RAM-PRESSURE STRIPPING Jellyfish: evidence of extreme rampressure stripping in massive galaxies clusters H. Ebeling, L.N. Stephenson, A.C. Edge 2014, ApJL, 781, 40
The problem Distant (compact) clusters have a considerable fraction of blue (spiral?) galaxies (Butcher & Oemler 1978a) Local (compact) cluster are dominated by red galaxies (Butcher & Oemler 1978b) Ratio of S0 to Spirals increases as a function of local density (Dressler 1980), and fraction of S0 increases from z=0.5 to z=0 (Dressler 1997) Galaxies transform: both in colour and morphology Environmental dependance (in the field mergers are dominating; in the clusters mergers are not efficient) What is the origin of S0? Stripped spirals? (1st (?) were Spitzer & Baade 1951 [collisions in Coma])
Cluster mechanisms ram pressure stripping (Gunn & Gott 1972) thermal evaporation (Cowie & Songalia 1977) turbulent/viscous stripping (Nulson 1982) starvation/strangulation (Larson et al. 1990) tidal compression (Byrd & Valtonen 1990) galaxy harassment (Moore et al. 1996)
Gunn & Gott 1972 Sections 1-5: creation of clusters from density perturbations (starting at z~1000) spherically symmetric pressure-less infall of matter from an originally expanding medium (Universe) Section 6: astrophysical implications (on Coma) Ram-pressure stripping of gas in in-falling spirals Conclusions: galaxy formation could be efficient during cluster collapse removing most of gas from the collapsed region remaining medium (if any!) is shock heated to the kinetic energy of the cluster - normal spiral are swept clean of the ISM; cds could grow by cooling ICM infalling gas (from outside the cluster) is heated to the temp of ICM and distributed smoothly difference between irregular and regular clusters in age: they are younger/older than the collapse times (hence, spirals can be found in irregular)
Ram - pressure stripping gas in clusters is hot ~ 10 7 K and thin ~ 10-29 - 10-26 g cm -3 galaxy moving in the ICM feels ram pressure of hot gas: P=ρ cl v g 2 ISM is stripped if the force exceeds: F=2πG stars gas Consequences: - enrichment of ICM with metals (Schindler & Diaferio 2008) - enhanced/quenched SF (Giovanelli & Haynes 1985, Boselli et al. 2006) - gaseous tail with embedded SF knots (Yoshida et al. 2008, Yagi et al. 2010) - asymmetric morphologies of (gas) disks - atomic gas displaced and removed (Scott et al. 2010); HI disks smaller than stellar disks (Chung et al. 2009) - molecular gas unperturbed (Boselli et al. 1997) - stripped galaxies can (temporarily) become brighter than BCGs (Ebeling et al. 2014)
Simulations of ram-pressure stripping Many: Takeda et al. 1984, Abadi et al. 1999, Vollmer et al. 2001, Bekki & Couch 2003, Roediger & Henslet 2005, Kronberger et al. 2008, Kapferer et al. 2009, Jachym et al. 2009, Steinhauser et al. 2012... in low-mass clusters: stripping can happen but inefficient in massive clusters: complete stripping of gas content Gunn & Gott prescription is validated Bulge potential has to be taken into account (gas retained in the bulge) Spiral passing through Coma: - loses ~80% of its diffuse gas - timescale ~10 7 yr (fraction of a crossing time) strong dependance on the orientation (wrt to the ICM wind) ram-pressure alone can not fully explain Butcher-Oemler effect.
