ScienceProblem: HiZQuasars

PrimaryActor:

Astronomer

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ScienceGoal:

Discovery of very high redshift quasars in the range z=5 to 10.

The most distant quasar currently known are at redshifts > 6 and discovered by the Sloan Digital Sky Survey collaboration ( Fan et al, 2003; Fan et al, 2001; Fan et al, 2000).

Prior to the SDSS surveys most high redshift(defined here as redshifts greater than 4) were discovered using APM scans of UK Schmidt Telescope photographic surveys and the the the optical waveband (B,R,I) Storrie-Lombardi etal 2001. A figure showing how the quasars are selected on the basis of B-R colours is shown here. In this case the z=4 to 4.7 quasars are selected as outliers in the B-R colour distribution of stellar objects. There are around 50,000 stars per high redshift quasar. The work above involved the digitisation of over 2000 photographic plates each with 2GB of pixel data. The resulting catalogue of objects consisted of around 10^8 stars and 10^8 galaxies.

The SDSS survey extended the search for quasars to z>5 with the addition of longer wavelength optical filters e.g. the z band(850-950nm). The discovery of the first z>5 quasar is is described in Fan et al, 2000). The use of the i-z colours is shown in Fan_etal_2001_Fig1. The spectrum of the z=5.8 quasar is shown here. Note the lack of much flux shortward of the Lyman-alpha emission line at NN nm.

Sharp et al, 2001 carried out a survey using for z>5 quasars using r, i and z band CCD observations; see Sharp_et_al_Fig1 which shows how the r-i and i-z colours of quasars change with redshift.

Fan et al, 2003 and Fan et al, 2001 report the discovery of 6 quasars with redshifts around 6. The spectra are shown in Fan_etal_2001_Fig5. and Fan_etal_2003_Fig5. The first stage of the selection is via i-z colours see Fan_etal_2001_Fig1 and Fan_etal_2003_Fig1. This colour selection criterion selects both high redshift quasars and low mass cool stars called L and T dwarfs. In order to discriminate between these cool galactic stars which are more common that the high redshift quasars one uses longer wavelength observations. Fan etal used J band observations and here we show the J-z v i-z figures (Fan_etal_2001_Fig2, Fan_etal_2003_Fig3).

A useful paper that describes the general ideas involved in searches of quasars at z<5 is Richards et al, 2002 which describes the use of photometric catalogue data in the 5 SDSS bands (u'g'r'i'z') to select quasars. High redshift quasars are red due to absorption from neutral hydrogen in the intergalactic medium. A useful paper which describes this absorption is Madau, (1995)

Quasars at larger redshifts still will provide vital clues to the processes involved in the formation of the first bound objects. Near-IR survey data from UKIRT's WFCAM (via the UKIDSS survey) and later VISTA survey programmes will enable many quasars in the redshift range 5 < z < 8 to be discovered. This will enable a number of principal scientific goals to be met.

A key primary rational is that quasars at the highest redshifts may enable the investigation of the epoch of reionisation of the Universe. Such an effect is already being reported for the reionisation of He II via studies of quasars between 3 < z <4 (see Theuns et al, 2002). Higher redshift HiZQuasars would probe the neutral Inter Galactic Medium at this at this epoch.

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DataSets:

Searches will require comparison of optical (i, z bands) and near-IR data over thousands of square degrees.

Radio and X-ray surveys may also be used to select hi-z quasars (e.g. Hook et al, 2002).

See also DeepFieldSurveys likely to contain hi-z QSO.

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ProblemDescription:

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CurrentSolution:

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VOSolution:

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Iteration Breakdown:

• Astrogrid.Itn04HiZQuasars - science workflow for case in Iteration 04
• Astrogrid.Itn06HiZQuasars - science workflow for case in Iteration 06
• Astrogrid.Itn08HiZQuasars - science workflow for case in Iteration 08

KeyReferences:

Fan, X., Strauss, M.A., et al, 2003, AJ, 125, 1649 'A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at z>6'

Fan, X., et al, 2001, AJ, 122, 2833 A Survey of z>5.8 Quasars in the Sloan Digital Sky Survey. I. Discovery of Three New Quasars and the Spatial Density of Luminous Quasars at z~6

Fan, X., White. R.L. etal, 2000, AJ, 120, 1167 The Discovery of a Luminous Z=5.80 Quasar from the Sloan Digital Sky Survey

Hook, I. M., McMahon^?, R.G. et al, 2002 A&A, 391, 509, 'Discovery of radio-loud quasars with redshifts above 4 from the PMN sample'

Madau, P., 1995, ApJ, 441, 18, 'Radiative transfer in a clumpy universe: The colors of high-redshift galaxies'

Richards et al, 2002, AJ, 123, 294, 'Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample' astro-ph/0202251

Stern, D., et al, 2001, 'Chandra detection of a Type II Quasar at z=3.288', astro-ph/0111513

Storrie-Lombardi, L. et al, 2001, MNRAS, 322, 933 'The Second APM UKST Colour Survey for z>4 quasars'

Theuns et al, 2002, ApJ, 574, 111, 'Detection of He II Reionization in the Sloan Digital Sky Survey Quasar Sample'

Warren, S, Hewett, P, 2002, 'WFCAM, UKIDSS, and z=7 quasars', astro-ph/0201216

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-- GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Science Problems Forum.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

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Needs more details but will be an AG driver

-- NicholasWalton - 17 Apr 2002

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-- NicholasWalton - 22 Jan 2002

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-- RichardMcMahon - 29 Nov 2003

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Related UseCases

See also CommonGroup

LibraryFunctions which will be needed include:

Astrometric alignment; Least squares fit; Express result as probability; Apply K-correction; Calculate colour; Compare reults of cosmological models using different parameters; Fit spectra to templates.

Specific use cases

RedshiftDetermination

LocateOutliers

PhotometrySearch

FindQSOsByPosition

GetFluxOrUpperLimitAtPosition