Starburst and AGN activity in ultraluminous infrared galaxies

23 Pages·2003·1.69 MB·English

Mon.Not.R.Astron.Soc.343,585–607(2003)
Starburst and AGN activity in ultraluminous infrared galaxies
(cid:2)
D. Farrah,1 J. Afonso,2,3 A. Efstathiou,4 M. Rowan-Robinson,5 M. Fox5
and D. Clements5
1SIRTFScienceCentre,CaliforniaInstituteofTechnology,JetPropulsionLaboratory,Pasadena,CA91125,USA
2CAAUL,Observato´rioAstrono´micodeLisboa,TapadadaAjuda,1349-018Lisboa,Portugal
3OnsalaSpaceObservatory,S-43992Onsala,Sweden
4DepartmentofComputerScienceandEngineering,CyprusCollege,6DiogenousStreet,POBox22006,1516Nicosia,Cyprus
5AstrophysicsGroup,BlackettLaboratory,ImperialCollege,PrinceConsortRoad,LondonSW72BW D
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Accepted2003April7.Received2003April7;inoriginalform2002December13 d
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ABSTRACT h
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We examine the power source of 41 local ultraluminous infrared galaxies (ULIRGs) using s
archivalinfrared(IR)andopticalphotometry.Wefittheobservedspectralenergydistributions ://a
c
a
withstarburstandactivegalacticnucleus(AGN)components,eachcomponentbeingdrawn d
e
m
fromafamilyoftemplates.Wefindthatallofthesamplerequireastarburst,whereasonlyhalf ic
requireanAGN.In90percentofthesamplethestarburstprovidesoverhalftheIRemission, .ou
p
withameanfractionalluminosityof82percent.Whencombinedwithothergalaxysampleswe .c
o
m
findthatstarburstandAGNluminositiescorrelateoversixdecadesinIRluminosity,suggesting
/m
thatacommonfactorgovernsbothluminosities,plausiblythegasmassesinthenuclearregions. n
ra
We find no trend for increasing fractional AGN luminosity with increasing total luminosity, s
/a
contrary to previous claims. We find that the mid-IR F7.7/C7.7 line-continuum ratio is no rtic
indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that le-a
wFi7t.h7/tChe7.7stiasrbnuortsatrleulmiaibnloesditiya,gbnuotstsihcoowfsthneopcoowrreerlasotiuorncewiinthUthLeIRAGGsN.Tlhuemriandoisoitflyu,xincloinrreelwatieths bstrac
previous results. We propose that the scatter in this correlation is due to a skewed starburst t/34
3
initial mass function and/or relic relativistic electrons from a previous starburst, rather than /2
/5
contaminationfromanobscuredAGN.WeshowthatmostULIRGsundergomultiplestarbursts 8
5
duringtheirlifetime,andbyinferencethatmergersbetweenmorethantwogalaxiesmaybe /10
4
commonamongstULIRGs.OurresultssupporttheevolutionarymodelforULIRGsproposed 1
7
9
byFarrahetal.,wheretheycanfollowmanydifferentevolutionarypathsofstarburstandAGN 9
b
activityintransformingmergingspiralgalaxiesintoellipticalgalaxies,butthatmostdonot y g
u
gothroughanopticalquasi-stellarobjectphase.ThelowerlevelofAGNactivityinourlocal e
s
sample compared with z ∼ 1 hyperluminous infrared galaxies implies that the two samples t o
n
aredistinctpopulations.Wepostulatethatdifferentgalaxyformationprocessesathighzare 2
0
responsibleforthisdifference. N
o
v
e
Key words: galaxies: active – quasars: general – galaxies: Seyfert – galaxies: starburst – m
b
infrared:galaxies. er 2
0
1
8
These ‘luminous infrared galaxies’ (LIRGs), become the domi-
1 INTRODUCTION
nant extragalactic population at infrared (IR) luminosities above
OneofthemostimportantresultsfromtheInfraredAstronomical 1011 L(cid:3), with a higher space density than all other classes of
Satellite (IRAS) all-sky surveys was the detection of a new class galaxy of comparable bolometric luminosity. At the most lumi-
of galaxy where most of the bolometric emission lies in the in- nous end of the IRAS galaxy population lie the ultraluminous in-
frared waveband (Soifer et al. 1984; Sanders & Mirabel 1996). frared galaxies (ULIRGs), those with L > 1012 L(cid:3). Although
ir
ULIRGs are rare in the local Universe, their luminosity function
shows strong evolution with redshift (Veilleux, Sanders & Kim
(cid:2)
E-mail:[email protected] 1999)anddeepsubmillimetresurveys(Bargeretal.1998;Hughes
(cid:4)C 2003RAS
586 D.Farrahetal.
et al. 1998; Eales et al. 2000; Fox et al. 2002; Scott et al. 2002) tions 3 and 4, and excluded those objects that did not satisfy our
have found that systems with ULIRG-like luminosities are very luminositycriterion.Fromaparentsampleof73objects,32were
numerous at z (cid:1) 1. ULIRGs are thus an important population in excluded.Thefinalsampleof41objects,presentedinTable1,areall
understanding the cosmic history of star formation. ULIRGs are containedwithintheIRASPointSourceCatalogue.Thisfinalsam-
alsothoughttoplayaroleintheevolutionofspiralandelliptical plethuscomprisesacompletesampleofULIRGsatz <0.1with
galaxies.NearlyallULIRGsareobservedtobeongoingmergers L >1012L(cid:3),andisthusfreefromselectioneffectsarisingfromin-
ir
betweentwoormorespirals(Sandersetal.1988;Farrahetal.2001), fraredcolours,orluminositiesmeasuredacrosssmaller-wavelength
anditisthoughtthatsuchamergerwillformanelliptical(Barnes ranges.
