Galaxies with Active Nuclei

1
Galaxies with Active Nuclei

• Seeds chapter 14

2
Objective

• Study generally distant, luminous galaxies
  erupting in outburst

3
Introduction

• Some galaxies show emission indicating colossal
  violence at their cores.
• These galaxies can be billions of light years
  away, yet the emission from this activity is
  easily detected.

4
Active Galactic Nuclei

• 1950s powerful radio galaxies
• Today active galaxies (radioIR,UV,X)
• Active galactic nuclei (AGN)
• Radio lobes also possible

5
Double-Lobed Radio Galaxies

• Giant with radio lobes 1053 J 106 Msun
• Hot spot of intense emission on far lobe
• Double exhaust modelEruption in core drives out
  jets of material
• Windswept head-tail radio galaxies

6
Galaxies with Erupting Nuclei

• Seyferts spirals, bright nuclei (no lobes), some
  with fast gas motion. Accompany interactions (Our
  galaxy few 100 Myr ago?)
• BL Lac objects active cores dominates spectrum
  of host elliptical
• Some ellipticals (eg M87) AGN, jet (no lobes) 2
  billion solar-mass black hole?

7
The Search for a Unified Model

• Black hole surrounded by cavity, thickened disc
  which emits jets
• Black hole accretion model may explain power
  source of active galaxies
• BL Lac is jet seen head on
• viewing angle for Seyfert explains motions

8
Galaxy Collisions Active Cores

• What makes a galaxy erupt?
• Collision can feed dormant hole
• Evidence Seyfert companions, NGC5128

9
Quasars

• Quasi-stellar objects / QSOs
• Some of most distant objects in universe

10
The Discovery of Quasars

• 1960s powerful radio point sources
• Look like stars
• Huge redshift
• Distant, luminous yet rapidly variable
• What are they?

11
Quasar Distances

• Receding at up to almost light-speed
• Billions of ly away
• Quasars with identical spectragravitational
  lensing by intervening galaxies

12
LENSING BY ABELL 2218
13
Evidence of Quasars in Distant Galaxies

• z5 Universe at 10 of present age
• Deep photos show galaxy around quasar
• Supernova in host galaxy
• Distorted, jet, companions, radio lobes
• QUASARS Erupting cores of very distant galaxies
  triggered into activity by collisions with other
  galaxies

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A Model Quasar

• Black hole, accretion disc, jets
• Up billion Msun, 1 Msun/yr intake
• Magnetic fields control jets
• Black holes are messy eaters
• Active galaxies as buried quasars
• Beyond quasars lies the early universe...

15
Summary

• Active galaxies suffer erupting cores
• Radio lobes, bright cores with jets
• Black hole accretion
• Galaxy interactions feed hole
• Quasars are distant, very active
• Feeding frenzy cores of young galaxies