John Phillips edited Intro.tex  over 9 years ago

Commit id: 3d464f160ea146fc1102f09c03005953bc3fe9c0

deletions | additions      

       

Local group satellites are highly anisotropically distributed both around the Milky Way and M31. The disk-like arrangement of MW satellites was first pointed out by \citet{Lynden-Bell74}. Later studies argued further for the existence of a disk-like structure of Milky Way satellites \cite{Metz07,Metz09}, and argued that the MW satellite disk was rotationally supported \cite{Metz08}. \citet{Kroupa_2005} further argues that the distribution of satellite galaxies around the MW is not predicted by LCDM. Around M31, dramatic evidence has been found for a disk of satellites, many of which exhibit coherent rotation along the line of sight \cite{Ibata_2013}. The M31 structure seems particularly difficult to square with our picture of galaxy evolution; \cite{Ibata_2014} argues that \cite{Ibata_2014} that alignments similar to the one found around M31 are essentially non-existant in numerical simulations.  Much recent work has gone into investigating the possibility of similar satellite distributions around galaxies outside of the local group. Recently, work by \citet{Ibata_2014} (hereafter I14) pointed to the possibility of corotation seen in diametrically opposed satellite pairs in Sloan Digital Sky Survey (SDSS), finding 20 out of 22 oppositely aligned satellite pairs corotating along the line of sight. This result was contested by \citet{Cautun14}, arguing that the results of \citet{Ibata_2014} are strongly dependant on selection criteria and are not robust. The original authors then claimed that less-massive satellites than originally considered exhibit a spacial over-density consistent with the claimed existence of co-rotating sturctures frequently seen in SDSS \cite{2014arXiv1411.3718I}. Still, the consensus is far from clear as to on  the prevelence of co-rotating satellite disks in the non-local Universe is unclear. In this paper we examine kinematic evidence for the existence of rotating planes. We compare the kinematic results we obtain from selection criteria modelled after that of I14 to simple numerical models of satellite behavior. The structure of the paper is as follows: In Section \ref{sec:data} we discuss the selection of the observational sample and the presense of the co-rotation signal. In Section \ref{sec:models} we introduce our numerical models and compare the mock observations derived from the models to the true observational data. In Section \ref{sec:discuss} we discuss our results in the context of the search for M31-like planes elsewhere in the Universe. Throughout our analysis, we employ a $\Lambda$ cold dark