1989). Fluxeswereassembledfromon-linecataloguesandfromthelit-
Despitethis,theevolutionofULIRGs,theirpowersourceandthe erature.Opticalandnear-IRfluxesweretakenfromtheAPMand
triggerbehindtheIRemissionarepoorlyunderstood.Althoughitis 2MASSdatabasesandalsofromCaricoetal.(1988)andSpinoglio
nowacceptedthatamixtureofstarformationandactivegalacticnu- etal.(1995).IRASfluxesweretakenfromtheIRASFaintSource
D
cleus(AGN)activitypowerstheIRemission,thedominantpower Survey.TheXSCANPIsoftwarewasusedtoderiveIRASfluxeswhere ow
source, and how ULIRGs evolve, are unknown. There are simi- onlyupperlimitswerepresentinthecatalogues.Otherinfrareddata nlo
laritiesbetweenULIRGsandstarburstgalaxies(Joseph&Wright weretakenfromCaricoetal.(1988),Maiolinoetal.(1995),Klaas ad
e
1985; Rowan-Robinson & Crawford 1989; Condon et al. 1991). etal.(1997),Rigopoulouetal.(1999),Daleetal.(2000),Zinketal. d
Conversely,manyULIRGsdisplayemissionlinescharacteristicof (2000), Klaas et al. (2001) and Tran et al. (2001). Submillimetre fro
m
Seyferts (Sanders et al. 1988). An early evolutionary model for dataweretakenfromRigopoulou,Lawrence&Rowan-Robinson h
ULIRGs was that of Sanders et al. (1988) who suggested, based (1996), Dunne et al. (2000) and Dunne & Eales (2001). The as- ttp
s
on the similar space density, bolometric emission and luminosity sembledopticalandnear-infraredphotometryislistedinTable2. ://a
functionofULIRGsandquasi-stellarobjects(QSOs)inthelocal Theassembledinfraredandsubmillimetrephotometryislistedin ca
d
Universe,thatULIRGsarethedustenshroudedprecursorstoop- Table3. e
m
tical QSOs and that all QSOs emerge from a luminous infrared ic
phase.Conversely,amorerecentevolutionarymodel(Farrahetal. .ou
p
2001)proposesthatULIRGsarenotasimpledust-shroudedpre- 3 INFRARED EMISSION MODELS .c
o
cursor to optical QSOs but instead follow multiple evolutionary m
paths. 3.1 Starburstmodels /m
n
In this paper we examine the power source in ULIRGs, their ra
evolution,andtheirrelationshiptohigh-zIRluminousgalaxiesus- To model the IR emission due to starburst activity we used the s/a
ingarchivalphotometryforasampleof41localULIRGs,andad- starburstmodelsofEfstathiou,Rowan-Robinson&Siebenmorgen rtic
vancedradiativetransfermodelsforstarburstsandAGN.Wealso (2000).ThesemodelsconsideranensembleofevolvingHIIregions le-a
containinghotyoungstars,embeddedwithingiantmolecularclouds b
examinetheoriginoftheradio–IRcorrelationinULIRGsandthe s
powerofmid-IRspectroscopyasadiagnosticoftheactivepower (GMCs)ofgasanddust.Thecompositionofthedustisgivenby trac
source. Sample selection and data analysis are described in Sec- the dust grain model of Siebenmorgen & Kruegel (1992), which t/3
tviiodnusa2loabnjdec3t.sRaeresugltivseanreinprSeescetnitoend5in.ASedcitsiocnus4siaonndisnoptreesseonnteinddiin- irnescpluodnessibthleefpoorltyhcey7c.l7ic-µarmomematiiscshioyndrfoecaaturbreo.nTsh(ePAstHelsla)rthpooupguhlatttioobnes 43/2/5
withintheGMCsevolveaccordingtothestellarsynthesiscodesof 8
Section6andconclusionsaresummarizedinSection7.Weadopt Bruzual & Charlot (1993). The star formation rate is assumed to 5/1
H0 =65kms−1 Mpc−1,(cid:7)0 =1.0and(cid:8)=0.0andquotealllu- decayexponentiallywithane-foldingtime-scaleof2×107yr.The 041
minosities in this system. Unless otherwise stated, the terms ‘IR 7
modelsvaryinstarburstagefromzeroyearsupto7.2×107yr(11 9
luminosity’,‘starburstluminosity’and‘AGNluminosity’referto discretevalues)andineffectivevisualopticaldepthfromτ =50 9 b
theluminosityoverthewavelengthrange1–1000µm.Luminosi- to200(fourdiscretevalues).AplotshowingtherangeinstVarburst y g
tLie(cid:3)s=are3.q8u2o6t×ed1i0n26uWni.ts of bolometric solar luminosities, where sinpeficgtr.a3l oenfeErgfsytadthisiotruibeuttiaoln.((2S0E0D0)),twemithplaadtedistihoanpaelsincfaonrmbeatifoonunidn uest o
n
fig.1ofthesamepaper. 2
0
N
o
2 THE SAMPLE ve
3.2 AGNtorusmodels m
Weassembledfromtheliteratureasampleofobjectscomprisingall be
ULIRGswithz(cid:2)0.1.Thiswascomplicatedbythefactthatdiffer- TomodeltheIRemissionduetoAGN,weusedtheAGNmodels r 2
0
entauthorsusedifferentminimumluminositiesforULIRGs(e.g. of Efstathiou & Rowan-Robinson (1995). These models incorpo- 18
Condon et al. 1991, L40−120 (cid:1) 1011.02 L(cid:3); Clements et al. 1996, rate accurate solutions to the axially symmetric radiative-transfer
L (cid:1) 1011.77 L(cid:3)). We first adopted our own minimum IR lumi- problemindustcloudstomodeltheIRemissionfromdustinactive
60
nosity for a ULIRG, namely a rest-frame 1–1000 µm luminosity galactic nuclei. Dust composition is given by the multigrain dust
(hereafterreferredtoasL )ofgreaterthan1012L(cid:3).Usingalumi- modelofRowan-Robinson(1992).Wehaveusedthethicktapered
ir
nosityderivedacrossabroadwavelengthrangeistobepreferred, disc models following an r−1 density distribution, as this subset
asluminositiesderivedacrosssmallerwavelengthrangesmayer- of models has been found to be most successful in satisfying the
roneouslyexcludeorincludeobjectsduetotheircontinuumshape. observationalconstraintsofAGN.TheAGNmodelsvaryintorus
We then assembled a parent sample of all objects claimed to be openinganglefrom0◦ to90◦ (15discretevalues)andinultravio-
ULIRGs,orclosetoULIRGluminosity,atz(cid:2)0.1,fromtheIRAS let(UV)equatorialopticaldepth,fromτUV=1000to1500(three
PointSourceCatalogue,theIRASFaintSourceCatalogue,andthe discretevalues).AplotshowingtherangeinAGNtorusSEDtem-
sample presented by Clements et al. (1996). We then determined plateshapescanbefoundinfig.5ofEfstathiou&Rowan-Robinson
their1–1000µmluminositiesusingthemethodsdescribedinSec- (1995).
