Oral Presentation

High-resolution ALMA study of structure and gas kinematics of cluster galaxies at z=1.46

Author(s): Ryota Ikeda (NAOJ/SOKENDAI)

Presenter: Ryota Ikeda (NAOJ/SOKENDAI)

We present an ALMA study obtained from spatially resolved CO J=2–1 line (0.4" resolution) and 870 μm continuum (0.2" resolution) observations of galaxies in a massive cluster, XMMXCS J2215.9-1738 at z = 1.46. Our sample comprises 17 CO emitters within ∼0.5 Mpc (0.6R_200) from the cluster center. We measure the sizes of both CO J=2–1 line and 870 μm dust continuum emissions for nine CO emitters by modeling the visibilities. We find that the CO J=2–1 line emission in all of the nine galaxies is more extended than the dust continuum emission by a factor of 2.8 ± 1.4. The spatially resolved Kennicutt-Schmidt relation reveals that the central region (0 < r < Re,870μm) of galaxies tends to have a shorter gas depletion timescale, i.e. a higher star formation efficiency (SFE), compared to the extended region (Re,870μm < r < Re,CO). Our result suggests that star formation activities are concentrated inside the extended gas reservoir, resulting in the formation of a bulge structure. We further conduct the kinematical modeling of CO J=2-1 line, using 3DBarolo for 10 CO emitters. We find that for all galaxies, the dynamical mass within 5 kpc is comparable or even smaller than the baryonic mass, which indicates that our baryonic mass estimates are somehow overestimated. We attribute this discrepancy to the CO-to-H2 conversion factor, and calculate the optimized value of〈α_CO〉= 2.9±1.9. Finally, all of the CO emitters show flat rotation curve from 1-5 kpc, qualitatively suggesting that the bulge growth has already in progress in these cluster galaxies.