Active Galaxies, Quasars, &
Large-Scale Structure in the Early Universe

	Lecture 13 Ay-1

Active galaxies

Categories of Active Galaxies

	Seyfert galaxies
		like normal spirals but with bright (> 1011L¤), point-like (rapid variability) nuclei; dusty - 75% radiation in infrared, internal Doppler motions 1000 - 3000 km /s
	Radio galaxies (10%)
		often appear like elliptical galaxies; BUT strong radio emission (lobes) outside galactic nucleus, extend 50 - 1000 kpc ! ® result from very energetic processes in nucleus                                e.g. Centaurus A: visible ® seems like E2, 500 kpc diameter
	All active galaxies
		vast amounts of energy emitted from or generated in central compact nucleus - jets common (indicate bursts of activity), probable origin? – galaxy-galaxy interactions

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Quasars

	many strong radio sources (3C catalog) - no obvious optical counterparts
	3C48 (1960), 3C273 (1962) identified with faint star-like optical sources – but spectra inexplicable
	1963 - Schmidt & Greenstein (Caltech)                                  ® highly redshifted hydrogen Balmer lines
	3C 273 at 620 Mpc , 3C 48 at 1300 Mpc (from Hubble Law)
	(recessional velocity of 3C 48 ~ 1/3 velocity of light)
	L > 1012 L¤ !!
	light varies within 1 month ® size < 0.1 lyr
	¯
	QUAsi-Stellar radio sources – QUASARS
	now Quasi-Stellar Objects QSOs

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Blazars/Quasars

	synchrotron radiation ® jets of relativistic particles
	blazars: double radio sources seen end-on
	motions superluminal – appear to exceed speed of light
		usually 5 to 10 x c
	superluminal motions observed in some quasars (1 to 5 x c)
	3C 273: radio emission separating at 0.001 arsec/yr
		® 10 x 3 x 105 km/s !

Superluminal Motion?

Other viewing angle effects

How are active galaxies powered?

	Have to account for:
	high luminosities
	non-stellar radiation
	variability ® compact nuclei (£ 1 pc diam)
	explosive activity – jets
	rapid internal motions (broad emission lines)
	¯
	accretion onto a compact object
	® supermassive black hole
	millions – billions x M¤ can have radius 20 AU
	infalling material ® gravitational energy® kinetic energy® thermal energy® radiation
	jets accompany accretion disks

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Cosmology : structure and evolution of the universe

	Questions and issues:
	size of universe - infinite or finite?
	structure – hierarchies?
	age - limited or forever (in future and in past)?
	evolution - relative amounts of matter and radiation?
	atomic composition?
	Speed of light finite ® we can effectively look
	back in time!!

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Big Bang –creation of universe

	Our cosmic particle horizon = how far can we detect phenomena within age of universe
	Rhoriz = tuniv  x c
	Can’t see stars further than 14 Blyrs
	& redshifts decrease photon energy (even harder to detect)
	Horizon increasing
	Planck time tp =( Gh/c5)1/2
	= 1.35 x 10-43 secs   time, space behave as today
	Between Big Bang and Planck time nothing known

Cosmic Microwave Background (CMB)                         –  radio emission  filling all of universe
- “sound” of Big Bang

CMB istropic® universe isotropic

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