AstroSat detection of Lyman continuum emission from a z = 1.42 galaxy

Abstract

One of the outstanding problems of current observational cosmology is to understand the nature of sources that produced the bulk of the ionizing radiation after the Cosmic Dark Age. Direct detection of these reionization sources1 is practically infeasible at high redshift (z) due to the steep decline of intergalactic medium transmission2,3. However, a number of low-z analogues emitting Lyman continuum at 900 Å restframe are now detected at z < 0.4 (refs. 4,5,6,7,8) and there are also detections in the range 2.5 < z < 3.5 (refs. 9,10,11,12,13,14). Here we report the detection of Lyman continuum emission with a high escape fraction (>20%) from a low-mass clumpy galaxy at z = 1.42, in the middle of the redshift range where no detection has been made before and near the peak of the cosmic star-formation history15. The observation was made in the Hubble Extreme Deep Field16 by the wide-field Ultraviolet Imaging Telescope17 onboard AstroSat18. This detection of extreme ultraviolet radiation from a distant galaxy at a restframe wavelength of 600 Å opens up a new window to constrain the shape of the ionization spectrum. Further observations with AstroSat should substantially increase the sample of Lyman-continuum-leaking galaxies at cosmic noon.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Detection of the source in the AstroSat.
Fig. 2: Emission-line mapping and clumps.
Fig. 3: Modelling of SED.
Fig. 4: Comparison of AUDFs01 with other confirmed LyC detection and IGM distribution.

Data availability

The HST data are available at https://3dhst.research.yale.edu/Data.php and https://archive.stsci.edu/prepds/hlf. The VLT/ISAAC H- and Ks-band data are available at ESO Science Archive Facility (http://archive.eso.org/scienceportal/home). The Spitzer GOODS-South data used in the analysis are available from https://irsa.ipac.caltech.edu/data/SPITZER/GOODS. The SDSS data are available at the Sloan Digital Sky Survey (https://www.sdss.org). The MUSE spectroscopic data for AUDFs01 is available The other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

We have used standard data reduction tools in Python, IDL, IRAF and the publicly available code SExtractor (https://www.astromatic.net/software/sextractor) for this study. For SED fitting and analysis, we have used publicly available code CIGALE (https://cigale.lam.fr), EASY (http://www.astro.yale.edu/eazy/) and BPASS (https://bpass.auckland.ac.nz/2.html). The photoionization code CLOUDY used in this paper is in the public domain (https://trac.nublado.org/). The pipeline used to process the level 1 AstroSat/UVIT data can be downloaded from http://astrosat-ssc.iucaa.in.

References

  1. 1.

    Stiavelli, M., Fall, S. M. & Panagia, N. Observable properties of cosmological reionization sources. Astrophys. J. 600, 508–519 (2004).

    ADS  Google Scholar 

  2. 2.

    Madau, P. Radiative transfer in a clumpy universe: the colors of high-redshift galaxies. Astrophys. J. 441, 18–27 (1995).

    ADS  Google Scholar 

  3. 3.

    Inoue, A. K., Shimizu, I., Iwata, I. & Tanaka, M. An updated analytic model for attenuation by the intergalactic medium. Mon. Not. R. Astron. Soc. 442, 1805–1820 (2014).

    ADS  Google Scholar 

  4. 4.

    Leitet, E., Bergvall, N., Hayes, M., Linné, S. & Zackrisson, E. Escape of Lyman continuum radiation from local galaxies. Detection of leakage from the young starburst Tol 1247-232. Astron. Astrophys. 553, A106 (2013).

    ADS  Google Scholar 

  5. 5.

    Borthakur, S., Heckman, T. M., Leitherer, C. & Overzier, R. A. A local clue to the reionization of the Universe. Science 346, 216–219 (2014).

    ADS  Google Scholar 

  6. 6.

    Izotov, Y. I. et al. Eight per cent leakage of Lyman continuum photons from a compact, star-forming dwarf galaxy. Nature 529, 178–180 (2016).

    ADS  Google Scholar 

  7. 7.

    Leitherer, C., Hernandez, S., Lee, J. C. & Oey, M. S. Direct detection of Lyman continuum escape from local starburst galaxies with the cosmic origins spectrograph. Astrophys. J. 823, 64 (2016).

    ADS  Google Scholar 

  8. 8.

