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Discovery of an Extremely Massive and Evolved Galaxy at z ~ 6.5

Discovery of an Extremely Massive and Evolved Galaxy at z ~ 6.5. B. Mobasher (STScI). STScI: B. Mobasher, T. Wiklind, H. Ferguson, M. Giavalisco, M. Stiavelli, A. Koekemoer NOAO: M. Dickinson Padova: A. Renzini ESO: P. Rosati, J. Walsh, J. Venet Caltech: R. S. Ellis, D. Stark

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Discovery of an Extremely Massive and Evolved Galaxy at z ~ 6.5

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  1. Discovery of an Extremely Massive and Evolved Galaxy at z ~ 6.5 B. Mobasher (STScI) Venice – March 2006

  2. STScI: B. Mobasher, T. Wiklind, H. Ferguson, M. Giavalisco, M. Stiavelli, A. Koekemoer NOAO: M. Dickinson Padova: A. Renzini ESO: P. Rosati, J. Walsh, J. Venet Caltech: R. S. Ellis, D. Stark JPL: L. Moustakas, D. Stern, P. Eisenhardt Gemini: B. Rodgers Zurich: C. Scarlata Carnegie: I. Labbe Venice – March 2006

  3. It is generally accepted that galaxies we see today, form by mergers of smaller sub-units throughout the age of the Universe Galaxies are younger and less massive at higher redshifts Is there NO massive and evolved system at high redshifts, when the Universe was < 1 Gyrs old ? Only recently, with combined optical, near-Infrared and mid-Infrared observations one could explore this. Venice – March 2006

  4. The Balmer break is a prominent feature for stellar populations age t > 100 Myrs z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr Venice – March 2006

  5. Post starburst at z ~ 7 Dusty starburst at z ~ 2.5 old Elliptical at z ~ 2.5 3.6mm 3.6mm K H K H J J dusty starburst z ~ 2.5 dust-free post-starburst z ~ 7 Venice – March 2006

  6. Alternate way of selecting very high redshift candidates: Color-color selection: H - 3.6mm vs K - 3.6mm The slope of the short-l side of the Balmer break is different for dusty starburst and dust-free post-starburst galaxies Avoids using J-band - often faint Post starburst at z ~ 7 Dusty starburst at z ~ 2.5 old Elliptical at z ~ 2.5 3.6mm 3.6mm K H K H J J dusty starburst z ~ 2.5 dust-free post-starburst z ~ 7 Venice – March 2006

  7. Selecting Massive Evolved Galaxies at high-z No detection at optical bands (BViz) Red J-H colors (undetected in J-band) Blue H-K ( i.e. flat H/K SED) Red K- m 3.6 (K/IRAC(3.6mm) break) 18 galaxies found with 5 < z < 7 and stellar mass 8 x 1010 – 5 x 1011 Msun Wiklind et al (2006) Venice – March 2006

  8. HUDF vs GOODS GOODS CDFS – 13 orbits HUDF – 400 orbits Venice – March 2006

  9. further constraints No detection at optical bands (BViz) to the HUDF limit at 2s level J110 - H160 > 1.3 corresponding to the observed color of an LBG at z=8, taking into account IGM opacity Venice – March 2006

  10. Selection criteria (Mobasher et al Ap.J 2005) • no detection at optical bands • close to slope unit line on H-3.6 vs. K-3.6 • red K-3.6 color (Mobasher et al 2005) J-band dropout candidates in the HUDF Venice – March 2006

  11. Venice – March 2006

  12. ACS Venice – March 2006

  13. ACS+NICMOS+ISAAC Venice – March 2006

  14. ACS+NICMOS+ISAAC+IRAC Venice – March 2006

  15. Venice – March 2006

  16. K K H H IRAC J J z z B B V V i i Venice – March 2006

  17. Bruzual and Charlot models (BC03) • Starburst99 models (SB99) • Simultaneously fitting: • Redshift z • Extinction EB-V • Age, t • Star formation history e-folding time t • Metallicity Z K K H H IRAC J J z z B B V V i i Venice – March 2006

  18. Summary of fitted parameters: • High redshift, z = 6.5 • Luminous, LBOL ~ 1 1012 Lo • No extinction, EB-V = 0.0 • No on-going star formation • ‘Old’, age ~ 1 Gyr • Very, very massive, M* ~ 5 1011 Mo Venice – March 2006

  19. c2 vs. EB-V and redshift BC03 Starburst99 Best fit region covers : 6.0 < z < 7.7 Secondary fit for a dusty galaxy at z ~ 2.5 black : c2 minimum (1.9) white : c2 = 10 How stable is the solution? Venice – March 2006

