Lecture 7 Active Galactic Nuclei - I

i) Brief History

 emission-line galaxies   Radio-astronomy radio sources    discovery of quasars theoretical interpretations going through the details

ii) General properties of AGNs iii) AGN spectra iv) General properties of “different” AGNs

 LINERs      Seyfert galaxies QSOs Quasars OVVs BL Lacs  Radio galaxies

v) AGN host galaxies

Depto. de Astronomía (UGto) Astronomía Extragaláctica y Cosmología Observacional



Brief History: emission-line galaxies

1909 – E. Fath [Lick Obs. Bull. 5, 71] found that

NGC 1068

(M77) have “a composite spectra, showing both

bright

(emission: H β , [OII] 3727Å, [NIII] 3869Å, [OIII] 4364, 4959 and 5007Å)

and absorption lines

”, different from other S (that presented nuclear continuum absorption spectra) 1917 – 1926 – V. Slipher [Lower Obs. Bull. 3, 59] confirmed emission and absorption lines of M77 E. Hubble [ApJ 624, 321] mentioned that “relatively rare spirals” with stellar nuclei show a planetary nebula-type spectrum (notably M77, NGC 4051 and 4151) N1068 1943 – C. Seyfert [ApJ, 97, 28]

first systematic study of galaxies with nuclear emission line

s – spectrograms of 6 S (the above plus NGC 1265, 3516 and 7469): attributed large widths of permitted lines (much larger than the ones of diffuse nebulae and differing from object to object) to Doppler broadening, reaching 8500 km/s. These are now called “

Seyfert galaxies ¨

N4151 - spectra



Brief History: radio-astronomy

1933 – K. Jansky [Proc. IRE 21, 1387] discovered that the MW emits in radio wavelengths - birth of

radioastronomy

1944 – G. Reber [ApJ 100, 279] published a map of the radio sky at 160 Mhz, showing

several local maxima

(including one in Cygnus constellation) 1948 – other than the MW plane and the Sun J. Bolton [Nature 162, 141] published a catalog of 6 discrete sources (

CasA , CygA, CenA, HerA, TauA

and

VirA

) 1949 – Bolton, Stanley & Slee [Nature 164, 101] sources: Crab Nebulae (M1, TauA),

M87

made the first optical identification of radio (VirA) and

NGC 5128

(CenA). Original radiotelescope Used by G. Reber 11 cm (2.7 Ghz) all-sky map (extragalactic sources brighter than 2 Jy) [Wall & Peacock MNRAS 216, 173]



Brief History: radio sources

1953 – Jennison & Das Gupta [Nature 172, 996] CygA shows

2 equal components

discovered, by using radio

interferometry

, that separated by 1.5'. After this proved to be very common among extragalactic radio sources CygA 1954 – Baade & Minkowski [ApJ 119, 206] , using interferometric positions obtained by Smith [1951, Nature 168, 555] , located optically

CygA

and CasA, the first being an

extragalactic

source (v LOS = 26 830 km/s), with emission lines ([NeV], [OII], [NeIII], [OIII], [OI], [NII] and H  ) presenting widths of about 400 km/s, and with a distorted morphology (galaxies in collision?). Optical identification of extragalactic radio sources became known as

radio-galaxies

1959 – Edge et al. [MNRAS 67, 37] published the Third Cambridge (

3C

)

Catalog

, with 471 radio sources, brighter than 9 Jy, at 159 MHz (and after at 177 MHz) in the Northern Hemisphere (some are Galactic, particularly SN remnants, but most are extragalactic)



Brief History: discovery of quasars

1960 – R. Minkowski [ApJ 132, 908] identified the

3C295

radio source with a member of a

cluster

of galaxies at

z ~ 0.46

1960 – A. Sandage , with accurate radio positions from T. Matthews , identified

3C48

with a 16 mag

variable stellar object

(with a faint nebulosity), showing

excess in UV

as compared to normal stars, and a spectrum with

broad emission lines at “unfamiliar” wavelengths

.

