X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue

AGN are known to have complex X-ray spectra that depend on both the properties of the accreting SMBH (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity ("torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with X-ray data and photometric redshifts. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. For a sample of 350 AGN in the 4 Ms Chandra Deep Field South field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (abridged). Simpler models are ruled out with decisive evidence in favour of a geometrically extended structure with significant Compton scattering. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed or entirely open toroidal geometry, in favour of an intermediate case. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue with estimated parameters such as the accretion luminosity in the 2-10 keV band and the column density, $N_{H}$, of the obscurer.Comment: 28 pages, 18 figures, catalogue available from https://www.mpe.mpg.de/~jbuchner/agn_torus/analysis/cdfs4Ms_cat/, software available from https://github.com/JohannesBuchner/BX

Stability of fermionic Feshbach molecules in a Bose-Fermi mixture

In the wake of successful experiments in Fermi condensates, experimental attention is broadening to study resonant interactions in degenerate Bose-Fermi mixtures. Here we consider the properties and stability of the fermionic molecules that can be created in such a mixture near a Feshbach resonance (FR). To do this, we consider the two-body scattering matrix in the many-body environment, and assess its complex poles. The stability properties of these molecules strongly depend on their centre-of-mass motion, because they must satisfy Fermi statistics. At low centre-of-mass momenta the molecules are more stable than in the absence of the environment (due to Pauli-blocking effects), while at high centre-of-mass momenta nontrivial many body effects render them somewhat less stable

Electronic energy relaxation and transition frequency jumps of single molecules at 30 mK

Transition frequency jumps for single terrylene molecules in a polyethylene matrix caused by resonant laser irradiation are investigated at 30 mK. These jumps are not accompanied by substantial sample heating. A model for the effect is: proposed, based on the interaction of tunneling two-level systems (TLSs) surrounding the single molecule with high-energy nonthermal phonons emitted by the molecule during electronic energy relaxation. The radius of the effective interaction volume is estimated to be r(m) approximate to 12.5 nm, and the interaction cross section for nonequilibrium phonon -TLS scattering is estimated as similar to 10(-22) cm(-2)

Microscopic Dynamics in a Strongly Interacting Bose-Einstein Condensate

An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a carefully controlled magnetic field pulse in the vicinity of a Feshbach resonance. This pulse probed the strongly interacting regime for the condensate, with calculated values for the diluteness parameter (na^3) ranging from 0.01 to 0.5. The field pulse was observed to cause loss of atoms from the condensate on remarkably short time scales (>=10 microsec). The dependence of this loss on magnetic field pulse shape and amplitude was measured. For triangular pulses shorter than 1 ms, decreasing the pulse length actually increased the loss, until extremely short time scales (a few tens of microseconds) were reached. Such time scales and dependencies are very different from those expected in traditional condensate inelastic loss processes, suggesting the presence of new microscopic BEC physics.Comment: 4 pages in latex2E, 4 eps figures; revised Fig.1, revised scatt.lengths, added discussion, new refs., resubmitted to PR

Constraints on the star-formation rate of z~3 LBGs with measured metallicity in the CANDELS GOODS-South field

We analyse 14 LBGs at z~2.8-3.8 constituting the only sample where both a spectroscopic measurement of their metallicity and deep IR observations (CANDELS+HUGS survey) are available. Fixing the metallicity of population synthesis models to the observed values, we determine best-fit physical parameters under different assumptions about the star-formation history and also consider the effect of nebular emission. For comparison we determine the UV slope of the objects, and use it to estimate their SFR_UV99 by correcting the UV luminosity following Meurer et al. (1999). A comparison between SFR obtained through SED-fitting (SFR_fit) and the SFR_UV99 shows that the latter are underestimated by a factor 2-10, regardless of the assumed SFH. Other SFR indicators (radio, far-IR, X-ray, recombination lines) coherently indicate SFRs a factor of 2-4 larger than SFR_UV99 and in closer agreement with SFR_fit. This discrepancy is due to the solar metallicity implied by the usual beta-A1600 conversion factor. We propose a refined relation, appropriate for sub-solar metallicity LBGs: A1600 = 5.32+1.99beta. This relation reconciles the dust-corrected UV with the SED-fitting and the other SFR indicators. We show that the fact that z~3 galaxies have sub-solar metallicity implies an upward revision by a factor of ~1.5-2 of the global SFRD, depending on the assumptions about the age of the stellar populations. We find very young best-fit ages (10-500 Myrs) for all our objects. From a careful examination of the uncertainties in the fit and the amplitude of the Balmer break we conclude that there is little evidence of the presence of old stellar population in at least half of the LBGs in our sample, suggesting that these objects are probably caught during a huge star-formation burst, rather than being the result of a smooth evolution.Comment: 16 pages, 13 figures, A&A in press. Matched to the published versio

