We present the SEDs of a hard X-ray selected sample containing 136 sources with FSUB2-10keV/SUB>10SUP-14/SUP erg cmSUP-2/SUP sSUP-1/SUP 132 are AGNs. The sources are detected in a 1 degSUP2/SUP area ...of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with sigma(1+z)=0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17SUP+9/SUPSUB-6/SUB% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33SUP+6/SUPSUB-1/SUB%) and AGN2 (50SUP+6/SUPSUB-11/SUB%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low LSUB3-20mum/SUB/LSUPcorr/SUPSUB0.5-10keV/SUB ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E>10 keV are too faint to be detected even in the deepest current radio surveys.
This study numerically investigated the improvement of heat transmission to phase change material (PCM) paraffin wax in a triangular cell with and without fins. The enthalpy–porosity combination was ...quantitatively evaluated using the ANSYS/FLUENT 20 program. Materials with the phase shifts of paraffin wax were used in this study (RT42). According to the study findings, fins significantly accelerate the melting process and decrease the time required to finish it. The time difference between melting with and without fins is 125%. Moreover, the inclusion of v-shaped fins contributed to a 200% reduction in the melting process time. Thus, the use of v-shaped fins facilitates faster heat transfer to and from the applications wherein the phase change materials are used.
In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven ...groups/clusters at z∼ 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter-American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z∼ 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z= 0 and z∼ 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity.
In this paper we focus on the much debated Butcher-Oemler effect: the increase with redshift of the fraction of blue galaxies in clusters. Considering a representative cluster sample made of seven ...groups/clusters at z similar to 0.35, we have measured the blue fraction from the cluster core to the cluster outskirts and the field mainly using wide-field Cerro Tololo Inter-American Observatory images. This sample represents a random selection of a volume complete X-ray selected cluster sample, selected so that there is no physical connection with the studied quantity (blue fraction), to minimize observational biases. In order to statistically assess the significance of the Butcher-Oemler effect, we introduce the tools of Bayesian inference. Furthermore, we have modified the blue fraction definition in order to take into account the reduced age of the Universe at higher redshifts, because we should no longer attempt to reject an unphysical universe in which the age of the Universe does depend on redshift, whereas the age of its content does not. We have measured the blue fraction from the cluster centre to the field and we find that the cluster affects the properties of the galaxies up to two virial radii at z similar to 0.35. Data suggest that during the last 3 Gyr no evolution of the blue fraction, from the cluster core to the field value, is seen beyond that needed to account for the varying age with the redshift of the Universe and of its content. The agreement of the radial profiles of the blue fraction at z= 0 and z similar to 0.35 implies that the pattern infall did not change over the last 3 Gyr, or, at least, its variation has no observational effect on the studied quantity.
Phase change materials (PCMs) are capable of storing and removing a significant quantity of latent heat from heating storage systems. PCMs such as paraffin wax are used because they store a large ...amount of energy in a relatively small space while maintaining a nearly constant temperature between solidification and melting. An investigation into the numerical effects of increases in heat transmission to paraffin wax (RT58), within a half-cylindrical cell which included a range of copper rods, was conducted to determine their impact. The enthalpy-porosity combination program ANSYS/FLUENT 16, was used in this study to ascertain levels of heat transmission that occur when varying numbers of copper rods are inserted in the container, as well as the impact this has on melting time. The findings show that increasing the number of rods results in a decrease in melting time. When comparing cells with three and five copper rods against a cell with no rods, the melting time is reduced by 45% and 52%, respectively. The findings of this research can benefit thermal energy storage applications such as cooling microelectronic devices, and storing and discharging thermal energy.
Enhancing heat transfer is crucial for improving the performance of heat transfer applications. Therefore, a novel method is proposed in this study for improving the heat transfer using a new rib ...geometry within a circular channel. The performance of the novel method was evaluated by comparing the results of the channel with ribs with that of an ordinary channel. In this study, numerical investigations were conducted on the temperature distribution and fluid flow properties of a 500 mm tube with an external diameter of 50 mm and an internal surface of 47 mm. To evaluate the effects of the ribs on the heat transfer via the tube wall, the tube was maintained at a steady temperature of 673 K, and the Reynolds number (Re) was set in the range of 1000–20000. Different cases were simulated using CFD-FLUENT (v. 16.1). For the three cases, three types of ribs (7 in total) with triangular transverse sections of 5 mm were set 62.5 mm apart in the tube. Subsequently, the turbulent parameters (k, ε) affecting the turbulent flow were evaluated. Moreover, the heat transfer coefficient and friction coefficient of the tube with ribs were calculated using the enhancement technique and compared with those of the plain tube. It was observed that the ribs inside the tube increased the temperature of the cooling air in the first, second, and third cases by 6.25%, 12.5%, and 17.5%, respectively. Furthermore, the difference in the velocity and temperature distribution across the centreline of the tube was observed for all three cases and a smooth tube. It was observed that the heat flow rate increased, particularly around Re = 14,000, in the ribbed tube. The tube with ribs exhibited a 90% increase in the flow rate compared to the flow rate in the tube with no ribs. The tube with ribs also exhibited better performance in terms of turbulent flow.
•A theoretical study to improvement of heat transfer through the use of new geometry of ribs inside a circular channel.•CFD predictions for the Case of circular channel tube with ribs and compared against the tube without ribs.•Study effect of fixing three types of ribs inside a smooth channel with a new geometry.•Comparing the friction factor ratios with varying Reynolds numbers using numerical simulations.
