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The Millimetre White Paper: a strategy for high-frequency radio astronomy in Australia
Contributors to this document
Peter Barnes (U Sydney), Kate Brooks (ATNF), Michael Burton (UNSW), Maria Cunningham (UNSW), John Dickey (U Tasmania), Phil Edwards (ISAS), Ron Ekers (ATNF), Yasuo Fukui (U Nagoya), Annie Hughes (Swinburne U), Ilana Klamer (U Sydney / ATNF), Vincent Minier (CEA Saclay), Erik Mueller (ATNF), Juergen Ott (ATNF), Bob Sault (ATNF), Mark Thompson (U Hertfordshire), Andrew Walsh (UNSW), Tony Wong (UNSW / ATNF). Edited by Michael Burton.

Overview
This document describes a strategy for high frequency radio astronomy in Australia. It has resulted from process of public consultation in the Australian astronomical community, together with some input and advice from colleagues overseas. It has been produced through submissions made via a wiki page established at mmscience.atnf.csiro.au. The process also involved presentations at three meetings and workshops: Millimetre Astronomy Science Meeting: the 2005 Season Held at UNSW on 30/11/05, presenting results from the 2005 millimetre-wave observing season using Australia's radio telescopes. The first draft of this report was presented there. Australia Telescope Users Committee Held at ATNF, Epping on 01/12/05, during the public session of this meeting. The first draft was presented to ATUC. Future Directions for Southern Hemisphere Millimetre Wave Astronomy A workshop held at the Sydney Harbour Institute for Marine Studies (SHIMS), at Chowder Bay in Sydney on 30-31/03/06. The second draft of the white paper was presented there. The workshop examined the status of current facilities and their future science programs, both in Australia and elsewhere. An international perspective on the future role for Australia's millimetre wave facilities was also provided by an number of overseas visitors who attended. The meeting finished with a discussion on future priorities for millimetre astronomy in Australia. This final document was presented to the Australia Telescope Users Committee at its meeting on June 5-6, 2006.

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Contents
Future Priorities for Millimetre-Wave Astronomy in Australia for the Next Decade Vision Current developments Modest future developments Future priorities and strategies Introduction ­ Goals of the White Paper Overview of Current Capabilities Stocktake of current facilities Demand for ATCA and Mopra Science Drivers for Millimetre Wave Astronomy Introduction The evolution of circumstellar disks around young stellar objects The search for biogenic molecules The evolutionary sequence for massive star formation Turbulence and star formation Star formation in the Magellanic system The star formation history of the Universe The cosmic microwave background radiation Unique objects: SN1987A, The central molecular zone, Sgr A* Capabilities and needs Facility Developments within Australia Receivers ATCA 3mm bandwidth and polarization upgrades Spectrometers Other telescope upgrades Operations and Support Operations at Mopra and ATCA Flexible scheduling at ATCA Millimetre calibration User support Facilities in the Global Context A brief history of millimetre astronomy in Australia What Australia can offer Synergies with other telescopes: Chilean, Antarctic and Space & Airborne telescopes, SKA developments An International Perspective on Opportunities in the field for Australia Galactic star formation up to the high-mass regime The JCMT legacy survey program and the context for southern mm-wave telescopes VSOP­2 and the need for the millimetre Submillimetre surveys of the southern galactic plane: NANTEN2 and the need for mm Appendices: Program for Millimetre Astronomy Science Meeting, UNSW, 30/11/05 Program for Future Directions for Southern Hemisphere Millimetre Wave Astronomy workshop, SHIMS, Chowder Bay, Sydney 30-31/03/06

