Halo radius and mass definitions

This unit handles definitions of halo extent, boundary, and mass. Most importantly, it converts a uniquely defined string-based format for definitions to a machine-readable format, and vice versa. Halo definitions are encapsulated by an object with the following main properties:

• quantity: Indicates the actual quantity described, e.g., radius, mass, peak height, of circular velocity. Perhaps counter-intuitively, this field can be unknown, in which case a general type of definition is described.

• type: The main type of definition, e.g. friends-of-friends, overdensity, or splashback.

• subtype: A refinement of type. For example, there are SO defintions wrt critical or mean density, and many types of splashback definitions.

The string format is then generated as <quantity><type><subtype>_<other-properties>. The user can generate a HaloDefinition object from a string using strToDef() and convert the object back using HaloDefinition.toStr().

There are also a number of less important, optional descriptors for which a default is set so that they do not need to be explicitly spelled out in the string format. This unit determines which definitions can be requested in SPARTA or MORIA configuration files, as long as they can be computed by the code.

The implementation exactly shadows the C implementation contained in SPARTA, so that the numerical values of all settings are the same in both languages:

Property	Value	String	Explanation
Quantity	HDEF_Q_UNKNOWN	Default	Could describe any, general type
	HDEF_Q_RADIUS	R	Halo radius
	HDEF_Q_MASS	M	Halo mass
	HDEF_Q_PEAKHEIGHT	nu	Peak height
	HDEF_Q_VCIRC	V	Cirular velocity
Type	HDEF_TYPE_SO	m/c/vir	Spherical overdensity
	HDEF_TYPE_SPLASHBACK	sp	Splashback
	HDEF_TYPE_FOF	fof	Friends-of-friends
	HDEF_TYPE_VMAX	max	Maximum circular velocity
	HDEF_TYPE_ORBITING	orb	Orbiting particles
Subtype	HDEF_SUBTYPE_SO_MATTER	<int>m	Matter-based SO (e.g., 200m)
	HDEF_SUBTYPE_SO_CRITICAL	<int>c	Critical-based SO (e.g., 200c)
	HDEF_SUBTYPE_SO_VIRIAL	vir	Virial-based SO (varying overdensity)
	HDEF_SUBTYPE_SP_SLOPE_PROFILE	slp-prf	Radius where slope is steepest
	HDEF_SUBTYPE_SP_SLOPE_MEDIAN	slp-med	Steepest slope radius in median of angular bins
	HDEF_SUBTYPE_SP_SLOPE_SHELL	slp-shl	Non-isotropic steepest slope (e.g. SHELLFISH)
	HDEF_SUBTYPE_SP_APOCENTER_RADIUS_MEAN	apr-mn	Mean of first apocenter radii of halo particles
	HDEF_SUBTYPE_SP_APOCENTER_RADIUS_PERCENTILE	apr-p<int>	Percentile of first apocenter radii of ptl.
	HDEF_SUBTYPE_SP_APOCENTER_SHELL_MEAN	aps-mn	Non-isotropic apocenter mean
	HDEF_SUBTYPE_SP_APOCENTER_SHELL_PERCENTILE	aps-p<int>	Non-isotropic apocenter percentile
	HDEF_SUBTYPE_ORB_ALL	all	All orbiting particles that ever entered the halo
	HDEF_SUBTYPE_ORB_PERCENTILE	p<int>	Percentile of orbiting ptl (within some radius)
Time	HDEF_TIME_NOW	Default	Current state of halo
	HDEF_TIME_ACC	acc	State of subhalo at last accretion
	HDEF_TIME_PEAK	peak	State of halo at peak of this property
Particle selection	HDEF_PTLSEL_DEFAULT	Default	Not specified
	HDEF_PTLSEL_ALL	all	Definition includes all halo particles
	HDEF_PTLSEL_BOUND	bnd	Definition includes only grav. bound particles
	HDEF_PTLSEL_TRACER	tcr	Definition includes only traced ptl (for subhalos)
	HDEF_PTLSEL_ORBITING	orb	Definition includes only orbiting particles
Source	HDEF_SOURCE_ANY	Default	Unknown source, unspecified
	HDEF_SOURCE_CATALOG	cat	Taken from halo catalog
	HDEF_SOURCE_SPARTA	spa	Computed by SPARTA
	HDEF_SOURCE_SHELLFISH	sfish	Computed by SHELLFISH
Value or error	HDEF_ERR_NO	Default	This is the indicated quantity
	HDEF_ERR_1SIGMA	err	This is the 1-sigma uncertainty on the quantity
	HDEF_ERR_2SIGMA	err2s	This is the 2-sigma uncertainty on the quantity
Other flags	HDEF_FLAG_INTERNAL	internal	Flag for internally used values

