Astronomía Extragaláctica y Cosmología Observacional

Astronomía Extragaláctica y Cosmología ObservacionalDepto. de Astronomía (UGto)

Lecture 7Active 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 AGNsiii) AGN spectra iv) General properties of “different” AGNs

LINERs Seyfert galaxies QSOs Quasars OVVs BL Lacs Radio galaxies

v) AGN host galaxies

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: Hβ, [OII] 3727Å, [NIII] 3869Å, [OIII] 4364, 4959 and 5007Å) and absorption lines”, different from other S (that presented nuclear continuum absorption spectra)1917 – V. Slipher [Lower Obs. Bull. 3, 59] confirmed emission and absorption lines of M771926 – 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)

1943 – C. Seyfert [ApJ, 97, 28] first systematic study of galaxies with nuclear emission lines – 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¨

N1068

N4151 - spectra

Brief History: radio-astronomy

1933 – K. Jansky [Proc. IRE 21, 1387] discovered that the MW emits in radio wavelengths - birth of radioastronomy1944 – G. Reber [ApJ 100, 279] published a map of the radio sky at 160 Mhz, showing several local maxima (including one in Cygnus constellation) other than the MW plane and the Sun1948 – 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] made the first optical identification of radio sources: Crab Nebulae (M1, TauA), M87 (VirA) and NGC 5128 (CenA).

11 cm (2.7 Ghz) all-sky map(extragalactic sources

brighter than 2 Jy)[Wall & Peacock MNRAS 216, 173]

Original radiotelescope Used by G. Reber

Brief History: radio sources

1953 – Jennison & Das Gupta [Nature 172, 996] discovered, by using radio interferometry, that CygA shows 2 equal components separated by 1.5'. After this proved to be very common among extragalactic radio sources

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 (vLOS = 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)

CygA

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 ~ 0.461960 – 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 quasars1962 – Hazard, Mackey & Shimmins [Nature 197, 1037], using lunar occultation of 3C273, located (to better than 1”) 2 components: a 13 mag star-like object and a jet pointing away from the “star”

3C 295

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 Hβ, Hγ, Hδ and Hε at z = 0.16, and also MgII 2798Å could be seen in the UV. J. Oke also found the Hα 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] reported the discovery of a large population of radio-quiet objects resembling quasars (identified by their UV excess), after known as “blue stellar objects” (BSO) or “quasi-stellar objects” (QSO), soon noted to be more common than the original quasars

Brief History: theoretical interpretations

1950 – Alfvén & Herlofson [Phys. Rev. 78, 616] proposed synchrotron process as the source of radio from “radio stars”

1964 – E. Salpeter [ApJ 140, 796] and Ya. Zeldovich [Dokl. Akad. Nauk. SSRS 155, 67] suggested the idea of quasars energy production from accretion onto a supermassive BH

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] measured z = 0.07 for the BL Lacertæ 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)

1980 – Heckman [A&A 87, 152] identified emission line galaxies with lower luminosity, only able to produce lines of low ionization elements, called LINERs

BL Lac

General properties of AGNs

Active Galactic Nuclei (AGNs) are luminous cores of galaxies (-9 < MB < -30, 1038 < LX < 1048 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 and UV) and longer (IR and radio) wavelengths than normal galaxies (“broad SED”)

strong emission lines (broader than the ones of SB galaxies) are also characteristic of AGN spectra

their engine must be physically small (less than a pc across) because their huge luminosity frequently change dramatically in less than a year (even in a instantaneous change, the observed brightness of an object of size a 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 Low Ionization Nuclear Emission-line Regions (capable of producing only low ionization element lines: [OI], [OII], [NII], [SII], etc) Originally defined by the ratios: [OII] 3227 / [OIII] 5007 1 and [OI] 6300 / [OIII] 5007 1/3 also: [NII] / Hα 0.6 and [OIII] / Hβ 3 relatively low luminosity AGNs ~ 80% of the nearby LINERs are S(B)a or S(B)b [S(B)c and E are less frequent] currently they are considered to represent the low luminosity tail of Sy phenomenon

M94

NGC 7814


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

may be of type: Sy 2 - present both permitted and forbidden lines broadened by Doppler velocities of the order of 500 km/s - 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 Sy 1 - 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)

NGC 3277NGC 5548


Seyfert Galaxies


Quasars Quasi-Stellar Radio Sources radio sources that in the optical are marked by an unresolved point source (brilliance of their nuclei completely swamps their stellar light) present cosmological (high) redshifts (the currently most distant quasars have z > 6) their spectra resembles the one of Sy 1, with the profile of the broader components sometimes strongly asymmetric MB < -22.3, LX > 1044 erg/s, U-B < 0.4

PKS 1117

Composite FIRST quasars


QSOs Quasi-Stellar Objects 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 than quasars on average mags fainter than quasars


BAL QSOs Broad Absorption Line QSOs show very broad blueshifted absorptions, associated with strong UV resonance lines


OVVs Optically Violently Variable quasars can vary in brightness by large factors on timescales of weeks are strong compact radio emitters radio and optical emissions are strongly polarized possess spectra similar to that of quasars are currently classified as blazars, together with BL Lac objects tend to lie at relatively high redshifts compared to BL Lacs

3C 345


BL Lac objects also strong compact radio sources (like OVVs) also unresolved optical point sources (like quasars) also rapidly variable (can vary in lum by an order of mag in less than

a month) present a smooth nonthermal power law continuum spectra almost devoided of spectral lines in either absorption or emission (continuum is so bright that hide emission lines!) linearly polarized (associated with large Faraday rotation)

3C 371

VLBI 0235+164


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: P1.4GHz ³1024.5 W/Hz)


Radio-galaxies


Radio-galaxies

AGN zoo

Galaxies

active “normal” (7%) (93%)

SB LINER AGN (85%) (15%) (0.5%)

radio-quiet → S? radio-loud → E? (99%) (1%)

Seyfert NELG QSO quasars blazar radio-galaxy (97.5%) (<1%) (2.5%)

(radio)Sy2 Sy1.5-1.9 Sy1 BAL OVV BL Lac FR I FRII(60%) (10%) (30%) (opt—UV)

NLRG BLRG

AGN spectra

AGN hosts

3C 273 [SDSS]

3C 273 - host3C 273 [HST]

LINERs – mostly S Seyferts – mostly S QSOs – some gE, others S (exponential profile)

(HST detected hosts on only 3/8 of the quasars – all observed seem to be hosted by gE observed QSOs and quasars) or interacting systems blazars – vast majority of BLLac appear to be hosted by E (but PKS 1413+135 is edge-on S) radio-gal – almost without exception E

radio-loud

radio-qu

iet

AGN hosts

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

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Astronomía Extragaláctica y Cosmología Observacional