scholarly journals Proper-motion studies of Milky Way starburst clusters – a new definition of starburst cluster templates

2009 ◽  
Vol 5 (S266) ◽  
pp. 123-128
Author(s):  
Andrea Stolte ◽  
Wolfgang Brandner
Keyword(s):  
Adaptive Optics ◽  
Proper Motion ◽  
Milky Way ◽  
Hubble Space Telescope ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Galactic Centre ◽  
Limiting Factor ◽  
Motion Studies

AbstractStarburst clusters in the Milky Way have the advantage that individual stars down to subsolar masses can be resolved. Thus far, field contamination along the line of sight towards the Galactic Centre and spiral arms was the limiting factor in deriving an unbiased census of the stellar population in Milky Way starbursts and, hence, the spatial extent and initial mass function in starburst clusters. As the next generation of telescopes with higher sensitivity and spatial resolution are being developed, these resolved clusters become increasingly important as templates for young, massive extragalactic systems, which will be resolved at the high-mass end of the stellar mass function. With the aim to obtain a uniform characterisation of starburst cluster properties in the Milky Way, we have initiated a proper-motion membership survey. This technique became feasible for clusters out to distances of 8 kpc with diffraction-limited imaging using adaptive optics from the ground and with Hubble Space Telescope from space.

scholarly journals Infrared Imaging of the Arches Cluster - Adaptive Optics in the Densest Region of the Milky Way

2002 ◽  
Vol 207 ◽  
pp. 132-134
Author(s):  
Andrea Stolte ◽  
Eva K. Grebel ◽  
Wolfgang Brandner ◽  
Donald F. Figer
Keyword(s):  
Adaptive Optics ◽  
Milky Way ◽  
Infrared Imaging ◽  
Galactic Center ◽  
Cluster Formation ◽  
Extreme Environment ◽  
Mass Function ◽  
Cluster Center ◽  
Limiting Factor ◽  
Dense Cluster

The Arches cluster - located only 11′ from the Galactic Center (GC) - is one of the densest and richest young star clusters in the Milky Way. With an age of only about 2 Myr, it is ideally suited to study massive cluster formation in an extreme environment. We find an IMF slope of Γ = −0.77 from 5 to 100 M⊙, in good agreement with the results from HST/NICMOS from Figer et al. (1999). The limiting factor in the dense cluster center is crowding. With the new AO systems, high resolution analysis of the dense cluster region combined with very deep infrared photometry is available. We have analysed deep H and K′ images of the cluster center obtained with the GEMINI/Hokupa'a adaptive optics system. Colour-magnitude diagrams and the IMF are constructed from these data. A comparison with isochrones yields the mass function.

scholarly journals The future of IMF studies with the ELT and MICADO

2020 ◽  
Vol 639 ◽  
pp. A120
Author(s):  
K. Leschinski ◽  
J. Alves
Keyword(s):  
Adaptive Optics ◽  
Milky Way ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
High Mass ◽  
Stellar Clusters ◽  
Local Universe ◽  
Space Telescope ◽  
Young Clusters ◽  
The Imf

Context. Young stellar cluster cores in the local Universe provide the most pristine information available on the stellar initial mass function (IMF), but their stellar densities are too high to be resolved by present-day instrumentation. With a resolving power 100 times better than the Hubble Space Telescope, the Multi-Adaptive Optics Imaging CameraA for Deep Observations (MICADO), which is the near-infrared camera on the Extremely Large Telescope (ELT), will for the first time provide access to a significant number of dense young stellar clusters that are critical for direct studies on the universality and shape of the IMF. Aims. In this work we aim to estimate the lowest stellar mass that MICADO will be able to reliably detect given a stellar density and distance. We also show that instrumental effects that will play a critical role, and report the number of young clusters that will be accessible for IMF studies in the local Universe with the ELT. Methods. We used SimCADO*, the instrument simulator package for the MICADO camera, to generate observations of 56 dense stellar regions with densities similar to the cores of young stellar clusters. We placed the cluster fields at distances between 8 kpc and 5 Mpc from the Earth, implying core densities from 102 to 105 stars arcsec−2, and determined the lowest reliably observable mass for each stellar field through point-spread function fitting photometry. Results. Our results show that stellar densities of <103 stars arcsec−2 will be easily resolvable by MICADO. The lowest reliably observable mass in the Large Magellanic Cloud will be around 0.1 M⊙ for clusters with densities <103 stars arcsec−2. MICADO will be able to access the stellar content of the cores of all dense young stellar clusters in the Magellanic Clouds, allowing the peak and shape of the IMF to be studied in great detail outside the Milky Way. At a distance of 2 Mpc, all stars with M > 2 M⊙ will be resolved in fields of <104 stars arcsec−2, allowing the high-mass end of the IMF to be studied in all galaxies out to and including NGC 300. Conclusions. We show that MICADO on the ELT will be able to probe the IMF of star clusters that are ten times denser than what the James Webb Space Telescope will be able to access, and over one hundred times denser than the clusters that the Hubble Space Telescope can successfully resolve. While the sensitivity of MICADO will not allow us to study the brown dwarf regime outside the Milky Way, it will enable access to all stellar members of over 1000 young clusters in the Milky Way and the Magellanic Clouds. Furthermore, direct measurements of the Salpeter slope of the IMF will be possible in over 1500 young clusters out to a distance of 5 Mpc. MICADO on the ELT will be able to measure resolved IMFs for a large ensemble of young clusters under starkly different environments and test the universality of the IMF in the local Universe.

