This week at Astro 3303

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Audrey Cole
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1 This week at Astro 3303 HW #8-10 deal with your final project! (HW#8 is posted already) The project counts 20% of the grade and is expected to be a significant piece of work. HW#8 for next Wed: prepare a first outline. copies to both Dominik and me; print a paper copy to hand in. 2 nd 30min test is Nov 11. Covers material through Wed Nov 6 (emphasis on material since Oct 7 th but some background might have been introduced earlier) Today: Galaxy environments Reading: Chapters 5 and 6

2 HW#8-10 & final project For Wednesday HW #8 Write a first draft outline/summary (bullets? some references/links; your first thoughts on how to proceed) Print a copy to hand in a copy to both Dominik and Martha Be prepared to give a 3 minute oral report in class: what is your project about Save the draft for yourself; you will add to it as part of next week s assignment

3 Interactions in distant clusters

4 Quasar Host Galaxies Bahcall et al. 1997, Ap.J. 479, 642

5 Elliptical versus Spiral Galaxies Morphological segregation: Initial conditions or evolution over time??? 100% Percent of total Percent galaxy of population total population 80% 60% 40% 20% E + S0 Spiral Low density Field High density Cluster

6 Morphological alteration mechanisms Gravitational mechanisms Galaxy-galaxy interactions Direct collisions Tidal encounters Mergers Galaxy-cluster interactions Harassment (multiple rapid tidal encounters) GRAVITY Galaxy-intracluster medium interactions Thermal evaporation Ram pressure sweeping INTRACLUSTER GAS

7 Interactions, Tides and Mergers Galaxy - galaxy interactions Galaxy ICM interactions

Galaxy-galaxy interactions Barnes & Hernquist See: http://www.ifa.hawaii.

8 Galaxy-galaxy interactions Barnes & Hernquist See: During tidal interactions and mergers, gas tends to be driven towards the centers of galaxies through gravitational torques on it by tidally induced stellar bars dissipation and shocks Starbursts Globular cluster formation Feeding of AGN

Tides and collisions Disturbed morphological appears: bridges, tails,

formation in otherwise dormant galaxy => starburst Disturbed material

gravitational attraction of supermassive black hole => falls towards

9 Tides and collisions Disturbed morphological appears: bridges, tails, asymmetry Gaseous material accreted by gas-poor galaxy induces star formation in otherwise dormant galaxy => starburst Disturbed material (velocity as well as location changes) may not be able to resist gravitational attraction of supermassive black hole => falls towards black hole => heated/collides with other material => photons emitted => luminosity!

10 N-body simulations: binary stars 1. Adopt the masses of the 2 objects (so here N=2) 2. Adopt characteristics of the orbits (eccentricity, inclination, orientation) 3. Apply the laws of gravity to predict the relative positions of the two objects after every time step.

11 N-body simulations: Sun-Earth-Moon 1. Adopt the masses of the 3 bodies (so here N=3) 2. Adopt characteristics of the orbits (eccentricity, inclination, orientation) 3. Apply the laws of gravity to predict the relative positions of the N objects after every time step.

Toomre & Toomre 1972 The galaxy s mass is concentrated at a point The outer disk particles are arranged in 5 rings They do not interact with each other (no selfgravity) All passages involve two

12 Toomre & Toomre 1972 The galaxy s mass is concentrated at a point The outer disk particles are arranged in 5 rings They do not interact with each other (no selfgravity) All passages involve two galaxies that have a close, slow moving parabolic approach Each time unit is 100 million years Although much more sophisticated codes exist today, T&T72 demonstrated the overall damage done by tides.

13 Toomre 2 results Galaxy encounters are not accidental; most pairs are bound already Direct encounters cause more damage than retrograde ones Tails (nice) are easier to make than bridges (messy) Viewing geometry is critically important

14 Retrograde passages Toomre & Toomre found that retrograde passage (ones in the opposite direction to a galaxy s spin) have little tidal effect. See Picture below Flat retrograde From now, we will only (i=180 discuss direct º ) parabolic passages, passage of a companion which are far more of equal mass. disruptive

15 TT72 Direct passages are more effective More damage from equal mass companion

16 Bridge Building and Inclination

Like bridges, tail making is less effective at higher inclination planes.

