Abstract
Abstract Redshift z = 9–10 object selection is the effective limit of Hubble Space Telescope (HST) imaging capability, even when confirmed with Spitzer. If only a few photometry data points are available, it becomes attractive to add criteria based on their morphology in these J- and H-band images. One could do so through visual inspection, a size criterion, or alternate morphometrics. We explore a vetted sample of Brightest of Reionizing Galaxies (BoRG) z ∼ 9 and z ∼ 10 candidate galaxies and the object rejected by Morishita+ to explore the utility of a size criterion in z = 9–10 candidate selection. A stringent, point-spread function (PSF)-corrected effective radius criterion ( ) would result in the rejection of 65%–70% of the interlopers visually rejected by Morishita et al. It may also remove up to ∼20% of bona fide brightest ( ) z = 9 or 10 candidates from a BoRG selected sample based on the Mason et al. luminosity functions, assuming the Holwerda et al. size–luminosity relation. We argue that including a size constraint in lieu of a visual inspection may serve in wide-field searches for these objects in, e.g., Euclid or HST archival imaging with the understanding that some brightest ( ) candidates may be missed. The sizes of the candidates found by Morishita et al. follow the expected size distribution of z ∼ 9 for bright galaxies, consistent with the log normal in Shibuya et al. and single objects. Two candidates show high star formation surface density ( ) and all merit further investigation and follow-up observations.
Highlights
Near-infrared deep observations with the Hubble and Spitzer Space Telescopes as well as ground-based surveys have resulted in a boon in the numbers of high-redshift galaxies (z > 6) identified by the Lyman-break in their optical and near-infrared colors
The Brightest of Reionizing Galaxies (BoRG) survey (Trenti et al 2011, 2012; Bradley et al 2012; Schmidt et al 2014; Calvi et al 2016) has been designed to contribute toward an unbiased measurement of the number density of the brightest galaxies at z ∼ 8 initially and focuses on z ~ 9–10, using Hubble Space Telescope (HST) pure-parallel opportunities to cover a comparable area with medium-deep optical and infrared imaging but with effectively random pointings (5σ, mAB < 26.5) over ∼140 independent sight lines so far
Source Extractor but for the luminosity and size we are working with here, the difference will be minimal. We convert these effective radii to kiloparsec by correcting for the point-spread function (PSF), re = re2 - 0.132, and converting it to kiloparsec for the appropriate photometric redshift as determined in the H160 combined image by Morishita et al (2018)
Summary
Near-infrared deep observations with the Hubble and Spitzer Space Telescopes as well as ground-based surveys have resulted in a boon in the numbers of high-redshift galaxies (z > 6) identified by the Lyman-break in their optical and near-infrared colors. The BoRG survey (Trenti et al 2011, 2012; Bradley et al 2012; Schmidt et al 2014; Calvi et al 2016) has been designed to contribute toward an unbiased measurement of the number density of the brightest galaxies at z ∼ 8 initially and focuses on z ~ 9–10, using HST pure-parallel opportunities to cover a comparable area with medium-deep optical and infrared imaging but with effectively random pointings (5σ, mAB < 26.5) over ∼140 independent sight lines so far. Source Extractor but for the luminosity and size we are working with here, the difference will be minimal (see, e.g., Oesch et al 2010) We convert these effective radii to kiloparsec by correcting for the point-spread function (PSF), re (cor) = re2 - 0.132 (the WFC3 PSF is 0 13 for H160), and converting it to kiloparsec for the appropriate photometric redshift as determined in the H160 combined image by Morishita et al (2018).
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