.64
78	0.1517	5.59
79	0.1528	5.55
80	0.1538	5.50

Group catalogs are stored using the HDF5 data format. Each catalog contains an header group, whose attributes contain general information about the simulation setup and the current group catalog. The available attributes are listed here (click to open).

Header attributes ▾

Attribute	Dimensions	Units	Description
BoxSize	1	\( ckpc / h \)	Spatial extent of the periodic box (in comoving units).
HubbleParam	1	-	Little \( h \), defined as \( h = H_0 / (100 km/s/Mpc) \)
Ngroups_ThisFile	1	-	Number of FoF groups in this chunk file.
Ngroups_Total	1	-	Total number of FoF groups in the entire catalog.
Nsubgroups_ThisFile	1	-	Number of SUBFIND subgroups in this chunk file.
Nsubgroups_Total	1	-	Number of SUBFIND subgroups in the entire catalog.
NumFiles	1	-	Number of file chunks per group catalog.
Omega0	1	-	The cosmological density parameter for matter.
OmegaLambda	1	-	The cosmological density parameter for the cosmological constant.
Redshift	1	-	The redshift corresponding to the current snapshot.
Time	1	-	The scale factor \( a = 1/(1+z) \) corresponding to the current snapshot.

Within each catalog, haloes are saved in the Group HDF5 group, ranked by dark matter mass (from the most massive to the least massive one). Subhaloes are saved in the Subhalo HDF5 group, ranked by parent halo first, and then by DM mass within each parent halo. Each halo or subhalo property is saved in a separate dataset. The list of available datasets for groups and subhaloes is shown in the tables below (click to open).
NOTE: Most fields have identical meaning to those in the IllustrisTNG outputs. Those that differ have the tag (modified), while the new ones show the tag (new).