Such class of objects became known as “quasi-stellar radio sources” or

quasars

3C 295 1962 – Hazard, Mackey & Shimmins [Nature 197, 1037] from the “star” , using

lunar occultation

of

3C273

, located (to better than 1”) 2 components: a 13 mag star-like object and a jet pointing away 3C 48 3C 273



Brief History: discovery of quasars

1963 – M. Schmidt [Nature 197, 1040] found that the 4 broad emission lines of

3C273

star-like object agreed with expected wavelengths of H β , H γ , H δ and H ε 2798Å could be seen in the UV. J. Oke also found the H α at

z = 0.16

, and also MgII line of 3C273 in the IR, and J. Greenstein identified MgII in the spectrum of

3C48

at

z = 0.37

, conclusively demonstrating that quasars are extragalactic 1965 – A. Sandage [ApJ 141, 1560] objects” (BSO) or “ reported the discovery of a large population of objects resembling quasars (identified by their UV excess), after known as “blue stellar

quasi-stellar objects radio-quiet

” (QSO), soon noted to be more common than the original quasars



Brief History: theoretical interpretations

1950 – Alfvén & Herlofson [Phys. Rev. 78, 616] radio from “radio stars” proposed

synchrotron

process as the source of 1964 – E. Salpeter [ApJ 140, 796] and Ya. Zeldovich [Dokl. Akad. Nauk. SSRS 155, 67] the idea of quasars energy production from

accretion onto a supermassive BH

suggested 1965 – Bahcall & Salpeter [ApJ 142, 1677] suggest the possibility of intervening clouds of gas imposing absorption spectra blueward of Lyα (now known as

Lyα forests

) 1967 – De Young & Axford [Nature 216, 129] proposed that the double

lobes

are plasma confined by ram pressure when trying to expand into intergalactic medium



Brief History: going throw the details

1974 – Khachikian & Weedman [ApJ 192, 581] proposed the division of

Seyfert

galaxies (Sy) in

type 1

(with broad wings on permitted lines and narrower forbidden ones) and

type 2

(with both permitted and forbidden lines narrower) 1974 – Fanaroff & Riley [MNRAS 167, 31] classified the radio-galaxies (or

radio loud sources

), according to the morphology or their lobe components, as

type I

(two sided jets, diffuse edges all around, and lower luminosity) and

type II

(hot spots on the outer edges, higher luminosity, possibly one sided jets or pairs with different intensities) 1978 – Miller et al. [ApJ 219, 85] for the

BL Lacertæ

measured z = 0.07 object, identified as a short period (1-2 weeks) variable “star” in 1926 [Hoffmeister] and as a radio source in the 60's [M. Schmidt] , which would became the prototype of a new class of radio loud objects (compact, variable, almost without emission lines) BL Lac 1980 – Heckman [A&A 87, 152] identified emission line galaxies with lower luminosity, only able to produce lines of low ionization elements, called

LINERs

 G

eneral properties of AGNs

 Active Galactic Nuclei (AGNs) are

luminous

cores of galaxies (-9 < M B < -30, 10 38 < L X < 10 48 erg/s) which can be so bright that they outshine the entire surrounding

host galaxy

 their

continuum is markedly nonthermal

, brighter both in shorter (

X-rays

longer (

IR

and

radio

) wavelengths than normal galaxies (“broad SED”) and

UV

) and 

strong emission lines

spectra (broader than the ones of SB galaxies) are also characteristic of AGN  their

engine must be physically small

(less than a pc across) because their huge luminosity frequently

change dramatically in less than a year

observed brightness of an object of size a (even in a instantaneous change, the would only adjust to its new level over a time comparable to t » a /c that it takes light to pass from the back to the front of the source!)  there is no direct correspondence between the luminosity of an AGN and the luminosity of its host galaxy (the very energetic processes that take place are relatively

independent of the global properties of the galaxy

)



AGN broadband spectra



Properties of the “different” AGN LINERs



L

ow

I

onization

N

uclear

E

mission-line

R

egions (capable of producing only low ionization element    lines: [OI], [OII], [NII], [SII], etc) Originally defined by the ratios: [OII] also:  3227 / [OIII]  5007 [NII] / H α  0.6

 1 and and [OI]  6300 [OIII] / H β  3

relatively low luminosity AGNs

~ 80% of the nearby LINERs are

S(B)a

or / [OIII]

S(B)b

 5007  1/3 [S(B)c and E are less frequent]  currently they are considered to represent the

low luminosity tail

of Sy phenomenon M94 NGC 7814



Properties of the “different” AGN Seyfert Galaxies



nucleus

is particularly

bright

 shows

strong emission lines

of high excitation elements  usually show strong and variable X-ray emission and also emits strongly in the IR 

~ 90%

of the Sy are

S(B)b

NGC 5548 NGC 3277  may be of type:

Sy 2

- present both permitted and order of 500 km/s

forbidden lines

broadened by Doppler velocities of the

Sy 1

- have the continuum systematically lower than Sy1, from UV to IR - X-ray continuum has spectral index G~ 1.75, and breaks at about 130 keV - present forbidden lines similar to Sy2, but their

permitted lines

have very broad

wings

, broadened by Doppler velocities of 1000-5000 km/s - X-ray continuum has spectral index G~ 1.9, and breaks at about 200 keV

