The survey speed of ASKAP makes it a prime instrument with which to survey
the HI universe, enabling it to carry out both wide surveys of the entire sky,
as well as deep surveys covering cosmologically representative volumes. Here,
the use of ASKAP to study deep HI fields is discussed as proposed by the Deep
Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP science survey
project anticipates observing in excess of 10^5 sources out to redshift z~0.4.
Key science goals include: Omega_HI and its evolution, the cosmic web as traced
by distributions such as the HI mass function and the 2pt correlation function,
and the formation and evolution of galaxies. Science returns are maximised by
targeting the GAMA survey regions, enabling the HI content of galaxies to be
studied and understood in full context with all the major galactic constituents
over the past 4 Gyr.Comment: Panoramic Radio Astronomy conference, Groningen, The Netherlands;
  2009 June 2-

Meyer, Martin

English

arXiv

The survey speed of ASKAP makes it a prime instrument with which to survey the HI universe,
enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cosmologically
representative volumes. Here, the use of ASKAP to study deep HI fields is discussed
as proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey.

Meyer, Martin,

University of Groningen Digital Archive

Exploring the HI Universe with ASKAP

The survey speed of ASKAP makes it a prime instrument with which to survey the HI universe, enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cosmologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussed as proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey

ARTS repository - University of Groningen

   University of GroningenExploring the HI Universe with ASKAPMeyer, MartinPublished in:EPRINTS-BOOK-TITLEIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Meyer, M. (2009). Exploring the HI Universe with ASKAP. In EPRINTS-BOOK-TITLE University ofGroningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 09-09-2023Exploring the HI Universe with ASKAPMartin Meyer∗International Centre for Radio Astronomy ResearchM468, The University of Western Australia35 Stirling Highway, Crawley 6009, AustraliaE-mail: martin.meyer@icrar.orgThe DINGO teamhttp://www.physics.uwa.edu.au/∼mmeyer/dingoThe survey speed of ASKAP makes it a prime instrument with which to survey the HI universe,enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cos-mologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussedas proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP sci-ence survey project anticipates observing in excess of 105 sources out to redshift z ∼ 0.4. Keyscience goals include: ΩHI and its evolution, the cosmic web as traced by distributions such as theHI mass function and the 2pt correlation function, and the formation and evolution of galaxies.Science returns are maximised by targeting the GAMA survey regions, enabling the HI content ofgalaxies to be studied and understood in full context with all the major galactic constituents overthe past 4 Gyr.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/arXiv:0912.2167v1  [astro-ph.CO]  11 Dec 2009DINGO Martin Meyer1. IntroductionUnderstanding how galaxies form and evolve is one of the key astrophysical problems of the 21stcentury. Recent observations of galaxies, supernovae, and the Cosmic Microwave Backgroundhave refined measurements of key cosmological parameters and simulations have accurately mod-elled how dark matter halos collapse from the miniscule density perturbations carried over fromthe inflationary era. But understanding how baryons collapse into these potential wells and ulti-mately form stars, how black holes are formed, how the baryons interact with the dark matter, whatthe balance is between accretion and outflow, heating and cooling, are problems which require adeep understanding of physics on an immense range of spatial scales and particle densities. Theseproblems remain largely unsolved.One of the keys to a deeper understanding is to observe and model the gaseous component ofthe Universe. Baryons are believed to have existed entirely in gaseous form before the epoch ofgalaxy formation, and it is by the continual collapse of this gas into the filamentary structures ofthe cosmic web, its accretion into the deepest potential wells, the creation of cool gaseous disksand their ultimate collapse into dense molecular clouds, that galaxies are able to form stars. Theon-going feedback between gas and stars, and the governing role of the host dark matter potentials,continue to determine the evolution of galaxies today. To date, our ability to observe the gaseouscontent of the universe, and hence to explain the manner in which these processes have occurred, isextremely limited. Observations have largely been restricted to small samples of gas in emission inthe local universe, or to sparse samples of absorption line systems at higher redshifts, and the highlevel of uncertainty inherent in interpreting such observations.2. DINGO and ASKAPThe Australian SKA Pathfinder telescope (ASKAP) [1] has been designed as a survey instrumentand is particularly well-suited to the search for 21cm neutral hydrogen emission. Its large field ofview (30 deg2), in combination with its collecting area (4072 m2) and system temperature (50K)give it a fast survey speed, enabling the telescope to go both wide and deep in a comparativelyshort period of time. Its wide 300 MHz instantaneous bandwidth similarly facilitates surveys ofcosmologically representative volumes in HI.Where WALLABY will perform a shallow survey of the southern sky, DINGO aims to providea legacy deep dataset for HI emission out to z ∼ 0.4. To enable multiwavelength studies, DINGOwill target the GAMA survey areas [2]. GAMA is composed of several imaging and spectroscopicsurveys using the world’s pre-eminent facilities, spanning all wavelengths from the ultraviolet tothe far infrared (GALEX, VST, VISTA, UKIRT, WISE, Herschel-ATLAS), in addition to 250k AAΩspectra in key overlap regions. A tiered HI survey strategy is proposed covering regions 150 deg2(500 hours per pointing, 0.15 < z < 0.29) and 60 deg2 (2500 hours per pointing, 0.1 < z < 0.43) tomeet the science goals described in the following section.DINGO is a major SKA pathfinder experiment and will provide an ideal dataset for SKA plan-ning. This will be acheived scientifically through its study of the evolving HI universe, and tech-nologically through the use of ASKAP’s phased-array feeds for extended integrations.2DINGO Martin MeyerFigure 1: Simulated spatial distribution of galaxies in a 2500 hr, 30 deg2 ASKAP pointing. Our proposedultradeep low-z data includes two fields 0.1 < z < 0.43 (2500 hr integrations) while the deep includes fivefields 0.15 < z < 0.29 (500 hr integrations) to provide adequate cosmic volumes and galaxy numbers fordependency analysis.3. Key Science GoalsThe core DINGO science themes and goals are:• Evolution of the cosmic HI density: On the largest scales, evolution of the gaseous uni-verse is traced by measuring changes in the cosmic gas-mass density with time. The HIParkes All-Sky Survey (HIPASS) [3] and other large blind HI surveys have provided accuratemeasurements of the local HI cosmic mass density [4]. However, beyond z = 0 the sheer dif-ficulty of HI detection has limited our ability to detect HI in emission in individual galaxies,necessitating the use of stacking techniques [5] and a hetergeneous mix of methods at thehighest redshifts [6, 7] with significant uncertainty in both measurement and interpretation.DINGO aims to measure ΩHI directly through HI emission with HIPASS-like errors out toz∼ 0.4• The cosmic web: As well as changes in the HI cosmic mass density, it is also important tounderstand the way in which the distribution of HI gas has changed with time. This has var-ied significantly over the history of the universe, evolving from a near uniform distributionwith only small density fluctuations at the start of the dark ages, to its current highly clus-tered state, mostly restricted to galactic halos where its density is high enough to self-shield.DINGO will examine the most recent changes in the HI mass distribution through evolution-ary measurements of the HI mass function [4], the 2pt correlation function [8], and HODmodelling [9]. The simulated spatial distribution of