Finding New Star Forming Objects in the Stephan’s Quintet with GMOS :

1. a b c d Figure 2 - Spectra of IHII a to d. Each inset presents a zoom in the region from 6500 to 6900 Å. Zero flux is indicated with a dashed line. Finding New Star Forming Objects in the Stephan’s Quintet with GMOS: Intergalactic HII Regions (IHII) Claudia M. de Oliveira, Eduardo S. Cypriano1, Laerte Sodré Jr.(IAG/USP) e Chantal Balkowski (Obs. Paris-Meudon) Abstract: In the course of doing a spectroscopic survey of the field of the Stephan's Quintet with GMOS-N we discovered four intergalactic HII regions (IHII), more than 25 kpc projected distance from the center of the nearest group galaxy. They have MB ranging from -11.9 to -12.5 mag, colors B-R = 0.7 to 1.1 mag, radial velocities from 6565 to 6651 km s-1 and are superposed onto the HI tail east of NGC 7319, with a mean radial velocity of 6610 km s-1. In addition, they have metalicities of the order of 12+log(O/H) = 8.58±0.04, which suggests that they were formed from pre-enriched material. We derive a mean age of 4.6±0.6 Myr and a mean stellar mass of (2.0±0.3)  105 M for the four objects. These characteristics suggest that they are HII regions that were formed far away from the galaxies through compression of the intergalactic HI gas by galaxy collisions. Observations • Gemini-N/GMOS • Imaging: r’, g’ (15, 22 min.) • MOS: • 1 Mask with 72 slitlets • Slit width: 1.0 arcsec • Grating: R400 • Resolution: ~8Å • Integration: 15 min. General Characteristics of the IHII • Compact objects (except b) • Blue Colors • Associated with the HI tail • Metalicities: 12+log(O/H) = 8.58±0.04 • Masses: (2.0±0.3)  105 M • Ages: 4.6±0.6 Myr Determination of the StarBurst Parameters • Metalicity: [NII]6584/H estimator (Denicoló, Terlevich & Terlevich 2002) • Model: Instantaneous starburst (Starburst99;Leitherer et al. 1999) • H equivalent width  Ages • Ages + Absolute Magnitudes Masses & Internal Extinction Figure1 - Color composite image of the Stephan’s Quintet. Overplotted in red are the HI contours from Williams et al.(2002). The boxes in the upper left corner indicate the new IHII found. Zoomed views of these are seen in the top panels. Conclusions • The IHII regions could not preexist the main collision (between NGC 7318B and the group) given their high metalicities • Their extremely young ages suggest that they are located where they were born • We favor a scenario in which the IHII were formed far away the galaxies through compression of the intergalactic HI gas by galaxy collisions This work has been partially supported by FAPESP 1email: eduardo@astro.iag.usp.br