Constraining the Initial Mass Function in Extreme Environments: Detecting Young Low-Mass Stars in Unresolved Starbursts

Meyer, Michael; Greissl, Julia

doi:10.1086/491647

Cited by 10 publications

(15 citation statements)

References 38 publications

(53 reference statements)

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“…None appears to be robust enough, however, as theoretical estimates are very uncertain and observations can usually be reconciled with the Galactic IMF (e.g. see further references in Portegies Zwart et al 2002; Meyer & Greissl 2005).…”

Section: Discussionmentioning

confidence: 99%

“…The problem one faces when attempting to constrain the number of young stars in the infrared observations of the Galactic Centre, however, is that a million solar-type stars emit bolometrically as little as a single bright O star. In particular, Meyer & Greissl (2005) calculate that low-mass pre-main-sequence (PMS) stars may account for (as much as or as little as) ∼4-12 per cent of the integrated light at the near-infrared frequency for young starbursts, and suggest that high-resolution observations may discern that in high-resolution spectra. It is not clear to us if this method could be applied to the extremely bright and confusion-limited field of the Galactic Centre (Genzel et al 2003;Ghez et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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The ‘missing’ young stellar objects in the central parsec of the Galaxy: evidence for star formation in a massive accretion disc and a top-heavy initial mass function

Nayakshin

Sunyaev

2005

Monthly Notices of the Royal Astronomical Society: Letters

149

157

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A few dozen young high‐mass stars orbit Sgr A* at distances as short as ∼0.1 pc, where star formation should be quenched by the strong tidal shear from Sgr A*. The puzzling young stellar population is believed to come into existence in one of two ways: (i) ‘normal’ star formation at several tens of parsecs in a very massive star cluster that then spiralled in; or (ii) star formation in situ in a massive self‐gravitating disc. We propose to constrain these two scenarios via the expected X‐ray emission from young low‐mass stars that should have formed alongside the massive stars. To this end we compare the recent Chandra observations of X‐ray emission from young stars in the Orion nebula, and the Chandra observations of the Sgr A* field. We show that the cluster spiral‐in model is ruled out irrespectively of the initial mass function (IMF) of the young stars. In addition, for the in situ model, we find that no more than a few thousand low‐mass stars could have formed alongside the massive stars. This is more than a factor of 10 fewer than expected if these stars were formed with the standard IMF as elsewhere in the Galaxy. The young stars in the Galactic Centre are thus the first solid observational evidence for star formation in active galactic nucleus (AGN) discs and also require the IMF of these stars to be top‐heavy. We briefly consider the implications of these results for AGN in general.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The ‘missing’ young stellar objects in the central parsec of the Galaxy: evidence for star formation in a massive accretion disc and a top-heavy initial mass function

Nayakshin

Sunyaev

2005

Monthly Notices of the Royal Astronomical Society: Letters

149

157

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“…In extremely young clusters, however, low mass pre-main sequence stars are bright enough in the near-IR that their spectral features can be detected in high S/N spectra (Meyer & Greissl 2005). Quantitative analysis of these spectra can then place constraints on the ratio of high-to-low mass stars in the cluster.…”

Section: Super Star Clustersmentioning

confidence: 99%

A Universal Stellar Initial Mass Function? A Critical Look at Variations

Bastian

Covey

Meyer

2010

Annu. Rev. Astron. Astrophys.

Self Cite

925

453

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Few topics in astronomy initiate such vigorous discussion as whether or not the initial mass function (IMF) of stars is universal, or instead sensitive to the initial conditions of star formation. The distinction is of critical importance: the IMF influences most of the observable properties of stellar populations and galaxies, and detecting variations in the IMF could provide deep insights into the process by which stars form. In this review, we take a critical look at the case for IMF variations, with a view towards whether other explanations are sufficient given the evidence. Studies of the field, local young clusters and associations, and old globular clusters suggest that the vast majority were drawn from a "universal" IMF: a power-law of Salpeter index (Γ = 1.35) above a few solar masses, and a log normal or shallower power-law (Γ ∼ 0 − 0.25) between a few tenths and a few solar masses (ignoring the effects of unresolved binaries). The shape and universality of the IMF at the stellar-substellar boundary is still under investigation and uncertainties remain large, but most observations are consistent with a IMF that declines (Γ < −0.5) well below the hydrogen burning limit. Observations of resolved stellar populations and the integrated properties of most galaxies are also consistent with a "universal IMF", suggesting no gross variations in the IMF over much of cosmic time. There are indications of "non-standard" IMFs in specific local and extragalactic environments, which clearly warrant further study. Nonetheless, there is no clear evidence that the IMF varies strongly and systematically as a function of initial conditions after the first few generations of stars. We close with suggestions for future work that might uncover more subtle IMF variations than those that could be discerned to date.

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“…Moreover, in a newborn cluster a large fraction of stars may still be in the contracting phase as pre‐main‐sequence (PMS) objects. Meyer & Greissl (2005) estimated that PMS stars contributed between 1 and 17 per cent of the integrated H band flux of an unresolved cluster, depending on the stellar population age (from 1 to 10 Myr) and the IMF used. Recently, Greissl et al (2010) found direct evidence of PMS stars in NIR spectroscopic data of a young knot (89/90) in the Antennae system.…”

Section: The Cluster Red Excess In Eso 185: Differences and Analogimentioning

confidence: 99%

The massive star clusters in the dwarf merger ESO 185−IG13: is the red excess ubiquitous in starbursts?*

Adamo

Östlin

Zackrisson

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We have investigated the starburst properties of the luminous blue compact galaxy ESO 185−IG13. The galaxy has been imaged with the high‐resolution cameras onboard the Hubble Space Telescope. From the ultraviolet (UV) to the infrared (IR), the data reveal a system shaped by hundreds of young star clusters, and fine structures, like a tidal stream and a shell. The presence of numerous clusters and the perturbed morphology indicate that the galaxy has been involved in a recent merger event. Using previous simulations of shell formation in galaxy mergers we constrain potential progenitors of ESO 185−IG13. The analysis of the star cluster population is used to investigate the properties of the present starburst and to date the final merger event, which has produced hundreds of clusters younger than 100 Myr. We have found a peak of cluster formation only 3.5 Myr old. A large fraction of these clusters will not survive after 10–20 Myr due to the ‘infant mortality’ caused by gas expulsion. However, this sample of clusters represents a unique chance to investigate the youngest phases of cluster evolution. As already observed in the analogue blue compact galaxy Haro 11, a fraction of young clusters are affected by a flux excess at wavelengths longer than 8000 Å. Ages, masses and extinctions of clusters with this near‐IR (NIR) excess are estimated from UV and optical data. We discuss similarities and differences of the observed NIR excess in ESO 185−IG13 clusters with other cases in the literature. The cluster ages and masses are used to distinguish among the potential causes of the excess. We observe, as in Haro 11, that the use of the IR and the (commonly used) I band data results in overestimates of age and mass in clusters affected by the NIR excess. This has important implications for a number of related studies of star clusters.

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Constraining the Initial Mass Function in Extreme Environments: Detecting Young Low-Mass Stars in Unresolved Starbursts

Cited by 10 publications

References 38 publications

The ‘missing’ young stellar objects in the central parsec of the Galaxy: evidence for star formation in a massive accretion disc and a top-heavy initial mass function

The ‘missing’ young stellar objects in the central parsec of the Galaxy: evidence for star formation in a massive accretion disc and a top-heavy initial mass function

A Universal Stellar Initial Mass Function? A Critical Look at Variations

The massive star clusters in the dwarf merger ESO 185−IG13: is the red excess ubiquitous in starbursts?*

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