low-Z Objects Research Articles

The CaFe Project: Optical Fe II and Near-infrared Ca II Triplet Emission in Active Galaxies. II. The Driver(s) of the Ca II and Fe II and Its Potential Use as a Chemical Clock

Abstract In this second paper in the series, we carefully analyze the observational properties of the optical Fe ii and near-IR Ca ii triplet in active galactic nuclei (AGNs), as well as the luminosity, black hole mass, and Eddington ratio in order to define the driving mechanism behind the properties of our sample. The Ca ii shows an inverse Baldwin effect, bringing out the particular behavior of this ion with respect to the other low-ionization lines such as H β. We performed a principal component analysis, where 81.2% of the variance can be explained by the first three principal components drawn from the FWHMs, luminosity, and equivalent widths. The first principal component (PC1) is primarily driven by the combination of black hole mass and luminosity with a significance over 99.9%, which in turn is reflected in the strong correlation of the PC1 with the Eddington ratio. The observational correlations are better represented by the Eddington ratio; thus, it could be the primary mechanism behind the strong correlations observed in the Ca ii–Fe ii sample. Since calcium belongs to the α-elements, the Fe ii/Ca ii flux ratio can be used as a chemical clock for determining the metal content in AGNs and trace the evolution of the host galaxies. We confirm the de-enhancement of the ratio Fe ii/Ca ii by the Eddington ratio, suggesting a metal enrichment of the BLR in intermediate-z with respect to low-z objects. A larger sample, particularly at z > 2, is needed to confirm the present results.

Implementation of Talbot–Lau x-ray deflectometry in the pulsed power environment using a copper X-pinch backlighter

A Talbot–Lau x-ray deflectometer can map electron density gradients in high energy density plasmas, as well as provide information about plasma elemental composition through single-image x-ray refraction and attenuation measurements. A new adaptation to a pulsed power environment used backlighting from copper X-pinches, allowing for electron density mapping of a low-Z object. Even though the X-pinch backlighter is not properly optimized for emitting x-rays in terms of source size and photon fluence, Moire fringe patterns with contrast up to 14% and fringe shift due to refraction on a beryllium object are obtained. Due to the proximity of the deflectometer with the X-pinch (∼6 cm), it is shown that a protective filter is required to avoid damage in the closest (i.e., source) grating due to both plasma debris and mechanical shock. Regarding grating survival, these did not show any damage due to the intense magnetic field or heating induced by plasma radiation. Electron density on beryllium was measured with a difference lower than 16%. The areal electron density mapping of the sample was limited by source size characteristics, in similarity to transmission radiography. These results show the potential of plasma electron density as well as material mapping through Talbot–Lau x-ray deflectometry in a pulsed power environment.

Demonstration of soft X-ray 3D scanning and modeling with a glass gas electron multiplier

A new detector, based on an optical-readout glass gas electron multiplier was developed for a soft X-ray CT scanner. Soft X-ray imaging (<20 keV) provides high-contrast images of low-Z elements, such as soft tissues. We model a three-dimensional (3D) copy of a low-Z object with a high-resolution gaseous detector and a 3D printer. The detector was used to acquire high-resolution images to reconstruct a 3D computed tomography (CT) image. As an example, a fine 3D X-ray CT image of a hornet was reconstructed with high contrast. The 3D CT data were converted into 3D computer-automated design data, and a copy of the scanned object was printed with a commercial 3D printer. Overall, this work demonstrates a new use of gaseous detectors, rapid and precise soft X-ray 3D scanning, and modeling of soft tissues.

Dense gas in low-metallicity galaxies

Stars form out of the densest parts of molecular clouds. Far-IR emission can be used to estimate the star formation rate (SFR) and high dipole moment molecules, typically HCN, trace the dense gas. A strong correlation exists between HCN and far-IR emission, with the ratio being nearly constant, over a large range of physical scales. A few recent observations have found HCN to be weak with respect to the far-IR and CO in subsolar metallicity (low-Z) objects. We present observations of the Local Group galaxies M 33, IC 10, and NGC 6822 with the IRAM 30 m and NRO 45 m telescopes, greatly improving the sample of low-Z galaxies observed. HCN, HCO+, CS, C2H, and HNC have been detected. Compared to solar metallicity galaxies, the nitrogen-bearing species are weak (HCN, HNC) or not detected (CN, HNCO, N2H+) relative to far-IR or CO emission. HCO+ and C2H emission is normal with respect to CO and far-IR. While 13CO is the usual factor 10 weaker than 12CO, C18O emission was not detected down to very low levels. Including earlier data, we find that the HCN/HCO+ ratio varies with metallicity (O/H) and attribute this to the sharply decreasing nitrogen abundance. The dense gas fraction, traced by the HCN/CO and HCO+/CO ratios, follows the SFR but in the low-Z objects the HCO+ is much easier to measure. Combined with larger and smaller scale measurements, the HCO+ line appears to be an excellent tracer of dense gas and varies linearly with the SFR for both low and high metallicities.

Quantitative analysis of the field of view for X-ray differential phase contrast imaging

Grating-based X-ray differential phase contrast imaging provides excellent image contrast for low-Z objects that cannot be acquired by conventional X-ray imaging, which has great potential applications in the early diagnosis of cancer and non-destructive detections of low-Z materials and devices. Large field of view imaging is a crucial factor for this technology from the laboratory to practical application. For the objective need of large field of view, on the basis of the Fresnel diffraction theory and the structure characteristics of gratings, we establish a quantitative physical model to analyze the factors that affect the imaging field of view and give a feasible way for large imaging field of view. This work provides a theoretical basis for the large field of view grating-based X-ray differential phase contrast imaging in the future.

