TY - JOUR
T1 - Condition for dust evacuation from the first galaxies
AU - Fukushima, Hajime
AU - Yajima, Hidenobu
AU - Omukai, Kazuyuki
N1 - Funding Information:
The authors wish to express their cordial thanks to Prof Takahiro Tanaka and Takashi Hosokawa for their continual interest and advice. We also thank Daisuke Nakauchi, Kazu Sugimura and Ryoki Matsukoba for fruitful discussions. We would like to thank the anonymous reviewer for their constructive comments and advice, especially for Section 4. This work is supported in part by MEXT/JSPS KAKENHI (grants 25287040 and 17H01102 to KO and 17H04827 to HY).
Publisher Copyright:
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2018/6/11
Y1 - 2018/6/11
N2 - Dust enables low-mass stars to form from low-metallicity gas by inducing fragmentation of clouds via cooling by thermal emission. Dust may, however, be evacuated from star-forming clouds due to the radiation force from massive stars. We study here the condition for dust evacuation by comparing the dust evacuation time with the time of cloud destruction due to either expansion of HII regions or supernovae. The cloud destruction time has a weak dependence on cloud radius, while the dust evacuation time is shorter for a cloud with a smaller radius. Dust evacuation, thus, occurs in compact star-forming clouds whose column density is NH ≃ 1024-1026 cm-2. The critical halo mass above which dust evacuation occurs is lower for higher formation red shift, e.g. ~109M⊙ at red shift z ~ 3 and ~107M⊙ at z ~ 9. In addition, the metallicity of the gas should be less than ~10-2 Z⊙, otherwise attenuation by dust reduces the radiation force significantly. From the dust-evacuated gas, massive stars are likely to form, even with a metallicity above ~10-5 Z⊙, the critical value for low-mass star formation due to dust cooling. This can explain the dearth of ultra-metal-poor stars with a metallicity lower than ~10-4 Z⊙.
AB - Dust enables low-mass stars to form from low-metallicity gas by inducing fragmentation of clouds via cooling by thermal emission. Dust may, however, be evacuated from star-forming clouds due to the radiation force from massive stars. We study here the condition for dust evacuation by comparing the dust evacuation time with the time of cloud destruction due to either expansion of HII regions or supernovae. The cloud destruction time has a weak dependence on cloud radius, while the dust evacuation time is shorter for a cloud with a smaller radius. Dust evacuation, thus, occurs in compact star-forming clouds whose column density is NH ≃ 1024-1026 cm-2. The critical halo mass above which dust evacuation occurs is lower for higher formation red shift, e.g. ~109M⊙ at red shift z ~ 3 and ~107M⊙ at z ~ 9. In addition, the metallicity of the gas should be less than ~10-2 Z⊙, otherwise attenuation by dust reduces the radiation force significantly. From the dust-evacuated gas, massive stars are likely to form, even with a metallicity above ~10-5 Z⊙, the critical value for low-mass star formation due to dust cooling. This can explain the dearth of ultra-metal-poor stars with a metallicity lower than ~10-4 Z⊙.
KW - Dust
KW - Extinction
KW - Galaxies: Evolution
KW - Stars: Formation
KW - Stars: Low-mass
KW - Stars: Population II
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U2 - 10.1093/mnras/sty799
DO - 10.1093/mnras/sty799
M3 - Article
AN - SCOPUS:85046649704
VL - 477
SP - 1071
EP - 1085
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 1
ER -