* Astronomy

Title: Shocked Superwinds from the z~2 Clumpy Star-forming Galaxy, ZC406690
Authors: Sarah F. Newman, Kristen Shapiro Griffin, Reinhard Genzel, Ric Davies, Natascha M. Foerster-Schreiber, Linda J. Tacconi, Jaron Kurk, Stijn Wuyts, Shy Genel, Simon J. Lilly, Alvio Renzini, Nicolas Bouche, Andreas Burkert, Giovanni Cresci, Peter Buschkamp, C. Marcella Corollo, Frank Eisenhauer, Erin Hicks, Dieter Lutz, Chiara Mancini, Thorsten Naab, Yingjie Peng, Daniela Vergani

We have obtained high-resolution data of the z 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with AO (in K-band) and in seeing-limited mode (in H- and J-band). Our data includes all of the main strong optical emission lines: [OII], [OIII], Ha, Hb, [NII] and [SII]. We find broad, blueshifted Ha and [OIII] emission line wings in the spectra of the galaxy's massive, star-forming clumps (sigma ~ 85 km s^-1) and even broader wings (up to 70% of the total Ha flux, with sigma ~ 290 km s^-1) in regions spatially offset from the clumps by ~ 2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1-8x the SFR of the clumps. Based on emission line ratio diagnostics ([NII]/Ha and [SII]/Ha) and photoionisation and shock models, we find that the emission from the clumps is due to a combination of photoionisation from the star-forming regions and shocks generated in the outflowing component, with 5-30% of the emission deriving from shocks. In terms of the ionisation parameter (6x10^7-10^8 cm/s, based on both the SFR and the O32 ratio), density (local electron densities of 300-1800 cm^-3 in and around the clumps, and ionised gas column densities of 1200-8000 Msol/pc^2), and SFR (10-40 Msol/yr), these clumps more closely resemble nuclear starburst regions of local ULIRGs and dwarf irregulars than HII regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal properties, energetics and relative ages, and thus we are given a glimpse at two different stages in the formation and evolution of rapidly star-forming giant clumps at high-z.

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