Probing CO-dark Gas within the Planck Galactic Cold Clumps

Project: Research project

Project Details


The Planck Catalogue of Galactic Cold Clumps (PGCC) has identified the coldest regions of interstellar dust across the entire sky based on submillimeter emission. These sources range from relatively diffuse cold clouds to pre-stellar cores embedded in giant molecular clouds. In recent years, theoretical and observational evidence has shown that there exists a component of the cold molecular ISM that is "CO-dark" - that is, it contains very little carbon monoxide, the most common tracer of molecular hydrogen, and thus is hidden and unaccounted for in our measurements of the molecular content of the ISM. The PGCC represents an excellent test bed to probe for this CO-dark gas. To do so, we can use the high-resolution UV absorption line capabilities of the STIS instrument to probe for CO at higher sensitivities than CO emission line surveys. Furthermore, we can independently measure both the molecular hydrogen and total hydrogen content, which have been shown to correlate well with Cl I and O I absorption, respectively. As part of a previous archival survey, we identified existing STIS sightlines in the sky vicinity of PGCC objects, and found that a surprisingly small number of these sightlines displayed strong CO absorption. This general lack of CO absorption directly indicates the presence of CO-dark gas near these cold dust emission sources. However, our archival study found no high-resolution far-UV STIS spectra of any stars that lie directly behind a PGCC source. We now propose to observe seven sightlines that probe the central cores of these regions, allowing us to better characterize the prevalence and nature of CO-dark gas in these sources.
Effective start/end date6/1/185/31/21


  • Space Telescope Science Institute (HST-GO- 15104.001-A/NAS5-26555 // HST-GO- 15104.001-A/NAS5-26555)
  • National Aeronautics and Space Administration (HST-GO- 15104.001-A/NAS5-26555 // HST-GO- 15104.001-A/NAS5-26555)


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