The First Supernovae: Source Density And Observability Of Pair Instability Supernovae

Theoretical models predict that some of the first stars ended their lives as extremely energetic Pair Instability Supernovae (PISNe). With energies approaching 10(53) erg, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST) allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic Press-Schecter based approach informed by cosmological simulations, with an upper limit of similar to 0.2 PISNe visible per JWST field of view at any given time. We find that the main obstacle to observing PISNe is their scarcity rather than their faintness. Given this we suggest a mosaic style search strategy for detecting PISNe from the first stars.Astronom

The need for a second black hole at the Galactic center

Deep infra-red observations and long-term monitoring programs have provided dynamical evidence for a supermassive black hole of mass 3.e6 solar masses associated with the radio source Sagitarrius A* at the center of our Galaxy. The brightest stars orbiting within 0.1 parsecs of the black hole appear to be young, massive main sequence stars, n spite of an environment near the black hole that is hostile to star formation. We discuss mechanisms by which stars born outside the central parsec can sink towards the black hole and conclude that the drag coming from plausible stellar populations does not operate on the short timescales required by the stellar ages. We propose that these stars were dragged in by a second black hole of mass of 1.e3-1.e4 solar masses, which would be classified as an intermediate-mass black hole. We discuss the implications for the stellar populations and the kinematics in the Galactic center. Finally we note that continued astrometric monitoring of the central radio source offers the prospect for a direct detection of such objects.Comment: 5 pages, 2 postscript figures, submitted to ApJ letters The introduction section has been updated since submission to Ap

Consequences of gravitational radiation recoil

Coalescing binary black holes experience an impulsive kick due to anisotropic emission of gravitational waves. We discuss the dynamical consequences of the recoil accompanying massive black hole mergers. Recoil velocities are sufficient to eject most coalescing black holes from dwarf galaxies and globular clusters, which may explain the apparent absence of massive black holes in these systems. Ejection from giant elliptical galaxies would be rare, but coalescing black holes are displaced from the center and fall back on a time scale of order the half-mass crossing time. Displacement of the black holes transfers energy to the stars in the nucleus and can convert a steep density cusp into a core. Radiation recoil calls into question models that grow supermassive black holes from hierarchical mergers of stellar-mass precursors.Comment: 5 pages, 4 figures, emulateapj style; minor changes made; accepted to ApJ Letter

On the Origin of Nuclear Star Clusters in Late Type Spiral Galaxies

A large fraction of bulgeless disk galaxies contain young compact stellar systems at their centers, in spite of the local gravitational stability of these disks. We evaluate two contrasting hypotheses for the origin of the nuclear star clusters in late-type disk galaxies. The clusters could not have migrated from distant eccentric locations in the disk. Instead they must have formed in situ, requiring radial transport of gas toward the center of the disk. This transport could be a consequence of the development of the magnetorotational instability in the differentially rotating warm neutral medium. We evaluate the rate of gas transport into the disk center and find that it is sufficient to support continuous star formation in that location. Enhanced stellar surface brightness in the inner few hundred parsecs and the formation of a compact stellar system in the central few parsecs are unavoidable in dark matter halos with divergent density profiles. We illustrate our conclusions on a model of the nearest late-type disk galaxy M33.Comment: 4 pages, ApJ Letters, in pres

Determination of masses of the central black holes in NGC524 and NGC2549 using Laser Guide Star Adaptive Optics

[abridged] We present observations of NGC524 and NGC2549 with LGS AO obtained at GEMINI North telescope using the NIFS IFU in the K band. The purpose of these observations, together with previously obtained observations with the SAURON IFU, is to determine the masses (Mbh) of the supermassive black holes (SMBH). The targeted galaxies were chosen to have central light profiles showing a core (NGC524) and a cusp (NGC2549), to probe the feasibility of using the galaxy centre as the NGS required for LGS AO. We employ an innovative `open loop' technique. The data have spatial resolution of 0.23" and 0.17" FWHM, showing that high quality LGS AO observations of these objects are possible. We construct axisymmetric three-integral dynamical models which are constrained with both the NIFS and SAURON data. The best fitting models yield Mbh=(8.3 +2.7 -1.3) x 10^8 Msun for NGC524 and Mbh=(1.4 +0.2 -1.3) x 10^7 Msun for NGC2549 (all errors are at the 3 sigma CL). We demonstrate that the wide-field SAURON data play a crucial role in the M/L determination increasing the accuracy of M/L by a factor of at least 5, and constraining the upper limits on Mbh. The NIFS data are crucial in constraining the lower limits of Mbh and in combination with the large scale data reducing the uncertainty by a factor of 2 or more. We find that the orbital structure of NGC524 shows significant tangential anisotropy, while at larger radii both galaxies are consistent with having almost perfectly oblate velocity ellipsoids. Tangential anisotropy in NGC524 coincides with the size of SMBH sphere of influence and the core region in the light profile. We test the accuracy to which Mbh can be measured using seeings obtained from typical LGS AO observations, and conclude that for a typical conditions and Mbh the expected uncertainty is of the order of 50%.Comment: 19 pages, 14 figure

Formation of a galaxy with a central black hole in the Lemaitre-Tolman model

We construct two models of the formation a galaxy with a central black hole, starting from a small initial fluctuation at recombination. This is an application of previously developed methods to find a Lemaitre-Tolman model that evolves from a given initial density or velocity profile to a given final density profile. We show that the black hole itself could be either a collapsed object, or a non-vacuum generalisation of a full Schwarzschild-Kruskal-Szekeres wormhole. Particular attention is paid to the black hole's apparent and event horizons.Comment: REVTeX, 22 pages including 11 figures (25 figure files). Replacement has minor changes in response to the referee, and editorial corrections. To appear in PR

Original scientific paper Far-infrared spectroscopy of PbTe doped with iron

Far infrared reflection spectra, at room and liquid nitrogen temperature, of PbTe single crystals doped with iron are presented. Plasma minima were observed at about 160 cm –1 and 180 cm –1 for room and liquid nitrogen temperature, respectively. Using the reflectivity diagrams and their minima, the values of the hole concentrations and their mobility at both temperatures were calculated and compared with galvanomagnetic measurements. All these results indicated that when PbTe is doped with a small concentration of Fe, the hole concentration is reduced by one order of magnitude and the free carrier mobility is larger when compared to pure PbTe