The Three-mm Ultimate Mopra Milky Way Survey (ThrUMMS)
What is ThrUMMS?
Galaxies are the basic building blocks of the Universe, and the Milky Way is our galactic home. Our position within it gives us the opportunity to understand its internal constitution and evolution in more detail than any other galaxy. To this end, many comprehensive surveys of the Milky Way's luminous matter have been undertaken over the past 50 years, using many different telescopes operating at many different wavelengths, from cm-wave radio to high-energy gamma rays. Each wavelength highlights a particular constituent of our Galaxy, including various stellar populations and different phases of the gas between the stars (called the interstellar medium, or ISM).
Most recently, such surveys have included the spectacular GLIMPSE and MIPSGAL surveys (utilising the Spitzer Space Telecope), and the Hi-GAL survey (using the Herschel Space Observatory). At the mid- and far-infrared wavelengths of these surveys, we observe mainly the agents and results of star formation, i.e. cold gas clouds and young stellar clusters. However, these continuum surveys by themselves lack the velocity information that can be obtained from observations of spectral lines, effectively giving a third dimension to our understanding of the physical processes involved. A standard spectroscopic survey is the Columbia-CfA survey of Giant Molecular Clouds, as mapped by their emission from the CO molecule.
However, this venerable survey, while highly cited, is by now somewhat dated: it has limited angular resolution (8 arcmin) compared to the much higher-resolution satellite surveys and to GASKAP, a planned survey of the atomic hydrogen (HI) phase of the ISM. Also, most previous molecular gas surveys have only used one species of the many available for study in the chemically rich GMCs. The Three-mm Ultimate Mopra Milky Way Survey is a dramatically updated version of such CO surveys which will allow us to answer fundamental questions (see below) about the formation and evolution of GMCs, the engines that drive star formation in the Milky Way and hence, Galactic evolution.
ThrUMMS will use two new techniques at Mopra1, using the MOPS digital filterbank2, to map most of the fourth quadrant (4Q) of the Galaxy simultaneously in 4 molecular species (12CO, 13CO, C18O, and CN), at ~arcminute & 0.1 km s-1 resolution and ~1.5 K km s-1 sensitivity. ThrUMMS will also provide many opportunities for complementary science with several other multi-species Mopra surveys, such as CHaMP, MALT90, HOPS, and others.
Motivations and Objectives
- To investigate several problems on the large-scale yet detailed structure, dynamics, and evolution of the Galaxy’s molecular interstellar medium (ISM).
- To create a unique resource for future users of ALMA and for general ISM studies in the Milky Way.
- We will seek a detailed understanding of the interplay between the atomic and molecular ISM, such as understanding the roles of turbulence and feedback in structure generation and star formation, by making high resolution maps over large scales using several molecular tracers that sample different physical conditions.
- This complete, high resolution survey of a virtually unexplored part of the molecular Milky Way will make a large range of spatial and density scales in the cold gas uniformly accessible to study for the first time.
Fig. 1: Spectacular sample map from pilot ThrUMMS project in Nov 2010. Top: extract from the Columbia-CfA survey (Dame et al 2001) over a 1.5°×0.5° wide region of relatively low brightness in 12CO. Bottom: same region mapped during the ThrUMMS pilot in just 5hr clock time, including pointing and calibration. The ThrUMMS map, however, is of a single velocity component (from –50 to –40 kms−1, rms ∼2 K kms−1), while the CfA map is integrated over all emission (rms ∼1 Kkms−1). Regardless, there is good correlation of the brightness scale and overall structure. These data were taken in poor atmospheric conditions, hence most of the low-level stripes are weather artifacts. In better conditions such features are much reduced.
For more information contact co-PIs and Erik Muller.
1The Mopra telescope is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.
2 The University of New South Wales Digital Filter Bank used for the observations with the Mopra telescope was provided with support from the Australian Research Council.