Astron. Nachr./AN999,No.88,789–??(2006)/DOIpleasesetDOI! Gas and stars in compact (young) radio sources R.Morganti1,2,⋆ B.Emonts3,J.Holt4,C.Tadhunter5,T.Oosterloo1,2andC.Struve1,2 1 NetherlandsFoundationforResearchinAstronomy,Postbus2,7990AADwingeloo,TheNetherlands 2 KapteynAstronomicalInstitute,UniversityofGroningenPostbus800,9700AVGroningen,TheNetherlands 3 AustraliaTelescopeNationalFacility,CSIRO,POBox76,Epping,NSW1710,Australia 4 LeidenObservatory,LeidenUniversity,POBox9513,NL-2300RALeiden,TheNetherlands 9 5 DepartmentofPhysicsandAstronomy,UniversityofSheffield,Sheffield,S73RH,UK 0 0 Received1,accepted1 2 Publishedonlinelater n a J Keywords Galaxies:active,Galaxies:evolution,ISM 5 Gascanbeusedtotracetheformationandevolutionofgalaxiesaswellastheimpactthatthenuclearactivityhasonthe surroundingmedium.Fornearbycompactradiosources,wehaveusedobservationsofneutralhydrogen-thatwedetected ] inemissiondistributedoververylargescales-combinedwiththestudyofthestellarpopulationanddeepopticalimages A toinvestigatethehistoryoftheformationoftheirhostgalaxyandthetriggeringoftheactivity.Formoredistantandmore G powerfulcompactradiosources,wehaveusedopticalspectraandHI-inabsorption-toinvestigatethepresenceoffast outflowsthatsupporttheideathatcompactradiosourcesareyoungradioloudAGNobservedduringtheearlystagesof . h theirevolutionandcurrentlyshedding theirnatalcocoonsthrough extremecircumnuclear outflows.Wewillreviewthe p mostrecentresultsobtainedfromtheseprojects. - o (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim r t s a 1 Introduction sources.Theyare,therefore,theidealtargetstolearnmore [ about the relation between formation and evolution of the 1 The origin of the onset of the nuclear activity in galaxies host galaxy,the triggerof the activity and its effecton the v is still a matter of debate. As radio astronomers, we are nuclearregionsofthehostgalaxy. 3 3 in theluckypositionofknowinghowtofinda newlyborn Inordertogainabetterinsightonthesetopics,wecom- 4 or youngradio source (and even organisea meeting about bineopticalinformationofCSS/GPSsourceswithextensive 0 them!)andthereforewecanattempttoinvestigatewhether studies of the cool neutral hydrogen (HI) gas. The large- . 1 thecharacteristicsoftheirhostgalaxycantellusaboutthe scale distribution and kinematics of the HI gas, combined 0 possibletriggeroftheradioactivity.Theoverwhelmingma- withaspectroscopicstudyofthestellarpopulationsacross 9 jorityof bright,low-z (z < 1)radiosourcesare hostedby the hostgalaxy,provideessential informationaboutpossi- 0 early-typegalaxies(ETGs).ETGsarethoughttoformhier- ble mergeror interaction eventsthat may be related to the : v archically,growinginmassandsizebymergingofsmaller triggeringof radiosources,while the characteristicsof the i X systems. However, it is now clear that ETGs are complex HIandionisedgasinthecentralregioncanbeusedtostudy systems (see e.g. Emsellem et al. 2007). They often host in greatdetail the totalfeedbackthatthe radio sourcesex- r a sub-componentsintheirstructureandtheirdynamics,stel- ert on the ISM of the host galaxy. Our work concentrates lar populations and nuclear activity is characterised by a on:i)nearby,relativelylowpowerradiosources(Fanaroff- surprisingly wide variety. This diversity goes beyond cur- RileytypeIsources)thatwestudyusingHIdetectedboth rent simulationsand predictionsfrom hierarchicalmodels. inemissionandinabsorptioncombinedwiththeproperties Gasandassociateddissipativeprocessescanplayanimpor- of their stellar population;ii) more distant FRII-like radio tantroleinexplainingsuchadiversity.Atthesametime,the sources for which we use, for lack of sensitivity to detect effectsofthefeedbackonthegasproducedbysupernovae HI emission, observations of the HI absorption and com- windsorbythenuclearactivityisalsoextremelyimportant binethiswithobservationsoftheionisedgas. (Silk & Rees 1998; Hopkins et al. 2005). Thus,theinitial phaseofAGNcanbecrucialintheevolutionofthehost 2 Nearby extended and compactradio galaxy. sources -presence ofneutral hydrogen Asextensivelydiscussedinthismeeting,GPSandCSS (GigahertzPeakedSpectrumandCompactSteepSpectrum) In the last few years we have searched for HI around the radiosourcesaregenerallyconsideredrecentlystartedradio hostsofnearbyradiogalaxies.Initialresultsarepresentedin ⋆ Correspondingauthor:e-mail:[email protected] Emontsetal.