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Title: An intensely star-forming galaxy at z ∼ 7 with low dust and metal content revealed by deep ALMA and HST observations

We report deep ALMA observations complemented by associated Hubble Space Telescope (HST) imaging for a luminous (m {sub UV} = 25) galaxy, 'Himiko', at a redshift of z = 6.595. The galaxy is remarkable for its high star formation rate, 100 M {sub ☉} yr{sup –1}, which has been securely estimated from our deep HST and Spitzer photometry, and the absence of any evidence for strong active galactic nucleus activity or gravitational lensing magnification. Our ALMA observations probe an order of magnitude deeper than previous IRAM observations, yet fail to detect a 1.2 mm dust continuum, indicating a flux of <52 μJy, which is comparable to or weaker than that of local dwarf irregulars with much lower star formation rates. We likewise provide a strong upper limit for the flux of [C II] 158 μm, L{sub [C} {sub II]}<5.4×10{sup 7} L{sub ⊙}, which is a diagnostic of the hot interstellar gas that is often described as a valuable probe for early galaxies. In fact, our observations indicate that Himiko lies off the local L{sub [C} {sub II]}-star formation rate scaling relation by a factor of more than 30. Both aspects of our ALMA observations suggest that Himiko is a uniquemore » object with a very low dust content and perhaps nearly primordial interstellar gas. Our HST images provide unique insight into the morphology of this remarkable source, highlighting an extremely blue core of activity and two less extreme associated clumps. Himiko is undergoing a triple major merger event whose extensive ionized nebula of Lyα emitting gas, discovered in our earlier work with Subaru, is powered by star formation and the dense circumgalactic gas. We are likely witnessing an early massive galaxy during a key period of its mass assembly close to the end of the reionization era.« less
Authors:
; ;  [1] ;  [2] ;  [3] ; ;  [4] ;  [5] ; ; ;  [6] ;  [7] ;  [8]
  1. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
  2. Department of Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States)
  3. The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
  4. Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)
  5. Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago 763-0355 (Chile)
  6. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  7. Research Center for the Early Universe (WPI), University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 (Japan)
  8. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
Publication Date:
OSTI Identifier:
22345247
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COSMOLOGY; DUSTS; GALAXIES; GALAXY NUCLEI; GRAVITATIONAL LENSES; IMAGES; MASS; METALS; NEBULAE; PHOTOMETRY; RED SHIFT; SPACE; STARS; TELESCOPES