(cid:4)C 2003RAS,MNRAS343,585–607
StarburstandAGNactivityinULIRGs 587
Table1. Allultraluminousinfraredgalaxiesatz<0.1.
IRASname Othernames RA(2000) Dec. z Opticalspectrum F25/Fa60
(hh:mm:ss) (degarcminarcsec)
00198−7926 002152.9 −791008.0 0.0728 Sy2 0.370
00199−7426 002207.0 −740941.6 0.0964 – 0.078
00262+4251 002854.2 +430815.3 0.0927 LINER 0.112
00335−2732 003600.5 −271534.5 0.0693 Starburst 0.147
01388−4618 014055.9 −460253.3 0.0903 HII 0.121
02364−4751 023813.1 −473810.5 0.0983 – 0.063
03068−5346 030821.3 −533512.0 0.0745 – 0.057
04232+1436 042605.0 +144338.0 0.0796 LINER 0.113
05189−2524 052101.5 −252145.4 0.0426 Sy2 0.252 Do
06035−7102 060254.0 −710310.3 0.0795 HII 0.112 wn
06206−6315 062101.2 −631723.2 0.0924 Sy2 0.074 lo
a
08572+3915 090025.4 +390354.4 0.0584 LINER 0.229 de
0099131210−[phone] UGC05101 009913353581..87 −[phone]..33 00..00534914 HLINII+ESRy+2Sy2 00..006970 d fro
m
09583+4714 100131.2 +465944.0 0.0859 Sy1+Sy2 0.182 h
10035+4852 100646.1 +483744.1 0.0648 Starburst 0.062 ttp
1100419940++41432242 110052212432..65 ++414300864573..39 00..00972616 LHINIIER 00..014174 s://ac
a
10565+2448 105918.1 +243234.3 0.0431 HII+LINER 0.094 de
12112+0305 121345.7 +024840.3 0.0733 LINER 0.060 m
12540+5708 Mrk231 125614.2 +565225.2 0.0422 Sy1 0.271 ic.o
13428+5608 Mrk273 134442.1 +555312.6 0.0378 Sy2 0.105 up
14348−1447 143738.4 −150022.8 0.0827 LINER 0.072 .co
14378−3651 144058.9 −370433.0 0.0676 LINER+Sy2 0.085 m
15250+3609 152659.4 +355837.5 0.0552 LINER 0.182 /mn
15327+2340 Arp220 153457.1 +233011.5 0.0181 LINER 0.076 ra
s
17132+5313 171420.5 +531030.4 0.0509 HII+AGN 0.109 /a
17208−0014 172321.9 −001700.4 0.0428 HII 0.053 rtic
18470+3233 184854.2 +323731.0 0.0784 HII 0.104 le-a
19254−7245 Super-Antenna 193121.6 −723921.7 0.0617 Sy2 0.226 b
s
19297−0406 193220.7 −040006.0 0.0857 HII 0.084 tra
19458+0944 194815.7 +095205.0 0.0999 – 0.066 ct/3
20046−0623 200719.4 −061426.0 0.0844 Starburst 0.141 4
3
20414−1651 204418.2 −164016.2 0.0871 HII 0.079 /2
20551−4250 205826.9 −423906.2 0.0428 HII 0.149 /58
21130−4446 211618.5 −443337.7 0.0926 HII 0.048 5/1
21504−0628 215305.5 −061449.9 0.0776 – 0.111 04
22491−1808 225149.3 −175223.4 0.0778 HII 0.101 17
9
2233132685−[phone] 223313594071..03 −[phone]..97 00..00464465 HHIIII++SLyIN2ER 00..114174 9 by
23389−6139 234143.6 −612250.9 0.0928 HII 0.067 gu
e
s
Coordinates,opticalspectralclassificationsandredshiftsweretakenfromtheNASAExtragalacticDatabase.aRatioof t o
theIRAS25-µmfluxtotheIRAS60-µmflux. n 2
0
N
o
v
andcaremustbetakeninaccountingforthis,asarecentHubble e
4 RESULTS m
SpaceTelescope(HST)studyofULIRGs(Farrahetal.2001)found b
e
4.1 Spectralenergydistributions thattheopticalemissionwasinmostcasesdominatedbyoldstellar r 2
0
populationsandnotbylightfromastarburstorAGN.Therangein 1
8
Wecombinedthearchivalphotometryfromtheopticaltothemil- possibleoptical/near-IRSEDsforevolvedstellarpopulationsisvery
limetretofitspectralenergydistributionsforeachobject.Thegood- large,andinadditionanobscuredstarburstorAGNcan,inprinci-
nessoffitwasexaminedusingthereducedχ2statistic.Fitsforall ple,contributesignificantlyintheopticalornear-IR.Constraining
sourcesweregood,withχ2 (cid:2)5inallcasesandχ2 (cid:2)4inall thepropertiesoftheevolvedstellarcomponentinanyofoursample
best best
butonecase(thisobject,IRAS17208-0014,isdiscussedfurtherin withthelimitedavailableopticalphotometrythereforeprovedim-
Section5).Todeterminetheerrorsonthemodelparametersweex- possible.Wehavethereforeassumedthatallemissionshortwards
ploredreducedχ2spacebetweenχ2 andχ2 +2.Theresulting of3.5µmintherestframeoftheobjectscontainsasignificantbut
best best
luminosities,modelparametersanderrorsaregiveninTable4.The unquantifiedcontributionfromoldstellarpopulations.Asthiscon-
SEDsarepresentedinFig.1. tributioncouldliebetween0and100percent,anymeasuredflux
EmissionfromunobscuredpopulationIIstarsfromthemerger atarest-framewavelengthshorterthan3.5µmistreatedasa3σ
progenitorsisnotincludedineitherthestarburstorAGNmodels, upperlimitinthefitting.
(cid:4)C 2003RAS,MNRAS343,585–607
588 D.Farrahetal.
Table2. Ultraluminousinfraredgalaxies:opticalandnear-IRdata.
