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Discovery of a multiply-imaged Ly- α galaxy at the redshift of a SCUBA galaxy at z=2.56

Discovery of a multiply-imaged Ly- α galaxy at the redshift of a SCUBA galaxy at z=2.56. Helmut Dannerbauer (MPIA) in collaboration with M.D. Lehnert (OBSPM) L. Douglas (OBSPM), J.-P. Kneib (Marseille), N. Nesvadba (OBSPM), J. Richard (Caltech), C. Tapken (MPIA). H α of field of Abell 1835.

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Discovery of a multiply-imaged Ly- α galaxy at the redshift of a SCUBA galaxy at z=2.56

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  1. Discovery of a multiply-imaged Ly-α galaxy at the redshift of a SCUBA galaxy at z=2.56 Helmut Dannerbauer (MPIA)in collaboration withM.D. Lehnert (OBSPM)L. Douglas (OBSPM), J.-P. Kneib (Marseille), N. Nesvadba (OBSPM), J. Richard (Caltech), C. Tapken (MPIA) Hα of field of Abell 1835

  2. Studying the surroundingof a bright SCUBA galaxy • Searching for protocluster at high-z: • finding them is important to understand growth of structure • several approaches: e.g. X-ray, Red Sequence, LBGs, Lyα-emitters, S-Z-effect • successful approach by targeting high-z radio galaxies(signposts of overdensities) • (e.g. Kurk et al. 2000,2004a,b; Pentericci et al. 2000;Venemans et al. 2002, 2004, 2005) • Submm galaxies (SMGs): • are ULIRGs at z ~1-4 with LFIR~1x1012–1x1013 Lsun • are massive galaxies (>1011 Msun) • have complex morphology → ellipticals in formation • are predicted to lie in the most massive haloes • at high-z (Ouchi et al. 2004) • → have similar properties like high-z radio galaxies (HzRGs) Pentericci et al. 2000 one would expect to find overdensity structure around SMGs SMGs a factor 10 more numerous than HZRGs (Reuland et al. 2003)

  3. How LAEs (and HAEs) can help see also Nina Hatch and Bram Venemans talks • reveal possible overdensities around high-z massive galaxies like SMGs or HzRGs • study properties of the member galaxies of overdensity structure will yield valuable constraints on the past evolutionary history and past and future mass assembly in high-density environments • probe the overall dynamics within the overdensity in order to constrain the mass of the underlying dark matter halos out to Mpc scales

  4. Nesvadba, Lehnert ea 2007 Mikroskop Ivison et al. (2001) Tecza et al. (2004) Source Selection • How do we search for protocluster (overdensity) around a SMG? • detecting an narrowband (NB) flux excess → follow-up spectroscopy • prominent emission line (Lyα, [OIII], Hα) has to fall in NB-filter best-studied (sub)mm source: SMM J14011+0252 @ z=2.56 →Ly-α-line falls in 3.6m-EFOSC2 NB-filter at 4330 Å →Hα-line falls in VLT-ISAAC NB-filter at 2.34μm →but lies in the field of z=0.25 lensing cluster A1835 great laboratory for detailed studies Shapley et al. (2003) expected velocity dispersion ~1000kms-1 Hα-image

  5. Observations • Archival data on field of Abell 1835: • rich of exquisite multiwavelength dataset including deep VLT-FORS/ISAAC, ACS, WFPC2, Spitzer-IRAC/MIPS imaging and VLA • Hα-Imaging at z~2.56 – VLT-ISAAC: • one ISAAC pointing; 2.5´x2.5´; not centered on SMG • 9.3 hrs in NB 2.34 down to 1-2x10-17 ergs s-1 cm-2 • 2.1 hrs in Ks down to KVega=22 mag (3σ) • Lyα-Imaging – ESO 3.6m-EFOSC2: • one EFOSC2 pointing; 5´x5´; not centered on SMG • 18.0 hrs in NB 4330 Å (and B) down to 1-3x10-17 ergs s-1 cm-2 • Optical Spectroscopy – VLT-FORS2: • Multi-object spectroscopy with Mask Exchange Unit (MXU) • GRISM 300V with a resolution R~600 (4.3 hrs split into two diff masks) • GRISM 600B with a resolution R~1000 (only 2 hours → not deep enough!) • →similar approach as done by e.g. Kurk et al. (2000,2004a,b), Pentericci et al. (2000) for HzRG at z=2.16

