This document discusses active galactic nuclei (AGN) across the electromagnetic spectrum from radio to gamma-rays. It describes various classifications of AGN like Seyfert galaxies, quasars, and radio galaxies. It discusses emission mechanisms in different wavelength regimes from infrared dust emission to broad emission lines in the optical. It also introduces the unified model of AGN where differences are explained by orientation and obscuration effects rather than distinct phenomena.

1. M.P. Birla Institute of Fundamental Research
Multi-Wavelength Analysis of Active Galactic Nuclei
Candidate
Sameer Patel
December 14, 2014

2. Introduction
Highly energetic manifestations in the nuclei of galaxies, powered
by accretion onto supermassive massive black holes.
Empirical classi

3. cation schemes have been developed, on the
basis of the spectra; but recently, various uni

4. cation schemes
have been developed ( the same underlying phenomenon).
Evolve strongly in time, with the comoving densities of luminous
ones increasing by 103 from z 0 to z 2.
At z 0, at least 30% of all galaxies show some sign of a nuclear
activity; 1% can be classi

5. ed as Seyferts, and 106 contain
luminous quasars.
Most (or all) non-dwarf galaxies contain SMBHs, and thus
probably underwent at least one AGN phase.
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6. Seyfert Galaxies
Carl Seyfert, in his

7. rst observation, had reported a small percentage
of galaxies had very bright nuclei that were the source of broad
emission lines produced by atoms in a wide range of ionization
states.
Seyfert I- Spectra contain very broad emission lines that include
both allowed lines (H I, He I, He II) and narrower forbidden lines
(O [III]); sources with speeds typically between 1000 and 5000
km s1.
Seyfert II- Spectra contain only narrow lines (both permitted and
forbidden), with characteristic speeds of about 500 km s1.
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8. Seyfert Spectra
NGC 5548-Seyfert I Galaxy
(Peterson et al., 1991)
NGC 1667-Seyfert II Galaxy
(Barth et al., 1999)
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9. Quasars and QSOs
Terms often used interchangeably.
Scaled up versions of Type I Seyferts.
Small fraction (5-10%) are the strong radio sources which
originally de

10. ned the quasar class.
Nuclear emission normally dominates host galaxy light. The
nucleus has luminosity MB 21:5 + log h0.
Spectra very similar to Seyfert galaxies, except that:
Stellar absorption lines are very weak, if detectable at all.
Quasars are all `Type I' in Seyfert jargon - i.e can see the broad lines.
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11. Typical Quasar Spectrum
(www.astr.ua.edu/keel/agn/forest.html) 6 of 28
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12. Radio Galaxies
Strong radio sources typically associated with giant elliptical
galaxies. Two types of radio galaxies have optical spectra that
show AGN activity:
Broad-line radio galaxies (BLRG) like Type I Seyferts
Narrow-line radio galaxies (NLRG) like Type II Seyferts
These look like radio loud Seyferts, but they seem to occur in
ellipticals rather than spirals. . .
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13. The Fanaro-Riley Dichotomy
3C 338, FR-I classi