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Future Priorities for Millimetre Wave Astronomy in Australia for the Next Decade (2006-2016)
Vision
Millimetre-wave astronomy will provide the primary focus for developments in radio astronomy for at least the next decade, offering the promise of furthering our understanding of the formation of planets, stars and galaxies across the universe. In Australia, using our current facilities and their new mm-wave instrumentation, we will be able to make significant contributions to these fields of study. This includes conducting effective searches for new molecules in interstellar space, including those which might provide the seeds for life, the unveiling of star formation across the Galaxy, and a comparative examination of the environment in which stars form in nearby galaxies to that in the Milky Way, as well as in the distant universe. When completed around 2012, ALMA will become the principal instrument used by the international radio astronomy community. Its large collecting area and comprehensive baseline coverage will provide an ability to image in the millimetre bands with far higher sensitivity and spatial resolution than has been achieved before. ALMA will not provide, however, a comprehensive view of the millimetre-wave universe. It must work with other facilities that have differing capabilities in order to obtain the full picture that is available. This provides an important opportunity for Australia, to meet this need. Wide-field imaging, undertaken with wide bandpasses, and access to the long-wavelength end of the millimetre spectrum, are domains which ALMA will not serve well. Such capabilities can be provided by Australia's millimetre facilities if they are maintained with leading-edge technologies over the next decade. They would serve to keep Australia's facilities internationally competitive for a relatively modest investment, in comparison to that being made in ALMA and associated facilities in Chile. The ATCA, fitted out with phased focal plane arrays that could operate across bands at 3 mm and longward, would be a uniquely powerful facility that would serve Australia's science community well in the ALMAera. Supported for open time allocation, it would continue to attract the best from the rest of the world to Australia to use it. It would maintain the vitality and reputation of our radioscience community, and provide us with access to the best facilities elsewhere through the collaborations this would engender. It would also serve to make Australia a provider of focal plane array technology, together with the commercial opportunities that offers. Wide field capability is also a route that has been successfully demonstrated at the Anglo Australian Observatory. The 4m AAT has remained one of the most productive optical/IR telescopes in the world despite the operation of 8m class telescopes overseas for the past decade. It managed this through the development of wide-field spectroscopic instrumentation, enabling extensive sky surveys to be undertaken with the telescope. Providing such a capability has proved to be financially beyond the ability of the 8m telescopes to match, so maintaining the AAT's own competitiveness. 3


Our challenge is to make this vision happen for the radio community too, while at the same time continuing along the path towards the SKA, the international radio telescope that will follow ALMA. We need to keep open the doors to opportunities in the millimetre bands, while also working towards opening news doors in the centimetre bands. The challenge can be met by following a staged development path that takes advantage of synergies with the technologies needed for the SKA, as well as the needs of the international radio community. It involves completing projects currently underway, undertaking a few modest enhancements which will improve the efficiency of operation of our facilities, and redeploying resources to ensure that the path towards developing phased focal plane arrays at millimetre wavelengths is followed. We outline this approach below.

Current Developments
There are four current instrumentation projects underway that should be completed. The 8 GHz digital filter bank (MOPS) for the Mopra Telescope. This will provide a uniquely powerful instrument for line surveys in the 3 and 12 mm bands using existing receivers. The 2 GHz backend (CABB) for the ATCA. This provides greatly increased coverage for spectral line studies and increased sensitivity for continuum imaging in both millimetre and centimetre wavebands. The 7 mm upgrade for both the ATCA and Mopra, with the receiver band extending to at least 49 GHz. Used with either the CABB or the MOPS, this provides a correspondingly powerful instrument for line and continuum studies in this band. The 12 mm single-element receiver designed for Parkes, with the project also addressing some of the performance issues related to the future development of focal plane arrays operating at 12 mm for that telescope.

Modest Future Developments
There are several smaller projects which should be continued under ongoing maintenance and development programs of the national facility, and in the broader community. The study regarding the use of water vapour radiometers for phase correction at 3 mm for the ATCA should be completed and recommendations regarding its suitability made. This might be conducted, for instance, as a student project. Real time phase correction offers the promise of 3 km baselines at 3 mm, yielding sub-arcsecond resolution imaging. Noise diode calibrators for use at 3 mm should be installed on the receivers of the ATCA. This would not only improve observing efficiency and the accuracy of flux calibration, but would make possible polarization measurements in the band as well. The net of calibrators available for 3 mm observation with the ATCA needs to be expanded, in order to improve phase correction by using calibrators nearby to all objects under study, and to facilitate fast switching between source and calibrator.

