TY - JOUR
T1 - Dust temperature and time-dependent effects in the chemistry of photodissociation regions
AU - Esplugues, G.
AU - Cazaux, S.
AU - Caselli, P.
AU - Hocuk, S.
AU - Spaans, M.
PY - 2019/6/1
Y1 - 2019/6/1
N2 - When studying chemistry of photodissociation regions (PDRs), time dependence becomes important as visual extinction increases, since certain chemical time-scales are comparable to the cloud lifetime. Dust temperature is also a key factor, since it significantly influences gas temperature and mobility on dust grains, determining the chemistry occurring on grain surfaces. We present a study of the dust temperature impact and time effects on the chemistry of different PDRs, using an updated version of theMeijerink PDR code and combining it with the time-dependent code Nahoon. We find the largest temperature effects in the inner regions of highG0 PDRs,where high dust temperatures favour the formation of simple oxygen-bearing molecules (especially that of O2), while the formation of complex organic molecules is much more efficient at low dust temperatures. We also find that time-dependent effects strongly depend on the PDR type, since long time-scales promote the destruction of oxygen-bearing molecules in the inner parts of low G0 PDRs, while favouring their formation and that of carbon-bearing molecules in high G0 PDRs. From the chemical evolution, we also conclude that, in dense PDRs, CO2 is a late-forming ice compared to water ice, and confirm a layered ice structure on dust grains, with H2O in lower layers than CO2. Regarding steady state, the PDR edge reaches chemical equilibrium at early times (≲105 yr). This time is even shorter (<104 yr) for high G0 PDRs. By contrast, inner regions reach equilibrium much later, especially low G0 PDRs, where steady state is reached at ∼106-107 yr.
AB - When studying chemistry of photodissociation regions (PDRs), time dependence becomes important as visual extinction increases, since certain chemical time-scales are comparable to the cloud lifetime. Dust temperature is also a key factor, since it significantly influences gas temperature and mobility on dust grains, determining the chemistry occurring on grain surfaces. We present a study of the dust temperature impact and time effects on the chemistry of different PDRs, using an updated version of theMeijerink PDR code and combining it with the time-dependent code Nahoon. We find the largest temperature effects in the inner regions of highG0 PDRs,where high dust temperatures favour the formation of simple oxygen-bearing molecules (especially that of O2), while the formation of complex organic molecules is much more efficient at low dust temperatures. We also find that time-dependent effects strongly depend on the PDR type, since long time-scales promote the destruction of oxygen-bearing molecules in the inner parts of low G0 PDRs, while favouring their formation and that of carbon-bearing molecules in high G0 PDRs. From the chemical evolution, we also conclude that, in dense PDRs, CO2 is a late-forming ice compared to water ice, and confirm a layered ice structure on dust grains, with H2O in lower layers than CO2. Regarding steady state, the PDR edge reaches chemical equilibrium at early times (≲105 yr). This time is even shorter (<104 yr) for high G0 PDRs. By contrast, inner regions reach equilibrium much later, especially low G0 PDRs, where steady state is reached at ∼106-107 yr.
KW - astrochemistry
KW - ISM: abundances
KW - ISM: clouds
KW - photodissociation region (PDR).
UR - http://www.scopus.com/inward/record.url?scp=85067964772&partnerID=8YFLogxK
U2 - 10.1093/mnras/stz1009
DO - 10.1093/mnras/stz1009
M3 - Article
AN - SCOPUS:85067964772
SN - 0035-8711
VL - 486
SP - 1853
EP - 1874
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -