Multi-Wavelength Data Mining of the ISOPHOT Serendipity Sky Survey

Abstract

The ISOPHOT C200 stressed Ge:Ga array aboard the Infrared Space Observatory was used to carry out scientific observations while the telescope was moved from one target to the next. These strip scanning measurements of the sky in the far-infrared (FIR) at 170 μm comprise the ISOPHOT Serendipity Survey, the first slew survey designed as an integral part of a space observatory mission. The ISOPHOT Serendipity Survey is the only large scale sky survey in the unexplored wavelength region beyond the IRAS 100 μm limit to date. Within nearly 550 hours more than 12000 slew measurements with a total slew length of more than 150000 degrees were collected, corresponding to a sky coverage of about 15%. The slew data analysis has been focused on the detection of compact sources, which required the development of special algorithms. A severe problem at 170 μm is the confusion of genuine compact sources with foreground galactic cirrus knots and ridges. The selection and identification of objects therefore necessarily requires a multi-wavelengths approach, which makes use of a broad variety of additional data from databases and other surveys. Known galaxies were identified by cross-correlating the Serendipity Survey source positions with galaxy entries in the NED and Simbad databases and a subsequent cross-check of optical images from the Digital Sky Survey. A large catalogue with 170 μm fluxes for ≈2000 galaxies is being complied. The particularly interesting rare galaxies with very cold dust and very large dust masses further require additional FIR data from the IRAS survey as well as measured redshifts. A large fraction of the compact galactic structures are prestellar cores inside cold star forming regions. Early stages of medium and high mass star forming regions are identified by combining compact bright and cold Serendipity Survey sources with the near-infrared 2MASS and MSX surveys, the combination of which indicates large dust masses in conjunction with embedded young stars of early spectral types. In all the studied samples of different object classes the 170 μm flux provides the crucial data point for a complete characterization of the FIR spectral energy distributions and the derivation of total dust masses. Follow-up observations are underway to study selected objects in more detail.