The epic adventures of detecting Hii regions wtih SITELLE data

Gabriel Savard ( Université Laval )

The study of the ionized gas in galaxies is crucial to understand how stars are formed within their environment. With the help of the imaging spectrograph SITELLE at the CFHT, we undertook an investigation of the emission regions over the whole spiral galaxy NGC 7479 (at 36 Mpc). SITELLE’s large field of view (11’×11’) allows the study of the whole galaxy while its high spatial resolution (0.32’’/pixel) enables the individual identification of HII regions. Using SITELLE filters (SN1:364-385nm, SN2:484-512nm, SN3:648-686nm), we cover the main emission lines needed for the extraction of the gas physical properties (kinematics, metallicity…). For this work, and for the ongoing systematic study of more than 40 nearby galaxies with SITELLE, as part as the SIGNALS survey, a new detection code for the emission regions has been developed. It identifies emission peaks (based on the Hα Laplacian map and the noise map), the physical domain surrounding each peak (fitting 2D Gaussian profiles), and their background emission. Taking into account the stellar populations underneath the emission lines, we can separate diffuse emission regions from HII regions and draw an accurate Hα luminosity function. We present here the basic functionalities of the detection code and the results obtained for NGC 7479. Hundreds of HII regions are found and their properties are being compared taking into account their location in the galaxy’s strong bar, asymmetric arms and extended disk.