A DEEP HUBBLE SPACE TELESCOPE SEARCH FOR ESCAPING LYMAN CONTINUUM FLUX AT z ∼ 1.3: EVIDENCE FOR AN EVOLVING IONIZING EMISSIVITY

By B. Siana, H. Teplitz, H. Ferguson, T. Brown, M. Giavalisco, Mark Dickinson, R. Chary, D. D. de Mello, Christopher J. Conselice, C. Bridge and 3 more. 2010

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We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z ∼ 1.3 in the GOODS fields to search for escaping Lyman continuum (LyC) photons. These are the deepest far-UV images (mAB = 28.7, 3σ, 1″ diameter) over this large an area (4.83 arcmin2) and provide some of the best escape fraction constraints for any galaxies at any redshift. We do not detect any individual galaxies, with 3σ limits to the LyC (∼700 Å) flux 50–149 times fainter (in fν) than the rest-frame UV (1500 Å) continuum fluxes. Correcting for the mean intergalactic medium (IGM) attenuation (factor ∼2), as well as an intrinsic stellar Lyman break (factor ∼3), these limits translate to relative escape fraction limits of fesc,rel < [0.03, 0.21]. The stacked limit is fesc,rel(3σ) < 0.02. We use a Monte Carlo simulation to properly account for the expected distribution of line-of-sight IGM opacities. When including constraints from previous surveys at z ∼ 1.3 we find that, at the 95% confidence level, no more than 8% of star-forming galaxies at z ∼ 1.3 can have relative escape fractions greater than 0.50. Alternatively, if the majority of galaxies have low, but non-zero, escaping LyC, the escape fraction cannot be more than 0.04. In light of some evidence for strong LyC emission from UV-faint regions of Lyman break galaxies (LBGs) at z ∼ 3, we also stack sub-regions of our galaxies with different surface brightnesses and detect no significant LyC flux at the fesc,rel < 0.03 level. Both the stacked limits and the limits from the Monte Carlo simulation suggest that the average ionizing emissivity (relative to non-ionizing UV emissivity) at z ∼ 1.3 is significantly lower than has been observed in LBGs at z ∼ 3. If the ionizing emissivity of star-forming galaxies is in fact increasing with redshift, it would help to explain the high photoionization rates seen in the IGM at z>4 and reionization of the IGM at z>6.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/52c3c1049e720521da385ca40e072f2ed4d3eb2c

