arXiv subjects

A. Finoguenov

Publications and source records attributed to A. Finoguenov.

241 records · Page 14Linked to original sources

arXiv2000

XMM-Newton observation of the Lockman Hole; I. The X-ray Data

We report on the first deep X-ray survey with the XMM-Newton observatory during the performance verification phase. The field of the Lockman Hole, one of the best studied sky areas over a very wide range of wavelengths, has been observed. A total of ~100 ksec good exposure time has been accumulated. Combining the images of the European Photon Imaging Camera (EPIC) detectors we reach a flux limit of 0.31, 1.4 and 2.4 X 10^{-15} erg cm^{-2} s^{-1}, respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of 10 arcmin we detect 148, 112 and 61 sources, respectively. The log(N)-log(S) relation in the three bands is compared with previous results. In particular in the 5-10 keV band these observations present the deepest X-ray survey ever, about a factor 20 more sensitive than the previous BeppoSAX observations. Using X-ray spectral diagnostics and the set of previously known, spectroscopically identified ROSAT sources in the field, the new sources can be classified. XMM-Newton detects a significant number (~40%) of X-ray sources with hard, probably intrinsically absorbed X-ray spectra, confirming a prediction of the population synthesis models for the X-ray background.

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arXiv2000

Chandra Observation of M84, Radio Lobe Elliptical in Virgo cluster

We analyzed a deep Chandra observation of M84, a bright elliptical galaxy in the core of the Virgo cluster. We find that the spatial distribution of the soft X-ray emission is defined by the radio structure of the galaxy. In particular we find two low density regions associated with the radio lobes and surrounded by higher density X-ray filaments. In addition to a central AGN and a population of galactic sources, we find a diffuse hard source filling the central 10 kpc region. Since the morphology of the hard source appears round and is different from that seen in the radio or in soft X-rays, we propose that it is hot gas heated by the central AGN. Finally, we find that the central elemental abundance in the X-ray gas is comparable to that measured optically.

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arXiv2000

An ASCA Study of the Heavy Element Distribution in Clusters of Galaxies

We perform a spatially resolved X-ray spectroscopic study of a set of 11 relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a method which corrects for the energy dependent effects of the ASCA PSF based on ROSAT images, we constrain the spatial distribution of Ne, Si, S and Fe in each cluster. Theoretical prescriptions for the chemical yields of Type Ia and II supernovae, then allow determination of the Fe enrichment from both types of supernovae as a function of radius within each cluster. Using optical measurements from the literature, we also determine the iron mass-to-light ratio (IMLR) separately for Fe synthesized in both types of supernovae. For clusters with the best photon statistics, we find that the total Fe abundance decreases significantly with radius, while the Si abundance is either flat or decreases less rapidly, resulting in an increasing Si/Fe ratio with radius. This result indicates a greater predominance of Type II SNe enrichment at large radii in clusters. We suggest that the high Si/Fe ratios in the outskirts of rich clusters may arise from enrichment by Type II SNe released to ICM via galactic star burst driven winds. Abridged.

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arXiv2000

SN Ia Enrichment in Virgo Early-Type Galaxies from ROSAT and ASCA Observations

We analyzed nine X-ray bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profile and abundances of Mg, Si and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of a cooler region at the galaxy center. We present new evidence for iron abundance gradients in NGC4472 and NGC4649 and confirm the previous results on NGC4636. Mg and Si abundance gradients on average are flatter compared to those of iron and correspond to an underabundance of alpha-process elements at high Fe values, while at low iron, the element ratios favor enrichment by type II SNe. We explain the observed trend by the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia (Kobayashi et al. 1998). Our results imply a cut-off metallicity in the range 0.07-0.3 solar and require a lower limit of 0.3 solar on the Fe contribution of SN Ia. We estimate an SN Ia rate at the centers of the brightest galaxies in our sample of ~0.08 (h_75)^3 SNu (supernova units). The rates inferred from optical searches should be corrected for the presence of `faint' SN Ia events, since these release limited metals and therefore do not contribute significantly to the measured metallicity in the X-ray gas. With this correction the present-epoch SN Ia rate in early-type galaxies is 0.10+/-0.06 (h_75)^2 SNu (Cappellaro et al. 1997) and is therefore comparable with the X-ray estimates. Abridged.

