The Maximum Mass of Star Clusters

When an universal untruncated star cluster initial mass function (CIMF) described by a power-law distribution is assumed, the mass of the most massive star cluster in a galaxy (M_max) is the result of the size-of-sample (SoS) effect. This implies a dependence of M_max on the total number of star clusters (N). The SoS effect also implies that M_max within a cluster population increases with equal logarithmic intervals of age. This is because the number of clusters formed in logarithmic age intervals increases (assuming a constant cluster formation rate). This effect has been observed in the SMC and LMC. Based on the maximum pressure (P_int) inside molecular clouds, it has been suggested that a physical maximum mass (M_max[phys]) should exist. The theory predicts that M_max[phys] should be observable, i.e. lower than M_max that follows from statistical arguments, in big galaxies with a high star formation rate. We compare the SoS relations in the SMC and LMC with the ones in M51 and model the integrated cluster luminosity function (CLF) for two cases: 1) M_max is determined by the SoS effect and 2) M_max=M_max[phys]=constant. The observed CLF of M51 and the comparison of the SoS relations with the SMC and LMC both suggest that there exists a M_max[phys] of 5*10^5 M_sun in M51. The CLF of M51 looks very similar to the one observed in the ``Antennae'' galaxies. A direct comparison with our model suggests that there M_max[phys]=2*10^6 M_sun.Comment: 4 pages, contribution to "Globular Clusters: Guides to Galaxies", March 6th-10th, 200

The young star cluster system of the Antennae galaxies

“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s10509-009-0103-xThe study of young star cluster (YSC) systems, preferentially in starburst and merging galaxies, has seen great interest in the recent past, as it provides important input to models of star formation. However, even some basic properties (such as the luminosity function; LF) of YSC systems are still being debated. Here, we study the photometric properties of the YSC system in the nearest major merger system, the Antennae galaxies. We find evidence for the existence of a statistically significant turnover in the LF.Peer reviewe

Search for varying constants of nature from astronomical observation of molecules

The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope is discussed in the context of varying constants, and in connection to different theoretical scenarios. Radio astronomy provides an alternative search strategy bearing the advantage that molecules as NH$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ statistical significance). Existing bottlenecks and prospects for future improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the International Space Science Institute, Bern 201

Predicted Pleistocene-Holocene range shifts of the tiger (Panthera tigris)

Aim In this article, we modelled the potential range shifts of tiger (Panthera tigris) populations over the Late Pleistocene and Holocene, to provide new insights into the evolutionary history and interconnectivity between populations of this endangered species. Location Asia. Methods We used an ecological niche approach and applied a maximum entropy (Maxent) framework to model potential distributions of tigers. Bioclimatic conditions for the present day and mid-Holocene, and for the Last Glacial Maximum (LGM), were used to represent interglacial and glacial conditions of the Late Pleistocene, respectively. Results Our results show that the maximum potential tiger range during modern climates (without human impacts) would be continuous from the Indian subcontinent to north-east Siberia. During the LGM, distributions are predicted to have contracted to southern China, India and Southeast Asia and remained largely contiguous. A potential distribution gap between Peninsular Malaya and Sumatra could have effectively separated tigers on the Sunda Islands from those in continental Asia during interglacials. Main conclusions The continuous modelled distribution of tigers in mainland Asia supports the idea of mainly unimpeded gene flow between all populations throughout the Late Pleistocene and Holocene. Thus, our data support a pragmatic approach to tiger conservation management, especially of mainland populations, as it is likely that only recent anthropogenic changes caused separation of these populations. In contrast, Sunda tigers are likely to have separated and differentiated following the Last Glacial Maximum and thus warrant separate management

Sapling size influences shade tolerance ranking among southern boreal tree species

1 Traditional rankings of shade tolerance of trees make little reference to individual size. However, greater respiratory loads with increasing sapling size imply that larger individuals will be less able to tolerate shade than smaller individuals of the same species and that there may be shifts among species in shade tolerance with size. 2 We tested this hypothesis using maximum likelihood estimation to develop individual-tree-based models of the probability of mortality as a function of recent growth rate for seven species: trembling aspen, paper birch, yellow birch, mountain maple, white spruce, balsam fir and eastern white cedar. 3 Shade tolerance of small individuals, as quantified by risk of mortality at low growth, was mostly consistent with traditional shade tolerance rankings such that cedar > balsam fir > white spruce > yellow birch > mountain maple = paper birch > aspen. 4 Differences in growth-dependent mortality were greatest between species in the smallest size classes. With increasing size, a reduced tolerance to shade was observed for all species except trembling aspen and thus species tended to converge in shade tolerance with size. At a given level of radial growth larger trees, apart from aspen, had a higher probability of mortality than smaller trees. 5 Successional processes associated with shade tolerance may thus be most important in the seedling stage and decrease with ontogeny