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Automated tilting of sub-reflectors as the elevation angle varies would improve telescope efficiency at millimetre wavelengths, in particular the beam profiles. It is a cost effective (though somewhat inferior) alternative to actively controlling antennae shape. Site testing on the Antarctica plateau for THz frequency astronomy should proceed, at South Pole, Dome C, Dome A and other high plateau sites, as well as including comparative measurements from the Atacama plateau, all conducted with identical instrumentation. Extending the frequency coverage of all ATCA dishes at 3 mm to the same as available at Mopra (i.e. 77­116 GHz) is desirable and an eminently feasible project. It would facilitate studies of the molecular environment in nearby galaxies, where the 115 GHz transition of CO may often be the only molecular line bright enough to be readily observable. However, this is a project that cannot be started until the current mm-wave projects (i.e. MOPS, CABB, 7 mm, 12 mm-Parkes) are completed. At this stage this project should be prioritised, taking into account the then projected timeline for 3 mm operation with ALMA, and the outcomes of the focal plane array engineering studies discussed below. Alternative sources should also be explored for funding an extension of the frequency coverage at 3 mm.

Future Priorities and Strategies
The development of phased focal plane arrays (pFPA) for millimetre-wave astronomy would have far reaching consequences. Provision of such arrays with >100 elements on the ATCA would guarantee its competitiveness in the ALMA-era, enabling wide-field imaging that could not readily be undertaken using ALMA. It would also position Australia as a supplier of such devices to observatories elsewhere. pFPAs would, for instance, be a powerful addition to the total power antennae planned for the ALMA-ACA, where they could provide essential zero spacing information needed by the main array. We believe the ATNF should devote resources to investigating how such arrays could be built, and estimating the costs involved. Such an effort would also have synergies with the need to develop FPAs for use at centimetre wavelengths with the SKA. While it would be desirable, we rate as a lower priority, in relation to development, the broad-banding of current operations at 3 mm in order to make measurement of the entire 40 GHz wide window at a single setting. The MOPS possible to observe the entire 3 mm band at Mopra with five settings, partially capability needed here. that of FPA possible the will make it meeting the

We propose that resources be deployed to develop a technology roadmap for FPA studies that includes the needs for mm-band, and well as cm-band, devices. Initially, we recommend studying the merits of two systems: A 4- or 7-element 3 mm wavelength multibeam (i.e. multiple feed horns) for the Mopra telescope. This is the maximum size array that could be built without serious beam efficiency losses due to the shaping of the antenna. Larger arrays would either require it to be re-shaped, or a pFPA installed. However, even such a modest system would greatly improve the ability to undertake mapping projects. 5


A pFPA at 12 mm for the Parkes telescope. Given that this would be installed at prime focus, this is an easier option than building a pFPA for ATCA or Mopra (the number of elements goes as (f/D)2, giving a gain of ~25 for Parkes). The size of the pFPA would also be considerably smaller than a corresponding device working at 21cm, as for instance needed by SKA, and so may prove easier to construct? A prototype then needs to be built. The study should also examine the challenges and needs to produce elements, first working at 12 mm on Parkes, and then working at 3-12 and Mopra. It should also consider the prospects for extending these operation beyond this, to sub-mm wavelengths (e.g. for use with antennae) and to THz frequencies (e.g. for use in Antarctica). a pFPA with ~100 mm with the ATCA to higher frequency ALMA total power

The study should result in an options paper so that decisions regarding future developments to the mm-wave capability can be quantitatively assessed. The study should also consider what aspects might be outsourced, and what needs to be developed in-house at CSIRO. Additional resources should be identified for funding such developments beyond those available from the CSIRO. This could include university partners, through, for instance, the ARC-LIEF scheme, and international partners, perhaps as the provider of instrumentation for other observatories. By preparing such an engineering white paper on pFPAs, it will allow us to properly assess the feasibility of, and options for, future developments for mm-wave systems in Australia. It will allow a path to be mapped out for the next decade that will allow the ATCA to remain an internationally competitive facility, and to continue Australia's influential role in the radio astronomy community worldwide.

