spatstat.data (version 3.1-2)

shapley: Galaxies in the Shapley Supercluster

Description

A point pattern recording the sky positions of 4215 galaxies in the Shapley Supercluster.

Usage

data(shapley)

Format

shapley is an object of class "ppp" representing the point pattern of galaxy locations (see ppp.object).

shapley.extra is a list containing additional data described under Notes.

Notes

This dataset comes from a survey by Drinkwater et al (2004) of the Shapley Supercluster, one of the most massive concentrations of galaxies in the local universe. The data give the sky positions of 4215 galaxies observed using the FLAIR-II spectrograph on the UK Schmidt Telescope (UKST). They were kindly provided by Dr Michael Drinkwater through the Centre for Astrostatistics at Penn State University.

Sky positions are given using the coordinates Right Ascension (degrees from 0 to 360) and Declination (degrees from -90 to 90).

The point pattern has three mark variables:

Mag

Galaxy magnitude (a negative logarithmic measure of visible brightness).

V

Recession velocity (km/sec) inferred from redshift, with corrections applied.

SigV

Estimated standard error for V.

The region covered by the survey was approximately the UKST's standard quadrilateral survey fields 382 to 384 and 443 to 446. However, a few of the galaxy positions lie outside these fields.

The point pattern dataset shapley consists of all 4215 galaxy locations. The observation window for this pattern is a dilated copy of the convex hull of the galaxy positions, constructed so that all galaxies lie within the window.

Note that the data contain duplicated points (two points at the same location). To determine which points are duplicates, use duplicated.ppp. To remove the duplication, use unique.ppp.

The auxiliary dataset shapley.extra contains the following components:

UKSTfields

a list of seven windows (objects of class "owin") giving the UKST standard survey fields.

UKSTdomain

the union of these seven fields, an object of class "owin".

plotit

a function (called without arguments) that will plot the data and the survey fields in the conventional astronomical presentation, in which Right Ascension is converted to hours and minutes (1 hour equals 15 degrees) and Right Ascension decreases as we move to the right of the plot.

References

Drinkwater, M.J., Parker, Q.A., Proust, D., Slezak, E. and Quintana, H. (2004) The large scale distribution of galaxies in the Shapley Supercluster. Publications of the Astronomical Society of Australia 21, 89-96. DOI 10.1071/AS03057

Examples

  data(shapley)
  if(require(spatstat.geom)) {
  shapley.extra$plotit(main="Shapley Supercluster")
  }