    Izotov, Y. I. et al. J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons. Mon. Not. R. Astron. Soc. 474, 4514–4527 (2018).

    ADS  Google Scholar 

  9. 9.

    Shapley, A. E. et al. Q1549-C25: a clean source of Lyman-continuum emission at z = 3.15. Astrophys. J. 826, L24 (2016).

    ADS  Google Scholar 

  10. 10.

    Vanzella, E. et al. Hubble imaging of the ionizing radiation from a star-forming galaxy at Z = 3.2 with fesc > 50%. Astrophys. J. 825, 41 (2016).

    ADS  Google Scholar 

  11. 11.

    Bian, F., Fan, X., McGreer, I., Cai, Z. & Jiang, L. High Lyman continuum escape fraction in a lensed young compact dwarf galaxy at z = 2.5. Astrophys. J. 837, L12 (2017).

    ADS  Google Scholar 

  12. 12.

    Vanzella, E. et al. Direct Lyman continuum and Ly α escape observed at redshift 4. Mon. Not. R. Astron. Soc. 476, L15–L19 (2018).

    ADS  Google Scholar 

  13. 13.

    Steidel, C. C. et al. The Keck Lyman Continuum Spectroscopic Survey (KLCS): the emergent ionizing spectrum of galaxies at z ~ 3. Astrophys. J. 869, 123 (2018).

    ADS  Google Scholar 

  14. 14.

    Fletcher, T. J. et al. The Lyman continuum escape survey: ionizing radiation from [O iii]-strong sources at a redshift of 3.1. Astrophys. J. 878, 87 (2019).

    ADS  Google Scholar 

  15. 15.

    Madau, P. & Dickinson, M. Cosmic star-formation history. Ann. Rev. Astron. Astrophys. 52, 415–486 (2014).

    ADS  Google Scholar 

  16. 16.

    Illingworth, G. D. et al. The HST Extreme Deep Field (XDF): combining all ACS and WFC3/IR data on the HUDF region into the deepest field ever. Astrophys. J. Suppl. 209, 6 (2013).

    ADS  Google Scholar 

  17. 17.

    Tandon, S. N. et al. In-orbit performance of UVIT and first results. J. Astron. Astrophys. 38, 28 (2017).

    ADS  Google Scholar 

  18. 18.

    Singh, K. P. et al. ASTROSAT mission. Proc. SPIE 9144, 91441S (2014).

    Google Scholar 

  19. 19.

    Naidu, R. P., Forrest, B., Oesch, P. A., Tran, K.-V. H. & Holden, B. P. A low Lyman continuum escape fraction of <10 per cent for extreme [O iii] emitters in an overdensity at z ~ 3.5. Mon. Not. R. Astron. Soc. 478, 791–799 (2018).

    ADS  Google Scholar 

  20. 20.

    Momcheva, I. G. et al. The 3D-HST survey: Hubble Space Telescope WFC3/G141 grism spectra, redshifts, and emission line measurements for ~100,000 galaxies. Astrophys. J. Suppl. 225, 27 (2016).

    ADS  Google Scholar 

  21. 21.

    Bacon, R. et al. The MUSE Hubble Ultra Deep field survey. I. Survey description, data reduction, and source detection. Astron. Astrophys. 608, A1 (2017).

    Google Scholar 

  22. 22.

    Brammer, G. B., van Dokkum, P. G. & Coppi, P. EAZY: A fast, public photometric redshift code. Astrophys. J. 686, 1503–1513 (2008).

    ADS  Google Scholar 

  23. 23.

    Pettini, M. & Pagel, B. E. J. [O iii]/[N ii] as an abundance indicator at high redshift. Mon. Not. R. Astron. Soc. 348, L59–L63 (2004).

    ADS  Google Scholar 

  24. 24.

    Inami, H. et al. The MUSE Hubble Ultra Deep Field Survey. II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies. Astron. Astrophys. 608, A2 (2017).

    Google Scholar 

  25. 25.

    Cardamone, C. et al. Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies. Mon. Not. R. Astron. Soc. 339, 1191–1205 (2009).

    ADS  Google Scholar 

  26. 26.

    de Barros, S. et al. An extreme [O iii] emitter at z = 3.2: a low metallicity Lyman continuum source. Astron. Astrophys. 585, A51 (2016).

    Google Scholar 

  27. 27.

