GeminiFocus December 2012 | Page 14

Figure 1. The Ha intensity, velocity, and velocity dispersion maps of two of the SMGs observed with NIFS. We show HST imaging also. All the SMG systems observed show disturbed dynamics and multiple peaks of star formation intensity. Triggering the Rapid Star Formation SMGs have large reservoirs of molecular gas that provide the fuel for rapid star formation. Indeed, SMGs can grow quickly, creating a massive galaxy in only 100 million years. SMGs therefore represent an immensely active phase in galaxy evolution and are thought to be the progenitors of the massive elliptical galaxies observed in the local universe. After 15 years of intense study, our detailed understanding of SMGs is still limited to only a handful of objects with spatially resolved images and spectra. In particular, we still don’t fully understand what triggers the extreme star formation in SMGs. Galaxy simulations predict that two galaxies merging could cause an ultra-luminous burst, as observed in SMGs. To test this hypothesis, we need to observe the dynamics and morphologies of the gas within the SMGs, hunting for the signatures of multiple colliding components. Tracing the gas dynamics within high-redshift systems has only been made possible in recent years with the development of Integral Field Units (IFUs), such as the Near-Infrared Integral Field Spectrometer (NIFS) on Gemini 14 GeminiFocus North and the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) on the Very Large Telescope (VLT). These units enable us to trace the emission lines across the galaxies. The gas dynamics can then be spatially resolved by tracing the shape and position of emission lines detected. Tracing the Star Forming Gas The hydrogen-alpha (Hα) spectral line is emitted from regions where hydrogen is ionized by hot young stars and therefore traces the star-forming gas. We mapped this emission line within five SMGs using NIFS and also three SMGs using SINFON to gain spatially resolved information about the intensity of star formation and the velocity and dispersion of the gas. The intensities of the Hα line map the star formation distribution across the galaxy; the position of the line (in wavelength) gives the velocity map of the gas, and the width of the line gives the velocity dispersion map of the gas. We established that the gas within SMGs is disturbed and turbulent, often tracing multiple interacting components (Figure 1). There are no clear rotation curves in these systems, December2012