Does radiative feedback make faint z > 6 galaxies look small?. Issue 3 (16th January 2019)

• Record Type: Journal Article
• Authors: Ploeckinger, Sylvia; Schaye, Joop; Hacar, Alvaro; Maseda, Michael V; Hodge, Jacqueline A; Bouwens, Rychard J
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Issue 3(2019)
• Page Start: 4379
• Page End: 4392
• Publication Date: 2019-01-16
• Subjects: methods: analytical -- galaxies: dwarf -- galaxies: high-redshift -- galaxies: star clusters: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz173
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Recent observations of lensed sources have shown that the faintest ($M_{\mathrm{UV}} \approx -15\, \mathrm{mag}$ ) galaxies observed at $z$ = 6−8 appear to be extremely compact. Some of them have inferred sizes of less than 40 pc for stellar masses between 10 6 and $10^7\, {\mathrm{M}}_{\odot }$, comparable to individual super star clusters or star cluster complexes at low redshift. High-redshift, low-mass galaxies are expected to show a clumpy, irregular morphology and if star clusters form in each of these well-separated clumps, the observed galaxy size would be much larger than the size of an individual star-forming region. As supernova explosions impact the galaxy with a minimum delay time that exceeds the time required to form a massive star cluster, other processes are required to explain the absence of additional massive star-forming regions. In this work, we investigate whether the radiation of a young massive star cluster can suppress the formation of other detectable clusters within the same galaxy already before supernova feedback can affect the galaxy. We find that in low-mass ($M_{200} \lesssim 10^{10}\, {\mathrm{M}}_{\odot }$ ) haloes, the radiation from a compact star-forming region with an initial mass of $10^{7}\, {\mathrm{M}}_{\odot }$ can keep gas clumps with Jeans masses larger than ${\approx } 10^{7}\, {\mathrm{M}}_{\odot }$ warm and ionized throughout the galaxy. In this picture, the small intrinsic sizes measured in the faintest $z$ = 6−8 galaxies are a natural consequence of the strong radiation field that stabilizes massive gas clumps. A prediction of this mechanism is that the escape fraction for ionizing radiation is high for the extremely compact, high-$z$ sources.