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We present VLT/MUSE integral-field spectroscopy ($R\approx 1\,800$) of four giant gravitational arcs exhibiting strong C IV absorption at 8 intervening redshifts, $z_{abs}\approx 2.0$--$2.5$. We detect C IV absorption in a total of 222 adjacent and seeing-uncorrelated sightlines, whose spectra sample beams of ("de-lensed") linear size $\approx 1$ kpc. Our data show that (1) absorption velocities cluster at all probed transverse scales, $\Delta r_\perp\approx0$--$15$ kpc, depending on system; (2) the (transverse) velocity dispersion never exceeds the mean (line-of-sight) absorption spread; and (3) the (transverse) velocity autocorrelation function does not resolve kinematic patterns at the above spatial scales, but its velocity projection, $\xi^{arc}(\Delta v)$, exhibits a similar shape to the known two-point correlation function toward quasars, $\xi^{QSO}(\Delta v)$. An empirical kinematic model suggests that these results are a natural consequence of wide-beam observations of an unresolved clumpy medium. Our model recovers both the underlying velocity dispersion of the clumps ($70$--$170$ \kms) and the mean number of clumps per unit area ($2$--$13$ kpc$^{-2}$). The latter constrains the projected mean inter-clump distance to within $\approx0.3$--$0.8$ kpc, which we argue is a measure of clump size for near-unity covering fraction. The model is also able to predict $\xi^{arc}(\Delta v)$ from $\xi^{QSO}(\Delta v)$, suggesting that the strong systems that shape the former and the line-of-sight velocity components that define the latter trace the same kinematic population. Consequently, the clumps must possess an internal density structure that generates both weak and strong components. We discuss how our interpretation is consistent with previous observations using background galaxies and multiple quasars., Comment: Accepted for publication in A&A

The Gemini South telescope is now equipped with a new high-resolution spectrograph called GHOST (the Gemini High-resolution Optical SpecTrograph). This instrument provides high-efficiency, high-resolution spectra covering 347-1060 nm in a single exposure of either one or two targets simultaneously, along with precision radial velocity spectroscopy utilizing an internal calibration source. It can operate at a spectral element resolving power of either 76000 or 56000, and can reach a SNR$\sim$5 in a 1hr exposure on a V$\sim$20.8 mag target in median site seeing, and dark skies (per resolution element). GHOST was installed on-site in June 2022, and we report performance after full integration to queue operations in November 2023, in addition to scientific results enabled by the integration observing runs. These results demonstrate the ability to observe a wide variety of bright and faint targets with high efficiency and precision. With GHOST, new avenues to explore high-resolution spectroscopy have opened up to the astronomical community. These are described, along with the planned and potential upgrades to the instrument., Comment: Accepted in the Astronomical Journal; 26 pages, 24 figures and 4 tables

We present the first VLT/MUSE observations of a quasar featuring a proximate molecular absorption system, SDSS J125917.31+030922.5. The proximate damped Ly$\alpha$ absorption acts as a natural coronagraph, removing the quasar emission over $\sim$40 {\AA} in wavelength, and allows us to detect extended Ly$\alpha$ emission without the necessity of subtracting the quasar emission. This natural coronagraph permits the investigation of the quasar environment down to its inner regions ($r < 20$ kpc), where galaxy interactions or feedback processes should have the most noticeable effects. Our observations reveal a dense environment, with a highly asymmetric Ly$\alpha$ emission within $2"$ ($\sim 15$ kpc), possibly shaped by a companion galaxy, and a southern extension of the nebulae at about 50~kpc, with rotation-like kinematic signature. The width of the Ly$\alpha$ emission is broadest closer to the quasar, indicating perturbed kinematics as expected if interactions and significant gas flows are present. The foreground absorbing system itself is redshifted by $\approx $400 km/s relative to the background quasar, and therefore is likely arising from gas moving towards the quasar. Finally two additional Ly$\alpha$ emitters are detected with $>10\,\sigma$ significance at 96 and 223 kpc from the quasar, making this field overdense relative to other similar observations of quasars at $z\sim 3$. Our results support the hypothesis that quasars with proximate neutral/molecular absorption trace rich environments where galaxy interactions are at play and motivates further studies of H$_2$-selected quasars to shed light on feeding and feedback processes., Comment: Accepted for publication in A&A