Group ▾

Dataset	Dim.	Units	Description
GroupBHMass	N	\( 10^{10} M_\odot / h\)	Sum of the BH_Mass field of all blackholes (type 5) in this group.
GroupBHMdot	N	\( 10^{10} M_\odot / h \)\( /(0.978 Gyr/h) \)	Sum of the BH_Mdot field of all blackholes (type 5) in this group.
GroupCM	(N,3)	\( ckpc/h \)	Center of mass of the group, computed as the sum of the mass weighted relative coordinates of all particles/cells in the group, of all types. Comoving coordinate.
GroupFirstSub	N	-	Index into the `Subhalo` table of the first/primary/most massive Subfind group within this FoF group. Note: This value is signed (or should be interpreted as signed)! In this case, a value of -1 indicates that this FoF group has no subhalos.
GroupGasDustMetallicity (new)	N	-	Mass-weighted dust-to-gas ratio of the group. The dust mass is obtained multiplying this value by the total gas mass of the group.
GroupGasMetalFractions (modified)	(N,9)	-	Individual abundances: H, He, C, N, O, Ne, Mg, Si, Fe (in this order). Each is the dimensionless ratio of the total mass in that species divided by the total gas mass, both computed summing all gas cells in the group. Unlike IllustrisTNG, the untracked metals are not stored separately. Their mass can be inferred from the total metal mass (computed from the gas metallicity). Note: Abundances include the metals locked in dust.
GroupGasMetallicity (modified)	N	-	Mass-weighted average metallicity (Mz/Mtot, where Z = any element above He) of all gas cells in this FOF group. Note: \( M_Z \) includes (metals locked in) dust.
GroupLen	N	-	Integer counter of the total number of particles/cells of all types in this group.
GroupLenType	(N,6)	-	Integer counter of the total number of particles/cells, split into the six different types, in this group. Note: Wind phase cells are counted as stars (type 4) for `GroupLenType`.
GroupMass	N	\( 10^{10} M_\odot / h\)	Sum of the individual masses of every particle/cell, of all types, in this group.
GroupMassType	(N,6)	\( 10^{10} M_\odot / h\)	Sum of the individual masses of every particle/cell, split into the six different types, in this group. Note: Wind phase cells are counted as gas (type 0) for `GroupMassType`.
GroupNsubs	N	-	Count of the total number of Subfind groups within this FoF group.
GroupPos	(N,3)	\( ckpc/h \)	Spatial position within the periodic box (of the particle with the minimum gravitational potential energy). Comoving coordinate.
GroupSFR	N	\( M_\odot / yr \)	Sum of the individual star formation rates of all gas cells in this group.
GroupStarMetalFractions (modified)	(N,9)	-	Individual abundances: H, He, C, N, O, Ne, Mg, Si, Fe, total (in this order). Each is the dimensionless ratio of the total mass in that species divided by the total stellar mass, for all stars in the group. Unlike IllustrisTNG, the untracked metals are not stored separately. Their mass can be inferred from the total metal mass (computed from the gas metallicity). Note: Abundances include the metals locked in dust.
GroupStarMetallicity (modified)	N	-	Mass-weighted average metallicity \( (M_Z/M_{tot} \), where Z = any element above He) of all star particles in this FOF group. Note: \( M_Z \) includes the metals locked in dust.
GroupVel	(N,3)	\( km/s/a \)	Velocity of the group, computed as the sum of the mass weighted velocities of all particles/cells in this group, of all types. The peculiar velocity is obtained by multiplying this value by 1/a.
GroupWindMass	N	\( 10^{10} M_\odot / h \)	Sum of the individual masses of all wind phase gas cells (type 4, BirthTime \(<= 0\)) in this group.
Group_M_Crit200	N	\( 10^{10} M_\odot / h \)	Total Mass of this group enclosed in a sphere whose mean density is 200 times the critical density of the Universe, at the time the halo is considered.
Group_M_Crit500	N	\( 10^{10} M_\odot / h \)	Total Mass of this group enclosed in a sphere whose mean density is 500 times the critical density of the Universe, at the time the halo is considered.
Group_M_Mean200	N	\( 10^{10} M_\odot / h \)	Total Mass of this group enclosed in a sphere whose mean density is 200 times the mean density of the Universe, at the time the halo is considered.
Group_M_TopHat200	N	\( 10^{10} M_\odot / h \)	Total Mass of this group enclosed in a sphere whose mean density is \( \Delta_c \) times the critical density' of the Universe, at the time the halo is considered. \( \Delta_c \) derives from the solution of the collapse of a spherical top-hat perturbation (fitting formula from Bryan+ 1998). The subscript 200 can be ignored.
Group_R_Crit200	N	\( ckpc / h \)	Comoving Radius of a sphere centered at the `GroupPos` of this Group whose mean density is 200 times the critical density of the Universe, at the time the halo is considered.
Group_R_Crit500	N	\( ckpc / h \)	Comoving Radius of a sphere centered at the `GroupPos` of this Group whose mean density is 500 times the critical density of the Universe, at the time the halo is considered.
Group_R_Mean200	N	\( ckpc / h \)	Comoving Radius of a sphere centered at the `GroupPos` of this Group whose mean density is 200 times the mean density of the Universe, at the time the halo is considered.
Group_R_TopHat200	N	\( ckpc / h \)	Comoving Radius of a sphere centered at the `GroupPos` of this Group whose mean density is \( \Delta_c \) times the critical density' of the Universe, at the time the halo is considered.

