Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization

Abstract

Within one billion years of the Big Bang, intergalactic hydrogen was ionized by sources emitting ultraviolet and higher energy photons. This was the final phenomenon to globally affect all the baryons (visible matter) in the Universe. It is referred to as cosmic reionization and is an integral component of cosmology. It is broadly expected that intrinsically faint galaxies were the primary ionizing sources due to their abundance in this epoch1,2. However, at the highest redshifts (z > 7.5; lookback time 13.1 Gyr), all galaxies with spectroscopic confirmations to date are intrinsically bright and, therefore, not necessarily representative of the general population3. Here, we report the unequivocal spectroscopic detection of a low luminosity galaxy at z > 7.5. We detected the Lyman-α emission line at 10,504 Å in two separate observations with MOSFIRE4 on the Keck I Telescope and independently with the Hubble Space Telescope’s slitless grism spectrograph, implying a source redshift of z = 7.640 ± 0.001. The galaxy is gravitationally magnified by the massive galaxy cluster MACS J1423.8+2404 (z = 0.545), with an estimated intrinsic luminosity of MAB = −19.6 ± 0.2 mag and a stellar mass of M = 3.0 0.8 + 1.5 × 10 8 solar masses. Both are an order of magnitude lower than the four other Lyman-α emitters currently known at z > 7.5, making it probably the most distant representative source of reionization found to date.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Integrated detection of the Lyα emission line at z = 7.640 with Keck/MOSFIRE at a signal-to-noise ratio of 6.7.
Figure 2: HST spectra from the GLASS survey.
Figure 3: Photometric data and spectral energy distribution of MACS1423-z7p64.

References

  1. 1

    Robertson, B. E., Ellis, R. S., Furlanetto, S. R. & Dunlop, J. S. Cosmic reionization and early star-forming galaxies: a joint analysis of new constraints from Planck and the Hubble space telescope. Astrophys. J. 802, L19 (2015).

    ADS  Article  Google Scholar 

  2. 2

    Bouwens, R. J. et al. UV luminosity functions at redshifts z 4 to z 10: 10,000 galaxies from HST legacy fields. Astrophys. J. 803, 34 (2015).

    ADS  Article  Google Scholar 

  3. 3

    Stark, D. P. et al. Lyman-α and Ciii] emission in z = 7–9 galaxies: accelerated reionization around luminous star-forming systems? Mon. Not. R. Astron. Soc. 464, 469–479 (2017).

    ADS  Article  Google Scholar 

  4. 4

    McLean, I. S. et al. MOSFIRE, the multi-object spectrometer for infra-red exploration at the Keck Observatory. Proc. SPIE 8446, 84460J (2012).

  5. 5

    Schmidt, K. B. et al. The Grism Lens-Amplified Survey from Space (GLASS). III. A census of Lyα emission at z 7 from HST spectroscopy. Astrophys. J. 818, 38 (2016).

    ADS  Article  Google Scholar 

  6. 6

    Postman, M. et al. The cluster lensing and supernova survey with Hubble: an overview. Astrophys. J. Suppl. Ser. 199, 25 (2012).

    ADS  Article  Google Scholar 

  7. 7

    Schmidt, K. B. et al. Through the looking GLASS: HST spectroscopy of faint galaxies lensed by the frontier fields cluster MACSJ0717.5+3745. Astrophys. J. 782, L36 (2014).

    ADS  Article  Google Scholar 

  8. 8

    Treu, T. et al. The Grism Lens-Amplified Survey from Space (GLASS). I. Survey overview and first data release. Astrophys. J. 812, 114 (2015).

    ADS  Article  Google Scholar 

  9. 9

    Bradač, M. et al. Focusing cosmic telescopes: exploring redshift z 5–6 galaxies with the bullet cluster 1E0657-56. Astrophys. J. 706, 1201–1212 (2009).

    ADS  Article  Google Scholar 

  10. 10

    Schenker, M. A. et al. Keck spectroscopy of faint 3 < z < 8 Lyman break galaxies: evidence for a declining fraction of emission line sources in the redshift range 6 < z < 8. Astrophys. J. 744, 179 (2012).

    ADS  Article  Google Scholar 

  11. 11

    Treu, T., Schmidt, K. B., Trenti, M., Bradley, L. D. & Stiavelli, M. The changing Lyα optical depth in the range 6 < z < 9 from the MOSFIRE spectroscopy of Y-dropouts. Astrophys. J. 775, L29 (2013).