One of the biggest puzzles regarding the circumgalactic medium (CGM) is the structure of its cool ($T\sim10^4$ K) gas phase. While the kinematics of quasar absorption systems suggests the CGM is composed of a population of different clouds, constraining the clouds' extent and spatial distribution has proven challenging, both from the theoretical and observational points of view. In this work we study the spatial structure of the $z\sim 1$ CGM with unprecedented detail via resolved spectroscopy of giant gravitational arcs. We put together a sample of Mg II$\lambda\lambda 2796,2803$ detections obtained with VLT/MUSE in 91 spatially independent and contiguous sight-lines toward 3 arcs, each probing an isolated star-forming galaxy believed to be detected in absorption. We constrain the coherence scale of this gas ($C_{\rm{length}}$), which represents the spatial scale over which the Mg II equivalent width (EW) remains constant, by comparing EW variations measured across all sight-lines with empirical models. We find $1.4

The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H]<-2) stars, characterized by high abundances of carbon over iron ([C/Fe]>+0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z~3-4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars.

We use spatially-resolved spectroscopy of a distant giant gravitational arc to test orientation effects on MgII absorption equivalent width (EW) and covering fraction (kappa) in the circumgalactic medium of a foreground star-forming galaxy (G1) at z~0.77. Forty-two spatially-binned arc positions uniformly sample impact parameters (D) to G1 between 10 and 30 kpc and azimuthal angles alpha between 30 and 90 degrees (minor axis). We find an EW-D anti-correlation, akin to that observed statistically in quasar absorber studies, and an apparent correlation of both EW and kappa with alpha, revealing a non-isotropic gas distribution. In line with our previous results on MgII kinematics suggesting the presence of outflows in G1, at minimum a simple 3-D static double-cone model (to represent the trace of bipolar outflows) is required to recreate the EW spatial distribution. The D and alpha values probed by the arc cannot confirm the presence of a disc, but the data highly disfavor a disc alone. Our results support the interpretation that the EW-alpha correlation observed statistically using other extant probes is partly shaped by bipolar metal-rich winds., Comment: Accepted in Monthly Notices of the Royal Astronomical Society

We investigate the abundance and distribution of metals in the high-redshift intergalactic medium and circum-galactic medium through the analysis of a sample of almost 600 SiIV absorption lines detected in high and intermediate resolution spectra of 147 quasars. The evolution of the number density of SiIV lines, the column density distribution function and the cosmic mass density are studied in the redshift interval 1.7 <= z <= 6.2 and for log N(SiIV) >= 12.5. All quantities show a rapid increase between z~6 and z< 5 and then an almost constant behaviour to z~2 in very good agreement with what is already observed for CIV absorption lines. The present results are challenging for numerical simulations: when simulations reproduce our SiIV results, they tend to underpredict the properties of CIV, and when the properties of CIV are reproduced, the number of strong SiIV lines (log N(SiIV) > 14) is overpredicted., Comment: 14 pages, 8 figures, accepted for publication in MNRAS

