366 research outputs found
Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy Cluster
Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters
are typically quenched giant ellipticals. A recent study hinted that
star-forming galaxies with large disks, so-called superluminous spirals and
lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing
optical data it was not possible to constrain whether the superluminous disk
galaxies reside at the center of galaxy clusters. In this work, we utilize
XMM-Newton X-ray observations of five galaxy clusters to map the morphology of
the intracluster medium (ICM), characterize the galaxy clusters, determine the
position of the cluster center, and measure the offset between the cluster
center and the superluminous disk galaxies. We demonstrate that one
superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center
of a low-mass () galaxy cluster. This
represents the first conclusive evidence that a superluminous disk galaxy is
the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX
J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed
due to the merger of galaxies. We exclude the possibility that the other four
superluminous disk galaxies reside at the center of galaxy clusters, as their
projected distance from the cluster center is kpc, which corresponds
to . We conclude that these clusters host quiescent
massive elliptical galaxies at their center.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Chandra and ROSAT observations of Abell 194: detection of an X-ray cavity and mapping the dynamics of the cluster
Based on Chandra and ROSAT observations, we investigated the nearby poor
cluster Abell 194, which hosts two luminous radio galaxies, NGC547 (3C 40B) and
NGC541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r~34
kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC547. The
estimated age of the cavity is t=7.9 x 10^7 years and the total work of the AGN
is 3.3 x 10^59 erg, hence the cavity power is P_cav=1.3 x 10^44 erg/s.
Furthermore, in the Chandra images of NGC545 and NGC541 we detected sharp
surface brightness edges, identified as merger cold fronts, and extended tails.
Using the pressure ratios between inside and outside the cold fronts we
estimated that the velocities of NGC545 and NGC541 correspond to Mach-numbers
of M=1.0^{+0.3}_{-0.5} and M=0.9^{+0.2}_{-0.5}, respectively. The low radial
velocities of these galaxies relative to the mean radial velocity of Abell 194
imply that their motion is oriented approximately in the plane of the sky.
Based on these and earlier observations, we concluded that NGC545 and NGC541
are falling through the cluster, whose center is NGC547, suggesting that Abell
194 is undergoing a significant cluster merger event. Additionally, we detected
20 bright X-ray sources around NGC547 and NGC541, a surprisingly large number,
since the predicted number of resolved LMXBs and CXB sources is 2.2 and 4.1,
respectively. To explain the nature of additional sources, different
possibilities were considered, none of which are satisfactory. We also studied
the origin of X-ray emission in Minkowski's Object, and concluded that it is
most likely dominated by the population of HMXBs rather than by hot diffuse
ISM. Moreover, in view of the galaxy dynamics in Abell 194, we explored the
possibility that the starburst in Minkowski's Object was triggered by its past
interaction with NGC541, and concluded that it may be a viable path.Comment: 12 pages, 7 figures, accepted for publication in Ap
The protective layer of biofilm:A repellent function for a new class of amphiphilic proteins
Bacteria can survive harsh conditions when growing in complex communities of cells known as biofilms. The matrix of the biofilm presents a scaffold where cells are attached to each other and to the surface. The biofilm matrix is also a protective barrier that confers tolerance against various antimicrobial agents. In this issue of Molecular Microbiology, Kobayashi and Iwano (2012) show that the liquid permeability of Bacillus subtilis biofilms is determined by a small secreted protein, i.e. BslA (formerly called YuaB). BslA is important for the proper development of biofilms, but unlike exopolysaccharide and TasA, is not directly involved in cell cluster formation, and is synthesized following the production of exopolysaccharide and amyloid fibres. The amphiphilic BslA protein forms a polymer in vitro and localizes in vivo to the surface of the biofilm. The microstructures of the biofilm wrinkles are reduced in the bslA mutant strain and the liquid repellency of the biofilm surface is diminished. Exogenously added BslA42181 protein complements the bslA mutation and restores not only water repellency, but also the formation of aerial structures. This study demonstrates that amphiphilic proteins have an important role in liquid repellency of biofilms and it suggests that these polymers contribute to antimicrobial resistance
Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models
Luminous X-ray gas coronae in the dark matter halos of massive spiral
galaxies are a fundamental prediction of structure formation models, yet only a
few such coronae have been detected so far. In this paper, we study the hot
X-ray coronae beyond the optical disks of two normal massive spirals, NGC1961
and NGC6753. Based on XMM-Newton X-ray observations, hot gaseous emission is
detected to ~60 kpc - well beyond their optical radii. The hot gas has a
best-fit temperature of kT~0.6 keV and an abundance of ~0.1 Solar, and exhibits
a fairly uniform distribution, suggesting that the quasi-static gas resides in
hydrostatic equilibrium in the potential well of the galaxies. The bolometric
luminosity of the gas in the (0.05-0.15)r_200 region (r_200 is the virial
radius) is ~6e40 erg/s for both galaxies. The baryon mass fractions of NGC1961
and NGC6753 are f_b~0.1, which fall short of the cosmic baryon fraction. The
hot coronae around NGC1961 and NGC6753 offer an excellent basis to probe
structure formation simulations. To this end, the observations are confronted
with the moving mesh code Arepo and the smoothed particle hydrodynamics code
Gadget. Although neither model gives a perfect description, the observed
luminosities, gas masses, and abundances favor the Arepo code. Moreover, the
shape and the normalization of the observed density profiles are better
reproduced by Arepo within ~0.5r_200. However, neither model incorporates
efficient feedback from supermassive black holes or supernovae, which could
alter the simulated properties of the X-ray coronae. With the further advance
of numerical models, the present observations will be essential in constraining
the feedback effects in structure formation simulations.Comment: 19 pages, 13 figures, 6 tables, accepted for publication in Ap
Young AGN outburst running over older X-ray cavities
Although the energetic feedback from active galactic nuclei (AGN) is believed
to have a profound effect on the evolution of galaxies and clusters of
galaxies, details of the AGN heating remain elusive. Here, we study NGC 193 - a
nearby lenticular galaxy - based on X-ray (Chandra) and radio (VLA and GMRT)
observations. These data reveal the complex AGN outburst history of the galaxy:
we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front,
and radio lobes extending beyond the inner cavities. We suggest that the inner
cavities were produced ~78 Myr ago by a weaker AGN outburst, while the outer
cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr)
and (4-8) times more powerful outburst. Combining this with the observed
morphology of NGC 193, we conclude that NGC 193 likely represents the first
example of a second, more powerful, AGN outburst overrunning an older, weaker
outburst. These results help to understand how the outburst energy is
dissipated uniformly in the core of galaxies, and therefore may play a crucial
role in resolving how AGN outbursts suppress the formation of large cooling
flows at cluster centers.Comment: 6 pages, 3 figures, 1 table, accepted for publication in ApJ
Genetic Tool Development for a New Host for Biotechnology, the Thermotolerant Bacterium Bacillus coagulans
Bacillus coagulans has good potential as an industrial production organism for platform chemicals from renewable resources but has limited genetic tools available. Here, we present a targeted gene disruption system using the Cre-lox system, development of a LacZ reporter assay for monitoring gene transcription, and heterologous D-lactate dehydrogenase expression
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