Multi-resolution angular momentum measurements of z ∼ 1.5 − 2 star-forming galaxies

Abstract

We present detailed stellar specific angular momentum (j*) measurements of ten star-forming galaxies at z ∼ 1.5 − 2 using both high and low spatial resolution integral field spectroscopic data. We developed a code that simultaneously models the adaptive optics (AO) assisted observations from OSIRIS/SINFONI along with their natural seeing (NS) counterparts from KMOS at spatial resolutions of [0.1 − 0.4] arcsec and [0.6 − 1.0] arcsec respectively. The AO data reveals 2/10 systems to be mergers and for the remaining eight the mean uncertainties Δ¯j∗ decrease from 49 per cent (NS), and 26.5 per cent (AO), to 16 per cent in the combined analysis. These j* measurements agree within 20 per cent with simple estimates (⁠j∗~⁠) calculated from the Hubble Space Telescope photometry and NS kinematics, however higher resolution kinematics are required to first identify these disks. We find that the choice of surface mass density model and the measurement of effective radius from photometry are the key sources of systematic effects in the measurement of j* between different analyses. Fitting the j* versus M* relations (Fall, 1983) with a fixed power-law slope of β = 2/3, we find a zero-point consistent with prior NS results at z ≥ 1 within ∼0.3 dex. Finally, we find a ∼0.38 dex scatter about that relation that remains high despite the AO data so we conclude it is intrinsic to galaxies at z > 1. This compares to a scatter of ≤0.2 dex for disks at z ≃ 0 pointing to a settling of the Fall relation with cosmic time.