We present gravitational-arc tomography of the cool-warm enriched circumgalactic medium (CGM) of an isolated galaxy (``G1'') at $z \approx 0.77$. Combining VLT/MUSE adaptive-optics and Magellan/MagE echelle spectroscopy we obtain partially-resolved kinematics of MgII in absorption and [OII] in emission. The unique arc configuration allows us to probe 42 spatially independent arc positions transverse to G1, plus 4 positions in front of it. The transverse positions cover G1's minor and major axes at impact parameters of $\approx 10-30$ kpc and $\approx 60$ kpc, respectively. We observe a direct kinematic connection between the cool-warm enriched CGM (traced by MgII) and the interstellar medium (traced by [OII]). This provides strong evidence for the existence of an extended disc that co-rotates with the galaxy out to tens of kiloparsecs. The MgII velocity dispersion ($\sigma \approx 30-100$ km s$^{-1}$, depending on position) is of the same order as the modeled galaxy rotational velocity ($v_{\rm rot} \approx 80$ km s$^{-1}$), providing evidence for the presence of a turbulent and pressure-supported CGM component. We regard the absorption to be modulated by a galactic-scale outflow, as it offers a natural scenario for the observed line-of-sight dispersion and asymmetric profiles observed against both the arcs and the galaxy. An extended enriched co-rotating disc together with the signatures of a galactic outflow, are telltale signs of metal recycling in the $z\sim 1$ CGM., Comment: MNRAS accepted. Moderate changes after addressing referee feedback, including a correction in the systemic redshift; all qualitative results and conclusions remain the same

We present a theory of conducting quantum networks that accounts for Abelian and non-Abelian fields acting on spin carriers. We apply this approach to model the conductance of mesoscopic spin interferometers of different geometry (such as squares and rings), reproducing recent experimental findings in nanostructured InAsGa quantum wells subject to Rashba spin-orbit and Zeeman fields (as, e.g., the manipulation of Aharonov-Casher interference patterns by geometric means). Moreover, by introducing an additional field-texture engineering, we manage to single out a previously unnoticed spin-phase suppression mechanism. We notice that our approach can also be used for the study of complex networks and the spectral properties of closed systems., Comment: 13 pages with 9 figures

We investigate the effects of spin-momentum locking on the interference and diffraction patterns due to a double- or single-slit in an electronic \emph{Gedankenexperiment}. We show that the inclusion of the spin-degree-of-freedom, when coupled to the motion direction of the carrier -- a typical situation that occurs in systems with spin-orbit interaction -- leads to a modification of the interference and diffraction patterns that depend on the geometrical parameters of the system., Comment: 10 pages and 8 figures

We demonstrate single-charge occupation of ambipolar quantum dots in silicon via charge sensing. We have fabricated ambipolar quantum dot (QD) devices in a silicon metal-oxide-semiconductor heterostructure comprising a single-electron transistor next to a single-hole transistor. Both QDs can be tuned to simultaneously sense charge transitions of the other. We further detect the few-electron and few-hole regimes in the QDs of our ambipolar device by active charge sensing., Comment: 13 pages, 4 figures

Electrical quantum conductors coupled to microwave resonators have in the last decade emerged as a versatile testbed for controllable light-matter interaction on the nanometer scale. Recent experimental progress with high impedance resonators has resulted in conductor-resonator systems with a large, dimensionless coupling parameter $\lambda \gtrsim 0.1$, well beyond the small coupling regime $\lambda \ll 1$. Motivated by this progress, we here analyse theoretically the joint statistics of transported electrons and emitted photons in a single level quantum dot coupled to a microwave resonator, for arbitrarily large $\lambda$. Describing the electron-photon dynamics via a number-resolved master equation, we evaluate the joint long-time probability distribution as well as joint short-time, $g^{(2)}(t)$, correlation functions. Considering the high-bias regime, with sequential electron tunneling and working in the damping basis, allows us to obtain analytical results for both transport cumulants and $g^{(2)}(t)$ functions. It is found that the photons emitted out of the resonator are bunched and display a super-Poissonian statistics, for all system parameters. However, the electron transport properties are found to be unaffected by the coupling to the resonator, anti-bunched and with sub-Poissonian statistics. From the joint distribution we identify regimes of electron tunneling induced photon cascades and very large $g^{(2)}(t)$ functions. All $g^{(2)}(t)$-functions are found to be independent of $\lambda$. We also identify conditions for and transport signatures of a thermal resonator photon state., Comment: 13 pages, 5 figures

