Western Kentucky University

Dust Infrared Emission in an H2-Forming, Perseus-Arm Cloud

Institution

Western Kentucky University

Abstract

The birth of a star is a heavily studied and complex process. Much has been done in the past few decades to outline the steps involved, but there are still crucial gaps in our understanding. An essential step in the formation of new stars is the condensation of ambient neutral atomic hydrogen (HI) into the molecular phase (H2). It is well known that molecular clouds collapse to form the precursors to stars, but less understood is how molecular clouds themselves begin to form. The process is difficult to study because the transition from HI to H2 is not very energetic and is thus difficult to detect. This limits direct observations. We studied this process indirectly, by examining the interstellar dust within these H2-forming clouds. Although dust absorbs and scatters visible light, it emits infrared heat radiation that we could observe. We used data from NASA's IRAS and Spitzer Space Telescopes to investigate a target cloud in the Perseus spiral arm in which the HI-to-H2 transition appeared to be underway. We have sampled the dust spectral energy distribution at many positions on and off this cloud in all IRAS and Spitzer wavelengths. We interpreted these data by comparing them to data generated by the DustEM computer model, which simulates dust emission according to certain assumptions. We used this information to constrain the composition and evolutionary status of the dust grains in this H2- forming cloud and others like it.

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Dust Infrared Emission in an H2-Forming, Perseus-Arm Cloud

The birth of a star is a heavily studied and complex process. Much has been done in the past few decades to outline the steps involved, but there are still crucial gaps in our understanding. An essential step in the formation of new stars is the condensation of ambient neutral atomic hydrogen (HI) into the molecular phase (H2). It is well known that molecular clouds collapse to form the precursors to stars, but less understood is how molecular clouds themselves begin to form. The process is difficult to study because the transition from HI to H2 is not very energetic and is thus difficult to detect. This limits direct observations. We studied this process indirectly, by examining the interstellar dust within these H2-forming clouds. Although dust absorbs and scatters visible light, it emits infrared heat radiation that we could observe. We used data from NASA's IRAS and Spitzer Space Telescopes to investigate a target cloud in the Perseus spiral arm in which the HI-to-H2 transition appeared to be underway. We have sampled the dust spectral energy distribution at many positions on and off this cloud in all IRAS and Spitzer wavelengths. We interpreted these data by comparing them to data generated by the DustEM computer model, which simulates dust emission according to certain assumptions. We used this information to constrain the composition and evolutionary status of the dust grains in this H2- forming cloud and others like it.