Geodetic VLBI Lecture 3 18 October 2010

Lecture plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. Exercises 18 October 2010

Lecture plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. 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 (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 plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. Exercises 18 October 2010

Doppler 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” 18 October 2010

Cosmological red shift Red shift, V>0, z>0 Blue shift, V<0, z<0 18 October 2010

Calculation of redshift 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 18 October 2010

Cosmological red shift Minkovsky metric FLRW metric 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 Hubble law For local vicinity Distance – redshift 18 October 2010

“Distance – redshift” relation FLRW metric Hubble law 18 October 2010

“Distance – redshift” relation 18 October 2010

Lecture plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. 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 60 th 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

Geoscience Australia 18 October 2010 Instability of ICRF sources ( , in sky plane, )

Geoscience Australia 18 October 2010 Kellermann et al. (2004) Position angle of the brightest jet ~ 158º Geodetic 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  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 μ arcsec/year (predicted many authors; Bastian, 1995) Geoscience Australia 25 September 2009

4C September 2009 The longer period of time, the better proper motion

Lecture plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. 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 shift 3.…

Identification of quasars (radio/optics) … we need to be sure that the observed object is a quasar rather than a star on foreground

System Aladin Optic – radio Potential confusion with the close star Faint in optics ~23 mag Strong in radio: total flux is about Jy in S-,X-bands

Blue rays SuperCosmos (photographic plates)

SuperCosmos Red rays

Identification of quasars More problems nearby the Galaxy plane

Radio source Flux >1 Jy in S-,X-band A lot of observations made by VLBI But! Galactic latitude b=+2

VLBI image

Galactic latitude b=+2 This radio source looks very attractive in radio, but Galactic latitude b=+2

SuperCosmos Blue rays

NTT image of ? Several objects in the field SuperCosmos Blue rays (photographic plates) NTT image (CCD)

NTT image of Several objects in the field No one is a quasar! Galactic extinction is ~8 mag 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 Ly β

Lecture plan 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis 4. Super luminous relativistic jets 5. Practical issues 6. Exercises

Exercise 1 Calculation of redshift Answer???

Exercise 2 Distance to galaxy with redshift Z= H=60 km/sec·Mpc Answer??? 15 Mpc