    Kennicutt, R. C. Jr. Star formation in galaxies along the Hubble sequence. Ann. Rev. Astron. Astrophys. 36, 189–232 (1998).

    ADS  Google Scholar 

  28. 28.

    Leitherer, C. et al. Starburst99: synthesis models for galaxies with active star formation. Astrophys. J. Suppl. 123, 3–40 (1999).

    ADS  Google Scholar 

  29. 29.

    Baldwin, J. A., Phillips, M. M. & Terlevich, R. Classification parameters for the emission-line spectra of extragalactic objects. Publ. Astron. Soc. Pac. 93, 5–19 (1981).

    ADS  Google Scholar 

  30. 30.

    Luo, B. et al. The Chandra Deep Field-south Survey: 7 Ms source catalogs. Astrophys. J. Suppl. 228, 2 (2017).

    ADS  Google Scholar 

  31. 31.

    Boquien, M. et al. CIGALE: a Python code investigating galaxy emission. Astron. Astrophys. 622, A103 (2019).

    Google Scholar 

  32. 32.

    Eldridge, J. J. et al. Binary population and spectral synthesis version 2.1: construction, observational verification, and new results. Pub. Astron. Soc. Aus. 34, e058-61 (2017).

    ADS  Google Scholar 

  33. 33.

    Ferland, G. J. et al. The 2013 release of Cloudy. Rev. Mex. Astron. Astrofis. 49, 137–163 (2013).

    ADS  Google Scholar 

  34. 34.

    Elmegreen, D. M. et al. Clumpy galaxies in goods and gems: massive analogs of local dwarf irregulars. Astrophys. J. 701, 306–329 (2009).

    ADS  Google Scholar 

  35. 35.

    Inoue, A. K. & Iwata, I. A Monte Carlo simulation of the intergalactic absorption and the detectability of the Lyman continuum from distant galaxies. Mon. Not. R. Astron. Soc. 387, 1681–1692 (2008).

    ADS  Google Scholar 

  36. 36.

    Izotov, Y. I. et al. Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies. Mon. Not. R. Astron. Soc. 461, 3683–3701 (2016).

    ADS  Google Scholar 

  37. 37.

    Izotov, Y. I. et al. Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios. Mon. Not. R. Astron. Soc. 478, 4851–4865 (2018).

    ADS  Google Scholar 

  38. 38.

    Rivera-Thorsen, T. E. et al. Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy. Science 366, 738–741 (2019).

    ADS  Google Scholar 

  39. 39.

    Tandon, S. N. et al. In-orbit calibrations of the ultraviolet imaging telescope. Astron. J. 154, 128 (2017).

    ADS  Google Scholar 

  40. 40.

    Steidel, C. C. et al. A survey of star-forming galaxies in the 1.4 z 2.5 redshift desert: overview. Astrophys. J. 604, 534–550 (2004).

    ADS  Google Scholar 

  41. 41.

    Renzini, A. & Daddi, E. Wandering in the redshift desert. Messenger 137, 41–45 (2009).

    ADS  Google Scholar 

  42. 42.

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

    ADS  Google Scholar 

  43. 43.

    Martins, F., Schaerer, D. & Hillier, D. J. A new calibration of stellar parameters of galactic O stars. Astron. Astrophys. 436, 1049–1065 (2005).

    ADS  Google Scholar 

  44. 44.

    Wold, I. G. B. et al. Faint flux-limited Ly emitter sample at ~ 0.3. Astrophys. J. 848, 108 (2017).

    ADS  Google Scholar 

  45. 45.

    Siana, B. et al. New constraints on the Lyman continuum escape fraction at z ~ 1.3. Astrophys. J. 668, 62–73 (2007).

    ADS  Google Scholar 

  46. 46.

    Teplitz, H. et al. Far-ultraviolet imaging of the Hubble Deep Field-north: star formation in normal galaxies at z < 1. Astron. J. 132, 853–865 (2006).

    ADS  Google Scholar 

  47. 47.

    Timothy, J. G. Review of multianode microchannel array detector systems. J. Astron. Telesc. Instrum. Syst. 2, 030901 (2016).

    ADS  Google Scholar 

  48. 48.

    Nordon, R. et al. The far-infrared, UV, and molecular gas relation in galaxies up to z = 2.5. Astrophys. J. 762, 125 (2013).