galaxies in a single DINGO ultradeepfield is shown in Figure 1.3DINGO Martin Meyer• Galaxy evolution: Large, comprehensive datasets with galaxy-by-galaxy data will ultimatelybe required to fully understand the baryonic processes in galaxies. GAMA is the best multi-wavelength dataset in existence over the areas and depths relevant to DINGO, and by targetingthese survey regions, DINGO will enable an understanding of the evolution of HI in thecontext of all the other major galactic constituents over the past 4 Gyr. Our models based oncurrent ASKAP specifications indicate that DINGO will be sensitive to M∗HI galaxies over theentire redshift range probed.4. Design StudyDINGO is now in the design study phase of the ASKAP survey science process. During this time, anumber of scientific and technical aspects necessary to making DINGO a success will be examined.Survey DesignA core task of the design study will be to determine the location of the DINGO fields within theGAMA survey regions. We will additionally examine other survey parameters during the designstudy to ensure that the final DINGO configuration will best meet the aims outlined in the sciencecase using simulations, observations and analytic methods. Additional studies will be made of keyissues such as cosmic variance and the survey volumes required for environmental analysis.Simulated Catalogues and Mock SkiesSimulated HI datasets provide a central means for evaluating the likely science outcomes forDINGO. To date, our simulations have been a combination of non-evolving semi-empirical meth-ods taking into account the locally measured cosmic mass density and the HI mass function, alongwith basic semi-analytic methods for the spatial distribution of galaxies. During the design study,we plan to advance on these through the use of fully semi-analytic methods such as the recent workof Obreschkow et al. [10]. Given the current relatively high mass limit of semi-analytic models, itmay remain necessary to combine semi-analytic and semi-empirical approaches to deliver simula-tions covering the full mass spectrum, although we will seek to advance work on this issue as faras possible. These catalogues will be developed in parallel to those proposed for WALLABY andwe will investigate a number of simulation issues:• an analysis of semi-empirical and semi-analytic methods to yield simulations consistent withknown observational constraints on the cosmic HI density, the HI mass function, the cluster-ing properties of HI rich galaxies, and correlations between HI properties and environment• simulations that cover a range of plausible evolutionary scenarios• mock science analyses based on these simulated catalogues to examine our sensitivity, antic-ipated errors, and discriminatory power for separating various evolutionary models• assistance in the development of mock skies for ASKAP pipeline testing4DINGO Martin MeyerRadio Frequnecy Interference and Cube CombinationThe deep observations of DINGO make RFI an issue that will require special attention. The stackingof multiple observations will mean that RFI features may only become apparent some time afterobservations have begun. A methodology needs to be developed to deal with this given the limitedcurrent storage capability of visibility data.Source Finding and ParametrizationMultiple approaches to source detection need to be examined and tested. It is likely that smoothingwith a matched filter or wavelet filtering may improve the detectability of point-like sources, whichwill be the vast majority of our likely detections. The processing overheads for these approacheswill need to be evaluated, as the wavelet filtering in particular can be computationally intensive.One of the primary tasks will be to test the completeness and reliability of the detections made withthe source-finder. Due to the automated nature of the processing, the source-finder needs to be ascomplete (ie. maximise the number of real sources found) and reliable (ie. minimise the number ofnon-real sources identified) as possible, and we will develop tools to measure both these quantities.DINGO will make use of, and contribute to, the standard end-to-end simulation/imaging/analysispipeline under development by the ASKAP computing group, which will enable us to incorpo-rate different simulations and observational strategies into our testing, and to provide uniform testresults to aid the analysis.Early Science CommissioningCritical to early ASKAP commissioning are tests of: receiver performance and stability; beam per-formance and stability; calibration accuracy; techniques to ensure spatial and spectral invariance ofcalibration, including across beams; quality of sky models; dynamic range (continuum and spectralline); spectral bandpass stability (as a function of time, beam, position and polarization angle);mosaicing strategies for full beam combination; measurement of sidelobe response, including atequatorial latitudes; and the characterization of map noise as a function of angle and integrationtime. This last issue is particularly critical given the deep nature of this survey. BETA will be usedas a valuable testbed for assessing these issues.Ancillary DatasetsMulti-wavelength data is vital for meeting the DINGO science goals. We will monitor the devel-opment of the GAMA datasets to ensure that the final DINGO field locations are best positionedto take advantage of the data products that are ultimately available, and to fill any gaps that arisewhere feasible and necessary.SKA Pathfinder CoordinationThere are a large number of major radio astronomy facilities currently undergoing simultaneousdevelopment, including APERTIF, the eVLA, ATA, MeerKAT, and of course ASKAP itself. TheASKAP legacy surveys will not be operating in isolation, and numerous major programs can beexpected on the other pathfinder facilities. In developing an HI survey strategy, it is important tobest target legacy surveys in ways that exploit the advantages of each facility and ideally operate in5DINGO Martin Meyera complimentary rather than overlapping manner. MeerKAT will also be an ideal instrument withwhich to survey distant HI, and in combination with ASKAP these facilities have the opportunity todevelop a layered survey strategy that will be able to provide a comprehensive view of the universe,starting with WALLABY over the largest areas∼ 3×104 deg2, DINGO over areas 60-150 deg2, andMeerKAT surveying areas ∼ 10 deg2 and less. The exact parameters and configurations of thesefuture facilities continue to evolve, as do the projects their user communities seek to carry out, andas such it is important to maintain collaborative links to ensure the overall science outcomes aremaximised.References[1] I. Feain, S. Johnston, and R. Braun, The Australian Square Kilometre Array Pathfinder(ASKAP) an SKA pre-cursor, 2010, this proceedings.[2] S. Driver, P. Norberg, I. Baldry, S. Bamford, A. Hopkins, J. Liske, J. Loveday, andJ. Peacock, GAMA: towards a physical understanding of galaxy formation, 2010, Astronomyand Geophysics, 50, 5.12.[3] M. J. Meyer et. al., The HIPASS Catalogue - I. Data Presentation, 2004, Monthly Notices ofthe Royal Astronomical Society, 350, 1195.[4] M. A. Zwaan, M. J. Meyer, L. Staveley-Smith, and R. L. Webster, The HIPASS Catalogue:ΩHI and environmental effects on the HI mass function of galaxies, 2005, Monthly Notices ofthe Royal Astronomical Society: Letters, 359, L30.[5] P. Lah et. al., The HI content of star-forming galaxies at z = 0.24, 2007, Monthly Notices ofthe Royal Astronomical Society, 376, 1357.[6] S. M. Rao, D. A. Turnshek, and D. B. Nestor, Damped Lyα systems at z<1.65: Theexpanded sloan digital sky survey hubble space telescope sample, 2006, The AstrophysicalJournal, 636, 610.[7] J. X. Prochaska and A. M. Wolfe, On the (non)evolution of HI gas in galaxies over cosmictime, 2009, The Astrophysical Journal, 696, 1543.[8] M. J. Meyer, M. A. Zwaan, R. L. Webster, M. J. I. Brown, and L. Staveley-Smith, The weakclustering of gas-rich galaxies, 2007, The Astrophysical Journal, 654, 702.[9] S. Wyithe, M. J. I. Brown, M. A. Zwaan, and M. J. Meyer, The Halo OccupationDistribution of HI Galaxies, 2010, astro-ph/0908.2854.[10] D. Obreschkow, D. Croton, G. DeLucia, S. Khochfar, and S. Rawlings, Simulation of thecosmic evolution of atomic and molecular hydrogen in galaxies, 2009, The AstrophysicalJournal, 698, 1467.6