14. ed AGN
(Ge Owen, 1994)
3C 173P1, FR-II classi

15. ed AGN
(Leahy Perley, 1991)
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16. Composite AGN Spectrum
(Tengstrand et al., 2009) 9 of 28
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17. AGNs in IR/Sub-mm Wavelengths
Most of the emission in the NIR and MIR bands due to secondary
dust emission (emission by cold, warm, or hot dust grains heated
by the primary AGN radiation source).
The temperature of the NIR- and MIR-emitting dust is between
100 and 2000 K.
Broad and narrow emission lines seen in the NIR-FIR part of the
spectrum of many AGNs.
Ability to detect highly obscured (Compton thick) AGNs
For Type I Seyferts, 10% of the bolometric luminosity is
emitted in the IR.
IR emission at wavelengths longward of 1 m accounts for
50% of the bolometric luminosity of Type II Seyferts.
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18. The Dusty Torus
HST Image of NGC 4261
(Courtesy-Wikipedia) 11 of 28
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19. The Radio Regime
About 10% of all AGNs are core-dominated radio-loud sources.
Stars are extremely weak radio sources =) an optical point
source that is a strong radio source is likely to be a radio-loud
AGN.
Radio lobes and jets often seen in radio-loud AGNs.
The dividing line between radio-loud and radio-quiet AGNs is
usually set at R = 10, where R is a measure of the ratio of radio
(5 GHz) to optical (B-band) monochromatic luminosity,
R = L(5 Ghz)
L(4400A
)
= 1:5 105 L(5 Ghz)
L(4400A
)
;
The spectrum of core-dominated radio sources suggests emission
by a self-absorbed synchrotron source, whose spectrum is
represented well by a single power law, F / R.
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20. Cygnus A
Contour images of the Cygnus A
radio jet on various scales.
(Carilli et al., 1996)
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21. Superluminal Motion
The apparent superluminal motion
of M87's jet
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22. AGNs in Optical-UV Wavelengths
Optical images of luminous Type I AGNs show clear signatures of
point-like central sources with excess emission over the
surrounding stellar background of their host galaxy.
In early observations, the continuum spectral distribution was very
distinct from an integrated stellar continuum characteristic of
normal galaxies.
Observationally, AGN were comparatively very blue.
The blue colors were due to both the fact that the continuum
emission extended into the UV and beyond and that structure was
often seen in the blue continua { the so-called big blue bump
(Richstone Schmidt, 1980).
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23. Probing the Central Engine Through X-Rays
Provides insight about the inner parts of the accretion disk and
some information about the parameters of the SMBH like its
intrinsic angular momentum or spin (Brenneman Reynolds,
2009).
Basic idea- the asymmetry of a line pro

24. le produced in the inner
AGN accretion disk depends in a predictable manner on the black
hole's spin.
Speci

25. c spectral signatures are attributed to the characteristics of
the gas in
ow and out
ow near the central most regions in AGN.
X-ray observations also provide signatures of reprocessing of
radiation in material withing approximative distance of hundreds
of gravitational radii.
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26. Probing the Central Engine Through X-Rays (Contd.)
The resultant emergent spectrum consists of direct radiation from
the central source plus a scattered or re
ected spectrum that
includes imprinted photoabsorption,
uorescent emission and
Compton scattering from matter within the surrounding accretion
ow.
The reprocessing (vis a vis | re
ection), leads to yet another
bump in the hard X-ray spectrum (like in the IR).
This bump has its maximum around 20-30 keV, where the
re
ection eciency reaches its maximum.
A soft (E . 2 keV) excess over the power law component
dominant at higher energies has been found in the X-ray spectra
of many Seyfert galaxies (Saxton et al., 1993) | open issue!
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27. X-Ray Spectrum
Hard X-ray spectrum of the narrow-line Seyfert I Arakelian 564
(Smith et al., 2008) 18 of 28
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28. Lineless AGNs
Subpopulation of AGNs with extremely weak, sometimes
completely undetected emission lines.
High-redshift sources with extremely weak broad emission lines
that are 1 or 2 orders of magnitude fainter compared to other
Type-I sources.
Exhibit, usually, a non-stellar continuum with occasional
ux
variations.
Clear indication for the active BH is an observed point X-ray
source in many of the sources.
Do not show a power law continuum.
Are mostly radio quiet.
Variability, if any, is of very small amplitude.
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29. Lineless AGN Spectrum Comparison
(Trump et al., 2009) 20 of 28
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30. Lineless AGNs (Contd.)
Extremely large L=LEdd is one possible explanation for the weak
broad emission line.
For the low-luminosity sources, a very low accretion rate =)
RIAF =) systems can lack much or all of the (otherwise strong)
UV ionizing radiation.
For the high-luminosity sources, the Lyman continuum radiation
by the disk depends on the BH mass and accretion rate and can
be extremely weak in disks around very massive BHs =) such
systems are likely to show very luminous continua but no line
emission.
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31. BLR Vs. RIAF
(Trump et al., 2011)
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32. AGNs in
-Rays
Many blazars are also powerful
-ray emitters, and some of them
show one or more of the following properties:-
Intense, highly variable high-energy emission in the
-ray part of
the spectrum.
Intense, highly variable radio emission associated with a
at radio
spectrum and occasional superluminal motion.
Radio, X-ray, and/or
-ray jet with clear indications for relativistic
motion.
A double-peak SED with a lower-frequency peak at radio-to-X-ray
energies and a high-frequency peak at X-ray-to-
-ray energies.
Very weak broad and/or narrow emission lines indicative of
photoionization by a non-stellar source of radiation on top of a
highly variable continuum.
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33. -Ray Spectrum of 3C 279
(Bottcher et al., 2007) 24 of 28
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34. The Uni

