Con lusions

rangeof

10 < d ⊙ < 25

^kp^(see ^their ^Fig. ^9), strengthing thehypothesis of its originfrom thetidaldisruptionof anan ientdwarf galaxy. That distan erange

is ompatiblewiththeone derivedfrom ourCMDsand suggeststhat NGC7006

mightbewellembeddedin(andpossiblyasso iatedto)thisgiant loudofdebris.

Interestingly, Simion et al. (2014) also found that the Her ulesAquila loud is

barelyvisibleasaRR Lyraeover-densityinthenorthernhemisphere,suggesting

thatthis loudispossiblynotsymmetri withrespe ttotheGala ti plane. This

is onsistentwiththelowsigni an eoverdensity(

S < 2.5

⁾^of^this^omponentⁱⁿ

thesurroundingsofNGC6229(seeFigure 5.14).

NGC1261

NGC1261,liesinaproje tedpositionalignedwithtwoothermassiveGCs

show-inganextended-HBmorphologyintheirCMDs,NGC1851andNGC1904. Around

this lusterwehaveunveiledastellarpopulation(seeFigure5.10)thatstandsout

signi antlywhentheba kgrounddiagram is omparedwiththeones generated

withthe onsideredGala ti modelsanditisalsoapparentintheresultsobtained

throughthe ross- orrelationmethod(seeTable5.4). Theradialdistan e tothe

underlying omponentissimilartothatofthe luster,suggestingthateitheritis

omposedof luster membersor ofanunknownstellarpopulation. Thepossible

relationwiththegroupof lustersdes ribedinSe tion5.5.2en ouragestoexplore

thearea betweenNGC1261andthose GCs.

5.5.3 Negative dete tions

Therearenosignaturesofthepresen eofsigni antsubja entpopulationsaround

the remaining andidates (AM4, NGC1904, NGC2298, NGC4590, NGC5024,

NGC5272, NGC5466, NGC5694, NGC5824, NGC6229, NGC6864, NGC7078,

Pal15 and Rup106) as we nd no eviden e of distin t stellar population

on- entratedat a spe i distan e within theprobed olour-magnitude rangeusing

both the ross- orrelation and the iso hrone tting methods. The photometri

non-dete tionoftidal debrisaroundthe haloGCs in this studyis animportant

result to onsider in the ontext of hierar hi al stellar halo assembly theories.

Whether or not su h non-dete tions an rule out an a retion origin for these

GCs(andaportionoftheMilkyWaystellarhalo)dependsontwo mainfa tors:

1)howmassiveweretheprogenitordwarfgalaxiestheseGCswerea retedwith,

and 2) when were these dwarf galaxies and their GCs a reted into the Milky

Way? Indeed, GCs hosted in lowluminosity dwarfs whi h were a reted early,

mayshowminimalasso iatedstellardebriswhenobservedatpresent.

debris. Thesepopulationsareinsome ases onsistentwithknownstreamsinthe

sameline-of-sightof theGCs,while in other asesthese over-densities mightbe

asso iatedwithextendedhalosortidaltails. Unfortunatelyourdatadonot over

aregionwideenoughtodete tthefullextensionoftheobservedoverdensitiesand

theirsymmetrywithrespe tto the luster entre.

We identify theSgr tidal stream in thedire tion of6 GCs in our sample (4

"probable", 1 "possible" and 1 "un ertain" dete tion ) and at distan es

om-patible with the P10 orbital model. However, the helio entri distan es to the

subja entpopulations are onsistentwiththose oftherelated GCsonly for2 of

them (Whiting1 and NGC7492). Around NGC4147, NGC5634 and Pal5 (and

witha smallerlevelofsigni an eNGC5053), previouslysuggested as members

of the Sgr GC system, there are no signi ant dete tions orresponding to the

same luster distan e,although thesignatureoftheSgrMSisvisible asa

ba k-groundfeature. These negative dete tions might be related with our ability of

unveilingfaintsubja enttidalstreams(at

µ V > 32

^mag^se

⁻²

^). ^It^is^possible^that

theseglobularswerea retedfromtheSgrdSphalongtimeagoandthe

surfa e-brightness of the tidal remnants lies beyond our dete tion threshold above the

fore/ba kgroundpopulations. Onthe ontrary,Whiting1andNGC7492seemto

be immersed in the mostre ently a reted fra tion ofthe stream (

<

^0.75^Gyr).

Follow-upspe tros opy isneededto onrm thenatureofthestellar population

revealedbyourphotometry,moreimportantlyinthelatter ase,wherethe

dete -tionismore un ertainandthereexistsa signi antdeviationbetweentheradial

velo itiesofthe lusterandthepredi tionofthemodel byP10.

A subja ent stellarpopulation hasbeenalso unveiled in thesurroundings of

NGC1851,NGC1261and(possibly)NGC7006. These lustersliefarfromtheSgr

predi tedorbitand ouldbethereforerelatedtootherstreamsliketheMono eros

ring(NGC1851)theHer ules-Aquila loud(NGC7006)orotherunknowndebris.

A knowledgements

Based on observations made with the Isaa Newton Teles ope operated on the

islandof LaPalmabytheIsaa NewtonGroupin theSpanish Observatorio del

Roque de los Mu ha hos of the Instituto de Astrofísi a de Canarias and with

2.2m ESO teles ope at the La Silla Observatory under programme IDs

072.A-9002(A),082.B-0386, 084.B-0666and085.B-0765. JC-Bre eivedpartialsupport

from Centre of Ex ellen e in Astrophysi s and Asso iated Te hnologies (PFB

06). ASa knowledgesthePRINMIUR2010-2011"TheChemi alandDynami al

EvolutionoftheMilkyWayandLo alGroupGalaxies"(PI.Matteu i). RL

a -knowledgesnan ialsupporttotheDAGALnetworkfromthePeopleProgramme

(MarieCurie A tions) of the European Unions Seventh Framework Programme

FP7/2007- 2013/ under REA grant agreement number PITN-GA-2011-289313.

