A Global 86 GHz VLBI Survey of Compact Radio Sources

Sang-Sung LeeMPIfR

In collaboration withA.P. Lobanov, T.P. Krichbaum, A. Witzel, J.A. Zensus (MPIfR, Bonn)

M. Bremer, A. Greve, M. Grewing (IRAM, Grenoble)

26.09.20068th EVN Symposium, Torun, Poland

Outline

Introduction - mm VLBI, Previous Surveys

Results - Images

Brightness temperature (TB) and jet physics

- TB distribution, TB vs. Apparent jet speed, TB along the jets

Summary

Millimeter VLBIIntroduction Results Tb and Jet physics Summary

1. VLBI experiments at mm wavelengths (e.g. 43GHz, 86GHz, 150GHz, 230GHz)

2. A unique tool for exploring the physics of compact radio sources with about 6 times better resolution (40 micro-arcsec at 86 GHz) than space-VLBI at 6 cm wavelength

3. At mm wavelengths, synchrotron radiation becomes optically thin, so mm-VLBI makes it possible to look deeper in the “VLBI core”, invisible at cm wavelengths

1983

First VLBI fringe

detection at 89GHz

Readhead et al. 1983

1995

CMVA (86GHz)

(The Coordinated MM VLBI Array)

2004

GMVA (86 GHz)

(The Global MM-VLBI Array)

present

Haystack + (Ef, On, Pv, Pb, Mh) + VLBA ( 8x25m)

VLBA (8x25m) + (Ef, On,Pv,Pb,Mh)

GMVA web - http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm/

Previous surveysIntroduction Results Tb and Jet physics Summary

VLBI Surveys at 86 GHz

0

20

40

60

80

100

120

140

Numberof

sources

1 2 3 4 5

Surveys

Comparison of VLBI surveys at 86 GHz

ObservedDetectedImaged

1. Beasley et al. (1996)

2. Lonsdale et al. (1998)

3. Rantakyro et al. (1998)

4. Lobanov et al. (2000)

5. This survey

- 3~4 times better sensitivity

- larger sample (127sources)

taken from surveys at lower freq.

- 121(95%) were detected and 109 imaged

This Survey

ImagesIntroduction Results Tb and Jet physics Summary

Lee et al. 2006 in prep

Brightness Temperature (TB)Introduction Results Tb and Jet physics Summary

And if , then the lower limit of TB is obtained with d = dmin.

(e.g. SNR = 6.5; Beam ( a x b ) = ( 0.1 x 0.07 mas) => dmin = 0.035mas)

2

2tot

ΒΒ

z)(1λS

k

π2log(2)Τ

d

(A.P. Lobanov 2005)

TB distributionIntroduction Results Tb and Jet physics Summary

(Lobanov et al. 2000)

limit)ion Equipartit(~

105

limit)compton Inverse(~

104~1

10int,

11int,

KT

KT

jet

core

VLBI cores Jet components

(Lee et al. 2006, in prep.)

VLBI cores Jet components

TB vs. Apparent jet speedIntroduction Results Tb and Jet physics Summary

TB,core vs. Jet speed (N=86)

Apparent Jet speeds from 2cm survey (Kellermann et al. 1998)

TB,jet vs. Jet speed (N=39)

Red triangles are lower limits of TB

Evolution of TB along the jetsIntroduction Results Tb and Jet physics Summary

NRAO 140

3C 454.3OJ 287

NRAO 190

Red circles are the predicted TB in shocks with adiabatic losses dominating the radio emission. Blue circles are the observed TB. (Lee et al. 2006 in prep.)

Assumptions are made like the following:

(Lobanov et al. 2000)

SummaryIntroduction Results Tb and Jet physics Summary

1. We conducted a large global 86 GHz VLBI survey of compact radio sources, using a global 3mm VLBI array.

2. The survey is the largest and most sensitive one (rmsImage< 10 mJy/beam)

3. It provides a detection rate of 95% out of 127 sources and a total set of images of 109 sources.

4. We estimated brightness temperatures (TB) of the cores and secondary jet components from the measurements of flux densities and sizes of the components, taking into account resolution limits of the data.

5. The TB of the cores are higher than those of the secondary jet components and seem to be correlated with apparent jet speeds rather than those of the secondary jet components.