We present the rest-frame Js-band and Ks-band luminosity function ( LF ) of a sample of about 300 galaxies selected in the HDF-S at Ks \leq 23 ( Vega ) .
We use calibrated photometric redshift together with spectroscopic redshift for 25 % of the sample .
The accuracy reached in the photometric redshift estimate is 0.06 ( rms ) and the fraction of outliers is 1 % .
We find that the rest-frame Js-band luminosities obtained by extrapolating the observed Js-band photometry are consistent with those obtained by extrapolating the photometry in the redder H and Ks bands closer to the rest-frame Js , at least up to z \sim 2 .
Moreover , we find no significant differences among the luminosities obtained with different spectral libraries .
Thus , our LF estimate is not dependent either on the extrapolation made on the best-fitting template or on the library of models used to fit the photometry .
The selected sample has allowed to probe the evolution of the LF in the three redshift bins [ 0 ; 0.8 ) , [ 0.8 ; 1.9 ) and [ 1.9 ; 4 ) centered at the median redshift z _ { m } \simeq [ 0.6 , 1.2 , 3 ] and to probe the LF at z _ { m } \simeq 0.6 down to the unprecedented faint luminosities M _ { Js } \simeq - 13 and M _ { Ks } \simeq - 14 .
We find hints of a raise of the faint end ( M _ { Js } > -17 and M _ { Ks } > -18 ) near-IR LF at z _ { m } \sim 0.6 , raise which can not be probed at higher redshift with our sample .
The values of \alpha we estimate are consistent with the local value and do not show any trend with redshift .
We do not see evidence of evolution from z = 0 to z _ { m } \sim 0.6 suggesting that the population of local bright galaxies was already formed at z < 0.8 .
On the contrary , we clearly detect an evolution of the LF to z _ { m } \sim 1.2 characterized by a brightening of M ^ { * } and by a decline of \phi ^ { * } .
To z _ { m } \sim 1.2 M ^ { * } brightens by about 0.4-0.6 mag and \phi ^ { * } decreases by a factor 2-3 .
This trend persists , even if at a less extent , down to z _ { m } \sim 3 both in the Js-band and in the Ks-band LF .
The decline of the number density of bright galaxies seen at z > 0.8 suggests that a significant fraction of them increases their stellar mass at 1 < z < 2 - 3 and that they underwent a strong evolution in this redshift range .
On the other hand , this implies also that a significant fraction of local bright/massive galaxies was already in place at z > 3 .
Thus , our results suggest that the assembly of massive galaxies is spread over a large redshift range and that the increase of their stellar mass has been very efficient also at very high redshift at least for a fraction of them .