ThrUMMS - The Three-mm Ultimate Mopra Milky Way Survey

ThrUMMS Science Goals


ThrUMMS is designed to provide major legacy science opportunities for many years. Thus, the various ThrUMMS team members are interested in a wide variety of science projects that will make use of the ThrUMMS data. Below is a list of some of these projects.


Members of the wider astronomical community can also download and make use of ThrUMMS data for any purpose, although we ask users to please follow the Data Use Policy as outlined on the DR Bank page. Alternatively, since ThrUMMS is an open project, anyone can volunteer to join any of the existing science teams and contribute to the work of that group.

 

  • Make complete maps of all 4 species over the 4Q at 72" angular resolution, equivalent to a spatial resolution of ~1 pc at typical distances of 2-3 kpc, with ~1 K/chan rms sensitivity in the public data.

  • Obtain uniform, simultaneous information on ISM properties from large to small scales. The formation of molecular clouds, or more accurately the conversion of atomic to molecular gas, is still a matter of active study (Li & Goldsmith 2003; Goldsmith et al 2007; Vasquez-Semadeni et al 2010), as is the longevity of turbulent energy in the ISM across the various phases (Brunt 2003), and indeed, overall cloud lifetimes (Barnes et al 2010, 2011, 2018). We are working on comprehensive maps of the physical conditions (i.e., full 3D cubes of τ, Tex, NCO) across the survey area, using a plane-parallel calculation with the 12CO/13CO line ratio to solve for both Tex and τ in the radiative transfer equation (Hernandez et al 2011; Barnes et al 2018).

  • Comparison with GASKAP will also allow us to resolve the distance ambiguity for GMCs within the 4Q, a fundamental problem for Galactic structure and astrophysics. Together, ThrUMMS and GASKAP will directly lead to a highly-resolved (~1 pc) calculation of the large-scale surface mass density of the Milky Way’s molecular clouds and atomic gas, and in a more uniform and consistent way across more of the Galaxy than even the GRS (Jackson et al 2006) and VGPS (Stil et al 2006) have allowed.

  • Compile the CO-derived properties of the >10,000 GMC-clumps (based on SCIMES segmentation) we are likely to detect, such as the size, mass, density, temperature, velocity field, and linewidth/degree of turbulence of each cloud. We will use maps of excitation temperature and optical depth as inputs into modelling the data and deriving physical conditions in these IRDCs and dense clumps.

  • Identify all dense clouds with potentially measurable magnetic (B) field strengths. The role of B fields in star formation, in particular their strength as a function of density, is still being widely studied (Crutcher 2012; Mouschovias & Tassis 2009). Measuring the CN molecule's Zeeman effect, and hence B field strength, in dense clouds is critical to this debate, but is feasible only where CN is quite bright and has been done in only ∼12 (mostly northern) objects (Falgarone et al 2008). ThrUMMS will easily find all CN clouds in the 4Q bright enough to have their Zeeman effect measured at ALMA, perhaps 40 such clouds.