424 research outputs found
Spitzer Observations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores
Spitzer observations of extended dust in two optically normal elliptical
galaxies provide a new confirmation of buoyant feedback outflow in the hot gas
atmospheres around these galaxies. AGN feedback energy is required to prevent
wholesale cooling and star formation in these group-centered galaxies. In NGC
5044 we observe interstellar (presumably PAH) emission at 8 microns out to
about 5 kpc. Both NGC 5044 and 4636 have extended 70 microns emission from cold
dust exceeding that expected from stellar mass loss. The sputtering lifetime of
this extended dust in the ~1keV interstellar gas, ~10^7 yrs, establishes the
time when the dust first entered the hot gas. Evidently the extended dust
originated in dusty disks or clouds, commonly observed in elliptical galaxy
cores, that were disrupted, heated and buoyantly transported outward. The
surviving central dust in NGC 5044 and 4636 has been disrupted into many small
filaments. It is remarkable that the asymmetrically extended 8 micron emission
in NGC 5044 is spatially coincident with Halpha+[NII] emission from warm gas. A
calculation shows that dust-assisted cooling in buoyant hot gas moving out from
the galactic core can cool within a few kpc in about ~10^7 yrs, explaining the
optical line emission observed. The X-ray images of both galaxies are
disturbed. All timescales for transient activity - restoration of equilibrium
and buoyant transport in the hot gas, dynamics of surviving dust fragments, and
dust sputtering - are consistent with a central release of feedback energy in
both galaxies about 10^7 yrs ago.Comment: 13 pages. Accepted by ApJ; minor typos correcte
Origin of Radio Emission from Nearby Low-Luminosity Active Galactic Nuclei
We use the observational data in radio, optical and X-ray wavebands, for a
sample of active galactic nuclei (AGNs) with measured black hole masses, to
explore the origin of radio emission from nearby low-luminosity active galactic
nuclei (LLAGNs). We find that the radio luminosities are higher than the
maximal luminosities expected from the ADAF model, for most sources in this
sample. This implies that the radio emission is dominantly from the jets in
these sources. The radio emission from a small fraction of the sources in this
sample can be explained by the ADAF model. However, comparing the observed
multi-band emission data with the spectra calculated for the ADAF or ADIOS
cases, we find that neither ADAF nor ADIOS models can reproduce the observed
multi-band emission simultaneously, with reasonable magnetic field strengths,
for these radio-weak sources. A variety of other possibilities are discussed,
and we suggest that the radio emission is probably dominated by jet emission
even in these radio-weak LLAGNs.Comment: 25 pages, some references were added, accepted for publication in Ap
Intrinsic regulation of FIC-domain AMP-transferases by oligomerization and automodification
Filamentation induced by cyclic AMP (FIC)-domain enzymes catalyze adenylylation or other posttranslational modifications of target proteins to control their function. Recently, we have shown that Fic enzymes are autoinhibited by an α-helix (αinh) that partly obstructs the active site. For the single-domain class III Fic proteins, the αinh is located at the C terminus and its deletion relieves autoinhibition. However, it has remained unclear how activation occurs naturally. Here, we show by structural, biophysical, and enzymatic analyses combined with in vivo data that the class III Fic protein NmFic from Neisseria meningitidis gets autoadenylylated in cis, thereby autonomously relieving autoinhibition and thus allowing subsequent adenylylation of its target, the DNA gyrase subunit GyrB. Furthermore, we show that NmFic activation is antagonized by tetramerization. The combination of autoadenylylation and tetramerization results in nonmonotonic concentration dependence of NmFic activity and a pronounced lag phase in the progress of target adenylylation. Bioinformatic analyses indicate that this elaborate dual-control mechanism is conserved throughout class III Fic proteins
Winter Counts as Transformative Inquiry: The Role of Creative Imagery as an Expression of Adaptive Change
Pre-service teachers face a complex educational context and Transformative Inquiry is a useful approach for negotiating this terrain. We interpret the movement of students via the adaptive cycle put forth in panarchy theory as they engage in the inquiry process through ‘winter counts’, a Plains First Nation tradition, as expressions of their understanding. These image-based expressions demonstrate the emotional, mental, spiritual and physical movement students have made within their inquiry. Panarchy theory moves beyond interpreting systems using simplistic equilibrium models and acknowledging the more complex and dynamic set of equilibria that describes transformation in ecological, social, and economic systems and considers the multiple complexities of systems thinking while providing insight into how change occurs as a constantly adaptive cycle process. Used sparingly within social sciences until recently, we argue it as particularly relevant for seeing Transformative Inquiry through Indigenist and interconnected lenses
Quantificação não destrutiva do contéudo de clorofilas em folhas de milho através de método colorimétrico.
