Transcript Astrofisica - Istituto di Radioastronomia

Gabriele Giovannini
[email protected]
051 6399415 c/o IRA - INAF
051 2095716 via Ranzani 1 - DIFA
II piano – ex Dip.to Astronomia
Ricevimento: Lunedi e Martedi 12 - 13
Appuntamento tramite posta elettronica
Esami: argomento a scelta
date: possibili accordi – appelli circa mensili
Outline del corso di Astrofisica:
Basi Generali di Evoluzione Stellare:
proprieta’ osservative
diagramma H-R
oggetti colassati
PULSAR e Supernovae
Radiazione di Sincrotrone (cenni
Galassie a Spirale
Massa Oscura
Misure di massa di galassie Ellittiche ed Ammassi
Universo in espansione – legge di Hubble
Cosmologia Moderna ed il Big Bang (cenni)
Possibili testi:
Observational Astrophysics – Smith
Introduction to Stellar Astrophysics – Bohm Vithense
Stellar Structure and Evolution
Astrofisica – Gratton vecchio
Introduction to Astrophysics – Carrol and Ostlie
Dispense di Radioastronomia – Fanti vecchio, nuova versione?
Astrofisca Stellare – Castellani
Dalle Stelle all’Universo Lezioni di Astrofisica - Braccesi
Stelle, galassie e universo – fondamenti di astrofisica A.Ferrari
Energy= 1.69x10^-6 eV
Frequency= 408x10^6 Hz
(408MHz) Wavelength= 73.5 cm
Energy= 5.18x10^-3 eV
Frequency= 1.25x10^12 Hz
Wavelength= 2.40x10^-2 cm (240
microns)
Energy= 2.5 eV Frequency=
6.0x10^14 Hz Wavelength=
5.0x10^-5 cm(5000 Angstroms)
Energy= 2keV 10keV Frequency=
5x10^17 Hz 2.5x10^18 Hz
Wavelength=
6.2x10^-8 cm 1.2x10^-8 cm (6.2 1.2 angstroms)
Energy= > 100MeV
Frequency= >
2.5x10^22 Hz
Wavelength= < 1.2
x 10^-12 cm ( <
0.00012 angstroms
)
Stelle: emettono onde e.m.
Sole: Massa 1.989 10^33 g
Raggio: 6.960 10^10 cm
Luminosita’ integrata su tutto lo spettro (bolometrica):
3.90 x 10^33 erg/s
Temperatura superficiale 5800 gradi K
Eta’ > 4.5 x 10^9 yr
Se perdita di energia costante: 5.5 x 10^50 erg
E= mc^2  6.1 x 10^29 g circa 0.1%
 Massa costante
Essendo angolo piccolo: p = U.A./D
Angolo piccolo: p =a/r a=UA=1.4960 10^13 cm
P” = 206265a/r
R= 3.0857 10^18 cm/p
P=1”  r = 1pc = 3.0857 10^18 cm = 3.26 YR luce
1yr luce = 9.4606 10^15 cm
Alpha centauri = 0.76” = 1.32 pc
Altro problema: coordinate: come individuare oggetti su
Sfera celeste:
Due sono i metodi maggiormente usati:
Azimut ed Altezza (o elevazione)
Comodo per singolo sito, difficilmente esportabile
Il piu’ usato si basa su Ascensione retta e Declinazione ed e’ simile
A queela usato sulla terra (latitudine e longitudine)
RA in
Dec
hms
o‘“
Oggetto a 10h 50m 30s +45 30 00
E’ sullo zenith a 10h 50m 30s ora siderale
Giorno siderale e’ + corta di 4m/day di giorno solare
Ora siderale = ora solare il 21/09
21/03 = RA = 0
21/06
6h
21/09
12
21/12
18
Dec = 0 (il sole)
Dec = + 23 27
0
-23 27
Precessione:
B1950
J2000
Radio galaxies of high and low power have quite different morphologies
on the large scale (Fanaroff & Riley 1974)
FR II : High power: P1.4 GHz > 1024.5 W Hz-1
CLASSICAL DOUBLES
EDGE BRIGHTNED : Radio core, asymmetric collimated jets, hot-spots
Cyg A
3C 109
3C 219
FR I : Low power: P1.4 GHz < 1024.5 W Hz-1
EDGE DARKENED : Radio core, symmetric jets with opening angles  10-15o,
low brightness lobe
3C 296
3C 449
3C 31
QUASAR
Proprieta’:
-- Starlike identificati con sorgenti radio
-- Continuo variabile
-- eccesso UV
-- Broad Lines
-- Alto z
-- Emissione X
-- continuo  spettro non termico
Da colore metodo per identificare quasar  scoperta radio quieti
Colore cambia con redshift
HST immagine di 3C273 – galassia attorno a QSS ben visibile con struttura ottica
Quasar radio quieti, simili a QSS ma no o bassa potenza radio
Distribuzione continua?
