arXiv subjects

A. Contursi

Publications and source records attributed to A. Contursi.

56 records · Page 4Linked to original sources

arXiv2000

Mid-infrared imaging and spectrophotometry of N 66 in the SMC with ISOCAM

We present observations with the mid-infrared camera ISOCAM on board ISO of the major star-forming region N66 in the Small Magellanic Cloud and of its surroundings. These observations were performed with broad filters and the CVF giving a spectral resolution of about 40. In addition, CO(2-1) data are presented, allowing us to identify and study how hot dust relates with the different phases of the Interstellar Medium present in N66. The spectra are dominated by the strong emission of fine structure line. Monochromatic maps have been made in the [NeIII] 15.6 microns and [SIV] 10.5 microns line. There are significant differences between their distributions, due to the effects of density and of shocks. Aromatic Infrared Bands are seen at various places in the field but they are generally faint. They exhibit a variety of shapes and relative intensities, suggesting that a diversity of carbonaceous materials are present. Silicate emission is also clearly visible in the central condensation and in a few others and emission from hot small grains longward of 10 microns is present in the whole region. All these dust components are heated by the very strong far UV radiation of the many young, massive stars contained in the region. The interstellar radiation field (ISRF) at 1600 A is >= 10^5 times the ISRF of the solar neighborhood in the peaks of MIR emission. The relative contributions of the dust components to the MIR spectra seem to depend on the intensity and the hardness of the far UV field. In general the 15/6.75 microns intensity ratio is higher than in relatively quiescent galactic regions but it is not as high as expected for a linear increase with ISRF. We interpret this behavior as due to the destruction of both AIBs carriers and VSGs in a very high ISRF.

astro-ph↗

arXiv1998

The star formation properties of disk galaxies: Halpha imaging of galaxies in the Coma supercluster

We present integrated H alpha measurements obtained from imaging observations of 98 late-type galaxies, primarily selected in the Coma supercluster. These data, combined with H alpha photometry from the literature, include a magnitude selected sample of spiral (Sa to Irr) galaxies belonging to the "Great Wall" complete up to mp=15.4, thus composed of galaxies brighter than Mp=-18.8 (H0=100 km Mpc^-1 s^-1). The frequency distribution of the H alpha E.W., determined for the first time from an optically complete sample, is approximately gaussian peaking at E.W. ~25 A. We find that, at the present limiting luminosity, the star formation properties of spiral+Irr galaxies members of the Coma and A1367 clusters do not differ significantly from those of the isolated ones belonging to the Great Wall. The present analysis confirms the well known increase of the current massive star formation rate (SFR) with Hubble type. Moreover perhaps a more fundamental anticorrelation exists between the SFR and the mass of disk galaxies: low-mass spirals and dwarf systems have present SFRs ~50 times higher than giant spirals. This result is consistent with the idea that disk galaxies are coeval, evolve as "closed systems" with exponentially declining SFR and that the mass of their progenitor protogalaxies is the principal parameter governing their evolution. Massive systems having high initial efficiency of collapse, or a short collapse time-scale, have retained little gas to feed the present epoch of star formation. These findings support the conclusions of Gavazzi & Scodeggio (1996) who studyed the color-mass relation of a local galaxy sample and agree with the analysis by Cowie et al. (1996) who traced the star formation history of galaxies up to z>1.

astro-ph↗