COMPLEX GAS KINEMATICS IN COMPACT, RAPIDLY ASSEMBLING STAR-FORMING GALAXIES

Deep, high-resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z similar to 0.1-0.3, most of them also known as green peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including Ha, [N II] lambda lambda 6548, 6584, and [S II] lambda lambda 6717, 6731, consisting of the superposition of different kinematical components on a spatial extent of few kiloparsecs: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their two-dimensional spectra, whereas for another one a faint detached H alpha blob lacking stellar continuum is detected at the same recessional velocity similar to 7 kpc away from the galaxy. The individual narrower H alpha components show high intrinsic velocity dispersion (sigma similar to 30-80 km s(-1)), suggesting together with unsharped masking Hubble Space Telescope images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to similar to 500 km s(-1). The broad underlying H alpha components indicate in all cases large expansion velocities (full width zero intensity >= 1000 km s(-1)) and very high luminosities (up to similar to 10(42) erg s(-1)), probably showing the imprint of energetic outflows from supernovae. These intriguing results underline the importance of green peas for studying the assembly of low-mass galaxies near and far.