Rapporto radio-ottico usando emissione radio a 5 GHz
ed emissione ottica a 4400 Amstrong
Rr-o = 10--100 radio loud
= 0.1--1 radio quiet
BAL = QSO con BLR in assorbimento
3 – Curve di rotazione
NGC 4258 curve di rotazione water maser
L’emissione Maser si estende da 0.16 a 0.28 pc
Mbh = 3.6 107 M● (Myoshi et al. 1995 Nature 373, 127)
Moto delle stelle al centro della nostra galassia (near IR)
La stella con orbita piu’ stretta si avvicina a 130 AU
Posizione BH coincide con radio ed X-ray sorgente, variabile
Mbh ≈ 3 x 106 M●
Se misuriamo velocita’ stelle vicino a sfera di infuenza BH ci
aspettiamo che la loro velocita’ aumenti a causa del BH
Se Mbh = 108 M● la sfera di influenza e’ 11pc = 0.14” per Virgo
Se mettiamo 3 x 106 M● in un raggio < 130 AU abbiamo un tempo di
collisione tra stelle di circa 10 anni per cui non puo’ essere stabile
Centaurus a – NGC 5128
EVN
Very Long Baseline Interferometry : VLBI
V
L
B
A
Spatial VLBI
1144+35
3C 264
VLBI studies of radio galaxy nuclei :
one of the most important results is the
detection of proper superluminal motion
Expansion of about
6 pc in 3.5 years:
 velocity  6c
QUASAR
1642+690
z = 0.75
The southernmost feature is moving at about 9c (Venturi et al. 1997)
QUASAR
1928+738
z = 0.302
Aug 97
Sep 01
Observation performed with the space VLBI at 5 GHz
(Murphy et al. 2003)
SUPERLUMINAL MOTION
By the time that light leaves from position
(2), light emitted from position (1) will have
travelled a distance AC
The difference in arrival time for the
observer is :
AC  AB ct  vtcos 
t(OBS) 

c
c
The apparent velocity as seen by the
observer is
BD
vtsin
vsin
v(OBS) 


t(OBS) t(OBS) 1 - v cos
c
 sin 
app 
1   cos
For example :  = 10o and v = 0.999c
then : v(OBS) = 10.7 c
The detection of superluminal motions and
of one-sided jets in the majority of both
low power and high power radio galaxies
indicates that the jets at their basis are
all strongly relativistic
Effetto Doppler e boosting relativistico
Se una sorgente si muove con v = βc in una direzione che forma
angolo θ con la linea di vista abbiamo
o = e/((1-βcosθo)) = e D
Dove  e’ il fattore di Lorentz e
D = 1/((1-βcosθo)) e’ il Doppler factor (velocita’ positiva in
avvicinamento D > 1 quando β > 0 e o > e
Se velocita’ bassa  ≈ 1 e D  (1 + β cosθo) Doppler classico
Consideriamo sorgente con Luminosita’ totale Le e luminosita’
monocromatica L(e)
La potenza irradiata in banda e sara’ ricevuta in banda
o = e D
Consideriamo come varia luminosita’ – essendo radiazione per unita’
di tempo teniamo conto
trasformazione energia fotoni
o = e x D
Trasformazione dei tempi
dto = dte - dte  v cosθ/c = dte(1 – β cosθ) = dte/D
sorgente si e’ avvicinata tra tempo emissione 2 fotoni
La radiazione ricevuta in superficie unitaria compresa in cono angolo
solido do che sara’ diverso da de
do = de/D2
si ottiene da aberrazione relativistica ricordando che do ≈ π dθo2
In conclusione
Lo = Le x D4
Boosting relativistico o Doppler boosting o relativistic beaming
Se lavoriamo con luminosita’ monocromatiche
Lo(o)do = Le(e)de x D4
da cui
Lo(o) = Le(e) x D3
Se lo spettro e’ di sincrotrone L()  - possiamo scrivere
Lo(o) = Le(e) x D3+ = Le(o) x D4 D-(1-)
Il termine D-(1-) e’ noto come correzione K
JET RELATIVISTIC EFFECTS (DOPPLER BOOSTING) :
Doppler factor
Jet pointing toward the observer is AMPLIFIED
From the ratio between the approaching and the receding jet,
the jet velocity and orientation can be constrained
JET SIDEDNESS RATIO
Ma se parliamo di getti o plasmoidi quasi continui si parla di
brillanza: la lunghezza della struttura nella direzione
del moto e’ influenzato da D ma lo spessore della struttura no
(moto unidimensionale) ne segue che:
Jet sidedness
Se  = 5 (β = 0.98) e  = 0.7 e θ = 0 risulta Ba/Br = R = 2 x 104
Ne consegue che dati 2 getti intrinsecamente uguali vedo solo
quello che si muove verso di me e non l’altro
From the jet to cj brightness ratio R we derive:
 1   cos  

R  
 1   cos  
2 
Main problem: low luminosity radio jets do not give strong
constraints: in 3C264 the highest j/cj ratio is > 37
corresponding to θ < 52o and β > 0.62
What’s all this Unification?
