Galaxy Clusters Associated with Short GRBs. II. Predictions for the Rate of Short GRBs in Field and Cluster Early-Type Galaxies

We determine the relative rates of short GRBs in cluster and field early-type galaxies as a function of the age probability distribution of their progenitors, P(\tau) \propto \tau^n. This analysis takes advantage of the difference in the growth of stellar mass in clusters and in the field, which arises from the combined effects of the galaxy stellar mass function, the early-type fraction, and the dependence of star formation history on mass and environment. This approach complements the use of the early- to late-type host galaxy ratio, with the added benefit that the star formation histories of early-type galaxies are simpler than those of late-type galaxies, and any systematic differences between progenitors in early- and late-type galaxies are removed. We find that the ratio varies from R(cluster)/R(field) ~ 0.5 for n = -2 to ~ 3 for n = 2. Current observations indicate a ratio of about 2, corresponding to n ~ 0 - 1. This is similar to the value inferred from the ratio of short GRBs in early- and late-type hosts, but it differs from the value of n ~ -1 for NS binaries in the Milky Way. We stress that this general approach can be easily modified with improved knowledge of the effects of environment and mass on the build-up of stellar mass, as well as the effect of globular clusters on the short GRB rate. It can also be used to assess the age distribution of Type Ia supernova progenitors.Comment: ApJ accepted versio

The Physics of Star Cluster Formation and Evolution

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe

Automated classification of gaze direction using spectral regression and support vector machine

This paper presents a framework to automatically estimate the gaze direction of an infant in an infant-parent face-to-face interaction. Commercial devices are sometimes used to produce automated measurement of the subjects' gaze direction. This approach is intrusive, requiring cooperation from the participants, and cannot be employed in interactive face-to-face communication scenarios between a parent and their infant. Alternately, the infant gazes that are at and away from the parent's face may be manually coded from captured videos by a human expert. However, this approach is labor intensive. A preferred alternative would be to automatically estimate the gaze direction of participants from captured videos. The realization of a such a system will help psychological scientists to readily study and understand the early attention of infants. One of the problems in eye region image analysis is the large dimensionality of the visual data. We address this problem by employing the spectral regression technique to project high dimensionality eye region images into a low dimensional sub-space. Represented eye region images in the low dimensional sub-space are utilized to train a support vector machine (SVM) classifier to predict the gaze direction (i.e., either looking at parent's face or looking away from parent's face). The analysis of more than 39,000 video frames of naturalistic gaze shifts of multiple infants demonstrates significant agreement between a human coder and our approach. These results indicate that the proposed system provides an efficient approach to automating the estimation of gaze direction of naturalistic gaze shifts