Initial mass function of intermediate mass black hole seeds

We study the Initial Mass Function (IMF) and host halo properties of Intermediate Mass Black Holes (IMBH, 10^{4-6} Msun) formed inside metal-free, UV illuminated atomic cooling haloes (virial temperature T_vir > 10^4 K) either via the direct collapse of the gas or via an intermediate Super Massive Star (SMS) stage. We achieve this goal in three steps: (a) we derive the gas accretion rate for a proto-SMS to undergo General Relativity instability and produce a direct collapse black hole (DCBH) or to enter the ZAMS and later collapse into a IMBH; (b) we use merger-tree simulations to select atomic cooling halos in which either a DCBH or SMS can form and grow, accounting for metal enrichment and major mergers that halt the growth of the proto-SMS by gas fragmentation. We derive the properties of the host halos and the mass distribution of black holes at this stage, and dub it the "Birth Mass Function"; (c) we follow the further growth of the DCBH due to accretion of leftover gas in the parent halo and compute the final IMBH mass.We consider two extreme cases in which minihalos (T_vir < 10^4 K) can (fertile) or cannot (sterile) form stars and pollute their gas leading to a different IMBH IMF. In the (fiducial) fertile case the IMF is bimodal extending over a broad range of masses, M= (0.5-20)x10^5 Msun, and the DCBH accretion phase lasts from 10 to 100 Myr. If minihalos are sterile, the IMF spans the narrower mass range M= (1-2.8)x10^6 Msun, and the DCBH accretion phase is more extended (70-120 Myr). We conclude that a good seeding prescription is to populate halos (a) of mass 7.5 < log (M_h/Msun) < 8, (b) in the redshift range 8 < z < 17, (c) with IMBH in the mass range 4.75 < log (M_BH/Msun) < 6.25.Comment: MNRAS, in press. Comments welcom

On the [CII]-SFR relation in high redshift galaxies

After two ALMA observing cycles, only a handful of [CII] $158\,\mu m$ emission line searches in z>6 galaxies have reported a positive detection, questioning the applicability of the local [CII]-SFR relation to high-z systems. To investigate this issue we use the Vallini et al. 2013 (V13) model, based on high-resolution, radiative transfer cosmological simulations to predict the [CII] emission from the interstellar medium of a z~7 (halo mass $M_h=1.17\times10^{11}M_{\odot}$) galaxy. We improve the V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background on the [CII] line luminosity. We study the relative contribution of diffuse neutral gas to the total [CII] emission ($F _{diff}/F_{tot}$) for different SFR and Z values. We find that the [CII] emission arises predominantly from PDRs: regardless of the galaxy properties, $F _{diff}/F_{tot}\leq 10$% since, at these early epochs, the CMB temperature approaches the spin temperature of the [CII] transition in the cold neutral medium ($T_{CMB}\sim T_s^{CNM}\sim 20$ K). Our model predicts a high-z [CII]-SFR relation consistent with observations of local dwarf galaxies ($0.02<Z/Z_{\odot}<0.5$). The [CII] deficit suggested by actual data ($L_{CII}<2.0\times 10^7 L_{\odot}$ in BDF3299 at z~7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities ($Z<0.1 Z_{\odot}$).Comment: 9 pages, 6 figures, replaced with the version accepted for pubblication in Ap