Aims. Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X- ray flux, luminosity and redshift within a hard X-ray ...selected sample with wide multiwavelength coverage. Methods. We selected a sample of 136 X-ray sources detected at a significance of \geq3 \sigma in the 2-10 keV band ( F sub(2-10) \ga 10 super(-14) erg cm super(-2) s super(-1)) in a similar to 1 deg super(2) area in the XMM Medium Deep Survey (XMDS). The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data from the SWIRE survey. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical-IR identification. The observed optical and IR spectral energy distributions of all identified sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. X-ray spectral analysis is performed individually for sources with a sufficient number of counts and using a stacking technique for subsamples of sources at different flux levels. Hardness ratios are used to estimate X-ray absorption in individual weak sources. Results. 70% of the AGN are fitted by a type 2 AGN or a star forming galaxy template. We group them together in a single class of "optically obscured" AGN. These have "red" optical colors and in about 60% of cases show significant X-ray absorption (N_{\rm H} > 10 super(22) cm super(-2)). Sources with SEDs typical of type 1 AGN have "blue" optical colors and exhibit X-ray absorption in about 30% of cases. The stacked X-ray spectrum of obscured AGN is flatter than that of type 1 AGN and has an average spectral slope of \Gamma = 1.6. The subsample of objects fitted by a star forming galaxy template has an even harder stacked spectrum, with \Gamma \sim 1.2- 1.3. The obscured fraction is larger at lower fluxes, lower redshifts and lower luminosities. X-ray absorption is less common than "optical" obscuration and its incidence is nearly constant with redshift and luminosity. This implies that at high luminosities X-ray absorption is not necessarily related to optical obscuration. The estimated surface densities of obscured, unobscured AGN and type 2 QSOs are respectively 138, 59 and 35 deg super(-2) at 10 logical and --> F > 10 super(-14) erg cm super(-2) s super(-1).
Aims.Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods.We present a ...sample of 99 spectroscopically identified (R ≤ 22 mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (≥3σ) in the 2-10 keV band with fluxes between 8 $\times$ 10-15 and 8 $\times$ 10-14 erg s-1 cm-2, and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme. Results.Introducing the fourfold point correlation coefficient r, we find a mild correlation between the X-ray and the optical classifications (r = 0.28), as up to 32 X-ray sources out of 99 have differing X-ray and optical classifications: on one hand, 10% of the type 1 sources (7/32) present broad emission lines in their optical spectra and strong absorption (N$_{{\rm H}}$$^{{\rm int}}$ ≥ 1022 cm-2) in the X-rays. These objects are highly luminous AGN lying at high redshift and thus dilution effects by the host galaxy light are totally ruled out, their discrepant nature being an intrinsic property instead. Their X-ray luminosities and redshifts distributions are consistent with those of the unabsorbed X-ray sources with broad emission lines (L2-10 ~ 4 $\times$ 1044 erg s-1; z ~ 1.9). On the other hand, 25/32 are moderate luminosity (L2-10 ≤ 5 $\times$ 1043 erg s-1) AGN, which are both unabsorbed in the X-rays and only present narrow emission lines in their optical spectra. Based on their line ratios in the optical, the majority of them have an optical spectrum which is more representative of the host galaxy rather than of a reddened AGN. We finally infer that dilution of the AGN by the host galaxy seems to account for their nature. 5/25 have been defined as Seyfert 2 based on their optical spectra. In conclusion, most of these 32 discrepant cases can be accounted for by the standard AGN unified scheme, as its predictions are not met for only 12% of the 99 X-ray sources.
The XMM-LSS survey : The XMDS/VVDS 4σ catalogue CHIAPPETTI, L; TAJER, M; LE FEVRE, O ...
Astronomy and astrophysics (Berlin),
08/2005, Letnik:
439, Številka:
1
Journal Article, Web Resource
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Odprti dostop
We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed ...and used to derive a well defined catalogue of X-ray sources. The present catalogue is limited to a sub-sample of 286 sources detected at 4 sigma in the 1 deg super(2) area covered by the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide optical and radio identifications. We also discuss the X-ray properties of a larger X-ray sample of 536 sources detected at >4 sigma in the full 3 deg super(2) area of the XMM Medium Deep Survey (XMDS) independently of the optical identification. We also derive the log N - log S relationship for a sample of more than one thousand sources that we discuss in the context of other surveys at similar fluxes.
We obtained a sample of 143 normal galaxies with X-ray luminosity in the range $10^{38}{-}10^{43}$ erg s-1 from the cross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW–HRI) Catalogue ...with the Lyon-Meudon Extragalactic Database (LEDA). We find that the average X-ray properties of this sample are in good agreement with those of other samples of galaxies in the literature. We selected a complete flux limited serendipitous sample of 32 galaxies from which we derived the $\log N-\log S$ distribution of normal galaxies in the flux range $1.1{-} 110 \times 10^{-14}$ erg cm-2 s-1. The resulting distribution is consistent with the Euclidean -1.5 slope. Comparisons with other samples, such as the Extended Medium Sensitivity Survey, the ROSAT All Sky Survey, the XMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate that the $\log N -\log S$ distribution of normal galaxies is consistent with a Euclidean slope over a flux range of about 6 decades.
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