1301.0628 (J. Freundlich et al.)

Towards a resolved Kennicutt-Schmidt law at high redshift    [PDF]

J. Freundlich, F. Combes, L. J. Tacconi, M. C. Cooper, R. Genzel, R. Neri, A. Bolatto, F. Bournaud, A. Burkert, P. Cox, M. Davis, N. M. Förster Schreiber, S. Garcia-Burillo, J. Gracia-Carpio, D. Lutz, T. Naab, S. Newman, A. Sternberg, B. Weiner

Massive galaxies in the distant Universe form stars at much higher rates than today. Although direct resolution of the star forming regions of these galaxies is still a challenge, recent molecular gas observations at the IRAM Plateau de Bure interferometer enable us to study the star formation efficiency at sub-galactic scales around redshift z = 1.2. We present a method to obtain the gas and star formation rate (SFR) surface densities of ensembles of clumps composing galaxies at this redshift, even though the corresponding scales are not resolved. This method is based on the identification of these structures in position-velocity diagrams corresponding to slices within the galaxies. We use unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of four massive star forming distant galaxies - EGS13003805, EGS13004291, EGS12007881 and EGS13019128 in the AEGIS terminology - to determine the gas and SFR surface densities of the identifiable ensembles of clumps that constitute them. The integrated CO line luminosity is assumed to be directly proportional to the total gas mass, and the SFR is deduced from the [OII] recombination line. We identify the ensembles of clumps with the angular resolution available in both CO and [OII] spectroscopy, i.e. 1-1.5". SFR and gas surface densities are averaged in areas of this size, which is also the thickness of the DEEP2 slits and of the extracted IRAM slices, and we derive a spatially resolved Kennicutt-Schmidt (KS) relation at a scale of ~ 8 kpc. The data points globally follow a power law of exponent N=1 corresponding to a depletion time of 1.0 Gyr, but with a large scatter, which means that the depletion time varies from point to point within the galaxies. We find a depletion time of 1.4 +/- 0.9 Gyr.

View original: http://arxiv.org/abs/1301.0628