Depending on the choices, a number of numerical values can become active, in particular:

• overdensity: if type is HDEF_TYPE_SO and subtype is HDEF_SUBTYPE_SO_MATTER or HDEF_SUBTYPE_SO_CRITICAL.

• linking_length: if type is HDEF_TYPE_FOF.

• percentile: if type is HDEF_TYPE_SPLASHBACK and subtype is HDEF_SUBTYPE_SP_APOCENTER_RADIUS_PERCENTILE or HDEF_SUBTYPE_SP_APOCENTER_SHELL_PERCENTILE.

Examples

Valid examples of mass definitions would include:

• 200m, vir

• R200m, M200m, nu200m

• Vmax

• Mfof-b0.2, Rfof-b0.15

• Rsp-slp-prf, Msp-slp-prf

• Rsp-apr-p75

Not strictly correct, but also accepted when converting from a string are different capitalizations of the quantity (but only the quantity), e.g.:

• r200m, m200m, mfof-b0.2

• NU200m, Nu200m

• vmax

While those strings will be converted into a halo definition without an error, converting the definition back to a string will result in the standard capitalization. Thus, it is recommended to stick with R, M and so on whenever possible.

All additional properties are separated by underscores and can be ordered at will. Defaults are used if no value is specified. Valid definitions thus include:

• R200m

• R200m_peak, R200m_acc

• R200m_all, R200m_bnd

• R200m_cat, R200m_spa

• R200m_err, R200m_err2s

The best way to test whether a definition is valid is to try converting it with strToDef(), which will throw an error if the string is not a correct definition.

Module reference

class sparta_tools.halodef.HaloDefinition

Object that encapsulates a halo definition.

Methods

overdensityStr()	Convert an SO halo definition to a short overdensity identifier, such as "200m" or "500c".
toLabel([add_dollars, add_units, ...])	Convert halo definition to a latex label.
toStr()	Convert halo definition to string.

toStr()

Convert halo definition to string.

Returns

defstr: str

A string that uniquely describes the halo definition, and that can be converted back into the same definition.

toLabel(add_dollars=True, add_units=False, suppress_source=False, suppress_time=False, suppress_bound=False, suppress_flags=False)

Convert halo definition to a latex label.

Parameters

add_dollars: bool

Whether or not to add $ signs at the beginning and end of the string.

add_units: bool

Add units in brackets behind the label.

suppress_source: bool

Do not output source identifiers (e.g., _cat).

suppress_time: bool

Do not output time identifiers (e.g., _peak or _acc).

suppress_bound: bool

Do not output all-particle and bound-only identifiers (e.g., _all and _bnd).

suppress_flags: bool

Do not output additional flag info (e.g., _internal).

Returns

label: str

A string that can be fed to latex, e.g. for figure labels.

overdensityStr()

Convert an SO halo definition to a short overdensity identifier, such as “200m” or “500c”.

This function fails if the definition is not an SO definition, and ignores any additional properties of the definition.

Returns

so_str: str

A string that identifies the overdensity of an SO definition.

sparta_tools.halodef.strToDef(defstr)

Convert a halo definition string to a halo definition object.

Parameters

defstr: str

A string that uniquely describes the halo definition in the correct format.

Returns

hdef: HaloDefinition

A halo definition object that can be converted back into the same string.