   University of GroningenExploring the HI Universe with ASKAPMeyer, MartinPublished in:EPRINTS-BOOK-TITLEIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Meyer, M. (2009). Exploring the HI Universe with ASKAP. In EPRINTS-BOOK-TITLE University ofGroningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 16-07-2023Exploring the HI Universe with ASKAPMartin Meyer∗International Centre for Radio Astronomy ResearchM468, The University of Western Australia35 Stirling Highway, Crawley 6009, AustraliaE-mail: martin.meyer@icrar.orgThe DINGO teamhttp://www.physics.uwa.edu.au/∼mmeyer/dingoThe survey speed of ASKAP makes it a prime instrument with which to survey the HI universe,enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cos-mologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussedas proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP sci-ence survey project anticipates observing in excess of 105 sources out to redshift z ∼ 0.4. Keyscience goals include: ΩHI and its evolution, the cosmic web as traced by distributions such as theHI mass function and the 2pt correlation function, and the formation and evolution of galaxies.Science returns are maximised by targeting the GAMA survey regions, enabling the HI content ofgalaxies to be studied and understood in full context with all the major galactic constituents overthe past 4 Gyr.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/arXiv:0912.2167v1  [astro-ph.CO]  11 Dec 2009DINGO Martin Meyer1. IntroductionUnderstanding how galaxies form and evolve is one of the key astrophysical problems of the 21stcentury. Recent observations of galaxies, supernovae, and the Cosmic Microwave Backgroundhave refined measurements of key cosmological parameters and simulations have accurately mod-elled how dark matter halos collapse from the miniscule density perturbations carried over fromthe inflationary era. But understanding how baryons collapse into these potential wells and ulti-mately form stars, how black holes are formed, how the baryons interact with the dark matter, whatthe balance is between accretion and outflow, heating and cooling, are problems which require adeep understanding of physics on an immense range of spatial scales and particle densities. Theseproblems remain largely unsolved.One of the keys to a deeper understanding is to observe and model the gaseous component ofthe Universe. Baryons are believed to have existed entirely in gaseous form before the epoch ofgalaxy formation, and it is by the continual collapse of this gas into the filamentary structures ofthe cosmic web, its accretion into the deepest potential wells, the creation of cool gaseous disksand their ultimate collapse into dense molecular clouds, that galaxies are able to form stars. Theon-going feedback between gas and stars, and the governing role of the host dark matter potentials,continue to determine the evolution of galaxies today. To date, our ability to observe the gaseouscontent of the universe, and hence to explain the manner in which these processes have occurred, isextremely limited. Observations have largely been restricted to small samples of gas in emission inthe local universe, or to sparse samples of absorption line systems at higher redshifts, and the highlevel of uncertainty inherent in interpreting such observations.2. DINGO and ASKAPThe Australian SKA Pathfinder telescope (ASKAP) [1] has been designed as a survey instrumentand is particularly well-suited to the search for 21cm neutral hydrogen emission. Its large field ofview (30 deg2), in combination with its collecting area (4072 m2) and system temperature (50K)give it a fast survey speed, enabling the telescope to go both wide and deep in a comparativelyshort period of time. Its wide 300 MHz instantaneous bandwidth similarly facilitates surveys ofcosmologically representative volumes in HI.Where WALLABY will perform a shallow survey of the southern sky, DINGO aims to providea legacy deep dataset for HI emission out to z ∼ 0.4. To enable multiwavelength studies, DINGOwill target the GAMA survey areas [2]. GAMA is composed of several imaging and spectroscopicsurveys using the world’s pre-eminent facilities, spanning all wavelengths from the ultraviolet tothe far infrared (GALEX, VST, VISTA, UKIRT, WISE, Herschel-ATLAS), in addition to 250k AAΩspectra in key overlap regions. A tiered HI survey strategy is proposed covering regions 150 deg2(500 hours per pointing, 0.15 < z < 0.29) and 60 deg2 (2500 hours per pointing, 0.1 < z < 0.43) tomeet the science goals described in the following section.DINGO is a major SKA pathfinder experiment and will provide an ideal dataset for SKA plan-ning. This will be acheived scientifically through its study of the evolving HI universe, and tech-nologically through the use of ASKAP’s phased-array feeds for extended integrations.2DINGO Martin MeyerFigure 1: Simulated spatial distribution of galaxies in a 2500 hr, 30 deg2 ASKAP pointing. Our proposedultradeep low-z data includes two fields 0.1 < z < 0.43 (2500 hr integrations) while the deep includes fivefields 0.15 < z < 0.29 (500 hr integrations) to provide adequate cosmic volumes and galaxy numbers fordependency analysis.3. Key Science GoalsThe core DINGO science themes and goals are:• Evolution of the cosmic HI density: On the largest scales, evolution of the gaseous uni-verse is traced by measuring changes in the cosmic gas-mass density with time. The HIParkes All-Sky Survey (HIPASS) [3] and other large blind HI surveys have provided accuratemeasurements of the local HI cosmic mass density [4]. However, beyond z = 0 the sheer dif-ficulty of HI detection has limited our ability to detect HI in emission in individual galaxies,necessitating the use of stacking techniques [5] and a hetergeneous mix of methods at thehighest redshifts [6, 7] with significant uncertainty in both measurement and interpretation.DINGO aims to measure ΩHI directly through HI emission with HIPASS-like errors out toz∼ 0.4• The cosmic web: As well as changes in the HI cosmic mass density, it is also important tounderstand the way in which the distribution of HI gas has changed with time. This has var-ied significantly over the history of the universe, evolving from a near uniform distributionwith only small density fluctuations at the start of the dark ages, to its current highly clus-tered state, mostly restricted to galactic halos where its density is high enough to self-shield.DINGO will examine the most recent changes in the HI mass distribution through evolution-ary measurements of the HI mass function [4], the 2pt correlation function [8], and HODmodelling [9]. The simulated spatial distribution of galaxies in a single DINGO ultradeepfield is shown in Figure 1.3DINGO Martin Meyer• Galaxy evolution: Large, comprehensive datasets with galaxy-by-galaxy data will ultimatelybe required to fully understand the baryonic processes in galaxies. GAMA is the best multi-wavelength dataset in existence over the areas and depths relevant to DINGO, and by targetingthese survey regions, DINGO will enable an understanding of the evolution of HI in thecontext of all the other major galactic constituents over the past 4 Gyr. Our models based oncurrent ASKAP specifications indicate that DINGO will be sensitive to M∗HI galaxies over theentire redshift range probed.4. Design StudyDINGO is now in the design study phase of the ASKAP survey science process. During this time, anumber of scientific and technical aspects necessary to making DINGO a success will be