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.
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
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.
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.
Stiavelli, M., Fall, S. M. & Panagia, N. Observable properties of cosmological reionization sources. Astrophys. J. 600, 508–519 (2004).
Madau, P. Radiative transfer in a clumpy universe: the colors of high-redshift galaxies. Astrophys. J. 441, 18–27 (1995).
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).
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).
Borthakur, S., Heckman, T. M., Leitherer, C. & Overzier, R. A. A local clue to the reionization of the Universe. Science 346, 216–219 (2014).
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).
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).
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).
Shapley, A. E. et al. Q1549-C25: a clean source of Lyman-continuum emission at z = 3.15. Astrophys. J. 826, L24 (2016).
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).
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).
Vanzella, E. et al. Direct Lyman continuum and Ly α escape observed at redshift 4. Mon. Not. R. Astron. Soc. 476, L15–L19 (2018).
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).
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).
Madau, P. & Dickinson, M. Cosmic star-formation history. Ann. Rev. Astron. Astrophys. 52, 415–486 (2014).
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).
Tandon, S. N. et al. In-orbit performance of UVIT and first results. J. Astron. Astrophys. 38, 28 (2017).
Singh, K. P. et al. ASTROSAT mission. Proc. SPIE 9144, 91441S (2014).
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).
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).
Bacon, R. et al. The MUSE Hubble Ultra Deep field survey. I. Survey description, data reduction, and source detection. Astron. Astrophys. 608, A1 (2017).
Brammer, G. B., van Dokkum, P. G. & Coppi, P. EAZY: A fast, public photometric redshift code. Astrophys. J. 686, 1503–1513 (2008).
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).
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).
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).
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).
Kennicutt, R. C. Jr. Star formation in galaxies along the Hubble sequence. Ann. Rev. Astron. Astrophys. 36, 189–232 (1998).
Leitherer, C. et al. Starburst99: synthesis models for galaxies with active star formation. Astrophys. J. Suppl. 123, 3–40 (1999).
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).
Luo, B. et al. The Chandra Deep Field-south Survey: 7 Ms source catalogs. Astrophys. J. Suppl. 228, 2 (2017).
Boquien, M. et al. CIGALE: a Python code investigating galaxy emission. Astron. Astrophys. 622, A103 (2019).
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).
Ferland, G. J. et al. The 2013 release of Cloudy. Rev. Mex. Astron. Astrofis. 49, 137–163 (2013).
Elmegreen, D. M. et al. Clumpy galaxies in goods and gems: massive analogs of local dwarf irregulars. Astrophys. J. 701, 306–329 (2009).
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).
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).
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).
Rivera-Thorsen, T. E. et al. Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy. Science 366, 738–741 (2019).
Tandon, S. N. et al. In-orbit calibrations of the ultraviolet imaging telescope. Astron. J. 154, 128 (2017).
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).
Renzini, A. & Daddi, E. Wandering in the redshift desert. Messenger 137, 41–45 (2009).
Bertin, E. & Arnouts, S. SExtractor: software for source extraction. Astron. Astrophys. Suppl. 117, 393–404 (1996).
Martins, F., Schaerer, D. & Hillier, D. J. A new calibration of stellar parameters of galactic O stars. Astron. Astrophys. 436, 1049–1065 (2005).
Wold, I. G. B. et al. Faint flux-limited Ly emitter sample at ~ 0.3. Astrophys. J. 848, 108 (2017).
Siana, B. et al. New constraints on the Lyman continuum escape fraction at z ~ 1.3. Astrophys. J. 668, 62–73 (2007).
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).
Timothy, J. G. Review of multianode microchannel array detector systems. J. Astron. Telesc. Instrum. Syst. 2, 030901 (2016).
Nordon, R. et al. The far-infrared, UV, and molecular gas relation in galaxies up to z = 2.5. Astrophys. J. 762, 125 (2013).
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).
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).
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).
Osterbrock, D. E. & Ferland, G. J. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei 2nd edn (University Science Books, 2006).
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).
Osterbrock, D. E. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei (University Science Books, 1989).
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).
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).
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).
Dunlop, J. S. et al. A deep ALMA image of the Hubble Ultra Deep Field. Mon. Not. R. Astron. Soc. 466, 861–883 (2017).
Franco, M. et al. GOODS-ALMA: 1.1 mm galaxy survey. I. Source catalog and optically dark galaxies. Astron. Astrophys. 620, A152 (2018).
Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003).
Salpeter, E. E. The luminosity function and stellar evolution. Astrophys. J. 121, 161 (1955).
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).
Calzetti, D. et al. The dust content and opacity of actively star-forming galaxies. Astrophys. J. 533, 682–695 (2000).
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).
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).
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).
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).
Fisher, D. B. et al. The rarity of dust in metal-poor galaxies. Nature 505, 186–189 (2014).
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.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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.
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.
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”.
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)).
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.
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.
Magnitudes of the galaxy AUDFs01 and its clumps at different passband. All magnitudes are aperture and foreground dust corrected.
About this article
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 4, 1185–1194 (2020). https://doi.org/10.1038/s41550-020-1173-5
Journal of Astrophysics and Astronomy (2021)
Monthly Notices of the Royal Astronomical Society (2021)
The Astrophysical Journal (2021)
Monthly Notices of the Royal Astronomical Society (2021)
Nature Astronomy (2020)