Interpreting the Morphology of Diffuse Light around Satellite Galaxies

Recent observations of surface brightness distributions of both Milky Way andM31 satellite galaxies have revealed many instances of sudden changes or breaksin the slope of the surface brightness profiles (at some break radius,r_break). These breaks are often accompanied by increasingly ellipticalisophotes and sometimes by isophote twisting. We investigate the hypothesis ofa tidal origin for these features by applying the same ellipse fittingtechniques that are used on observed galaxies to numerical simulations of thedestruction of satellites, represented by spherical, single-component systems.We examine how observed quantities such as r_break, ellipticity and positionangle of the fitted ellipses and amplitude of extra-break population vary withthe satellite's orbital eccentricity and phase, and our viewpoint relative tothe orbit. We also look at orbit and viewpoint dependence of the rate of changeof the latter three quantities with radius. We find that there are trends with orbital phase and eccentricity in allobserved quantities, many of which are preserved through a wide variety ofviewing angles. In particular, a generic feature of all simulations is adepletion zone just interior to an excess zone, regions in which the surfacebrightness is lower and higher, respectively, than the initial profile. A clearinterpretation of any individual image, however, is likely to be hampered bythe dependence of the observable features on these multiple parameters. Forexample, breaks can be excited by several physical processes and can occur wellwithin the bound satellite population. Nevertheless, we do find we can placeloose constraints on the tidal radius, mass loss rate, orbital type and phaseof the satellite, and nature of breaks using photometric data alone.Comment: 41 pages, including 17 figures; accepted for publication in AJ; minor changes made to the text, Figure 1 adde