  6. LAEs and HAEs in field of A1835 LAEs ESO 3.6m/EFOSC2: NB @ 4330 Å HAEs 5 arcmin x 5 arcmin • Current Status: • VLT/ISAAC NIR-NB imaging revealed ~10 HAEs • 3.6m/EFOSC2 opt-NB imaging revealed ~30 LAEs • up to now two VLT/FORS2-MXU campaigns • Obtaining wide-field imaging data with • 2.2m WFI (U/R) and CFHT-WIRCAM (J/H)

  7. Selecting Hα-emitters at z~2.56 ∑=deviation from the predicted mag of a source in K using the NB-flux and assuming flat spectrum (Bunker et al. 1995) → excess significance ∑=3 ∑=2 SMM J14011+0252 - Vega

  8. MXU-Spectroscopy z=2.567 V=23.9 Fl(Lyα) = 1.00x10 -16 ergs s-1 cm-2 EW(Lyα) = 26 Å z=2.567 V=23.3 Fl(Lyα) = 1.41x10 -16 ergs s-1 cm-2 EW(Lyα) = 24 Å exquisite rest-frame UV spectra → allows detailed rest-frame UVanalysis (following Heckman ea 1998 and Shapley et al. 2003)

  9. MXU-Spectroscopy recently data taken z=2.567 V=23.9 Fl(Lyα) = 1.00x10 -16 ergs s-1 cm-2 EW(Lyα) = 26 Å Higher resolution but only 2 hours of data! z=2.567 V=23.3 Fl(Lyα) = 1.41x10 -16 ergs s-1 cm-2 EW(Lyα) = 24 Å

  10. Shapley et al.(2003) LBG IV UV-analysis local SFG (H98) z=2.567 WIS LBG I LBG (S03) X 14011-J1 WW LBG I-IV LBG I-IV β β WIS WLyα WW Star-forming galaxies with properties of LBGs of class III-IV

  11. SHM-197 SHM-268 SED-fitting B V R Z J H K Spi1 2 3 B V R Z J H K Spi1 2 3 4 • using Bruzual & Charolot (2003): • „good fit“ (least square fit) • exp. Declining bursty star-form. histors • Chabrier IMF (masses a factor • 2 lower than using Salpeter IMF) • first results: • stellar ages a few x 108 yrs • stellar masses of a few x 109 Msun

  12. SHM-197 & SHM-268 The two sources – indeed SF-galaxies SHM-197 SHM-268 • Starburst99: • LMC/SMC Metallicity • const. SFR • Age=40Myr • Calzetti-Law E(B-V)=0.15 • →star-forming galaxy

  13. MW-Properties • outflow • LBG class III-IV (see Shapley ea 03) • LUV=1.6/1.7x1011 Lsun • SFR(UV)~5/9 (42/47) Msun/yr • SFR(Lyα)~4/7 Msun/yr • UV slope β -1.46 (197) and -1.68 (268) • blue star-forming galaxies • MIPS F(24μm)<45/36μJy • → SFR(IR)<346/225 Msun/yr • →LIR<2.0/1.3x1012 Lsun • sources not detected in SCUBA (<5.1mJy) • and radio map (<45 μJy) • → SFR<1000 Msun/yr • detected in all four IRAC bands • velocity difference to 14011-J1 250km/s • Open Questions: • are the two sources the same lensed object? • sources could be (significantly) magnified SHM-268 SHM-197 4.0“ 3.5“ Image:V-band Cont: ACS z

  14. Location of the two Sources in A1835 – Lensing? SMM J14011 ACS z (F850LP) SHM-268 SHM-197

  15. Location of the two Sources in A1835 – Lensing? SMM J14011 Lyα (FWHM~1.8“) Lyα (FWHM~1.8“) SHM-268 SHM-268 SHM-197 12 arcsec 3 arcsec 2.6 arcsec 3rd source? ACS z (F850LP) 8.2 kpc/arcsec SHM-268 3rd source? 51 arcsec 65 arcsec 92 arcsec SHM-197 Improved Lensing model - Richards, Kneib et al. in preparation

  16. Summary • NB-flux excess technique works • about 10 HAEs and 30 LAEs candidates • discovery of two strong LAEs through Hα-imaging • two blue young star-forming galaxies @ z=2.567 (LBG class III-IV) • most probably multiply-image imaged lensed source (3 counterparts) • two more sources with Lyα emission identifed at z=2.56

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