35. ed AGN Model
Fundamental question | can all the distinct appearances of the
AGN phenomenon be explained by a common underlying model?
Or are the dierent classes are intrinsically distinct?
At a 1978 BL Lac conference in Pittsburgh, the foundations for
the beaming uni

36. cation were outlined (Blandford Rees, 1978),
a concept still believed to be true.
Scheuer Readhead (1979) | radio-core dominated quasars
could be uni

37. ed with the radio-quiet quasars by assuming the
former ones are beamed towards the observer.
Later studies: dierence in orientation, and dierence in
obscuration (Barthel, 1989).
Most simpli

38. ed picture | two types of AGN: radio-quiet and
radio-loud.
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39. The Uni

40. ed AGN Model (Contd.)
For each type, a range of luminosities is observed, leading for
example to the Fanaro-Riley classes as well as to the distinction
between a Seyfert and a quasar, and all other observed dierences
would be explained by orientation eects.
Antonucci (1993) | existence of an optically thick torus
surrounding the central regions of an AGN on scales of 1-100 pc
would lead to the absence of broad emission lines in the case of
Seyfert II if they were observed edge-on.
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41. The Uni

42. ed Model
(Beckmann Schrader, 2012) 27 of 28
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43. References
Antonucci, R. 1993, ARAA, 31, 473
Barth, A. J., Filippenko, A. V., Moran, E. C. 1999, ApJ, 525, 673
Barthel, P. D. 1989, ApJ, 336, 606
Blandford, R. D., Rees, M. J. 1978, in BL Lac Objects, ed. A. M. Wolfe, 328{341
Bottcher, M., Basu, S., Joshi, M., et al. 2007, ApJ, 670, 968
Brenneman, L. W., Reynolds, C. S. 2009, ApJ, 702, 1367
Carilli, C. L., Perley, R. A., Bartel, N., Sorathia, B. 1996, in Astronomical Society of
the Paci

44. c Conference Series, Vol. 100, Energy Transport in Radio Galaxies and
Quasars, ed. P. E. Hardee, A. H. Bridle, J. A. Zensus, 287
Ge, J., Owen, F. N. 1994, AJ, 108, 1523
Leahy, J. P., Perley, R. A. 1991, AJ, 102, 537
Peterson, B. M., Balonek, T. J., Barker, E. S., et al. 1991, ApJ, 368, 119
Richstone, D. O., Schmidt, M. 1980, ApJ, 235, 361
Saxton, R. D., Turner, M. J. L., Williams, O. R., et al. 1993, MNRAS, 262, 63
Scheuer, P. A. G., Readhead, A. C. S. 1979, Nature, 277, 182
Smith, R. A. N., Page, M. J., Branduardi-Raymont, G. 2008, AA, 490, 103
Tengstrand, O., Guainazzi, M., Siemiginowska, A., et al. 2009, AA, 501, 89
Trump, J. R., Impey, C. D., Taniguchi, Y., et al. 2009, ApJ, 706, 797
Trump, J. R., Impey, C. D., Kelly, B. C., et al. 2011, ApJ, 733, 60 28 of 28
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