examined.Survey DesignA core task of the design study will be to determine the location of the DINGO fields within theGAMA survey regions. We will additionally examine other survey parameters during the designstudy to ensure that the final DINGO configuration will best meet the aims outlined in the sciencecase using simulations, observations and analytic methods. Additional studies will be made of keyissues such as cosmic variance and the survey volumes required for environmental analysis.Simulated Catalogues and Mock SkiesSimulated HI datasets provide a central means for evaluating the likely science outcomes forDINGO. To date, our simulations have been a combination of non-evolving semi-empirical meth-ods taking into account the locally measured cosmic mass density and the HI mass function, alongwith basic semi-analytic methods for the spatial distribution of galaxies. During the design study,we plan to advance on these through the use of fully semi-analytic methods such as the recent workof Obreschkow et al. [10]. Given the current relatively high mass limit of semi-analytic models, itmay remain necessary to combine semi-analytic and semi-empirical approaches to deliver simula-tions covering the full mass spectrum, although we will seek to advance work on this issue as faras possible. These catalogues will be developed in parallel to those proposed for WALLABY andwe will investigate a number of simulation issues:• an analysis of semi-empirical and semi-analytic methods to yield simulations consistent withknown observational constraints on the cosmic HI density, the HI mass function, the cluster-ing properties of HI rich galaxies, and correlations between HI properties and environment• simulations that cover a range of plausible evolutionary scenarios• mock science analyses based on these simulated catalogues to examine our sensitivity, antic-ipated errors, and discriminatory power for separating various evolutionary models• assistance in the development of mock skies for ASKAP pipeline testing4DINGO Martin MeyerRadio Frequnecy Interference and Cube CombinationThe deep observations of DINGO make RFI an issue that will require special attention. The stackingof multiple observations will mean that RFI features may only become apparent some time afterobservations have begun. A methodology needs to be developed to deal with this given the limitedcurrent storage capability of visibility data.Source Finding and ParametrizationMultiple approaches to source detection need to be examined and tested. It is likely that smoothingwith a matched filter or wavelet filtering may improve the detectability of point-like sources, whichwill be the vast majority of our likely detections. The processing overheads for these approacheswill need to be evaluated, as the wavelet filtering in particular can be computationally intensive.One of the primary tasks will be to test the completeness and reliability of the detections made withthe source-finder. Due to the automated nature of the processing, the source-finder needs to be ascomplete (ie. maximise the number of real sources found) and reliable (ie. minimise the number ofnon-real sources identified) as possible, and we will develop tools to measure both these quantities.DINGO will make use of, and contribute to, the standard end-to-end simulation/imaging/analysispipeline under development by the ASKAP computing group, which will enable us to incorpo-rate different simulations and observational strategies into our testing, and to provide uniform testresults to aid the analysis.Early Science CommissioningCritical to early ASKAP commissioning are tests of: receiver performance and stability; beam per-formance and stability; calibration accuracy; techniques to ensure spatial and spectral invariance ofcalibration, including across beams; quality of sky models; dynamic range (continuum and spectralline); spectral bandpass stability (as a function of time, beam, position and polarization angle);mosaicing strategies for full beam combination; measurement of sidelobe response, including atequatorial latitudes; and the characterization of map noise as a function of angle and integrationtime. This last issue is particularly critical given the deep nature of this survey. BETA will be usedas a valuable testbed for assessing these issues.Ancillary DatasetsMulti-wavelength data is vital for meeting the DINGO science goals. We will monitor the devel-opment of the GAMA datasets to ensure that the final DINGO field locations are best positionedto take advantage of the data products that are ultimately available, and to fill any gaps that arisewhere feasible and necessary.SKA Pathfinder CoordinationThere are a large number of major radio astronomy facilities currently undergoing simultaneousdevelopment, including APERTIF, the eVLA, ATA, MeerKAT, and of course ASKAP itself. TheASKAP legacy surveys will not be operating in isolation, and numerous major programs can beexpected on the other pathfinder facilities. In developing an HI survey strategy, it is important tobest target legacy surveys in ways that exploit the advantages of each facility and ideally operate in5DINGO Martin Meyera complimentary rather than overlapping manner. MeerKAT will also be an ideal instrument withwhich to survey distant HI, and in combination with ASKAP these facilities have the opportunity todevelop a layered survey strategy that will be able to provide a comprehensive view of the universe,starting with WALLABY over the largest areas∼ 3×104 deg2, DINGO over areas 60-150 deg2, andMeerKAT surveying areas ∼ 10 deg2 and less. The exact parameters and configurations of thesefuture facilities continue to evolve, as do the projects their user communities seek to carry out, andas such it is important to maintain collaborative links to ensure the overall science outcomes aremaximised.References[1] I. Feain, S. Johnston, and R. Braun, The Australian Square Kilometre Array Pathfinder(ASKAP) an SKA pre-cursor, 2010, this proceedings.[2] S. Driver, P. Norberg, I. Baldry, S. Bamford, A. Hopkins, J. Liske, J. Loveday, andJ. Peacock, GAMA: towards a physical understanding of galaxy formation, 2010, Astronomyand Geophysics, 50, 5.12.[3] M. J. Meyer et. al., The HIPASS Catalogue - I. Data Presentation, 2004, Monthly Notices ofthe Royal Astronomical Society, 350, 1195.[4] M. A. Zwaan, M. J. Meyer, L. Staveley-Smith, and R. L. Webster, The HIPASS Catalogue:ΩHI and environmental effects on the HI mass function of galaxies, 2005, Monthly Notices ofthe Royal Astronomical Society: Letters, 359, L30.[5] P. Lah et. al., The HI content of star-forming galaxies at z = 0.24, 2007, Monthly Notices ofthe Royal Astronomical Society, 376, 1357.[6] S. M. Rao, D. A. Turnshek, and D. B. Nestor, Damped Lyα systems at z<1.65: Theexpanded sloan digital sky survey hubble space telescope sample, 2006, The AstrophysicalJournal, 636, 610.[7] J. X. Prochaska and A. M. Wolfe, On the (non)evolution of HI gas in galaxies over cosmictime, 2009, The Astrophysical Journal, 696, 1543.[8] M. J. Meyer, M. A. Zwaan, R. L. Webster, M. J. I. Brown, and L. Staveley-Smith, The weakclustering of gas-rich galaxies, 2007, The Astrophysical Journal, 654, 702.[9] S. Wyithe, M. J. I. Brown, M. A. Zwaan, and M. J. Meyer, The Halo OccupationDistribution of HI Galaxies, 2010, astro-ph/0908.2854.[10] D. Obreschkow, D. Croton, G. DeLucia, S. Khochfar, and S. Rawlings, Simulation of thecosmic evolution of atomic and molecular hydrogen in galaxies, 2009, The AstrophysicalJournal, 698, 1467.6

