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|Title:||Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time||Authors:||Zhang, Zhi-Yu
Ivison, R. J.
Papadopoulos, Padelis P.
|Issue Date:||2018||Journal:||NATURE||Number:||558||Issue:||7709||First Page:||260||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<SUP>1</SUP>. The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time<SUP>2</SUP>. 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 galaxies<SUP>2,3</SUP>, 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) wavelengths<SUP>4,5</SUP>. The <SUP>13</SUP>C/<SUP>18</SUP>O isotope abundance ratio in the cold molecular gas—which can be probed via the rotational transitions of the <SUP>13</SUP>CO and C<SUP>18</SUP>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 of <SUP>13</SUP>CO and C<SUP>18</SUP>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 low <SUP>13</SUP>CO/C<SUP>18</SUP>O ratio for all our targets—alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way<SUP>6</SUP>—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 galaxies<SUP>7</SUP>, although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.||URI:||http://hdl.handle.net/20.500.12386/28204||URL:||https://www.nature.com/articles/s41586-018-0196-x
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jun 21, 2021
checked on Jun 21, 2021
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