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Citations in the corpus

EXTREME FEEDBACK AND THE EPOCH OF REIONIZATION: CLUES IN THE LOCAL UNIVERSE (2011, background): “…al. 2001; Heckman et al. 2001 - hereafter H01; Bergvall et al. 2006; Grimes et al. 2009 - hereafter G09), intermediate redshift (Malkan et al. 2003, Siana et al. 2007,2010; Cowie et al. 2009) and high- redshift (Steidel et al. 2001; Giallongo et al. 2002; Fernandez-Soto et al. 2003; Inoue et al.…”
A characteristic scale for cold gas (2016, background): “The escape fraction fesc is perhaps the most uncertain and hotly debated parameter in models of reionization, with few available empirical constraints (e. g., Siana et al., 2010).”
ARE ULTRA-FAINT GALAXIES AT z = 6–8 RESPONSIBLE FOR COSMIC REIONIZATION? COMBINED CONSTRAINTS FROM THE HUBBLE FRONTIER FIELDS CLUSTERS AND PARALLELS (2015, background): “Very few detections were reported however and show very low escape fractions relative to the UV radiation, of the order of few percent (Shapley et al. 2006; Iwata et al. 2009; Siana et al. 2010; Nestor et al. 2013).”
The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, background): “%) escape fraction (e.g., Siana et al. 2010, 2015; Vanzella et al. 2012, 2016; Nestor et al. 2013), and what the total emissivity is in the rest-frame UV in faint galaxies beyond the limits of current surveys in the Hubble Ultra Deep Field (HUDF: Beckwith et al. 2006; Ellis et al. 2013; Illingworth…”
New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization (2013, background): “Siana et al. (2010), for example, find fesc < 0.04 at z ∼ 1, while Nestor et al. (2013) find fesc ∼ 5 − 7 per cent for Lyman break galaxies (LBGs) and fesc ∼ 10 − 30 per cent for fainter Lyman-alpha emitters (LAEs) (see also Mostardi et al. 2013).”
An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “Several other surveys reported only upper limits (Siana et al. 2010; Bridge et al. 2010; Malkan et al. 2003; Vanzella et al. 2010b, 2012; Boutsia et al. 2011; Grazian et al. 2015).”
THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, background): “Although bright galaxies at z ~ 1 have very low escape fractions (relative to the UV emission) of fesc,rel< 2% (Siana et al. 2010), escaping ionizing emission has been observed from small fractions of galaxies probed by studies at z ~ 3–4 (e.g., Steidel et al. 2001; Shapley et al. 2006; Iwata et…”
NEW OBSERVATIONS OF z ∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION (2014, background): “This work is clearly rather speculative, since fesc is a very elusive quantity to measure and we only have tentative indications on its value from upper limits (e.g. Nestor et al. 2013, Vanzella et al. 2012, Boutsia et al. 2011) and on its evolution (e.g. Cowie et al. 2009, Siana et al. 2010).”
The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization★ (2018, background): “…ow nloaded from https://academ ic.oup.com /m nras/article/479/1/994/5043230 by guest on 03 M arch 2021 the escape of ionizing photons from dwarf galaxies, resulting in upper limits of a few per cent (e.g. Cowie, Barger & Trouille 2009; Bridge et al. 2010; Siana et al. 2010; Leitet et al. 2013).”
CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION (2012, background): “Siana et al. (2010) searched for ionizing photons with UV imaging ofz∼ 1 star-forming galaxies, finding only nondetections, resulting in an upper limit on the relative escape fraction of ionizing photons to UV photons of fesc,rel < 2% (see also Siana et al. 2007).”
Using Lyman-α to detect galaxies that leak Lyman continuum (2014, background): “…that have been studied in LyC at z ∼ 1 with the Galaxy Evolution Explorer (GALEX) and the Hubble Space Telescope (HST), the situation still does not change much, and still no individual LyC-leaking galaxies are reported (Malkan et al. 2003; Siana et al. 2007; Cowie et al. 2009; Siana et al. 2010).”
The difficulty of getting high escape fractions of ionizing photons from high-redshift galaxies: A view from the FIRE cosmological simulations (2015, methodology): “At z ∼ 1, stacked samples have been used to derive upper limits as low as fesc < 1%–2% (e.g. Cowie et al. 2009; Siana et al. 2010; Bridge et al. 2010).”
THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE “GREEN PEA” GALAXIES (2013, background): “At low redshift, observations of star-forming galaxies give upper limits on the escape fraction of only a few percent (e.g., Leitherer et al. 1995; Heckman et al. 2001; Siana et al. 2010).”
Concordance models of reionization: implications for faint galaxies and escape fraction evolution (2012, background): “Note that such evolution is nonetheless allowed by the data, and in fact suggested by direct Lyman continuum observations (e.g., Inoue et al. 2006; Siana et al. 2010).”
The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “At z ∼ 1, no objects with leaking ionising photons have been detected (Siana et al. 2010; Bridge et al. 2010), but at z ∼ 3, the highest redshift at which the opacity of the inter-galactic medium for ionising photons is approximately less than unity, ionising photons have been detected in∼ 10% of…”
ON THE REDSHIFT EVOLUTION OF THE Lyα ESCAPE FRACTION AND THE DUST CONTENT OF GALAXIES (2010, background): “At these redshifts, measurements of fLyCesc are emerging that do seem to be consistent with these values (Iwata et al. 2009; Vanzella et al. 2010), which continue to evolve to lower values with decreasing redshift (see Siana et al. 2010).”