Galaxies with Active Nuclei

Seyfert Galaxies• Broad emission lines of highly ionized atoms.• Velocities of matter near center ~ 10,000 km/s supermassive black holes.• 2% of all galaxies are Seyferts.• Seyfert 1: very luminous at X and UV, broad emission lines with sharp,

narrow cores.• Seyfert 2: No strong X-ray emission, width of lines greater than normal

galaxies but smaller than Seyfert 1.• Rapid fluctation of core brightness nucleus smaller than a few light

minutes.• Brightest have luminosities about

100 times that of the Milky Way Galaxy.• Activity due to interactions with other

galaxies.

Radio Galaxies

• Double lobed radio sources with a galaxy between the two lobes.• Deformed or interacting with other galaxies.• Complex shapes of some radio lobes related to motions of galaxies.• Due to matter flowing into an accretion disk around a black hole.• Emit synchrotron radiation, indicating the presence of relativistic charged

particles moving in a magnetic field.• “Hot” spots at outer extremes of the lobes.

500,000 ly

Cygnus A

Centaurus A

Supermassive Black Holes

• M87: Accretion disk + jet along rotation axis.60 ly from center gas orbits at 750 km/s 2.4 billion solar mass black hole.

• NGC7052: 300 million solar mass black hole.• Milky Way galaxy: 2.6 million solar mass black hole.• Most galaxies observed so far contain black holes with

mass equal to about 0.05 times the mass of their nuclear bulges.

• In these galaxies, the nuclear bulge formed first, material with low angular momentum settled into the center and evolved to become a black hole.

• Disk material accumulated later.

Unified Model

• Supermassive black hole.• Hot, thick inner disk.• Outer disk, cooler, thick, dusty, and doughnut shaped.• Inclination of accretion disk inclination of the galaxy.• Accretion disk seen edge-on – Seyfert 2.• Accretion disk seen tipped at a small angle – Seyfert 1.• Line of sight into the central cavity – Blazar (BL Lac

object) – 10,000 times more luminous than the Milky Way Galaxy.

Quasars (QSO’s)

• Initially observed as star-like points of light.• Very large redshifts (as large as 6+): Hubble law

very distant.• First one discovered: 3C48 (redshift = 0.37).• L = 10 – 1000 times the L of a large galaxy.• Rapid fluctuations small objects.• Quasar “fuzz” with spectrum like that of a normal

galaxy (stellar absorption lines) suggests that quasars are distant galaxies.

• About 100,000 have been found.

QSO 0957+561: Gravitational Lens Effect

Images of QSO 0957+561 (z = 1.4136)

Galaxy between Earth and the QSO bends space to produce two images of the QSO (z = 0.36).

Gravitational Lensing by a Cluster of Galaxies 7 Billion Light Years Away

Quasar with Jets and Radio Lobes

LBQS 1429-008 (z = 2.1)(3 Distinct QSO’s in Interacting Galaxies)

This false-color composite of the triple quasar system was made using a combination of Keck Observatory's and the European Very Large Telescope's visible and infrared data.S. G. Djorgovski and colleagues, Caltech, and EPFL