On the Similarity between Cluster and Galactic Stellar Initial Mass Functions

Elmegreen, Bruce G.

doi:10.1086/505785

Cited by 105 publications

(143 citation statements)

References 80 publications

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“…The magnitude of this discrepancy depends on the sampling method. Contrary to results by Elmegreen (2006), we do not find the β = 2 CMF to be singular. All sampling methods reproduce the input cluster mass functions well.…”

Section: Discussioncontrasting

confidence: 99%

“…For any value of β there is some number of clusters which will lack high mass stars, which makes β = 2 a normal case without singular features. The claim by Elmegreen (2006) is correct only if the lower limit of the CMF is higher than the maximum stellar mass, in agreement with our own findings. Fig.…”

Section: The β = 2 Cmfsupporting

confidence: 90%

“…The vanishing effects found by Elmegreen (2006) were not reproduced in our simulations. In the Monte Carlo simulations described in Elmegreen (2006) a small difference was already visible.…”

Section: The β = 2 Cmfcontrasting

confidence: 68%

“…A series of papers (Kroupa & Weidner 2003;, 2006, the latter WK06 from now on) pointed out that the distribution of initial stellar masses in a galaxy may significantly deviate from the initial mass function (IMF) the stars have when they are born, if the vast majority of stars is born in clusters. These clusters follow a power-law mass function (the cluster mass function, CMF), which means that most stars form in low-mass clusters.…”

Section: Introductionmentioning

confidence: 99%

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Variations in integrated galactic initial mass functions due to sampling method and cluster mass function

Haas¹,

Anders

2010

A&A

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Context. Stars are thought to be formed predominantly in clusters. The star clusters are formed according to a cluster initial mass function (CMF) similar to the stellar initial mass function (IMF). Both the IMF and the CMF can be approximated by (broken) powerlaws, which favour low-mass objects. The numerous low-mass clusters will lack high mass stars compared to the underlying IMF, since the most massive star cannot be more massive than its host cluster. If the integrated galactic initial mass function (IGIMF, i.e. the total stellar mass function of all stars in a galaxy) originates from stars formed in star clusters, the IGIMF could be steeper than the IMF in clusters. Aims. We investigate how well constrained this steepening is and how it depends on the choice of sampling method and CMF. We investigate the observability of the IGIMF effect in terms of galaxy photometry and metallicities. Methods. We study various ways to sample the stellar IMF within star clusters and build up the IGIMF from these clusters. We compare analytic sampling to several implementations of random sampling of the IMF and different CMFs. We implement different IGIMFs into the galev evolutionary synthesis package to obtain colours and metallicities for galaxies.Results. Choosing different ways of sampling the IMF results in different IGIMFs. Depending on the lower cluster mass limit and the slope of the cluster mass function, the steepening varies between very strong and negligible. We find the size of the effect is continuous as a function of the power-law slope of the CMF if the CMF extends to masses smaller than the maximum stellar mass. The number of O-stars detected by GAIA will, if some uncertain factors are better understood, help to judge the importance of the IGIMF effect. The impact of different IGIMFs on integrated galaxy photometry is small, within the intrinsic scatter of observed galaxies. Observations of gas fractions and metallicities could rule out at least the most extreme sampling methods, if other sources of error are sufficiently understood. Conclusions. As we still do not understand the details of star formation and the sampling of the stellar IMF in clusters, one sampling method cannot be favoured over another. Also, the CMF at very low cluster masses is not well constrained observationally. These uncertainties therefore need to be taken into account when using an IGIMF, with severe implications for galaxy evolution models and interpretations of galaxy observations.

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Section: Discussioncontrasting

confidence: 99%

Section: The β = 2 Cmfsupporting

confidence: 90%

Section: The β = 2 Cmfcontrasting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

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Variations in integrated galactic initial mass functions due to sampling method and cluster mass function

Haas¹,

Anders

2010

A&A

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“…This correlation leads to the question of whether the upper limit to the stellar mass in a particular cluster depends on the cluster mass because of some physically limiting process, or it is simply the result of random sampling of the IMF. In the first case, low-mass clusters cannot produce high-mass stars (Weidner & Kroupa 2004, 2006. In the second case they could as long as there is enough gas, and intermediate-mass clusters should occasionally be found with unusually massive stars -"outliers" in the IMF (Elmegreen 2006;Cerviño & Luridiana 2006).…”

Section: The Massive Stellar Population Of Yscsmentioning

confidence: 99%

The population of young stellar clusters throughout the disk of M 33

Sharma

Corbelli

Giovanardi

et al. 2011

A&A

105

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Aims. The properties of young stellar clusters (YSCs) in M 33, identified from the center out to about twice the size of the bright star-forming disk, are investigated to determine possible spatial and time variations of the star formation process in this Local Group blue galaxy. Methods. 915 MIR sources have been extracted from the Spitzer 24 μm image. Upon inspection of Hα and GALEX images and exclusion of evolved AGB stars, a sample of 648 objects is selected as candidate YSCs and their luminosity function is examined. The spectral energy distribution of each object, based on aperture photometry, is compared with Starburst99 models to derive age, mass and A V of individual clusters. In the analysis we allow for different values of the upper mass cutoff of the stellar initial mass function (IMF), the porosity of the ISM, and the dustiness of HII regions. We also examine the influence of different dust models and include corrections for incompleteness of the IMF. Results. We find discrete MIR sources as far as the extent of the warped HI disk, i.e. 16 kpc from the galaxy center. Their surface density has a steep radial decline beyond 4.5 kpc, and flattens out beyond the optical radius at 8.5 kpc. We are able to identify YSCs out to 12 kpc. At large galactocentric radii, the paucity of luminous clusters and the relevance of hot dust emission become evident from the analysis of the bolometric and MIR luminosity functions. The YSC mass and size are correlated with a log-log slope of 2.09±0.01, similar to that measured for giant molecular clouds in M 33 and the Milky Way, which represent the protocluster environment. Most of the YSCs in our sample have A V ∼ 0−1 mag and ages between 3 and 10 Myr. In the inner regions of M 33 the clusters span a wide range of mass (10 2 < M < 3 × 10 5 M ) and luminosity (10 38 < L bol < 3 × 10 41 erg s −1 ), while at galactocentric radii larger than ∼4 kpc we find a deficiency of massive clusters. Beyond 7 kpc, where the Hα surface brightness drops significantly, the dominant YSC population has M < 10 3 M and a slightly older age (10 Myr). This implies the occurrence of star formation events about 10 Myr ago as far as 10−12 kpc from the center of M 33. The cluster L FUV vs. L Hα relation is non-linear for L FUV < 10 39 erg s −1 , in agreement with randomly sampled models of the IMF which, furthermore, shows no appreciable variation throughout the M 33 disk.

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