University of Groningen Research Database

  
 University of Groningen
Exploring the HI Universe with ASKAP
Meyer, Martin
Published in:
EPRINTS-BOOK-TITLE
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
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of Groningen.
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Download date: 11-02-2018
Exploring the HI Universe with ASKAP
Martin Meyer∗
International Centre for Radio Astronomy Research
M468, The University of Western Australia
35 Stirling Highway, Crawley 6009, Australia
E-mail: martin.meyer@icrar.org
The DINGO team
http://www.physics.uwa.edu.au/∼mmeyer/dingo
The survey speed of ASKAP makes it a prime instrument with which to survey the HI universe,
enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cos-
mologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussed
as proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP sci-
ence survey project anticipates observing in excess of 105 sources out to redshift z ∼ 0.4. Key
science goals include: ΩHI and its evolution, the cosmic web as traced by distributions such as the
HI mass function and the 2pt correlation function, and the formation and evolution of galaxies.
Science returns are maximised by targeting the GAMA survey regions, enabling the HI content of
galaxies to be studied and understood in full context with all the major galactic constituents over
the past 4 Gyr.
Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009
June 02 - 05 2009
Groningen, the Netherlands
∗Speaker.
c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/
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1. Introduction
Understanding how galaxies form and evolve is one of the key astrophysical problems of the 21st
century. Recent observations of galaxies, supernovae, and the Cosmic Microwave Background
have refined measurements of key cosmological parameters and simulations have accurately mod-
elled how dark matter halos collapse from the miniscule density perturbations carried over from
the inflationary era. But understanding how baryons collapse into these potential wells and ulti-
mately form stars, how black holes are formed, how the baryons interact with the dark matter, what
the balance is between accretion and outflow, heating and cooling, are problems which require a
deep understanding of physics on an immense range of spatial scales and particle densities. These
problems remain largely unsolved.
One of the keys to a deeper understanding is to observe and model the gaseous component of
the Universe. Baryons are believed to have existed entirely in gaseous form before the epoch of
galaxy formation, and it is by the continual collapse of this gas into the filamentary structures of
the cosmic web, its accretion into the deepest potential wells, the creation of cool gaseous disks
and their ultimate collapse into dense molecular clouds, that galaxies are able to form stars. The
on-going feedback between gas and stars, and the governing role of the host dark matter potentials,
continue to determine the evolution of galaxies today. To date, our ability to observe the gaseous
content of the universe, and hence to explain the manner in which these processes have occurred, is
extremely limited. Observations have largely been restricted to small samples of gas in emission in
the local universe, or to sparse samples of absorption line systems at higher redshifts, and the high
level of uncertainty inherent in interpreting such observations.
2. DINGO and ASKAP
The Australian SKA Pathfinder telescope (ASKAP) [1] has been designed as a survey instrument
and is particularly well-suited to the search for 21cm neutral hydrogen emission. Its large field of
view (30 deg2), in combination with its collecting area (4072 m2) and system temperature (50K)
give it a fast survey speed, enabling the telescope to go both wide and deep in a comparatively
short period of time. Its wide 300 MHz instantaneous bandwidth similarly facilitates surveys of
cosmologically representative volumes in HI.
Where WALLABY will perform a shallow survey of the southern sky, DINGO aims to provide
a legacy deep dataset for HI emission out to z ∼ 0.4. To enable multiwavelength studies, DINGO
will target the GAMA survey areas [2]. GAMA is composed of several imaging and spectroscopic
surveys using the world’s pre-eminent facilities, spanning all wavelengths from the ultraviolet to
the far infrared (GALEX, VST, VISTA, UKIRT, WISE, Herschel-ATLAS), in addition to 250k AAΩ
spectra in key overlap regions. A tiered HI survey strategy is proposed covering regions 150 deg2
(500 hours per pointing, 0.15 < z < 0.29) and 60 deg2 (2500 hours per pointing, 0.1 < z < 0.43) to
meet the science goals described in the following section.
DINGO is a major SKA pathfinder experiment and will provide an ideal dataset for SKA plan-
ning. This will be acheived scientifically through its study of the evolving HI universe, and tech-
nologically through the use of ASKAP’s phased-array feeds for extended integrations.
2
DINGO Martin Meyer
Figure 1: Simulated spatial distribution of galaxies in a 2500 hr, 30 deg2 ASKAP pointing. Our proposed
ultradeep low-z data includes two fields 0.1 < z < 0.43 (2500 hr integrations) while the deep includes five
fields 0.15 < z < 0.29 (500 hr integrations) to provide adequate cosmic volumes and galaxy numbers for
dependency analysis.
3. Key Science Goals
The core DINGO science themes and goals are:
• Evolution of the cosmic HI density: On the largest scales, evolution of the gaseous uni-
verse is traced by measuring changes in the cosmic gas-mass density with time. The HI
Parkes All-Sky Survey (HIPASS) [3] and other large blind HI surveys have provided accurate
measurements of the local HI cosmic mass density [4]. However, beyond z= 0 the sheer dif-
ficulty of HI detection has limited our ability to detect HI in emission in individual galaxies,
necessitating the use of stacking techniques [5] and a hetergeneous mix of methods at the
highest redshifts [6, 7] with significant uncertainty in both measurement and interpretation.
DINGO aims to measure ΩHI directly through HI emission with HIPASS-like errors out to
z∼ 0.4
• The cosmic web: As well as changes in the HI cosmic mass density, it is also important to
understand the way in which the distribution of HI gas has changed with time. This has var-
ied significantly over the history of the universe, evolving from a near uniform distribution
with only small density fluctuations at the start of the dark ages, to its current highly clus-
tered state, mostly restricted to galactic halos where its density is high enough to self-shield.
DINGO will examine the most recent changes in the HI mass distribution through evolution-
ary measurements of the HI mass function [4], the 2pt correlation function [8], and HOD
modelling [9]. The simulated spatial distribution of galaxies in a single DINGO ultradeep
field is shown in Figure 1.
3
DINGO Martin Meyer
• Galaxy evolution: Large, comprehensive datasets with galaxy-by-galaxy data will ultimately
be required to fully understand the baryonic processes in galaxies. GAMA is the best multi-
wavelength dataset in existence over the areas and depths relevant to DINGO, and by targeting
these survey regions, DINGO will enable an understanding of the evolution of HI in the
context of all the other major galactic constituents over the past 4 Gyr. Our models based on
current ASKAP specifications indicate that DINGO will be sensitive to M∗HI galaxies over the
entire redshift range probed.
4. Design Study
DINGO is now in the design study phase of the ASKAP survey science process. During this time, a
number of scientific and technical aspects necessary to making DINGO a success will be examined.
Survey Design
A core task of the design study will be to determine the location of the DINGO fields within the
GAMA survey regions. We will additionally examine other survey parameters during the design
study to ensure that the final DINGO configuration will best meet the aims outlined in the science
case using simulations, observations and analytic methods. Additional studies will be made of key
issues such as cosmic variance and the survey volumes required for environmental analysis.
Simulated Catalogues and Mock Skies
Simulated HI datasets provide a central means for evaluating the likely science outcomes for
DINGO. To date, our simulations have been a combination of non-evolving semi-empirical meth-
ods taking into account the locally measured cosmic mass density and the HI mass function, along
with basic semi-analytic methods for the spatial distribution of galaxies. During the design study,
we plan to advance on these through the use of fully semi-analytic methods such as the recent work
of Obreschkow et al. [10]. Given the current relatively high mass limit of semi-analytic models, it
may remain necessary to combine semi-analytic and semi-empirical approaches to deliver simula-
tions covering the full mass spectrum, although we will seek to advance work on this issue as far
as possible. These catalogues will be developed in parallel to those proposed for WALLABY and
we will investigate a number of simulation issues:
• an analysis of semi-empirical and semi-analytic methods to yield simulations consistent with
known observational constraints on the cosmic HI density, the HI mass function, the cluster-
ing properties of HI rich galaxies, and correlations between HI properties and environment
• simulations that cover a range of plausible evolutionary scenarios
• mock science analyses based on these simulated catalogues to examine our sensitivity, antic-
ipated errors, and discriminatory power for separating various evolutionary models
• assistance in the development of mock skies for ASKAP pipeline testing
4
DINGO Martin Meyer
Radio Frequnecy Interference and Cube Combination
The deep observations of DINGO make RFI an issue that will require special attention. The stacking
of multiple observations will mean that RFI features may only become apparent some time after
observations have begun. A methodology needs to be developed to deal with this given the limited
current storage capability of visibility data.
Source Finding and Parametrization
Multiple approaches to source detection need to be examined and tested. It is likely that smoothing
with a matched filter or wavelet filtering may improve the detectability of point-like sources, which
will be the vast majority of our likely detections. The processing overheads for these approaches
will need to be evaluated, as the wavelet filtering in particular can be computationally intensive.
One of the primary tasks will be to test the completeness and reliability of the detections made with
the source-finder. Due to the automated nature of the processing, the source-finder needs to be as
complete (ie. maximise the number of real sources found) and reliable (ie. minimise the number of
non-real sources identified) as possible, and we will develop tools to measure both these quantities.
DINGO will make use of, and contribute to, the standard end-to-end simulation/imaging/analysis
pipeline under development by the ASKAP computing group, which will enable us to incorpo-
rate different simulations and observational strategies into our testing, and to provide uniform test
results to aid the analysis.
Early Science Commissioning
Critical to early ASKAP commissioning are tests of: receiver performance and stability; beam per-
formance and stability; calibration accuracy; techniques to ensure spatial and spectral invariance of
calibration, including across beams; quality of sky models; dynamic range (continuum and spectral
line); spectral bandpass stability (as a function of time, beam, position and polarization angle);
mosaicing strategies for full beam combination; measurement of sidelobe response, including at
equatorial latitudes; and the characterization of map noise as a function of angle and integration
time. This last issue is particularly critical given the deep nature of this survey. BETA will be used
as a valuable testbed for assessing these issues.
Ancillary Datasets
Multi-wavelength data is vital for meeting the DINGO science goals. We will monitor the devel-
opment of the GAMA datasets to ensure that the final DINGO field locations are best positioned
to take advantage of the data products that are ultimately available, and to fill any gaps that arise
where feasible and necessary.
SKA Pathfinder Coordination
There are a large number of major radio astronomy facilities currently undergoing simultaneous
development, including APERTIF, the eVLA, ATA, MeerKAT, and of course ASKAP itself. The
ASKAP legacy surveys will not be operating in isolation, and numerous major programs can be
expected on the other pathfinder facilities. In developing an HI survey strategy, it is important to
best target legacy surveys in ways that exploit the advantages of each facility and ideally operate in
5
DINGO Martin Meyer
a complimentary rather than overlapping manner. MeerKAT will also be an ideal instrument with
which to survey distant HI, and in combination with ASKAP these facilities have the opportunity to
develop a layered survey strategy that will be able to provide a comprehensive view of the universe,
starting with WALLABY over the largest areas∼ 3×104 deg2, DINGO over areas 60-150 deg2, and
MeerKAT surveying areas ∼ 10 deg2 and less. The exact parameters and configurations of these
future facilities continue to evolve, as do the projects their user communities seek to carry out, and
as such it is important to maintain collaborative links to ensure the overall science outcomes are
maximised.
References
[1] I. Feain, S. Johnston, and R. Braun, The Australian Square Kilometre Array Pathfinder
(ASKAP) an SKA pre-cursor, 2010, this proceedings.
[2] S. Driver, P. Norberg, I. Baldry, S. Bamford, A. Hopkins, J. Liske, J. Loveday, and
J. Peacock, GAMA: towards a physical understanding of galaxy formation, 2010, Astronomy
and Geophysics, 50, 5.12.
[3] M. J. Meyer et. al., The HIPASS Catalogue - I. Data Presentation, 2004, Monthly Notices of
the Royal Astronomical Society, 350, 1195.
[4] M. A. Zwaan, M. J. Meyer, L. Staveley-Smith, and R. L. Webster, The HIPASS Catalogue:
ΩHI and environmental effects on the HI mass function of galaxies, 2005, Monthly Notices of
the Royal Astronomical Society: Letters, 359, L30.
[5] P. Lah et. al., The HI content of star-forming galaxies at z = 0.24, 2007, Monthly Notices of
the Royal Astronomical Society, 376, 1357.
[6] S. M. Rao, D. A. Turnshek, and D. B. Nestor, Damped Lyα systems at z<1.65: The
expanded sloan digital sky survey hubble space telescope sample, 2006, The Astrophysical
Journal, 636, 610.
[7] J. X. Prochaska and A. M. Wolfe, On the (non)evolution of HI gas in galaxies over cosmic
time, 2009, The Astrophysical Journal, 696, 1543.
[8] M. J. Meyer, M. A. Zwaan, R. L. Webster, M. J. I. Brown, and L. Staveley-Smith, The weak
clustering of gas-rich galaxies, 2007, The Astrophysical Journal, 654, 702.
[9] S. Wyithe, M. J. I. Brown, M. A. Zwaan, and M. J. Meyer, The Halo Occupation
Distribution of HI Galaxies, 2010, astro-ph/0908.2854.
[10] D. Obreschkow, D. Croton, G. DeLucia, S. Khochfar, and S. Rawlings, Simulation of the
cosmic evolution of atomic and molecular hydrogen in galaxies, 2009, The Astrophysical
Journal, 698, 1467.
6


