Geminis Fast Turnaround program is intended to greatly decrease the time from having an idea to acquiring the supporting data. The scheme will offer monthly proposal submission opportunities, and proposals will be reviewed by the principal investigat
ors or co-investigators of other proposals submitted during the same round. Here, we set out the design of the system and outline the plan for its implementation, leading to the launch of a pilot program at Gemini North in January 2015.
Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of S
MBHs from seed intermediate-mass black holes (IMBHs, 10^2 to 10^5 M_{odot}) formed in star clusters. In this context, and also with respect to the low mass end of the M-sigma relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Among Galactic star clusters, the massive cluster $omega$ Centauri is a special target due to its central high velocity dispersion and also its multiple stellar populations. We study the central structure and dynamics of the star cluster $omega$ Centauri to examine whether an IMBH is necessary to explain the observed velocity dispersion and surface brightness profiles. We perform direct N-body simulations to follow the dynamical evolution of $omega$ Centauri. The simulations are compared to the most recent data-sets in order to explain the present-day conditions of the cluster and to constrain the initial conditions leading to the observed profiles. We find that starting from isotropic spherical multi-mass King models and within our canonical assumptions, a model with a central IMBH mass of 2% of the cluster stellar mass, i.e. a 5x10^4 M_{odot} IMBH, provides a satisfactory fit to both the observed shallow cusp in surface brightness and the continuous rise towards the center of the radial velocity dispersion profile. In our isotropic spherical models, the predicted proper motion dispersion for the best-fit model is the same as the radial velocity dispersion one. (abridged)
A key open issue for galaxy evolution and formation models is the understanding of the different mechanisms of galaxy assembly at various cosmic epochs. The aim of this study is to derive the global and spatially-resolved metal content in high-redshi
ft galaxies. Using VLT/SINFONI IFU spectroscopy of a first sample of 50 galaxies at z~1.2 in the MASSIV survey, we are able to measure the Ha and [NII]6584 emission lines. Using the N2 ratio as a proxy for oxygen abundance in the interstellar medium, we measure the metallicity of the sample galaxies. We develop a tool to extract spectra in annular regions of these galaxies, leading to a spatially-resolved estimate of the oxygen abundance in each galaxy. We derive a metallicity gradient for 26 galaxies in our sample and discover a significant fraction of galaxies with a positive gradient. Using a simple chemical evolution model, we derive infall rates of pristine gas onto the disks. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting and one is a chain galaxy. We suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. We also identify two interesting correlations in our sample: a) galaxies with higher gas velocity dispersion have shallower/positive gradients; and b) metal-poor galaxies tend to show a positive gradient whereas metal-rich ones tend to show a negative one. This last observation can be explained by the infall of metal-poor gas into the center of the disks. We address the question of the origin of this infall under the influence of gas flows triggered by interactions and/or cold gas accretion.
Intermediate-mass black holes (IMBHs) are of interest in a wide range of astrophysical fields. In particular, the possibility of finding them at the centers of globular clusters has recently drawn attention. IMBHs became detectable since the quality
of observational data sets, particularly those obtained with HST and with high resolution ground based spectrographs, advanced to the point where it is possible to measure velocity dispersions at a spatial resolution comparable to the size of the gravitational sphere of influence for plausible IMBH masses. We present results from ground based VLT/FLAMES spectroscopy in combination with HST data for the globular cluster NGC 6388. The aim of this work is to probe whether this massive cluster hosts an intermediate-mass black hole at its center and to compare the results with the expected value predicted by the $M_{bullet} - sigma$ scaling relation. The spectroscopic data, containing integral field unit measurements, provide kinematic signatures in the center of the cluster while the photometric data give information of the stellar density. Together, these data sets are compared to dynamical models and present evidence of an additional compact dark mass at the center: a black hole. Using analytical Jeans models in combination with various Monte Carlo simulations to estimate the errors, we derive (with 68% confidence limits) a best fit black-hole mass of $ (17 pm 9) times 10^3 M_{odot}$ and a global mass-to-light ratio of $M/L_V = (1.6 pm 0.3) M_{odot}/L_{odot}$.