    ADS  Article  Google Scholar 

  12. 12

    Pentericci, L. et al. New observations of z 7 galaxies: evidence for a patchy reionization. Astrophys. J. 793, 113 (2014).

    ADS  Article  Google Scholar 

  13. 13

    Finkelstein, S. L. et al. A galaxy rapidly forming stars 700 million years after the Big Bang at redshift 7.51. Nature 502, 524–527 (2013).

    ADS  Article  Google Scholar 

  14. 14

    Oesch, P. A. et al. A spectroscopic redshift measurement for a luminous Lyman break galaxy at z = 7.730 using Keck/MOSFIRE. Astrophys. J. 804, L30 (2015).

    ADS  Article  Google Scholar 

  15. 15

    Zitrin, A. et al. Lymanα emission from a luminous z = 8.68 galaxy: implications for galaxies as tracers of cosmic reionization. Astrophys. J. 810, L12 (2015).

    ADS  Article  Google Scholar 

  16. 16

    Song, M. et al. Keck/MOSFIRE spectroscopy of z = 7–8 galaxies: Lyα emission from a galaxy at z = 7.66. Astrophys. J. 826, 113 (2016).

    ADS  Article  Google Scholar 

  17. 17

    Castellano, M. et al. First observational support for overlapping reionized bubbles generated by a galaxy overdensity. Astrophys. J. 818, L3 (2016).

    ADS  Article  Google Scholar 

  18. 18

    Bauer, A. et al. Hydrogen reionization in the Illustris universe. Mon. Not. R. Astron. Soc. 453, 3593–3610 (2015).

    ADS  Article  Google Scholar 

  19. 19

    Hutter, A., Dayal, P., Müller, V. & Trott, C. Exploiting 21cm-Lyα emitter synergies: constraints on reionization. Astrophys. J. 836, 176 (2017).

    ADS  Article  Google Scholar 

  20. 20

    Wyithe, J. S. B. & Loeb, A. A characteristic size of 10 Mpc for the ionized bubbles at the end of cosmic reionization. Nature 432, 194–196 (2004).

    ADS  Article  Google Scholar 

  21. 21

    Labbé, I. et al. The spectral energy distributions of z 8 galaxies from the IRAC ultra deep fields: emission lines, stellar masses, and specific star formation rates at 650 Myr. Astrophys. J. 777, L19 (2013).

    ADS  Article  Google Scholar 

  22. 22

    Roberts-Borsani, G. W. et al. z ≥ 7 galaxies with red Spitzer/IRAC [3.6]–[4.5] colours in the full CANDELS data set: the brightest-known galaxies at z 7–9 and a probable spectroscopic confirmation at z = 7.48. Astrophys. J. 823, 143 (2016).

    ADS  Article  Google Scholar 

  23. 23

    Nakajima, K. et al. A hard ionizing spectrum in z = 3–4 Lyα emitters with intense O iii. emission: analogs of galaxies in the reionization era? Astrophys. J. 831, L9 (2016).

    ADS  Article  Google Scholar 

  24. 24

    Henry, A. et al. Low masses and high redshifts: the evolution of the mass-metallicity relation. Astrophys. J. 776, L27 (2013).

    ADS  Article  Google Scholar 

  25. 25

    Bertin, E. & Arnouts, S. SExtractor: software for source extraction. Astron. Astrophys. Suppl. Ser. 117, 393–404 (1996).

    ADS  Article  Google Scholar 

  26. 26

    Merlin, E. et al. The ASTRODEEP frontier fields catalogues. I. Multiwavelength photometry of Abell-2744 and MACS-J0416. Astron. Astrophys. 590, A30 (2016).

    Article  Google Scholar 

  27. 27

    Bradač, M. et al. Spitzer Ultra Faint SUrvey Program (SURFS UP). I. An overview. Astrophys. J. 785, 108 (2014).

    ADS  Article  Google Scholar 

  28. 28

    Merlin, E. et al. T-PHOT: a new code for PSF-matched, prior-based, multiwavelength extragalactic deconfusion photometry. Astron. Astrophys. 582, A15 (2015).

    Article  Google Scholar 

  29. 29

    Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003).

    ADS  Article  Google Scholar 

  30. 30

    Chabrier, G. Galactic stellar and substellar initial mass function. Publ. Astron. Soc. Pacif. 115, 763–795 (2003).

    ADS  Article  Google Scholar 

  31. 31

    Huang, K.-H. et al. Spitzer UltRa Faint SUrvey Program (SURFS UP). II. IRAC-detected Lyman-break galaxies at 6 ≤ z ≤ 10 behind strong-lensing clusters. Astrophys. J. 817, 11 (2016).

