The stream gap DF

class galpy.df.streamgapdf(*args, **kwargs)

The DF of a gap in a tidal stream

__init__(*args, **kwargs)

Initialize the DF of a gap in a stellar stream

Parameters:

• sigv (float or Quantity) – Radial velocity dispersion of the progenitor.

• progenitor (galpy.orbit.Orbit) – Progenitor orbit as Orbit instance (will be re-integrated, so don’t bother integrating the orbit before).

• pot (galpy.potential.Potential or list thereof, optional) – Potential instance or list thereof.

• aA (actionAngle instance) – ActionAngle instance used to convert (x,v) to actions. Generally a actionAngleIsochroneApprox instance.

• useTM (bool, optional) – If set to an actionAngleTorus instance, use this to speed up calculations.

• tdisrupt (float or Quantity, optional) – Time since start of disruption (default: 5 Gyr).

• sigMeanOffset (float, optional) – Offset between the mean of the frequencies and the progenitor, in units of the largest eigenvalue of the frequency covariance matrix (along the largest eigenvector), should be positive; to model the trailing part, set leading=False (default: 6.0).

• leading (bool, optional) – If True, model the leading part of the stream; if False, model the trailing part (default: True).

• sigangle (float or Quantity, optional) – Estimate of the angle spread of the debris initially (default: sigv/122/[1km/s]=1.8sigv in natural coordinates).

• deltaAngleTrack (float or Quantity, optional) – Angle to estimate the stream track over (rad; or can be Quantity) (default: None).

• nTrackChunks (int, optional) – Number of chunks to divide the progenitor track in (default: floor(deltaAngleTrack/0.15)+1).

• nTrackIterations (int, optional) – Number of iterations to perform when establishing the track; each iteration starts from a previous approximation to the track in (x,v) and calculates a new track based on the deviation between the previous track and the desired track in action-angle coordinates; if not set, an appropriate value is determined based on the magnitude of the misalignment between stream and orbit, with larger numbers of iterations for larger misalignments (default: None).

• progIsTrack (bool, optional) – If True, then the progenitor (x,v) is actually the (x,v) of the stream track at zero angle separation; useful when initializing with an orbit fit; the progenitor’s position will be calculated (default: False).

• ro (float or Quantity, optional) – Distance scale for translation into internal units (default from configuration file).

• vo (float or Quantity, optional) – Velocity scale for translation into internal units (default from configuration file).

• Vnorm (float or Quantity, optional) – Deprecated. Use vo instead (default: None).

• Rnorm (float or Quantity, optional) – Deprecated. Use ro instead (default: None).

• R0 (float or Quantity, optional) – Galactocentric radius of the Sun (kpc) (can be different from ro) (default: 8.0).

• Zsun (float or Quantity, optional) – Sun’s height above the plane (kpc) (default: 0.0208).

• vsun (numpy.ndarray or Quantity, optional) – Sun’s motion in cylindrical coordinates (vR positive away from center) (can be Quantity array, but not a list of Quantities) (default: [-11.1, 8.0 * 30.24, 7.25]).

• multi (int, optional) – If set, use multi-processing (default: None).

• interpTrack (bool, optional) – Interpolate the stream track while setting up the instance (can be done by hand by calling self._interpolate_stream_track() and self._interpolate_stream_track_aA()) (default: _INTERPDURINGSETUP).

• useInterp (bool, optional) – Use interpolation by default when calculating approximated frequencies and angles (default: _USEINTERP).

• nosetup (bool, optional) – If True, don’t setup the stream track and anything else that is expensive (default: False).

• nospreadsetup (bool, optional) – If True, don’t setup the spread around the stream track (only for nosetup is False) (default: False).

• approxConstTrackFreq (bool, optional) – If True, approximate the stream assuming that the frequency is constant along the stream (only works with useTM, for which this leads to a significant speed-up) (default: False).

• useTMHessian (bool, optional) – If True, compute the basic Hessian dO/dJ_prog using TM; otherwise use aA (default: False).

• custom_transform (numpy.ndarray, optional) – Matrix implementing the rotation from (ra,dec) to a custom set of sky coordinates (default: None).

• impactb (float or Quantity, optional) – Impact parameter (can be Quantity) (default: 1.0).

• subhalovel (numpy.ndarray or Quantity, optional) – Velocity of the subhalo shape=(3) (default: [0.0, 1.0, 0.0]).

• timpact (float or Quantity, optional) – Time since impact (can be Quantity) (default: 1.0).

• impact_angle (float or Quantity, optional) – Angle offset from progenitor at which the impact occurred (rad) (can be Quantity) (default: 1.0).

• GM (float or Quantity, optional) – Mass of the subhalo when using a Plummer or Hernquist model.

• rs (float or Quantity, optional) – Scale parameter of the subhalo when using a Plummer or Hernquist model.

• hernquist (bool, optional) – If True, use Hernquist kicks for GM/rs (default: False –> Plummer).

• subhalopot (Potential or list thereof, optional) – Gravitational potential of the subhalo (alternative to specifying GM and rs)

• deltaAngleTrackImpact (float or Quantity, optional) – Angle to estimate the stream track over to determine the effect of the impact [similar to deltaAngleTrack] (rad) (default: None).

• nTrackChunksImpact (int, optional) – Number of chunks to divide the progenitor track in near the impact [similar to nTrackChunks] (default: floor(deltaAngleTrack/0.15)+1).

• nKickPoints (int, optional) – Number of points along the stream to compute the kicks at (kicks are then interpolated); ‘30’ chosen such that higherorderTrack can be set to False and get calculations accurate to > 99% (default: 30xnTrackChunksImpact).

• nokicksetup (bool, optional) – If True, only run as far as setting up the coordinate transformation at the time of impact (useful when using this in streampepperdf) (default: False).

• spline_order (int, optional) – Order of the spline to interpolate the kicks with (default: 3).

• higherorderTrack (bool, optional) – If True, calculate the track using higher-order terms (default: False).

• nTrackChunks – Number of chunks to divide the progenitor track into (default: 8).

• interpTrack – If True, interpolate the track (default: True).

• useInterp – If True, use the interpolated track to calculate actions and angles (default: True).

Notes

• Parameters above up to impactb are streamdf parameters used to setup the underlying smooth stream.

• 2015-06-02 - Started - Bovy (IAS)