NARCIS 

University of Groningen

   University of GroningenExploring the HI Universe with ASKAPMeyer, MartinPublished in:EPRINTS-BOOK-TITLEIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Meyer, M. (2009). Exploring the HI Universe with ASKAP. In EPRINTS-BOOK-TITLE Groningen: Universityof Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019Exploring the HI Universe with ASKAPMartin Meyer∗International Centre for Radio Astronomy ResearchM468, The University of Western Australia35 Stirling Highway, Crawley 6009, AustraliaE-mail: martin.meyer@icrar.orgThe DINGO teamhttp://www.physics.uwa.edu.au/∼mmeyer/dingoThe survey speed of ASKAP makes it a prime instrument with which to survey the HI universe,enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cos-mologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussedas proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP sci-ence survey project anticipates observing in excess of 105 sources out to redshift z ∼ 0.4. Keyscience goals include: ΩHI and its evolution, the cosmic web as traced by distributions such as theHI mass function and the 2pt correlation function, and the formation and evolution of galaxies.Science returns are maximised by targeting the GAMA survey regions, enabling the HI content ofgalaxies to be studied and understood in full context with all the major galactic constituents overthe past 4 Gyr.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/arXiv:0912.2167v1  [astro-ph.CO]  11 Dec 2009DINGO Martin Meyer1. IntroductionUnderstanding how galaxies form and evolve is one of the key astrophysical problems of the 21stcentury. Recent observations of galaxies, supernovae, and the Cosmic Microwave Backgroundhave refined measurements of key cosmological parameters and simulations have accurately mod-elled how dark matter halos collapse from the miniscule density perturbations carried over fromthe inflationary era. But understanding how baryons collapse into these potential wells and ulti-mately form stars, how black holes are formed, how the baryons interact with the dark matter, whatthe balance is between accretion and outflow, heating and cooling, are problems which require adeep understanding of physics on an immense range of spatial scales and particle densities. Theseproblems remain largely unsolved.One of the keys to a deeper understanding is to observe and model the gaseous component ofthe Universe. Baryons are believed to have existed entirely in gaseous form before the epoch ofgalaxy formation, and it is by the continual collapse of this gas into the filamentary structures ofthe cosmic web, its accretion into the deepest potential wells, the creation of cool gaseous disksand their ultimate collapse into dense molecular clouds, that galaxies are able to form stars. Theon-going feedback between gas and stars, and the governing role of the host dark matter potentials,continue to determine the evolution of galaxies today. To date, our ability to observe the gaseouscontent of the universe, and hence to explain the manner in which these processes have occurred, isextremely limited. Observations have largely been restricted to small samples of gas in emission inthe local universe, or to sparse samples of absorption line systems at higher redshifts, and the highlevel of uncertainty inherent in interpreting such observations.2. DINGO and ASKAPThe Australian SKA Pathfinder telescope (ASKAP) [1] has been designed as a survey instrumentand is particularly well-suited to the search for 21cm neutral hydrogen emission. Its large field ofview (30 deg2), in combination with its collecting area (4072 m2) and system temperature (50K)give it a fast survey speed, enabling the telescope to go both wide and deep in a comparativelyshort period of time. Its wide 300 MHz instantaneous bandwidth similarly facilitates surveys ofcosmologically representative volumes in HI.Where WALLABY will perform a shallow survey of the southern sky, DINGO aims to providea legacy deep dataset for HI emission out to z ∼ 0.4. To enable multiwavelength studies, DINGOwill target the GAMA survey areas [2]. GAMA is composed of several imaging and spectroscopicsurveys using the world’s pre-eminent facilities, spanning all wavelengths from the ultraviolet tothe far infrared (GALEX, VST, VISTA, UKIRT, WISE, Herschel-ATLAS), in addition to 250k AAΩspectra in key overlap regions. A tiered HI survey strategy is proposed covering regions 150 deg2(500 hours per pointing, 0.15 < z < 0.29) and 60 deg2 (2500 hours per pointing, 0.1 < z < 0.43) tomeet the science goals described in the following section.DINGO is a major SKA pathfinder experiment and will provide an ideal dataset for SKA plan-ning. This will be acheived scientifically through its study of the evolving HI universe, and tech-nologically through the use of ASKAP’s phased-array feeds for extended integrations.2DINGO Martin MeyerFigure 1: Simulated spatial distribution of galaxies in a 2500 hr, 30 deg2 ASKAP pointing. Our proposedultradeep low-z data includes two fields 0.1 < z < 0.43 (2500 hr integrations) while the deep includes fivefields 0.15 < z < 0.29 (500 hr integrations) to provide adequate cosmic volumes and galaxy numbers fordependency analysis.3. Key Science GoalsThe core DINGO science themes and goals are:• Evolution of the cosmic HI density: On the largest scales, evolution of the gaseous uni-verse is traced by measuring changes in the cosmic gas-mass density with time. The HIParkes All-Sky Survey (HIPASS) [3] and other large blind HI surveys have provided accuratemeasurements of the local HI cosmic mass density [4]. However, beyond z= 0 the sheer dif-ficulty of HI detection has limited our ability to detect HI in emission in individual galaxies,necessitating the use of stacking techniques [5] and a hetergeneous mix of methods at thehighest redshifts [6, 7] with significant uncertainty in both measurement and interpretation.DINGO aims to measure ΩHI directly through HI emission with HIPASS-like errors out toz∼ 0.4• The cosmic web: As well as changes in the HI cosmic mass density, it is also important tounderstand the way in which the distribution of HI gas has changed with time. This has var-ied significantly over the history of the universe, evolving from a near uniform distributionwith only small density fluctuations at the start of the dark ages, to its current highly clus-tered state, mostly restricted to galactic halos where its density is high enough to self-shield.DINGO will examine the most recent changes in the HI mass distribution through evolution-ary measurements of the HI mass function [4], the 2pt correlation function [8], and HODmodelling [9]. The simulated spatial distribution of galaxies in a single DINGO ultradeepfield is shown in Figure 1.3DINGO Martin Meyer• Galaxy evolution: Large, comprehensive datasets with galaxy-by-galaxy data will ultimatelybe required to fully understand the baryonic processes in galaxies. GAMA is the best multi-wavelength dataset in existence over the areas and depths relevant to DINGO, and by targetingthese survey regions, DINGO will enable an understanding of the evolution of HI in thecontext of all the other major galactic constituents over the past 4 Gyr. Our models based oncurrent ASKAP specifications indicate that DINGO will be sensitive to M∗HI galaxies over theentire redshift range probed.4. Design StudyDINGO is now in the design study phase of the ASKAP survey science process. During this time, anumber of scientific and technical aspects necessary to making DINGO a success will be examined.Survey