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B Is 200my enough for galaxies to form

  1. Mar 8, 2017 #1

    wolram

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    I thought that z= 7.5 was the maximum for galaxies to form after re ionization but this paper puts it at z=8.38,
    can galaxies have formed this early?

    arXiv:1703.02039 [pdf, other]
    Dust in the reionization era: ALMA observations of a z=8.38 Galaxy
    Nicolas Laporte, Richard S. Ellis, Frederic Boone, Franz E. Bauer, David Quénard, Guido W. Roberts-Borsani, Roser Pelló, Ismael Pérez-Fournon, Alina Streblyanska
    Comments: Accepted for publication in ApJL
    Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

    We report on the detailed analysis of a gravitationally-lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of z≃8. Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman α emission at a redshift z=8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88μm emission at the same redshift. Although both emission features are only significant at the 4 σ level, we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification (μ≃2) indicates A2744_YD4 has a stellar mass of ∼ 2×109 M⊙, a star formation rate of ∼20 M⊙/yr and a dust mass of ∼6×106 M⊙. We discuss the implications of the formation of such a dust mass only ≃200 Myr after the onset of cosmic reionisation.
     
  2. jcsd
  3. Mar 8, 2017 #2

    Jorrie

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    Look at this time-line diagram. Galaxies started to form quite soon after reionization started (T~400 Myr). Redshift z=8.38 translates to T~600 Myr, which looks reasonable. I think the question may rather be if such a massive galaxy could have formed in that time.
     
  4. Mar 8, 2017 #3

    wolram

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    Thanks for the reply jorrie.
    I have been looking for a cited paper that will give me the earliest possible time after re ionization for a massive galaxy to form with no luck,I think it is reasonable to suspect that the galaxy in the paper is not the last most distant galaxy we will detect.
     
  5. Mar 8, 2017 #4

    Chronos

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    The current king of confirmed high z galaxies appears to be GN-z11 at z = 11.09; https://arxiv.org/abs/1603.00461, A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space Telescope Grism Spectroscopy, This corresponds to 400 million years after the big event and reaches back to the fringe of the so-called 'dark ages'. An unconfirmed candidate at z~11.8, UDFj-39546284, http://iopscience.iop.org/article/10.1088/2041-8205/765/1/L16/pdf, has also been reported. It is reasonable to expect JWST will find additional contenders after it launches [currently scheduled for 2018].
     
  6. Mar 8, 2017 #5

    wolram

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    Thank you for your reply Cronos.
    Am i right in saying that a massive galaxy would need several mergers of smaller galaxies, and these smaller galaxies would have to have formed earlier than the massive one, also would dark matter have time to clump during the re ionization period?
     
  7. Mar 8, 2017 #6

    Chronos

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    The consensus view is the progenitors of massive galaxies were what is called protogalaxies, which are basically huge unstructured star clusters believed to consist of of pop IIi stars. The stars are expected to be extraordinarily bright which gives us hope they will be visible to JWST.
     
  8. Mar 8, 2017 #7

    wolram

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    Thank you Cronos..
     
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