Name U B V R J H K L
00198−7926 619±41 764±51 565±38 232±15
00199−7426 1.0±0.1 5.4±0.6 6.4±0.7
00262+4251 5.4±1.6 5.5±1.6
00335−2732 0.94±0.1 4.2±0.4 3.3±0.3 5.0±0.5
01388−4618 0.31±0.04
02364−4751 0.44±0.05
03068−5346
04232+1436 5.5±1.6 10.6±3.2
05189−2524 0.66±0.07 0.65±0.07 0.76±0.08 14.7±0.9 30.8±2.1 57.1±3.8 136±30
06035−7102 2.1±0.2 2.8±0.3 4.2±0.4 Do
06206−6315 1.3±0.1 1.7±0.2 2.8±0.3 wn
08572+3915 0.51±0.05 0.65±0.07 0.90±0.1 1.7±0.1 3.0±0.2 3.9±0.3 50±10 lo
a
09111−1007 3.4±0.3 5.5±0.6 7.4±0.7 de
0099538230++46711344 0.96±0.1 10.91±1.2 1.11±0.1 112.2.9±±00.1.9 211.5.2±±01.2.4 229.0.2±±01.2.9 33±7 d fro
m
10035+4852 h
10190+1322 2.3±0.2 3.0±0.3 2.1±0.2 ttp
1100546954++24444284 114..00±±01..14 127..00±±01..27 128..80±±01..38 s://ac
a
12112+0305 0.16±0.02 0.25±0.03 0.32±0.03 2.0±0.2 2.9±0.3 3.5±0.4 2.2±0.5 d
e
12540+5708 2.77±0.5 7.34±1.24 13.1±2.2 11.5±0.1 49±3 107±7 186±12 368±72 m
13428+5608 0.74±0.07 1.03±0.1 1.76±0.2 9.0±0.9 13.5±1.4 16.1±1.6 17.4±1.7 ic.o
14348−1447 0.22±0.02 0.24±0.02 0.43±0.04 1.7±0.2 2.5±0.3 3.3±0.3 up
14378−3651 2.5±0.3 2.8±0.3 5.0±0.5 .co
15250+3609 0.26±0.03 0.27±0.03 0.42±0.04 3.1±0.3 4.0±0.4 4.1±0.4 4.0±0.4 m
15327+2340 0.96±0.1 3.16±0.3 4.07±0.4 9.6±1.0 17.9±1.8 23.0±2.3 22.7±2.3 /mn
17132+5313 5.6±0.6 8.2±0.8 8.9±0.9 10.5±1.6 ra
s
17208−0014 /a
18470+3233 2.7±0.4 3.6±0.5 rtic
19254−7245 le-a
19297−0406 b
s
19458+0944 tra
20046−0623 3.9±0.6 4.0±0.6 ct/3
20414−1651 4
3
20551−4250 3.93±0.34 5.04±0.34 22.9±5.9 30.2±7.8 25.7±6.7 /2
21130−4446 0.89±0.09 /58
21504−0628 5.5±0.8 5.7±0.9 5/1
22491−1808 0.22±0.02 0.20±0.02 0.26±0.03 2.1±0.2 2.7±0.3 2.6±0.3 2.4±0.2 04
23128−5919 4.09±0.4 7.69±0.7 9.6±0.6 12.6±0.8 11.9±.08 17
9
23365+3604 7.5±0.4 6.5±0.3 9
23389−6139 0.35±0.04 by
g
AllfluxesaregiveninmJyandareintheobservedframe.1σ errorsarequoted. ue
s
t o
n
2
4.2 Starformationrates OBA-typestars,i.e.1.6<M(cid:3) <100).Wehaveassumedthatall 0
oftheoptical/UVlightfromthestarburstisabsorbed((cid:14)∼1.0),and No
EstimatingobscuredstarformationratesfromIRdataisbasedon v
silicateandgraphitedustgrainsabsorbingtheopticalandUVlight thattheIMFofthestarburstisaSalpeterIMFformingstarsacross em
from young stars and reradiating at IR and submillimetre wave- tfhoeromuarsssarmanpglee0ca.1lc<ulMate(cid:3)du<si1n0g0e(qφu=ati1o.n0)(.1T)haerestgairvefonrminaTtiaobnlera4t.es ber 2
lengths.ArecentestimateforderivingstarformationratesfromIR 0
1
luminositieshasbeenmadebyRowan-Robinsonetal.(1997): 8
4.3 Dustmassesandtemperatures
. φ L
M∗,all=2.6×10−10(cid:14) L(cid:3)60, (1) ThestarburstandAGNmodelsdonotassumeamonolithicdusttem-
perature,butinsteadinvokearangeofdusttemperaturesspanning
whereM. ∗,allisthestarformationrate,(cid:14)isthefractionofoptical/UV 10–1000K.Anestimateofthemass-weightedmeandusttempera-
turecanbeobtainedbyfittinganopticallythingreybodyfunction
lightfromthestarburstthatisabsorbedbydustandre-emittedin
the IR, and L is the 60-µm starburst luminosity. The factor φ oftheform
60
i(nIMcoFrp)oarnadtethsethtreuceoIrMreFct(io×n1b.0etfworeeanSaalSpaeltperetIeMrFin,i×tia3l.3mfaosrsafuMnicltlieorn– Sν =νβB(ν,Tdust) (2)
ScaloIMF),andacorrectionfortheassumedupperandlowerstellar to the far-infrared (FIR) SED over the wavelength range 200–
massboundsforthestarsforminginthestarburst(×1.0ifthemass 1000µm,whichmeasuresthecolourtemperatureofthesystem.In
range is 0.1 < M(cid:3) < 100, ×0.323 if the mass range spans only equation(2),Sν isthesourcefluxatafrequencyν,Tdustisthedust
(cid:4)C 2003RAS,MNRAS343,585–607
StarburstandAGNactivityinULIRGs 589
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1 3 1 1 1 82 17 1 1 1 eptper /10
metrefluxes. 15 50.070.01000150110 2702002900500<270<360 1140 150342 <770<390<180500<450150110360150<260 dframe,excmand20µ 41799 by g
mid-IR,far-IRandsubmilli 1012 27757.0100<.87430.600100.500<.63400<.10865060072990.0116<.72400260318167107250<85.984120.60018221765.010014251872100235<96108<<276116<267238.1474837.84.01217 135123120110<396150<84125<.168800<204284<.90550.40.0500<.39800126245<.120800<.75310 nmJyandareintheobserveallotherIRfluxesupto200 uest on 20 November 201
ousinfraredgalaxies: 5.97.7 ..56739 ..12849..00651 .89158..23675 .90274 .6810761208.62294..26859 .80173583 .22223 .88150 ..70534 .53232 ..84593.17230.26106.289 nm.Allfluxesareiµfluxes,30percenton 8
3.Ultralumin −7926−7426+4251−2732−46181−47517−5346+1436−2524−71024−63151+3915−1007+61345+4714+4852+1322+4424+2448+03051+570860+56087−14471−3651+36092+2340+5313−00143+3233−72458−0406+0944−0623−1651−42504−4446−0628−1808−59194+36041−6139 velengthsarei0-and15-mµ
Table Name 0019800199002620033501388023640306804232051890603506206085720911109320095831003510190104941056512112125401342814348143781525015327171321720818470192541929719458200462041420551211302150422491231282336523389 Allwa7.7-,1