Subhalo ▾

Dataset	Dim.	Units	Description

SubhaloBHMass	N	\( 10^{10} M_\odot / h\)	Sum of the BH_Mass field of all blackholes (type 5) in this subhalo.
SubhaloBHMdot	N	\( 10^{10} M_\odot / h \)\( /(0.978 Gyr/h) \)	Sum of the BH_Mdot field of all blackholes (type 5) in this subhalo.
SubhaloBfldDisk	N	\( (h/a^2) \) `UnitPressure`\(^{1/2} \)	The square root of the volume weighted value of \(B^2\) for all gas cells within the canonical two times the stellar half mass radius. This value gives a magnetic field strength which would have the same amount of mean magnetic energy as the galaxy cells.
SubhaloBfldHalo	N	\( (h/a^2) \) `UnitPressure`\(^{1/2} \)	The square root of the volume weighted value of \(B^2\) for all gas cells in the subhalo. This value gives a magnetic field strength which would have the same amount of mean magnetic energy as the subhalo cells.
SubhaloCM	(N,3)	\( ckpc/h \)	Comoving center of mass of the Subhalo, computed as the sum of the mass weighted relative coordinates of all particles/cells in the Subhalo, of all types.
SubhaloGasDustMetallicity (new)	N	-	Mass-weighted dust-to-gas ratio of all subhalo particles within twice the stellar half mass radius. The subhalo dust mass (within twice the stellar half mass radius) is obtained multiplying this value by the total gas mass within twice the stellar half mass radius.
SubhaloGasDustMetallicityHalfRad (new)	N	-	Same as `SubhaloGasDustMetallicity`, but for cells within the stellar half mass radius.
SubhaloGasDustMetallicityMaxRad (new)	N	-	Same as `SubhaloGasDustMetallicity`, but for cells within the radius of \( V_{max} \).
SubhaloGasDustMetallicitySfr (new)	N	-	Same as `SubhaloGasDustMetallicity`, but for cells with star-formation rate SFR \( > 0 \).
SubhaloGasDustMetallicitySfrWeighted (new)	N	-	Same as `SubhaloGasDustMetallicity`, but weighted by the cell star-formation rate rather than the cell mass.
SubhaloGasMetalFractions (modified)	(N,9)	-	Individual abundances: H, He, C, N, O, Ne, Mg, Si, Fe (in this order). Each is the dimensionless ratio of the total mass in that species divided by the total gas mass, both restricted to gas cells within twice the stellar half mass radius. Unlike IllustrisTNG, the untracked metals are not stored separately. Their mass can be inferred from the total metal mass (computed from the gas metallicity). Note: Abundances include the metals locked in dust.
SubhaloGasMetalFractionsHalfRad (modified)	(N,9)	-	Same as `SubhaloGasMetalFractions`, but for cells within the stellar half mass radius.
SubhaloGasMetalFractionsMaxRad (modified)	(N,9)	-	Same as `SubhaloGasMetalFractions`, but for cells within the radius of \( V_{max} \).
SubhaloGasMetalFractionsSfr (modified)	(N,9)	-	Same as `SubhaloGasMetalFractions`, but for cells with star-formation rate SFR \( > 0 \).
SubhaloGasMetalFractionsSfrWeighted (modified)	(N,9)	-	Same as `SubhaloGasMetalFractions`, but weighted by the cell star-formation rate rather than the cell mass.
SubhaloGasMetallicity (modified)	N	-	Mass-weighted average metallicity (Mz/Mtot, where Z = any element above He) of all gas cells within twice the stellar half mass radius. Note: \( M_Z \) includes (metals locked in) dust.
SubhaloGasMetallicityHalfRad (modified)	N	-	Same as `SubhaloGasMetallicity`, but for cells within the stellar half mass radius.
SubhaloGasMetallicityMaxRad (modified)	N	-	Same as `SubhaloGasMetallicity`, but for cells within the radius of \( V_{max} \).
SubhaloGasMetallicitySfr (modified)	N	-	Same as `SubhaloGasMetallicity`, but for cells with star-formation rate SFR \( > 0 \).
SubhaloGasMetallicitySfrWeighted (modified)	N	-	Same as `SubhaloGasMetallicity`, but weighted by the cell star-formation rate rather than the cell mass.
SubhaloGrNr	N	-	Index into the Group table of the FOF host/parent of this subhalo.
SubhaloHalfmassRad	N	\( ckpc / h \)	Comoving radius containing half of the total mass (`SubhaloMass`) of this subhalo.
SubhaloHalfmassRadType	(N,6)	\( ckpc / h \)	Comoving radius containing half of the mass of this Subhalo split by Type.
SubhaloIDMostbound	N	-	The ID of the particle with the smallest binding energy (could be any type).
SubhaloLen	N	-	Total number of member particle/cells in this subhalo, of all types.
SubhaloLenType	(N,6)	-	Total number of member particle/cells in this subhalo, separated by type. Note: Wind phase cells are counted as stars (type 4) for `SubhaloLenType`.
SubhaloMass	N	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells which are bound to this subhalo, of all types. Particle/cells bound to subhaloes of this Subhalo are NOT accounted for.
SubhaloMassType	(N,6)	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells which are bound to this subhalo, separated by type. Particle/cells bound to subhaloes of this Subhalo are NOT accounted for. Note: Wind phase cells are counted as gas (type 0) for `SubhaloMasssType`.
