Elucidating the properties of galaxies with intense high ionization emission lines

Kimihiko Nakajima (NAOJ)


Recent deep spectroscopic observations of z>6 galaxies identify strong high ionization UV emission lines such as HeII. This indicates galaxies in the early universe could have a radiation field more intense than those of galaxies seen in later epochs. We construct a large grid of well-defined photoionization models to interpret UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium. These models are applied to spectroscopic observations from the VIMOS Ultra Deep Survey (VUDS). Using newly developed diagnostics with the line ratios and equivalent widths of low-to-high ionization UV lines, we find that a conventional stellar photoionization is clearly insufficient to reproduce the spectra of high ionization sources. We discuss implications for a hidden non-thermal source to characterize the properties of galaxies with intense high ionization lines.