(cid:4)C 2003RAS,MNRAS343,585–607
590 D.Farrahetal.
temperature,B(ν,T )isthePlanckfunctionandβisthefrequency thatthisobjectalsocontainsaburiedstarburst.TheX-rayspectrum
dust
dependenceofthegrainemissivity.Monolithicdusttemperatures (Risalitietal.2000)iswellfittedbyatwo-componentmodel,con-
derivedinthiswayareunphysicalsimplificationsinAGN,butcan sistingofapowerlawwith(cid:18) =1.89+0.35,absorbedbyacolumn
−0.34
serveasausefulcomparisonwithpreviouswork.Mass-weighted densityofN =4.7+1.4cm−2,andathermalcomponentwithkT=
H −1.1
meandusttemperaturesforoursamplearepresentedinTable4. 0.88+0.89keV.Overallthepower-lawcomponentcanbeinterpreted
−0.35
Gasanddustmassescanbeestimatedintwoways.Thefirstwayis asarisingfromaComptonthinAGN,withthethermalcomponent
tocalculatethegasmassdirectlyfromthemodelsusingequation(4) eitherduetotheAGNortostarburstactivity.ForourSEDfittingwe
ofFarrahetal.(2002b).This,however,givesthetotalgasmassat compiledanadditionalN-band(10.6µm)fluxof498±100mJy
thecurrentageofthestarburstwithoutaccountingforgasthatis fromMaiolinoetal.(1995).Fromourresults,wefindthatthisob-
blownoutofthenuclearregionsbysupernovaeorsuperwinds,and jectcontainsbothastarburstandanAGN,wheretheAGNprovides
thusmayoverestimatetheamountofgasanddustinthesystem. asignificantfractionofthetotalIRluminosity.
The second approach is to estimate the dust mass directly from
09320+6134. Thisobjectpossessesasinglebrightnucleusanda D
the submillimetre SED. An approach for estimating dust and gas disturbedspiralstructure(Scovilleetal.2000).Thereisonelarge ow
misaospsteicsainllygathlainxiaetstuhseisnegwsuavbemleilnligmthest,reanddattaoifsotloloawsstuhmeeprtehsecsryipsttieomn tpalielteexrtienngdiwngith∼3a8toktpacl,laenndgtahseocfo∼nd65taiklpthc.atTfhoermmsoarlpmhoosltoagycohmas- nloade
ofHildebrand(1983): d
Mdust= 1+1 zκ(νr)SBν(oνDr,L2Tdust), (3) bgdaweleaanrxfiiengstae(lrSapxarynetde(edMrsaaesjetwaalsl.ka1tie9e-8st8taa)g,l.ep1om9ss9ei3rbg)le.yrTinbhveeotwlovepietningcatalwtsohpierladcrtgrgueamss-ppioisroaarl from http
wspheecrteivνeloy,anSdνoνisr tahreeflthuexoinbstehrevoedbsaenrvderdefsrtafmraem,eB(fνrerq,uTednucsti)eiss,trhee- Vcoe´mrobnin1a9ti9o9n).oNfeaarL-IIRNEsRpecatnrdosacoSpyy2b(yGIomnac¸nalivsheis,,DVue´droleny-C&etMtya&l- s://aca
PlanckfunctionintherestframeandT isthedusttemperature. oney(2001)showsthatthisobjectislikelytocontainaheavilyob- d
dust e
Thegasmassisthenobtainedbyassumingafixedgas-to-dustratio. scuredAGN.Conversely,Lutz,Veilleux&Genzel(1999)classify m
ic
ForthemostextremeIRASgalaxies,thebestcurrentestimateofthe thisobjectasstarburstpoweredonthebasisofmid-IRspectroscopy, .o
u
gas-to-dustratiois540±290(Sanders,Scoville&Soifer1991). andthesubmillimetreemissionisalsoconsistentwithastarburst p
.c
Forcomparison,thegas-to-dustratioinspiralgalaxiesisthought (Rigopoulouetal.1996).Wecompiledanadditional350-µmupper o
m
to be ∼500 (Devereux & Young 1990), and ∼700 in ellipticals limitof2664mJy,andanadditional800-µmfluxof143±25mJy /m
(Wiklind&Henkel1995).Themassabsorptioncoefficientinthe fromRigopoulouetal.(1996).Wefindthatthissystemisacom- nra
rκers=tfr0a.m06e7,κ(cid:1)r2,.i5st×νark1e0n11to(cid:2)bβe (4) pcFooigns.ist1iestioetbncjtaewnctbitcehospnerteeanvinitoihnuagstbothobetsheAravGsaNttaiorhbnaussr.saFtrhaoingmdhteahrnenASeGEarDN-I,Rfiatflrpeursexustlehtnatthneadtthiines s/article-a
starburstcomponent,butthattheAGNcontributioninthemid-IR b
inunitsofm2kg−1.Dustmassesandtemperaturescalculatedusing issmall,andisnegligibleinthesubmillimetre.Thisobjectisacase stra
equations(2)and(3)aregiveninTable4. c
inpointthat,inordertounderstandthepowersourceinULIRGsit t/3
isnecessarytohavedataspanningawidewavelengthrange. 4
3
5 INDIVIDUAL OBJECTS 10565+2448. Wecompiledanadditional350-µmfluxof1240± /2/5
8
Inthissectionwepresentfurtherdiscussiononobjectsinoursam- 248mJy,anda750-µmfluxof85±17mJyfromRigopoulouetal. 5/1
ple that are either well-studied by previous authors, or that show (1996).TheAGNinthisobject,althoughweakcomparedwiththe 04
1
interestingorunusualfeatures. starburst,isrequiredforanacceptableSEDfit. 7
9
9
00198−7926. Thissourceisadouble-nucleussystemwithalarge 12112+0305. Thissystemcontainstwoseparatenucleiwithapair b
y
tail,withaSy2opticalspectrum.Thesecondnucleusisprobably of tidal tails (Scoville et al. 2000). The optical spectrum is that g
