Intergalactic Tidal Debris

Cluster tides are quite effective at stripping stars from galaxies and building up an intergalactic stellar population and potentially account for the envelopes of the cD galaxies (Richstone 1976; Merritt 1985). The recent discovery of intergalactic stars in the Virgo and Fornax clusters in the form of planetary nebulae and red giant-branch stars (Theuns & Warren 1996; Arnaboldi et al. 1996; Feldmeier et al. 1998; Ferguson et al. 1998) along with the likelihood of intergalactic globular clusters have revived interest in the dynamics of the tidal-stripping process.

Analysis of the poor cluster simulation shows that about 10% of the stars are distributed diffusely throughout the cluster with surface brightness dimmer than $\mu =26.5$ assuming an M/L=5(Dubinski, Murali, & Ouyed 1999). The radial light distribution is approximately a continuation of a deVaucouleurs profile out to r=1 Mpc from the center of the BCG. The Virgo-cluster simulation shows similar results and there is the hint of a cD envelope.

There are also a significant number of streams and swathes of stars in the intracluster light that originate in stripping events of spirals and ellipticals. These streams often trace the orbits of galaxies on radial orbits that have suffered a strong, tidal encounter with the cluster center. Examples of streams just forming in tidal encounters have recently been detected in the Coma cluster (Gregg and West 1998). Streams may be difficult to detect directly because of their low surface brightness. However, the contrast may increase when viewed in the r-v_losphase-plane. A kinematic survey of several hundred planetary nebulae and globular clusters in the intergalactic space surrounding M87 in Virgo or NGC 1399 in Fornax may reveal coherent streams on top of a diffuse population. New analysis shows how the kinematics of the tidal debris streams present a new way to measure the gravitational potential of nearby clusters (Dubinski et al. 1999).

A high contrast image (left) showing the tidal debris streams in a cluster simulation. Surface brightness contours are shown (right) going from mu=26 to 34 in steps of 1.0 magnitudes. The streams visible on the left have an effective surface brightness of m=31-32 assuming M/L=5 for the stellar population.