Star formation in the early universe

Beyond the tip of the iceberg

N. R. Tanvir, A. J. Levan, A. S. Fruchter, J. P U Fynbo, J. Hjorth, K. Wiersema, M. N. Bremer, J. Rhoads, P. Jakobsson, P. T. O'Brien, E. R. Stanway, D. Bersier, P. Natarajan, J. Greiner, D. Watson, A. J. Castro-Tirado, R. A M J Wijers, R. L C Starling, K. Misra, J. F. Graham & 1 others C. Kouveliotou

Research output: Contribution to journalArticle

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Abstract

We present late-time Hubble Space Telescope (HST) imaging of the fields of six Swift gamma-ray bursts (GRBs) lying at 5.0 ≲ z ≲ 9.5. Our data include very deep observations of the field of the most distant spectroscopically confirmed burst, GRB090423, at z = 8.2. Using the precise positions afforded by their afterglows, we can place stringent limits on the luminosities of their host galaxies. In one case, that of GRB060522 at z = 5.11, there is a marginal excess of flux close to the GRB position which may be a detection of a host at a magnitude J AB 28.5. None of the others are significantly detected, meaning that all the hosts lie below L* at their respective redshifts, with star formation rates (SFRs) ≲ 4 M yr -1 in all cases. Indeed, stacking the five fields with WFC3-IR data, we conclude a mean SFR <0.17 M yr-1 per galaxy. These results support the proposition that the bulk of star formation, and hence integrated UV luminosity, at high redshifts arises in galaxies below the detection limits of deep-field observations. Making the reasonable assumption that GRB rate is proportional to UV luminosity at early times allows us to compare our limits with expectations based on galaxy luminosity functions (LFs) derived from the Hubble Ultra-Deep Field and other deep fields. We infer that an LF, which is evolving rapidly toward steeper faint-end slope (α) and decreasing characteristic luminosity (L*), as suggested by some other studies, is consistent with our observations, whereas a non-evolving LF shape is ruled out at ≳ 90% confidence. Although it is not yet possible to make stronger statements, in the future, with larger samples and a fuller understanding of the conditions required for GRB production, studies like this hold great potential for probing the nature of star formation, the shape of the galaxy LF, and the supply of ionizing photons in the early universe.

Original languageEnglish (US)
Article number46
JournalAstrophysical Journal
Volume754
Issue number1
DOIs
StatePublished - Jul 20 2012

Fingerprint

star formation
universe
luminosity
gamma ray bursts
galaxies
star formation rate
shape functions
afterglows
Hubble Space Telescope
stacking
confidence
bursts
slopes
photons
rate

Keywords

  • galaxies: evolution
  • galaxies: luminosity function, mass function

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Tanvir, N. R., Levan, A. J., Fruchter, A. S., Fynbo, J. P. U., Hjorth, J., Wiersema, K., ... Kouveliotou, C. (2012). Star formation in the early universe: Beyond the tip of the iceberg. Astrophysical Journal, 754(1), [46]. https://doi.org/10.1088/0004-637X/754/1/46

Star formation in the early universe : Beyond the tip of the iceberg. / Tanvir, N. R.; Levan, A. J.; Fruchter, A. S.; Fynbo, J. P U; Hjorth, J.; Wiersema, K.; Bremer, M. N.; Rhoads, J.; Jakobsson, P.; O'Brien, P. T.; Stanway, E. R.; Bersier, D.; Natarajan, P.; Greiner, J.; Watson, D.; Castro-Tirado, A. J.; Wijers, R. A M J; Starling, R. L C; Misra, K.; Graham, J. F.; Kouveliotou, C.

In: Astrophysical Journal, Vol. 754, No. 1, 46, 20.07.2012.

Research output: Contribution to journalArticle

Tanvir, NR, Levan, AJ, Fruchter, AS, Fynbo, JPU, Hjorth, J, Wiersema, K, Bremer, MN, Rhoads, J, Jakobsson, P, O'Brien, PT, Stanway, ER, Bersier, D, Natarajan, P, Greiner, J, Watson, D, Castro-Tirado, AJ, Wijers, RAMJ, Starling, RLC, Misra, K, Graham, JF & Kouveliotou, C 2012, 'Star formation in the early universe: Beyond the tip of the iceberg', Astrophysical Journal, vol. 754, no. 1, 46. https://doi.org/10.1088/0004-637X/754/1/46
Tanvir NR, Levan AJ, Fruchter AS, Fynbo JPU, Hjorth J, Wiersema K et al. Star formation in the early universe: Beyond the tip of the iceberg. Astrophysical Journal. 2012 Jul 20;754(1). 46. https://doi.org/10.1088/0004-637X/754/1/46
Tanvir, N. R. ; Levan, A. J. ; Fruchter, A. S. ; Fynbo, J. P U ; Hjorth, J. ; Wiersema, K. ; Bremer, M. N. ; Rhoads, J. ; Jakobsson, P. ; O'Brien, P. T. ; Stanway, E. R. ; Bersier, D. ; Natarajan, P. ; Greiner, J. ; Watson, D. ; Castro-Tirado, A. J. ; Wijers, R. A M J ; Starling, R. L C ; Misra, K. ; Graham, J. F. ; Kouveliotou, C. / Star formation in the early universe : Beyond the tip of the iceberg. In: Astrophysical Journal. 2012 ; Vol. 754, No. 1.
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AU - Hjorth, J.

AU - Wiersema, K.

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AU - O'Brien, P. T.

AU - Stanway, E. R.

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AU - Natarajan, P.

AU - Greiner, J.

AU - Watson, D.

AU - Castro-Tirado, A. J.

AU - Wijers, R. A M J

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