Angular Momentum of Early and Late Type Galaxies: Nature or Nurture?
  We investigate the origin, the shape, the scatter, and the cosmic evolution
in the observed relationship between specific angular momentum $j_\star$ and
the stellar mass $M_\star$ in early-type (ETGs) and late-type galaxies (LTGs).
Specifically, we exploit the observed star-formation efficiency and chemical
abundance to infer the fraction $f_{\rm inf}$ of baryons that infall toward the
central regions of galaxies where star formation can occur. We find $f_{\rm
inf}\approx 1$ for LTGs and $\approx 0.4$ for ETGs with an uncertainty of about
$0.25$ dex, consistent with a biased collapse. By comparing with the locally
observed $j_\star$ vs. $M_\star$ relations for LTGs and ETGs we estimate the
fraction $f_j$ of the initial specific angular momentum associated to the
infalling gas that is retained in the stellar component: for LTGs we find
$f_j\approx 1.11^{+0.75}_{-0.44}$, in line with the classic disc formation
picture; for ETGs we infer $f_j\approx 0.64^{+0.20}_{-0.16}$, that can be
traced back to a $z<1$ evolution via dry mergers. We also show that the
observed scatter in the $j_{\star}$ vs. $M_{\star}$ relation for both galaxy
types is mainly contributed by the intrinsic dispersion in the spin parameters
of the host dark matter halo. The biased collapse plus mergers scenario implies
that the specific angular momentum in the stellar components of ETG progenitors
at $z\sim 2$ is already close to the local values, in pleasing agreement with
observations. All in all, we argue such a behavior to be imprinted by nature
and not nurtured substantially by the environment.
