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Geodetic VLBI

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. 18 October 2010. Lecture plan. 1. Quasars as astrophysical objects 2. Redshift 3. Spectral analysis

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Geodetic VLBI

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  1. Geodetic VLBI Lecture 3 18 October 2010

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

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

  4. 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

  5. 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

  6. Quasars (definition) Quasar – a very energetic and distant galaxy with an active galactic nucleus; Quasar – the nucleus of the host galaxy 18 October 2010

  7. Quasar 18 October 2010

  8. 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

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

  10. 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

  11. 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

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

  13. Calculation of redshift 18 October 2010

  14. The Expansion of the Universe • Distances between galaxies are increasing uniformly. • There is no need for a center of the universe. 18 October 2010

  15. The Expansion of the Universe Friedman-Lemaitre-Robertson-Walker (FLRW) metric a(t) – expansion parameter 18 October 2010

  16. Cosmological red shift Minkovsky metric FLRW metric 18 October 2010

  17. 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

  18. “Distance – redshift” relation Minkovsky metric Hubble law For local vicinity Distance – redshift 18 October 2010

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

  20. “Distance – redshift” relation 18 October 2010

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

  22. 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

  23. Super luminous relativistic jets The jets were found at the late 60th 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 18 October 2010

  24. ICRF source instability (structure) Quasar 2201+315 Geoscience Australia 18 October 2010

  25. Instability of ICRF sources( 2201+315, in sky plane, 2001-2004) Geoscience Australia 18 October 2010

  26. Instability of ICRF sources( 2201+315, in sky plane, 2001-2004) Kellermann et al. (2004) Position angle of the brightest jet ~ 158º Geodetic VLBI: Position angle ~ 148º apparent proper motion ~ 0.6 mas/year Geoscience Australia 18 October 2010

  27. 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

  28. 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

  29. 4C39.25 The longer period of time, the better proper motion 25 September 2009

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

  31. Identification of quasars(radio/optics) • It is very important for many reasons • To tie radio and optical reference frames • To measure red shift • …

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

  33. 2318-087 System Aladin Optic – 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

  34. SuperCosmos (photographic plates) Blue rays 2318-087 2318-087

  35. Identification of quasars More problems nearby the Galaxy plane

  36. Radio source 1923+210 Flux >1 Jy in S-,X-bandA lot of observations made by VLBIBut!Galactic latitude b=+2

  37. 1923+210 - VLBI image

  38. 1923+210 This radio source looks very attractive in radio, butGalactic latitude b=+2

  39. SuperCosmos Blue rays 1923+210

  40. NTT image of 1923+210 SuperCosmos Blue rays (photographic plates) NTT image (CCD) 1923+210 ? Several objects in the field

  41. NTT image of 1923+210 Several objects in the field We measured 3 spectra No one is a quasar! Galactic extinction is ~8 mag 1923+210 is not visible in optics!

  42. Quasar spectra Z=1.55 No Ly

  43. Quasar spectra Z=2.51 Ly

  44. Quasar spectra Z=3.16 Ly Very faint object Lydoes not dominates

  45. Quasar spectra Z=3.38 Ly Faint object but Lydominates

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