On the occurrence of galaxy harassment

Abstract

Context. Tidal interactions of galaxies in galaxy clusters have been proposed as one potential explanation of the morphology-density relation at low masses. Earlier studies have shown that galaxy harassment is a suitable mechanism for inducing a morphological transformation from low-mass late-type disk galaxies to the abundant early-type galaxies. Aims. The efficiency of tidal transformation is expected to depend strongly on the orbit of a galaxy within the cluster halo. The orbit determines both the strength of the cluster's global tidal field and the probability of encounters with other cluster members. Here we aim to explore these dependencies. Methods. We use a combination of N-body simulation and Monte-Carlo method to study the efficiency of the transformation of late-type galaxies by tidal interactions on different orbits in a galaxy cluster. Additionally, we investigate the effect of an inclination between the disk of the infalling galaxy and its orbital plane. We compare our results to observational data to assess the possible relevance of such transformations for the existing cluster galaxy population. Results. We find that galaxies that entered a cluster from the outskirts are unlikely to be significantly transformed (stellar mass loss ≤6%). Closer to the cluster centre, tidal interactions are a more efficient mechanism (stellar mass loss up to 50%) for producing harassed galaxies. The inclination of the disk can reduce the mass loss significantly, yet it amplifies the thickening of the galaxy disk. Galaxies with smaller sizes on intermediate orbits are nearly unaffected by tidal interactions. The tidal influence on an infalling galaxy and the likelihood that it leads to galaxy harassment make a very stochastical process that depends on the galaxy's specific history. Conclusions. We conclude that harassment is a suitable mechanism that could explain the transformation of at least a fraction of galaxies inside galaxy clusters. However, the transformation would have to start at an early epoch in protocluster environments and continue until today, in order to result in a complete morphological transformation.

The Preferential Tidal Stripping of Dark Matter Versus Stars in Galaxies

“…Simulations show group preprocessing can influence group members, and that the inclination of a galaxy's disk to its orbital plane can influence the efficiency of stellar stripping (Villalobos et al 2012). This same dependence has since been noted in cluster harassment simulations as well (Bialas et al 2015). Indeed a significant fraction of galaxies, that may have suffered effects from the group environment, may be found in clusters by redshift zero (Mihos 2004;McGee et al 2009;De Lucia et al 2012).…”

The sensitivity of harassment to orbit: mass loss from early-type dwarfs in galaxy clusters

“…In comparison, a circular orbit near the cluster centre, that spends a much greater fraction of its time where the potential is most destructive, suffers strong mass loss from harassment. Bialas et al (2015) also find that, in addition to orbit, disk inclination with respect to the orbital plane and disk size can also influence the amount of stellar mass lost. Smith et al (2013c) found that most of the mass loss arises from the tides of the cluster potential, with a small additional amount of mass loss (∼ 30%) due to high speed tidal encounters with other cluster galaxies, in agreement with previous studies (Gnedin 2003;Knebe et al 2006).…”

“…Mastropietro et al 2005;Smith et al 2010;Bialas et al 2015). The cool, thin disks of previous studies are often so thin that they have no known observable counterpart (Sánchez-Janssen et al 2010).…”

On the Tidal Radius of Satellites on Prograde and Retrograde Orbits

“…Interactions of galaxies with the potential of larger objects have proved capable of transforming their morphology and kinematics on various scales: those of dwarf galaxies orbiting the Milky-Way-like galaxy (Mayer et al 2001;Kazantzidis et al 2011), galaxies in groups (Villalobos et al 2012), and clusters (Mastropietro et al 2005;Bialas et al 2015). One of the factors influencing the final outcome of such a process is the initial inclination of the galaxy disk with respect to its orbit (Villalobos et al 2012;Łokas et al 2015).…”