Search for the Rare Decay KL --> pi0 ee

The KTeV/E799 experiment at Fermilab has searched for the rare kaon decay KL--> pi0ee. This mode is expected to have a significant CP violating component. The measurement of its branching ratio could support the Standard Model or could indicate the existence of new physics. This letter reports new results from the 1999-2000 data set. One event is observed with an expected background at 0.99 +/- 0.35 events. We set a limit on the branching ratio of 3.5 x 10^(-10) at the 90% confidence level. Combining the results with the dataset taken in 1997 yields the final KTeV result: BR(KL --> pi0 ee) < 2.8 x 10^(-10) at 90% CL.Comment: 4 pages, three figure

HI in the Outskirts of Nearby Galaxies

The HI in disk galaxies frequently extends beyond the optical image, and can trace the dark matter there. I briefly highlight the history of high spatial resolution HI imaging, the contribution it made to the dark matter problem, and the current tension between several dynamical methods to break the disk-halo degeneracy. I then turn to the flaring problem, which could in principle probe the shape of the dark halo. Instead, however, a lot of attention is now devoted to understanding the role of gas accretion via galactic fountains. The current $\rm \Lambda$ cold dark matter theory has problems on galactic scales, such as the core-cusp problem, which can be addressed with HI observations of dwarf galaxies. For a similar range in rotation velocities, galaxies of type Sd have thin disks, while those of type Im are much thicker. After a few comments on modified Newtonian dynamics and on irregular galaxies, I close with statistics on the HI extent of galaxies.Comment: 38 pages, 17 figures, invited review, book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628

We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes $\sim -2$ and a truncation of a few times 105 ${M}_{\odot }$. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find mass-independent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (≤104 ${M}_{\odot }$) clusters, suggesting that a mass-dependent component is necessary to fully describe the YSC disruption process in NGC 628

Greenhouse gas emissions from inland waters: A perspective and research agenda for the tropics and subtropics

peer reviewedStrong consensus indicates that inland waters emit globally significant quantities of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. Tropical inland waters are often considered major contributors to higher greenhouse gas fluxes, yet accurate estimates of aquatic greenhouse gas fluxes are limited for the tropics. We provide a historical perspective on research carried out across low latitudes since the 1980s, synthesize current understanding of the sources and drivers of greenhouse gas emissions, and highlight priority research areas for future tropical inland water greenhouse gas research. We show that much of the focus has been on the humid tropics while the wet-dry, (semi)arid, and mountainous regions remain underrepresented in global datasets. Consistent and reliable greenhouse gas emission estimates will require (1) addressing the observational mismatch with new data from understudied ecoregions, (2) favoring direct and high-resolution carbon dioxide measurements over indirect estimates based on water chemistry parameters, (3) developing approaches that cross boundaries between ecosystem types and scales, and (4) sharing and publishing data more systematically

Globular cluster luminosity function as distance indicator

Globular clusters are among the first objects used to establish the distance scale of the Universe. In the 1970-ies it has been recognized that the differential magnitude distribution of old globular clusters is very similar in different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the so-called Globular Cluster Luminosity Function has been then established as a secondary distance indicator. The intrinsic accuracy of the method has been estimated to be of the order of ~0.2 mag, competitive with other distance determination methods. Lately the study of the Globular Cluster Systems has been used more as a tool for galaxy formation and evolution, and less so for distance determinations. Nevertheless, the collection of homogeneous and large datasets with the ACS on board HST presented new insights on the usefulness of the Globular Cluster Luminosity Function as distance indicator. I discuss here recent results based on observational and theoretical studies, which show that this distance indicator depends on complex physics of the cluster formation and dynamical evolution, and thus can have dependencies on Hubble type, environment and dynamical history of the host galaxy. While the corrections are often relatively small, they can amount to important systematic differences that make the Globular Cluster Luminosity Function a less accurate distance indicator with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review paper based on the invited talk at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13 pages, 8 figures