• Historically it is attempt to explain as much
as the spread of observational properties
as possible in terms of orientation effects.
– Assume some axis; i.e. rotation
• More generally, it is an attempt to explain
the diversity of observational properties in
terms of a simple model
The AGN Paradigm
Introduction
• AGN are not spherically symmetric and thus
what you see depends on from where you view
them. This is the basis of most unification
models.
• It was the discovery of superluminal motion and
the interpretation in terms of bulk relativistic
motion of the emitter that first made people
realize that orientation in AGN was important.
• I will outline the consequences of Doppler
boosting, describe the historical development of
schemes and then review the modern evidence.
– N.B. Relativistic beaming is not the only mechanism
that can make AGN emission anisotropic
Doppler boosting
• When an emitting body is moving
relativistically the radiation received by an
observer is a very strong function of the angle
between the line of sight and the direction of
motion.
sobs  sem ( 2  )
– The Doppler effect changes the energy and
frequency of arrival of the photons.
– Relativistic aberration changes the angular
distribution of the radiation.
Parent populations
• To every beamed source there will be
many unbeamed sources – the parent
population.
• How to identify the parent population?
– Look at some emission that’s isotropic; e.g.
radio lobe emission, far infrared emission,
narrow-line emission, etc in the beamed
population and look for another population
having the same luminosity function for the
isotropic emission.
History of Unification
• Rowan-Robinson (1976, ApJ, 213,635) tried to
unify Seyfert galaxies and radio sources.
– Mostly wrong – no beaming
– But the importance of dust and IR emission correct.
• Blandford and Rees (Pittsburgh BL Lac meeting
1978) laid the foundations for beaming
unification. (Radio loud only).
History continued
• Scheuer and Readhead (1979,
Nature,277,182) proposed that radio coredominated quasars and radio quiet quasars
could be unified – the former being beamed
versions of the latter.
• Orr and Browne (1982,MNRAS,200,1067 )
realized the the Scheuer and Readhead
scheme could not work because MERLIN and
VLA had shown that most of the coredominated quasars had extended (isotropic)
radio emission and thus their parent
population could not be radio quiet. We
looked for a non-radio quiet parent population
– Proposed core-dominated/lobe-dominated
unification for quasars
Radio Galaxy/Quasar
Unification
(Both are FR2s)
• Widely discussed before, but first published by
Barthel (1989, ApJ, 336,606) – an extension of coredominated/lobe-dominated quasar unification.
• Quasars have strong continuum and broad lines and
radio galaxies (FR2s) have little continuum (other than
starlight) and no broad lines.
• How could they be the same thing? Only if one could
hide the quasar nucleus with something optically thick
(a molecular torus).
– N.B. In a parallel line of development Antonucci and Miller
had discovered polarized broad lines in the Seyfert 2
NGC1068 which they interpreted as being scattered nuclear
radiation from a hidden BLR.
The AGN Paradigm
BL Lacs and FR1 RGs
• Similar arguments apply to these intrinsically
lower luminosity objects; BL Lacs are the
beamed cores of FR1 RGs. (Note FR1 RGs
generally have only weak and narrow emission
lines and BLLacs are almost lineless.)
•
•
•
•
Blandford and Rees (1978)
Browne (1983, MNRAS,204,23)
Antonucci and Ulvestad (1985,ApJ,294,158)
Padovani and Urry (1991, ApJ,368,373)
Evidence for BL Lac/FR1
unification
• The statistics look ok (Browne; Padovani and
Urry) for reasonable Lorentz factors
• The required relativistic jets are seen in a few
FR1s, most notably in M87 (Biretta AJ,520,621).
• The strength of optical cores in FR1s seems to
correlate with the strength of the radio core
consistent with both being beamed (Capetti
&Celotti,1999,MNRAS,303,434, Chiaberge et al.
2000,A&A,358,104)
=> No hidden BLR in FR1s (but BL Lac has a broad
line)
HST Image of jet in M87
• M87 is and FR1 radio
galaxy
• Superluminal motion
has been detected in
both radio and optical
Evidence for superluminal
motion in M87
Radio map of 3C175