Astrophysics & Cosmology Erik Elfgren Lecture 8 Large scale sctructures 2dF Galaxy Redshift Survey Large scale structures Clusters . Galaxies are not scattered randomly throughout the universe . Galaxies are found in clusters, such as our Local group (with 3 galaxies and some 45 dwarf galaxies) . Galaxy clusters are group together in super clusters, such as the Virgo cluster, where the Milky way resides (with some 2000 galaxies) . The majority of space contains no galaxies at all and these spaces are called voids Large scale structures Clusters Large scale structures The local group 3-D map of the Local group Large scale structures The local group Most of the galaxies in the local group (distances to scale) Large scale structures The local group Neighbors Maffei 1 group . Mafei 1: Large elliptical galaxy . 5 Mpc away . Dim reddish glow clouded by disk dust Sculptor group . Sculptor galaxy: intermediate spiral . 4 Mpc away . Weakly bound M81 group . Contains M81 and M82 . 3.6 Mpc away Centaurus A / M83 group . One or two groups . 3.7 Mpc away Large scale structures Galaxy dynamics . The local group is dynamical . Galaxy group Maffei 1 have belonged to the Local group . The LMC & SMC have The most prominent galaxies in the belonged to Andromeda Local group (sizes to scale) and will merge with us . Andromeda and the Milky way will collide in 2–7×109 years Large scale structures Galaxy dynamics Galaxy mergers . Stars do not collide . The gravitational potential becomes chaotic towards the end and the orbits of the stars become random . The galaxy resulting from a merger of to similar The Antennæ galaxies galaxies is an elliptical . 1000-fold star formation Large scale structures Galaxy dynamics Gravitationally bound? . Recent research shows that all apparent groups are not bound . 10–50% of the apparent galaxies are only passing . The results are based on N-body simulations of An N-body simulation something like our local group (16,8×106 particles) Large scale structures Galaxy dynamics Collision of Andromeda and Milky way . Andromeda larger but less massive . Approaching with the speed 120 km/s Artist’s impression of the view of the merger from the . Transverse speed not well Earth known, ~ 100 km/s (certainly < 200 km/s) . Most likely, the solar system would be unaffected Large scale structures Superclusters Virgo . 100 groups . 2000 galaxies . 200 Mly 15 . 10 M . Pulls us in Large scale structures Superclusters Evolution Coma . Thousands of galaxies . 99 Mpc away . Old cluster . Numerous ellipticals Large scale structures Superclusters Evolution The Hercules cluster . Part of supercluster . 100 galaxies . 175 Mpc away . Young cluster . Numerous spirals . Mergers in middle and bottom left Large scale structures Structures At close range, gravitational attraction overcomes the Hubble explansion: . We see a peculiar velocity (=deviation from Hubble law) . The universe expands but locally galaxies attract each other Peculiar velocities of nearby galaxies . Measurements out to 100 Mpc Large scale structures Structures The structure began with slight enhancements in the density of matter in the early Universe: t=0,21 Gy . These regions became protogalactic clouds, then collapsed into galaxies t=1,0 Gy . Individual galaxies fell in towards each other to form clusters and then superclusters t=13,6 Gy . DM crucial influence Large scale structures Structures On scales of ~ 50 Mpc we see structures, such as: . Filaments . Walls . Voids On scales > 500 Mpc the universe seems homogeneous and isotropic Large scale structures Structures 2dF sky survey . 221 283 galaxies . Max distance: 1,29 Gpc Large scale structures Structures Sloan sky survey . ~800 000 galaxies . Normal galaxies + Luminous Red Galaxies . Max distance: 2,03 Gpc . Objective: 100 000 000 galaxies Large scale structures Structures Filaments . Gravitationally bound galaxies . Threadlike structure . Length: 100 Mpc . Boundaries between the voids Large scale structures Structures Walls CfA2 Great wall . 250 Mpc long . 100 Mpc wide . 5 Mpc thick . 60 Mpc away Sloan Great wall . 433 Mpc long . 300 Mpc away . Biggest known galactic structure Grus, Fomax, Scultor Large scale structures Structures Voids . Empty spaces between filaments . Largest known structures . 10–150 Mpc radius Large scale structures Structures Voids The WMAP coldspot . 3000 Mpc away . 300 Mpc radius . Discovered from its Integrated Sachs-Wolfe effect . Unlikely in the current model of the cosmic evolution ISW effect Large scale structures Cosmological N-body simulations Requirements . Spatial size Hubble volume ~ 5 Gpc . Mass resolution 9 << 10 M Large scale structures Cosmological N-body simulations . Number of particles size of simulation . Put the particles in the box . Only gravity is allowed to affect the evolution . The equations of motion are solved for the particles as the time evolves . Snapshots are saved every once in a while Large scale structures Cosmological N-body simulations Millennium simulation . Size: 2 billion ly . Particles: 10 billion . Resulted in some 20 million galaxies Large scale structures Cosmological N-body simulations Horizon simulation . Size: 2 billion ly . Particles: 4096^3 . Resolution: Milky way has 100 particles.