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Rich cluster [M ~ 10 15 M sun ]

Environmental effects on neutral and molecular hydrogen of galaxies. (From APOD). Large groups (Small clusters) [M ~ 10 13 - 10 14 M sun ]. Small/compact groups [M < 10 13 M sun ]. Rich cluster [M ~ 10 15 M sun ]. Kenji Bekki (ICRAR at UWA, Australia).

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Rich cluster [M ~ 10 15 M sun ]

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  1. Environmental effects on neutral and molecular hydrogen of galaxies (From APOD) Large groups (Small clusters) [M ~ 1013 - 1014 Msun] Small/compact groups [M < 1013 Msun] Rich cluster [M ~ 1015 Msun] Kenji Bekki (ICRAR at UWA, Australia)

  2. Outline: five key physical processes in HI/H2 evolution of galaxies. Mass-scale Size-scale [1012-1013 Msun] [1014 Msun] [1015 Msun] 1.Galaxy interaction (e.g., Noguchi 1987) 3. Ram pressure stripping (e.g., Gunn & Gott 1971) 2.Galaxy Merging (e.g., Barnes & Hernquist 1992) 5. Galaxy harassment (e.g., Moore et al. 1996) 4.Group tide (e.g., Icke 1985) The relative importance of these processes is different in different environments, so, how do these influence the HI/H2 evolution of galaxies ?

  3. Evolution of Rmol (=M(H2)/M(HI)), HI/H2 disk sizes, and HI-to-star-mass ratios. HI-deficient galaxy HI-normal galaxy (Boselli et al. 2014) Why is Rmol so different in different environments ?

  4. H2 formation on dust grains and formation/destruction processes of dust in galaxy-scale simulations (1) H2 formation on dust grains Simulation H2 H Dust particle (Gould & Salpeter 1963) (2) Dust growth and destruction Destruction Formation Growth Metal (Bekki 2014) SNe

  5. (1)The roles of galaxy interaction/merging in HI/H2 evolution of small/compact groups. • How does galaxy interaction and merging change the HI/H2 contents and their spatial distributions ? (Stephan’s Quintet from APOD)

  6. Evolution of a small group of galaxies (Cosmic Front:NHK 2014 based on my simulations)

  7. The roles of galaxy interaction inHI/H2 evolution. Companion • Enhancement of collisions of giant molecular clouds (GMCs) Induced starburst (a factor of ~ 5) in gas-rich disks (Noguchi & Ishibashi 1986; Mihos et al. 1993) • Gas inflow to the central regions of disk galaxies by gravitational torque (bar)  Central concentration of gas. Gas disk SFR Time (Noguchi & Ishibashi 1986)

  8. Enhancement of H2 formation in interacting disk galaxies. T=0 (Gyr) 0.3 Companion 0.6 M(H2) Gas disk 0.8 1.1 1.4 Rmol Stellar Disk size 210 kpc A factor of 3-5 enhancement depending on orbital configurations and mass-ratios of two galaxies. (Bekki 2014)

  9. Evolution of HI/H2 in interacting galaxies. HI H2

  10. HI/H2 distributions in interacting disks. HI H2 T=0.3 Gyr 0.6 T=0.3 Gyr 0.6 H2 formation in tidal arms 0.8 1.1 1.1 0.8 More clumpy distribution (Bekki 2014)

  11. Isolated H2 clouds and tidal dwarf galaxies (TDGs) in multiple mergers. New stars T=2.1 Gyr 2.8 5 Sp  E + SP  E (Rmol =0.1  0.5-1) Sp E 140 kpc TDG H2 T=2.1 Gyr 2.8 (1) H2-rich TDGs ? (2) Isolated H2 clouds in collapsing groups ? No TDGs H2 in TDGs (Bekki et al. 2014)

  12. Implications Dust distribution in a gas-rich group • Molecular fractions should be significantly higher in small groups with interacting/merging galaxies. • TDGs should be much more H2-rich than normal dwarfs ( ALMA targets ?). • Intra-group Isolated H2 clouds may exist ( ALMA targets?). • Abundant dust can be found in intra-group gas. 2.8 Gyr 140 kpc E Sp

  13. (2) Ram pressure stripping (RPS) and tidal fields in large group & small clusters.. • Ram pressure stripping of halo and disk gas can be effective in groups  A mechanism for `strangulation’ (e.g., Kawata & Mulchaey 2008) • Group tide can be responsible for morphological transformation of small dwarfs (e.g., Meyer et al. 2001).

