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Register a new userMassive Star Birth in the Inner Galaxy: Obscured Massive Star Clusters
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The current census of, and stellar population in, massive Galactic star clusters is reviewed. In particular, we concentrate on a recent survey of obscured Galactic Giant H II (GHII) regions and the associated stellar clusters embedded in them. The regions have been selected as the most luminous radio continuum sources, and as such the stellar clusters appear to be among the youngest massive clusters in the Galaxy. The emergent stellar populations are further studied through near infrared spectroscopy of the brighter members. We also discuss the massive stellar clusters within 50 pc of the Galactic center (GC), comparing their known properties to those found in the GHII region survey. It is suggested that the somewhat younger clusters associated with the GHII regions are more suited to measuring the initial mass function in massive star clusters. Narrow band images in the central pc of the GC are presented which identify the young stellar sequence associated with the evolved He I emission line stars.
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We present high resolution (0.2, 1000 AU) 1.3 mm ALMA observations of massive infrared dark cloud clump, G028.37+00.07-C1, thought to harbor the early stages of massive star formation. Using $rm N_2D^+$(3-2) we resolve the previously identified C1-S core, separating the bulk of its emission from two nearby protostellar sources. C1-S is thus identified as a massive ($sim50:M_odot$), compact ($sim0.1:$pc diameter) starless core, e.g., with no signs of outflow activity. Being highly deuterated, this is a promising candidate for a pre-stellar core on the verge of collapse. An analysis of its dynamical state indicates a sub-virial velocity dispersion compared to a trans-Alfvenic turbulent core model. However, virial equilibrium could be achieved with sub-Alfvenic conditions involving $sim2:$mG magnetic field strengths.
We study the formation of massive Population III binary stars using a newly developed radiation hydrodynamics code with the adaptive mesh refinement and adaptive ray-tracing methods. We follow the evolution of a typical primordial star-forming cloud obtained from a cosmological hydrodynamics simulation. Several protostars form as a result of disk fragmentation and grow in mass by the gas accretion, which is finally quenched by the radiation feedback from the protostars. Our code enables us, for the first time, to consider the feedback by both the ionizing and dissociating radiation from the multiple protostars, which is essential for self-consistently determining their final masses. At the final step of the simulation, we observe a very wide ($gtrsim 10^4,mathrm{au}$) binary stellar system consisting of $60$ and $70,M_odot$ stars. One of the member stars also has two smaller mass ($10,M_odot$) companion stars orbiting at $200$ and $800,mathrm{au}$, making up a mini-triplet system. Our results suggest that massive binary or multiple systems are common among Population III stars.
The circumnuclear starburst of M83 (NGC 5236), the nearest such example (4.6 Mpc), constitutes an ideal site for studying the massive star IMF at high metallicity (12+log[O/H]=9.1$pm$0.2, Bresolin & Kennicutt 2002). We analyzed archival HST/STIS FUV imaging and spectroscopy of 13 circumnuclear star clusters in M83. We compared the observed spectra with two types of single stellar population (SSP) models, semi-empirical models, which are based on an empirical library of Galactic O and B stars observed with IUE (Robert et al. 1993), and theoretical models, which are based on a new theoretical UV library of hot massive stars described in Leitherer et al. (2010) and computed with WM-Basic (Pauldrach et al. 2001). The models were generated with Starburst99 (Leitherer & Chen 2009). We derived the reddenings, the ages, and the masses of the clusters from model fits to the FUV spectroscopy, as well as from optical HST/WFC3 photometry.
We determine the inner density profiles of massive galaxy clusters (M$_{200}$ > $5 times 10^{14}$ M$_{odot}$) in the Cluster-EAGLE (C-EAGLE) hydrodynamic simulations, and investigate whether the dark matter density profiles can be correctly estimated from a combination of mock stellar kinematical and gravitational lensing data. From fitting mock stellar kinematics and lensing data generated from the simulations, we find that the inner density slopes of both the total and the dark matter mass distributions can be inferred reasonably well. We compare the density slopes of C-EAGLE clusters with those derived by Newman et al. for 7 massive galaxy clusters in the local Universe. We find that the asymptotic best-fit inner slopes of generalized NFW (gNFW) profiles, ${gamma}_{rm gNFW}$, of the dark matter haloes of the C-EAGLE clusters are significantly steeper than those inferred by Newman et al. However, the mean mass-weighted dark matter density slopes of the simulated clusters are in good agreement with the Newman et al. estimates. We also find that the estimate of ${gamma}_{rm gNFW}$ is very sensitive to the constraints from weak lensing measurements in the outer parts of the cluster and a bias can lead to an underestimate of ${gamma}_{rm gNFW}$.
Several dynamical scenarios have been proposed that can lead to prompt mass segregation on the crossing time scale of a young cluster. They generally rely on cool and/or clumpy initial conditions, and are most relevant to small systems. As a counterpoint, we present a novel dynamical mechanism that can operate in relatively large, homogeneous, cool or cold systems. This mechanism may be important in understanding the assembly of large mass-segregated clusters from smaller clumps.
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