The Three-mm Ultimate Mopra Milky Way Survey (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, much of which is organised into Giant
Molecular Clouds (GMCs) of size 10-100 pc (30-300 light years). 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 GMCs,
as mapped by their emission from the CO molecule. However, this venerable and very wide-area survey, while highly cited, is by now slightly
dated: it has limited angular resolution (8 arcmin) compared to the much higher-resolution spacecraft
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, of 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 ~0.3 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. Fig. 1: Spectacular sample map from ThrUMMS pilot 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 5 hr clock time, including
pointing and calibration. The ThrUMMS map, however, is of a single velocity component
(from –50 to –40 kms−1, rms ∼2 Kkms−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 or more recent data products, such features are much reduced (see
the Data Release Bank for the latest data products; an example
from DR6 is shown in the banner to these web pages.
For more information contact co-PIs Peter Barnes
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.What is ThrUMMS?
Motivations and Objectives
More Information