Published online by Cambridge University Press: 10 November 2010
We present a kinematical study of NGC 604 in the emission lines of Hα and [OIII] λ5007 Å, based on data obtained with TAURUS-2, a Fabry-Perot imaging spectrograph. The main result is that the global supersonic velocity value is dominated by emission coming from the two maximum brightness peaks covering an area of about 12 arcsec.
NGC 604, located in M33, is one of the most prominent giant extragalactic HII regions (GEHR). It was observed with TAURUS-2 at the 4.2-m William Herschel Telescope (La Palma), with the Image Photon Counting System (IPCS) as detector. Two data cubes, each with an integration time of 3600 sec, were obtained in the emission line of Hα and [OIII] λ5007. The 125-µm etalon was used, which gave a free spectral range for Hα of 17.6 Å (806.6 km s−1) and 10.0 Å (596.1 km s−1) for [OIII]. The velocity resolution (σ of the calibration line) was 23.1 km s−1 for Hα and 19.6 km s−1 for [OIII].
In order to determine the origin of the supersonic mass motion in NGC 604, the kinematics of the region were analyzed by means of individual spectra, applying automatic fitting routines with single Gaussian fits. The measured velocity dispersions were corrected for instrumental and thermal broadening. The thermal velocity dispersion correction was calculated assuming Te = 10,000 K.