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Introduction ­ Goals of the White Paper
Australian radio astronomy has a long history of accomplishment. Recent high-frequency upgrades to the ATNF facilities promise to usher in a new era of scientific productivity. We seek to establish a broad strategy for maintaining and extending Australia's capabilities in high-frequency radio astronomy. We will lay out some ideas for high-impact science, discuss possibilities for future upgrades, and identify resources needed to make these visions a reality. For purposes of this document we focus on capabilities in the 15­115 GHz range, though related developments at lower and higher frequencies are important to bear in mind as well. A key component of this strategy is international collaboration, for three reasons. First, Australian experience in this field is still limited. We have much to learn from colleagues overseas who have operated high-frequency radio facilities for several decades. Second, a new generation of telescopes is emerging in northern Chile, at sites higher and drier than any available in Australia. We need to be complementing rather than competing with these facilities. Finally, since a large fraction of our telescope users are from overseas, providing an essential boost to our community's vitality, we need to be responsive to their wishes and needs as well. This "white paper" has been compiled through the contributions of those listed on the cover page, making use of a wiki. It was divided into several themes, each with a separate wiki page and an organiser who coordinated the contributions to the themes. The first draft of the white paper was presented at a meeting on 30/11/05 at UNSW on science results from Australia's millimetre facilities in 2005, followed by a presentation the following day to the Australia Telescope User Committee. The second draft developed through responses to that document, and was presented at a workshop on future directions for southern hemisphere millimetre wave astronomy, held in Sydney on 30-31/03/06. Further input to the document was sought at the workshop, in particular an international perspective on the future use and role of Australia's facilities, and on the prioritisation of future developments. This final document was presented to the Australia Telescope User Committee at its June 2006 meeting.

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Overview of Current Capabilities
Stocktake of Current Facilities
Currently, millimetre telescopes in Australia fit into two wavelength regimes: 12 mm facilities, including the ATCA, Mopra, Tidbinbilla and Parkes, 3 mm facilities, including the ATCA and Mopra. A summary comparison of these facilities and their capabilities is given below.

12 mm Facilities
ATCA Frequency Range (GHz) Wavelength Range (mm) Diameter (m) Primary Beam (arcsec) Maximum Synthesised Beam (arcsec) Typical System Temperature (K) Maximum Bandwidth (MHz) Maximum number of Channels Continuum Sensitivity (1 sec) (mJy/beam) Line Sensitivity (10min, 10km/s) (mJy/beam) 16 ­ 25 Mopra 16 ­ 25 Tidbinbilla 19.9 ­ 20.5 21.8 ­ 22.4 23.6 ­ 24.2 14.8 13.5 12.6 70 48 ­ Parkes 21 ­ 24 Tid 34m 31.8 ­ 32.3

19 ­ 12

19 ­ 12

14 ­ 12.5

9.4 ­ 9.3

6 x 22 175 ­ 112 0.5

22 120 ­

45 80 ­

34 61 ­

30 ­ 38 2 x 128 1024 5

45 8000 8192 ­

50 64 4096 9

140 128 8192 590

30 64 2048 160

12

24

3.4

320

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3 mm Facilities
Frequency range (GHz) Wavelength range (mm) Diameter (m) Primary beam FWHM (") Maximum synthesised beam (") Typical system temperature (K) Maximum bandwidth (MHz) Maximum number of channels Continuum sensitivity (1s) (mJy/beam) Line sensitivity (10min, 10 km/s) (mJy/beam) ATCA 12 mm Facility Currently works with all 6 antennas over a broad characteristics in the mm-bands. High spectral astronomy. 128 MHz bandwidth is acceptabl translates to 1700 km/s. High spatial resolution is CA06, which has the longest baselines. ATCA 85 ­ 105 3.5 ­ 2.9 5 x 22 35 2 310 ­ 440 2 x 128 1024 100 24 Mopra 77 ­ 116 3.9 ­ 2.6 22 37 ­ 33 ­ 140 ­ 290 8000 8192 ­ 60 ­ 155

frequency range. Highest signal to noise resolution is excellent for Galactic line e for extragalactic work, as it typically often tempered by poor phase stability for

Mopra 12 mm Facility It has not so far been used much outside of water maser VLBI due to the narrow frequency range available. However, the new receiver (installed in March 2006) has broader frequency coverage. Taken with the wide bandwidth (8 GHz) correlator, this will make Mopra a sensitive and versatile line detector in this waveband. Tidbinbilla 12+7 mm Facility Three narrow bands are available, which include the important water maser as well as ammonia lines. Excellent line sensitivity means it is well suited to Galactic line work, although limited bandwidth makes it difficult for extragalactic work. The large dish diameter makes it an excellent complement to the ATCA when zero UV spacing observations are needed. Currently the telescope only works in a pointed mode, but on-the-fly mapping will be available in the near-future. Only a small fraction of the time is available to astronomers, however. The Tidbinbilla 34m also provides a facility for 7 mm work, though only in the narrow frequency range from 31.8-32.3 GHz. A number of molecular lines are accessible in this range (these include C6H, H2COH+, HCC13CCN, HC5N and HC9N). Such species are typically found in hot molecular cores, and might be used to provide an internal clock measuring the progress of star formation within them. Parkes 12 mm Facility High system temperatures lead to poor sensitivity in this band, relative to other telescopes. Broader frequency coverage than Tidbinbilla may make it useful for lines that Tidbinbilla cannot see. The inner 45 metres of the dish is used for 12 mm observations. An improved receiver that illuminates 55m of the dish will be installed in 2007. 9