scholarly journals The initial mass function in the extended ultraviolet disc of M83

2019 ◽  
Vol 491 (2) ◽  
pp. 2366-2390 ◽  
Author(s):  
S M Bruzzese ◽  
David A Thilker ◽  
G R Meurer ◽  
Luciana Bianchi ◽  
A B Watts ◽  
...  
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Main Sequence Stars ◽  
Red Giant ◽  
The Imf

ABSTRACT Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\rm u}=25_{-3}^{+17} \, \mathrm{M}_\odot$. This IMF is consistent with the observed H $\rm \alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.

scholarly journals The Arches cluster revisited

2019 ◽  
Vol 623 ◽  
pp. A84 ◽  
Author(s):  
J. S. Clark ◽  
M. E. Lohr ◽  
L. R. Patrick ◽  
F. Najarro
Keyword(s):  
Main Sequence ◽  
Mass Function ◽  
Initial Mass Function ◽  
Galactic Centre ◽  
Complete Dataset ◽  
Subsequent Determination ◽  
The Galaxy ◽  
First Time ◽  
Massive Clusters

The Arches is one of the youngest, densest and most massive clusters in the Galaxy. As such it provides a unique insight into the lifecycle of the most massive stars known and the formation and survival of such stellar aggregates in the extreme conditions of the Galactic Centre. In a previous study we presented an initial stellar census for the Arches and in this work we expand upon this, providing new and revised classifications for ∼30% of the 105 spectroscopically identified cluster members as well as distinguishing potential massive runaways. The results of this survey emphasise the homogeneity and co-evality of the Arches and confirm the absence of H-free Wolf-Rayets of WC sub-type and predicted luminosities. The increased depth of our complete dataset also provides significantly better constraints on the main sequence population; with the identification of O9.5 V stars for the first time we now spectroscopically sample stars with initial masses ranging from ∼16 M⊙ to ≥120 M⊙. Indeed, following from our expanded stellar census we might expect ≳50 stars within the Arches to have been born with masses ≳60 M⊙, while all 105 spectroscopically confirmed cluster members are massive enough to leave relativistic remnants upon their demise. Moreover the well defined observational properties of the main sequence cohort will be critical to the construction of an extinction law appropriate for the Galactic Centre and consequently the quantitative analysis of the Arches population and subsequent determination of the cluster initial mass function.

Methanol Masers in the Andromeda Galaxy

2017 ◽  
Vol 13 (S336) ◽  
pp. 113-116
Author(s):  
Ylva M. Pihlström ◽  
Loránt O. Sjouwerman
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Local Group ◽  
Angular Resolution ◽  
Transverse Velocity ◽  
High Angular Resolution ◽  
Dynamic Force ◽  
Group Members ◽  
Methanol Masers ◽  
Motion Studies

AbstractIs M31 going to collide with the Milky Way, or spiral around it? Determining the gravitational potential in the Local Group has been a challenge since it requires 3D space velocities and orbits of the members, and most objects have only had line-of-sight velocities measured. Compared to the less massive group members, the transverse velocity of M31 is of great interest, as after the Milky Way, M31 is the most dominant constituent and dynamic force in the Local Group. Proper motion studies of M31 are preferentially done using masers, as continuum sources are much weaker, and are enabled through the high angular resolution provided by VLBI in the radio regime. The challenges of achieving high astrometric accuracy at high VLBI frequencies (> 20 GHz) makes observations at lower frequencies attractive, as long as sufficient angular resolution is obtained. In particular, we have discovered 6.7 GHz methanol masers in M31 using the VLA, and here we will address their feasibility as VLBI proper motion targets using a set of global VLBI observations.