Fast Neutron Tomography of Low-Z Object in High-Z Material Shielding

The technique and first results of Fast Neutron Tomography (FNCT) experiments are presented which are performed at the accelerator facility of PTB, Germany. A high-intensity neutron beam of broad spectral distribution with an average energy of 5.5 MeV, was produced by 11.5 MeV deuterons impinging upon a thick beryllium target. The capability of FNCT for high contrast imaging of low-Z materials embedded in thick high-Z shielding materials is demonstrated, which is superior to more conventional high-energy X-ray imaging techniques. For demonstrating the method special test objects were prepared: One consisted of an assembled polyethylene cylinder with holes of various diameters and directions drilled in its surface and inner parts. The plastic phantom was inserted into lead cylinders of different thicknesses. The detector system consisted of a plastic scintillator along with a dedicated optics, image-intensifier and a CCD camera. Two scintillator screens were compared: a bulk plastic scintillator screen and a fibres optical scintillator screen. The tomographic scans were taken in two geometrical configurations: cone beam and semi-fan beam configuration. The image quality favours the semi-fan beam configuration which on the other hand is more time consuming The obtained tomographic images and a comparison of the imaging quality between the different experimental conditions will be presented.

Constraints on dark energy with the LOSS SN Ia sample

We present a cosmological analysis of the Lick Observatory Supernova Search (LOSS) Type Ia supernova (SN Ia) photometry sample introduced by Ganeshalingam et al. (2010). These SNe provide an effective anchor point to estimate cosmological parameters when combined with datasets at higher redshift. The data presented by Ganeshalingam et al. (2010) have been rereduced in the natural system of the KAIT and Nickel telescopes to minimise systematic uncertainties. We have run the light-curve-fitting software SALT2 on our natural-system light curves to measure light-curve parameters for LOSS light curves and available SN Ia datasets in the literature. We present a Hubble diagram of 586 SNe in the redshift range z=0.01-1.4 with a residual scatter of 0.176 mag. Of the 226 low-z objects in our sample, 91 objects are from LOSS, including 45 SNe without previously published distances. Assuming a flat Universe, we find that the best fit for the dark energy equation-of-state parameter w = -0.86^+0.13_-0.16 (stat) +- 0.11 (sys) from SNe alone, consistent with a cosmological constant. Our data prefer a Universe with an accelerating rate of expansion with 99.999% confidence. When looking at Hubble residuals as a function of host-galaxy morphology, we do not see evidence for a significant trend, although we find a somewhat reduced scatter in Hubble residuals from SNe residing within a projected distance < 10 kpc of the host-galaxy nucleus (\sigma = 0.156 mag). We find that Hubble residuals do not correlate with the expansion velocity of Si II \lambda 6355 measured in optical spectra near maximum light. Our data are consistent with no presence of a local "Hubble bubble." Improvements in cosmological analyses within low-z samples can be achieved by better constraining calibration uncertainties in the zero points of photometric systems.

Fast X-Ray Phase-Contrast Imaging Using High Resolution Detector

X-ray phase-contrast imaging is a potential nondestructive testing and diagnostic technology in medicine, biology and materials science. It provides high sensitivity and contrast of weakly absorbing low-Z objects by measuring phase shifts of the X-rays. In this paper, we propose a novel phase-contrast imaging method using only one absorption grating and a high-resolution detector. The intensity distribution downstream of the grating is recorded and analyzed by the high-resolution detector directly. We use a spatial phase demodulation method to retrieve the phase information. Only one image is needed. Numerical simulations are performed to validate that the setup of our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming and the unnecessary dose.

Differential Phase-Contrast Imaging Experimental System Under the Incoherent Condition With Conventional X-Ray Tubes

Hard X-ray phase-contrast imaging provides high sensitivity of weakly absorbing low-Z objects in medicine, biology and materials science. The traditional viewpoint is that coherent X-rays and coherent measurements are essential to hard X-ray phase-contrast imaging. In this paper, a differential phase-contrast imaging experimental system is introduced to obtain refraction-angle images based on the theory of infinite fringe moire deflectometry under the incoherent condition with weakly coherent X-rays from the conventional X-ray tube without Talbot effect. The experiments on material and biological samples prove that differential phase-contrast imaging can be realized under more relaxed condition.

Subaru Deep Survey. IV. Discovery of a Large-Scale Structure at Redshift ≃5

We report the discovery of a large-scale structure of Lyα emitters (LAEs) at z = 4.86 based on wide-field imaging with the prime-focus camera (Suprime-Cam) on the Subaru Telescope. We observed a 25' × 45' area of the Subaru Deep Field in a narrow band (NB711, λc = 7126 A and FWHM = 73 A) together with R and i'. We isolate from these data 43 LAE candidates down to NB711 = 25.5 mag using color criteria. Follow-up spectroscopy of five candidates suggests the contamination by low-z objects to be ~20%. We find that the LAE candidates are clustered in an elongated region on the sky of 20 Mpc in width and 50 Mpc in length at z = 4.86, which is comparable in size to present-day large-scale structures (we adopt H0 = 70 km s-1 Mpc-1, Ω0 = 0.3, and λ0 = 0.7). This elongated region includes a circular region of 12 Mpc radius of higher surface overdensity (δΣ = 2), which may be the progenitor of a cluster of galaxies. Assuming this circular region to be a sphere with a spatial overdensity of 2, we compare our observation with predictions by cold dark matter models. We find that an Ω0 = 0.3 flat model with σ8 = 0.9 predicts the number of such spheres consistent with the observed number (one sphere in our survey volume) if the bias parameter of LAEs is b 6. This value suggests that the typical mass of dark halos hosting LAEs at z 5 is of the order of 1012 M☉. Such a large mass poses an interesting question about the nature of LAEs.