Abstract. For the first time in the history of high energy astronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and its in-flight behavior and performances. Having a sensitive area of 2621 cm 2 with a spatial resolution of 4.6 mm, a low threshold around 12 keV and an energy resolution of ∼8% at 60 keV, ISGRI shows absolutely no signs of degradation after 9 months in orbit. All aspects of its in-flight behavior and scientific performance are fully nominal, and in particular the observed background level confirms the expected sensitivity of 1 milliCrab for a 10 6 s observation.
Absolute integrated line fluxes of H ii regions have been measured using a Fabry–Perot spectrophotometer. We describe the observations and calibration procedures. Fluxes are given for 36 H ii regions with Galactocentric distances ranging from 6.6 to 17.7 kpc. Several emission lines have been measured, mainly [O ii] λλ3726 and 3629, Hβ, [O iii] λ5007, He iλ5876 and Hα. The very faint [O iii] λ4363 line has been measured in six regions, allowing a direct determination of the electron temperature. New photometric distances have been derived based on data from the literature. A discussion of these results in terms of extinction, electron density and temperature, and oxygen and helium abundances is given in Paper II.
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