Astro/CSI 765

1. Astro/CSI 765 An Introduction to Active Galactic Nuclei (AGN) http://www.physics.gmu.edu/~rms/csi765 Prof. Rita Sambruna rms@physics.gmu.edu http://www.physics.gmu.edu/~rms 3-4165 Office hours: by appointment only

2. Outline of the course • DESCRIPTION:Phenomenology of AGN (emission • processes, observed properties at various wavelengths, • standard model for AGN) • PRE-REQUISITES: PYHS 502, 613, or Astro530 • TEXTBOOK:Quasars and Active Galactic Nuclei • by A.Kembhavi and J.Narlikar • (for a list of additional books, see me)

3. Structure of the course • LECTURES:review of concepts, expansion of reading material • HOMEWORK: • Reading from assigned papers • Writing essays/answering questionnaires • Solving (occasional) numerical problems • EXAMS:No “traditional” mid-term/final • Grading based on homework (25%), in-class discussion • (25%), and final project (50%) • GRADES: 93-100 A 83-86 B 70-74 C • 90-92 A- 80-82 B- 60-69 D • 87-89 B+ 75-79 C+ <59 F

4. Reading Assignments • Every week I will assign readings from papers or book • chapters for the following class • At the beginning of every class, there will be 30 minutes • or more discussion on the readings • I will ask one of you to present the reading material and • lead the discussion • 25% of your final grade (or more) will be based on the • in-class discussion

5. FINAL PROJECT: (50% of the final grade) • Goal: a deeper understanding of a particular issue/problem • analyzed in class, or a totally new AGN-related topic we did • not have time to talk about • Either a literature search or original data analysis (using • data from public archives) • Submit an outline for pre-approval by November 1 • Your paper (< 20 pages) in ApJ-style due December 2 • Seminar (30 minutes) on December 4 • Both the paper and the seminar are required

6. Lecture 1: • What is an AGN? • Historical discovery of AGN • The importance of the multi-wavelength • perspective • Notes and Useful quantities (some AGN lingo)

7. What is an Active Galactic Nucleus? • A point-like source at the center of an otherwise • normal galaxy • Nucleus light overwhelms the light from the • galaxy

8. Notation: AGN observed quantities • Image: a map of intensity versus position (x, y) • Light curve: a plot of flux/luminosity versus time • Spectrum: a plot of flux/luminosity versus • energy/frequency/wavelength (usually log-log) • Spectral Energy Distribution (SED): spectrum over a • broad energy range, usually radio through gamma-rays • (usually log-log)

9. The first AGN: 3C273 Optical image

10. The first AGN: 3C273 Optical spectrum Optical image

11. What is an Active Galactic Nucleus? • A point-like source at the center of an • otherwise normal galaxy • Main defining property of an AGN: Large luminosities from a compact region

12. What is an Active Galactic Nucleus? • A point-like source at the center of an • otherwise normal galaxy • Main defining property of an AGN: Large luminosities from a compact region What causes the AGN prodigious emission??

13. Spectral Energy Distribution of AGN Non-thermal processes dominate AGN emission

14. Observational properties of AGN • Point-like source at center of host galaxy • Non-thermal continuum emission • Rapid flux variability • Broad (FWHM > 1,000 km/s) optical/IR emission lines • Narrow (FWHM < 1,000 km/s) optical/IR emission lines • Polarized emission • Extended components (radio jets and lobes)

15. Optical spectrum of a quasar

16. What variability tells us If variability is observed on a timescale Dtvar in the source frame, then the radiation must be produced in a region with size: If the region is larger different parts would not be causally connected and different timescale can be observed. The minimum timescale is used to get the source size.

17. Currently, ~1000 AGN are known and identified • They span a large range of redshifts: z=0.002 to z=6 • (for comparison, the recombination era z=1,000 • first protogalaxies at z=10-20) • Several thousands more expected in the next few • years from Chandra, XMM, XEUS, NGST, SIRTF • Active galaxies are 10% of the total number of galaxies • A further 10% of AGN are radio-loud

18. The multi-wavelength perspective Observing AGN at different wavelengths is crucial to understand their complexity, as each wavelength probes different parts/processes of the same source Example: the nearby active galaxy Centaurus A (z=0.0018)

19. Optical (NOAO)

20. Optical (NOAO) Radio (NRAO)

21. Optical (NOAO) Radio (NRAO) Infrared (2MASS)

22. Optical (NOAO) Radio (NRAO) Infrared (2MASS) X-rays (Chandra)

23. Hubble Law • At the beginning of the century, Edwin Hubble • discovered that the further away a galaxy is, the • faster it is receding from us: • V=H0D • where V=radial velocity of the galaxy, D=distance • and H0=Hubble’s constant. • Hubble Law implies the Universe is expanding

24. Cosmological redshift z • Shift redwards of a given wavelength caused by the • expansion of the Universe:  l1, t1 l0, t0 • If Universe is expanding: R(t0)>R(t1) Z>0 andl0 > l1 (red-shift) Example: wave on an expanding balloon

25. Flux and Luminosity Assume a galaxy at a distance D is emitting light isotropically at a given rate L(n) [energy per unit time] or Luminosity The light propagates on the surface of an expanding sphere of radius D. The amount of radiation we receive or Flux is D=Luminosity Distance and is related to z (eq. 2.62)

26. Notation on Units • Luminosity: erg s-1 • Flux: erg s-1cm-2 • Distance: parsec (pc) and multiples • 1 pc = 3.09 x 1018 cm • = 3.3 light years • Frequency n (Hz) • Wavelength l (Angstroms, cm, …)

27. Homework Assignment (due next week; 10 points) • The measured redshift from 3C273 is z=0.158, • and the measured optical flux at 5500 A is • F=3x10-10 erg cm-2 s-1. Its optical flux is observed • to vary on timescales of 1 day down to 1 minute. • Determine: • The luminosity of the quasar • The size of the emitting region in pc • Assume H0=75 km/s/Mpc and q0=0.5. • Extra Credit (5 points): Estimate the mass of the • black hole (Hint: Eddington luminosity may be useful)