Este trabalho foi conduzido visando avaliar a viabilidade da utilização de um colorÃmetro, como alternativa ao medidor de clorofila para a quantificação não destrutiva de clorofilas em folhas de milho.Suplemento. Trabalho apresentado no 52. Congresso Brasileiro de Olericultura, Salvador, 2012
ROSAT Evidence for Intrinsic Oxygen Absorption in Cooling Flow Galaxies and Groups
Using spatially resolved, deprojected ROSAT PSPC spectra of 10 of the
brightest cooling flow galaxies and groups with low Galactic column densities
we have detected intrinsic absorption over energies ~0.4-0.8 keV in half of the
sample. Since no intrinsic absorption is indicated for energies below ~0.4 keV,
the most reasonable model for the absorber is collisionally ionized gas at
temperatures T=10^{5-6} K with most of the absorption arising from ionized
states of oxygen but with a significant contribution from carbon and nitrogen.
The soft X-ray emission of this warm gas can explain the sub-Galactic column
densities of cold gas inferred within the central regions of most of the
systems. Attributing the absorption to ionized gas reconciles the large columns
of cold H and He inferred from EINSTEIN and ASCA with the lack of such columns
inferred from ROSAT. Within the central ~10-20 kpc, where the constraints are
most secure, the estimated mass of the ionized absorber is consistent with most
(perhaps all) of the matter deposited by a cooling flow over the lifetime of
the flow. Since the warm absorber produces no significant H or He absorption
the large absorber masses are consistent with the negligible atomic and
molecular H inferred from HI and CO observations of cooling flows. It is also
found that if T > ~2x10^5 K then the optical and UV emission implied by the
warm gas does not violate published constraints. Finally, we discuss how the
prediction of warm ionized gas as the product of mass drop-out in these and
other cooling flows can be verified with new CHANDRA and XMM observations.
(Abridged)Comment: 17 pages (5 figures), Accepted for publication in ApJ, expanded
discussion of multiphase spectral models, theoretical implications of warm
gas in cooling flows, and the statistical significance of the oxygen
absorptio
The BID Domain of Type IV Secretion Substrates Forms a Conserved Four-Helix Bundle Topped with a Hook
The BID (Bep intracellular delivery) domain functions as secretion signal in a subfamily of protein substrates of bacterial type IV secretion (T4S) systems. It mediates transfer of (1) relaxases and the attached DNA during bacterial conjugation, and (2) numerous Bartonella effector proteins (Beps) during protein transfer into host cells infected by pathogenic Bartonella species. Furthermore, BID domains of Beps have often evolved secondary effector functions within host cells. Here, we provide crystal structures for three representative BID domains and describe a novel conserved fold characterized by a compact, antiparallel four-helix bundle topped with a hook. The conserved hydrophobic core provides a rigid scaffold to a surface that, despite a few conserved exposed residues and similarities in charge distribution, displays significant variability. We propose that the genuine function of BID domains as T4S signal may primarily depend on their rigid structure, while the plasticity of their surface may facilitate adaptation to secondary effector functions
AGN feedback and gas mixing in the core of NGC 4636
Chandra observations of NGC 4636 show disturbances in the galaxy X-ray halo,
including arm-like high surface brightness features (tentatively identified as
AGN driven shocks) and a possible cavity on the west side of the galaxy core.
We present Chandra and XMM spectral maps of NGC 4636 which confirm the presence
of the cavity and show it to be bounded by the arm features. The maps also
reveal a ~15 kpc wide plume of low temperature, high abundance gas extending
25-30 kpc to the southwest of the galaxy. The cavity appears to be embedded in
this plume, and we interpret the structure as being entrained gas drawn out of
the galaxy core during previous episodes of AGN activity. The end of the plume
is marked by a well defined edge, with significant falls in surface brightness,
temperature and abundance, indicating a boundary between galaxy and
group/cluster gas. This may be evidence that as well as preventing gas cooling
through direct heating, AGN outbursts can produce significant gas mixing,
disturbing the temperature structure of the halo and transporting metals out
from the galaxy into the surrounding intra-group medium.Comment: 4 Pages, 2 colour figures, accepted for publication in ApJ Letters.
Version with high quality images at
http://hea-www.harvard.edu/~ejos/files/N4636_hires.pd
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