  14. Gas stripping in groups Z=0.51 Z=0 DM distribution in a group (M=8*1012 Mo) • Gas stripping  Gradual SF suppression (Larson et al. 1980, Balogh et al. 2000, Bekki et al. 2002; McCarthy et al. 2008) Disk (Face-on) Gas density contour Disk (Edge-on) (Kawata & Mulchaey 2008)

  15. SF enhancement in the stripped clumps SFR Gas 83 Myr 183 Myr • Stripping of diffuse gas: The stripping efficiency depends on Vrel and rIGM (Abadi et al. 1999; Quills et al. 2000; Vollmer et al. 2006; Tonnesen & Bryan 2008). • Enhancement of SF formation (e.g., Bekki & Couch 2003; Kronberger et al. 2008; Mastropietro et al. 2009). (Roediger et al. 2014)

  16. Two key questions: • How do the two ram pressure effects (i.e., stripping + SF enhancement) depend on galaxy masses ? • How does ram pressure influence the HI and H2 fractions of galaxies in groups and clusters ?

  17. 2.1 Outside-in truncation of SF in disks under ram pressure stripping (RPS). Gas distribution SFR density IGM Disk Group (IGM) 70 kpc Mgr=1014 Msun, Rvir=1.2 Mpc, T=2.6*107K, FIGM=0.15, Mdisk=6*1010 Msun, MW-type galaxy (Bekki 2014)

  18. RPS effects dependent on galaxy mass M=1010 Msun, SMC-type 15 kpc For the same environment, orbits, inclination…. • RPS is more effective in less massive disk galaxies: SF is more likely to be quenched in dwarf disks. M=1011 Msun, M33-type M=1012 Msun, MW-type 33 kpc 70 kpc Stellar disk size

  19. Enhancement of H2 formation in disks under moderately strong ram pressure. • High-density gaseous regions can be formed in the inner disks owing to compression of gas by ram pressure of IGM, but only for a short timescale. Isolated M(H2) RPS (Bekki et al. 2014)

  20. HI H2

  21. Rmol(=M(H2)/M(HI)) increase: 0.10.3 T=0.4 Gyr T=1.4 Gyr IGM flow HI HI clumps H2 53 kpc Stripped H2 clump H2 distributions look clumpier than HI before and during RPS.

  22. Significant Rmol increase in disks after RPS. For 16 disk models after ~ 3 Gyr evolution (under RPS) in groups/ small clusters • Main reason is that the outer HI-rich gas disk can be preferentially stripped (while the inner H2-rich gas remains intact). Evolutionary direction Initial disk (Field) (Bekki et al. 2014)

  23. A correlation between HI-to-star-size ratios and M(HI)/Ms? Initial disk (Field) For 16 disk models after ~ 3 Gyr evolution (under RPS) in groups/ small clusters • Selective stripping of outer HI gas by RPS Outside-in truncation of SF in massive groups/small clusters. Evolutionary direction (Bekki et al.2014)

  24. Implications • The observed flat HI mass function for less massive galaxies in groups (e.g., Kilborn et al. 2009) can be understood in terms of `selective stripping’ of HI gas from less massive galaxies. However we need to estimate more quantitatively the evolution of the HI mass function in future theoretical studies. • H2 formation from HI on dust grains can not continue to be efficient owing to the HI-deficient disks  HI-deficient galaxies are likely to be H2-deficent too. • The projected distributions of SF regions in disk galaxies can be diverse after RPS.

  25. Characteristic 2D distributions of Ha (e.g., Broken ring, crescent-shape, arcs etc... in disks under RPS) (Bekki 2014)

  26. (2b) Group tide (+slow galaxy encounter) S0 formation via repetitive slow galaxy interaction. Group member galaxy Mgr=2*1013 Msun, Rvir=0.54 Mpc, Rperi=4rs, Ngal=87. (Bekki & Couch 2011)

  27. S0 formation via repetitive slow galaxy interaction. (Bekki & Couch 2011)

  28. (2b) Group tide (+slow encounter) • Basic roles: Morphological transformation from spirals into S0s (Bekki & Couch 2011) and disk thickening (Villalobos et al. 2012). • Gas stripping and intra-group HI formation. • Enhancement of H2 formation (this work). • Unlike RPS, group tide (+interaction) can not cause rather small RHI/Rs (<1), because both stars and gas can be efficiently stripped.