Mapping metals at high redshift with far-infrared lines

Cosmic metal enrichment is one of the key physical processes regulating galaxy formation and the evolution of the intergalactic medium (IGM). However, determining the metal content of the most distant galaxies has proven so far almost impossible; also, absorption line experiments at $z\sim6$ become increasingly difficult because of instrumental limitations and the paucity of background quasars. With the advent of ALMA, far-infrared emission lines provide a novel tool to study early metal enrichment. Among these, the [CII] line at 157.74 $\mu$m is the most luminous line emitted by the interstellar medium of galaxies. It can also resonant scatter CMB photons inducing characteristic intensity fluctuations ($\Delta I/I_{CMB}$) near the peak of the CMB spectrum, thus allowing to probe the low-density IGM. We compute both [CII] galaxy emission and metal-induced CMB fluctuations at $z\sim 6$ by using Adaptive Mesh Refinement cosmological hydrodynamical simulations and produce mock observations to be directly compared with ALMA BAND6 data ($\nu_{obs}\sim 272$ GHz). The [CII] line flux is correlated with $M_{UV}$ as $\log(F_{peak}/\mu{\rm Jy})=-27.205-2.253\,M_{UV}-0.038\,M_{UV}^2$. Such relation is in very good agreement with recent ALMA observations (e.g. Maiolino et al. 2015; Capak et al. 2015) of $M_{UV}<-20$ galaxies. We predict that a $M_{UV}=-19$ ($M_{UV}=-18$) galaxy can be detected at $4\sigma$ in $\simeq40$ (2000) hours, respectively. CMB resonant scattering can produce $\simeq\pm 0.1\,\mu$Jy/beam emission/absorptions features that are very challenging to be detected with current facilities. The best strategy to detect these signals consists in the stacking of deep ALMA observations pointing fields with known $M_{UV}\simeq-19$ galaxies. This would allow to simultaneously detect both [CII] emission from galactic reionization sources and CMB fluctuations produced by $z\sim6$ metals.Comment: 13 pages, 6 figure

Generalized tt-jj Model

By parameterizing the t-j model we present a new electron correlation model with one free parameter for high-temperature superconductivity. This model is of $SU_{q}(1,2)$ symmetry. The energy spectrums are shown to be modulated by the free parameter in the model. The solution and symmetric structures of the Hilbert space, as well as the Bethe ansatz approach are discussed for special cases.Comment: 13 page, Latex, to appear in J. Phys.

Research Program towards Observation of Neutrino-Nucleus Coherent Scattering

The article describes the research program pursued by the TEXONO Collaboration towards an experiment to observe coherent scattering between neutrinos and the nucleus at the power reactor. The motivations of studying this process are surveyed. In particular, a threshold of 100-200 eV has been achieved with an ultra-low-energy germanium detector prototype. This detection capability at low energy can also be adapted to conduct searches of Cold Dark Matter in the low-mass region as well as to enhance the sensitivities in the study of neutrino magnetic moments.Comment: 5 pages, 8 figures ; Proceedings of TAUP-2005 Workshop, Spain, 2005. Updated on 2006/9/15 for Proceedings of Neutrino-2006 Conference, Santa Fe, 200

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using a method of an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024 %. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.Comment: 44 page

Thermally stimulated relaxation and behaviors of oxygen vacancies in SrTiO<inf>3</inf> single crystals with (100), (110) and (111) orientations

Abstract The strontium titanate (SrTiO3) single crystals with different orientations of (100), (110) and (111) were investigated using thermally stimulated depolarization current (TSDC) measurements, which has been proved to be an effective strategy to fundamentally study the relationship between relaxation phenomena and defect chemistry in dielectrics. The origins of different relaxations in SrTiO3 crystals were identified and the activation energy of oxygen vacancies was estimated from TSDC measurements. It was further found that oxygen-treated SrTiO3 crystals exhibit different relaxation behaviors. Noticeable changes of thermal relaxation associated with oxygen vacancies have taken place in relation to the crystalline anisotropy. The SrTiO3 (110) samples display higher concentration and activation energy of oxygen vacancies. First-principles calculations were carried out on SrTiO3 (110) crystals to study the effect of oxygen vacancy on different surface microstructure. From the resulting minimum formation energy of 0.63 eV, it demonstrates that the oxygen vacancies tend to form on the TiO-terminated surfaces. Considering the band structure, oxygen vacancies near the surface contribute to the transition of crystal from insulator to metallic characteristic.</jats:p