Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-heavy Initial Mass Function

Sliwa, Kazimierz; Wilson, C. D.; Aalto, S.; Privon, George C.

doi:10.3847/2041-8213/aa6ea4

Cited by 51 publications

(81 citation statements)

References 48 publications

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“…At the other extreme, a recent analysis of starburst galaxies by Romano et al (2017), using updated chemical models to track CNO isotopes and accounting for stellar rotation, finds a need for an excess of high mass stars (α h = −1.95, for m > 0.5 M ⊙ ) to reproduce observed isotope abundances. This result is consistent with the conclusions of Sliwa et al (2017) who find a need for an excess of high mass stars to explain the CO isotopic abundances in the starburst galaxy IRAS 13120-5453.…”

Section: Chemical Abundance Measurementssupporting

confidence: 92%

“…Despite these difficulties, a range of the early approaches toward inferring the IMF have been refined over the past decade, and are now used routinely. These include an update of the Kennicutt (1983) approach used by Hoversten & Glazebrook (2008) and Gunawardhana et al (2011), use of the Wing-Ford band to infer dwarf-to-giant ratio (e.g., Cenarro et al 2003;van Dokkum & Conroy 2010;Smith et al 2012) following the early work of Whitford (1977), use of kinematics (e.g., Cappellari et al 2012), gravitational lensing observations (e.g., Treu et al 2010;Smith & Lucey 2013), chemical abundance constraints (e.g., Portinari et al 2004a;Komiya et al 2007;Sliwa et al 2017) and more. The 2.3 µm CO index has also been proposed for probing the dwarf-togiant ratio (Kroupa & Gilmore 1994;Mieske & Kroupa 2008).…”

Section: Overview and Historymentioning

confidence: 99%

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The Dawes Review 8: Measuring the Stellar Initial Mass Function

Hopkins

2018

Publ. Astron. Soc. Aust.

104

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The birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the birth mass distribution of stars, referred to as the stellar initial mass function (IMF), is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. A star's initial mass determines its luminosity, lifetime, and eventual return of material enriched by nuclear fusion back to the interstellar medium to be incorporated in later generations of stars. The distribution of stellar masses created in star formation events therefore determines the evolution of galaxies over cosmic time, and accurately measuring it is crucial. The past decade has seen a growing number and variety of methods for measuring or inferring the shape of the IMF, along with progressively more detailed simulations, paralleled by refinements in the way the concept of the IMF is applied or conceptualised on different physical scales. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the IMF is universal. Here I review and compare the growing wealth of approaches to our understanding of this fundamental property that defines so much of astrophysics. I summarise the observational measurements from stellar analyses, extragalactic studies and cosmic constraints, and highlight the importance of considering potential IMF variations, reinforcing the need for measurements to quantify their scope and uncertainties carefully, in order for this field to progress. I present a new framework to aid the discussion of the IMF and promote clarity in the further development of this fundamental field.

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Section: Chemical Abundance Measurementssupporting

confidence: 92%

Section: Overview and Historymentioning

confidence: 99%

The Dawes Review 8: Measuring the Stellar Initial Mass Function

Hopkins

2018

Publ. Astron. Soc. Aust.

104

View full text Add to dashboard Cite

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“…To make these ratio maps, we convert each moment map in Figure 1 from Jy beam −1 km s −1 to K km s −1 before computing the ratio using CASA's IMMATH routine. In all 4 targets, the values of 12 CO/C 18 O J=1-0 are consistent with those reported previously for Mrk 231, IRAS 13120-5453, and Arp 220 (∼20-140; González & Koenigsberger 2014;Falstad et al 2015;Sliwa et al 2017). Similarly, the 12 CO/ 13 CO J=1-0 line ratios exhibit a large range of values, from ∼ 20 − 30 in central regions of Arp 220 and IRAS 13120-5453 to ∼ 50 − 150 across the disks of IRAS 17208-0014 and NGC 2623.…”

Section: Observationssupporting

confidence: 91%

Extreme CO Isotopologue Line Ratios in ULIRGS: Evidence for a Top-heavy IMF

Brown

Wilson

2019

ApJ

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We present high-resolution ALMA observations of the C 18 O, 13 CO and 12 CO J=1-0 isotopologues in 3 nearby ultra-luminous infrared galaxies (ULIRGS; Arp 220, IRAS 13120-5453, IRAS 17208-0014) and 1 nearby post-merger galaxy (NGC 2623). In all 4 systems, we measure high 12 CO/C 18 O and 12 CO/ 13 CO integrated line ratios while the 13 CO/C 18 O ratio is observed to be extremely low in comparison to typical star-forming disks, supporting previous work. We investigate whether these unusual line ratios are due to dynamical effects, astrochemistry within the gas, or nucleosynthesis in stars. Assuming both lines are optically thin, low 13 CO/C 18 O values suggest that C 18 O is more abundant than 13 CO in the interstellar medium of these systems. A plausible explanation is that local ULIRGs and their progeny have an excess in massive star formation; in other words, they are producing a top-heavy stellar initial mass function.

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“…A clear trend is shown in Fig. 2: the more top-heavy the IMF, the lower the I( 13 CO)/I(C 18 O) ratio, which is also compatible with the ratios found in local ULIRGs and the exceptionally small I( 13 CO)/I(C 18 O) ratio found in the centre of IRAS 13120−5453 12 . This paints a consistent picture in which a top-heavy IMF operates within both local ULIRGs and the much more numerous, distant starburst galaxies, where starburst events can quickly enrich the 18 Multiple evidence in the local Universe has shown that the stellar IMF in galaxies with very high SFR densities are likely biased to massive stars, such as ultra-compact dwarf galaxies 20 , ULIRGs 21 , and progenitors of early-type galaxies 22 .…”

supporting

confidence: 80%

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time

Zhang

Romano

Ivison

et al. 2018

Nature

227

215

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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 . 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 . 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, 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. The C/O isotope abundance ratio in the cold molecular gas-which can be probed via the rotational transitions of the CO and CO 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 CO and CO 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 CO/CO ratio for all our targets-alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way -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 , although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.

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Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-heavy Initial Mass Function

Cited by 51 publications

References 48 publications

The Dawes Review 8: Measuring the Stellar Initial Mass Function

The Dawes Review 8: Measuring the Stellar Initial Mass Function

Extreme CO Isotopologue Line Ratios in ULIRGS: Evidence for a Top-heavy IMF

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time

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