Speaker
Description
HII regions, ionized nebulae associated to massive star formation, exhibit a wealth of emission lines that are the fundamental basis for estimating the chemical composition of the Universe. Heavy element abundances are particularly important because they are essential to the understanding of nucleosynthesis, star formation and chemical evolution. For more than 80 years, however, a discrepancy between heavy-element abundances derived with collisional excited lines (CELs) and recombination lines (RLs) has thrown our absolute abundance determinations into doubt in Galactic and extragalactic systems. Only recently it has been shown that there are temperature inhomogeneities concentrated within the highly ionized gas of the HII regions, causing the reported discrepancy by introducing systematic underestimations of the metallicities based on CELs. Observations of Galactic ring nebulae created by mass-loss episodes from young very massive stars seems to link the temperature inhomogeneities with stellar feedback processes.
The LVM will be a crucial project to understand this long-standing problem by taking integral-field spectroscopy of the internal structures of hundreds of HII regions and revealing the environmental dependences of the stellar feedback on the nebular gas. Furthermore, Galactic HII regions show intricate clumply structures due to density variations of several orders of magnitude, whose understanding is critical for studies based on far-infrared fine structure lines, such as those observed by the JWST in local star forming regions. Here the LVM will again be essential to correctly interpret the nebular conditions whose impact goes far beyond our Milky Way.
