Vulnerability to pine sawfly damage decreases with site fertility but the opposite is true with Scleroderris canker damage; results from Finnish ICP Forests and NFI data

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X-ray total mass estimate for the nearby relaxed cluster A3571

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_50 Mpc) is M_500 = 7.8[+1.4,-2.2] 10^14/ h_50 Msun 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_50^{-3/2} (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 Omega_m < 0.4.Comment: 10 pages, 4 figures, accepted by Ap

GMRT observations of the Ophiuchus galaxy cluster

VLA observations at 1477 MHz revealed the presence of a radio mini-halo surrounding the faint central point-like radio source in the Ophiuchus cluster of galaxies. In this work we present a study of the radio emission from this cluster of galaxies at lower radio frequencies. We observed the Ophiuchus cluster at 153, 240, and 614 MHz with the GMRT. The mini-halo is clearly detected at 153 and 240 MHz while it is not detected at 610 MHz. The most prominent feature at low frequencies is a patch of diffuse steep spectrum emission located at about 5' south-east from the cluster center. By combining these images with that at 1477 MHz, we derived the spectral index of the mini-halo. Globally, the mini-halo has a low-frequency spectral index of alpha_240^153 ~1.4 +/- 0.3 and an high-frequency spectral index of alpha_1477^240 ~ 1.60 +/- 0.05. Moreover, we measure a systematic increase of the high-frequency spectral index with radius: the azimuthal radial average of alpha_1477^240 increases from about 1.3, at the cluster center, up to about 2.0 in the mini-halo outskirts. The observed radio spectral index is in agreement with that obtained by modeling the non-thermal hard X-ray emission in this cluster of galaxies. We assume that the X-ray component arises from inverse Compton scattering between the photons of the cosmic microwave background and a population of non-thermal electrons which are isotropically distributed and whose energy spectrum is a power law with index p. We derive that the electrons energy spectrum should extend from a minimum Lorentz factor of gamma_min < 700 up to a maximum Lorentz factor of gamma_max =3.8 x 10^4 with an index p=3.8 +/- 0.4. The volume-averaged strength for a completely disordered intra-cluster magnetic field is B_V ~0.3 +/- 0.1 micro-G.Comment: 14 pages, 8 figures, accepted for publication in Astronomy and Astrophysics. For a version with high-quality figures see http://erg.ca.astro.it/preprints/ophi_2010

ROSAT and BeppoSAX evidence of soft X-ray excess emission in the Shapley supercluster: A3571, A3558, A3560 and A3562

Excess soft X-ray emission in clusters of galaxies has so far been detected for sources that lie along lines-of-sight to very low Galactic HI column density (such as Coma, A1795, A2199 and Virgo, N_H 0.9-2.0 10^{20} cm-2). We show that the cluster soft excess emission can be investigated even at higher N_H, which provides an opportunity for investigating soft X-ray emission characteristics among a large number of clusters. The ROSAT PSPC analysis of some members of the Shapley concentration (A3571, A3558, A3560 and A3562, at N_H 4-4.5 10^{20} cm-2) bears evidence for excess emission in the 1/4 keV band. We were able to confirm the finding for the case of A3571 by a pointed SAX observation. Within the current sample the soft X-ray flux is again found to be consistently above the level expected from a hot virialized plasma. The data quality is however insufficient to enable a discrimination between alternative models of the excess low energy flux.Comment: ApJL in press, 5 figure

The cluster M-T relation from temperature profiles observed with ASCA and ROSAT

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)/h_50 10^15 Msun (T/10 keV)^{1.79 +- 0.14} with 90% confidence errors, or significantly (99.99% confidence) steeper than the self-similar relation M propto 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 propto 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.Comment: 8 pages, 2 figures, accepted by Ap

Substructure and halo density profiles in a Warm Dark Matter Cosmology

We performed a series of high-resolution simulations designed to study the substructure of Milky Way-size galactic halos (host halos) and the density profiles of halos in a warm dark matter (WDM) scenario with a non-vanishing cosmological constant. The virial masses of the host halos range from 3.5 x 10^12 to 1.7 x 10^12 solar masses and they have more than 10^5 particles each. A key feature of the WDM power spectrum is the free-streaming length R_f which fixes an additional parameter for the model of structure formation. We analyze the substructure of host halos using three R_f values: 0.2, 0.1, and 0.05 Mpc and compare results to the predictions of the cold dark matter (CDM) model. We find that guest halos (satellites) do form in the WDM scenario but are more easily destroyed by dynamical friction and tidal disruption than their counterparts in a CDM model. The small number of guest halos that we find within the virial radii of host halos at z = 0 in the WDM models is the result of a less efficient halo accretion and a higher satellite destruction rate. Under the assumption that each guest halo hosts a luminous galaxy, we find that the observed circular velocity function of satellites around the Milky Way and Andromeda is well described by the R_f = 0.1 Mpc WDM model. In the R_f = 0.1-0.2 Mpc models, the surviving subhalos at z=0 have an average concentration parameter c_1/5 which is approximately twice smaller than that of the corresponding CDM subhalos. This difference, very likely, produces the higher satellite destruction rate found in the WDM models. The density profile of host halos is well described by the NFW fit whereas guest halos show a wide variety of density profiles (abridged).Comment: Uses emulateapj.sty: 10 pages, 4 figures, ApJ accepted. Some changes have been introduced as suggested by the referee: (1) the description of the numerical simulations was sligthly modified to make it clearer, (2) the ellipticities of the host halos are now measured, and (3) the discussion section was divided in two subsections and enlarge

XMM−NewtonXMM-Newton Ω\Omega project: III. Gas mass fraction shape in high redshift clusters

We study the gas mass fraction, $f\_{\rm gas},$ behavior in $XMM-Newton$ $\Omega$ project. The typical $f\_{\rm gas}$ shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean $f\_{\rm gas} in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our$XMM$ clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.Comment: Accepted, A&A, in pres

On the ICS interpretation of the Hard X-Ray Excesses in Galaxy Clusters: the case of Ophiuchus

(Abridged) High-E electrons produce Hard X-Ray (HXR) emission in galaxy clusters by via Inverse Compton Scattering (ICS) of CMB photons. We derive the ICS HXR emission of Ophiuchus under various scenarios: primary cosmic ray model, secondary cosmic rays model and neutralino DM annihilation scenario. We further discuss the predictions of the Warming Ray model for the cluster atmosphere. Under the assumption to fit the observed HXR emission, we find that the high-E electrons induce various consequences on the cluster atmosphere: i) primary electrons can be marginally consistent with the data provided that their spectrum is cutoff at E~30(90) MeV for spectral index of 3.5 (4.4); ii) secondary electron models from pp collisions are inconsistent with gamma-ray limits, cosmic ray protons produce too much heating of the IC gas and their pressure at the cluster center largely exceeds the thermal one; iii) secondary electron models from DM annihilation are inconsistent with gamma-ray and radio limits and electrons produce too much heating of the IC gas at the cluster center, unless the neutralino annihilation cross section is much lower than the proposed value. We conclude that ICS by secondary electrons from both neutralino DM annihilation and pp collisions cannot be the mechanism responsible for the HXR excess emission; primary electrons are still a marginally viable solution provided that their spectrum has a low-energy cutoff at E~30-90 MeV. The WR model offers, so far, the best description of the cluster in terms of temperature distribution, heating, pressure and spectral energy distribution. Fermi observations of Ophiuchus will set further constraints to this model.Comment: 10 pages, 9 figures, A&A in pres

Temperature and total mass profiles of the A3571 cluster of galaxies

We present BeppoSAX results of a spatially resolved spectral analysis of A3571, a relaxed nearby cluster of galaxies. In the central 2' (130/h_50 kpc) radius the metal abundance is 0.49 +- 0.08 solar and the absorption (1.13 +-0.28) x 10^21 atom/cm^2 whereas elsewhere within an 8'(520/h_50 kpc) radius the abundance is 0.32 \+- 0.05 solar and the absorption consistent with the galactic value of 4.4 x 10^20 atom/cm2. The significant central metal abundance enhancement is consistent with the supernova enrichment scenario. The excess absorption may be attributed to the cooling flow, whose mass flow rate is 80 +- 40 M_Sun/yr from our spectral fit. The BeppoSAX and ASCA radial temperature profiles agree over the entire overlapping radial range r < 25' = 1.6/h_50 Mpc. The combined BeppoSAX and ASCA temperature profile exhibits a constant value out to a radius of 10' (650/h_50 kpc) and a significant decrease (T propto r^-0.55, corresponding to gamma=1.28) at larger radii. These temperature data are used to derive the total mass profile. The best fit NFW dark matter density model results in a temperature profile that is not convectively stable, but the model is acceptable within the uncertainties of the data. The temperature profile is acceptably modeled with a ``core'' model for the dark matter density, consisting of a core radius with a constant slope at larger radii. With this model the total mass and formal 90% confidence errors within the virial radius r_178 (2.5/h_50 Mpc) are 9.1+3.6-1.5 x 10^14 h_50^-1 M_Sun, by a factor of 1.4 smaller than the isothermal value. The gas mass fraction increases with radius, reaching f_gas(r_178) = 0.26+0.05-0.10 x h_50^-3/2. Assuming that the measured gas mass fraction is the lower limit to the primordial baryonic fraction gives Omega_m < 0.4 at 90% confidence