A square shape multi-anode micro-channel-plate photomultiplier tube (MCP-PMT) was developed for the Belle II TOP counter. It has a 2323 mm super(2) multi-alkali photocathode with a peak quantum ...efficiency (QE) of 28% around a wavelength of 360 nm. It has a 210 super(6)2106 gain and is capable of detecting a single photon with a transit time spread (TTS) of 40 ps or less. The QE, gain and TTS were measured for each MCP-PMT to check the quality in the mass production of 550 MCP-PMTs. The lifetime of the MCP-PMT was extended to 10 C/cm super(2) by adapting the atomic layer deposition technique for the MCP coating. Other properties of the MCP-PMT are also discussed: the angle and polarization dependence of the QE, and the effects of charge sharing and cross-talk. A prototype TOP counter was tested with a 2 GeV/c positron beam. The distribution of the time of propagation was consistent with the calculated expectation which included those properties of the MCP-PMT.
The mass-metallicity relation (MZR) of type-2 active galactic nuclei (AGNs) at 1.2 < z < 4.0 is investigated by using high-z radio galaxies (HzRGs) and X-ray selected radio-quiet AGNs. We combine new ...rest-frame ultraviolet (UV) spectra of two radio-quiet type-2 AGNs obtained with FOCAS on the Subaru Telescope with existing rest-frame UV emission lines, i.e., C IVλ1549, He IIλ1640, and C IIIλ1909, of a sample of 16 HzRGs and 6 additional X-ray selected type-2 AGNs, whose host stellar masses have been estimated in literature. We divided our sample in three stellar mass bins and calculated averaged emission-line flux ratios of C IVλ1549/He IIλ1640 and C IIIλ1909/C IVλ1549. Comparing observed emission-line flux ratios with photoionization model predictions, we estimated narrow line region (NLR) metallicities for each mass bin. We found that there is a positive correlation between NLR metallicities and stellar masses of type-2 AGNs at z ~ 3. This is the first indication that AGN metallicities are related to their hosts, i.e., stellar mass. Since NLR metallicities and stellar masses follow a similar relation as the MZR in star-forming galaxies at similar redshifts, our results indicate that NLR metallicities are related to those of the host galaxies. This study highlights the importance of considering lower-mass X-ray selected AGNs in addition to radio galaxies to explore the metallicity properties of NLRs at high redshift.
We present an investigation into how well the properties of the accretion flow on to a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure ...the characteristic spectral index, Γ, of a power-law energy distribution, over an energy range of 2-10 keV, for X-ray selected, broad-lined radio-quiet active galactic nuclei (AGN) up to z ∼ 2 in Cosmic Evolution Survey (COSMOS) and Extended Chandra Deep Field South (E-CDF-S). We test the previously reported dependence between Γ and black hole mass, full width at half-maximum (FWHM) and Eddington ratio using a sample of AGN covering a broad range in these parameters based on both the Mg ii and Hα emission lines with the later afforded by recent near-infrared spectroscopic observations using Subaru/Fibre Multi Object Spectrograph. We calculate the Eddington ratios, λEdd, for sources where a bolometric luminosity (L
Bol) has been presented in the literature, based on spectral energy distribution fitting, or, for sources where these data do not exist, we calculate L
Bol using a bolometric correction to the X-ray luminosity, derived from a relationship between the bolometric correction and L
X/L
3000. From a sample of 69 X-ray bright sources (>250 counts), where Γ can be measured with greatest precision, with an estimate of L
Bol, we find a statistically significant correlation between Γ and λEdd, which is highly significant with a chance probability of 6.59× 10−8. A statistically significant correlation between Γ and the FWHM of the optical lines is confirmed, but at lower significance than with λEdd indicating that λEdd is the key parameter driving conditions in the corona. Linear regression analysis reveals that Γ = (0.32 ± 0.05) log10λEdd + (2.27 ± 0.06) and Γ = (−0.69 ± 0.11) log10(FWHM/km s−1) + (4.44 ± 0.42). Our results on Γ-λEdd are in very good agreement with previous results. While the Γ-λEdd relationship means that X-ray spectroscopy may be used to estimate black hole accretion rate, considerable dispersion in the correlation does not make this viable for single sources, however could be valuable for large X-ray spectral samples, such as those to be produced by eROSITA.
The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses ...superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0 T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap.
Melting at the base of the Antarctic Ice Sheet influences ice dynamics and our ability to recover ancient climatic records from deep ice cores. Basal melt rates are affected by geothermal flux, one ...of the least constrained properties of the Antarctic continent. Estimates of Antarctic geothermal flux are typically regional in nature, derived from geological, magnetic or seismic data, or from sparse point measurements at ice core sites. We analyse ice-penetrating radar data upstream of South Pole revealing a ~100 km long and 50 km wide area where internal ice sheet layers converge with the bed. Ice sheet modelling shows that this englacial layer configuration requires basal melting of up to 6 ± 1 mm a
and a geothermal flux of 120 ± 20 mW m
, more than double the values expected for this cratonic sector of East Antarctica. We suggest high heat producing Precambrian basement rocks and hydrothermal circulation along a major fault system cause this anomaly. We conclude that local geothermal flux anomalies could be more widespread in East Antarctica. Assessing their influence on subglacial hydrology and ice sheet dynamics requires new detailed geophysical observations, especially in candidate areas for deep ice core drilling and at the onset of major ice streams.
