The Flux Auto- and Cross-Correlation of the Lyman-alpha Fore

The Lyman-alpha forest has opened a new redshift regime for cosmological investigation. At z > 2 it provides a unique probe of cosmic geometry and an independent constraint on dark energy that is not subject to standard candle or ruler assumptions. In Pape

PUBLISHEDINTHEASTROPHYSICALJOURNALSUPPLEMENTSERIES(2008,APJS,175,29)

APreprinttypesetusingLTEXstyleemulateapjv.03/07/07

THEFLUXAUTO-ANDCROSS-CORRELATIONOFTHELYαFOREST.

I.SPECTROSCOPYOFQSOPAIRSWITHARCMINUTESEPARATIONSANDSIMILARREDSHIFTS1

ANDREWR.MARBLE,KRISTOFFERA.ERIKSEN,CHRISD.IMPEY,LEIBAI

StewardObservatory,UniversityofArizona,Tucson,AZ85721

AND

LANCEMILLER

DepartmentofPhysics,OxfordUniversity,KebleRoad,OxfordOX13RH,UK

arXiv:0803.1851v1 [astro-ph] 12 Mar 2008

ABSTRACT

TheLyαforesthasopenedanewredshiftregimeforcosmologicalinvestigation.Atz>2itprovidesauniqueprobeofcosmicgeometryandanindependentconstraintondarkenergythatisnotsubjecttostandardcandleorrulerassumptions.InPaperIofthisseriesonusingtheLyαforestobservedinpairsofQSOsforanewapplicationoftheAlcock-Paczy´nskitest,wepresentanddiscusstheresultsofacampaigntoobtainmoderate-resolutionspectroscopy(FWHM 2.5Å)oftheLyαforestinpairsofQSOswithsmallredshiftdifferences( z<0.25,z>2.2)andarcminuteseparations(θ<5′).Thisdataset,composedofseveninpidualQSOs,35pairs,andonetriplet,isalsowell-suitedforfutureinvestigationsofthecoherenceofLyαabsorberson～1Mpctransversescalesandthetransverseproximityeffect.WenotesevenrevisionsforpreviouslypublishedQSOidenti cationsand/orredshifts.

Subjectheadings:cosmology:observations—errata,addenda—intergalacticmedium—quasars:absorption

lines

1.INTRODUCTION

Fortyyearsafteritsexistencewas rstpredicted(Gunn&PetersontheLyαforesthasemergedasapowerfulcosmologicaltool(seeRauchforare-view).Observedindirectlyinthespectraofbrightback-groundsources,generallyQSOs,non-uniformneutralhy-drogengasalongthelineofsightresultsinvaryingde-greesofabsorptioncausedbytheredshiftedLyαtransitionline.Theopacityofthegasmapsontotheunderlyingmassdistributionviathe uctuatingGunn-Petersonmodel.Re-markableagreementbetweencosmologicalsimulationsandhigh-resolutionobservationshascon rmedtherobustnessofthisrelativelysimpleformalism(Cenetal.1994;Zhangetal.1995;Hernquistetal.Theunsetal.Lyαforestobservationsalonginpiduallinesofsightarelimitedinthattheyprovideonlyone-dimensionalinforma-tion.Thiscanbeextendedtothetransversedirectionwhentwoormoresuf cientlybrightQSOshappentolieincloseangularproximity.ApproximatelyadozenpairsandatriplethavebeenpreviouslyusedtoconstrainthesizeandnatureofLyαabsorbers(Bechtoldetal.etCrotts&FangWilligeretThe2dFQSORedshiftSurvey(2QZ;andSloanDigitalSkySurvey(SDSS;Adelman-McCarthyetal.2006)havegreatlyincreasedthenumberofknownQSOs.Thefainterspectroscopiclimitingmagnitudeof2QZ(B<21)hasalsoresultedintheidenti cationofrelativelyrarepairsofQSOswitharcminuteseparationsandsimilarredshifts,whereasfollow-upspectroscopyisgenerallyrequiredtocon- rmcandidatesidenti edphotometricallyinSDSS.Inaddi-tiontostudiesofthenatureofLyαforestabsorbers,suchpairs

ObservationsreportedherewereobtainedattheMMTObservatory,ajointfacilityoftheUniversityofArizonaandtheSmithsonianInstitution,and1

areusefulforthetransverseproximityeffectandtheAlcock-Paczy´nski(AP)testfordarkenergy.

Motivatedbythelatterapplication,wehaveusedtheMMTandMagellantelescopestoobtainscience-gradespectraforQSOpairswitharcminuteseparationsandsimilarredshifts.Inwede nethesamplecriteria,anddetailtheobservationsanddatareductionin§§3and4,respectively.The naldatasetispresentedanddiscussedinInwenotesevenre-visionstoidenti cationsand/orredshiftsfoundinpreviouslypublishedQSOcatalogues,beforesummarizingin§8.How-ever, rstwebrie ydiscusstheprimarysciencemotivatorsforthisnewdataset.

1.1.Alcock-Paczy´nskiTest

Ifsomesupernovaeareindeedtruestandardcandles,then

observationsoftheirlightcurvesasafunctionofredshiftre-vealthattheexpansionoftheUniverseispresentlyacceler-ating,followingaperiodofdecelerationinthedistantpastetal.Tonryetal.Thisin ectionintheexpansionrateprovidestheonlydirectevidenceforanonzerocosmologicalconstant,as Λcannotbemeasureddirectlyfromthecosmicmicrowavebackground(Spergelet2003).However,alternativemodels,characterizedbysupernovawithevolvingpropertiesandnocosmologicalconstant,arealsoinagreementwiththesupernovaedata.Themeritsofanin-dependenttestfordarkenergyinadifferentredshiftregime(z>2)andsubjecttounrelatedsystematicerrorsareclear.McDonald&Miralda-EscudéandHuietal.newapplicationoftheAPtest&usingtheLyαforestsofQSOpairsseparatedbyseveralarcminutesorless.TheAPtestisapurelygeometricmethodformeasuringcosmologicalparameters,whichatz>1isparticularlysensitiveto Λ.Simplystated,sphericalobjectsobservedathighredshiftwillonlyappearsphericalifthecorrectcosmologyisusedto

The Lyman-alpha forest has opened a new redshift regime for cosmological investigation. At z > 2 it provides a unique probe of cosmic geometry and an independent constraint on dark energy that is not subject to standard candle or ruler assumptions. In Pape

2Marbleetal.

tracer,suchastheLyαforest.McDonald(2003)investigatedthisapplicationoftheAPtestindetailandfoundthatneitherhighsignal-to-noiseratio(S/N>10)norhighresolution(FWHM 2Å)arenecessary.Rather,alargenumberofmoderatequalitydatapairsisneededtoreducetheeffectsofsamplevariance(approximately13θ2pairswithseparationlessthanθarcminutesforameasurementof ThemoresimilartheredshiftsofthepairedΛtowithin5%).QSOs,thegreatertheoverlapintheportionoftheLyαforestunaffectedbyLyβabsorption( z 0.6providesnooverlapatz=2.25).

1.2.TransverseProximityEffect

Therearetwomethodsformeasuringtheintensityofthebackgroundradiationresponsibleforionizingthein-tergalacticmedium.Providedthatthemeanbaryonden-sity,gastemperatureandpowerspectrumamplitudeareknown,itcanbederivedfromacomparis …… 此处隐藏：29152字，全部文档内容请下载后查看。喜欢就下载吧 ……