presentation-multi-wavelength analysis of active galactic nuclei

M.P. Birla Institute of Fundamental Research

Multi-Wavelength Analysis of Active Galactic Nuclei

Candidate

Sameer Patel

December 14, 2014

Introduction

• Highly energetic manifestations in the nuclei of galaxies, poweredby accretion onto supermassive massive black holes.

• Empirical classification schemes have been developed, on thebasis of the spectra; but recently, various unification schemeshave been developed ( ∼ the same underlying phenomenon).

• Evolve strongly in time, with the comoving densities of luminousones increasing by ∼ 103 from z ∼ 0 to z ∼ 2.

• At z ∼ 0, at least 30% of all galaxies show some sign of a nuclearactivity; ∼ 1% can be classified as Seyferts, and ∼ 10−6 containluminous quasars.

• Most (or all) non-dwarf galaxies contain SMBHs, and thusprobably underwent at least one AGN phase.

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Seyfert Galaxies

Carl Seyfert, in his first observation, had reported a small percentageof galaxies had very bright nuclei that were the source of broademission lines produced by atoms in a wide range of ionizationstates.

• Seyfert I- Spectra contain very broad emission lines that includeboth allowed lines (H I, He I, He II) and narrower forbidden lines(O [III]); sources with speeds typically between 1000 and 5000km s−1.

• Seyfert II- Spectra contain only narrow lines (both permitted andforbidden), with characteristic speeds of about 500 km s−1.

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Seyfert Spectra

NGC 5548-Seyfert I Galaxy(Peterson et al., 1991)

NGC 1667-Seyfert II Galaxy(Barth et al., 1999)

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Quasars and QSOs

• Terms often used interchangeably.

• Scaled up versions of Type I Seyferts.

• Small fraction (5-10%) are the strong radio sources whichoriginally defined the quasar class.

• Nuclear emission normally dominates host galaxy light. Thenucleus 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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Typical Quasar Spectrum

(www.astr.ua.edu/keel/agn/forest.html) 6 of 28


Radio Galaxies

• Strong radio sources typically associated with giant ellipticalgalaxies. Two types of radio galaxies have optical spectra thatshow 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 inellipticals rather than spirals. . .

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The Fanaroff-Riley Dichotomy

3C 338, FR-I classified AGN(Ge & Owen, 1994)

3C 173P1, FR-II classified AGN(Leahy & Perley, 1991)

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Composite AGN Spectrum

(Tengstrand et al., 2009) 9 of 28


AGNs in IR/Sub-mm Wavelengths

• Most of the emission in the NIR and MIR bands due to secondarydust emission (emission by cold, warm, or hot dust grains heatedby the primary AGN radiation source).

• The temperature of the NIR- and MIR-emitting dust is between100 and 2000 K.

• Broad and narrow emission lines seen in the NIR-FIR part of thespectrum 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 λ > 1 µm accounts for∼ 50% of the bolometric luminosity of Type II Seyferts.

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The Dusty Torus

HST Image of NGC 4261

(Courtesy-Wikipedia)11 of 28


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-loudAGN.

• 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 = Lν(5 Ghz)

Lν(4400A)= 1.5× 105 L(5 Ghz)

L(4400A),

• The spectrum of core-dominated radio sources suggests emissionby a self-absorbed synchrotron source, whose spectrum isrepresented well by a single power law, Fν ∝ ν−αR .

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Cygnus A

Contour images of the Cygnus Aradio jet on various scales.

(Carilli et al., 1996)

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Superluminal Motion

The apparent superluminal motionof M87’s jet

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AGNs in Optical-UV Wavelengths

• Optical images of luminous Type I AGNs show clear signatures ofpoint-like central sources with excess emission over thesurrounding stellar background of their host galaxy.

• In early observations, the continuum spectral distribution was verydistinct from an integrated stellar continuum characteristic ofnormal 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 wasoften seen in the blue continua – the so-called “big blue bump”(Richstone & Schmidt, 1980).

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Probing the Central Engine Through X-Rays

• Provides insight about the inner parts of the accretion disk andsome information about the parameters of the SMBH like itsintrinsic angular momentum or spin (Brenneman & Reynolds,2009).

• Basic idea- the asymmetry of a line profile produced in the innerAGN accretion disk depends in a predictable manner on the blackhole’s spin.

• Specific spectral signatures are attributed to the characteristics ofthe gas inflow and outflow near the central most regions in AGN.

• X-ray observations also provide signatures of reprocessing ofradiation in material withing approximative distance of hundredsof gravitational radii.

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Probing the Central Engine Through X-Rays (Contd.)

• The resultant emergent spectrum consists of direct radiation fromthe central source plus a scattered or “reflected” spectrum thatincludes imprinted photoabsorption, fluorescent emission andCompton scattering from matter within the surrounding accretionflow.

