The Hubble Deep Field Reveals a Supernova at z~0.95

We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which has brightened, during the 8.5 days sampled by the data, by more than 0.9 mag in I and about 0.7 mag in V, remaining stable in B. Subsequent observations of the HDF-N show that two years later this object has dimmed back to about its original brightness in I. The colors of this object, its brightness, its time behavior in the various filters and the evolution of its morphology are consistent with being a Type Ib supernova in a faint galaxy at z~0.95.Comment: 5 pages including 2 figures. Accepted for publication in MNRA

Nuclear star formation in the quasar PG1126-041 from adaptive optics assisted spectroscopy

We present adaptive optics assisted spectroscopy of three quasars obtained with NACO at VLT. The high angular resolution achieved with the adaptive optics (~0.08"), joined to the diagnostic power of near-IR spectroscopy, allow us to investigate the properties of the innermost 100 pc of these quasars. In the quasar with the best adaptive optics correction, PG1126-041, we spatially resolve the Pa-alpha emission within the nuclear 100 pc. The comparison with higher excitation lines suggests that the narrow Pa-alpha emission is due to nuclear star formation. The inferred intensity of the nuclear star formation (13 M(sun)/yr) may account for most of the far-IR luminosity observed in this quasar.Comment: 4 pages, 4 figures. Accepted for publication in A&

The Kinematics of Kepler's Supernova Remnant as revealed by Chandra

I determine the expansion of the supernova remnant of SN1604 (Kepler's supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006. The measurements were done in several distinct energy bands, and were made for the remnant as a whole, and for six individual sectors. The average expansion parameter indicates that the remnant expands as $r \propto t^{0.5}$, but there are significant differences in different parts of the remnant: the bright northwestern part expands as $r \propto t^{0.35}$, whereas the rest of the remnant's expansion shows an expansion $r \propto t^{0.6}$. The latter is consistent with an explosion in which the outer part of the ejecta has a negative power law slope for density ($\rho \propto v^{-n}$) of $n=7$, or with an exponential density profile($\rho \propto \exp(-v/v_e)$). The expansion parameter in the southern region, in conjunction with the shock radius, indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for a distance of 4 kpc. An higher explosion energy is consistent with the results, if the distance is larger. The filament in the eastern part of the remnant, which is dominated by X-ray synchrotron radiation seems to mark a region with a fast shock speed $r \propto t^{0.7}$, corresponding to a shock velocity of v= 4200 km/s, for a distance to SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron emission requires shock velocities in excess of ~2000 km/s. The X-ray based expansion measurements reported are consistent with results based on optical and radio measurements, but disagree with previous X-ray measurements based on ROSAT and Einstein observations.Comment: Accepted for publication in ApJ. This new version is the accepted version, which differs mainly in the discussion sectio

Age, metallicity and star formation history of spheroidal galaxies in cluster at z~1.2

We present the analysis, based on spectra collected at the Large Binocular Telescope, of the stellar populations in seven spheroidal galaxies in the cluster XLSSJ0223 at $z$$\sim$1.22. The aim is to constrain the epoch of their formation and their star formation history. Using absorption line strenghts and full spectral fitting, we derive for the stellar populations of the seven spheroids a median age =2.4$\pm$0.6 Gyr, corresponding to a median formation redshift $\sim2.6_{-0.5}^{+0.7}$ (lookback time = 11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that massive spheroids, at least in our targeted cluster, are not coeval. The median metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at 0$<z$<0.9. This lack of evolution of [Z/H] over the range 0$<$$z$$<$1.3, corresponding to the last 9 billions years, suggests that no significant additional star formation and chemical enrichment are required for cluster spheroids to reach the present-day population. We do not detect significant correlation between age and velocity dispersion$\sigma_e$, or dynamical mass M$_{dyn}$, or effective stellar mass density$\Sigma_e$. On the contrary, the metallicity [Z/H] of the seven spheroids is correlated to their dynamical mass M$_{dyn}$, according to a relation similar to the one for local spheroids. [Z/H] is also anticorrelated to stellar mass density$\Sigma_e$because of the anticorrelation between M$_{dyn}$and$\Sigma_e$. Therefore, the basic trends observed in the local universe were already established at$z\sim1.3$, i.e. more massive spheroids are more metal rich, have lower stellar mass density and tend to be older than lower-mass galaxies.Comment: 16 pages, 6 figures, 6 tables, published on MNRA

On Provably Safe and Live Multirobot Coordination With Online Goal Posting

A standing challenge in multirobot systems is to realize safe and efficient motion planning and coordination methods that are capable of accounting for uncertainties and contingencies. The challenge is rendered harder by the fact that robots may be heterogeneous and that their plans may be posted asynchronously. Most existing approaches require constraints on the infrastructure or unrealistic assumptions on robot models. In this article, we propose a centralized, loosely-coupled supervisory controller that overcomes these limitations. The approach responds to newly posed constraints and uncertainties during trajectory execution, ensuring at all times that planned robot trajectories remain kinodynamically feasible, that the fleet is in a safe state, and that there are no deadlocks or livelocks. This is achieved without the need for hand-coded rules, fixed robot priorities, or environment modification. We formally state all relevant properties of robot behavior in the most general terms possible, without assuming particular robot models or environments, and provide both formal and empirical proof that the proposed fleet control algorithms guarantee safety and liveness

Metallicity evolution, metallicity gradients and gas fractions at z~3.4

We used near-infrared integral field spectroscopic observations from the AMAZE and LSD programs to constrain the metallicity in a sample of 40 star forming galaxies at 3<z<5 (most of which at z~3.4). We measure metallicities by exploiting strong emission line diagnostics. We found that a significant fraction of star-forming galaxies at z~3.4 deviate from the Fundamental Metallicity Relation (FMR), with a metallicity up to a factor of ten lower than expected according to the FMR. This deviation does not correlate with the dynamical properties of the galaxy or with the presence of interactions. To investigate the origin of the metallicity deviations in more detail, we also infer information on the gas content, by inverting the Schmidt-Kennicutt relation. In agreement with recent CO observational data, we found that, in contrast with the steeply rising trend at 0<z<2, the gas fraction in massive galaxies remains constant, with indication of a marginal decline, at 2<z<3.5. When combined with the metallicity information, we infer that to explain both the low metallicity and gas content in z~3.4 galaxies, both prominent outflows and massive pristine gas inflows are needed. In ten galaxies we can also spatially resolve the metallicity distribution. We found that the metallicity generally anticorrelates with the distribution of star formation and with the gas surface density. We discuss these findings in terms of pristine gas inflows towards the center, and outflows of metal rich gas from the center toward the external regions. (Abridged)Comment: Replaced to match the published versio