Extended X-ray emission in radio galaxies: the peculiar case of 3C 305

Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C 305, in which the X-ray radiation appears to be associated with the optical emission line region, dominated by the [O III]5007. On the basis of a morphological study, performed using the comparison between the X-rays, the optical and the radio band, we argue that the high energy emission has a thermal nature and it is not directly linked to the radio jet and hotspots of this source. Finally, we discuss the origin of the extended X-ray structure connected with the optical emission line region following two different interpretations: as due to the interaction between matter outflows and shock-heated environment gas, or as due to gas photoionized by nuclear emission.Comment: 5 pages, 2 figures, Accepted for publication in The ApJL Comments: references and affilitations correcte

On the absence of radio halos in clusters with double relics

Pairs of radio relics are believed to form during cluster mergers, and are best observed when the merger occurs in the plane of the sky. Mergers can also produce radio halos, through complex processes likely linked to turbulent re-acceleration of cosmic-ray electrons. However, only some clusters with double relics also show a radio halo. Here, we present a novel method to derive upper limits on the radio halo emission, and analyse archival X-ray Chandra data, as well as galaxy velocity dispersions and lensing data, in order to understand the key parameter that switches on radio halo emission. We place upper limits on the halo power below the $P_{\rm 1.4 \, GHz}\, M_{500}$ correlation for some clusters, confirming that clusters with double relics have different radio properties. Computing X-ray morphological indicators, we find that clusters with double relics are associated with the most disturbed clusters. We also investigate the role of different mass-ratios and time-since-merger. Data do not indicate that the merger mass ratio has an impact on the presence or absence of radio halos (the null hypothesis that the clusters belong to the same group cannot be rejected). However, the data suggests that the absence of radio halos could be associated with early and late mergers, but the sample is too small to perform a statistical test. Our study is limited by the small number of clusters with double relics. Future surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte

The radio relic in Abell 2256: overall spectrum and implications for electron acceleration

The galaxy cluster Abell 2256 hosts one of the most intriguing examples in the class of radio relics. It has been found that this radio relic has a rather flat integrated spectrum at low frequencies that would imply an injection spectral index for the electrons that is inconsistent with the flattest allowed by the test particle diffusive shock acceleration (DSA). We performed new high-frequency observations at 2273, 2640, and 4850 MHz. Combining these new observations with images available in the literature, we constrain the radio integrated spectrum of the radio relic in Abell 2256 over the widest sampled frequency range collected so far for this class of objects (63 -10450 MHz). Moreover, we used X-ray observations of the cluster to check the temperature structure in the regions around the radio relic. We find that the relic keeps an unusually flat behavior up to high frequencies. Although the relic integrated spectrum between 63 and 10450 MHz is not inconsistent with a single power law with $\alpha_{63}^{10450}= 0.92\pm 0.02$, we find hints of a steepening at frequencies > 1400 MHz. The two frequency ranges 63-1369 MHz and 1369-10450 MHz are, indeed, best represented by two different power laws, with $\alpha_{63}^{1369}= 0.85\pm 0.01$ and $\alpha_{1369}^{10450}= 1.00\pm 0.02$. This broken power law would require special conditions to be explained in terms of test-particle DSA, e.g., non-stationarity of the spectrum and/or non-stationarity of the shock. On the other hand, the single power law would make of this relic the one with the flattest integrated spectrum known so far, even flatter than what allowed in the test-particle approach to DSA. We find a rather low temperature ratio of $T_2/T_1 \sim 1.7$ across the G region of the radio relic and no temperature jump across the H region.Comment: 18 pages, 11 figures, 9 tables. Accepted for publication in Astronomy & Astrophysic

Searching for Molecular Markers for Salt Tolerance in Rhodes Grass (\u3ci\u3eChloris gayana\u3c/i\u3e Kunth)

Rhodes grass (Chloris gayana Kunth), a C4 forage grass, is regarded as salttolerant and exhibits intra- and inter-cultivar variability for this trait. Plants of cv Boma were selected for salt tolerance at the seedling and adult stages, cloned and characterized by RAPD and AFLP amplification patterns. Both techniques were equally efficient for fingerprinting these clones. More bands were obtained by AFLP but the ratio of polymorphic bands and the proportion present only in tolerant clones were the same by both methods. These bands, along with those exclusive for sensitive clones could be useful as markers for assisted selection

Experimental assessment of the mixing quality in a circular cross-sectional t-shaped mixer for the precipitation of sparingly soluble compounds

Precipitation processes have been successfully proved to be a feasible route to extract high-value products from wastes. However, reactive crystallization is characterized by fast kinetics, especially when highly concentrated solutions are used or sparingly soluble compounds precipitate, thus requiring a fast mixing of the reactants. In this context, T-shaped mixers have been extensively investigated both experimentally and numerically as a mean to achieve a rapid reactants homogenization. Many research efforts have been focused on the analysis of rectangular cross-sectional T-shaped mixers, while less attention has been devoted to the study of circular cross-sectional ones. In the present work, mixing times in a 3 mm circular cross-sectional T-shaped mixer have been optically estimated by exploiting the extremely fast neutralization reaction between sodium hydroxide and hydrochloric acid solutions. Reynolds numbers ranging between 1,000 and 6,000 were investigated. Mixing phenomena were (i) captured by detecting the colour change of a pH indicator by means of a high frame rate camera and (ii) quantified by a suitable image analysis technique. The assessed mixing times were found in accordance with available data in the literature

A powerful double radio relic system discovered in PSZ1 G108.18-11.53: Evidence for a shock with non-uniform Mach number?

Diffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we found M = 2.33-0.26+0.19, while the northern shock Mach number goes fromM= 2.20-0.14+0.07 in the north part down toM= 2.00-0.08+0.03 in the southern region. If the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock

The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR

The grand-design spiral galaxy M51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarisation. This observation covered the frequencies between 115 MHz and 175 MHz. We produced an image of total emission of M51 at the mean frequency of 151 MHz with 20 arcsec resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300 MHz so far. The integrated spectrum of total radio emission is described well by a power law, while flat spectral indices in the central region indicate thermal absorption. We observe that the disk extends out to 16 kpc and see a break in the radial profile near the optical radius of the disk. Our main results, the scale lengths of the inner and outer disks at 151 MHz and 1.4 GHz, arm--interarm contrast, and the break scales of the radio--far-infrared correlations, can be explained consistently by CRE diffusion, leading to a longer propagation length of CRE of lower energy. The distribution of CRE sources drops sharply at about 10 kpc radius, where the star formation rate also decreases sharply. We find evidence that thermal absorption is primarily caused by HII regions. The non-detection of polarisation from M51 at 151 MHz is consistent with the estimates of Faraday depolarisation. Future searches for polarised emission in this frequency range should concentrate on regions with low star formation rates.Comment: 20 pages, 18 figures, accepted for publication in A&

Deep LOFAR observations of the merging galaxy cluster CIZA J2242.8+5301

Previous studies have shown that CIZA J2242.8+5301 (the 'Sausage' cluster, z = 0.192) is a massive merging galaxy cluster that hosts a radio halo and multiple relics. In this paper, we present deep, high-fidelity, low-frequency images made with the LOw-Frequency Array (LOFAR) between 115.5 and 179 MHz. These images, with a noise of 140 μJy beam- 1 and a resolution of θbeam = 7.3 arcsec × 5.3 arcsec, are an order of magnitude more sensitive and five times higher resolution than previous low-frequency images of this cluster. We combined the LOFAR data with the existing Giant Metrewave Radio Telescope (GMRT) (153, 323, 608 MHz) and Westerbork Synthesis Radio Telescope (WSRT) (1.2, 1.4, 1.7, 2.3 GHz) data to study the spectral properties of the radio emission from the cluster. Assuming diffusive shock acceleration (DSA), we found Mach numbers of Mn=2.7{}_{-0.3}^{+0.6} and Ms=1.9_{-0.2}^{+0.3} for the northern and southern shocks. The derived Mach number for the northern shock requires an acceleration efficiency of several percent to accelerate electrons from the thermal pool, which is challenging for DSA. Using the radio data, we characterized the eastern relic as a shock wave propagating outwards with a Mach number of Me=2.4_{-0.3}^{+0.5}, which is in agreement with MeX=2.5{}_{-0.2}^{+0.6} that we derived from Suzaku data. The eastern shock is likely to be associated with the major cluster merger. The radio halo was measured with a flux of 346 ± 64 mJy at 145 MHz. Across the halo, we observed a spectral index that remains approximately constant (α ^{145 MHz-2.3 GHz}_{{across ˜ 1 Mpc}^2}=-1.01± 0.10) after the steepening in the post-shock region of the northern relic. This suggests a generation of post-shock turbulence that re-energies aged electrons

Particle re-acceleration and Faraday-complex structures in the RXC\ua0J1314.4-2515 galaxy cluster

Radio relics are sites of electron (re)acceleration inmerging galaxy clusters but the mechanism of acceleration and the topology of the magnetic field in and near relics are yet to be understood. We are carrying out an observational campaign on double relic galaxy clusters starting with RXC J1314.4-2515. With Jansky Very Large Array multiconfiguration observations in the frequency range 1-4 GHz, we perform both spectral and polarization analyses, using the rotation measure (RM) synthesis technique. We use archival XMM-Newton observations to constrain the properties of the shocked region. We discover a possible connection between the activity of a radio galaxy and the emission of the eastern radio relic. In the northern elongated arc of the western radio relic, we detect polarized emission with an average polarization fraction of 31 % at 3 GHz and we derive the Mach number of the underlying X-ray shock. Our observations reveal low levels of fractional polarization and Faraday-complex structures in the southern region of the relic, which point to the presence of thermal gas and filamentary magnetic field morphology inside the radio emitting volume. We measured largely different RM dispersion from the two relics. Finally, we use cosmological magnetohydrodynamical simulations to constrain the magnetic field, viewing angle, and to derive the acceleration efficiency of the shock. We find that the polarization properties of RXC J1314.4-2515 are consistent with a radio relic observed at 70 degrees with respect to the line of sight and that the efficient re-acceleration of fossil electrons has taken place