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