Introduc8on Lecture 2 Galaxies are basic units within the Universe. Let s introduce some of their proper8es, and their distribu8on through space. 14 Billion years of History: the Birth and Matura8on of Galaxies Voyage to the Virgo Cluster Milky Way Galaxy Our Galaxy Earth 100 nm Sun 10 μm Earth orbit ¼ cm Solar system 20 cm Nearest star 250 m virus cell pin head saucer 2.5 football fields Jewel Box Cluster Naked eye stars Eagle Nebula All sky image of MW crossing the sky Scien8fically informed ar8st s Impression The three basic types of galaxy Ellip8cal All spheroid, no disk Spiral & Barred Spiral Spheroid and disk Galaxy Center Crab Nebula Solar system Many spirals have large hydrogen disks Irregular No spheroid or disk (though young stars) 1
Rota8on curves reveal dark mawer halos Galaxy Anatomy Disk: gas and stars in rough circular orbits Old & young stars Bulge Nucleus Disk Halo Galaxies can some8mes collide and merge Spheroid: bulge & halo stars in random orbits No gas, so no young stars only old stars. Dark MaWer Halo: huge surrounging region of dark mawer (par8cles?) with few stars. Complex pawerns of galaxy collisions Simula8on of the Mice collision (Josh Barnes) Galaxy collisions trigger star birth Many of these colliding galaxies are starburst galaxies, meaning they have high rates of star forma8on (>100 stars/year) The Distribution of Galaxies: Redshift Surveys Sloan Digital Sky Survey 100 inch Telescope 640 Fiber Spectrograph 2
Galaxy distribu8on in a slice of sky A Slice of Sky, Viewed in 3 D 2 D view of sky 3 D view of slice of sky Voids Clusters Lines/walls We are here Milky Way Galaxy is here Distance to Virgo Cluster Within 20 years: surveyed the en8re visible Universe The Visible Universe 13.7 Bly 2 Bly Visible Limit Region currently mapped MW galaxy (20 yds) Study galaxy evolu8on: look far away The Visible Universe 13.7 Bly 2 Bly Hubble Ultra Visible Limit Deep Field (HUDF) Region currently mapped MW galaxy (20 yds) 3
The Hubble Deep Fields Deep fields are small Most distant galaxies are smaller than 1 arcsecond: Size of football field on the moon, brightness of a single candle. Measuring distances is difficult: use dropout method HUDF reaches back into the first Byr 4
Young galaxies are small, chao8c, interac8ng, and merging: Young galaxies are small but grow quickly Rapid assembly of the first structures 140 Mly box 14 Mly box It takes ~8 Gyr for large modern spirals to form Star birth history Cosmic star birth history The young Universe was spectacular 5
One reason for decline in star birth Ac8ve Galaxies: Feeding Nuclear Black holes Quasars ( ) and Radio Galaxies ( ) Black holes in galaxy nuclei Feeding (and growing) black holes was common in the past, and it much rarer today. Accre8ng black hole Black holes at the center of today s old galaxies Black holes are revealed by rapid Doppler mo8on of stars or gas close to the center Black hole at the center of the Milky Way galaxy Star orbits around the black hole 6
Black hole bulge mass correla8on Feedback can clear out a galaxy s gas which prevents further star forma8on Black Hole blowout Supernova blowout in M82 Explaining the galaxy mass distribu8on Human mass distribu8on Explaining the galaxy mass distribu8on Dark halo mass distribu8on Explaining the galaxy mass distribu8on Summary Galaxies are the primary units of structure we find in the Universe. They are huge compared to stars and solar systems. They come in a range of sizes and shapes: spirals, ellip8cals, irregulars Each is embedded within a large halo of dark mawer Galaxies fill the visible Universe in a web like pawern of filaments, voids, and clusters as revealed by recent large redshim surveys. Deep surveys of small regions (e.g. the HUDF) allow us to study the life history of galaxies: they are ini8ally small, but quickly grow by collisions and mergers this growth also involves the birth of stars this also includes the feeding of massive black holes The mass distribu8on of galaxies comes from the mass distribu8on of dark mawer halos, with several suppression mechansims that prevent the forma8on of stars. 7