(2007)andEmonts(2006).Inordertounder- standwhetherthegascontentofnearbyradiogalaxiesisat (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 790 R.Morgantietal.:Gasinyoungradiosources B2 0258+35 NGC 2685 B2 0648+27 10 kpc 160 kpc NGC 3894 190 kpc 105 kpc 37 kpc NGC 4278 Morganti et al. 2006, MNRAS, 371, 157 Fig.1 Total HI mass detected in the host galaxy plotted against the radio power for the samples of radio-loud (log P > 1022 W Hz−1, where P is the radio power at v = 1.4 GHz) and radio-quiet (log P < 1022 W Hz−1)early-type galaxies(fromMorgantietal.2006,Oosterlooetal.inprep.).Severalgalaxieswithdisk-likeHIstructuresareshownto clarifytheirmorphology.Thefilledcirclesarethedetectionsofcompactradiosources,theopencirclesarethedetections forFRI sourceswhile theopensquaresarethe HIdetectionforradio-quietearly-typegalaxies.Thefill trianglesarethe HIupperlimits. alldifferentfromthatoftheirradio-quietcousins,wehave laritybetweenthetotalHImassdetectedinradio-loudand comparedthepresenceofneutralhydrogengasinthesetwo radio-quietearly-typegalaxies.Furthermore,inbothcases, types of objects. The aim was to determine whether e.g. the high-mass end of the HI detections consists of large- nearbyradio-loudearly-typegalaxiesmorefrequentlyshow scaledisk-andring-likestructures(withmassesuptoafew evidence for gas-rich merger or interaction events (in the ×1010M andsizesupto∼200kpc).Wethereforedonot ⊙ formofgaseoustidal-tails,bridges,shellsordisks). findevidenceinHIthatgas-richmergersaremorefrequent Our study targeted a complete sample of nearby (z ≤ among nearby low-power radio galaxies than among their 0.04)radiogalaxiesfromtheB2catalog,consistingofrela- radio-quietcounterparts. tivelylowradiopower(logP >22WHz−1)FR-Iandcom- However,intermsofradiosourcepropertieswefindan pact steep spectrum radio sources (see Emonts et al. 2007 interestingdichotomy.TheradiogalaxiesfromtheB2sam- and Emonts et al. in prep. for more details on the sample plethatcontainlargeamountsofHIgas(>few×108M⊙) selection). As a comparison sample we used the SAURON allhostacompactradiosource, while the more extended sample studied in HI by Morgantiet al. (2006) and Oost- FR-I radio sources do not contain similar amounts of HI erlooetal.(inprep).InFigure1weplotthetotalHImass (Emonts et al. 2007). In total about 50% of the compact detected in emission versusthe radiopower at1.4 GHz of sourcesinourB2samplecontaintheselarge-scaleHIdisks the source. From Fig. 1 the separation in radio power of and/orrings.TheHI-richcompactradiosourcesarethere- our B2 sample of radio galaxies and the SAURON sample fore not likely to evolve into extendedFR-I sources as we isclear.AlthoughthedetectionlimitsfortheHImassesof donotseesimilarHIstructuresintheseradiogalaxies.The thetwosamplesaredifferent(duetothefactthattheradio lackoflarge-scaleHIassociatedwiththeextendedFR-Ira- sourcestendtobefartheraway),thereisafirstordersimi- diogalaxiesmeansthattheyarelikelyfueledbyprocesses (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org Astron.Nachr./AN(2006) 791 otherthanmajormergers,e.g.thoughminoreventsorbyac- 3 Powerful CSS/GPS: HIandionisedgas cretingtheir hotgaseousatmospheres(see e.g.Hardcastle, Evans&Croston2007). The above mentioned B2 sample contains relatively low powercompactradiosources.MorepowerfulGPSandCSS sources are found at higher redshift, where the sensitivity becomestoolowforHIemission-linestudies.However,the 2.1 Originofthelarge-scaleHIdisks/rings strongradiocontinuumfluxofGPSandCSSsourcesisex- cellentforHIabsorptionstudies. ItisknownthatGPS/CSSsourcesoftencontainakine- Dothelarge-scaleHIstructuresthatwedetectaroundsev- matically complexISM, with outflowsof gasseen in vari- eralcompactradiosourcestellussomethingaboutthefor- ousphasesofthewarm/hotISM(e.g.Gelderman&Whittle mationhistoryofthehostgalaxy? 1994,Holt,Tadhunter& Morganti2008andrefs.therein). For one case, B2 0648+27, we studied in great detail As mentioned by Holt in these proceedings, we have per- the properties of the HI gas, star formation and AGN ac- formedadetailedstudyoftheseoutflowsofionisedgasina tivity (see Fig. 2). As discussed in detail in Emonts et al. sampleof14CSS/GPSradiogalaxiesfromthe3C,4Cand (2006,2008),theenormousHIringthatsurroundsthehost 2Jysamplesofradiosources(seeHoltetal.2008).Inpar- galaxy(MHI =8.5×109M⊙anddiameter=190kpc)was allel, we studythekinematicsofthe HI gasin theline-of- mostlikelyformedbyamergeroftwogas-richdiskgalax- sighttowardthecentralcontinuumoftheGPS/CSSsources. ies.Thismergeroccurredroughly1.5Gyrago,afterwhich From the long-slitspectra we derive detailed valuesof the the HI gas that was expelled in large-scale tidal features systemicvelocity(seeHoltetal.2008forafulldiscussion). during the initial stages of the merger,had the time to fall Thisis crucialif we want to understandhowcommonfast back onto the host galaxyand settle into the regular rotat- gaseousoutflowsareandhowrelevanttheyarefortheevo- ingringthatweobserve.Deepopticalimagingrevealsthat lutionofthegalaxy. afaintstellarringfollowstheHIgas,tracingthestellarde- Aninterestingresultofthisstudyisthattheneutralout- bristhatwasexpelledduringthemergerinasimilarfashion flows occur especially in young or restarted radio sources astheHI.Themergeroriginisconfirmedbythedetection (Morganti,Tadhunter&Oosterloo2005a).Inatleastsome ofa0.3-0.4Gyryoungpost-starburststellarpopulationthat cases we knowthattheyare originatingatfew hundredpc ispresentthroughoutthehostgalaxyandwhichcouldhave tokpcfromthenucleus,andtheyaremostlikelydrivenby givenB20648+27theappearanceofan(Ultra-)Luminous the interactions between the expanding radio jets and the Infra-Red Galaxy in the first epoch after the merger. The gaseousmediumenshroudingthe centralregions.We esti- activityinB20648+27occurredinseveralstages,withsig- matedthattheassociatedmassoutflowratesareupto∼50 nificanttime-delaysbetweentheinitialmergerandthestar- M yr−1, comparable (although at the lower end of the ⊙ burstevent,aswellasbetweenthemerger/starburstandthe distribution)to the outflowratesfoundfor starburst-driven onsetofthecurrentepisodeofradio-AGNactivity. superwinds in Ultra Luminous IR Galaxies (ULIRG), see Rupke,Veilleux&Sanders(2002).Thissuggeststhatmas- The other HI-rich compact radio sources from our B2 sive, jet-driven outflows of neutral gas in radio-loud AGN sample also show disks and rings of neutral hydrogengas can have as large an impact on the evolution of the host very similar to the case of B2 0648+27(see Emonts 2006 galaxiesastheoutflowsassociatedwithstarbursts.Thesim- for details) butthat appearmore settled. However,they do ilarities found between the kinematics of the neutral and notshowevidenceforsuchaprominentyoungstellarpop- ionisedgasindicatethatthetwophasesofthegasarepartof ulation.Theirspectraindicatethatthestellarpopulationsin thesameoutflow.However,theoutflowsofionisedgasare the main body of these systems are at least one to several typicallymuchlessmassive(Morgantietal.2005b,Emonts Gyrold(Emonts2006).Iftheselarge-scaleHI disks/rings etal.2005)thanthoseoftheneutralhydrogen. were also formed by major mergers, they must have hap- The GPS source 4C12.50 is a nice example of radio penedsignificantlylongeragothanthecaseofB20648+27. sourceshowingamassiveoutflowofHIgas.For4C12.50, Thiswouldalsoallowthemtoobtaintheirregularmorphol- abroadandblueshiftedHIabsorptioncoversatotalveloc- ogyandkinematics. ityrangeofalmost2000kms−1(seeMorgantietal.2005a), Insummary,itisinterestingtoseethatgalaxiesthatap- comparabletoanoutflowofionisedgasfoundbyHolt,Tad- peartooriginatefromgas-richmajormergersdonotseem hunter&Morganti(2003).AVLBIstudyoftheneutralhy- to evolve into an extended radio galaxy. This has implica- drogenin the nuclear regionsof this objectshows that the tion for the evolution of the host galaxy. Possibilities are narrowerHIcomponent(detectedclosetothesystemicve- thateitherthese radiosourcesare frustratedbythe ISM in locity)isassociatedwithanoff-nuclearcloud(∼50to100 the central region of the host galaxy, or the fuelling stops pc from the radio core. Thus, 4C12.50 is an example of a before the sources can expand (see also Giroletti, Giovan- youngradiosourcewithnuclearregionsthatareenshrouded nini&Taylor2005)perhapsbecauseofthetypeofmerger inadensecocoonofgasanddust.Theradiojetsareexpand- (progradevsretrograde,seediMatteoetal.2007)thatisat ingthroughthiscocoon,sweepingmaterialfromthenuclear theoriginofthesegalaxies. regions. www.an-journal.org (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 792 R.Morgantietal.:Gasinyoungradiosources Fig.2 Left: HI contours overlaid onto deep optical image of radio galaxy B2 0648+27. Contours: 0.22,0.36,0.52,0.71,0.95,1.2,1.5,1.8,2.1×1020cm−2.Right:resultsofstellarpopulationsynthesismodelingofoptical long-slitspectra;the stellar lightis dominatedbya 0.3Gyr youngstellar populationat variouslocationsacrossthe host galaxy.SeeEmontsetal.2006&2008fordetails. AnotherinterestingcaseisPKS1549–79,discussedin flows,bothintheionisedgasandintheHIabsorption-line greatdetailinHoltetal.(2006).Althoughthissystemdoes gas.ThisindicatesthatGPSandCSSsources,whetherfrus- not display an outflow of neutralhydrogen,HI absorption tratedornot,areavitalcomponentinthefeedbackofgalax- is detected and resolved against the extended radio struc- ies. ture at VLBI scales. In this case the HI absorption likely tracesaquiescentcocoonofHIthatsurroundsthecompact References radiojetsandwhichhasnotyetbeenperturbedbytheradio source.WeconcludethatPKS1549–79isaradiosourcein diMatteo,P.,Combes,F.,Melchior,A.-L.,Semelin,B.2007A&A a stagewherethe nucleusisstillhidden(intheoptical)by 468,61 thegas/dustcomingfromthemergerthattriggeredtheradio Emonts B.H.C., Morganti R., van Gorkom J.H., Oosterloo T.A., source.Young,smallscaleradiojetsareexpandingthrough BrogtE.,TadhunterC.N.2008A&A488,519 dense cocoon, sweeping aside gas and dust. Interestingly, Emonts,B.H.C.,Morganti,R.,Tadhunter,C.N.,etal.2007,A&A, boththesesourcesshowevidenceofayoungstellarpopula- 464,L1 tioncomponentintheiropticalspectra,consistentwiththe EmontsB.H.C.,Morganti,R.,Tadhunter,C.N.,etal.2006A&A scenariodescribedabove. 454,125 Emonts,B.H.C.2006,PhDthesis,UniversityofGroningen Emonts B.H.C., Morganti R., Tadhunter C.N., Oosterloo T.A., 4 Summary andconclusions HoltJ.,vanderHulstJ.M.2005,362,931 EmsellemE.,CappellariM.,Krajnovic´D.2007MNRAS379,401 We useddetailedobservationsofgasandstarformationin GeldermanR.,WhittleM.1994,ApJS91,491 GirolettiM.,GiovanniniG.,TaylorG.2005A&A441,89 ordertotracetheformationhistoryandevolutionofthehost Hardcastle M., Evans D. A., Croston J. H. 2007 MNRAS 376, galaxiesofnearbycompactradio sources.Observationsof 1849 large-scale HI emission-line gas reveal that about half of HoltJ.TadhunterC.N.,MorgantiR.2008MNRAS387,639 lowerpowercompactradiosourcesatlow redshiftcontain HoltJ.,TadhunterC.,MorgantiR.,BellamyM.,GonzlezDelgado large amounts of HI gas. The gas is distributed in large- R.M.,TzioumisA.,InskipK.J.2006MNRAS370,1633 scale disk- and ring-likestructures,which couldbe the re- HoltJ.,TadhunterC.N.,MorgantiR.2003,MNRAS342,227 sult of either recent or old merger events. Extended FR-I Hopkins P. F., Hernquist L., Cox T. J., di Matteo T., Martini P., sourcesdo notcontainsimilar largeamountsof HI, hence RobertsonB.,SpringelV.,2005,ApJ,630,705 MorgantiR.,DeZeeuwT.,OosterlooT.etal.2006,MNRAS371, theseHI-richlow-powercompactsourcesarenotexpected 157 togrowintoextendedFR-Isources.Forthelowestredshift MorgantiR.,TadhunterC.N.,OosterlooT.2005a,A&A444,L9 systemsasawhole,nocleardifferencebetweenradio-loud Morganti R., Oosterloo T.A., Tadhunter C.N., van Moorsel G., and radio-quiet early-type galaxies is seen. More power- EmontsB.2005b,A&A439,521 ful GPS and CSS sources (which are too far away for HI RupkeD.S.,VeilleuxS.,SandersD.B.2002,ApJ570,588 emission-linestudies)oftenshowevidenceformassiveout- SilkJ.,ReesM.J.1998,Mon.Not.Astron.Soc.331,L1 (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org