1	ASTR 5460, Wed. Apr. 30, 2003 Reminders/Assignments Quasars and Active Galactic Nuclei
2	Reminders/Assignments FIRST/NVSS and 2MASS reports Discussion/comments/questions regarding the Physics Today Articles? Research Homework Update Dan finished phase 1, will start phase 2 Chris, Sey, and Cassandra primary now Presentation topics Read Shields “A Brief History of AGN” astro-ph/9903401 Skip astro-ph Friday -- evaluations
3	Presentation Topics Last week of class, 2 Wed., 4 Fri. WHO WHEN? Plan for 20 minutes, plus questions. Other astronomy faculty invited. Topics: Gunn-Peterson Test and Reionization Supernovae and the Accelerating Universe Weighing Supermassive Black Holes The Hubble Deep Fields Sub-millimeter (SCUBA) Galaxies X-ray Background
4	Sloan Post-starburst Quasars Background in papers/proposals Tasks Identify from the SDSS EDR spectra (two levels) – lots of effort now vs. later Morphology from SDSS images (two levels) Bruzual & Charlot ISB modeling Quasar measurements, derived properties Compiling statistics, correlation analyses (lots of effort later vs. now) Oversight, science, figures/tables, etc. Will require individual meetings
5	Quasars and Active Galactic Nuclei (AGNs)
6	The (slightly) active nucleus of our galaxy Probable Black hole High velocities Large energy generation At a=275 AU P=2.8 yr Þ 2.7 million solar masses Radio image of Sgr A* about 3 pc across, with model of surrounding disk
7	Active Galactic Nuclei: AGNs A small fraction of galaxies have extremely bright “unresolved” star-like cores (active nuclei) Shown here is an HST image of NGC 7742, a so-called “Seyfert galaxy” after Carl Seyfert who did pioneering work in the 1940s
8	NGC4151 with a range of exposures
9	Spectra of Stars, Spectra of AGNs
10	Active Galactic Nuclei: AGNs Small fraction of galaxies have extremely bright “unresolved” star-like nuclei Very large energy generation Brightness often varies quickly Implies small size (changes not smeared out by light-travel time) High velocities often seen (> 10,000 km/s in lines) Emission all over the electro-magnetic spectrum Jets seen emerging from galaxies
11	3C31
12	Many Views of Radio Galaxy Centaurus A
13	The Central Engine of Centaurus A http://imgsrc.stsci.edu/op/pubinfo/pr/1998/14/content/centauf.mov
14	Quasar Images 1
15	A Quasar Tour with animations
16	Accretion Disks Black hole is “active” only if gas is present to spiral into it Isolated stars just orbit black hole same as they would any other mass Gas collides, tries to slow due to friction, and so spirals in (and heats up) Conservation of angular momentum causes gas to form a disk as it spirals in
17	Different Views of the Accretion Disk The torus of gas and dust can block part of our view Seyfert 2 galaxies: Edge on view Only gas well above and below disk is visible See only “slow” gas Þ narrow emission lines Seyfert 1 galaxies: Slightly tilted view Hot high velocity gas close to black hole is visible High velocities Þ broad emission lines BL Lac objects: Pole on view Looking right down the jet at central region Extremely bright – vary on time scales of hours Quasars: Very active AGN at large distances Can barely make out the galaxy surrounding them Were apparently more common in distant past
18	Different Views of the Accretion Disk The torus of gas and dust can block part of our view Seyfert 2 galaxies: Edge on view Only gas well above and below disk is visible See only “slow” gas Þ narrow emission lines Seyfert 1 galaxies: Slightly tilted view Hot high velocity gas close to black hole is visible High velocities Þ broad emission lines BL Lac objects: Pole on view Looking right down the jet at central region Extremely bright – vary on time scales of hours Quasars: Very active AGN at large distances Can barely make out the galaxy surrounding them Were apparently more common in distant past
19	Different Views of the Accretion Disk The torus of gas and dust can block part of our view Seyfert 2 galaxies: Edge on view Only gas well above and below disk is visible See only “slow” gas Þ narrow emission lines Seyfert 1 galaxies: Slightly tilted view Hot high velocity gas close to black hole is visible High velocities Þ broad emission lines BL Lac objects: Pole on view Looking right down the jet at central region Extremely bright – vary on time scales of hours Quasars: Very active AGN at large distances Can barely make out the galaxy surrounding them Were more common in distant past
20	Quasar Images II
21	Quasar Images III: “Starburst-Quasar”
22	What makes an AGN active? Need a supply of gas to feed to the black hole (Black holes from 1 million to >1 billion solar masses! Scales as a few percent of galaxy bulge mass.) Collisions disturb regular orbits of stars and gas clouds Could feed more gas to the central region Galactic orbits were less organized as galaxies were forming, also recall the “hierarchical” galaxy formation Expect more gas to flow to central region when galaxies are young => Quasars (“quasar epoch” around z=2 to z=3) Most galaxies may have massive black holes in them They are just less active now because gas supply is less
23	Next Time