We investigate the NV absorption signal along the line of sight of background quasars, in order to test the robustness of the use of this ion as criterion to select intrinsic (i.e. physically related to the quasar host galaxy) narrow absorption lines (NALs). We build composite spectra from a sample of $\sim$ 1000 CIV absorbers, covering the redshift range 2.55 < z < 4.73, identified in 100 individual sight lines from the XQ-100 Legacy Survey. We detect a statistical significant NV absorption signal only within 5000 km s$^{-1}$ of the systemic redshift, z$\rm_{em}$. This absorption trough is $\sim$ 15$\sigma$ when only CIV systems with N(CIV) > 10$^{14}$ cm$^{-2}$ are included in the composite spectrum. This result confirms that NV offers an excellent statistical tool to identify intrinsic systems. We exploit the stacks of 11 different ions to show that the gas in proximity to a quasar exhibits a considerably different ionization state with respect to gas in the transverse direction and intervening gas at large velocity separations from the continuum source. Indeed, we find a dearth of cool gas, as traced by low-ionization species and in particular by MgII, in the proximity of the quasar. We compare our findings with the predictions given by a range of Cloudy ionization models and find that they can be naturally explained by ionization effects of the quasar., Comment: 18 pages, 13 figures, 1 table. Accepted on MNRAS

Previous studies have shown that the incidence rate of intervening strong MgII absorbers towards GRBs were a factor of 2 - 4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong MgII absorbers with rest-frame equivalent widths $W_r^{2796} >$ 1 {\AA} towards GRBs and quasars in the redshift range 0.1 < z < 5. With large and similar sample sizes, and path length coverages of $\Delta$z = 57.8 and 254.4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1 sigma uncertainty levels at all redshifts. For absorbers at z < 2.3 the incidence towards GRBs is a factor of 1.5$\pm$0.4 higher than the expected number of strong MgII absorbers in SDSS quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4$\pm$0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high spectral resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS MgII catalogues and high spectral resolution studies. The rest-frame equivalent width distribution also agrees to within 1 sigma uncertainty levels between the GRB and quasar samples. Intervening strong MgII absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong., Comment: 10 pages, accepted for publication in A&A

The XQ-100 survey provides optical and near infrared coverage of 36 blindly selected, intervening damped Lyman alpha systems (DLAs) at 2 < z < 4, simultaneously covering the MgII doublet at 2796A, 2803A, and the Ly-alpha transition. Using the XQ-100 DLA sample, we investigate the completeness of selecting DLA absorbers based on their MgII rest-frame equivalent width (W2796) at these redshifts. Of the 29 DLAs with clean MgII profiles, we find that six (20% of DLAs) have W2796 < 0.6A. The DLA incidence rate of W2796 < 0.6A absorbers is a factor of ~5 higher than what is seen in z~1 samples, indicating a potential evolution in the MgII properties of DLAs with redshift. All of the W2796 < 0.6A DLAs have low metallicities (-2.5 < [M/H] < -1.7), small velocity widths (v90 < 50 km/s), and tend to have relatively low N(HI). We demonstrate that the exclusion of these low W2796 DLAs results in a higher mean N(HI) which in turn leads to a ~7% increase in the cosmological gas density of HI of DLAs at 2 < z < 4; and that this exclusion has a minimal effect on the HI-weighted mean metallicity., Comment: Accepted into MNRAS Letters. 6 pages, 2 figures