scholarly journals 13C/18O ratio as a litmus test of stellar IMF variations in high-redshift starbursts

2019 ◽  
Vol 15 (S352) ◽  
pp. 234-238
Author(s):  
Donatella Romano ◽  
Zhi-Yu Zhang ◽  
Francesca Matteucci ◽  
Rob J. Ivison ◽  
Padelis P. Papadopoulos
Keyword(s):  
Galaxy Formation ◽  
High Redshift ◽  
Indirect Evidence ◽  
Direct Methods ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Theoretical Ground ◽  
Litmus Test ◽  
The Universe

AbstractDetermining the shape of the stellar initial mass function (IMF) and whether it is constant or varies in space and time is the Holy Grail of modern astrophysics, with profound implications for all theories of star and galaxy formation. On a theoretical ground, the extreme conditions for star formation (SF) encountered in the most powerful starbursts in the Universe are expected to favour the formation of massive stars. Direct methods of IMF determination, however, cannot probe such systems, because of the severe dust obscuration affecting their starlight. The next best option is to observe CNO bearing molecules in the interstellar medium at millimetre/ submillimetre wavelengths, which, in principle, provides the best indirect evidence for IMF variations. In this contribution, we present our recent findings on this issue. First, we reassess the roles of different types of stars in the production of CNO isotopes. Then, we calibrate a proprietary chemical evolution code using Milky Way data from the literature, and extend it to discuss extragalactic data. We show that, though significant uncertainties still hamper our knowledge of the evolution of CNO isotopes in galaxies, compelling evidence for an IMF skewed towards high-mass stars can be found for galaxy-wide starbursts. In particular, we analyse a sample of submillimetre galaxies observed by us with the Atacama Large Millimetre Array at the peak of the SF activity of the Universe, for which we measure 13C/18O⋍1. This isotope ratio is especially sensitive to IMF variations, and is little affected by observational uncertainties. At the end, ongoing developments of our work are briefly outlined.

scholarly journals THE HIGH-MASS STELLAR INITIAL MASS FUNCTION IN M31 CLUSTERS

2015 ◽  
Vol 806 (2) ◽  
pp. 198 ◽  
Author(s):  
Daniel R. Weisz ◽  
L. Clifton Johnson ◽  
Daniel Foreman-Mackey ◽  
Andrew E. Dolphin ◽  
Lori C. Beerman ◽  
...  
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Stellar Initial Mass Function

scholarly journals The origin of very massive stars around NGC 3603

2019 ◽  
Vol 625 ◽  
pp. L2 ◽  
Author(s):  
V. M. Kalari ◽  
J. S. Vink ◽  
W. J. de Wit ◽  
N. J. Bastian ◽  
R. A. Méndez
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Future Data ◽  
Solar Type ◽  
Stellar Initial Mass Function ◽  
The Universe ◽  
Shed Light

The formation mechanism of the most massive stars in the Universe remains an unsolved problem. Are they able to form in relative isolation in a manner similar to the formation of solar-type stars, or do they necessarily require a clustered environment? In order to shed light on this important question, we study the origin of two very massive stars (VMS): the O2.5If*/WN6 star RFS7 (∼100 M⊙), and the O3.5If* star RFS8 (∼70 M⊙), found within ∼53 and 58 pc, respectively, of the Galactic massive young cluster NGC 3603, using Gaia data. The star RFS7 is found to exhibit motions resembling a runaway star from NGC 3603. This is now the most massive runaway star candidate known in the Milky Way. Although RFS8 also appears to move away from the cluster core, it has proper-motion values that appear inconsistent with being a runaway from NGC 3603 at the 3σ level (but with substantial uncertainties due to distance and age). Furthermore, no evidence for a bow-shock or a cluster was found surrounding RFS8 from available near-infrared photometry. In summary, whilst RFS7 is likely a runaway star from NGC 3603, making it the first VMS runaway in the Milky Way, RFS8 is an extremely young (∼2 Myr) VMS, which might also be a runaway, but this would need to be established from future spectroscopic and astrometric observations, as well as precise distances. If RFS 8 was still not found to meet the criteria for being a runaway from NGC 3603 from such future data, this would have important ramifications for current theories of massive star formation, as well as the way the stellar initial mass function is sampled.

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