Does radiative feedback make faint z > 6 galaxies look small?
Abstract
Recent observations of lensed sources have shown that the faintest (M_{UV} ≈ -15 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 106 and 10^7 {M}_{⊙ }, 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} ≲ 10^{10} {M}_{⊙ }) haloes, the radiation from a compact star-forming region with an initial mass of 107 {M}_{⊙ } can keep gas clumps with Jeans masses larger than {≈ } 107 {M}_{⊙ } 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2019
- DOI:
- 10.1093/mnras/stz173
- arXiv:
- arXiv:1901.05007
- Bibcode:
- 2019MNRAS.484.4379P
- Keywords:
-
- methods: analytical;
- galaxies: dwarf;
- galaxies: high-redshift;
- galaxies: star clusters: general;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 16 pages, 13 figures, accepted for publication in MNRAS, formatting error in previous version did not display certain characters in equations, Fig. 8 replaced to be consistent with published version