TY - JOUR
T1 - Rotationally warm molecular hydrogen in the orion bar
AU - Shaw, Gargi
AU - Ferland, G. J.
AU - Henney, W. J.
AU - Stancil, P. C.
AU - Abel, N. P.
AU - Pellegrini, E. W.
AU - Baldwin, J. A.
AU - Van Hoof, P. A.M.
PY - 2009
Y1 - 2009
N2 - The Orion Bar is one of the nearest and best-studied photodissociation or photon-dominated regions (PDRs). Observations reveal the presence of H 2 lines from vibrationally or rotationally excited upper levels that suggest warm gas temperatures (400-700 K). However, standard models of PDRs are unable to reproduce such warm rotational temperatures. In this paper, we attempt to explain these observations with new comprehensive models which extend from the H+ region through the Bar and include the magnetic field in the equation of state. We adopt the model parameters from our previous paper which successfully reproduced a wide variety of spectral observations across the Bar. In this model, the local cosmic ray density is enhanced above the galactic background, as is the magnetic field, and which increases the cosmic ray heating elevating the temperature in the molecular region. The pressure is further enhanced above the gas pressure in the H+ region by the momentum transferred from the absorbed starlight. Here, we investigate whether the observed H2 lines can be reproduced with standard assumptions concerning the grain photoelectric emission. We also explore the effects due to the inclusion of recently computed H2 + H2, H2 + H, and H2 + He collisional rate coefficients.
AB - The Orion Bar is one of the nearest and best-studied photodissociation or photon-dominated regions (PDRs). Observations reveal the presence of H 2 lines from vibrationally or rotationally excited upper levels that suggest warm gas temperatures (400-700 K). However, standard models of PDRs are unable to reproduce such warm rotational temperatures. In this paper, we attempt to explain these observations with new comprehensive models which extend from the H+ region through the Bar and include the magnetic field in the equation of state. We adopt the model parameters from our previous paper which successfully reproduced a wide variety of spectral observations across the Bar. In this model, the local cosmic ray density is enhanced above the galactic background, as is the magnetic field, and which increases the cosmic ray heating elevating the temperature in the molecular region. The pressure is further enhanced above the gas pressure in the H+ region by the momentum transferred from the absorbed starlight. Here, we investigate whether the observed H2 lines can be reproduced with standard assumptions concerning the grain photoelectric emission. We also explore the effects due to the inclusion of recently computed H2 + H2, H2 + H, and H2 + He collisional rate coefficients.
KW - ISM: individual (Orion Bar)
KW - ISM: molecules
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U2 - 10.1088/0004-637X/701/1/677
DO - 10.1088/0004-637X/701/1/677
M3 - Article
AN - SCOPUS:70549109221
SN - 0004-637X
VL - 701
SP - 677
EP - 685
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -