J. Nevalainen - Academia.edu (original) (raw)
Papers by J. Nevalainen
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of ... more In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of a new hypothetical instrument design. These simulations are folded through this X-ray spectrometer having a moderate size circular field of view (FoV)) of 1.6 • . This SCXM (Solar Coronal X-ray Mapper) is designed to compose of a single pixel silicon PIN detector equipped with a single reflection double frustum X-ray optics. A moderate FoV would enable a morphological study of the expanded X-ray emission from the solar corona during a high activity of the Sun. The main scientific task of SCXM would be the mapping of the coronal X-ray emission, i.e. to resolve the radial distribution of the X-ray surface brightness around the Sun. These kind of off-limb observations would help to interpret the coronal plasma diagnostics as a function of the elongation angle.
Physica Scripta, 1998
ABSTRACT We present simulated SIXA spectra of the hottest known cluster of galaxies Abell 2163. S... more ABSTRACT We present simulated SIXA spectra of the hottest known cluster of galaxies Abell 2163. SIXA is an array of solid state detectors located in the focal plane of one of the two SODART telescopes onboard SPECTRUM-RÖNTGEN-GAMMA. We hereby demonstrate the capabilities of SIXA to perform spatially resolved spectroscopy of hot clusters. In a 30 ksec exposure, the temperature of the hot gas can be reliably derived from the central pixel as well as in the 2nd and 3rd pixel rings whereas the iron abundance can be determined in the central pixel and the 2nd pixel ring. SIXA will thus significantly improve current temperature and abundance measurements of the hot gas in clusters.
Physica Scripta, 1998
Combined ASCA and SIGMA data of 1E1740.7-2942 during its standard state (September 1993 and 1994)... more Combined ASCA and SIGMA data of 1E1740.7-2942 during its standard state (September 1993 and 1994) were successfully fitted with a two-phase model ISM (iterative scattering method) [1]. The classical cold accretion disk does not extend up to the innermost stable orbit, but is truncated at 30GM=c 2 . A hot inner disk has electron temperature T e 60 keV and radial Thomson optical depth τ 2:4. The cold disk radiates 40 % of the total luminosity withṀ 0:04Ṁ Edd of 10M .
Nuclear Physics B - Proceedings Supplements, 1999
We combine measurements of the Hubble constant in MlOO, M96, NGC 5253 and IC 4182 including the c... more We combine measurements of the Hubble constant in MlOO, M96, NGC 5253 and IC 4182 including the correction due to the metallicity dependence of the period-luminosity relation of Cepheids, as determined by Beaulieu et al. [l] and Sasselov et al. (21. We pay special attention to error correlations.
Astronomy & Astrophysics, 2015
ABSTRACT We propose a new approach to the missing baryons problem. Building on the common assumpt... more ABSTRACT We propose a new approach to the missing baryons problem. Building on the common assumption that the missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM), we further assumed here that the galaxy luminosity density can be used as a tracer of the WHIM. The latter assumption is supported by our finding of a significant correlation between the WHIM density and the galaxy luminosity density in the hydrodynamical simulations of Cui et al. (2012). We further found that the fraction of the gas mass in the WHIM phase is substantially (by a factor of sim\simsim1.6) higher within the large scale galactic filaments, i.e. sim\simsim70\%, compared to the average in the full simulation volume of sim\simsim0.1\,Gpc$^3$. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with linear: deltarmwhim,=,0.7,pm,0.1,times,deltamathrmLD0.9pm0.2\delta_{\rm whim}\,=\,0.7\,\pm\,0.1\,\times\,\delta_\mathrm{LD}^{0.9 \pm 0.2}deltarmwhim,=,0.7,pm,0.1,times,deltamathrmLD0.9pm0.2. We applied our procedure to the line of sight to the blazar H2356-309 and found evidence for the WHIM in correspondence of the Sculptor Wall (z sim\simsim0.03 and logNH\log{N_H}logNH = 19.9+0.1−0.319.9^{+0.1}_{-0.3}19.9+0.1−0.3) and Pisces-Cetus superclusters (z sim\simsim0.06 and logNH\log{N_H}logNH = 19.7+0.2−0.319.7^{+0.2}_{-0.3}19.7+0.2−0.3), in agreement with the redshifts and column densities of the X-ray absorbers identified and studied by Fang et al. (2010) and Zappacosta et al. (2010). This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust in estimating the WHIM density. The signal that we detected cannot originate from the halos of the nearby galaxies since they cannot account for the large WHIM column densities that our method and X-ray analysis consistently find in the Sculptor Wall and Pisces-Cetus superclusters.
Astronomy & Astrophysics, 2015
ABSTRACT Cosmological constraints from clusters rely on accurate gravitational mass estimates, wh... more ABSTRACT Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological constraints. This is of special interest in the light of the tension between the Planck results of the primary temperature anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts analyses. We quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, we assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM temperatures through spectral fitting in the same, mostly isothermal, regions and compare them. Our work is an extension to a previous one using X-ray clusters by the IACHEC. Performing spectral fitting in the full energy band we find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. We demonstrate that effects like multitemperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. We conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints.
The temperature of X-ray emitting gas T X is often used to infer the total mass of galaxy cluster... more The temperature of X-ray emitting gas T X is often used to infer the total mass of galaxy clusters (under the assumption of hydrostatic equilibrium). Unfortunately, XMM-Newton and Chandra observatories measure inconsistent temperatures for the same gas, due to uncertain instrumental calibration. We translate the relative bias in temperature measurements of Schellenberger et al. (2014) into a bias on inferred mass for a sample of clusters with homogeneous weak lensing (WL) masses, in order to simultaneously examine the hydrostatic bias and instrument calibration. found consistent WL and Chandra hydrostatic X-ray masses for a sample of clusters at z∼0.5 and masses of a few 10 14 M . Re-evaluating the latter, we find their XMM-Newton masses to be lower by b xcal = 15-20% than their Chandra masses. At the massive end ( 5 · 10 14 M ), the XMM-Newton masses are ∼ 35 % lower than the WL masses. Assuming that the true hydrostatic bias is 20 %, as indicated by simulations, our results for the massive end indicate that Chandra's calibration of the energy dependence of the effective area is more accurate than XMM-Newton's. However, the opposite appears to be true at the low mass end, unless the hydrostatic bias vanishes there, although larger samples are required to firmly establish this trend.
The Astrophysical Journal, 2000
We calibrate the galaxy cluster mass -temperature relation using the temperature profiles of intr... more We calibrate the galaxy cluster mass -temperature relation using the temperature profiles of intracluster gas observed with ASCA (for hot clusters) and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters for which the total masses are derived assuming hydrostatic equilibrium. The sample provides data on cluster X-ray emission-weighted cooling flow-corrected temperatures and total masses up to r 1000 . The resulting M-T scaling in the 1-10 keV temperature range is M 1000 = 1.23 ± 0.20 10 15 h −1 50 M ⊙ T z=0 10 keV 1.79±0.14 with 90% confidence errors, or significantly (99.99% confidence) steeper than the self-similar relation M ∝ T 3/2 . For any given temperature, our measured mass values are significantly smaller compared to the simulation results of Evrard et al. (1996) that are frequently used for mass-temperature scaling. The higher-temperature subsample (kT ≥ 4 keV) is consistent with M ∝ T 3/2 , allowing the possibility that the self-similar scaling breaks down at low temperatures, perhaps due to heating by supernovae that is more important for low-temperature groups and galaxies as suggested by earlier works.
The Astrophysical Journal, 2007
We analyze four XMM-Newton galaxy clusters (Abell 1795, Abell S1101, Abell 1835 and MKW 3s) in or... more We analyze four XMM-Newton galaxy clusters (Abell 1795, Abell S1101, Abell 1835 and MKW 3s) in order to test whether their soft X-ray excess emission in the 0.2-0.5 keV band as reported by maintains after application of current knowledge of the XMM-Newton background and calibration. In this context, we examine the recent claim that the XMM-Newton sub-Galactic H I column density, and the accompanying soft excess continuum emission in the 0.2-0.5 keV band, is an artifact of an incorrect background subtraction. We show that since the cluster regions under scrutiny are within 500 kpc of the bright cluster center, the X-ray background level is negligible compared to the cluster emission level. Thus, a "matched" background subtraction á la and more traditional background subtraction methods (á la yield the same results for the H I measurements in the source-dominated central cluster regions. Thus, at least in the central 500 kpc regions of the studied clusters, the reported soft excess is not a background artifact. On the other hand, the same simple background-to-cluster flux ratio argument allows the possibility that the reported O VII line emission in the 0.5-0.6 keV band in the outskirts of some of these clusters ) is due to the geocoronal and heliospheric solar wind charge exchange . We also study the possibility that the incomplete calibration information in the early phase of the XMM-Newton mission resulted in sub-Galactic H I column density, which was interpreted with the presence of a soft excess emitter. Our re-analysis of the four XMM-Newton observations with the MOS instruments yields evidence for the soft excess in all clusters. However, using the PN instrument, the best-fit H I column densities in Abell 1795, Abell 1835 and MKW 3s are at odds with the 2003 analysis of Kaastra et al., and in general agreement with those measured from 21 cm data in the direction of the clusters . Abell S1101 continues to feature a sub-galactic NH also with the PN instrument, indicative of soft excess emission in both EPIC detectors. These differences are compatible with the current level of uncertainty in the calibration of both instruments.
The Astrophysical Journal, 2000
We constrain the total mass distribution in the cluster A3571, combining spatially resolved ASCA ... more We constrain the total mass distribution in the cluster A3571, combining spatially resolved ASCA temperature data with ROSAT imaging data with the assumption that the cluster is in hydrostatic equilibrium. The total mass within r 500 (1.7 h −1 50 Mpc) is M 500 = 7.8 +1.4 −2.2 ×10 14 h −1 50 M ⊙ at 90% confidence, 1.1 times smaller than the isothermal estimate. The Navarro, Frenk & White "universal profile" is a good description of the dark matter density distribution in A3571. The gas density profile is shallower than the dark matter profile, scaling as r −2.1 at large radii, leading to a monotonically increasing gas mass fraction with radius. Within r 500 the gas mass fraction reaches a value of f gas = 0.19 +0.06 −0.03 h −3/2 50 (90% confidence errors). Assuming that this value of f gas is a lower limit for the the universal value of the baryon fraction, we estimate the 90% confidence upper limit of the cosmological matter density to be Ω m < 0.4.
The Astrophysical Journal, 2004
We study the X-ray emission in a sample of galaxy clusters using the BeppoSAX PDS instrument in t... more We study the X-ray emission in a sample of galaxy clusters using the BeppoSAX PDS instrument in the 20 -80 keV energy band. We estimate the non-thermal hard X-ray cluster emission (HXR) by modeling the thermal contribution from the cluster gas and the non-thermal contamination from the unobscured AGN in the clusters. We also evaluate the systematic uncertainties due to the background fluctuations. Assuming negligible contamination from the obscured AGN, the resulting non-thermal component is detected at a 2σ level in ∼50% of the non-significantly AGN-contaminated clusters: A2142, A2199, A2256, A3376, Coma, Ophiuchus and Virgo. The data are consistent with a scenario whereby relaxed clusters have no hard X-ray component of non-thermal origin, whereas merger clusters do, with a 20 -80 keV luminosity of ∼ 10 43−44 h −2 50 erg s −1 . The co-added spectrum of the above clusters indicates a power-law spectrum for the HXR with a photon index of 2.8 +0.3 −0.4 in the 12 -115 keV band, and we find indication that it has extended distribution. These indications argue against significant contamination from obscured AGN, which have harder spectra and centrally concentrated distribution. These results are supportive of the assumption of the merger shock acceleration of electrons in clusters, which has been proposed as a possible origin of the non-thermal hard X-ray emission models. Assuming that the Cosmic Microwave Background photons experience Inverse Compton scattering from the mergeraccelerated relativistic electrons, and thus produce the observed HXR, the measured hard X-ray slope corresponds to a differential momentum spectra of the relativistic electrons with a slope of µ = 3.8 -5.0. In presence of cluster magnetic fields this relativistic electron population produces synchrotron emission with a spectral index of 1.4 -2.1, consistent with radio halo observations of merger clusters. Thus both hard X-ray and radio observations of merger clusters are consistent with the Inverse Compton model. The observed slope of HXR is also consistent with that predicted by the non-thermal bremsstrahlung, which thus cannot be ruled by the fit to the current data, even though this model requires an extreme, untenable cluster energetics. Assuming centrally concentrated distribution of HXR, the data requires a harder slope for the HXR spectrum, which is consistent with secondary electron models, but this model yields a worse fit to the PDS data and thus seems to be disfavored over the primary electron Inverse Compton model.
The Astrophysical Journal, 1999
We combine spatially resolved ASCA temperature data with ROSAT imaging data to constrain the tota... more We combine spatially resolved ASCA temperature data with ROSAT imaging data to constrain the total mass distribution in the cluster A401, assuming that the cluster is in hydrostatic equilibrium, but without the assumption of gas isothermality. We obtain a total mass within the X-ray core (290 h −1 50 kpc) of 1.2 +0.1 −0.5 × 10 14 h −1 50 M ⊙ at the 90 % confidence level, 1.3 times larger than the isothermal estimate. The total mass within r 500 (1.7 h −1 50 Mpc) is M 500 = 0.9 +0.3 −0.2 × 10 15 h −1 50 M ⊙ at 90 % confidence, in agreement with the optical virial mass estimate, and 1.2 times smaller than the isothermal estimate. Our M 500 value is 1.7 times smaller than that estimated using the mass-temperature scaling law predicted by simulations. The best fit dark matter density profile scales as r −3.1 at large radii, which is consistent with the Navarro, Frenk & White (NFW) "universal profile" as well as the King profile of the galaxy density in A401. From the imaging data, the gas density profile is shallower than the dark matter profile, scaling as r −2.1 at large radii, leading to a monotonically increasing gas mass fraction with radius. Within r 500 the gas mass fraction reaches a value of f gas = 0.21 +0.06 −0.05 h −3/2 50 (90 % confidence errors). Assuming that f gas (plus an estimate of the stellar mass) is the universal value of the baryon fraction, we estimate the 90 % confidence upper limit of the cosmological matter density to be Ω m < 0.31, in conflict with an Einstein-deSitter universe. Even though the NFW dark matter density profile is statistically consistent with the temperature data, its central temperature cusp would lead to convective instability at the center, because the gas density does not have a corresponding peak. One way to reconcile a cusp-shaped total mass profile with the observed gas density profile, regardless of the temperature data, is to introduce a significant non-thermal pressure in the center. Such a pressure must satisfy the hydrostatic equilibrium condition without inducing turbulence. Alternately, significant mass drop-out from the cooling flow would make the temperature less peaked, and the NFW profile acceptable. However, the quality of data is not adequate to test this possibility.
The Astrophysical Journal, 2007
Chandra ACIS-S observations of the galaxy cluster Abell 3112 feature the presence of an excess of... more Chandra ACIS-S observations of the galaxy cluster Abell 3112 feature the presence of an excess of X-ray emission above the contribution from the diffuse hot gas, which can be equally well modeled with an additional nonthermal power-law model or with a low-temperature thermal model of low metal abundance. We show that the excess emission cannot be due to uncertainties in the background subtraction or in the Galactic H i column density. Calibration uncertainties in the ACIS detector that may affect our results are addressed by comparing the Chandra data to XMM-Newton MOS and PN spectra. While differences between the three instruments remain, all detect the excess in similar amounts, providing evidence against an instrumental nature of the excess. Given the presence of nonthermal radio emission near the center of Abell 3112, we argue that the excess X-ray emission is of nonthermal nature and distributed throughout the entire X-ray bandpass, from soft to hard X-rays. The excess can be explained with the presence of a population of relativistic electrons with $7% of the cluster's gas pressure. We also discuss a possible thermal nature of the excess and examine the problems associated with such interpretation.
The Astrophysical Journal, 2005
Several nearby clusters exhibit an excess of soft X-ray radiation which cannot be attributed to t... more Several nearby clusters exhibit an excess of soft X-ray radiation which cannot be attributed to the hot virialized intra-cluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin, or due to an inverse Compton scattering of the cosmic microwave background. Using high resolution XMM-Newton data of Sérsic 159-03 we first show that strong soft excess emission is detected out to a radial distance of 0.9 Mpc. The data are interpreted using the two viable models available, i.e., by invoking a warm reservoir of thermal gas, or relativistic electrons which are part of a cosmic ray population. The thermal interpretation of the excess emission, slightly favored by the goodness-of-fit analysis, indicates that the warm gas responsible for the emission is high in mass and low in metallicity.
The Astrophysical Journal, 2005
We use XMM-Newton blank-sky and closed-cover background data to explore the background subtractio... more We use XMM-Newton blank-sky and closed-cover background data to explore the background subtraction methods for large extended sources filling the EPIC field of view, such as nearby galaxy clusters, for which local background estimation is difficult. In particular, we investigate the uncertainties of the background modeling in the 0.8-7.0 keV band that affect the cluster analyses. To model the background, we have constructed composite datasets from the blank-sky observations and compared them to the individual blank-sky observations to evaluate the modeling error. Our results apply to data obtained with thin and medium optical filters and in Full frame and Extended full frame modes.
Space Science Reviews, 2008
An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal ... more An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission.
Space Science Reviews, 2008
We present the work of an international team at the International Space Science Institute (ISSI) ... more We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.
Space Science Reviews, 2008
Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broade... more Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.
Monthly Notices of the Royal Astronomical Society, 2013
ABSTRACT We report the first Chandra detection of emission out to the virial radius in the cluste... more ABSTRACT We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the cluster's virial radius that is not in hydrostatic equilibrium with the cluster's potential. The observations are also consistent with an alternative scenario in which the gas is significantly clumped at large radii.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of ... more In this paper we present simulated solar coronal X-ray observations to verify the sensitivity of a new hypothetical instrument design. These simulations are folded through this X-ray spectrometer having a moderate size circular field of view (FoV)) of 1.6 • . This SCXM (Solar Coronal X-ray Mapper) is designed to compose of a single pixel silicon PIN detector equipped with a single reflection double frustum X-ray optics. A moderate FoV would enable a morphological study of the expanded X-ray emission from the solar corona during a high activity of the Sun. The main scientific task of SCXM would be the mapping of the coronal X-ray emission, i.e. to resolve the radial distribution of the X-ray surface brightness around the Sun. These kind of off-limb observations would help to interpret the coronal plasma diagnostics as a function of the elongation angle.
Physica Scripta, 1998
ABSTRACT We present simulated SIXA spectra of the hottest known cluster of galaxies Abell 2163. S... more ABSTRACT We present simulated SIXA spectra of the hottest known cluster of galaxies Abell 2163. SIXA is an array of solid state detectors located in the focal plane of one of the two SODART telescopes onboard SPECTRUM-RÖNTGEN-GAMMA. We hereby demonstrate the capabilities of SIXA to perform spatially resolved spectroscopy of hot clusters. In a 30 ksec exposure, the temperature of the hot gas can be reliably derived from the central pixel as well as in the 2nd and 3rd pixel rings whereas the iron abundance can be determined in the central pixel and the 2nd pixel ring. SIXA will thus significantly improve current temperature and abundance measurements of the hot gas in clusters.
Physica Scripta, 1998
Combined ASCA and SIGMA data of 1E1740.7-2942 during its standard state (September 1993 and 1994)... more Combined ASCA and SIGMA data of 1E1740.7-2942 during its standard state (September 1993 and 1994) were successfully fitted with a two-phase model ISM (iterative scattering method) [1]. The classical cold accretion disk does not extend up to the innermost stable orbit, but is truncated at 30GM=c 2 . A hot inner disk has electron temperature T e 60 keV and radial Thomson optical depth τ 2:4. The cold disk radiates 40 % of the total luminosity withṀ 0:04Ṁ Edd of 10M .
Nuclear Physics B - Proceedings Supplements, 1999
We combine measurements of the Hubble constant in MlOO, M96, NGC 5253 and IC 4182 including the c... more We combine measurements of the Hubble constant in MlOO, M96, NGC 5253 and IC 4182 including the correction due to the metallicity dependence of the period-luminosity relation of Cepheids, as determined by Beaulieu et al. [l] and Sasselov et al. (21. We pay special attention to error correlations.
Astronomy & Astrophysics, 2015
ABSTRACT We propose a new approach to the missing baryons problem. Building on the common assumpt... more ABSTRACT We propose a new approach to the missing baryons problem. Building on the common assumption that the missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM), we further assumed here that the galaxy luminosity density can be used as a tracer of the WHIM. The latter assumption is supported by our finding of a significant correlation between the WHIM density and the galaxy luminosity density in the hydrodynamical simulations of Cui et al. (2012). We further found that the fraction of the gas mass in the WHIM phase is substantially (by a factor of sim\simsim1.6) higher within the large scale galactic filaments, i.e. sim\simsim70\%, compared to the average in the full simulation volume of sim\simsim0.1\,Gpc$^3$. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with linear: deltarmwhim,=,0.7,pm,0.1,times,deltamathrmLD0.9pm0.2\delta_{\rm whim}\,=\,0.7\,\pm\,0.1\,\times\,\delta_\mathrm{LD}^{0.9 \pm 0.2}deltarmwhim,=,0.7,pm,0.1,times,deltamathrmLD0.9pm0.2. We applied our procedure to the line of sight to the blazar H2356-309 and found evidence for the WHIM in correspondence of the Sculptor Wall (z sim\simsim0.03 and logNH\log{N_H}logNH = 19.9+0.1−0.319.9^{+0.1}_{-0.3}19.9+0.1−0.3) and Pisces-Cetus superclusters (z sim\simsim0.06 and logNH\log{N_H}logNH = 19.7+0.2−0.319.7^{+0.2}_{-0.3}19.7+0.2−0.3), in agreement with the redshifts and column densities of the X-ray absorbers identified and studied by Fang et al. (2010) and Zappacosta et al. (2010). This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust in estimating the WHIM density. The signal that we detected cannot originate from the halos of the nearby galaxies since they cannot account for the large WHIM column densities that our method and X-ray analysis consistently find in the Sculptor Wall and Pisces-Cetus superclusters.
Astronomy & Astrophysics, 2015
ABSTRACT Cosmological constraints from clusters rely on accurate gravitational mass estimates, wh... more ABSTRACT Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological constraints. This is of special interest in the light of the tension between the Planck results of the primary temperature anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts analyses. We quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, we assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM temperatures through spectral fitting in the same, mostly isothermal, regions and compare them. Our work is an extension to a previous one using X-ray clusters by the IACHEC. Performing spectral fitting in the full energy band we find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. We demonstrate that effects like multitemperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. We conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints.
The temperature of X-ray emitting gas T X is often used to infer the total mass of galaxy cluster... more The temperature of X-ray emitting gas T X is often used to infer the total mass of galaxy clusters (under the assumption of hydrostatic equilibrium). Unfortunately, XMM-Newton and Chandra observatories measure inconsistent temperatures for the same gas, due to uncertain instrumental calibration. We translate the relative bias in temperature measurements of Schellenberger et al. (2014) into a bias on inferred mass for a sample of clusters with homogeneous weak lensing (WL) masses, in order to simultaneously examine the hydrostatic bias and instrument calibration. found consistent WL and Chandra hydrostatic X-ray masses for a sample of clusters at z∼0.5 and masses of a few 10 14 M . Re-evaluating the latter, we find their XMM-Newton masses to be lower by b xcal = 15-20% than their Chandra masses. At the massive end ( 5 · 10 14 M ), the XMM-Newton masses are ∼ 35 % lower than the WL masses. Assuming that the true hydrostatic bias is 20 %, as indicated by simulations, our results for the massive end indicate that Chandra's calibration of the energy dependence of the effective area is more accurate than XMM-Newton's. However, the opposite appears to be true at the low mass end, unless the hydrostatic bias vanishes there, although larger samples are required to firmly establish this trend.
The Astrophysical Journal, 2000
We calibrate the galaxy cluster mass -temperature relation using the temperature profiles of intr... more We calibrate the galaxy cluster mass -temperature relation using the temperature profiles of intracluster gas observed with ASCA (for hot clusters) and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters for which the total masses are derived assuming hydrostatic equilibrium. The sample provides data on cluster X-ray emission-weighted cooling flow-corrected temperatures and total masses up to r 1000 . The resulting M-T scaling in the 1-10 keV temperature range is M 1000 = 1.23 ± 0.20 10 15 h −1 50 M ⊙ T z=0 10 keV 1.79±0.14 with 90% confidence errors, or significantly (99.99% confidence) steeper than the self-similar relation M ∝ T 3/2 . For any given temperature, our measured mass values are significantly smaller compared to the simulation results of Evrard et al. (1996) that are frequently used for mass-temperature scaling. The higher-temperature subsample (kT ≥ 4 keV) is consistent with M ∝ T 3/2 , allowing the possibility that the self-similar scaling breaks down at low temperatures, perhaps due to heating by supernovae that is more important for low-temperature groups and galaxies as suggested by earlier works.
The Astrophysical Journal, 2007
We analyze four XMM-Newton galaxy clusters (Abell 1795, Abell S1101, Abell 1835 and MKW 3s) in or... more We analyze four XMM-Newton galaxy clusters (Abell 1795, Abell S1101, Abell 1835 and MKW 3s) in order to test whether their soft X-ray excess emission in the 0.2-0.5 keV band as reported by maintains after application of current knowledge of the XMM-Newton background and calibration. In this context, we examine the recent claim that the XMM-Newton sub-Galactic H I column density, and the accompanying soft excess continuum emission in the 0.2-0.5 keV band, is an artifact of an incorrect background subtraction. We show that since the cluster regions under scrutiny are within 500 kpc of the bright cluster center, the X-ray background level is negligible compared to the cluster emission level. Thus, a "matched" background subtraction á la and more traditional background subtraction methods (á la yield the same results for the H I measurements in the source-dominated central cluster regions. Thus, at least in the central 500 kpc regions of the studied clusters, the reported soft excess is not a background artifact. On the other hand, the same simple background-to-cluster flux ratio argument allows the possibility that the reported O VII line emission in the 0.5-0.6 keV band in the outskirts of some of these clusters ) is due to the geocoronal and heliospheric solar wind charge exchange . We also study the possibility that the incomplete calibration information in the early phase of the XMM-Newton mission resulted in sub-Galactic H I column density, which was interpreted with the presence of a soft excess emitter. Our re-analysis of the four XMM-Newton observations with the MOS instruments yields evidence for the soft excess in all clusters. However, using the PN instrument, the best-fit H I column densities in Abell 1795, Abell 1835 and MKW 3s are at odds with the 2003 analysis of Kaastra et al., and in general agreement with those measured from 21 cm data in the direction of the clusters . Abell S1101 continues to feature a sub-galactic NH also with the PN instrument, indicative of soft excess emission in both EPIC detectors. These differences are compatible with the current level of uncertainty in the calibration of both instruments.
The Astrophysical Journal, 2000
We constrain the total mass distribution in the cluster A3571, combining spatially resolved ASCA ... more We constrain the total mass distribution in the cluster A3571, combining spatially resolved ASCA temperature data with ROSAT imaging data with the assumption that the cluster is in hydrostatic equilibrium. The total mass within r 500 (1.7 h −1 50 Mpc) is M 500 = 7.8 +1.4 −2.2 ×10 14 h −1 50 M ⊙ at 90% confidence, 1.1 times smaller than the isothermal estimate. The Navarro, Frenk & White "universal profile" is a good description of the dark matter density distribution in A3571. The gas density profile is shallower than the dark matter profile, scaling as r −2.1 at large radii, leading to a monotonically increasing gas mass fraction with radius. Within r 500 the gas mass fraction reaches a value of f gas = 0.19 +0.06 −0.03 h −3/2 50 (90% confidence errors). Assuming that this value of f gas is a lower limit for the the universal value of the baryon fraction, we estimate the 90% confidence upper limit of the cosmological matter density to be Ω m < 0.4.
The Astrophysical Journal, 2004
We study the X-ray emission in a sample of galaxy clusters using the BeppoSAX PDS instrument in t... more We study the X-ray emission in a sample of galaxy clusters using the BeppoSAX PDS instrument in the 20 -80 keV energy band. We estimate the non-thermal hard X-ray cluster emission (HXR) by modeling the thermal contribution from the cluster gas and the non-thermal contamination from the unobscured AGN in the clusters. We also evaluate the systematic uncertainties due to the background fluctuations. Assuming negligible contamination from the obscured AGN, the resulting non-thermal component is detected at a 2σ level in ∼50% of the non-significantly AGN-contaminated clusters: A2142, A2199, A2256, A3376, Coma, Ophiuchus and Virgo. The data are consistent with a scenario whereby relaxed clusters have no hard X-ray component of non-thermal origin, whereas merger clusters do, with a 20 -80 keV luminosity of ∼ 10 43−44 h −2 50 erg s −1 . The co-added spectrum of the above clusters indicates a power-law spectrum for the HXR with a photon index of 2.8 +0.3 −0.4 in the 12 -115 keV band, and we find indication that it has extended distribution. These indications argue against significant contamination from obscured AGN, which have harder spectra and centrally concentrated distribution. These results are supportive of the assumption of the merger shock acceleration of electrons in clusters, which has been proposed as a possible origin of the non-thermal hard X-ray emission models. Assuming that the Cosmic Microwave Background photons experience Inverse Compton scattering from the mergeraccelerated relativistic electrons, and thus produce the observed HXR, the measured hard X-ray slope corresponds to a differential momentum spectra of the relativistic electrons with a slope of µ = 3.8 -5.0. In presence of cluster magnetic fields this relativistic electron population produces synchrotron emission with a spectral index of 1.4 -2.1, consistent with radio halo observations of merger clusters. Thus both hard X-ray and radio observations of merger clusters are consistent with the Inverse Compton model. The observed slope of HXR is also consistent with that predicted by the non-thermal bremsstrahlung, which thus cannot be ruled by the fit to the current data, even though this model requires an extreme, untenable cluster energetics. Assuming centrally concentrated distribution of HXR, the data requires a harder slope for the HXR spectrum, which is consistent with secondary electron models, but this model yields a worse fit to the PDS data and thus seems to be disfavored over the primary electron Inverse Compton model.
The Astrophysical Journal, 1999
We combine spatially resolved ASCA temperature data with ROSAT imaging data to constrain the tota... more We combine spatially resolved ASCA temperature data with ROSAT imaging data to constrain the total mass distribution in the cluster A401, assuming that the cluster is in hydrostatic equilibrium, but without the assumption of gas isothermality. We obtain a total mass within the X-ray core (290 h −1 50 kpc) of 1.2 +0.1 −0.5 × 10 14 h −1 50 M ⊙ at the 90 % confidence level, 1.3 times larger than the isothermal estimate. The total mass within r 500 (1.7 h −1 50 Mpc) is M 500 = 0.9 +0.3 −0.2 × 10 15 h −1 50 M ⊙ at 90 % confidence, in agreement with the optical virial mass estimate, and 1.2 times smaller than the isothermal estimate. Our M 500 value is 1.7 times smaller than that estimated using the mass-temperature scaling law predicted by simulations. The best fit dark matter density profile scales as r −3.1 at large radii, which is consistent with the Navarro, Frenk & White (NFW) "universal profile" as well as the King profile of the galaxy density in A401. From the imaging data, the gas density profile is shallower than the dark matter profile, scaling as r −2.1 at large radii, leading to a monotonically increasing gas mass fraction with radius. Within r 500 the gas mass fraction reaches a value of f gas = 0.21 +0.06 −0.05 h −3/2 50 (90 % confidence errors). Assuming that f gas (plus an estimate of the stellar mass) is the universal value of the baryon fraction, we estimate the 90 % confidence upper limit of the cosmological matter density to be Ω m < 0.31, in conflict with an Einstein-deSitter universe. Even though the NFW dark matter density profile is statistically consistent with the temperature data, its central temperature cusp would lead to convective instability at the center, because the gas density does not have a corresponding peak. One way to reconcile a cusp-shaped total mass profile with the observed gas density profile, regardless of the temperature data, is to introduce a significant non-thermal pressure in the center. Such a pressure must satisfy the hydrostatic equilibrium condition without inducing turbulence. Alternately, significant mass drop-out from the cooling flow would make the temperature less peaked, and the NFW profile acceptable. However, the quality of data is not adequate to test this possibility.
The Astrophysical Journal, 2007
Chandra ACIS-S observations of the galaxy cluster Abell 3112 feature the presence of an excess of... more Chandra ACIS-S observations of the galaxy cluster Abell 3112 feature the presence of an excess of X-ray emission above the contribution from the diffuse hot gas, which can be equally well modeled with an additional nonthermal power-law model or with a low-temperature thermal model of low metal abundance. We show that the excess emission cannot be due to uncertainties in the background subtraction or in the Galactic H i column density. Calibration uncertainties in the ACIS detector that may affect our results are addressed by comparing the Chandra data to XMM-Newton MOS and PN spectra. While differences between the three instruments remain, all detect the excess in similar amounts, providing evidence against an instrumental nature of the excess. Given the presence of nonthermal radio emission near the center of Abell 3112, we argue that the excess X-ray emission is of nonthermal nature and distributed throughout the entire X-ray bandpass, from soft to hard X-rays. The excess can be explained with the presence of a population of relativistic electrons with $7% of the cluster's gas pressure. We also discuss a possible thermal nature of the excess and examine the problems associated with such interpretation.
The Astrophysical Journal, 2005
Several nearby clusters exhibit an excess of soft X-ray radiation which cannot be attributed to t... more Several nearby clusters exhibit an excess of soft X-ray radiation which cannot be attributed to the hot virialized intra-cluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin, or due to an inverse Compton scattering of the cosmic microwave background. Using high resolution XMM-Newton data of Sérsic 159-03 we first show that strong soft excess emission is detected out to a radial distance of 0.9 Mpc. The data are interpreted using the two viable models available, i.e., by invoking a warm reservoir of thermal gas, or relativistic electrons which are part of a cosmic ray population. The thermal interpretation of the excess emission, slightly favored by the goodness-of-fit analysis, indicates that the warm gas responsible for the emission is high in mass and low in metallicity.
The Astrophysical Journal, 2005
We use XMM-Newton blank-sky and closed-cover background data to explore the background subtractio... more We use XMM-Newton blank-sky and closed-cover background data to explore the background subtraction methods for large extended sources filling the EPIC field of view, such as nearby galaxy clusters, for which local background estimation is difficult. In particular, we investigate the uncertainties of the background modeling in the 0.8-7.0 keV band that affect the cluster analyses. To model the background, we have constructed composite datasets from the blank-sky observations and compared them to the individual blank-sky observations to evaluate the modeling error. Our results apply to data obtained with thin and medium optical filters and in Full frame and Extended full frame modes.
Space Science Reviews, 2008
An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal ... more An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission.
Space Science Reviews, 2008
We present the work of an international team at the International Space Science Institute (ISSI) ... more We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.
Space Science Reviews, 2008
Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broade... more Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.
Monthly Notices of the Royal Astronomical Society, 2013
ABSTRACT We report the first Chandra detection of emission out to the virial radius in the cluste... more ABSTRACT We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the cluster's virial radius that is not in hydrostatic equilibrium with the cluster's potential. The observations are also consistent with an alternative scenario in which the gas is significantly clumped at large radii.