THE BRIGHTEST OF REIONIZING GALAXIES SURVEY: CONSTRAINTS ON THE BRIGHT END OF THEz∼ 8 LUMINOSITY FUNCTION

Abstract

We report the discovery of 33 Lyman break galaxy (LBG) candidates at z ∼ 8 detected in Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging as part of the Brightest of Reionizing Galaxies (BoRG) pure-parallel survey. The ongoing BoRG survey currently has the largest area (274 arcmin 2 ) with Y 098 (or Y 105 ), J 125 , and H 160 band coverage needed to search for z ∼ 8 galaxies, about three times the current CANDELS area, and slightly larger than what will be the final CANDELS wide component with Y 105 data (required to select z ∼ 8 sources). Our sample of 33 relatively bright Y 098 -dropout galaxies have J 125 band magnitudes between 25.5 and 27.4 mag. This is the largest sample of bright (J 125 27.4) z ∼ 8 galaxy candidates presented to date. Combining our dataset with the Hubble Ultra-Deep Field (HUDF09) dataset, we constrain the rest-frame ultraviolet galaxy luminosity function at z ∼ 8 over the widest dynamic range currently available. The combined datasets are well fitted by a Schechter function, i.e. φ(L) = φ * (L/L * ) α e −(L/L * ) , without evidence for an excess of sources at the bright end. At 68% confidence, for h = 0.7 we derive φ * = (4.3 +3.5 −2.1 ) × 10 −4 Mpc −3 , M * = −20.26 +0.29 −0.34 , and a very steep faint-end slope α = −1.98 +0.23 −0.22 . While the best-fit parameters still have a strong degeneracy, especially between φ * and M * , our improved coverage at the bright end has reduced the uncertainty of the faint-end power-law slope at z ∼ 8 compared to the best previous determination at ±0.4. With a future expansion of the BoRG survey, combined with planned ultradeep WFC3/IR observations, it will be possible to further reduce this uncertainty and clearly demonstrate the steepening of the faint-end slope compared to measurements at lower redshift, thereby confirming the key role played by small galaxies in the reionization of the universe.

Low-mass galaxy formation and the ionizing photon budget during reionization

“…The shaded regions are 1σ confidence limits estimated by bootstrap. The observations in black filled circles are based on the HUDF (Bouwens et al 2007(Bouwens et al , 2011bOesch et al 2012), the squares are the HUDF and eXtreme Deep Field with GOODS-South (Oesch et al 2013), the pentagon is from HUDF and eXtreme Deep Field with both GOODS-South and North , the upward pointing triangle is from BoRG (Bradley et al 2012;Schmidt et al 2014) and the downward pointing triangle is from CLASH (Bouwens et al 2012a;Zheng et al 2012;Coe et al 2013). The bottom grey horizontal curve indicates the UV ionisation density to completely reionize the Universe (hence case 'A' recombination rates for hydrogen are used), assuming a clumping factor of 3 Shull et al 2012), escape fraction of 0.2 (Ouchi et al 2009) and a (logarithmic) ratio of Lyman continuum photons to UV flux of 25.2 ).…”

Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

“…Over the past few years, ground-and space-based observations have allowed a statistically significant data set to be collected for z;6-10 Lyman Break galaxies (LBGs; Bouwens et al 2010Bouwens et al , 2011Bouwens et al , 2015bCastellano et al 2010;McLure et al 2010McLure et al , 2013Oesch et al 2010Oesch et al , 2013Oesch et al , 2016Bradley et al 2012;Bowler et al 2014Bowler et al , 2015Atek et al 2015;Livermore et al 2016). In this work, our aim is to revisit the constraints allowed on the WDM particle mass by combining these "galaxy" data sets with the latest limits on the cosmological electron scattering optical depth inferred by Planck.…”

SPITZER ULTRA FAINT SURVEY PROGRAM (SURFS UP). II. IRAC-DETECTED LYMAN-BREAK GALAXIES AT 6 ≲ z ≲ 10 BEHIND STRONG-LENSING CLUSTERS

“…Over a thousand z  6 galaxy candidates have been identified in deep Hubble Space Telescope (HST) extragalactic blank fields like CANDELS (Grogin et al 2011;Koekemoer et al 2011), HUDF/XDF (Beckwith et al 2006;Koekemoer et al 2013;Illingworth et al 2013;Bouwens et al 2015), BoRG (Trenti et al 2011Bradley et al 2012), and HIPPIES (Yan et al 2011). …”