    ADS  Google Scholar 

  49. 49.

    Calzetti, D., Kinney, A. L. & Storchi-Bergmann, T. Dust extinction of the stellar continua in starburst galaxies: The ultraviolet and optical extinction law. Astrophys. J. 429, 582–601 (1994).

    ADS  Google Scholar 

  50. 50.

    Reddy, N. et al. The HDUV Survey: a revised assessment of the relationship between UV slope and dust attenuation for high-redshift galaxies. Astrophys. J. 853, 56 (2018).

    ADS  Google Scholar 

  51. 51.

    Meurer, G. R., Heckman, T. M. & Calzetti, D. Dust absorption and the ultraviolet luminosity density at z ~ 3 as calibrated by local starburst galaxies. Astrophys. J. 521, 64–80 (1999).

    ADS  Google Scholar 

  52. 52.

    Osterbrock, D. E. & Ferland, G. J. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei 2nd edn (University Science Books, 2006).

  53. 53.

    Sobral, D. et al. Star formation at z = 1.47 from HiZELS: an Hα+[O ii] double-blind study. Mon. Not. R. Astron. Soc. 420, 1926–1945 (2012).

    ADS  Google Scholar 

  54. 54.

    Osterbrock, D. E. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei (University Science Books, 1989).

  55. 55.

    Schlegel, D. J., Finkbeiner, D. P. & Davis, M. Maps of dust infrared emission for use in estimation of reddening and cosmic microwave background radiation foregrounds. Astrophys. J. 500, 525–553 (1998).

    ADS  Google Scholar 

  56. 56.

    Juneau, Stéphanie et al. Active galactic nuclei emission line diagnostics and the mass–metallicity relation up to redshift z ~ 2: the impact of selection effects and evolution. Astrophys. J. 788, 88 (2014).

    ADS  Google Scholar 

  57. 57.

    Sobral, D. et al. HiZELS: a high-redshift survey of Hα emitters—II. The nature of star-forming galaxies at z = 0.84. Mon. Not. R. Astron. Soc. 398, 75–90 (2009).

    ADS  Google Scholar 

  58. 58.

    Dunlop, J. S. et al. A deep ALMA image of the Hubble Ultra Deep Field. Mon. Not. R. Astron. Soc. 466, 861–883 (2017).

    ADS  Google Scholar 

  59. 59.

    Franco, M. et al. GOODS-ALMA: 1.1 mm galaxy survey. I. Source catalog and optically dark galaxies. Astron. Astrophys. 620, A152 (2018).

    Google Scholar 

  60. 60.

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

    ADS  Google Scholar 

  61. 61.

    Salpeter, E. E. The luminosity function and stellar evolution. Astrophys. J. 121, 161 (1955).

    ADS  Google Scholar 

  62. 62.

    Reddy, N. A., Steidel, C. C., Pettini, M., Bogosavljević, M. & Shapley, A. E. The connection between reddening, gas covering fraction, and the escape of ionizing radiation at high redshift. Astrophys. J. 828, 108 (2016).

    ADS  Google Scholar 

  63. 63.

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

    ADS  Google Scholar 

  64. 64.

    Salim, S., Boquien, M. & Lee, J. C. Dust attenuation curves in the local universe: demographics and new laws for star-forming galaxies and high-redshift analogs. Astrophys. J. 859, 11 (2018).

    ADS  Google Scholar 

  65. 65.

    Reddy, N. A., Steidel, C. C., Pettini, M. & Bogosavljević, M. Spectroscopic measurements of the far-ultraviolet dust attenuation curve at z~3. Astrophys. J. 828, 107 (2016).

    ADS  Google Scholar 

  66. 66.

    Bergvall, N. et al. First detection of Lyman continuum escape from a local starburst galaxy. I. Observations of the luminous blue compact galaxy Haro 11 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Astron. Astrophys. 448, 513–524 (2006).

    ADS  Google Scholar 

  67. 67.

    Inoue, A. K. Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies. Mon. Not. R. Astron. Soc. 415, 2920–2931 (2011).

    ADS  Google Scholar 

  68. 68.

    Fisher, D. B. et al. The rarity of dust in metal-poor galaxies. Nature 505, 186–189 (2014).