The XQ-100 survey has provided high signal-noise spectra of 100 redshift 3-4.5 quasars with the X-Shooter spectrograph. The metal abundances for 13 elements in the 41 damped Lyman alpha systems (DLAs) identified in the XQ-100 sample are presented, and an investigation into abundances of a variety of DLA classes is conducted. The XQ-100 DLA sample contains five DLAs within 5000 km/s of their host quasar (proximate DLAs; PDLAs) as well as three sightlines which contain two DLAs within 10,000 km/s of each other along the same line-of-sight (multiple DLAs; MDLAs). Combined with previous observations in the literature, we demonstrate that PDLAs with logN(HI)<21.0 show lower [S/H] and [Fe/H] (relative to intervening systems with similar redshift and N(HI)), whilst higher [S/H] and [Si/H] are seen in PDLAs with logN(HI)>21.0. These abundance discrepancies are independent of their line-of-sight velocity separation from the host quasar, and the velocity width of the metal lines (v90). Contrary to previous studies, MDLAs show no difference in [alpha/Fe] relative to single DLAs matched in metallicity and redshift. In addition, we present follow-up UVES data of J0034+1639, a sightline containing three DLAs, including a metal-poor DLA with [Fe/H]=-2.82 (the third lowest [Fe/H] in DLAs identified to date) at z=4.25. Lastly we study the dust-corrected [Zn/Fe], emphasizing that near-IR coverage of X-Shooter provides unprecedented access to MgII, CaII and TiII lines (at redshifts 3-4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs., Comment: Accepted to MNRAS. 19 pages plus Appendix material (102 pages total)

We describe the execution and data reduction of the European Southern Observatory Large Programme "Quasars and their absorption lines: a legacy survey of the high-redshift universe with VLT/XSHOOTER" (hereafter `XQ-100'). XQ-100 has produced and made publicly available an homogeneous and high-quality sample of echelle spectra of 100 QSOs at redshifts z~3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from R~4000 to 7000, depending on wavelength. The median signal-to-noise ratios are 33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600 Angstrom, respectively. This paper provides future users of XQ-100 data with the basic statistics of the survey, along with details of target selection, data acquisition and data reduction. The paper accompanies the public release of all data products, including 100 reduced spectra. XQ-100 is the largest spectroscopic survey to date of high-redshift QSOs with simultaneous rest-frame UV/optical coverage, and as such enables a wide range of extragalactic research, from cosmology and galaxy evolution to AGN astrophysics., Comment: In press at A&A. Table A.2 updated to match the summary table in the ESO archive

We present a sample of 38 intervening Damped Lyman $\alpha$ (DLA) systems identified towards 100 $z>3.5$ quasars, observed during the XQ-100 survey. The XQ-100 DLA sample is combined with major DLA surveys in the literature. The final combined sample consists of 742 DLAs over a redshift range approximately $1.6 < z_{\rm abs} < 5.0$. We develop a novel technique for computing $\Omega_{\rm HI}^{\rm DLA}$ as a continuous function of redshift, and we thoroughly assess and quantify the sources of error therein, including fitting errors and incomplete sampling of the high column density end of the column density distribution function. There is a statistically significant redshift evolution in $\Omega_{\rm HI}^{\rm DLA}$ ($\geq 3 \sigma$) from $z \sim 2$ to $z \sim$ 5. In order to make a complete assessment of the redshift evolution of $\Omega_{\rm HI}$, we combine our high redshift DLA sample with absorption surveys at intermediate redshift and 21cm emission line surveys of the local universe. Although $\Omega_{\rm HI}^{\rm DLA}$, and hence its redshift evolution, remains uncertain in the intermediate redshift regime ($0.1 < z_{\rm abs} < 1.6$), we find that the combination of high redshift data with 21cm surveys of the local universe all yield a statistically significant evolution in $\Omega_{\rm HI}$ from $z \sim 0$ to $z \sim 5$ ($\geq 3 \sigma$). Despite its statistical significance, the magnitude of the evolution is small: a linear regression fit between $\Omega_{\rm HI}$ and $z$ yields a typical slope of $\sim$0.17$\times 10^{-3}$, corresponding to a factor of $\sim$ 4 decrease in $\Omega_{\rm HI}$ between $z=5$ and $z=0$., Comment: Submitted to MNRAS, this version follows the referee's report and minor revisions. Large tables are included in the source file tarball