17 Tails Unlike bridges, tails involve some particles escaping towards infinity To form major tails, the galaxies should be similar in mass. Like bridges, tail making is less effective at higher inclination planes. Again, the difference between 0 and 30 is small. However, in higher inclinations, the tail is raised from the orbit plane. This allows the tails to be crossed, as in NGC 4038/9

18 N-body simulations: Galaxies 1. Adopt the masses of the N objects (so here N is a very large numbers) 2. Adopt characteristics of the orbits (eccentricity, inclination, orientation) 3. Apply the laws of gravity to predict the relative positions of the N stars after every time step.

19 Tidal encounter of The Mice Simulation by J. Barnes (U. Hawaii)

20 The Antennae

21 Simulation of the Antennae Simulation by John Dubinski (CITA)

22 M81 group interactions Optical image, traces starlight Radio image, traces gas

23 M81 group interactions Optical image, traces starlight Radio image, traces gas

24 M81/M82/NGC3077 movie

25 A member of a group of galaxies Distance = 425 Million light years The Cartwheel

26 The Cartwheel A drop-through or head-on collision. Star formation in the ring => young stars Chris Mihos, Lars Hernquist et al

27 How likely are encounters? Slow encounters are unlikely in dense clusters Simulated passages are unlikely to be hyperbolic Tails and bridges are the least observed in dense clusters Close encounters unlikely in loose groups Disruption damage depends on relative velocity (lower in groups than clusters), distance of closest approach and relative spin/orbit orientation Therefore, most tidal effects must have been created by galaxies that are gravitationally bound

28 Chris Mihos GalCrash Applet

29 Large Scale Structure Galaxies cluster: Galaxies are found in different environments: The field Groups Cluster Superclusters (filaments)

30 The Local Group M(MW) + M(M31) ~ 4.1 x M ʘ Schematic from Sarah Maddison Includes ~35 galaxies MW & M31 are dominate Mostly dwarfs which cluster around giants van den Bergh 2000, PASP 112, 529 Mateo 1998, ARAA 36, 435 Grebel 2006, astro-ph/

31 The Magellanic Clouds LMC SMC The Magellanic Clouds are contained within a common HI envelope. The Magellanic Stream traces their interaction with the MW.

32 Morphological Segregation in the Local Group Galaxies mainly clustered around the two principal galaxies MW & M31 Morphological segregation evident de/dsph near large galaxies di at larger distances Diagram from Grebel 1999 Giant spirals dsph (+dell) dirr dirr/dsph strong segregation Reionization/stripping issues

33 The Local Supercluster Cartoon of Local Supercluster View from the Local Group

34 The Virgo Cluster

35 The Virgo Cluster

36 Markarian s Chain NGC4438 NGC4406 NGC4374 M87 NGC4388

37 The Virgo Cluster: Bad things are happening

38 Gas and Galaxies in the Virgo Cluster baryons : the heavy ones (protons, neutrons, electrons, atoms etc) The mass of the hot ICM gas is ~5X more than the combined mass of all the stars in all of the galaxies! But what is the actual mass of the cluster itself?

39 The Virgo Cluster Virgo Cluster Catalog ~2000 objects Based on morphological appearance Largely confirmed by redshift measurements Distance ~ 17 Mpc Binggeli, Sandage & Tammann 1985, AJ 90, 1681

40 Hot Gas in the Virgo Cluster Extended X-ray emission implies hot Intra Cluster Medium => temperature is 100 million degrees Kelvin The cluster contains thousands of galaxies within its radius of 2 Mpc (7.5 degrees) How can we measure its mass??? Yoni: HW#4

41 Determining cluster membership Examine how the observed heliocentric velocities are distributed as a function of radial distance from the central position. We expect the cluster members to have about the same redshift (with a dispersion of km/s) so the objects offset by 1000s of km/s cannot be members => they are clearly separated in this plot. Background objects Here: a more distant cluster than Virgo Foreground objects Virgo is tricky because it is so close to us => harder to figure out membership

42 Subclustering in Virgo Binggeli, Popescu & Tammann, AApS 1993, 98, 275

43 substructure in the Virgo Cluster Extended X-ray emission implies hot ICM (T~10 8 K) Redshift distribution implies substructure including main cluster around M87, secondary one around M49, plus infalling spiral groups => Cluster is dynamically young (still collapsing)

44 Subclustering in redshift space All T E + S0 + de Sp + Irr + BCD Binggeli, Popescu & Tammann, AApS 1993, 98, 275 AGC (< 5 deg from M87) Oct 2008 (mph)