• The reprocessing (vis a vis — reflection), 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 thereflection efficiency reaches its maximum.

• A soft (E . 2 keV) excess over the power law componentdominant at higher energies has been found in the X-ray spectraof many Seyfert galaxies (Saxton et al., 1993) — open issue!

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X-Ray Spectrum

Hard X-ray spectrum of the narrow-line Seyfert I Arakelian 564(Smith et al., 2008) 18 of 28


Lineless AGNs

• Subpopulation of AGNs with extremely weak, sometimescompletely undetected emission lines.

• High-redshift sources with extremely weak broad emission linesthat are 1 or 2 orders of magnitude fainter compared to otherType-I sources.

• Exhibit, usually, a non-stellar continuum with occasional fluxvariations.

• Clear indication for the active BH is an observed point X-raysource 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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Lineless AGN Spectrum Comparison

(Trump et al., 2009) 20 of 28


Lineless AGNs (Contd.)

• Extremely large L/LEdd is one possible explanation for the weakbroad 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 radiationby the disk depends on the BH mass and accretion rate and canbe extremely weak in disks around very massive BHs =⇒ suchsystems are likely to show very luminous continua but no lineemission.

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BLR Vs. RIAF

(Trump et al., 2011)22 of 28


AGNs in γ-Rays

Many blazars are also powerful γ-ray emitters, and some of themshow one or more of the following properties:-• Intense, highly variable high-energy emission in the γ-ray part of

the spectrum.• Intense, highly variable radio emission associated with a flat radio

spectrum and occasional superluminal motion.• Radio, X-ray, and/or γ-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-γ-ray energies.• Very weak broad and/or narrow emission lines indicative of

photoionization by a non-stellar source of radiation on top of ahighly variable continuum.

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γ-Ray Spectrum of 3C 279

(Bottcher et al., 2007) 24 of 28


The Unified AGN Model

• Fundamental question — can all the distinct appearances of theAGN phenomenon be explained by a common underlying model?Or are the different classes are intrinsically distinct?

• At a 1978 BL Lac conference in Pittsburgh, the foundations forthe beaming unification were outlined (Blandford & Rees, 1978),a concept still believed to be true.

• Scheuer & Readhead (1979) — radio-core dominated quasarscould be unified with the radio-quiet quasars by assuming theformer ones are beamed towards the observer.

• Later studies: difference in orientation, and difference inobscuration (Barthel, 1989).

• Most simplified picture — two types of AGN: radio-quiet andradio-loud.

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The Unified AGN Model (Contd.)

• For each type, a range of luminosities is observed, leading forexample to the Fanaroff-Riley classes as well as to the distinctionbetween a Seyfert and a quasar, and all other observed differenceswould be explained by orientation effects.

• Antonucci (1993) — existence of an optically thick torussurrounding the central regions of an AGN on scales of 1-100 pcwould lead to the absence of broad emission lines in the case ofSeyfert II if they were observed edge-on.

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The Unified Model

(Beckmann & Schrader, 2012) 27 of 28


References

Antonucci, R. 1993, ARA&A, 31, 473Barth, A. J., Filippenko, A. V., & Moran, E. C. 1999, ApJ, 525, 673Barthel, P. D. 1989, ApJ, 336, 606Blandford, R. D., & Rees, M. J. 1978, in BL Lac Objects, ed. A. M. Wolfe, 328–341Bottcher, M., Basu, S., Joshi, M., et al. 2007, ApJ, 670, 968Brenneman, L. W., & Reynolds, C. S. 2009, ApJ, 702, 1367Carilli, C. L., Perley, R. A., Bartel, N., & Sorathia, B. 1996, in Astronomical Society of

the Pacific Conference Series, Vol. 100, Energy Transport in Radio Galaxies andQuasars, ed. P. E. Hardee, A. H. Bridle, & J. A. Zensus, 287

Ge, J., & Owen, F. N. 1994, AJ, 108, 1523Leahy, J. P., & Perley, R. A. 1991, AJ, 102, 537Peterson, B. M., Balonek, T. J., Barker, E. S., et al. 1991, ApJ, 368, 119Richstone, D. O., & Schmidt, M. 1980, ApJ, 235, 361Saxton, R. D., Turner, M. J. L., Williams, O. R., et al. 1993, MNRAS, 262, 63Scheuer, P. A. G., & Readhead, A. C. S. 1979, Nature, 277, 182Smith, R. A. N., Page, M. J., & Branduardi-Raymont, G. 2008, A&A, 490, 103Tengstrand, O., Guainazzi, M., Siemiginowska, A., et al. 2009, A&A, 501, 89Trump, J. R., Impey, C. D., Taniguchi, Y., et al. 2009, ApJ, 706, 797Trump, J. R., Impey, C. D., Kelly, B. C., et al. 2011, ApJ, 733, 60 28 of 28


presentation-multi-wavelength analysis of active galactic nuclei

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