Context :

Aims : We determine the effective temperature , surface gravity and projected rotational velocity of nine T dwarfs from the comparison of high-resolution near-infrared spectra and synthetic models , and estimate the mass and age of the objects from state-of-the-art models .

Methods : We use the AMES-COND cloudless solar metallicity models provided by the PHOENIX code to match the spectra of nine T-type field dwarfs observed with the near-infrared high-resolution spectrograph NIRSPEC using ten echelle orders to cover part of the J band from 1.165 to 1.323 \mu m with a resolving power R \sim 20,000 .
The projected rotational velocity , effective temperature and surface gravity of the objects are determined based on the minimum root mean square of the differences between the modelled and observed relative fluxes .
Estimates of the mass and age of the objects are obtained from effective temperature-surface gravity diagrams , where our results are compared with existing solar metallicity models .

Results : The modelled spectra reproduce quite well the observed features for most of the T dwarfs , with effective temperatures in the range of 922-1009 K , and surface gravities between 10 ^ { 4.3 } and 10 ^ { 5.0 } cms ^ { -2 } .
Our results support the assumption of a dust free atmosphere for T dwarfs later than T5 , where dust grains form and then gravitationally sediment into the low atmosphere .
The modelled spectra do not accurately mimic some individual very strong lines like the K i doublet at 1.2436 and 1.2525 \mu m. Our modelled spectra does not match well the observed spectra of the two T dwarfs with earlier spectral types , namely SDSSp J125453.90-012247.4 ( T2 ) and 2MASS J05591914-1404488 ( T4.5 ) , which is likely due to the presence of condensate clouds that are not incorporated in the models used here .
By comparing our results and their uncertainties to evolutionary models , we estimate masses in the interval \approx 5–75 M _ { J } for T dwarfs later than T5 , which are in good agreement with those found in the literature .
We found apparent young ages that are typically between 0.1 and a few Gyr for the same T dwarfs , which is consistent with recent kinematical studies .

Conclusions :