Speaker
Jin Koda
(Stony Brook University)
Description
I will discuss the formation and evolution of giant molecular clouds (GMCs) in spiral galaxies. The evolution appears quite different between the molecule-rich and atom-rich galaxies. GMCs exist almost exclusively along HI spiral arms and filaments in atom-rich galaxies, suggesting that they form and finish their short lifetimes within the HI arms. However, in molecular-rich galaxies, GMCs are present everywhere independent of HI structures. Indeed, the molecular gas fraction remains high and almost constant during arm passage into the next inter-arm region. The gas remains molecular for a long time, suggesting long lifetimes of molecule, and presumably GMCs. The physical conditions of molecular gas change from spiral arms to inter-arm regions. An increase of the CO J=2-1 and 1-0 line ratio in spiral arms in M51 suggests density and/or temperature increases by a factor of 2-3 in GMCs in the arms, compared to their counterparts in the inter-arm regions. An analysis of high-resolution Milky Way survey data provided a more detailed, clear view - the fraction of dense (or warm) clumps increases dramatically in the spiral arms.
Author
Jin Koda
(Stony Brook University)