3-D density maps of the cold neutral gas within a 1kpc data-cube of the Sun

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

AST 0507244 Welsh Dr. Barry Welsh and colleagues will carry out the first well-sampled local absorption survey of the cold and neutral interstellar gas in order to produce a detailed 3-D density map for the 1kpc interstellar data-cube surrounding the Sun. These maps will be constructed using visible absorption lines of NaI and CaII seen in the spectra of ~ 2000 early-type stars located within +/-500pc of the Sun. Such maps will reveal the dimensions and nature of many types of nearby interstellar structures such as (i) local interstellar tunnels, (ii) local interstellar chimneys, (iii) conductive interfaces of nearby superbubbbles and (iv) Intermediate Velocity Cloud complexes in the inner galactic halo regions. These new absorption maps are necessary for understanding the details revealed in recent 21cm radio emission surveys of neutral hydrogen (HI), as well as for aiding in the interpretation of interstellar absorption studies carried out at other wavelengths. The data will provide accurate and important input parameters (such as the filling factor of the cold neutral gas) that can be used to test current theoretical models that attempt to describe the formation and possible evolution of the more global ISM. This study builds on a preliminary map of the local ISM constructed to a distance of ~200pc that has already been widely used by other astronomers in a variety of case studies. The new mapping of a 1kpc interstellar data-cube will be the first to reveal the absorption characteristics of both neutral and partially ionized gas throughout these regions, and will highlight several expanding large-scale structures that may affect the overlying galactic halo through a possible 'galactic fountain blow-out.. This study will be undertaken as an integral part of graduate student training. The research is being performed as a collaborative effort between scientists at UC Berkeley and CNRS in France, and the major scientific findings will be disseminated to K-12 educators at the Center for Science Education at the UC Berkeley Space Sciences Laboratory. Since interstellar cavities, tunnels and supernova remnants are to be found in many nearby galaxies, the very detailed spatial information gained from the present galactic study will provide a testable database against which observations of their extragalactic counterparts may be compared. Clearly if one can understand how such fundamental interstellar structures are formed and evolve locally, then this may have a significant impact on our understanding of the interstellar medium in other galaxies.