The Unified Model of Quasi-Stellar Objects

1. The Unified Model of Quasi-Stellar Objects Dr. Christopher Sirola Department of Physics & Astronomy University of Southern Mississippi

2. I am Spartacus! I am Spartacus! I am Spartacus! Finding quasars just by looking is like finding a renegade Roman gladiator…

3. Can you identify the quasar in this picture? Here!

4. A Brief History of Quasars attempts in vain to deduce the identity of .                                     attempts to determine is, but the prisoners will not identify him.  Many make the claim of "I am!".  As punishment the survivors are crucified on the road to Rome. In reality, 6,000 were nailed up along the road, but has him killed in the battle. "And so making directly towards himself, through the midst of arms and wounds, he missed him, but slew two centurions that fell upon him together. At last being deserted by those that were about him, he himself stood his ground, and, surrounded by the enemy, bravely defending himself, was cut in pieces." • The First Quasar – 3C 273 • Cyril Hazard used occultation of the Moon to identify radio emission with 3C 273 The abrupt disappearance of the radio emission from 3C 273 allowed Hazard to identify its optical counterpart. If the source is large, its light should gradually decrease as the Moon covers it. If it is a point source, its light should disappear abruptly.

5. The First Quasar – 3C 273 • Maarten Schmidt then discovered unknown emission lines in the spectrum of 3C 273 were actually Balmer hydrogen lines, but redshifted.

6. General properties of QSOs • Names • - “Quasar” = “quasi-stellar radio source” • - “QSO” = “quasi-stellar object” • - The difference is the presence or lack of radio emission • Location • - Objects are extragalactic • - Objects show enormous redshifts • - Objects must be extremely far away • - Objects also seen from extremely distant past • - Associated with cores of galaxies

7. An HST QSO Portrait Gallery

8. Photometric properties • Only  10% are bright radio emitters (“true” quasars) • Extremely bright (tens to thousands of times brighter than typical galaxies) • Highly variable • Outputs can rise or fall by several magnitudes • Outputs can change over very short periods of time (even as short as hours; also days, weeks, months, & years)

9. Spectral properties • Have large redshifts (NO blueshifts!) • Base of spectrum is flat • Implies energy emitted at variety of wavelengths • Usually have broad emission lines • Implies high velocities of emission region • ~ 10% have broad absorption lines • Many elements besides H & He: • C, N, O, Si, Fe, etc. • Implies copious star formation

10. A Sample Spectrum of a QSO Note the flat “base” of the spectrum with various emission peaks. This peak is a redshifted Hydrogen alpha emission line. Relative flux Si IV C IV Wavelength (angstroms)

11. The Unified Model • QSOs belong to a larger population of Active Galactic Nuclei (AGN) • Supermassive Black Hole at Core • Over 1 million solar masses • Can get as high as  1 billion solar masses

12. Accretion disk rotates rapidly around black hole • May extend several tens of AU (few mpc) • Gas heated by collisional excitation • Gas is hotter going toward black hole • Gives rise to flat spectrum • Extends from radio to x-ray • Black Hole + accretion disk referred to as “Central Engine” (CE) • Efficiency of energy production 10-20% • Compare to H fusion (0.7%)

13. A model of a QSO (courtesy NASA)

14. HST Images of Black Holes in the Cores of Galaxies

15. Black Hole inside here Accretion disk Overlapping optical & radio maps of NGC 4261

16. Comparisons between galaxies & quasars: Quasars typically overwhelm the light from the rest of the galaxies they inhabit.

17. An optical image of a Seyfert galaxy, an intermediate type of Active Galaxy that appears in some spirals.

18. Other regions surrounding the Central Engine • Broad Emission Line Region • Clouds near the CE in rapid, random orbits • Temperatures high enough for ultraviolet emission • Broad Absorption Line Region • Torus of thick gas surrounding CE and BEL region • Temperatures low enough for absorption of UV • Jets • Synchrotron radiation from particles caught in magnetic field of accretion disk

19. Another NASA representation of the Unified Model.

20. Various Subsets of AGN • Specific types depend on spectra • Looking down on jets • High & quick variability, washed-out spectral lines • Blazars, BL Lac objects, Optically Violent Variables • Looking through torus • High polarization • Quasars, Radio-lobe galaxies • Looking between torus & jets • Moderate variability • QSOs, Seyfert galaxies

21. Locations of QSOs & AGNs • Always seen in distant past • QSO population peaks at redshift ~ 2 • Universe was ~ 7% of its current age (i.e. ~ 1 billion years old) • Now known to inhabit cores of ancient galaxies • - Only 1 of every 1000 galaxies has a QSO • If QSOs came to be in the distant past, where are they now?

22. What fuels the black hole? • Black Holes are often viewed as oversize vacuum cleaners. • But black holes don’t move freely • Material (gas & dust) has to come to the black hole

23. PKS 2349: A collision between a QSO and a galaxy. The Central Engine needs a supply of material in order to keep generating light.

24. Q1229+204 swallowing a dwarf galaxy. Black holes are (by definition!) invisible. We see them only by their effects on their environments. The Central Engine can last up to 500 million years (0.5 billion years), a significant but small fraction of the age of the Universe.

25. Primordial QSOs may have formed as early as z  6 (about 9-10 billion years ago). At left: a painting of a primordial QSO.

26. Element abundances of QSOs • In general, most objects of the distant past (Population II stars in the Milky Way, for example) have low metal contents. • Recall that “metals” for astronomers are elements besides hydrogen and helium Nitrogen QSOs are ancient objects and tend to have high metal abundances. How? Silicon Carbon

27. When galaxies collide, gas is mixed & compressed, spurring explosive rates of star formation and subsequent supernovae. The same goes for QSOs. M82 – an example of a starburst galaxy.

28. Other Studies of QSOs QSOs can show up as gravitational lenses: intervening galaxies warp space & we see multiple images of the QSO. Above: The Einstein Cross.

29. Q0957+561 – the first known QSO gravitational lens. Component A Lensing galaxy Component B

30. By comparing the variations in light from each component of Q0957+561, it is possible to estimate the Hubble constant. Results are consistent with other methods (around 70 km/s/Mpc). Component A is in blue Component B is in red

31. Future questions regarding QSOs • o    Details regarding CE energy production • - Including questions regarding variability • - QSOs only vary  1/3 of the time (result from my Ph.D. work; implications for QSO search programs) • o    Development of supermassive black holes • §       - How do they form? • §       - Do the black holes come first or last? • §       - The “Maggorian Relation” – supermassive black hole tends to be ~ 0.5% of total mass of host galaxy (theory suggests ~ 0.1% to 0.2%) • o    Geometry of BALR • §       - Torus? - Spherically symmetric? - Special class? • (addressed by my work but results were inconclusive)

32. Thanks for your attention!