SubhaloMassInHalfRad	N	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within the stellar half-mass radius, of all types.
SubhaloMassInHalfRadType	(N,6)	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within the stellar half-mass radius, separated by type.
SubhaloMassInMaxRad	N	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within \( V_{max} \), of all types.
SubhaloMassInMaxRadType	(N,6)	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within \( V_{max} \), separated by type.
SubhaloMassInRad	N	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within twice the stellar half-mass radius, of all types.
SubhaloMassInRadType	(N,6)	\( 10^{10} M_\odot / h\)	Total mass of all member particle/cells within twice the stellar half-mass radius, separated by type.
SubhaloParent	N	-	Index back into this same Subhalo table of the unique Subfind host/parent of this Subhalo. This index is local to the group (i.e. 2 indicates the third most massive subhalo of the parent halo of this subhalo, not the third most massive of the whole snapshot). The values are often zero for all subhalos of a group, indicating that there is no resolved hierarchical structure in that group, beyond the primary subhalo having as direct children all of the secondary subhalos.
SubhaloPos	(N,3)	\( ckpc/h \)	Spatial position within the periodic box (of the particle with the minimum gravitational potential energy). Comoving coordinate.
SubhaloSFR	N	\( M_\odot / yr \)	Sum of the individual star formation rates of all gas cells in this subhalo.
SubhaloSFRinHalfRad	N	\( M_\odot / yr \)	Sum of the individual star formation rates of all gas cells within the stellar half-mass radius.
SubhaloSFRinMaxRad	N	\( M_\odot / yr \)	Sum of the individual star formation rates of all gas cells within \( V_{max} \).
SubhaloSFRinRad	N	\( M_\odot / yr \)	Sum of the individual star formation rates of all gas cellswithin twice the stellar half-mass radius.
SubhaloSpin	(N,3)	\( (ckpc/h)(km/s) \)	Total spin per axis, computed for each as the mass weighted average of the relative coordinate times relative velocity of all member particles/cells. Also known as specific angular momentum.
SubhaloStarMetalFractions (modified)	(N,9)	-	Individual abundances: H, He, C, N, O, Ne, Mg, Si, Fe, total (in this order). Each is the dimensionless ratio of the total mass in that species divided by the total stellar mass, both restricted to stars within twice the stellar half mass radius. Unlike IllustrisTNG, the untracked metals are not stored separately. Their mass can be inferred from the total metal mass (computed from the gas metallicity). Note: Abundances include the metals locked in dust.
SubhaloStarMetalFractionsHalfRad (modified)	(N,9)	-	Same as `SubhaloStarMetalFractions`, but for cells within the stellar half mass radius.
SubhaloStarMetalFractionsMaxRad (modified)	(N,9)	-	Same as `SubhaloStarMetalFractions`, but for cells within the radius of \( V_{max} \).
SubhaloStarMetallicity (modified)	N	-	Mass-weighted average metallicity \( (M_Z/M_{tot} \), where Z = any element above He) of stars within twice the stellar half mass radius. Note: \( M_Z \) includes the metals locked in dust.
SubhaloStarMetallicityHalfRad (modified)	N	-	Same as `SubhaloStarMetallicity`, but for cells within the stellar half mass radius.
SubhaloStarMetallicityMaxRad (modified)	N	-	Same as `SubhaloStarMetallicity`, but for cells within the radius of \( V_{max} \).
SubhaloStellarPhotometrics	(N,8)	mag	Eight bands: U, B, V, K, g, r, i, z. Magnitudes based on the summed-up luminosities of all the stellar particles of the group. For details on the bands, see the snapshot table entry for stars.
SubhaloStellarPhotometricsMassInRad	N	\( 10^{10} M_\odot / h\)	Sum of the mass of the member stellar particles, but restricted to stars within the radius `SubhaloStellarPhotometricsRad`.
SubhaloStellarPhotometricsRad	N	\( ckpc / h\)	adius at which the surface brightness profile (computed from all member stellar particles) drops below the limit of 20.7 mag arcsec\(^{-2}\) in the K band (in comoving units). .
SubhaloVel	(N,3)	\( km/s \)	Peculiar velocity of the group, computed as the sum of the mass weighted velocities of all particles/cells in this group, of all types. No unit conversion is needed.
SubhaloVelDisp	N	\( km/s \)	One-dimensional velocity dispersion of all the member particles/cells (the 3D dispersion divided by \(\sqrt{3}\)).
SubhaloVelMax	N	\( km/s \)	Maximum value of the spherically-averaged rotation curve.
SubhaloVmaxRad	N	\( ckpc / h \)	Comoving radius of rotation curve maximum (where \(V_{max}\) is achieved).
SubhaloWindMass	N	\( 10^{10} M_\odot / h\)	Sum of masses of all wind-phase cells in this subhalo (with Type==4 and BirthTime\(<=0\)).