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Four hot DOGs eaten up with the EVN

Four hot DOGs eaten up with the EVN. Sándor Frey (FÖMI SGO, Hungary) Zsolt Paragi (JIVE, the Netherlands ) Krisztina Gabányi (FÖMI SGO, Hungary) Tao An (SHAO, China ). 12th EVN Symposium , Cagliari, Italy , 7-10 October 2014. What are the hot DOGs ?.

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Four hot DOGs eaten up with the EVN

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  1. Four hot DOGs eatenupwiththe EVN Sándor Frey(FÖMI SGO, Hungary) Zsolt Paragi(JIVE, theNetherlands) Krisztina Gabányi(FÖMI SGO, Hungary) Tao An(SHAO, China) 12th EVN Symposium, Cagliari, Italy, 7-10 October 2014

  2. Whatarethe hot DOGs? = hot dust-obscuredgalaxies(Wu+ 2012, ApJ 756, 96) IdentifiedwiththeWide-fieldInfraredSurvey Explorer (WISE) satelliteasW1W2-dropout objects, i.e. prominentinthe W3 (12 μm) and W4 (22 μm) bands, butveryweakor undetectedinthe W1 (3.4 μm) and W2 (4.6 μm) bands The all-skypopulation of thesehyperluminousgalaxies contains ~1000 sources

  3. The prototype: W1814+3412 z=2.45 Eisenhardt+ 2012, ApJ 755, 173

  4. Red dots: hot DOGs (allsky) coloursalsofromfollow-upSpitzerdata The rest: a typical WISE sample (b>80°) inset: redshiftdistribution Eisenhardt+ 2012, ApJ 755, 173

  5. Ourcurrentunderstanding of hot DOGs Redshiftsaretypicallyhigh, with a distributionpeaking between 2 and 3 →atthepeak of cosmicstarformation and AGN activity Manyspectra show signs of obscured AGN Luminosities(~1013–1014L) arecomparabletothe most luminousquasars SEDsaredifferentfromotherknownpopulations, thehighmid-IR/submmluminosity ratio indicatesthatthedominantemissioncomesfromhot dust(60–120 K) Extreme and rarecases of luminousDOGs, representing a shortevolutionaryphaseingalaxyevolutionthroughmergers Starburst – AGNtransitions? Wu+ 2012, ApJ 756, 96; Wu+ 2014, ApJ 793, 8

  6. Hot DOGsinthemicrowave Some of theseWISE-selectedobjects show mJy-levelradioemissionat cm wavelenghts VLBI has a uniquecapabilitytodiscriminatebetweenthestrarburst and AGN origin of theradioemission VLBI detection → directconfirmation of radio AGN Ifthesesourcesreallyharbouryoung AGN, wemayfindcompactsymmetricstructures (CSOs) Iftheiractivity is triggeredbymergers, wemayseespatiallyresolveddual AGN sources

  7. Test of thecompactradiostructures Sensitivephase-referencedobservationsinitiatedwiththe EVN Project: EF025 2014 Feb 21/22, totaltime 14 h Observedine-VLBImode, butwithinthedisk session 8 stations: Ef, Wb, Jb (Lovell), On, Mc, Nt, Tr, Sh 1.6 GHzfrequency: higherchance of detection (presumablysteep-spectrumsources) Sourcesyetunexploredwith VLBI → pilot project, with4 targets

  8. The EVN sample Abby Bella Charlie Daisy A subsamplefrom 26 hot DOGs 12 inthe FIRST coverage, 3 withradiodetection (>1 mJy) +1 source (the “prototype”) with EVLA fluxdensitydata Wu+ 2012, ApJ 756, 96 Eisenhardt+ 2012, ApJ 755, 173

  9. Results FourmJy-leveltargets, fourdetections! – albeitthree (and especiallytwo) of themareratherweak The sourcesareallresolvedon~10-30 masangularscales VLBI phase-referencingprovidesthe most accuratepositionalinformationavailableforthesesources Eachone is differentworld – seethe 1.6-GHz EVN images of Abby, Bella, Charlie, and Daisy:

  10. Abby 200 pc 0.9 mJyinthe CLEAN components (~25% of the FIRST fluxdensity)

  11. Bella 200 pc 3.1 mJyinthe CLEAN components (~70% of the FIRST fluxdensity) The most compactradiosourceinthissample

  12. Charlie 200 pc Just 0.15 mJyinthe CLEAN components (~7 % of the FIRST value) a 7-σdetection

  13. Daisy ~600 mas 4.9 kpc 0.36 mJyintwodistinctsources (~1/3 of theexpectedtotalfluxdensity)

  14. Summary & outlook • A smallradiosubsample, four hot DOGswereobservedwiththe EVN at L band; allfourweredetected • Inone of them (Bella, alias W1146+4129), most of theradioemissioncomesfrom a compact AGN • Three of themareveryweakon ~10-mas scales; theirradioemission must be dominatedbystartburst-relatedactivity • Daisy, theprototype hot DOG (W1814+3412), has a symmetricdoublestructurewithnearly 5 kpc projected separation • Directionsforthefuture: • Interpretingtheresultsinthecontext of growingmulti-banddata • Targeting a largersampleof hot DOGswithknownradioemission • Obtainingspectralinformationat 5 GHz (wherefeasible)

  15. EVN’s

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