Galaxy harassment and the evolution of clusters of galaxies

Abstract

Disturbed spiral galaxies with high rates of star formation pervaded clusters of galaxies just a few billion years ago, but nearby clusters exclude spirals in favor of ellipticals. "Galaxy harassment" (frequent high speed galaxy encounters) drives the morphological transformation of galaxies in clusters, provides fuel for quasars in subluminous hosts and leaves detectable debris arcs. Simulated images of harassed galaxies are strikingly similar to the distorted spirals in clusters at z ∼ 0.4 observed by the Hubble Space Telescope.Clusters of galaxies are unique cosmological laboratories. There are several hundred galaxies moving at relative velocities up to several thousand km s −1 in regions no larger than the distance between the Milky Way and its nearest neighbor, the Andromeda galaxy (M31). Clusters of galaxies have been observed at redshifts up to 2 1 . By understanding their evolution over cosmic times, we probe the geometry of the Universe and the development of its largest structures.Nearby rich galaxy clusters are dominated by elliptical "E" and lenticular "S0" galaxies 2 , mostly low luminosity dwarfs. Twenty years ago Butcher and Oemler 3,4 discovered that clusters at z ∼ > 0.4 have a substantial population of "blue galaxies" seen only as fuzzy blobs in their ground based images. Recent Hubble Space Telescope (HST) images revealed that the "fuzzy blue blobs" are low luminosity, often disturbed, spiral galaxies "Sp" 5−8 . The HST imaging teams stress that the disturbed blue galaxies are ubiquitous, but few have other galaxies nearby 5 and there were multiple bursts of star formation spanning up to 2 Gyr 8 . The dramatic transformation of clusters (shown in Figure 1) occured during a "look-back time" of just 4-5 billion years, only a few cluster orbital times. In contrast, the morphological fraction in the field shows far less evolution 9 . Given a mechanism for distorting galaxies and promoting star formation that operates when a spiral first enters a cluster, hierarchical clustering models will naturally enhance the number of "Butcher-Oemler clusters" at z ∼ 0.4 13 . Proposed mechanisms include: mergers 14,15 , compression of gas in the high pressure cluster environment 16,17 and tidal compression by the cluster 18,19 . Each of these scenarios can produce star-bursts, but none address morphological evolution or identify the remnants of these distorted blue galaxies in present day clusters. By analyzing their HST images, Oemler et al 20 conclude that merging is implausible as the blue galaxy fraction is large and the merging probability is low. They observe disturbed spirals throughout the cluster, whereas both ram pressure stripping and global tides will only operate efficiently near the cluster's center.What mechanism drives star-bursts and rapid morphological evolution throughout a cluster of galaxies? Although direct mergers are extremely rare, every galaxy experiences a high speed close encounter with a bright galaxy once per Gyr. Here, "close" means within 50 kiloparsecs (several optical radii) ...

Local Environmental Dependence of Galaxy Properties in a Volume-Limited Sample of Main Galaxies

“…This suggests that in dense environments ther is the existence of the transformation from late to early type. Many physical mechanisms, such as galaxy harassment (Moore et al 1996), rampressure stripping (Gunn & Gott 1972) and galaxy-galaxy merging (Toomre & Toomre 1972) can explain such process. But we also note that other galaxy properties do not present significant dependence on local environment.…”

“…Many authors have investigated correlations between environment and galaxy properties, such as ones between environment and morphology (e.g., Postman & Geller 1984;Dressler et al 1997;Hashimoto & Oemler 1999;Fasano et al 2000;Tran et al 2001;Goto et al 2003;Helsdon & Ponman 2003;Treu et al 2003), ones between environment and star formation rate (e.g., Hashimoto et al 1998;Lewis et al 2002;G´omez et al 2003;Balogh et al 2004a;Tanaka et al 2004;Kelm, Focardi & Sorrentino 2005), and ones between environment and colour (e.g., Tanaka et al 2004;Balogh et al 2004b;Hogg et al 2004). In order to explain these correlations, various physical mechanisms have been proposed, including rampressure stripping (Gunn & Gott 1972;Kent 1981;Fujita & Nagashima 1999;Quilis, Moore & Bower 2000); galaxy harassment (Moore et al 1996(Moore et al , 1999; cluster tidal forces (Byrd &Valtonen 1990;Valluri 1993;Gnedin 2003); and interaction/merging of galaxies (Icke 1985;Lavery & Henry 1988;Mamon 1992;Bekki 1998).…”

The abundance and environment of dark matter haloes

“…Many of these suggest that environment can regulate the gas supply available to galaxies for star formation; processes such as harassment (wherein galaxy morphology is transformed due to frequent high speed encounters; e.g. Moore et al 1996), strangulation (wherein the hot gas supply is slowly removed, thereby gradually reducing a galaxy's star formation rate; e.g. Balogh, Navarro & Morris 2000), stripping via e.g.…”

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

“…Recent IFU observations demonstrate that many nearby spiral galaxies show negative gradients in stellar ages and metallicities, supporting this inside-out picture (González Delgado et al 2014;Sánchez-Blázquez et al 2014;Li et al 2015;Belfiore et al 2017;Goddard et al 2017). On the other hand, if "nurture" dominates galaxy evolution, external processes such as ram-pressure stripping (Gunn & Gott 1972), high speed galaxy encounters (Moore et al 1996), galaxy mergers (Mihos & Hernquist 1994), and "strangulation" (Larson et al 1980;Balogh et al 2000;Peng et al 2015) are responsible for quenching. In this picture, star formation quenching is likely to occur globally or in the outer regions of galaxies first due to the lack of continuous supply for the cold gas reservoir.…”