R.R.M.a knowledgespartialsupportfromCONICYTAnilloproje tACT-1122

andproje tBASALPFB-

06

aswellas FONDECYTproje tN

◦ 1120013

. JMC-S a knowledgesnan ialsupporttoCONICYTthroughtheFONDECYT

Postdo -toralFellowshipN

◦ 3140310

. Wewarmlythanktheanonymousrefereeforhis/her helpful omments and suggestions. We thank J. Peñarrubia for allowing us to

usethemodeloftheSagittariustidalstreamforthis work. ThankstoA. Robin

forher useful ommentsaboutthe Besançon model. Thanks to A. Apari io, S.

Hidalgo, R. Carrera and D.C. Bardalez-Gagliu for their parti ipation in the

observingruns.

Sear h for halo substru ture in

KiDS

Authors

B.Pila-Díez,J.T.A.deJong,K.KuijkenandtheKiDS onsortium

Abstra t

We use data from the data release 1 and data release 2 from the Kilo Degree

Survey,apubli surveyattheESOVLTSurveyTeles ope,tomapthehalousing

nearmainsequen estarsandred lumpstars. Wesear hforstellaroverdensities

atdierentdistan eormagnituderanges,aimingtodete tnewsatellitesortidal

debris. We re over broad stru tures like the Sagittarius stream (both in the

northernandinthesouthernhemisphere),theEasternBandStru ture,theVirgo

Overdensity and part of the Gala ti disk, and we also identify a pie e of the

Palomar 5 tails. Using Colour Magnitude Diagrams and derivedstellar density

maps, wetest several andidatenarrowoverdensities forboth olour-magnitude

andspatial oheren e,but on ludethatnoneofthe andidatesisarealsatellite

orapie e of olda retedsubstru ture.

6.1 Introdu tion

Thesear hforsatellitesandfortidalremnantsisoneofthemaingoalsofGala ti

halostudies, sin etheyprovide alook bothinto the urrenta retionhistory of

theGalaxyandinto thestarformationhistoryofthesatelliteortheprogenitor.

They analsoprovide onstraintsonthemassandshapeofthedarkmatterhalo.

Additionally they help set onstraintson the

Λ

-Cold DarkMatter osmologi al modelandserveas atestben h foritspredi tions.

Inthelast de ade,manysatellitegalaxieshavebeendis overed,andtherst

oldstellarstreamsin thehalooftheGalaxyhavebeenrevealed. Thishasbeen

possible thanks to the advent of deep multi- olour large area surveys su h as

2MASS,SDSS,Pan-STARRS,DESandothers. 2MASSwasparti ularly

su ess-fulin tra ing withred giantstars thetwo tails ofthe Sagittariusstellar stream

wrappingatleast

180 deg

ea haroundthegalaxy (Majewskiet al.2003). SDSS hasun overeda wealth ofnew satellitegalaxies (Belokurov et al.2007 ;Zu ker

et al. 2006) and a myriad of streams, asso iated both to dwarf galaxies

(Be-lokurovetal.2006b;Grillmair2006a;Newbergetal.2010)andtoglobular lusters

(Odenkir henetal.2001;Grillmair&Dionatos2006a;Grillmair&Johnson2006).

Pan-STARRS,ontheother hand,hasdis overed one thin oldstream(Bernard

etal.2014). AndthePAndASsurveywhi htargetedM31'shalohasprobed

atleastvestellarstru turesintheMilkyWay'shaloalongthelineofsighttothe

Andromedagalaxy: theMono eros ring,thePis es/Triangulum globular luster

stream and three stru tures possibly asso iated to the Triangulum/Andromeda

overdensity(Martinetal.2014). Mostre ently,DEShasreportedthedis overyof

9newsatellitesintheSouthernsky(TheDESCollaborationetal.2015;Koposov

etal.2015),andlastyearATLASalsounveiledanewstreamintheSouthernsky

(Koposovetal.2014).

TheKilo DegreeSurvey(KiDS), isone ofthree publi surveys urrently

un-derwayontheESOVLTSurveyTeles ope(VST).Itisdesignedtomapthelarge

s aledarkmatterdistributionthroughweakgravitationallensing,andis urrently

s anningtheskyto over

1500 deg ²

toadepthapproximately2magnitudesfainter than SDSS. Most of the planned footprint of KiDS targets the Southern

hemi-sphereoftheskywhi h,forlogisti reasons,hasnotbeenasextensivelysurveyed

as the Northern hemisphere thus far. Ongoing surveys in the Southsu h as

KiDSitselfbut alsoATLASandDESarenowreportingrstresults. Withthe

rstdatareleases,KiDSDR-1andDR-2,nowavailable,itistimetostarttesting

thedataset andexplorethehalo forsignsofsubstru ture.

In this hapter we briey review the observations, surveystrategy and data

pro essingofKiDS(se tion6.2),des ribethete hniqueswehaveusedtosear hfor

newsubstru ture(se tion 6.3.1),present re overed substru tures and andidate

overdensities(se tion6.3.2)anddis ussourresultsaswellasthefutureprospe ts

(se tion6.4). Finallywesummarizethemain ideasoftheworkin se tion6.5.

In document Title: Structure and substructure in the stellar halo of the Milky Way (pagina 151-156)