RAM-PRESSURE STRIPPING

Transcription

1 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

2 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])

3 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)

4 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)

5 Ram - pressure stripping gas in clusters is hot ~ 10 7 K and thin ~ 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)

6 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 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.

7 Simulations of ram-pressure stripping Abadi et al. (1999)

8 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

9 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

10 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...)

11 Fate of the gas typically in HI, X-rays, CO, Hα most if HI depleted from galaxies is not seen (Vollmer & Huchtmeier > 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

12 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

13 Virgo - morphology of HI Chung et al. (2009) 1st row: outskirts 2nd row: intermediate distances 3rd row: close to M87

14 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

15 Virgo Cluster - NGC4388 Hα HI Oosterlo & van Gorkum (2005) Yagi et al. (2013) image: 48 x36

16 HCG 44 - NGC3187 Serra et al. (2013) not a cluster but a group is it rampressure stripping?

17 NGC4402 Crowl et al. (2005) Dust follows (atomic) gas SF at the bottom of the dust distribution

18 ESO /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)

19 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

20 IFU observations of ram-pressure case Merluzzi et al. (2013) the only IFU observations of ram-pressure stripping (?) using ANU Telescope disk galaxy in Abell 3558, one of the Shapley Clusters z~0.04 (impressive data!) Model Hα

21 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

22 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

23 Jellyfish

24 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)

25 Cluster mechanisms: Hall of Fame Source: ram pressure thermal evaporation starvation viscous stripping tidal compression harassment