A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Results

We present the results of a Hubble Space Telescope (HST) survey of extended [OIII] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and 38 Seyfert 2's), selected by mostly isotropic properties. The comparison between the semi major axis size of their [OIII] emitting regions (R_Maj) shows that Seyfert 1's and Seyfert 2's have similar distributions, which seems to contradict Unified Model predictions. We discuss possible ways to explain this result, which could be due either to observational limitations or the models used for the comparison with our data. We show that Seyfert 1 Narrow Line Regions (NLR's) are more circular and concentrated than Seyfert 2's, which can be attributed to foreshortening in the former. We find a good correlation between the NLR size and luminosity, following the relation R_Maj propto L([OIII])^0.33, which is flatter than a previous one found for QSO's and Seyfert 2's. We discuss possible reasons for the different results, and their implications to photoionization models. We confirm previous results which show that the [OIII] and radio emission are well aligned, and also find no correlation between the orientation of the extended [OIII] emission and the host galaxy major axis. This agrees with results showing that the torus axis and radio jet are not aligned with the host galaxy rotation axis, indicating that the orientation of the gas in the torus, and not the spin of the black hole, determine the orientation of the accretion disk, and consequently the orientation of the radio jet.Comment: 17 pages including 12 figures, to appear in Ap

Probing dipolar effects with condensate shape oscillation

We discuss the low energy shape oscillations of a magnetic trapped atomic condensate including the spin dipole interaction. When the nominal isotropic s-wave interaction strength becomes tunable through a Feshbach resonance (e.g. as for $^{85}$Rb atoms), anisotropic dipolar effects are shown to be detectable under current experimental conditions [E. A. Donley {\it et al.}, Nature {\bf 412}, 295 (2001)].Comment: revised version, submitte

Discovery of Highly Obscured Galaxies in the Zone of Avoidance

We report the discovery of twenty-five previously unknown galaxies in the Zone of Avoidance. Our systematic search for extended extra-galactic sources in the GLIMPSE and MIPSGAL mid-infrared surveys of the Galactic plane has revealed two overdensities of these sources, located around l ~ 47 and 55 degrees and |b| less than 1 degree in the Sagitta-Aquila region. These overdensities are consistent with the local large-scale structure found at similar Galactic longitude and extending from |b| ~ 4 to 40 degrees. We show that the infrared spectral energy distribution of these sources is indeed consistent with those of normal galaxies. Photometric estimates of their redshift indicate that the majority of these galaxies are found in the redshift range z = 0.01 - 0.05, with one source located at z = 0.07. Comparison with known sources in the local Universe reveals that these galaxies are located at similar overdensities in redshift space. These new galaxies are the first evidence of a bridge linking the large-scale structure between both sides of the Galactic plane at very low Galactic latitude and clearly demonstrate the feasibility of detecting galaxies in the Zone of Avoidance using mid-to-far infrared surveys.Comment: Accepted for publication in the Astronomical Journal, 28 pages, 5 tables, 11 figure

Hydrodynamic modes of a 1D trapped Bose gas

We consider two regimes where a trapped Bose gas behaves as a one-dimensional system. In the first one the Bose gas is microscopically described by 3D mean field theory, but the trap is so elongated that it behaves as a 1D gas with respect to low frequency collective modes. In the second regime we assume that the 1D gas is truly 1D and that it is properly described by the Lieb-Liniger model. In both regimes we find the frequency of the lowest compressional mode by solving the hydrodynamic equations. This is done by making use of a method which allows to find analytical or quasi-analytical solutions of these equations for a large class of models approaching very closely the actual equation of state of the Bose gas. We find an excellent agreement with the recent results of Menotti and Stringari obtained from a sum rule approach.Comment: 15 pages, revtex, 1 figure

BEC Collapse and Dynamical Squeezing of Vacuum Fluctuations

We analyze the phenomena of Bose Novae, as described by Donley et al [Nature 412, 295 (2001)], by focusing on the behavior of excitations or fluctuations above the condensate, as driven by the dynamics of the condensate (rather than the dynamics of the condensate alone or the kinetics of the atoms). The dynamics of the condensate squeezes and amplifies the quantum excitations, mixing the positive and negative frequency components of their wave functions thereby creating particles which appear as bursts and jets. By analyzing the changing amplitude and particle content of these excitations, our simple physical picture (based on a test field approximation) explains well the overall features of the Bose Novae phenomena and provide excellent quantitative fits with experimental data on several aspects, such as the scaling behavior of the collapse time and the amount of particles in the jet. The predictions of the bursts at this level of approximation is less than satisfactory but may be improved on by including the backreaction of the excitations on the condensate. The mechanism behind the dominant effect -- parametric amplification of vacuum fluctuations and freezing of modes outside of horizon -- is similar to that of cosmological particle creation and structure formation in a rapid quench (which is fundamentally different from Hawking radiation in black holes). This shows that BEC dynamics is a promising venue for doing `laboratory cosmology'.Comment: Latex 36 pages, 6 figure