  20. z=6.5 evolved Massive c2n = 1.8 Single burst z=2.5 dusty Starburst c2n=6.7 Continous SFR z=3.4 old evolved c2n=29.9 Venice – March 2006

  21. Venice – March 2006

  22. Formation redshift (excluding those with ages > age of the universe) Results from Monte Carlo simulations: • z = 6.5 • EB-V = 0.0 • Age = 600 Myr • Z = 1.0 Zo • M* = 4.6 1011 Mo • zform ~ 10-15 median values A massive post-starburst galaxy at z ~ 7 Venice – March 2006

  23. Venice – March 2006

  24. Most frequently asked questions: Venice – March 2006

  25. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Venice – March 2006

  26. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Venice – March 2006

  27. z=6.5 evolved Massive c2n = 1.8 Single burst z=2.5 dusty Starburst c2n=6.7 Continous SFR z=3.4 old evolved c2n=29.9 Venice – March 2006

  28. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Venice – March 2006

  29. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Venice – March 2006

  30. Venice – March 2006

  31. Mrk 231 BL QSO ULIRG Venice – March 2006

  32. Mrk 231 +NGC 1068 highly obscured AGN Venice – March 2006

  33. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Venice – March 2006

  34. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Venice – March 2006

  35. Gemini GNIRS spectroscopy of the z ~ 7 candidate: No lines detected z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band Lya (l1216) z ~ 7 (0.97 micron) Ha (l6563) Venice – March 2006

  36. In addition: • Gemini-S GNIRS cross-dispersed • VLT FORS • HST ACS Grism • Keck NIRSPEC Keck and VLT: sensitive to Lya emission from galaxies at 6.8 < z < 8.0 with SFR 3-5 Mo/yr No lines detected z ~ 0.8 - 1.2 J-band z ~ 1.3 - 1.8 H-band z ~ 2.0 - 2.8 K-band Keck and Gemini: sensitive to Ha emission from galaxies at 0.8 < z < 2.8 (with gaps) with line fluxes 1 10-17 - 2 10-18 erg cm-2 s-1 Lya (l1216) z ~ 7 (0.97 micron) Ha (l6563) Venice – March 2006

  37. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Venice – March 2006

  38. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Venice – March 2006

  39. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? Venice – March 2006

  40. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? Venice – March 2006

  41. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? different dust models ? Venice – March 2006

  42. Most frequently asked questions: Could it be a dusty starburst at z~2 ? Could it be an evolved old galaxy at z~2-3 ? Does it have MIPS detection ? Do you have spectroscopic data ? Could it be gravitationally lensed ? Could it be a star ? Different dust models ? Have you found more objects like this ? Venice – March 2006

  43. Sample B J-band drop-out Venice – March 2006

  44. Sample A massive post-starburst candidates z = 4.9 EB-V = 0.10 age = 700 Myr M* = 8 1011 Mo z = 7.2 EB-V = 0.05 age = 400 Myr M* = 4 1011 Mo z = 5.3 EB-V = 0.0 age = 300 Myr M* = 0.8 1011 Mo z = 7.2 EB-V = 0.0 age = 300 Myr M* = 2 1011 Mo Venice – March 2006

  45. Sample A massive post-starburst candidates Venice – March 2006

  46. local galaxies m*>2.5E10 MO m*>1.0E11 MO LBGs K20 EROs sub-mm SDSS QSOs Somerville 2004 Venice – March 2006

  47. Summary • We present a technique for selecting very massive evolved galaxies at high redshift. • This is based on combining deep optical/near-IR data with medium deep Spitzer observations • An object is found in HUDF with an SED consistent with a post-starburst (evolved) galaxy with M=(2-5) x 1011 Msun at z=6.-7.5. The object has undergone a single burst of SF and has an age of 1 Gyr. Venice – March 2006

  48. Cont.. • A less likely possibility is a very dusty evolved galaxy at z=2.5 with an age of ~600 Myrs. However, this produces a significantly worse fit to the observed SED. • The low-z alternative requires the object to be detected in radio (1.4 GHz) or have spectral features indicative of SF. Our source has none of these. Venice – March 2006

  49. Venice – March 2006

  50. Case against dusty post-starburst at low-z No detection of diagnostic spectral features in the spectra No radio detection If the 24 micron flux is due to PAH feature in a star-forming galaxy at z~2, we would have expected to detect this to the depth of our radio survey. Venice – March 2006

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