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FarIR Properties of Submm and Optically-Faint Radio Galaxies using Herschel

FarIR Properties of Submm and Optically-Faint Radio Galaxies using Herschel. Scott C. Chapman (IoA ,Cambridge) Rob Ivison (ROE,ATC), Isaac Roseboom & Seb Oliver (Sussex) SAG1-HerMES team. July6 2010, Cumberland Lodge. OUTLINE. ~1000M/yr SFR at z>1 ? ULIRG/HyLIRG

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FarIR Properties of Submm and Optically-Faint Radio Galaxies using Herschel

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  1. FarIR Properties of Submm and Optically-Faint Radio Galaxies using Herschel Scott C. Chapman (IoA ,Cambridge) Rob Ivison (ROE,ATC), Isaac Roseboom & Seb Oliver (Sussex) SAG1-HerMES team July6 2010, Cumberland Lodge

  2. OUTLINE • ~1000M/yr SFR at z>1 ? ULIRG/HyLIRG • Submm-luminous galaxies and hotter dust versions • Clear evidence that a lot of this is star formation • Saga of guesswork at their farIR luminosities, energetics, and dust temperatures (SED shapes) • Leading to Herschel • WHY? • FarIR output verifies SFRs • Census of ULIRGs at z>1, how are galaxies built? • How many galaxies go through extreme starbursts? • Dust temperatures/SEDs: clues to evolution states (merger state, dust properties/heating/configuration, AGN, …)

  3. Submillimetre Galaxies • K-correction Millimetre-Submm UNIQUE: At ~1mm: galaxy has the same flux from z=1-10!!! (and you can detect them!) Flux-limit survey = luminosity-limited survey. Herschel-SPIRE SCUBA MAMBO SPT K-corr 1/D2 Expect high-z high-Luminosity objects to dominate!

  4. Radio: selection of galaxies by “far-IR” emission -Identify SMGs in radio -Known tight correlation with FIR -Good spatial resolution (MERLIN 0.3”, VLA 1.4”) FarIR/radio correlation holds at z=2.5 (Kovacs et al. 2006; Ivison+2010a,b) Far-IR correlates with synchrotron radio (SNe: shock accelerates CR electrons) 1.4GHz (Ivison et al. 1998,2002,2007)

  5. Radio as redshift indicator? • Carilli&Yun(1999,2000) suggested 850um/1.4GHz could be a good redshift indicator (if SMGs were ~similar to Arp220) • Technique exploited extensively to estimate redshifts of SMGs from SCUBA/MAMBO surveys from 1997-2003 (Hughes+98,Barger+98,00,Smail+00,Chapman+99,01, Eales+99,Webb+02,Bertoldi+02,Dannerbauer+01)

  6. Keck; LRIS-B redshift surveys of SMGs Chapman+2003,2005, Swinbank+2004, Ivison+2005 Now 180 radio-SMGs ~70 radio-SMGs • Radio-ID SMG N(z) peaks at z~2.2 • Good fortune of many strong LyAlpha emitters and new blue-sensitive spectrograph !!! • Total ~40% incompleteness due to: • z>3 need for radio-IDs (~25%) • z~1.5 spectroscopic desert (?) • All-z? weak spectral features

  7. Radio/850 is a poor indicator of z • Chapman+03,05 redshift surveys demonstrated that Radio/850 had huge (dz/z~1) redshift error. • Does tell you the bulk of population is likely at z~2.5

  8. Radio/850 as dust temperature indicator ? • C03/C05 speculation that 850um/1.4GHz flux ratio could reasonably characterize the farIR SED VLA 1.4GHz

  9. Fits to 20cm,850um with redshifts …SMG contribution to submm/FIRB • >0.5mJy SMGs (>1012 Lo) produces 80-100% of 850um background • Conclude that the SCUBA population will produce ~1/2 of the >400um FIRB Corrected for <5mJy sources >5mJy Arp220 SED >5mJy fitted SEDs ( Chapman et al. 2005)

  10. Fits to 20cm,1.2mm,850um,350um => dust properties • Accurate 350um SHARC2 / CSO observations provide the first true measurements of the Luminosities and dust properties of SMGs • Cool Td ~30K • Beta ~ 1.7 Corrected for <5mJy sources >5mJy Arp220 SED >5mJy fitted SEDs (Kovacs et al. 2006)

  11. Are we then missing ULIRGs? … SMGs only the cold half the story? OFRGs(optically faint radio galaxies) (Eales+2000; Chapman+2004; Blain+2004) Same radio fluxes and redshifts as SMGs: Same FIR luminosity? Undetected with SCUBA Mostly UV-Star Formers; … must be hotter Td’s?

