Context :

Aims : The aim of this work is twofold : first , to assess whether the population of elliptical galaxies in cluster at z \sim 1.3 differs from the population in the field and whether their intrinsic structure depends on the environment where they belong ; second , to constrain their properties 9 Gyr back in time through the study of their scaling relations .

Methods : We compared a sample of 56 cluster elliptical galaxies selected from three clusters at 1.2 < z < 1.4 with elliptical galaxies selected at comparable redshift in the GOODS-South field ( \sim 30 ) , in the COSMOS area ( \sim 180 ) , and in the CANDELS fields ( \sim 220 ) .
To single out the environmental effects , we selected cluster and field elliptical galaxies according to their morphology .
We compared physical and structural parameters of galaxies in the two environments and we derived the relationships between effective radius , surface brightness , stellar mass , and stellar mass density \Sigma _ { R _ { e } } within the effective radius and central mass density \Sigma _ { 1 kpc } , within 1 kpc radius .

Results : We find that the structure and the properties of cluster elliptical galaxies do not differ from those in the field : they are characterized by the same structural parameters at fixed mass and they follow the same scaling relations .
On the other hand , the population of field elliptical galaxies at z \sim 1.3 shows a significant lack of massive ( \mathcal { M } _ { * } > 2 \times 10 ^ { 11 } M _ { \odot } ) and large ( R _ { e } > 4 - 5 kpc ) elliptical galaxies with respect to the cluster .
Nonetheless , at \mathcal { M } _ { * } < 2 \times 10 ^ { 11 } M _ { \odot } , the two populations are similar .
The size-mass relation of cluster and field ellipticals at z \sim 1.3 clearly defines two different regimes , above and below a transition mass m _ { t } \simeq 2 - 3 \times 10 ^ { 10 } M _ { \odot } : at lower masses the relation is nearly flat ( R _ { e } \propto \mathcal { M } _ { * } ^ { -0.1 \pm 0.2 } ) , the mean radius is nearly constant at \sim 1 kpc and , consequenly , \Sigma _ { R _ { e } } \simeq \Sigma _ { 1 kpc } while , at larger masses , the relation is R _ { e } \propto \mathcal { M } _ { * } ^ { 0.64 \pm 0.09 } .
The transition mass marks the mass at which galaxies reach the maximum stellar mass density .
Also the \Sigma _ { 1 kpc } -mass relation follows two different regimes , above and below the transition mass ( \Sigma _ { 1 kpc } \propto { \mathcal { M } _ { * } } ^ { 0.64 > m _ { t } } _ { 1.07 < m _ { t } } ) defining a transition mass density \Sigma _ { 1 kpc } \simeq 2 - 3 \times 10 ^ { 3 } M _ { \odot } pc ^ { -2 } .
The effective stellar mass density \Sigma _ { R _ { e } } does not correlate with mass ; dense/compact galaxies can be assembled over a wide mass regime , independently of the environment .
The central stellar mass density , \Sigma _ { 1 kpc } , besides being correlated with the mass , is correlated to the age of the stellar population : the higher the central stellar mass density , the higher the mass , the older the age of the stellar population .

Conclusions : While we found some evidence of environmental effects on the elliptical galaxies as a population , we did not find differences between the intrinsic properties of cluster and field elliptical galaxies at comparable redshift .
The structure and the shaping of elliptical galaxies at z \sim 1.3 do not depend on the environment .
However , a dense environment seems to be more efficient in assembling high-mass large ellipticals , much rarer in the field at this redshift .
The correlation found between the central stellar mass density and the age of the galaxies beside the mass suggests a close connection of the central regions to the earliest phases of formation .