DesignA core task of the design study will be to determine the location of the DINGO fields within theGAMA survey regions. We will additionally examine other survey parameters during the designstudy to ensure that the final DINGO configuration will best meet the aims outlined in the sciencecase using simulations, observations and analytic methods. Additional studies will be made of keyissues such as cosmic variance and the survey volumes required for environmental analysis.Simulated Catalogues and Mock SkiesSimulated HI datasets provide a central means for evaluating the likely science outcomes forDINGO. To date, our simulations have been a combination of non-evolving semi-empirical meth-ods taking into account the locally measured cosmic mass density and the HI mass function, alongwith basic semi-analytic methods for the spatial distribution of galaxies. During the design study,we plan to advance on these through the use of fully semi-analytic methods such as the recent workof Obreschkow et al. [10]. Given the current relatively high mass limit of semi-analytic models, itmay remain necessary to combine semi-analytic and semi-empirical approaches to deliver simula-tions covering the full mass spectrum, although we will seek to advance work on this issue as faras possible. These catalogues will be developed in parallel to those proposed for WALLABY andwe will investigate a number of simulation issues:• an analysis of semi-empirical and semi-analytic methods to yield simulations consistent withknown observational constraints on the cosmic HI density, the HI mass function, the cluster-ing properties of HI rich galaxies, and correlations between HI properties and environment• simulations that cover a range of plausible evolutionary scenarios• mock science analyses based on these simulated catalogues to examine our sensitivity, antic-ipated errors, and discriminatory power for separating various evolutionary models• assistance in the development of mock skies for ASKAP pipeline testing4DINGO Martin MeyerRadio Frequnecy Interference and Cube CombinationThe deep observations of DINGO make RFI an issue that will require special attention. The stackingof multiple observations will mean that RFI features may only become apparent some time afterobservations have begun. A methodology needs to be developed to deal with this given the limitedcurrent storage capability of visibility data.Source Finding and ParametrizationMultiple approaches to source detection need to be examined and tested. It is likely that smoothingwith a matched filter or wavelet filtering may improve the detectability of point-like sources, whichwill be the vast majority of our likely detections. The processing overheads for these approacheswill need to be evaluated, as the wavelet filtering in particular can be computationally intensive.One of the primary tasks will be to test the completeness and reliability of the detections made withthe source-finder. Due to the automated nature of the processing, the source-finder needs to be ascomplete (ie. maximise the number of real sources found) and reliable (ie. minimise the number ofnon-real sources identified) as possible, and we will develop tools to measure both these quantities.DINGO will make use of, and contribute to, the standard end-to-end simulation/imaging/analysispipeline under development by the ASKAP computing group, which will enable us to incorpo-rate different simulations and observational strategies into our testing, and to provide uniform testresults to aid the analysis.Early Science CommissioningCritical to early ASKAP commissioning are tests of: receiver performance and stability; beam per-formance and stability; calibration accuracy; techniques to ensure spatial and spectral invariance ofcalibration, including across beams; quality of sky models; dynamic range (continuum and spectralline); spectral bandpass stability (as a function of time, beam, position and polarization angle);mosaicing strategies for full beam combination; measurement of sidelobe response, including atequatorial latitudes; and the characterization of map noise as a function of angle and integrationtime. This last issue is particularly critical given the deep nature of this survey. BETA will be usedas a valuable testbed for assessing these issues.Ancillary DatasetsMulti-wavelength data is vital for meeting the DINGO science goals. We will monitor the devel-opment of the GAMA datasets to ensure that the final DINGO field locations are best positionedto take advantage of the data products that are ultimately available, and to fill any gaps that arisewhere feasible and necessary.SKA Pathfinder CoordinationThere are a large number of major radio astronomy facilities currently undergoing simultaneousdevelopment, including APERTIF, the eVLA, ATA, MeerKAT, and of course ASKAP itself. TheASKAP legacy surveys will not be operating in isolation, and numerous major programs can beexpected on the other pathfinder facilities. In developing an HI survey strategy, it is important tobest target legacy surveys in ways that exploit the advantages of each facility and ideally operate in5DINGO Martin Meyera complimentary rather than overlapping manner. MeerKAT will also be an ideal instrument withwhich to survey distant HI, and in combination with ASKAP these facilities have the opportunity todevelop a layered survey strategy that will be able to provide a comprehensive view of the universe,starting with WALLABY over the largest areas∼ 3×104 deg2, DINGO over areas 60-150 deg2, andMeerKAT surveying areas ∼ 10 deg2 and less. The exact parameters and configurations of thesefuture facilities continue to evolve, as do the projects their user communities seek to carry out, andas such it is important to maintain collaborative links to ensure the overall science outcomes aremaximised.References[1] I. Feain, S. Johnston, and R. Braun, The Australian Square Kilometre Array Pathfinder(ASKAP) an SKA pre-cursor, 2010, this proceedings.[2] S. Driver, P. Norberg, I. Baldry, S. Bamford, A. Hopkins, J. Liske, J. Loveday, andJ. Peacock, GAMA: towards a physical understanding of galaxy formation, 2010, Astronomyand Geophysics, 50, 5.12.[3] M. J. Meyer et. al., The HIPASS Catalogue - I. Data Presentation, 2004, Monthly Notices ofthe Royal Astronomical Society, 350, 1195.[4] M. A. Zwaan, M. J. Meyer, L. Staveley-Smith, and R. L. Webster, The HIPASS Catalogue:ΩHI and environmental effects on the HI mass function of galaxies, 2005, Monthly Notices ofthe Royal Astronomical Society: Letters, 359, L30.[5] P. Lah et. al., The HI content of star-forming galaxies at z = 0.24, 2007, Monthly Notices ofthe Royal Astronomical Society, 376, 1357.[6] S. M. Rao, D. A. Turnshek, and D. B. Nestor, Damped Lyα systems at z<1.65: Theexpanded sloan digital sky survey hubble space telescope sample, 2006, The AstrophysicalJournal, 636, 610.[7] J. X. Prochaska and A. M. Wolfe, On the (non)evolution of HI gas in galaxies over cosmictime, 2009, The Astrophysical Journal, 696, 1543.[8] M. J. Meyer, M. A. Zwaan, R. L. Webster, M. J. I. Brown, and L. Staveley-Smith, The weakclustering of gas-rich galaxies, 2007, The Astrophysical Journal, 654, 702.[9] S. Wyithe, M. J. I. Brown, M. A. Zwaan, and M. J. Meyer, The Halo OccupationDistribution of HI Galaxies, 2010, astro-ph/0908.2854.[10] D. Obreschkow, D. Croton, G. DeLucia, S. Khochfar, and S. Rawlings, Simulation of thecosmic evolution of atomic and molecular hydrogen in galaxies, 2009, The AstrophysicalJournal, 698, 1467.6

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