    ADS  Article  Google Scholar 

  32. 32

    Pei, Y. C. Interstellar dust from the Milky Way to the Magellanic Clouds. Astrophys. J. 395, 130–139 (1992).

    ADS  Article  Google Scholar 

  33. 33

    Calzetti, D. et al. The dust content and opacity of actively star-forming galaxies. Astrophys. J. 533, 682–695 (2000).

    ADS  Article  Google Scholar 

  34. 34

    Vulcani, B. et al. The Grism Lens-Amplified Survey from Space (GLASS). V. Extent and spatial distribution of star formation in z 0.5 cluster galaxies. Astrophys. J. 814, 161 (2015).

    ADS  Article  Google Scholar 

  35. 35

    Bradač, M., Schneider, P., Lombardi, M. & Erben, T. Strong and weak lensing united. I. The combined strong and weak lensing cluster mass reconstruction method. Astron. Astrophys. 437, 39–48 (2005).

    ADS  Article  Google Scholar 

  36. 36

    Limousin, M. et al. MACS J1423.8+2404: gravitational lensing by a massive, relaxed cluster of galaxies at z = 0.54. Mon. Not. R. Astron. Soc. 405, 777–782 (2010).

    ADS  Google Scholar 

  37. 37

    Zitrin, A. et al. Hubble space telescope combined strong and weak lensing analysis of the CLASH sample: mass and magnification models and systematic uncertainties. Astrophys. J. 801, 44 (2015).

    ADS  Article  Google Scholar 

  38. 38

    Schrabback, T. et al. Evidence of the accelerated expansion of the Universe from weak lensing tomography with COSMOS. Astron. Astrophys. 516, A63 (2010).

    Article  Google Scholar 

  39. 39

    Schrabback, T. et al. Cluster mass calibration at high redshift: HST weak lensing analysis of 13 distant galaxy clusters from the South Pole Telescope Sunyaev-Zel’dovich survey. Preprint at https://arxiv.org/abs/1611.03866 (2016).

Download references

Acknowledgements

A.H. and this work were supported by NASA (National Aeronautics and Space Administration) Headquarters under the NASA Earth and Space Science Fellowship Program, Grant ASTRO14F-0007. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors thank L. Rizzi and M. Kassis for help with the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) observations and data reduction. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work is also based on observations made with the NASA/European Space Agency Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contracts NAS5-26555 and NNX08AD79G, and the European Southern Observatory Very Large Telescopes. Support for the Grism Lens-Amplified Survey from Space (GLASS) (HST-G0-13459) was provided by NASA through a grant from the STScI. We are very grateful to the staff of the Space Telescope Science Institute for their assistance in planning, scheduling and executing the observations, and in setting up the GLASS public release website. Support for this work was also provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology and through HST-AR-13235, HST-GO-13177, HST-GO-10200, HST-GO-10863 and HST-GO-11099 from STScI. Observations were also carried out using the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was also provided by NASA through a Spitzer award issued by the Jet Propulsion Laboratory, California Institute of Technology.

Author information

Affiliations

Authors

Contributions

A.H. handled the MOSFIRE reduction and analysis, led the lens modelling analysis and was the principal author of the paper. M.B. and M.T. designed and planned the MOSFIRE observations, contributed to the GLASS survey and contributed to writing the paper. M.B. also carried out the 27 May 2015 MOSFIRE observations. T.T. designed the GLASS survey and contributed to the design of the MOSFIRE observations and to writing the paper. K.B.S. handled the GLASS reduction and analysis and contributed to writing the paper. K.H.H. performed the HST and Spitzer photometry, led the stellar population modelling and contributed to writing the paper. B.C.L. contributed to the MOSFIRE analysis and to writing the paper. J.H. contributed to the lens modelling analysis. S.R.B. carried out the 19 March 2016 MOSFIRE observations. L.E.A., C.A.M., T.M. and L.P. contributed to the GLASS survey and to writing the paper. T.S. contributed to the lens modelling analysis.

Corresponding author

Correspondence to Austin Hoag.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Figure 1 and Supplementary References. (PDF 215 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hoag, A., Bradacˇ, M., Trenti, M. et al. Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization. Nat Astron 1, 0091 (2017). https://doi.org/10.1038/s41550-017-0091

Download citation

Further reading

Search

Quick links

Sign up for the Nature Briefing newsletter for a daily update on COVID-19 science.
Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing