Angular Momentum of Early- and Late-type Galaxies: Nature or Nurture?

We investigate the origin,. shape,. scatter, and. cosmic evolution of. the observed relationship between specific angular momentum j(star) and the stellar mass M-star in early-type galaxies. (ETGs) and late-type galaxies (LTGs). Specifically, we exploit the observed star formation efficiency and chemical abundance to infer the fraction f(inf) of baryons that infall toward the central regions of galaxies where star formation can occur. We find f(inf) approximate to 1 for LTGs and approximate to 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) versus M-star relations for LTGs and ETGs, we estimate the fraction f(j) of the initial specific angular momentum associated with. the infalling gas that is retained in the stellar component.. For LTGs, we find f(j) approximate to 1.11(-0.44)(+0.75), in line with the classic disk. formation picture; for ETGs, we infer f(j) approximate to 0.64(-0.16)(+0.20), which. can be traced back to a z less than or similar to 1 evolution via dry mergers. We also show that the observed scatter in the j(star) versus 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 merger. scenario implies that the specific angular momentum in the stellar components of ETG progenitors at z similar to 2 is already close to the local values, in good. agreement with observations. All in all, we argue that. such a behavior is imprinted by nature and not nurtured substantially by the environment.