u
alargeregionofextranuclearunobscuredstarformation,andthere of a LINER (Veilleux et al. 1999). This source is classified as a es
areanumberofHIIregionsembeddedinthetail(Heisler&Vader starburst on the basis of its mid-IR spectrum (Rigopoulou et al. t on
1994).AdeepBepposaxobservationgavenodetection,givingan 1999). We compiled an additional 800-µm flux of 50 ± 13 mJy 2
0
upperlimittotheX-rayfluxof F2−10 <1×10−13 ergcm−2 s−1 fromRigopoulouetal.(1996).TheextensiveIRdataavailablefor No
(Risalitietal.2000).Fromourresults,thepropertiesofthisobject thisobjectallowustoplacestrongconstraintsonthepowersource. ve
m
markitasunusual.WefindthattheIRemissionfromthisobjectis Wefindthatthisobjectispoweredbyastarburst,withasevereupper b
e
mostlystarburstinorigin.Thestarburstiscomparativelyold,and limitonanyAGNcontribution. r 2
canthusaccountforboththesubmillimetreemissionandallofthe 12540+5708. This galaxy is commonly known as Mrk 231 and 018
unobscuredstarformationobservedbyHeisler&Vader(1994).We
hasaSy1opticalspectrum.TheIRluminosityisthoughttobepow-
interpretthe‘warm’infraredcolourofthisobjectasbeingduetothe
eredbybothstarburstandAGNactivity(Cutri,Rieke&Lebofsky
oldstarburstratherthananAGN.Thereis,however,comparatively
1984; Condon et al. 1991). Mrk 231 possesses a single compact
littleIRdataavailableforthisobjectandtheresultingAGNupper
nucleussurroundedbyirregular‘rings’ofrecentstarformationand
limitisweak.Thebest-fittingmodel,showninFig.1,includesan
a small tidal arm containing numerous blue star-forming ‘knots’,
AGNcomponent.
andisthereforethoughttobeanadvancedmerger.Thenucleusis
05189−2524. Thisobjectappearstobealate-stagemerger.Itpos- unresolvedintheradioband(Condonetal.1991)andat11.7µm
sesses a single, compact, very red nucleus with a Sy2 spectrum (Miles et al. 1996), implying that the emission from the nucleus
(Veilleuxetal.1995),bisectedbyadustlane(Scovilleetal.2000). ispoweredbyanAGNratherthanastarburst.Mrk231isclassi-
Youngetal.(1996)observedbroadlinesinpolarized fluxinthis fiedasanAGNonthebasisofbothnear-IRspectroscopy(Imanishi
object,suggestingthepresenceofanobscuredAGN.Laterobserva- etal.2001)andmid-IRspectroscopy(Rigopoulouetal.1999).Con-
tions(Dudley1999)observedthe11.3-µmdustfeature,suggesting versely,theX-rayemissionfromthisobject,althoughweak,cannot
(cid:4)C 2003RAS,MNRAS343,585–607
StarburstandAGNactivityinULIRGs 591
Table4. Ultraluminousgalaxies:luminositiesandmodelparameters.
Name χ2,a LTot LSb LAGN Ageb SFRc θd Me Tf βg
IR IR IR d
(L(cid:3)) (L(cid:3)) (L(cid:3)) (Myr) (M(cid:3)yr−1) (◦) (M(cid:3)) (K)
00198−7926 3.50 12.72+−00..0012 12.65+−00..0053 <11.91 64–71 130±50 – 7.31+−00..1150 36±4 1.95±0.22
00199−7426 2.35 12.36+−00..0022 12.30+−00..0041 11.34+−00..1117 26-37 360±50 – 8.48+−00..0192 27±7 1.96±0.40
00262+4251 1.66 12.10+−00..0011 11.64+−00..0081 11.92+−00..0016 26–45 50±30 <15 8.42+−00..2500 25±5 1.87±0.05
00335−2732 1.33 12.01+−00..0044 11.99+−00..0034 <10.95 <57 170±20 – 7.07+−00..0092 42±3 1.97±0.20
01388−4618 2.08 12.11+−00..0034 12.03+−00..0034 <11.35 >26 200±20 – 8.10+−00..0197 28±4 1.92±0.10
02364−4751 1.93 12.20+−00..0011 12.15+−00..0012 11.23+−00..0170 >10 260±30 – 7.97+−00..0023 32±7 1.91±0.20
03068−5346 1.56 11.96+−00..0012 11.93+−00..0043 <10.94 1.6–6.6 180±40 – 7.62+−00..0192 35±3 1.97±0.20 Do
04232+1436 1.41 12.07+−00..0034 11.95+−00..1101 <11.70 <37 210±30 – 7.87+−00..1310 31±4 1.90±0.25 wnlo
05189−2524 2.20 12.16+−00..0042 11.99+−00..0066 11.67+−00..0172 6.6–26 170±30 25–54 7.61+−00..2280 33±5 1.94±0.06 ade
0066023056−−76130125 11..0000 1122..2241+−+−0000....00001211 1122..1198+−+−0000....00001516 1111..2015+−+−0000....20420503 1166––2266 239000±±3300 <>2455 77..7943+−+−0000....00004524 3351±±22 11..9952±±00..0032 d from
08572+3915 2.22 12.17+−00..0011 11.99+−00..0016 11.70+−00..0092 <57 180±20 – 7.04+−00..2006 45±5 1.92±0.10 http
000999135128103−++164017031744 121...910210 111222...000116+−+−+−000000......000000221156 111211...099180+−+−+−000000......000011231120 10<<.811601+−..680040..0130 2>6––1367 111966200±±±227050 >––25 87..3930–+−+−0000....11011641 322495±±±1435 111...999435±±±000...207830 s://academ
10035+4852 1.00 11.98+−00..0045 11.97+−00..0057 <11.50 – 180±30 – 7.87+−00..1105 29±5 1.95±0.20 ic.o