ATCA 3 mm Facility Five antennas can be used to observe with the ATCA at 3 mm over a broad frequency range. Currently two frequencies can be observed, as long as they are within 2.7 GHz of each other. However, available correlator configurations limit the maximum bandwidth to 128 MHz. This is not good for extragalactic work, but works well for Galactic line work. With two frequency windows, 200 MHz bandwidth is currently available for continuum measurements, but the sensitivity will be greatly enhanced when the 2 GHz backend is available. Mopra 3 mm Facility Mopra has recently been upgraded so that it will now work over the frequency range 77-116 GHz. The new MOPS correlator will also allow observations across an 8 GHz bandwidth. This is excellent for Galactic observations of more than one line, as well as for extragalactic line work. On-the-fly mapping has recently been introduced and works well.

Demand for ATCA and Mopra
Demand for Mopra 3 mm time has increased dramatically over the past 5 years, from 9 proposals per year in 2002 and 2003 to 38 in 2006, reflecting growing interest from the astronomy community, both within Australia and internationally.

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Demand for ATCA time at 3 mm has been high since completed. However, the number of hours requested in the number of proposals from both Australian and reflects that most millimetre observations occur during

2004, when the 5-element system was fell by 40% in 2006, reflecting a drop overseas PIs. The saw tooth demand the winter months.

Demand for ATCA time at 12 mm was highest in the winter terms of 2004 and 2005, but dropped in 2006.

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Science Drivers for Millimetre Wave Astronomy
Introduction
Millimetre-wave astronomy is a young field in comparison with optical and even radio astronomy, and so readily provides new opportunities for exploring the cosmos and furthering understanding of many fundamental phenomena. The millimetre regime is rich in observational signatures. Line densities are highest in the mm-bands for many categories of source, with the corresponding continuum fluxes also peaking at the short-wave end of the band. Yet the spectrum has remained little studied to date as observation has been impeded by the atmosphere and by immature detection technologies. Both these adversities can now be addressed through technology development, and this is driving the rapid growth of millimetre facilities world-wide in the twenty first century. The challenge of opening new windows for viewing the cosmos through is a particular attraction of the field, providing opportunities across broad ranges of study. It has also been the driving rationale behind the development of ALMA, the world's major ground-based astronomical project of the coming decade. The science potential has also spurred construction of a range of other mm-wave facilities, both in Australia and overseas. These will provide a focus for initiating some science that will later be tackled in depth by ALMA, but they will also provide complementary capability to ALMA, in a similar way that a suite of 1-4m class optical/IR telescopes are needed to support the science tackled by the 8m facilities. Millimetre-wave science can be divided into four broad arenas, aimed at studying formation processes and events throughout the Universe. These are to study when: planets are young, measuring the millimetre continuum emission from cold dust, to probe the protoplanetary environment as the process of planetary construction begins, stars are young, probing the rich chemical environment within the cores of protostellar clouds, and the organic chemistry driven by the incipient protostar, as evident through the plethora of molecular lines emitted in the millimetre bands, galaxies were young, probing the nature of protogalaxies in the first billion years of the universe, through the red-shifted emission from lines and continuum, now peaking in the (sub-)millimetre regime, the Universe was young, measuring ripples in the cosmic microwave background radiation emanating from the era of when hydrogen first formed, 300,000 years after the Big Bang, whose thermal spectrum now peaks in the millimetre regime. These four arenas cover some of the most challenging subjects of investigation in astronomy today. Our particular challenge in Australia is to find a way to ensure that we play an active role in their pursuit, and do not miss out on the opportunities that will arise as the field grows internationally. We can do this by ensuring that the science that Australia's millimetre-wave facilities conduct is both focussed on important questions in the field and is also designed to be complementary to the capabilities that the international facilities will provide. In the pages ahead we outline some of the major science areas that can be tackled from Australia. 12


From this list we are then able to determine what capabilities are needed to ensure that this program can be achieved. Other nations will be committing extensive resources to the field, and so international collaboration is the best way to leverage the geographic advantage of our facilities.