45 Elliptical versus Spiral Galaxies Morphological segregation: Initial conditions or evolution over time??? 100% Percent of total galaxy population Percent of total population 80% 60% 40% 20% E + S0 Spiral Low density Field High density Cluster

46 Morphology-clustercentric radius relation

47 Cluster environments: driving galaxy evolution Clusters contain 1000 gravitationally bound galaxies. Velocity dispersion ~ a few 100 to > 1000 km/s Most of the luminous material is in the hot intracluster medium (ICM) T ICM ~ K Extended X-ray emission Bremsstrahlung M gas ~10 13 M But remember: Clusters occupy only a small volume in the universe Most galaxies are not in clusters.

48 Formation of a cluster like Virgo Simulation by Ben Moore Ben Moore s web site

49 Surface brightness cd N4881 in Coma cd = cluster diffuse Much brighter than next brightest galaxy excess Log radius

50 cd surface brightness profile cd galaxy in the cluster A496 Note the excess light at R 1/4 > 2 SB(r) = SB(r eff ) exp (-7.67[(r/ r eff ) 1/4 1]) where r eff is the effective radius Morretti et al.

cd galaxies In the cores of regular rich clusters (or at a density enhancement) Local conditions are important Offset (too bright) from the luminosity

51 cd galaxies In the cores of regular rich clusters (or at a density enhancement) Local conditions are important Offset (too bright) from the luminosity function of normal galaxies Extensive (~1Mpc) stellar envelopes of low surface brightness Many have multiple nuclei cd galaxy in Abell 3827 Sarazin (1988)

brings massive galaxies to the center of clusters Merger of these

52 How do cd s form? Galactic Cannibalism (Ostriker & Hausman, 1977) Dynamical friction brings massive galaxies to the center of clusters Merger of these massive galaxies in the cluster cores Giant galaxy then swallows other galaxies going through the core Centaurus A

53 Dynamical friction Suppose an object of mass M is moving within a sea of other objects of mass m, with m < M. As M moves forward, the other objects are pulled towards it, with the closest ones feeling the strongest force. This produces a region of enhanced density along the path of M, including a wake trailing it. Dynamical friction = net gravitational force on M due to others that opposes its motion. Kinetic energy is transferred from M to surroundings, thus reducing its speed.

54 Cartoon of dynamical friction - V M Mass M sees stars approach at velocity V Stars are deflected a bit by M Slight excess of mass behind mass M

55 Galaxy harassment Multiple rapid encounters in a cluster may also seriously impact galaxy evolution. Blue: dark matter Red: gas Yellow: stars Animation courtesty of G. Lake

56 Supporting evidence: Intra cluster diffuse light (ICL) Harassment Intergalactic stars, ~10-40% of the cluster stellar population (Feldmeier et al., 2003) Tidal debris e.g. Plumes and arc-like structures The amount of tidal debris and ICL depends on local density, which supports the merger scenario (Combes, 2004) Rings of star formation that are more common than two-armed spirals (Oemler et al., 1997) Due to bars triggered during tidal interactions? Calcaneo-Roldan et al. (2000)

ICM V 2 > 2πG Σ gas Σ stars Ram pressure exerted by stationary gas on moving galaxy V is

57 Ram pressure sweeping Spirals in Virgo are HI deficient. Hydrodynamical simulations show effectiveness of ram pressure stripping Stripping occurs if ρ ICM V 2 > 2πG Σ gas Σ stars Ram pressure exerted by stationary gas on moving galaxy V is velocity of galaxy with respect to cluster Gravitational restoring force of stars and gas in galaxy Σ is surface density Vollmer et al. 2001

58 Ram Pressure Stripping Ram Pressure Stripping can remove the gas supply of galaxies that pass through clusters Interaction between ISM and ICM Could explain metal content of the ICM Episodes of starburst? Animation by Bengt Vollmer Simulation by B. Vollmer

59 Evidence of environmental effects: Morphological segregation Morphological disturbance HI deficiency HI/Hα distributions

HW#6 is due; please pass it in. HW#7 is posted; it requires you to write out answers clearly and completely explaining your logic.

HW#6 is due; please pass it in. HW#7 is posted; it requires you to write out answers clearly and completely explaining your logic. Oct 21, 2015 Basic properties of groups and clusters of galaxies Number density, structure X-ray emission from hot ICM Estimating cluster masses Cluster scaling relations Impact of environment on galaxies