  The probability of $\alpha$ particle emission for some recently observed
superheavy nuclei (SHN) are investigated. The $\alpha$-decay half lives of SHN
are calculated in a quantum tunneling model with density dependent M3Y (DDM3Y)
effective nuclear interaction using theoretical and measured $Q_\alpha$ values.
We determine the density distribution of $\alpha$ and daughter nuclei from the
relativistic mean field theory (RMF) using FSUGold force, NL3 and TM1 parameter
sets. The double folded nuclear potential is numerically calculated in a more
microscopic manner using these density distributions. The estimated values of
$\alpha$-decay half-lives are in good agreement with the recent data. We
compare our results with recently detected $\alpha$-decay chains from new
element with atomic number Z=117 reported by JINR, Dubna. Finally, we determine
the half-lives of superheavy elements with Z=108-120 and neutron number
N=152-190 to explore the long-standing predictions on the existence of an
"island of stability" due to possible spherical proton (Z$\sim 114$) and
neutron (N$\sim 184$) shell closures.
