Galaxies class

This stores and manipulates data for multiple galaxies and snaps.

class galaxy.galaxies.Galaxies(names=('MW', 'M31', 'M33'), snaps=(0, 0, 0), datadir=None, usesql=False, ptype=None, stride=1)

A class to manipulate data for multiple galaxies.

Kwargs:

names (iterable of str):

short names used in filename of type ‘name_000.txt’, eg ‘MW’, ‘M31’.

snaps (iterable of int):

Snap number, equivalent to time elapsed. Zero is starting conditions.

datadir (str):

Directory to search first for the required file. Optional, and a default list of locations will be searched.

usesql (bool):

If True, data will be taken from a PostgreSQL database instead of text files.

ptype (int):

Optional. Restrict data to this particle type, for speed. Only valid with usesql=True.

stride (int):

Optional. For stride=n, get every nth row in the table. Only valid with usesql=True.

Class attributes:

path (pathlib.Path object):

directory (probably) containing the data files

filenames (list of str):

in name_snap format, something like ‘MW_000’ (no extension)

galaxies (dict):

key is filename, value is the corresponding Galaxy object

read_data_files()

Attempts to create a Galaxy object for each name/snap combination set in self.names and self.snaps

No return value. Sets self.galaxies, a dictionary keyed on name_snap

get_pivot(aggfunc, values='m')

Generic method to make a pandas pivot table from the 9 combinations of galaxy and particle type.

Args:

aggfunc (str): ‘count’, ‘sum’, etc as aggregation method values (str): column name to aggregate

Returns: pandas dataframe

get_counts_pivot()

Pivots on count(‘m).

Returns: pandas dataframe

get_masses_pivot()

Pivots on sum(‘m).

Returns: pandas dataframe

get_full_df()

Combined data for all input files.

Returns:

Concatenated pandas dataframe from all galaxies Includes ‘name’ and ‘snap’ columns

get_coms(tolerance=0.1, ptypes=(1, 2, 3))

Center of Mass determination for all galaxies. Defaults to all particle types, but ptypes=(2,) may be more useful.

Args:

tolerance (float): convergence criterion (kpc)

Returns:

QTable with COM positions and velocities colnames: [‘name’, ‘ptype’, ‘x’, ‘y’, ‘z’, ‘vx’, ‘vy’, ‘vz’, ‘R’, ‘V’]

separations(g1, g2)

Position and velocity of galaxy g2 COM relative to g1 COM. Uses only disk particles for the COM determination.

Args:

g1, g2 (str): galaxies matching entries in self.filenames

Returns:

Dictionary containing relative position, distance, velocities in Cartesian and radial coordinates

total_com()

Center of Mass determination for the local group.

Uses all particles of all types. Position and velocity should be conserved quantities, subject to numerical imprecision in the sim.

Returns:

position, velocity: 3-vectors

total_angmom(origin)

Calculate angular momentum summed over all particles in the local group, abot point origin.

Arg:

origin (3-vector): x,y,z coordinates

Returns:

angular momentum: 3-vector