We present rest-frame optical spectra of 12 “nitrogen-loud” quasars at z ~ 2.2, whose rest-frame ultraviolet (UV) spectra show strong nitrogen broad emission lines. To investigate their narrow-line ...region (NLR) metallicities, we measure the equivalent width (EW) of the O iiiλ5007 emission line: if the NLR metallicity is remarkably high, as suggested by the strong UV nitrogen lines, the O iiiλ5007 line flux should be very weak due to the low equilibrium temperature of the ionized gas owing to significant metal cooling. In the result we found that our spectra show moderate EW of the O iiiλ5007 line similar to general quasars. This indicates that nitrogen-loud quasars do not have extremely metal-rich gas clouds in NLRs. This suggests that strong nitrogen lines from broad-line regions (BLRs) originate from exceptionally high abundances of nitrogen relative to oxygen without very high BLR metallicities. This result indicates that broad emission lines of nitrogen are not good indicators of the BLR metallicity in some cases. On the other hand, we also investigate virial black hole masses and Eddington ratios by using the Hβ and C ivλ1549 lines for our sample. As a result, we found that black hole masses and Eddington ratios of nitrogen-loud quasars tend to be low and high relative to normal quasars, suggesting that nitrogen-loud quasars seem to be in a rapidly accreting phase. This can be explained in terms of a positive correlation between Eddington ratios and nitrogen abundances of quasars, which is probably caused by the connection between the mass accretion onto black holes and nuclear star formation.
To elucidate the mechanism of H2 production during ethanol steam reforming over Co and Co–Fe particle catalysts, the role of Fe in Co–Fe particle catalysts was examined. Acetaldehyde and CH4 are key ...intermediates during H2 production in ethanol steam reforming. We therefore compared the performances of Co–Fe particle catalysts and a Co particle catalyst with respect to acetaldehyde steam reforming and CH4 production. Over Co–Fe catalysts with molar Co–Fe ratios of 95:5 and 90:10, CH4 production during ethanol steam reforming could be suppressed by adding Fe to Co particle catalysts. A face-centered-cubic CoO phase was formed by adding Fe to the Co particle catalyst, and CH4 production over the face-centered-cubic CoO phase was less than that over Co metal. Consequently, CH4 production during ethanol steam reforming over the 95:5 and 90:10 Co–Fe catalysts was lower than CH4 production over the Co particle catalyst, and H2 production was enhanced.
•Ethanol steam reforming at 723 K over Co and Co–Fe particle catalysts was examined.•An fcc CoO phase was formed by adding Fe to Co particle catalyst.•Methanation of CO and CO2 over the fcc CoO phase was suppressed.•CH4 production during ethanol steam reforming over Co–Fe catalysts was suppressed.
We present a near-infrared (NIR) spectrum of WISE J104222.11+164115.3, an extremely red dust-obscured galaxy (DOG), which has been observed with the Long-slit Intermediate Resolution Infrared ...Spectrograph (LIRIS) on the 4.2m William Hershel Telescope. This object was selected as a hyper-luminous DOG candidate at z ∼ 2 by combining the optical and IR photometric data based on the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE), although its redshift had not yet been confirmed. Based on the LIRIS observation, we confirmed its redshift of 2.521 and total IR luminosity of log(LIR/L⊙) = 14.57, which satisfies the criterion for an extremely luminous IR galaxy (ELIRG). Moreover, we indicate that this object seems to have an extremely massive black hole with MBH = 1010.92 M⊙ based on the broad Hα line: the host stellar mass is derived as M⋆ = 1013.55 M⊙ by a fit of the spectral energy distribution. Very recently, it has been reported that this object is an anomalous gravitationally lensed quasar based on near-IR high-resolution imaging data obtained with the Hubble Space Telescope. Its magnification factor has also been estimated with some uncertainty (i.e., μ = 53−122). We investigate the ratio of the black hole to galaxy mass, which is less strongly affected by a lensing magnification factor, instead of the absolute values of the luminosities and masses. We find that the MBH/M⋆ ratio (i.e., 0.0140–0.0204) is significantly higher than the local relation, following a sequence of unobscured quasars instead of obscured objects (e.g., submillimeter galaxies) at the same redshift. Moreover, the LIRIS spectrum shows strongly blueshifted oxygen lines with an outflowing velocity of ∼1100 km s−1, and our Swift X-ray observation also supports that this source is an absorbed AGN with an intrinsic column density of NHint = 4.9 × 1023 cm−2 N H int =4.9× 10 23 cm −2 $ N_{\rm{H}}^{{\rm{int}}} = 4.9 \times {10^{23}}\,{\rm{c}}{{\rm{m}}^{ - 2}} $ . These results imply that WISE J104222.11+164115.3 is in a blow-out phase at the end of the buried rapid black hole growth.
We present new deep optical spectra of 9 high-z radio galaxies (HzRGs) at $z > 2.7$ obtained with FORS2 on VLT. These rest-frame ultraviolet spectra are used to infer the metallicity of the ...narrow-line regions (NLRs) in order to investigate the chemical evolution of galaxies in the high-z universe. We focus mainly on the $\ion{C}{iv}$/$\ion{He}{ii}$ and $\ion{C}{iii}$ /$\ion{C}{iv}$ flux ratios that are sensitive to both the gas metallicity and ionization parameter. Although the $\ion{N}{v}$ emission has been widely used to infer the gas metallicity, it is often too weak to be measured accurately for NLRs. In combining our new spectra with data from the literature, we examine the possible redshift evolution of the NLR metallicity for 57 HzRGs at $1 \la z \la 4$. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations, we find no significant metallicity evolution in NLRs of HzRGs, up to $z \sim 4$. Our results imply that massive galaxies had almost completed their chemical evolution at much higher redshift ($z > 5$). Finally, although we detect strong $\ion{N}{v}$ emission lines in 5 HzRGs at $z > 2.7$, we point out that high $\ion{N}{v}$/$\ion{He}{ii}$ ratios are not indicative of high metallicities but correspond to high ionization parameters of gas clouds in NLRs.
Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. ...Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.
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