A forming, dust-enshrouded disk at z=0.43: the first example of a massive, late-type spiral rebuilt after a major merger?

By combining Ultra Deep Field imagery from HST/ACS with kinematics from VLT/GIRAFFE, we derive a physical model of distant galaxies in a way similar to that achievable for nearby galaxies. A significant part of the evolution in the density of cosmic star formation is related to the rapid evolution of both luminous IR galaxies (LIRGs) and Luminous Compact galaxies: here we study the properties of a distant, compact galaxy, J033245.11-274724.0, which is also a LIRG. Given the photometric and spectrophotometric accuracies of data of all wavelengths, we can decompose the galaxy into sub-components and correct them for reddening. Combination of deep imagery and kinematics provides a reasonable physical model of the galaxy. The galaxy is dominated by a dust-enshrouded disk revealed by UDF imagery. The disk radius is half that of the Milky Way and the galaxy forms stars at a rate of 20 M-circle dot/yr. Morphology and kinematics show that both gas and stars spiral inwards rapidly to feed the disk and the central regions. A combined system of a bar and two nonrotating spiral arms regulates the material accretion, induces high velocity dispersions, with sigma larger than 100 km s(-1) and redistributes the angular momentum. The detailed physical properties of J033245.11-274724.0 resemble the expectations of modeling the merger of two equal-mass, gaseous-rich galaxies, 0.5 Gyr after the merger. They cannot be reproduced by any combination of intrinsic disk perturbations alone, given the absence of any significant outflow mechanisms. In its later evolution, J033245.11-274724.0 could become a massive, late-type spiral that evolves to become part of the Tully-Fisher relation, with an angular momentum induced mostly by the orbital angular-momentum of the merger.