N.M. F örster Schreiber, R. Genzel, D. Lutz, A. Sternberg

1. The Nature of Starburst Activity in M82 MPE 3D: K-band emission Br line emission Global star formation history of the central regions of M82, reconstructed from the modeling of all individual pixels within the MPE 3D field of view. Two distinct starburst episodes are outlined, peaking  10 and 5 Myr ago and lasting each a few Myr only. Models of the integrated properties of the 500 pc starburst core of M82 (encompassing the 3D field of view) agree with the reconstructed history. However, the spatially detailed data and models enabled us to trace the progression of the starburst activity, relate it to the main morphological features of M82, and establish a plausible scenario for its triggering, evolution, and quenching. The short burst duration suggest strong negative feedback from massive stars formed in each starburst episode. Composite map and representative spectra of M82 from MPE 3D. The map covers the nucleus and extends to the west out to the inner edge of the molecular ring enclosing the starburst core. The K-band continuum emission and the absorption features trace evolved red (super)giants while H (e.g. Br) and He recombination lines trace HII regions around young OB stars. The relative spatial distributions and the relative strengths of the continuum, absorption, and emission features indicate important variations on scales ~ few tens of pc in the evolutionary stage of the starburst. Evolutionary synthesis modeling of these diagnostics allowed us to quantitatively constrain the burst ages, durations, and intensities, and the IMF. Starburst galaxies are important constituents of the universe at all accessible redshifts. However, a detailed and quantitative understanding of the starburst phenomenon is still lacking notably concerning the evolution and feedback effects of starburst activity, and the IMF of the stars formed in starbursts. Progress has been hindered by the scarcity of spatially resolved data and by dust obscuration often hampering high-resolution studies in the optical/UV. In this context, we carried out a detailed investigation of the nearby (3.3 Mpc) archetypal starburst galaxy M82. We used mainly near-IR integral field spectroscopy from the MPE 3D instrument and mid-IR spectroscopy from the ISO SWS, covering the central actively star-forming regions. The data, together with evolutionary synthesis, allowed us to model the starburst regions on scales of 25 pc. We derived a typical duration for individual burst sites of a few 106 yr. The data are consistent with the formation of very massive stars ( 50–100 M) and require a flattening of the IMF below a few M assuming a Salpeter slope at higher masses. The global starburst activity in M82 occurred in two successive episodes each lasting a few 106 yr, peaking  10 and 5106 yr ago. The first episode took place throughout the central regions and was particularly intense at the nucleus while the second episode occurred predominantly in a circumnuclear ring and along the stellar bar. This sequence likely resulted from the gravitational interaction between M82 and its neighbour M81, and subsequent bar-driven evolution. The short burst duration on all spatial scales indicates strong negative feedback effects due to the collective mechanical energy released by massive stars, rapidly inhibiting star formation after the onset of each starburst episode. • References: • Förster Schreiber, M. N., Genzel, R., Lutz, D., & Sternberg, A. 2003, ApJ, 599, 193 N.M. Förster Schreiber, R. Genzel, D. Lutz, A. Sternberg