THE ANGULAR MOMENTUM DISTRIBUTION AND BARYON CONTENT OF STAR-FORMING GALAXIES AT z ∼ 1–3*

Abstract

We analyze the angular momenta of massive star-forming galaxies (SFGs) at the peak of the cosmic star formation epoch ( z ∼ 0.8–2.6). Our sample of ∼360 log( M * / M ⊙ ) ∼ 9.3–11.8 SFGs is mainly based on the KMOS 3D and SINS/zC-SINF surveys of H α kinematics, and collectively provides a representative subset of the massive star-forming population. The inferred halo scale angular momentum distribution is broadly consistent with that theoretically predicted for their dark matter halos, in terms of mean spin parameter  ∼ 0.037 and its dispersion ( σ log λ ∼ 0.2). Spin parameters correlate with the disk radial scale and with their stellar surface density, but do not depend significantly on halo mass, stellar mass, or redshift. Our data thus support the long-standing assumption that on average, even at high redshifts, the specific angular momentum of disk galaxies reflects that of their dark matter halos ( j d =  j DM ). The lack of correlation between λ  × ( j d / j DM ) and the nuclear stellar density Σ * (1 kpc) favors a scenario where disk-internal angular momentum redistribution leads to “compaction” inside massive high-redshift disks. For our sample, the inferred average stellar to dark matter mass ratio is ∼2%, consistent with abundance matching results. Including the molecular gas, the total baryonic disk to dark matter mass ratio is ∼5% for halos near 10 12 M ⊙ , which corresponds to 31% of the cosmologically available baryons, implying that high-redshift disks are strongly baryon dominated.