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arXiv1999

Constraining the Role of SN Ia and SN II in Galaxy Groups by Spatially Resolved Analysis of ROSAT and ASCA Observations

We present the results of modelling the distribution of gas properties in the galaxy groups HCG51, HCG62 and NGC5044, and in the poor cluster AWM7, using both ASCA SIS and ROSAT data. The spectral quality of the ASCA data allows the radial distribution in the abundances of several elements to be resolved. In all systems apart from HCG51, we see both central cooling flows, and a general decline in metal abundances with radius. The ratio of iron to alpha-element abundances varies significantly, and in comparison with theoretical supernova yields, indicates a significant contribution to the metal abundance of the intergalactic medium (IGM) from type Ia supernovae. This is seen both within the groups, and also throughout much of the cluster AWM7. The total energy input into the IGM from supernovae can be calculated from our results, and is typically 20-40 per cent of the thermal energy of the gas, mostly from SNe II. Our results support the idea that the SN II ejecta have been more widely distributed in the IGM, probably due to the action of galaxy winds, and the lower iron mass to light ratio in groups suggests that some of this enriched gas has been lost altogether from the shallower potential wells of the smaller systems.

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arXiv1998

Stellar Metallicities and SNIa Rates in the Early-type Galaxy NGC5846 from ROSAT and ASCA Observations

In this paper we analyze the diffuse X-ray coronae surrounding the elliptical galaxy NGC5846, combining measurements from two observatories, ROSAT and ASCA. We map the gas temperature distribution and find a central cool region within an approximately isothermal gas halo extending to a radius of about 50 kpc, and evidence for a temperature decrease at larger radii. With a radially falling temperature profile, the total mass converges to 9.6+/-1.0 10^12 Msun at ~230 kpc radius. Using the spectroscopic measurements, we also derive radial distributions for the heavy elements silicon and iron and find that the abundances of both decrease with galaxy radius. The mass ratio of Si to Fe lies between the theoretical predictions for element production in SN Ia and SN II, suggesting an important role for SN Ia, as well as SN II, for gas enrichment in ellipticals. Using the SN Ia yield of Si, we set an upper limit of 0.012 SNU for the SN Ia rate at radii >50 kpc, which is independent of possible uncertainties in the iron L-shell modeling. We compare our observations with the theoretical predictions for the chemical evolution of ellipticals, taken from Matteucci & Gibson (1995). We conclude that the metal content in stars, if explained by the star formation duration, requires a significant decline in the duration of star formation with galaxy radius, ranging from ~1 Gyr at the center to ~0.01 Gyr at 100 kpc radius. Alternatively, the decline in metallicity with galaxy radius may be caused by a similar drop with radius in the efficiency of star formation. Based on the Si and Fe measurements presented in this paper, we conclude that the latter scenario is preferred, unless a dependence of the SN Ia rate on stellar metallicity is invoked. (Abridged).

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arXiv1996

A Comparison of the ISM in Ellipticals to the Hot Gas in a Dense Group from Combined ROSAT and ASCA Observations

We analyze diffuse X-ray emission from NGC4649, NGC5044 and NGC5846, combining data from two X-ray observatories, ROSAT and ASCA. With ASCA, we perform a detailed analysis of the X-ray emission which properly accounts for the ASCA PSF and also include a 3-dimensional source model. All three sources exhibit cooling flows in their centers. From the derived abundances of Si, S and Fe, we conclude that NGC5044 (a dense group of galaxies) was able to retain significant amounts of gas during an early galaxy wind phase. Fe abundance in NGC5846 (normal E galaxy) corresponds to current SNIa rate of ~0.2 of Tammann rate, while low Fe mass in NGC4649 (normal E in the Virgo cluster) could be an environmental effect.

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