Geodetic VLBI
Lecture 3Lecture 3
18 October 2010
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis4. Super luminous relativistic jets5. Practical issues6. Exercises
18 October 2010
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis4. Super luminous relativistic jets5. Practical issues6. Exercises
18 October 2010
Quasars
We use quasars for geodetic and astrometric research, but it is necessary to remember that the quasars are large and distant astrophysical objects. We should learn all their properties.
18 October 2010
Quasars (definition)
A quasi-stellar radio source ("quasar") is a very energetic and distant galaxy with an active galactic nucleus (AGN). They are the most luminous objects in the universe.
18 October 2010
Quasars (definition)
Quasar – a very energetic and distant galaxy with an active galactic nucleus;
Quasar – the nucleus of the host galaxy
18 October 2010
Quasar
18 October 2010
Active Galactic Nuclei Active Galactic Nuclei (AGN)(AGN)It’s likely that the core of an AGN contains a supermassive black hole surrounded by an accretion disk. As matter spirals in the black hole, electro-magnetic radiation and plasma jets spew outward from the poles.
Active galactic nuclei are a category of exotic objects that includes: luminous quasars, Seyfert galaxies, and blazars.
18 October 2010
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis4. Super luminous relativistic
jets5. Practical issues6. Exercises
18 October 2010
Doppler effectDoppler effect
Frequency decreases if the body moves out of the observer.Wavelength increases
Frequency increases if the body moves towards the observer.Wavelength decreases.
18 October 2010
Red shift
Frequency increases if the body moves towards the observer.
Wavelength decreases.
All spectral lines shift to the red part of spectrum. So, we observe “red shift”
emit obs
18 October 2010
Cosmological red shift
Red shift, V>0, z>0
Blue shift, V<0, z<0
c
Vz
emit obs
18 October 2010
Calculation of redshift
emit
emitobsz
emit obs
18 October 2010
The Expansion of the Universe
•Distances between galaxies are increasing uniformly.
•There is no need for a center of the universe.
18 October 2010
The Expansion of the Universe
Friedman-Lemaitre-Robertson-Walker (FLRW) metric
a(t) – expansion parameter
)]sin()[( 222222222 ddrdrtadtcds18 October 2010
Cosmological red shift
Minkovsky metricc
Vz
then
now
a
az 1
FLRW metric
nowa
thena
18 October 2010
Hubble’s law: v = HR where H is called Hubble’s constant.
Hubble’s Law
Hubble’s constant is related to a scale factor a that’s proportional to the distance between galaxies:
Hubble also found a linear relation between distance and recession velocity!
18 October 2010
Hubble’s measurements
Hubble also measured spectra of standard candles, observing that most were red-shifted.
He realized that this was a Doppler shift.
The universe is expanding!
18 October 2010
“Distance – redshift” relation
Minkovsky metric
c
Vz
Hubble law
RHVcz
RHV
For local vicinity
H
czR Distance – redshift 1z
18 October 2010
“Distance – redshift” relation
FLRW metric
Hubble law
RHV
)]sin()[( 222222222 ddrdrtadtcds
18 October 2010
“Distance – redshift” relation
z
km zzzzz
dz
H
cR
022 )2()1()1)(1(
18 October 2010
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis
4. Super luminous relativistic jets
5. Practical issues6. Exercises
18 October 2010
Super luminous relativistic jets
It’s likely that the core of an AGN contains a supermassive black hole surrounded by an accretion disk. As matter spirals in the black hole, electro-magnetic radiation and plasma jets spew outward from the poles.
18 October 2010
Super luminous relativistic jets
The jets were found at the late 60th
18 October 2010
They cause apparent motion of quasars, or “fake” proper motion
For decades this “fake” proper motion was considered as the only kind of the proper motion detectable by observations
ICRF source instability (structure)
Geoscience Australia
18 October 2010
Quasar 2201+315
Variations of the 2201+315, RA
Year
2000 2001 2002 2003 2004 2005 2006
as
-2000
-1500
-1000
-500
0
500
1000
1500
Geoscience Australia
18 October 2010
Variations of the 2201+315, DEC
Year
2000 2001 2002 2003 2004 2005 2006
as
-2000
-1500
-1000
-500
0
500
1000
1500
Instability of ICRF sources ( 2201+315, in sky plane, 2001-2004)
Instability of ICRF sources ( 2201+315, in sky plane, 2001-2004)
as
-1000-50005001000
as
-1000
-500
0
500
1000
Daily dataApproximation
Geoscience Australia
18 October 2010
Kellermann et al. (2004)
Position angle of the brightest jet ~ 158ºGeodetic VLBI:
Position angle ~ 148º apparent proper motion ~ 0.6 mas/year
Apparent proper motions
• Motion of radio source jets mimic physical proper motions;
• Such fake motions can reach 100-1000 as/year;
• Expected systematic <50 as/year;
• We could discover systematics through the irregular
apparent proper motions, for instance, using the
expansion on spherical functions
18 October 2009
Search for systematic has been done (Gwinn, Eubanks et al. 1997; MacMillan 2005)
Motivation – detection of the secular aberration drift – 4-5 μarcsec/year (predicted many authors; Bastian, 1995)
Geoscience Australia
25 September 2009
4C39.25
25 September 2009
Right ascension, 4C39.25
Year
1990 1995 2000 2005 2010
sec
3.01380
3.01385
3.01390
3.01395
3.01400
3.01405 The longer period of time,
the better proper motion
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis4. Super luminous relativistic jets
5. Practical issues6. Exercises
Identification of quasars(radio/optics)
It is very important for many reasons
1.To tie radio and optical reference frames
2.To measure red shift3.…
Identification of quasars(radio/optics)
… we need to be sure that the observed object is a quasar rather than a star on foreground
2318-087
SystemAladinOptic – radio
Potential confusion with the close star
2318-087
Faint in optics~23 mag
Strong in radio: total flux is about 0.2-0.3 Jy in S-,X-bands
Blue rays2318-087
2318-087
SuperCosmos (photographic plates)
SuperCosmosRed rays2318-087
Identification of quasars
More problems nearby the Galaxy plane
Radio source 1923+210
Flux >1 Jy in S-,X-bandA lot of observations made by
VLBI
But!Galactic latitude
b=+2
1923+210 - VLBI image
1923+210
This radio source looks very attractive in radio, but
Galactic latitude Galactic latitude b=+2b=+2
SuperCosmosBlue rays1923+210
NTT image of 1923+210
1923+210 ?Several objects in the field
SuperCosmos Blue rays (photographic plates)
NTT image (CCD)
NTT image of 1923+210
Several objects in the field
No one is a quasar!
Galactic extinction is ~8 mag
1923+210 is not visible in optics!
We measured 3 spectra
Quasar spectra
Z=1.55
No Ly
Quasar spectra
Z=2.51
Ly
Quasar spectra
Z=3.16
Ly
Very faint object
Ly does not dominates
Quasar spectra
Z=3.38
Ly
Faint object but
Ly dominates
Break after Lyβ
Lecture planLecture plan
1. Quasars as astrophysical objects
2. Redshift3. Spectral analysis4. Super luminous relativistic jets5. Practical issues
6. Exercises
Exercise 1
Calculation of redshift
Answer???
z
1861emit
7444obs
Exercise 2
Distance to galaxy with redshiftZ=0.0030
H=60 km/sec·Mpc
Answer???
15 Mpc
tVtV
D