1100149904++14342224 12..0004 1122..1200+−+−0000....00003222 1122..0116+−+−0000....00003322 11<.3161+−.0006..0183 <<2166 218905±±4105 –– 77..9875+−+−0000....00005555 3322±±35 11..9974±±00..1256 up.com
10565+2448 1.23 12.06+−00..0022 12.03+−00..0032 10.80+−00..1140 26–37 200±20 – 7.85+−00..0057 30±2 1.95±0.20 /mn
111111223445154332142475208880+++−−+055133376466000450588719 211112......359903069802 111111222222......251310985028+−+−+−+−+−+−000000000000............000000000000224343133234 111111222221......240106929838+−+−+−+−+−+−000000000000............000000001000236663440188 11112111<<....02581951461.+−+−+−+−.530000000006........1005120101502570 111121660660––––––221233666677 23423759761000000±±±±±±342533000000 2<<7––––315254 777777......899794145073+−+−+−+−+−+−000000000000............010110000201832772225082 333333361247±±±±±±224154 111111......999996545159±±±±±±000000......1000310182 ras/article-abstract/34
1157312372++25334103 21..0010 1121..1942+−+−0000....00002131 1121..1844+−+−0000....00002121 11<.194.+−9000..0111 2160––3276 214300±±3200 –– 87..3624+−+−0000....00105685 2371±±33 11..9935±±00..0023 3/2/585
17208−0014 4.70 11.99+−00..0034 11.99+−00..0045 <11.00 >16 150±30 – 8.25+−00..1295 26±6 1.95±0.3 /104
18470+3233 1.00 12.08+−00..0034 12.03+−00..0044 <11.42 6.6–37 200±40 – 7.54+−00..3310 35±6 1.95±0.05 179
19254−7245 1.52 12.24+−00..0180 12.17+−00..1005 <11.60 – 170±50 – 7.60+−00..1114 34±4 1.96±0.1 9 b
19297−0406 1.00 12.41+−00..0025 12.39+−00..0036 <11.50 <57 480±150 – 8.15+−00..1105 31±6 1.95±0.25 y gu
122900404541864+−−001966425431 111...701308 111222...412072+−+−+−000000......000000123412 111222...211516+−+−+−000000......000100313111 1111<..831311+−+−.600000....00014850 6<∼.6–221666 232108000±±±631005 ––– 787...894699+−+−+−000000......010111322864 233228±±±292 111...899966±±±000...051150 est on 20 N
20551−4250 1.95 12.05+−00..0045 11.90+−00..0110 11.53+−00..0137 10–57 160±20 – 7.05+−00..1035 44±3 1.91±0.04 ov
21130−4446 1.65 12.14+−00..0021 12.11+−00..0032 <10.90 37–64 250±15 – 7.99+−00..0053 30±2 1.94±0.10 emb
21504−0628 1.00 12.00+−00..0034 11.94+−00..0047 11.06+−10/.145 <57 180±20 – 7.15+−00..1115 42±4 1.97±0.10 er 2
22491−1808 2.38 12.16+−00..0012 11.61+−00..0027 12.02+−00..0033 ∼26 60±10 <10 8.04+−00..0034 27±3 1.80±0.02 018
23128−5919 2.15 12.02+−00..0022 11.93+−00..0047 11.30+−00..1007 26–37 150±30 – 7.75+−00..0078 30±3 1.93±0.03
23365+3604 2.90 12.19+−00..0011 12.00+−00..0012 11.73+−00..0029 ∼26 200±20 <10 7.81+−00..0023 33±2 1.86±0.02
23389−6139 1.22 12.16+−00..0011 12.15+−00..0012 10.48+−00..1128 16–26 290±30 – 7.70+−00..2009 33±4 1.94±0.05
Luminositiesarethelogarithmofthe1–1000µmluminositiesobtainedfromthebest-fittingcombinedstarburst/AGNmodel,inunitsofbolometricsolar
luminosities. aReduced χ2 of the combined SED fit. bStarburst age. cStar formation rate. dViewing angle of the AGN dust torus. eDust mass. fDust
temperature.gEmissivityindex.
befittedwithapurepower-laworthermalbremsstrahlungmodel aluminousstarburstandanAGN,wherethestarburstcontributes
(Iwasawa1999).Wecompiledadditionalmid-IRdatafromRieke ∼70percentofthe1–1000 µmIRluminosity.Interestingly,this
(1976) and additional submillimetre data from Rigopoulou et al. resultisinexcellentagreementwithindependentestimatesofthe
(1996)andCaricoetal.(1988).WefindthatMrk231containsboth starburstandAGNluminositiesinMrk231derivedfromvery-long
(cid:4)C 2003RAS,MNRAS343,585–607
592 D.Farrahetal.
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Figure1. Best-fittingspectralenergydistributionsforthe41ULIRGsinoursample.Ineachcasethesolidlineisthecombinedbest-fittingmodel,thedotted t o
lineistheStarburstcomponentandthelongdashedlineistheAGNcomponent. n 2
0
N
o
baselineinterferometry(VLBI)observations(Lonsdaleetal.2003). trum.Thebestfitisafour-componentmodel,consistingofadirect ve
m
FromFig.1wecanseethattheAGNdominatestheemissioninthe and scattered AGN power law, a thermal component and an iron b
e
near-andmid-IR,inagreementwithresultsofpreviousauthors,but line.Furthermore,theX-rayemissionappearsextendedratherthan r 2
thatthestarburstdominatesatsubmillimetrewavelengths. unresolved (Levenson, Weaver & Heckman 2001). We compiled 01
anadditional350-µmfluxof1004±230mJy,andanadditional 8
13428+5608. ThisobjectiscommonlyknownasMrk273.Itcon-
800-µmfluxof84±22mJy,bothfromRigopoulouetal.(1996).
