1. Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time.
- Author
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Zhang, Zhi-Yu, Romano, D., Ivison, R. J., Papadopoulos, Padelis P., and Matteucci, F.
- Abstract
All measurements of cosmic star formation must assume an initial distribution of stellar masses—the stellar initial mass function—in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum
1 . The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time2 . Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies2 ,3 , especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths4 ,5 . The13 C/18 O isotope abundance ratio in the cold molecular gas—which can be probed via the rotational transitions of the13 CO and C18 O isotopologues—is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of13 CO and C18 O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low13 CO/C18 O ratio for all our targets—alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way6 —implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the ‘main sequence’ of star-forming galaxies7 , although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities. Observations of13 CO and C18 O emission from four dusty starburst galaxies at redshifts of approximately two to three reveal that massive stars are more numerous in starburst events than in ordinary star-forming spiral galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2018
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