The Evolution of Circumstellar Disks around Young Stellar Objects: from nebulae to proto-planetary disks
Detection and study of planetary systems and proto-planetary disks around nearby stars is an exciting and rapidly growing area of research. These can be studied in various ways across the spectrum from optical to radio wavelengths. The coming decade will certainly lead to advances in all of them. Over the past ten years this branch of astrophysics has developed from a situation of hardly any data, to the present startling diversity of planetary systems and circumstellar disks. The physical, chemical, and ultimately biological questions raised by this rich new observational field are attracting wide theoretical interest. In the next few years the subject will mature, with observational advances guiding theoretical efforts to establish new paradigms for the formation and evolution of planetary systems. There are several niche topics where Australian telescopes can have a large impact. One example is contributing to the Spitzer space infrared telescope legacy program "from molecular cores to planet-forming disks" (or c2d). This involved mapping five nearby molecular clouds and ~80 isolated dense cores from 3.6 to 70 µm, providing information on the location of energy sources down to 5 Jupiter-mass substellar objects, young stellar objects, and disks with a few earth-masses. To complement this data, continuum maps at 1.2 mm have been obtained from the SEST and IRAM telescopes, as well as line maps for the northern sample in the N2H+ and CS molecules from the FCRAO telescope. The Mopra telescope is now undertaking corresponding line work for the southern cores. It is only with such a large sample as the c2d program has that it will be possible to study the full range of core evolution, from chemically young starless cores (these are strong in CS, weak in N2H+, and weak in mm-continuum emission), to evolved starless cores close to forming a protostar (which have a high column density in mm dust, and are strong in N2H+), to protostellar cores (which can exhibit CS outflows, strong mm dust emission, N2H+ and/or CS emission, depending on their age and luminosity). As a bonus, the new 8 GHz Mopra spectrometer will enable a number of other molecular tracers to be sampled at the same time, a project not feasible at any other facility. Determining the physical conditions of starless cores is critical for these studies as these define the initial conditions of star formation. The initial conditions in turn define the collapse dynamics, the likely mass of the star, and the evolutionary timescales. Another aspect of this problem is the origin of binarity in stars. Most stars in the sky are in fact not single, but part of a multiple (usually binary) system. For low-mass stars, the main physical characteristic that seems to determine whether a protostellar core will produce a single star or a binary appears to be how the gas sheds its angular momentum. Why some systems have high specific angular momentum (the binaries) and why some shed enough angular momentum to become single stars remains a mystery. To make progress it will be necessary to measure the properties of the disks that form. 13


The molecular gas in disks can be detected through observations in the millimetre regime. The recent upgrade of the ATCA to operate at 3 mm wavelength has made it the only millimetre interferometer in the southern hemisphere and one of the most sensitive instruments of its type in the world. It will play a major role in the next five years in making high-resolution observations of the molecular gas in disks in nearby low-mass star forming regions. Information on the molecular gas content for disks of different ages can be used to determine temperatures, densities and chemical compositions, and from these used to infer the evolution of the disk. Our knowledge of how planetary systems form from disks is poor and such observations will constitute a major advance and provide constraints for theoretical modelling. Similar observations are possible with northern millimetre interferometers, but the ATCA has an important role to play in the Southern Hemisphere in undertaking the first such observations, for later follow-up by ALMA in Chile. Habitable planetary systems are not likely to occur around high-mass stars, as they have lifetimes of the order of millions of years, rather than billions of years for stars like the Sun. How these high-mass stars form remains very much an open question. Once a star reaches a mass approximately eight times greater than the Sun, the pressure from the intense radiation it produces is sufficient to halt the further accretion of material. However, many such stars with masses are observed in the Galaxy, so there must be some means to create them. One possibility is that they form through coalescence, alternatively accretion may proceed through a thick or flared disk. To date, few disks have been detected around high-mass stars and their detection and study at radio and millimetre wavelengths is another area where Australia can reasonably expect