tainstwonucleiwithasingle,long(41-kpc)tidaltailanda‘ring’
OurresultsareconsistentwithMrk273containingbothastarburst
of star formation almost 100 kpc in diameter. The northern nu-
andanAGN,inagreementwithX-rayobservations.TheSEDfit
cleusisresolvedandissurroundedbyunobscuredstarformation,
inFig.1isconsistentwithastarburstinterpretationinthenear-IR,
whereas the southern nucleus is redder and unresolved (Scoville
and also gives a good fit in the mid-IR although the fit predicts
et al. 2000). The optical spectrum is that of a Sy2, and there are
thatthemid-IRemissionisduetoastarburstratherthananAGN.
nobroadlinesinthenear-IRspectrum,althoughtherearestrong
narrowlines(Veilleuxetal.1999).RadiocontinuumandHI21-cm 14348−1447. Wecompiledanadditional800-µmfluxof29±10
observationsofthissourceclassifyitasapurestarburst(Condon mJyfromRigopoulouetal.(1996).Thisobjectisveryluminous,
etal.1991;Carilli&Taylor2000).Conversely,mid-IRspectralob- wheretheluminosityisdominatedbyastarburst.Whilstthisobject
servations(Lutzetal.1999;Rigopoulouetal.1999)classifyitas doescontainaluminousAGN,theAGNonlycontributes∼17per
anAGN.ThisobjectisastrongX-raysource,withacomplexspec- centofthetotalinfraredflux.
(cid:4)C 2003RAS,MNRAS343,585–607
StarburstandAGNactivityinULIRGs 593
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Figure1–continued t o
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15250+3609. This object has one bright central nucleus, and a calspectrumwasfirstthoughttobeSy2-like(Sandersetal.1988), o
v
second,muchdimmernucleus0.7arcsecfromthecentre.Thereis andthiswasinterpretedasindicatinganAGNpowersource.Con- e
m
also a large ring-like structure 25 kpc in diameter (Scoville et al. versely, the broad-band optical-IR SEDs suggested a starburst as b
e
2000). The optical spectrum is a composite of H II and LINER themainpowersource(Joseph&Wright1985).Observationsand r 2
0
features(Veilleuxetal.1999).Lutzetal.(1999)classifythisobject modellingatotherwavelengthsrevealedamorecomplexpicture. 1
8
asastarburstbasedonitsmid-IRspectrum.Ourresults,however, Ground-basedmid-IRspectroscopy(Smith,Aitken&Roche1989)
showthatthisobjectcontainsbothastarburstandanAGN.This suggestedahybridnatureforArp220,includingbothstarburstand
isoneofonlythreeobjectsinthesamplewheretheAGNprovides AGN,whereasISOmid-IRspectroscopy(Sturmetal.1996)sug-
morethanhalfofthetotalIRemission.Interestingly,itcanbeseen gestedapurestarburst.High-resolutionVLBAimaging(Smithetal.
fromFig.1thatthesubmillimetreemissionfromthisobjectisnot 1998)revealedanumberofunresolvedsourcesinthenuclei,inferred
dominated by a starburst, but instead arises in almost equal parts toberadiosupernovae,supportingthepresenceofastarburst.Opti-
fromastarburstandanAGN.Weinterpretthisasarisingfroma calintegralfieldobservationsofthecentralregions(Arribas,Colina
heavilyobscuredAGNthatisorientednearlyedgeontous,rather &Clements2001)showedthatthespectrumisLINER-likeinmost
thananAGNwithanextendedtorus. regions, but with a Sy2-like spectrum in the brightest emission-
lineregion.Rieke(1988)searchedforhardX-raysinArp220with
15327+2340. This object, commonly known as Arp220, is both HEAO-A1 data, and concluded that an AGN similar to those in
theclosestULIRGtousandthemostintenselystudied.Theopti- quasars could not be the power source. Recent observations with
(cid:4)C 2003RAS,MNRAS343,585–607
594 D.Farrahetal.
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Chandra(Clementsetal.2002)detectweakhardX-rayemission tosetalowerlimitintheUVopticaldepthofanIRluminousAGN o
fromthenucleus,whichhasapossibleorigininaweakAGNre- inArp220,ofτ =1500. ve
UV m
sponsibleforapproximately5percentofthebolometricluminosity. b
e
Analternativeexplanation,withamuchlargerAGNcontribution 17208−0014. This source has a single nucleus surrounded by a r 2
0
tothebolometricluminosity,ispossibleiftheAGNisobscuredby disturbeddisccontainingseveralcompactstarclusters,withasin- 1
8
aCompton-thickscreenof∼1025cm−2ormore.Thereissomead- gle tail. The optical spectrum is that of an H II region (Veilleux
ditionalevidenceforanobscuredAGNinArp220,includingsub- et al. 1999) and near-IR imaging shows an extended nucleus, ar-
millimetre observations (Haas et al. 2001) and LWS spectra that guingagainstanAGN(Scovilleetal.2000).Thisobjectliesina
may indicate τ > 1 at∼100 µm (Fischer et al. 1999). We com- crowdedfield,andhighspatialresolution100-µmobservationswith
piledadditionalIRphotometryforArp220fromKlaasetal.(1997), theKuiperAirborneObservatory(Zinketal.2000)measurea100-
andadditionalsubmillimetrephotometryfromChinietal.(1986), µmfluxsubstantiallybelowthatfromIRAS,implyingthattheIRAS
Rigopoulouetal.(1996)andDunne&Eales(2001).Ourresultsare fluxesforthisobjectareconfused.The100-µmfluxusedinthefit
consistentwithastarburstinterpretationforArp220.Theextensive isfromZinketal.(2000).Thiswastheonlyobjectinoursample
IRdataarewellfittedbyapurestarburstmodel,andtheresulting where the fit was relatively poor (χ2 = 4.7), however, it can be
red
upper limit on the IR luminosity of any AGN component is very seenfromFig.1thatthispoornessoffitisduetoinconsistencies
strong.ThisupperlimitontheAGNIRluminosityalsoallowsus betweenthemodelandtheIRAS60-µmflux.Asthereareobserved
(cid:4)C 2003RAS,MNRAS343,585–607