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Register a new userFeedback through multiple outbursts in the cluster 2A 0335+096
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We examine the core of the X-ray bright galaxy cluster 2A 0335+096 using deep Chandra X-ray imaging and spatially-resolved spectroscopy, and include new radio observations. The set of around eight X-ray bright blobs in the core of the cluster, appearing like eggs in a birds nest, contains multiphase gas from ~0.5 to 2 keV. The morphology of the coolest X-ray emitting gas at 0.5 keV temperature is similar to the Halpha emitting nebula known in this cluster, which surrounds the central galaxy. XMM-Newton grating spectra confirm the presence of material at these temperatures, showing excellent agreement with Chandra emission measures. On scales of 80 to 250 kpc there is a low temperature, high metallicity, swirl of intracluster medium as seen in other clusters. In the core we find evidence for a further three X-ray cavities, in addition to the two previously discovered. Enhancements in 1.5 GHz radio emission are correlated with the X-ray cavities. The total 4PV enthalpy associated with the cavities is around 5x10^59 erg. This energy would be enough to heat the cooling region for ~5x10^7 yr. We find a maximum pressure discontinuity of 26 per cent (2 sigma) across the surface brightness edge to the south-west of the cluster core. This corresponds to an upper limit on the Mach number of the cool core with respect to its surroundings of 0.55.
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We present ALMA CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in the 2A 0335+096 galaxy cluster (z = 0.0346). The total molecular gas mass of (1.13+/-0.15) x 10^9 M_sun is divided into two components: a nuclear region and a 7 kpc long dusty filament. The central molecular gas component accounts for (3.2+/-0.4) x 10^8 M_sun of the total supply of cold gas. Instead of forming a rotationally-supported ring or disk, it is composed of two distinct, blueshifted clumps south of the nucleus and a series of low-significance redshifted clumps extending toward a nearby companion galaxy. The velocity of the redshifted clouds increases with radius to a value consistent with the companion galaxy, suggesting that an interaction between these galaxies <20 Myr ago disrupted a pre-existing molecular gas reservoir within the BCG. Most of the molecular gas, (7.8+/-0.9) x 10^8 M_sun, is located in the filament. The CO emission is co-spatial with a 10^4 K emission-line nebula and soft X-rays from 0.5 keV gas, indicating that the molecular gas has cooled out of the intracluster medium over a period of 25-100 Myr. The filament trails an X-ray cavity, suggesting that the gas has cooled from low entropy gas that has been lifted out of the cluster core and become thermally unstable. We are unable to distinguish between inflow and outflow along the filament with the present data. Cloud velocities along the filament are consistent with gravitational free-fall near the plane of the sky, although their increasing blueshifts with radius are consistent with outflow.
We report on a spatially resolved analysis of Chandra X-ray data on a nearby typical cooling flow cluster of galaxies 2A 0335+096, together with A 2199 for a comparison. As recently found in the cores of other clusters, the temperature around the central part of 2A 0335+096 is 1.3--1.5 keV, which is higher than that inferred from the cooling flow picture. Furthermore, the absorption column density is almost constant against the radius in 2A 0335+096; there is no evidence of excess absorption up to 200--250 kpc. This indicates that no significant amount of cold material, which has cooled down, is present. These properties are similar to those of A 2199. Since the cooling time in the central part is much shorter than the age of the clusters, a heating mechanism, which weakens the effect of radiative cooling, is expected to be present in the central part of both clusters of galaxies. Both 2A 0335+096 and A 2199 have radio jets associated with their cD galaxy. We discuss the possibility of heating processes caused by these radio jets by considering the thermal conduction and the sound velocity together with the observed disturbance of the ICM temperature and density. We conclude that the observed radio jets can produce local heating and/or cooling, but do not sufficiently reduce the overall radiative cooling. This implies that much more violent jets, whose emission has now decayed, heated up the cooling gas $>10^9$ years ago.
We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. The system shows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc from the central source, from three distinct outbursts of the central AGN, which occurred 3x10^6, 2x10^7, and 9x10^7 yr ago. The H-alpha and X-ray observations reveal filaments of cool gas that has been uplifted by the X-ray cavities. The inner two cavity pairs are filled with radio emitting plasma, and each pair is associated with an elliptical surface brightness edge, which we unambiguously identify as shocks (with measured temperature jumps) with Mach numbers of M~1.7 and M~1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise dynamically relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts differs by a factor of six, from 1.5--10x10^42 erg/s, indicating that the mean jet power changes significantly over long (~10^7 yr) timescales. The total energy output of the most recent outburst is also more than an order of magnitude less than the total energy of the previous outburst (1.5x10^56 erg versus 4x10^57 erg), which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. The outburst interval implied by both the shock and cavity ages (~10^7 yr) indicates that, in this system, shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the ICM and the central SMBH.
We present a 4 year light curve of a cataclysmic variable in M22, based on an analysis of accumulated data from the MOA microlensing survey. The position of the star coincides with that of a transient event observed by HST in 1999, originally attributed to microlensing but later suspected to be a dwarf nova outburst. Two outburst episodes, one in 2002 and one in 2003, with $Delta Isim3$ are seen in the MOA data thus confirming that the HST event was a dwarf nova outburst. The MOA and HST data show that this dwarf nova underwent at least three outburst episodes during 1999--2004. Further close monitoring of this event is encouraged as future outburst episodes are expected.
PKS 1749+096 is a BL Lac object showing weak extended jet emission to the northeast of the compact VLBI core on parsec scales. We aim at better understanding the jet kinematics and variability of this source and finding clues that may applicable to other BL Lac objects. The jet was studied with multi-epoch multi-frequency high-resolution VLBI observations. The jet is characterized by a one-sided curved morphology at all epochs and all frequencies. The VLBI core, located at the southern end of the jet, was identified based on its spectral properties. The equipartition magnetic field of the core was investigated, through which we derived a Doppler factor of 5, largely consistent with that derived from kinematics (component C5). The study of the detailed jet kinematics at 22 and 15 GHz, spanning a period of more than 10 years, indicates the possible existence of a bimodal distribution of the jet apparent speed. Ballistic and non-ballistic components are found to coexist in the jet. Superluminal motions in the range of 5-21 c were measured in 11 distinct components. We estimated the physical jet parameters with the minimum Lorentz factor of 10.2 and Doppler factors in the range of 10.2-20.4 (component C5). The coincidence in time of the components ejection and flares supports the idea that, at least in PKS 1749+096, ejection of new jet components is connected with major outbursts in flux density. For the best-traced component (C5) we found that the flux density decays rapidly as it travels downstream the jet, accompanied by a steepening of its spectra, which argues in favor of a contribution of inverse Compton cooling. These properties make PKS 1749+096 a suitable target for an intensive monitoring to decipher the variability phenomenon of BL Lac objects.
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