The Sizes of z ∼ 9−10 Galaxies Identified in the Brightest of Reionizing Galaxies (BoRG) Survey

• Published in: The Astronomical journal Vol. 160; no. 4; pp. 154 - 162
• Main Authors: Holwerda, Benne W., Bridge, Joanna S., Steele, Rebecca L., Kusmic, Samir, Bradley, Larry, Livermore, Rachael, Bernard, Stephanie, Jacques, Alice
• Format: Journal Article
• Language: English
• Published: Madison The American Astronomical Society 01.10.2020; IOP Publishing
• Subjects: Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Candidates; Criteria; Data points; DISTRIBUTION; Galactic and extragalactic astronomy; GALAXIES; Galaxy classification systems; Galaxy distances; Galaxy distribution; Galaxy evolution; Galaxy formation; Galaxy radii; Galaxy stellar content; High-redshift galaxies; Hubble Space Telescope; Inspection; LUMINOSITY; Lyman-break galaxies; Morphology; PHOTOMETRY; Point spread functions; RED SHIFT; Size distribution; SPACE; Space telescopes; Star & galaxy formation; Star formation; STARS
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/aba617

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.