Compact Star Clusters in HII Galaxies

1. Tol1457 UM461 Tol1223 Tol1004 Tol1345 Tol0957 1Kpc 1Kpc 1Kpc 1Kpc 1Kpc 1Kpc Zw40 Zw40 continuum Hβ line Zw40 15’’ 15’’ 15’’ - = Hβ line + continuum Mrk36 Mrk36 Figures Mrk36 20’’ 20’’ 20’’ = - Narrowband Hβ images of the HII galaxies obtained on NTT 3.6m at ESO with the SuSI2 (a high resolution imager) Hβ line continuum Hβ line + continuum Tol1334 Mrk1318 10’’ 5’’ 15’’ 1Kpc 1Kpc 20’’ 20’’ 10’’ CTS1022 Cam0840+1044 1Kpc 15’’ 10’’ 10’’ 1Kpc 5’’ Compact Star Clusters in HII Galaxies Carolina Kehrig & Eduardo Telles Observatório Nacional/MCT, Rio de Janeiro, Brazil Starbursts are regions where thousands of massive stars are formed in very short time scales and very small volumes. They are found in interacting galaxies but also in dwarf HII galaxies where the triggering mechanisms of star formation are not so obvious. Even the most compact HII galaxies seem to have very blobbly appearance with the starburst being composed of smaller star forming knots, presumably made up of emsembles of Super Star Clusters (SSCs). These knots seem to be spread over long extensions within the galaxies and their coeval nature rules out self-propagation. The internal and overall properties of the Interstellar Medium seem to dictate when a starburst will occur. To try to pin down which are these properties and identify the elementary entities of which the starburst consists, we first have to describe the physical conditions and stellar mix at very good spatial resolution and high enough S/N on the underlying galaxy. We can do that with Integral Field Unit (IFU) spectra of the starburst and with high resolution, high S/N near-infrared observations of these compact underlying galaxies, which requires both image quality and light-gathering power provided by modern instrumentation in large telescopes. One of the main issues in today´s astrophysics is how present-day galaxies formed and how they have evolved over time. One approach to understand that is to study in detail the properties of local active star-forming galaxies, as for example HII galaxies. They are the best examples in the local universe of young galaxies that can be studied in detail. In this respect, it is important to quantify the relative importance of the current episode of star formation in comparision to the underlying older stellar populations, their star formation histories, and efficiencies. Narrow band imaging in both optical and nearIR with large telescopes will help map the star forming regions and quantify the contribution of nebular emission both in lines and continuum to the broad band colours, which have proved to be important when comparing with models of population synthesis and of fotoionization to derive ages, metalicities, extinction and masses. The Properties of the SSCs and the distribution of Star Formation High spatial resolution surface photometry can be extremely useful in the characterization of the stellar populations in star-forming galaxies and in complementing spectroscopic observations. The study of the location, sizes and masses of spatially resolved star-forming knots, their intensity and concentration, give us a clear insight of the mode of star formation in starbursts and the underlying physics. Surface photometry with large telescopes will allow a detailed description of the very faint host galaxy in dwarf HII galaxies, particularly in the Near Infrared. Chemical and Physical property homogeneity The SOAR and GEMINI IFU spectrographs allow simultaneous spectra to be taken of extended objects. From this, we can learn how the Interstellar Medium is structured, derive physical conditions and chemical properties corresponding to individual star-forming regions. The study of the distribution and homogeneity of these properties is an important issue in our knowledge of the interplay between the massive stellar population and the ISM, unveiling the mechanisms that rule star formation. A IFU schematic representation is shown below.