Context : Very long baseline interferometry ( VLBI ) observations at 86 GHz ( wavelength , \lambda = 3 mm ) reach a resolution of about 50 \mu as , probing the collimation and acceleration regions of relativistic outflows in active galactic nuclei ( AGN ) .
The physical conditions in these regions can be studied by performing 86 GHz VLBI surveys of representative samples of compact extragalactic radio sources .

Aims : To extend the statistical studies of compact extragalactic jets , a large global 86 GHz VLBI survey of 162 compact radio sources was conducted in 2010–2011 using the Global Millimeter VLBI Array ( GMVA ) .

Methods : The survey observations were made in a snapshot mode , with up to five scans per target spread over a range of hour angles in order to optimize the visibility coverage .
The survey data attained a typical baseline sensitivity of 0.1 Jy and a typical image sensitivity of 5 mJy/beam , providing successful detections and images for all of the survey targets .
For 138 objects , the survey provides the first ever VLBI images made at 86 GHz .
Gaussian model fitting of the visibility data was applied to represent the structure of the observed sources and to estimate the flux densities and sizes of distinct emitting regions ( components ) in their jets .
These estimates were used for calculating the brightness temperature ( T _ { \mathrm { b } } ) at the jet base ( core ) and in one or more moving regions ( jet components ) downstream from the core .
These model-fit-based estimates of T _ { \mathrm { b } } were compared to the estimates of brightness temperature limits made directly from the visibility data , demonstrating a good agreement between the two methods .

Results : The apparent brightness temperature estimates for the jet cores in our sample range from 2.5 \times 10 ^ { 9 } K to 1.3 \times 10 ^ { 12 } K , with the mean value of 1.8 \times 10 ^ { 11 } K. The apparent brightness temperature estimates for the inner jet components in our sample range from 7.0 \times 10 ^ { 7 } K to 4.0 \times 10 ^ { 11 } K. A simple population model with a single intrinsic value of brightness temperature , T _ { \mathrm { 0 } } , is applied to reproduce the observed distribution .
It yields T _ { \mathrm { 0 } } = ( 3.77 ^ { +0.10 } _ { -0.14 } ) \times 10 ^ { 11 } K for the jet cores , implying that the inverse Compton losses dominate the emission .
In the nearest jet components , T _ { \mathrm { 0 } } = ( 1.42 ^ { +0.16 } _ { -0.19 } ) \times 10 ^ { 11 } K is found , which is slightly higher than the equipartition limit of \sim 5 \times 10 ^ { 10 } K expected for these jet regions .
For objects with sufficient structural detail detected , the adiabatic energy losses are shown to dominate the observed changes of brightness temperature along the jet .

Conclusions :