  29. (3a) Rich cluster environment: High-speed encounter • Galaxy harassment (multiple high-speed encounters + cluster tide) can transform low-mass late-type disks (Sd/Im) into dwarf spheroids and ellipticals (Moore et al. 1996, 1994). • What is the HI/H2 evolution in harassed galaxies ? Simulation Observation Time sequence (Moore et al .1996)

  30. Sporadic enhancement of H2 formation in dwarf disk galaxies. M(H2) (A) These epochs correspond to (i) when a galaxy passes through its orbital pericenter or (ii) when it interacts with a more massive galaxy. Rmol (B) Rmol is significantly lower than MW-type disk galaxies owing to low dust abundances. Still gas within the disk ! Tide & interaction Mcluster=1015 Msun, Rvir=2.6 Mpc, rapo=0.8 Mpc Ngalaxy~1000 Mdisk=6*108 Msun, SMC-type galaxy Isolated

  31. Complete stripping of HI and H2 gas by ram pressure in rich clusters • If dwarf disk galaxies are located within 0.3-0.5Rvir of a rich cluster, then they will lose all gas within 1-2 Gyr (before morphological transformation).

  32. Implications • Although galaxy interaction/cluster tide can be responsible for the morphological transformation from Sd/Im into dE/dSph, they alone can not completely truncate SF. Ram pressure stripping would be required to explain `dead’ dE/dSph. • Some low-mass disks first become red/dead disks (`passive spirals’) owing to gas stripping by ram pressure, and then are transformed into dE/dSph (or S0s) via high-speed galaxy interaction/cluster tide: Color evolution first, morphological transformation second.

  33. (3b) Suppression of disk-rebuilding in early-type galaxies. Post-merger evolution in fields and clusters: Stripping of tidal debris by cluster tide  Suppression of disk rebuilding ? Field Cluster 0.9 Mpc (6 Gyr Evolution of merging pairs: Mihos 2003, 2004)

  34. Ram pressure stripping of cold HI streams around E/S0s. Cluster T=0 Gyr • Gaseous tidal streams around E/S0s (formed from merging) can be converted into numerous `high-velocity’ clouds. 0.6 1.1 140 kpc IGM Field 1.7 2.3 Gas clumps 2.8 E IGM Rvir

  35. Effect of RPS of groups on cold gas streams around an elliptical galaxy 2.8Gyr evolution

  36. Effect of RPS of the MW-type galaxy on a BCD-like dwarf that is infalling onto the galaxy after strong tidal galaxy interaction. 2.8Gyr evolution

  37. Implications • Masses, sizes, morphologies, kinematics, and detection probabilities of low-density hydrogen gas around E/S0s can be quite different in different environment (in particular, kinematical differences should be investigated, e.g., by SAMI etc). • HI gas streams of satellite galaxies around MW and M31 can be broken into many high-velocity clouds via ram pressure effects, if the HI streams form before their accretion onto the Local Group.

  38. Conclusions • Galaxy interaction and merging in small/compact groups can enhance (at least temporarily) the H2 formation efficiency thus the fraction of molecular hydrogen (Rmol) in disk galaxies. • Ram pressure stripping can significantly increase Rmol due largely to the HI gas stripping from the outer parts of galactic gas disks. • Environmental effects can cause the changes of galaxy locations on the Rmol-MHI/Ms and Rmol-RHI/Rs diagrams.

  39. Conclusions Observation (Boselli et al. 2014) Too high to be consistent with simulations Zone of avoidance (?) Simulated disks under RPS (Bekki et al.2014)

  40. Conclusions • Group/cluster environments can suppress the rebuilding process of low-density gas disks around early-type galaxies (owing to tidal effects and ram pressure stripping). • The cold HI streams around merger remnants and interacting galaxies can be transformed into numerous compact (high-velocity) clouds in groups/clusters.

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