The Stellar IMF of Galactic Clusters and Its Evolution

Marchi, Guido De; Paresce, Francesco; Zwart, Simon Portegies

doi:10.1007/978-1-4020-3407-7_11

Cited by 30 publications

(20 citation statements)

References 27 publications

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“…This excludes any single-slope IMF and enforces a flattening of the IMF with respect to the Salpeter slope below ∼0.5−0.7 M (e.g., Renzini 2005). Consistently, direct stellar counts in Galactic globular clusters (Paresce & De Marchi 2000) and young clusters with ages ranging from a few Myr to 1 Gyr (de Marchi et al 2005; see also Bouvier et al 2005) point to an IMF with a log-normal form below 1 M . This conclusion holds for the present day mass function of fields in the Galactic Disc (Chabrier 2003;Moraux et al 2004) or Bulge (Zoccali 2005, and references therein).…”

Section: On the Choice Of Imf And Its Impact On The Best Fitting Masssupporting

confidence: 66%

Testing adiabatic contraction of dark matter in fossil group candidates

Démoclès

Pratt

Pierini

et al. 2010

A&A

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We present deep XMM-Newton observations and ESO WFI optical imaging of two X-ray-selected fossil group candidates, RXC J0216.7-4749 and RXC J2315.7-0222. Using the X-ray data, we derive total mass profiles under the hydrostatic equilibrium assumption. The central regions of RXC J0216.7-4749 are found to be dominated by an X-ray bright AGN, and although we derive a mass profile, uncertainties are large and the constraints are significantly weakened due to the presence of the central source. The total mass profile of RXC J2315.7-0222 is of high quality, being measured in fifteen bins from [0.075−0.75] R 500 and containing three data points interior to 30 kpc, allowing comprehensive investigation of its properties. We investigate several mass models based on the standard NFW profile or on the Sérsic-like model recently suggested by high-resolution N-body simulations. We find that the addition of a stellar component due to the presence of the central galaxy is necessary for a good analytical model fit. In all mass profile models fitted, the mass concentration is not especially high compared to non-fossil systems. In addition, the modification of the dark matter halo by adiabatic contraction slightly improves the fit. However, our result depends critically on the choice of IMF used to convert galaxy luminosity to mass, which leads to a degeneracy between the central slope of the dark matter profile and the normalisation of the stellar component. While we argue on the basis of the range of M * /L R ratios that lower M * /L R ratios are preferred on physical grounds and that adiabatic contraction has thus operated in this system, better theoretical and observational convergence on this problem is needed to make further progess.

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Section: On the Choice Of Imf And Its Impact On The Best Fitting Masssupporting

confidence: 66%

Testing adiabatic contraction of dark matter in fossil group candidates

Démoclès

Pratt

Pierini

et al. 2010

A&A

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“…The TPL combines in one expression the ubiquitous power-law shape above 1 M (e.g., Salpeter 1955) with the plateau and drop observed near the hydrogen-burning limit (e.g., Chabrier 2003). As we already showed (De Marchi et al 2005), the TPL fits remarkably well the MFs of both YCs and GCs over the entire stellar mass range. We stress here that it is irrelevant whether the IMF resulting from star formation takes on the shape of a TPL, as long as it suitably represents the observed mass distribution.…”

Section: The Tapered Power Lawsupporting

confidence: 76%

On the temporal evolution of the stellar mass function of Galactic clusters

Marchi¹,

Paresce

Zwart

2009

Proc. IAU

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Abstract. We show that we can obtain a good fit to the present-day stellar-mass functions of a large sample of young and old Galactic clusters with a tapered Salpeter power-law distribution function with an exponential truncation of the form dN/dm ∝ m. The average value of the power-law index α is ∼ −2.2, very close to the Salpeter value of −2.3, while the characteristic mass, mc , is in the range 0.1-0.6 M and does not seem to vary in any systematic way with the present cluster parameters such as metal abundance, total cluster mass or central concentration. However, the characteristic mass shows a remarkable correlation with the dynamical age of the cluster, namely m c /M 0.15 + 0.5 ×td yn , where t d yn is the dynamical time, taken as the ratio of cluster age and dissolution time. The small scatter around this correlation is likely due to uncertainties on the estimated value of t d yn . We attribute the observed trend to the onset of mass segregation through two-body relaxation in a tidal environment, causing preferential loss of low-mass stars from the cluster and hence a drift of the characteristic mass towards higher values. If dynamical evolution is indeed at the origin of the observed trend, it seems plausible that globular clusters, now with m c 0.35 M , were born with a stellar mass function very similar to that measured today in the youngest Galactic clusters and with a value of mc around 0.15 M . This is consistent with the absence of a turn-over in the mass function of the Galactic bulge down to the observational limit at ∼ 0.2 M and argues for the universality of the initial mass function of Population I and II stars.

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“…An additional parameterization of the IMF that is quite practical is that of a "tapered power-law" (de Marchi, Paresce & Portegies Zwart 2005). This has the form…”

Section: Functional Formsmentioning

confidence: 99%

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

Bastian

Covey

Meyer

2010

Annu. Rev. Astron. Astrophys.

933

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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The Stellar IMF of Galactic Clusters and Its Evolution

Cited by 30 publications

References 27 publications

Testing adiabatic contraction of dark matter in fossil group candidates

Testing adiabatic contraction of dark matter in fossil group candidates

On the temporal evolution of the stellar mass function of Galactic clusters

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

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