Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 0710.2882

The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics observations

Y. Harayama·F. Eisenhauer·F. Martins
View original source ↗Read source document ↗Export metadata ↓

Abstract

We study the initial mass function (IMF) of one of the most massive Galactic star-forming regions NGC 3603 to answer a fundamental question in current astrophysics: is the IMF universal, or does it vary? Using our very deep, high angular resolution JHKsL' images obtained with NAOS-CONICA at the VLT at ESO, we have successfully revealed the stellar population down to the subsolar mass range in the core of the starburst cluster. The derived IMF of NGC 3603 is reasonably fitted by a single power law with index Gamma ~ -0.74 within a mass range of 0.4 - 20 Msun, substantially flatter than the Salpeter-like IMF. A strong radial steepening of the IMF is observed mainly in the inner r < 30'' field, indicating mass segregation in the cluster center. We estimate the total mass of NGC 3603 to be about 1.0 - 1.6 x 10^4 Msun. The derived core density is > 6 x 10^4 Msun pc^-3, an order of magnitude larger than e.g., the Orion Nebula Cluster. The estimate of the half-mass relaxation time for solar-mass stars is about 10 - 40 Myr, suggesting that the intermediate- and low-mass stars have not yet been affected significantly by the dynamical relaxation in the cluster. The relaxation time for the high-mass stars can be comparable to the age of the cluster. We estimate that the stars residing outside the observed field cannot steepen the IMF significantly, indicating our IMF adequately describes the whole cluster. Analyzing thoroughly the systematic uncertainties in our IMF determination, we conclude that the power law index of the IMF of NGC 3603 is Gamma = -0.74^{+0.62}_{-0.47}. Our result thus supports the hypothesis of a potential top-heavy IMF in massive star-forming clusters and starbursts.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

Y. Harayama, F. Eisenhauer, F. Martins. 2008-03-09. The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics observations. https://doi.org/10.1086/524650

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2009

Memory effects in turbulent transport

In the mean-field theory of magnetic fields, turbulent transport, i.e. the turbulent electromotive force, is described by a combination of the alpha effect and turbulent magnetic diffusion, which are usually assumed to be proportional respectively to the mean field and its spatial derivatives. For a passive scalar there is just turbulent diffusion, where the mean flux of concentration depends on the gradient of the mean concentration. However, these proportionalities are approximations that are valid only if the mean field or the mean concentration vary slowly in time. Examples are presented where turbulent transport possesses memory, i.e. where it depends crucially on the past history of the mean field. Such effects are captured by replacing turbulent transport coefficients with time integral kernels, resulting in transport coefficients that depend effectively on the frequency or the growth rate of the mean field itself. In this paper we perform numerical experiments to find the characteristic timescale (or memory length) of this effect as well as simple analytical models of the integral kernels in the case of passive scalar concentrations and kinematic dynamos. The integral kernels can then be used to find self-consistent growth or decay rates of the mean fields. In mean-field dynamos the growth rates and cycle periods based on steady state values of alpha effect and turbulent diffusivity can be quite different from the actual values.

astro-ph↗
arXiv2009

Magnetic Reconnection During the Two-Phase Evolution of a Solar Eruptive Flare

We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare on October 24, 2003. The X-ray observations of the flare taken from the RHESSI spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for $\sim$11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed ($\sim$15 km s$^{-1}$) in this interval. During the second phase the two distinct hard X-ray footpoints (FP) sources are observed which correlate well with UV and H$α$ flare ribbons. The X-ray LT source now exhibits upward motion. The RHESSI spectra during the first phase are soft and indicative of hot thermal emission from flaring loops with temperatures $T>25$ MK at the early stage. On the other hand, the spectra at high energies ($\varepsilon \gtrsim$25 keV) follow hard power laws during the second phase ($γ= 2.6-2.8$). We show that the observed motion of the LT and FP sources can be understood as a consequence of three-dimensional magnetic reconnection at a separator in the corona. During the first phase of the flare, the reconnection releases an excess of magnetic energy related to the magnetic tensions generated before a flare by the shear flows in the photosphere. The relaxation of the associated magnetic shear in the corona by the reconnection process explains the descending motion of the LT source. During the second phase, the ordinary reconnection process dominates describing the energy release in terms of the standard model of large eruptive flares.

astro-ph↗
arXiv2009

Proper motion L and T dwarf candidate members of the Pleiades

We present the results of a deep optical-near-infrared multi-epoch survey covering 2.5 square degrees of the Pleiades open star cluster to search for new very-low-mass brown dwarf members. A significant (~ 5 year) epoch difference exists between the optical (CFH12k I-, Z-band) and near infrared (UKIRT WFCAM J-band) observations. We construct I,I-Z and Z,Z-J colour magnitude diagrams to select candidate cluster members. Proper motions are computed for all candidate members and compared to the background field objects to further refine the sample. We recover all known cluster members within the area of our survey. In addition, we have discovered 9 new candidate brown dwarf cluster members. The 7 faintest candidates have red Z-J colours and show blue near-infrared colours. These are consistent with being L and T-type Pleiads. Theoretical models predict their masses to be around 11 Jupiter masses. There is 1 errata for this paper

astro-ph↗