Simulations of ram-pressure stripping Abadi et al. (1999)
Simulations of ram-pressure stripping ICM ~10-27 g/cm 3 Steinhauser et al. (2012) v = 1000km/s TICM = 10 7 K Galaxy: standard GADGET-2 Spiral 25% gas (in mass) 2Gy in isolation, 1.5 M /yr SF
Ram-pressure in a nutshell there are multiple phases of ram-pressure stripping shock compressions of the ISM (at the galaxy-cluster interface) SF can be enhanced of shut down by ram-pressure stripping, depending on many details removal of the ISM star-formation in the tails of removed gas, star-burst in the compressed regions partial back-fall (oscillation of the stellar component) further processes (tidal-compression) induces more SF
Verdict Simulations are limited: e.g. multi-phase ISM in spirals + remember Binney talk? Ram-pressure is certainly invoked most often to explain the removal of gas It should work well only in dense cluster cores + depends on the mass (and gas density) of the cluster + orientation of the galaxy wrt ram-pressure wind It can not remove gas from bulges/nuclei Other processes are likely as important (for removing gas and morphological changes), especially in the outskirts (viscous stripping, harassment, tidal compression, starvations...)
Fate of the gas typically in HI, X-rays, CO, Hα most if HI depleted from galaxies is not seen (Vollmer & Huchtmeier 2007 --> it is probably heated) mix with the ICM --> multi phase gas? reach cluster core and heat it up via ram pressure drag features: bow shocks, tails, vortices
Virgo: X-rays and HI non-uniform mass distribution (M87, M86, M49) Chung et al. (2009) ROSAT X-rays (Böhringer et al. 1994) HI: Viva Chung et al. (2009) HI magnified by a factor of 10
Virgo - morphology of HI Chung et al. (2009) 1st row: outskirts 2nd row: intermediate distances 3rd row: close to M87
Virgo - galaxies with HI tails Chung et al. (2007) arrows show direction of tails most cases consistent with ram-pressure stripping recent arrivals to cluster on highly radial orbits
Virgo Cluster - NGC4388 Hα HI Oosterlo & van Gorkum (2005) Yagi et al. (2013) image: 48 x36
HCG 44 - NGC3187 Serra et al. (2013) not a cluster but a group is it rampressure stripping?
NGC4402 Crowl et al. (2005) Dust follows (atomic) gas SF at the bottom of the dust distribution
ESO137-001/2 Sun et al. (2010) Chandra double tail (unusual for ram-pressure) Difference in soft and hard X-rays (mixing of cold ISM with hot ICM)
IC3418 (dwarf irregular) Kenny et al. (2014) Virgo dwarf being stripped and forming stars some stars have V>V esc, but some are falling back
IFU observations of ram-pressure case Merluzzi et al. (2013) the only IFU observations of ram-pressure stripping (?) using WiFeS@2.3m ANU Telescope disk galaxy in Abell 3558, one of the Shapley Clusters z~0.04 (impressive data!) Model Hα
Jellyfish HST ACS/F606W and F814W images of Massive Cluster Survey (MACS Ebeling et al. 2001) several SNAP proposal with primary science: arcs, looking z>6 F814W dropouts, identification of sub-mm galaxies, galaxygalaxy and galaxy-gas interactions 128 clusters with 0.3 < z < 0.5 Paper reports: 1. report on galaxies with violent encounters with the ICM 2. identification of the brightest and most spectacular cases of ram-pressure stripping 3. future work: establish quantitative color and morphology criteria that will allow selection of less bright (and obvious) cases
Jellyfish Inspection of 37 ACS observed clusters: 1. strongly disturbed morphology indicative of unilateral external forces 2. a pronounced brightness and color gradient suggesting extensive triggered SF 3. compelling evidence of a debris tail Morphology and brightness varies (one galaxy outshines the BCG for 0.4 mag) Spatial distribution: same as red sequence galaxies (suggest stripping might not be rapid) deduced projected velocity vectors do not point to the center of clusters --> likely complex orientation, galaxies not necessary on radial orbits, and possible longer duration ram-pressure processes
Jellyfish
My opinion It presents 6 pictures with very little analysis orientation of the galaxies towards the projected center of the clusters brightness measurements (sextractor) a useful intro in the field of ram pressure stripping, but no proper analysis of properties of the discovered galaxies announces a future paper on how to find such (and less obvious) systems automatically Lacks: interpretation Not sure it warrants a letter (publication?), but it announces discovery of fancy looking galaxies (targets)
Cluster mechanisms: Hall of Fame Source: ADS@05.02.2014. ram pressure thermal evaporation starvation viscous stripping tidal compression harassment