26 research outputs found
Extragalactic Results from the Infrared Space Observatory
More than a decade ago the IRAS satellite opened the realm of external
galaxies for studies in the 10 to 100 micron band and discovered emission from
tens of thousands of normal and active galaxies. With the 1995-1998 mission of
the Infrared Space Observatory the next major steps in extragalactic infrared
astronomy became possible: detailed imaging, spectroscopy and
spectro-photometry of many galaxies detected by IRAS, as well as deep surveys
in the mid- and far- IR. The spectroscopic data reveal a wealth of detail about
the nature of the energy source(s) and about the physical conditions in
galaxies. ISO's surveys for the first time explore the infrared emission of
distant, high-redshift galaxies. ISO's main theme in extragalactic astronomy is
the role of star formation in the activity and evolution of galaxies.Comment: 106 pages, including 17 figures. Ann.Rev.Astron.Astrophys. (in
press), a gzip'd pdf file (667kB) is also available at
http://www.mpe.mpg.de/www_ir/preprint/annrev2000.pdf.g
Cosmic rays and molecular clouds
This paper deals with the cosmic-ray penetration into molecular clouds and
with the related gamma--ray emission. High energy cosmic rays interact with the
dense gas and produce neutral pions which in turn decay into two gamma rays.
This makes molecular clouds potential sources of gamma rays, especially if they
are located in the vicinity of a powerful accelerator that injects cosmic rays
in the interstellar medium. The amplitude and duration in time of the
cosmic--ray overdensity around a given source depend on how quickly cosmic rays
diffuse in the turbulent galactic magnetic field. For these reasons, gamma-ray
observations of molecular clouds can be used both to locate the sources of
cosmic rays and to constrain the properties of cosmic-ray diffusion in the
Galaxy.Comment: To appear in the proceedings of the San Cugat Forum on Astrophysics
2012, 27 pages, 10 figure
Gamma Rays from Molecular Clouds
High energy gamma-rays from individual giant molecular clouds contain unique information about the hidden sites of acceleration of galactic cosmic rays, and provide a feasible method for study of propagation of cosmic rays in the galactic disk on scales less than or equal to100 pc. I discuss the spectral features of pi(0)-decay gamma-radiation from clouds/targets located in proximity of relatively young proton accelerators, and speculate that such `accelerator+target' systems in our Galaxy can be responsible for a subset of unidentified EGRET sources. Also, I argue that the recent observations of high energy gamma-rays from the Orion complex contain evidence that the level of the `sea' of galactic cosmic rays may differ significantly from the flux and the spectrum of local (directly detected) particles
Source counts from the 15 mu m ISOCAM deep surveys
We present the results of the five mid-IR 15 mu m (12-18 mu m LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field. The roughly 1000 sources detected, 600 of which have a flux above the 80% completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to similar to 5 mJy. By adding the ISOCAM surveys of the HDF-North and South (plus flanking fields) and the lensing cluster A2390 at low fluxes and IRAS at high fluxes, we cover four decades in fur from 50 mu Jy to similar to 0.3 Jy. The slope of the differential counts is very steep (alpha = -3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of alpha = -2.5. When compared with no-evolution models based on IRAS, our counts show a factor similar to 10 excess at 400 mu Jy, and a fast convergence, with alpha = -1.6 at lower fluxes