  12. ULIRGs that SCUBA missed: higher Tdust SMGs? VLA 6x15m IRAM PdB Interferometer MERLIN 3”, ~25kpc • Chapman+2004,2008; Casey et al. 2009,2010: • 11/16 show CO(3-2) detections; similar SF efficiency to SMG • Narrower line widths => probing only unresolved inner disk? • Sample of 25 with resolved MERLIN radio: >8kpc scales (mergers) Everything possible without measuring farIR -- needs Herschel

  13. Lots of evidence for extended star formation in SMGs/OFRGs Swinbank et al. 2005/Tacconi et al. 2008 z=2.38 SMG n2.4 H z=2.01 SMG h254 Extended narrow (nebular) emission lines (Halpha, OIII) Extended CO gas (Tacconi+2008, Bothwell et al. 2009) CO(4-3) 1.5” ~13kpc CO(7-6) Biggs & Ivison 2008 0.3” MERLIN Radio Chapman+2004 Submm • SFR surface densities typically like local StarBursts Younger et al. 2008

  14. Herschel observations of high-z starbursts • Herschel maps detecting 1000’s of “submm galaxies”: redshift distribution? • Amblard+2010: while most ATLAS (14sqdeg) 6000 galaxies are at z<0.5: • many candidate z~2 galaxies, depth is >35mJy at 350um (~bright SMG: Kovacs06) & >5sigma at 500um,250um. • 1600 sources (25% of catalog), but rare, 118/sqdeg (~ >8mJy SCUBA galaxies) • z=2.2+-0.6 (similar to SMGs -- Chapman+05,Pope+08,Wardlow+10) • ARE THEY THE SAME GALAXIES? • Brightest HyLIRGs (>1000M/yr) • ATLAS will cover 550sq deg! • (HLS may cover 4000sq deg!) Above confusion limit

  15. Herschel observations of high-z starbursts • Elbaz+2010: uniformity of dust properties: • “Clean” confusion-free, deep sample • PACS+SPIRE • Accurately measure bolometric output of starbursts & AGN directly sampling peak of far-IR • No evolution in T_dust to z=1.5 • No evolution in L_24/L_IR to z=1.5 • z>1.5 things not so clear !!!

  16. Radio/850um in Herschel era • Magnelli+2010(PACS 160,100um), • SMGs in GOODS-N (z’s known) • OFRGs (Casey+2009 sample) • Verify farIR outputs (SFRs) • SMGs had good idea already • OFRGs were largely unconstrained • Verify T_dust predictions • show Radio/850um does a good job at characterizing the shape of the far-IR SED … the “dust temperature” of SMGs and OFRGs NOW time to turn back to detailed astrophysics of these galaxies with known farIR properties!

  17. Radio/850um in Herschel era • Chapman+2010(SPIRE 250, 350, 500um) (and others … e.g. Chanial+2010) • SMGs & OFRGs in Lockman (with z’s) • Verify farIR outputs (SFRs) • Verify T_dust predictions • Radio/850um: shape of the far-IR SED • CAUTION: not the whole story: CONFUSION

  18. CONCLUSIONS Progress in understanding high-z ULIRGs/SMGs facilitated with 1.4GHz radio surveys and Spitzer • Herschel has completed the characterization • FarIR output verifies SFRs • Census of ULIRGs at z>1, how are galaxies built? • How many galaxies go through extreme starbursts? • Dust temperatures/SEDs: clues to evolution states) • Confusion still big problem: Many z=1.5-3 SMGs undetected or poorly constrained w/ SPIRE • Clear need for CCAT30m and ALMA

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