Astr 2320 Thurs. April 27, 2017 Today s Topics. Chapter 21: Active Galaxies and Quasars

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1 Astr 2320 Thurs. April 27, 2017 Today s Topics Chapter 21: Active Galaxies and Quasars Emission Mechanisms Synchrotron Radiation Starburst Galaxies Active Galactic Nuclei Seyfert Galaxies BL Lac Galaxies Radio Galaxies Quasars Emission Line Characteristics Absorption Line Characteristics Unification Model for AGN 1

2 Chapter 20 & 21 Homework Chapter 20: #1, #2, #3, #7, #8 Chapter 21: # 3, 5, 6, 7 Due Tues. May 2 2

3 Chapter 21: Active Galaxies - I Starburst Galaxies Rare Galaxies with Strong, Narrow Emission Lines in Nucleus Strong H-α Indicates a Massive Burst of Star Formation 3

4 Chapter 21: Active Galaxies - II Active Galactic Nuclei Emit Over a Broad Range of Wavelengths Radio to X-rays Variability at All Wavelengths Non-Thermal Emission Mechanisms Synchrotron Emission Relativistic Electrons Spiraling in a Magnetic Field Radiate a Power-Law Spectrum Thermal Emission at Long Wavelengths Very Similar Starburst 4

5 Chapter 21: Types of Active Galaxies Seyfert Galaxies Spiral galaxies with luminous variable nuclei Two Classes Seyfert I: Broad permitted lines and narrow forbidden lines Seyfert II: Both permitted and forbidden lines are narrow Quasars Quasi-stellar, variable, blue Most are radio-quiet, most have x-ray emission Non-thermal emission Enormous luminosities: L > Watts BL-Lac have almost featureless, non-thermal spectra Radio Galaxies Extended synchrotron emission Jet and double-lobed structure surrounding compact source 5

Chapter 21: Active Galaxies - III Seyfert Galaxies Discovered by Carl Seyfert Properties Bright, Star-like Nuclei Emission Lines Broad: Type-I Narrow:

6 Chapter 21: Active Galaxies - III Seyfert Galaxies Discovered by Carl Seyfert Properties Bright, Star-like Nuclei Emission Lines Broad: Type-I Narrow: Type-II X-ray Emission Hot, thermal blackbody Rapid variability small size Infrared Emission Thermal Emisison from warm dust Hot Accretion Disk + Dusty Torus 6

7 Chapter 21: Active Galaxies - IV BL Lac Galaxies Almost featureless UV-bright spectra Most of the absorptions from Earth s Atmosphere Broad lines from galaxy Power-Law Spectrum from Synchrotron Emission Images Show Only Bright Point Source Spectra of low-luminosity examples reveal underlying galaxy at high-redshift High Polarization Enormously Luminous AGN 7

at a galaxy Jets leading to Large Bubbles Interpretation Hot

8 Chapter 21: Active Galaxies - V Radio Galaxies Discovered in Initial Radio Surveys Synchrotron Emission Structure Bright central source at a galaxy Jets leading to Large Bubbles Interpretation Hot relativistic jet emerging from AGN Blows bubble in diffuse intergalactic gas 8

9 M87: Nearby Radio Galaxy Synchrotron emission produces visible photons. M87 is Nearby (D ~ 16 Mpc) Radio Galaxy AGN is Within Nucleus of Elliptical Galaxy Relativistic Jet Synchrotron Emission Highly Polarized Featureless Spectra Blobs Move Along Jet Spectroscopy of Nucleus Red-shifted and Blue-shifted Emission Lines 10 7 M sun Black Hole 9

10 Chapter 21: Quasars Quasars Discovered as Radio Sources Stellar-like Blue Objects Spectra Revealed Broad, Redshifted Emission Lines Most quasars are radio-quite and x-ray sources HST images reveal underlying galaxy and neighbors at similar, high redshift. 10

11 Structure of Nearby AGN AGN is star-like Torus of Dust Chapter 21: Nearby AGN Outer Accretion Disk? Jets often seen in Ha Swept-up Material? Braiding (some) Suggests Magnetic Field 11

12 Chapter 21: Emission Mechanisms Supermassive Black Holes Only plausible mechanism for enormous energies from a compact source is accretion onto a black hole ΔE σ L 4πcr GM = r L = η M c e E 2 = BH GM r m BH + m p GM r m GM The luminosity depends on the efficiency of. 2 2 BH Sch r BH Sch m 1 2 mc 2 (mass passes event horizon with v ~ c) the process sinceaccretion disk isinvolved : The Eddington Limit occurs when the outward radiation force equals the gravitational force : Solving for L L E = 4πGm σ e p E : c M BH = 1.3x10 39 M Watts 8 10 BH M! 12

AGN Unification Model Unification Model AGN Properties Originate from Different Viewing Geometries Broad Lines from Inner Accretion Disk of Black Hole Narrow Lines from Clouds Ionized by UV from

13 AGN Unification Model Unification Model AGN Properties Originate from Different Viewing Geometries Broad Lines from Inner Accretion Disk of Black Hole Narrow Lines from Clouds Ionized by UV from Accretion Disk X-rays from Inner-most Accretion Disk Dusty Torus Surrounds Accretion Disk Can Hide Broad-line Region if Edge-On Jet Viewed Full-on is BL Lac Twisted Mag. Field of Disk Collimates the Jet 13

14 Quasars as Probes of the Intergalactic Medium Extreme luminosity makes ideal probe of IGM flashlight Most of atomic H gas should be in ground state Absorption lines from Ly α should be shortward of quasar s so easily identified Allows column densities and temperatures (using other species) Redshift (look-back time) dependence constrains models of galaxy formation 14

15 Chapter 20 & 21 Homework Chapter 20: #1, #2, #3, #7, #8 Chapter 21: # 3, 5, 6, 7 Due Tues. May 2 15

Lecture 9. Quasars, Active Galaxies and AGN

Lecture 9. Quasars, Active Galaxies and AGN Lecture 9 Quasars, Active Galaxies and AGN Quasars look like stars but have huge redshifts. object with a spectrum much like a dim star highly red-shifted enormous recessional velocity huge distance (Hubble