Recent experiments on nanoscale conductors coupled to microwave cavities put in prospect transport investigations of electron-photon interplay in the deep quantum regime. Here we propose a pump-probe scheme to investigate the transient dynamics of individual electron-photon excitations in a double quantum dot-cavity system. Excitations pumped into the system decay via charge tunneling at the double dot, probed in real time. We investigate theoretically the short-time charge transfer statistics at the dot, for periodic pumping, and show that this gives access to vacuum Rabi oscillations as well as excitation dynamics in the presence of double dot dephasing and relaxation., Comment: 5 Pages, 5 figures

The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100Mo and of the unstable isotope 93Mo were measured at the LAND/R3B setup at GSI Helmholtzzentrum f\"ur Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94Mo and 96,98Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93Mo(g,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94Mo(g,n) reaction is presented. Further analysis will complete the experimental database for the (g,n) production chain of the p-isotopes of molybdenum., Comment: Talk given at the Conference Nuclear Physice in Astrophysics VI (NPA6), Lisbon, Portugal, May 19-24 2013. To appear in the NPA6 Proceedings in Journal of Physics: Conference Series (JPCS). 6 pages, 6 figures

We consider a two-dimensional electron gas in an inversion asymmetric layer and in the presence of spatially distributed magnetic impurities. We investigate the relationship between the geometrical properties of the wave-function and the system's spin dependent transport properties. A localization transition, arising when disorder is increased, is exhibited by the appearance of a fractal state with finite inverse participation ratio. Below the transition, interference effects modify the carrier's diffusion, as revealed by the dependence on the scattering time of the power law exponents characterizing the spreading of a wave packet. Above the transition, in the strong disorder regime, we find that the states are spin polarized and localized around the impurities. A significant enhancement of the spin current develops in this regime., Comment: 12 pages, 10 figures

We investigate the spectral properties of the two-orbital Hubbard model, including the double hopping term, by means of the dynamical mean field method. This Hamiltonian describes materials in which ferromagnetism is realized by the double exchange mechanism, like for instance manganites, nickelates or diluted magnetic semiconductors. The spectral function of the unoccupied states is characterized by a specific equidistant three peak structure. We emphasize the importance of the double hopping term on the spectral properties. We show the existence of a ferromagnetic phase due to electron doping near n=1 by the double exchange mechanism. A quasi-particle excitation at the Fermi energy is found that we attribute to what we will call an orbital polaron. We derive an effective spin-pseudospin Hamiltonian for the two-orbital double exchange model at n=1 filling to explain the existence and dynamics of this quasi-particle., Comment: 11 pages, 8 figures

We consider a two dimensional semiconductor with carriers subject to spin-orbit interactions and scattered by randomly distributed magnetic impurities. We solve the time-dependent Schroedinger equation to investigate the relationship between the geometrical properties of the wavefunction and the system's spin dependent transport properties. Even in the absence of localized states, interference effects modify the carrier diffusion, as revealed by the appearance of power laws dependent on the impurity concentration. For stronger disorder, we find a localization transition characterized by a fractal wavefunction and enhanced spin transport., Comment: 8 pages; 5 figures; CCT11 conference

We investigate the intrinsic spin Hall effect in a quantum well semiconductor doped with magnetic impurities, as a means to manipulate the carriers' spin. Using a simple Hamiltonian with Rashba spin-orbit coupling and exchange interactions, we analytically compute the spin Hall conductivity. It is demonstrated that using the appropriate order of limits, one recovers the intrinsic universal value. Numerical computations on a tight-binding model, in the weak disorder regime, confirm that the spin Hall effect is preserved in the presence of magnetic impurities. The optical spin conductivity shows large sample to sample fluctuations in the low frequency region. As a consequence, for weak disorder, the static spin conductivity is found to follow a wide Gaussian distribution with its mean value near the intrinsic clean value., Comment: 10 pages, 11 figures