    ADS  Google Scholar 

Download references

Acknowledgements

The deep field imaging data in the FUV and NUV wavelengths are based on a proposed observation carried out by the AstroSat/UVIT, which was launched by the Indian Space Research Organization (ISRO). We thank ISRO for providing such observing facilities. K.S. and F.C. acknowledge the support of CEFIPRA-IFCPAR grant through the project number 5804-1. K.S. thanks D. Sobral for kindly providing the code to make in Extended Data Fig. 2d.

Author information

Affiliations

Authors

Contributions

K.S. led the project, and the writing of the manuscript; reduction of the the UVIT data (pipeline, photometry, astrometry) and analysis, SED modelling, dust extinction and escape fraction calculation. S.N.T. contributed to the UVIT data reduction pipeline and interpretation of the photometry. C.S., A.V. and D.S. performed the BPASS modelling as well as interpretation of the result in terms of IGM distribution. A.V. and D.S. wrote the contamination hypothesis part. A.P. performed the spectral fitting of the grism data and emission-line mapping, BPT diagram. A.B. contributed to the FUV image analysis, noise estimation. A.K.I. performed Monte Carlo simulations of the IGM at the FUV band and at the redshift of the object. M.R., B.E., F.C. and D.E. participated actively in the scientific discussion, interpretation throughout the project and contributed to the final version of the manuscript. M.P. contributed in the MUSE analayis.

Corresponding author

Correspondence to Kanak Saha.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 HST grism (G141) image.

a, Coloured rectangular regions (1,2,3,4) marked on the grism image are used to extract spectra for the clumps. North-East directions are marked on the grism image. b, 1D spectrum for the full galaxy. Red solid line represents the fitting of the spectrum. Redshift measurement is based on the fitting of Hα+[N II] line alone.

Extended Data Fig. 2 SF-AGN diagnostic diagram.

a, location of the clumpy galaxy AUDFs01 on the Hα - [O III] plane. The line fluxes are measured from HST grism G141 data20. AUDFs01 being the only galaxy having highest [O III] flux in the XDF region; the color bar indicates the stellar masses of the galaxies. b, c, Mass Excitation and BPT diagram using the SDSS galaxies. d, location of AUDFs01 on the Sobral et al. (2009) plot. The line ratios for all galaxies except AUDFs01 are taken from z-COSMOS survey57 at z ~ 0.84. The error bars represent 1σ uncertainties on the flux measurements.

Extended Data Fig. 3 Postage stamp images.

GALEX (FUV, NUV), HST (UV, Optical, IR), VLT/ISAAC (H, Ks), Spitzer/IRAC (3.4, 4.5 micron)-bands. The radius of the blue circle in each panel is 1.6”.

Extended Data Fig. 4 Distributions of LyC escape fractions.

a, For the first method, calculating the LyC escape fraction from the Hα luminosity following Eq. (8). b, Following Eq. (10), for the best-fit BPASS model with metallicity Z = 0.004, and an age of the stellar burst of ~ 4.5 × 106 years. Other BPASS models, varying ages, are shown with faded lines for comparison. On both panels, the vertical dashed line shows the value of the escape fraction assuming a transparent IGM (following Eq. (8) and Eq. (10)).

Extended Data Fig. 5 Emission-line fluxes and luminosities.

Col2: line flux as measured in the HST grism G141; [O ii] is from MUSE catalogue. col3: line fluxes after foreground dust plus internal extinction correction using Balmer decrement. Col4: same as col3 but internal extinction (E(B-V)=0.13) due to UV beta slope; the value of Hβ (marked bold-face in the bracket) is what would be expected as per the internal Balmer decrement given the measured Hα. Col5: line luminosity following UV beta slope.

Extended Data Fig. 6 SED fitting parameters for CIGALE and BPASS.

The best-fit parameters for cigale modelling are indicated by the bold-face letters. Dn4000 represents the ratio of the average flux density in two two narrow bands, 3850 − 3950 Å and 4000 − 4100 Å. IRX refers to the infrared excess.

Extended Data Fig. 7 Magnitudes of the galaxy AUDFs01 and its clumps.

Magnitudes of the galaxy AUDFs01 and its clumps at different passband. All magnitudes are aperture and foreground dust corrected.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Saha, K., Tandon, S.N., Simmonds, C. et al. AstroSat detection of Lyman continuum emission from a z = 1.42 galaxy. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1173-5

Download citation

Search

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing