Gas and stars in compact (young) radio sources

0.25 MB·English

by  R. Morganti

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