active galactic nuclei

STFC Summer School 2007

Paul O’BrienX-ray & Observational Astronomy Group

University of Leicester

Previously at: University College London

[PhD, UCL 1987: A study of the UV continuum of quasars]

IUE Project, UCL/RAL

University of Oxford

University of Leicester XMM-Newton, Faulkes Telescopes & Swift

Active Galactic NucleiIUEIUE SwiftSwift

Active Galactic Nuclei

• A little history

• Taxonomy (split them up)

• Unification (join them together again)

• Mass, size and structure

AGN: an object with nuclear, non-stellar energetic phenomena.

Power-source: accretion disc feeding a massive black hole.

But why, when, where, how…?

Radio mm IR Opt./UV X-ray


History lesson – start (almost) at the beginning

Leviathan, 1845, 1.8m telescope! Birr Castle, Parsonstown, Eire (wet)

Owned by Lord Rosse (optimist)

M51 – example of a “spiral nebula”

PhD student goes here


The first galaxy/AGN spectra

• Photography improved (dry plates) by late 1800s so could be used in a spectrograph stellar spectral classification (Pickering, Cannon etc.).

• Sir William Huggins, 1864 – spectroscopy of M31 (Andromeda). Saw (faint) absorption lines but unsure if they were reflected Moon-light

• Edward Fath, 1909 PhD – displayed nebulae spectra showing that galaxies look like stars – i.e. galaxies are made out of stars!

But, also found a galaxy (in 1908) that had: “bright lines in its spectrum, has also a strong continuous spectrum which contains absorption lines”.

Object: NGC1068 (M77) – the first AGN!


Seyfert Galaxies

• Fath followed by Slipher (M31 velocity), and Hubble…(fame, fortune?, telescope)

• Carl Seyfert (1943) – Postdoc at Mount Wilson

Isolated 6 spiral galaxies with blue nuclei which show “high-ionization emission lines much wider than absorption lines in normal galaxies”.

• Two basic types:

Seyfert 1 - broad permitted lines + narrow forbidden lines

Seyfert 2 - narrow permitted and forbidden lines H [OIII]


Example Seyfert spectra

Wavelength (Å)

HH

Blue continuum

Red continuum

HH


NGC 3783

See a large range in ionization species

(too large for normal nebulae)

Seyfert Type 1


Radio Galaxies

• Discovered after WWII (Ryle, Mills etc.)

• Example: M87 (NGC4486). Identified by Bolton, Stanley & Slee (1949). [Optical jet found by Curtis in 1918]

• Radio emission is non-thermal (Synchrotron. + Inverse Compton)

M87 optical

M87VLA

Quasars/QSOs

• 3C273 (Mararten Schmidt 1963).

• High redshift (0.158) implied huge luminosity. Also variable small size

• Most (~90%) are radio-quiet (QSOs).

• Quasars found in elliptical galaxies.

• QSOs found in either spirals or ellipticals.

STFC Summer School 2007 The Host Galaxy and the AGN

galaxies at same redshift

Disturbed morphology

Interaction?

Disturbed morphology

Interaction?


Need to explain the diverse properties of AGN

• AGN can be very luminous (1000x bright galaxies)

• The continuum varies on (fairly) short timescale small objects

• Broad-band continuum + wide range in emission line ionisation

• See both “broad” (10000 km s-1) and “narrow” (2000 km s-1) emission lines. The narrow lines are broader than normal galactic lines.

Solution: the accreting supermassive black hole (SMBH) model…


Size-scales

Black-hole: Rs = 3x109 M6 m

Accretion disc: ~3 – 104 Rs

Broad Line Region: ~1-100 light-days

Molecular Torus: ~1-10 light-years

AGN Type 1 and 2 Unification


Type 1 AGN

Type 2 AGN

Radio loud AGN Obscuring stuff


Black holes in every galaxy?

M87 – ionized gas rotation curve.

Large dark mass required (~109 M

Virial theorem: M (r V 2 /G)Magorrian et al. 1998


MBH-* relationship

Reverberation

Other methods

Calibrate AGN method vs. stellar (Ferrarese). AGN follow same relation as in-active galaxies.

“Bulge” mass correlates with mass of SMBH

Peterson et al.


PDS 456 – the most powerful object in the local Universe, but unknown until 1997…

Torres et al. (1997); Yun et al. (2004)

At z=0.184, 1'' = 3.1 kpc

QSO Luminosity vs. redshift

Nearby galaxies Interaction?


X-ray spectrum requires a massive, highly-ionized outflow moving at ~0.15c . Also see fast outflow in the UV.

Outflow mass-loss rate ~ 10 M yr-1

For 10% covering factor, outflow K.E. ~ 1039 J s-1 (10% Lbol)

(Reeves et al. 2003; O’Brien et al. 2005)

X-ray and UV observations of PDS 456

CIV 1549 v -5000 km s-1

Ly/NV

Ly BAL (12-22000 km s-1)

PDS456 3C273

Massive absorption


• Some outflows have a K.E. comparable to the radiation luminosity: are they common in the early Universe?

• Most SMBH mass probably assembled by luminous accretion. So perhaps built when the accretion rate is high/spin low?

• Over ~107 years X-ray outflows could deposit a total mechanical energy comparable to the binding energy of a Galactic bulge (~1052 J).

• Feedback between outflows and star formation??

What could outflows mean – the concept of “feedback”


Interaction in action…the Ultraluminous IR Galaxies

IRAS revealed a large population of “Ultraluminous IR Galaxies”.

Star-formation rate 100-1000 xGalactic.

Most are interacting or highly disturbed.

SMBHs (and galaxies?) grow through accretion, SF, outflows all driven by mergers, shocks, galactic bars etc.


How do we see into the heart of an AGN ?

Try radio interferometry

e.g. M87 , only ~18Mpc away (1" ~ 300 light-years)

But, we need to look in the optical/IR


Magdalena Ridge Observatory, NM – 10 x 1.4m optical/IR telescopes with baselines up to 340m. On schedule for 2008/2009 start. Observe from 0.6-2.4 microns with spatial scale of 0.3-30 mas.

Creech-Eakman et al. 2006

VLTI – 4x8.2m + 4x1.8m Baselines up to 200m, ~10mas

Optical interferometry

STFC Summer School 2007AGN – The Future

• More data of all kinds + better models

• Deep surveys in sub-mm, IR, X-ray, etc. to find all the AGN

• High-resolution imaging in radio, optical, IR (e.g. SKA, VLTI, MRO)

Time-dependent, 3-D, MHD disc(torus) simulation (Hawley et al.)

UK astronomers have UKAFF – the UK Astrophysics Fluids Facility at Leicester – build your own disc, jet, black hole…

Have fun!


The end

active galactic nuclei

Documents

narrow lines

bright lines

radio galaxies

normal galactic lines

normal galaxies

seyfert galaxies fath

spiral galaxies

faint absorption lines