Sy 1.5

,

1.8

and

1.9

- intermediate type Sy (both large and relatively narrow permitted lines are found)



Properties of the “different” AGN Seyfert Galaxies



Properties of the “different” AGN Quasars

 

Qua

si-

S

tellar

R

adio

S

ources radio sources that in the optical are marked by an unresolved

point source

(brilliance of their nuclei completely swamps their stellar light)   present

cosmological

their

spectra

(high)

redshifts

resembles the one of

Sy 1

(the currently most distant quasars have z > 6) , with the profile of the broader components sometimes  M strongly asymmetric B < -22.3, L X > 10 44 erg/s, U-B < 0.4

Composite FIRST quasars PKS 1117



Properties of the “different” AGN QSOs

  

Q

uasi-

S

tellar

O

bjects QSOs and quasars are the

most luminous AGNs

present almost the same observable properties of quasars (

point-like sources

,

cosmological redshifts

,

Sy1 spectra

), except that they are not strong radio sources (they are

radio-quiet

)   they are about

20 times more frequent

on average mags fainter than quasars than quasars



Properties of the “different” AGN

BAL

QSOs

 

B

road

A

bsorption

L

ine QSOs show very broad blueshifted absorptions, associated with strong UV resonance lines



Properties of the “different” AGN OVVs

      

O

ptically

V

iolently

V

ariable quasars can vary in brightness by large factors on are

strong compact radio emitters

radio and optical emissions are strongly

polarized

possess spectra similar to that of quasars are currently classified as tend to lie at

blazars

, together with BL Lac objects

relatively high redshifts timescales of weeks

compared to BL Lacs 3C 345

VLBI 0235+164 

Properties of the “different” AGN BL Lac objects

   also strong

compact radio sources

also rapidly

variable

(like OVVs) also unresolved optical point sources (like quasars) (can vary in lum by an order of mag in less than a

month

)  present a

smooth

nonthermal power law

continuum

spectra almost

devoided

3C 371 of spectral

lines

 linearly

polarized

in either absorption or emission (continuum is so bright that hide emission lines!) (associated with large Faraday rotation)



Properties of the “different” AGN Radio-galaxies

 extragalactic radio sources associated with more or less normal

E

galaxies  their optical and UV spectra

may or may not show emission lines

; when seen, the lines may be broad (

BLRG

) or narrow (

NLRG

)  usually present a

nuclear compact source

plus two amorphous regions of radio brightness (

radio-lobes

), often placed roughly symmetrically on opposite sides of the nucleus and hundred to million pcs from it  the nuclear source is often connected to one or both lobes by a thin straight structure (

radio jet

), occasionally the jet is also visible at optical frequencies (M87=3C274)  within the lobe, the surface brightness usually peaks at a well defined

hot spot

, so the radio-galaxy of type:

FRI

- when the hot spots are close to the AGN (present relatively

small radio power

)

FRII

- when the hot spots are far from the AGN (present

higher power

: P 1.4GHz

³10 24.5

W/Hz)



Properties of the “different” AGN Radio-galaxies



Properties of the “different” AGN Radio-galaxies



AGN zoo

SB (85%) active (7%) LINER (15%) radio-quiet (99%) → S?

Seyfert (97.5%) NELG (<1%) Sy2 Sy1.5-1.9

(60%) (10%) Sy1 (30%) QSO (2.5%) BAL Galaxies “normal” (93%) AGN (0.5%) quasars radio-loud (1%) → E?

blazar radio-galaxy OVV BL Lac (radio) FR I FRII (opt—UV) NLRG BLRG



AGN spectra



AGN hosts

  

LINERs Seyferts QSOs

– mostly

S

– mostly

S

– some g

E

, others

S

(exponential profile) (HST detected hosts on only 3/8 of the   

quasars

– all observed seem to be hosted by g

E

observed QSOs and quasars)

blazars

or

interacting systems

– vast majority of BLLac appear to be hosted by

E radio-gal

– almost without exception

E

(but PKS 1413+135 is edge-on S) 3C 273 [HST] 3C 273 - host 3C 273 [SDSS]



AGN hosts



References:

    Papers:  Malkan 1983, ApJ 268, 582   R. Antonucci 1993, ARAA 31, 473 P. Padovani 1996, arXiv-9610155   G.A. Shields 1999, PASP 111, 661  T. Courvoisier 2000, arXiv-0011090 B.M. Peterson 2002, arXiv-0208066 Maia et al. 2003, AJ 126, 1750