64 research outputs found
The dusty, albeit ultraviolet bright infancy of galaxies
The largest galaxies acquire their mass early on, when the Universe is still
youthful. Cold streams violently feed these young galaxies a vast amount of
fresh gas, resulting in very efficient star formation. Using a well resolved
hydrodynamical simulation of galaxy formation, we demonstrate that these
mammoth galaxies are already in place a couple of billion years after the Big
Bang. Contrary to local starforming galaxies, where dust re-emits a large part
of the stellar ultraviolet (UV) light at infrared and sub-millimetre
wavelengths, our self-consistent modelling of dust extinction predicts that a
substantial fraction of UV photons should escape from primordial galaxies. Such
a model allows us to compute reliably the number of high redshift objects as a
function of luminosity, and yields galaxies whose UV luminosities closely match
those measured in the deepest observational surveys available. This agreement
is remarkably good considering our admittedly still simple modelling of the
interstellar medium (ISM) physics. The luminosity functions (LF) of virtual UV
luminous galaxies coincide with the existing data over the whole redshift range
from 4 to 7, provided cosmological parameters are set to their currently
favoured values. Despite their considerable emission at short wavelengths, we
anticipate that the counterparts of the brightest UV galaxies will be detected
by future sub-millimetre facilities like ALMAComment: 5 pages, 3 figures, submitted to MNRAS-le
Summer CO2 evasion from streams and rivers in the Kolyma River basin, north-east Siberia
Inland water systems are generally supersaturated in carbon dioxide (CO2) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide (pCO2) and gas exchange velocities (k) were measured at a diverse set of streams and rivers to calculate CO2 evasion fluxes.
We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO2 emissions. Our results show that small streams are substantial sources of atmospheric CO2 owing to high pCO2 and k, despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO2. Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO2 evasion, accounting for 86% of the total summer CO2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget
Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634
We report on a deep, multiwavelength study of the galaxy cluster MACS
J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data.
This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet
discovered, with an equivalent mass cooling rate within the central 50 kpc is
approximately 700 solar masses/yr. Unique features observed in the central core
of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly
disrupted the original cool core. We observe a spiral of relatively cool,
dense, X-ray emitting gas connected to the cool core, as well as highly
elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio
emission is observed surrounding the central AGN, elongated in the east-west
direction, spatially coincident with X-ray cavities. The power input required
to inflate these `bubbles' is estimated from both the X-ray and radio emission
to reside between 4 and 14e45 erg/s, putting it among the most powerful jets
ever observed. This combination of a powerful AGN outburst and bulk motion of
the cool core have resulted in two X-ray bright ridges to form to the north and
south of the central AGN at a distance of approximately 25 kpc. The northern
ridge has spectral characteristics typical of cool cores and is consistent with
being a remnant of the cool core after it was disrupted by the AGN and bulk
motions. It is also the site of H-alpha filaments and young stars. The X-ray
spectroscopic cooling rate associated with this ridge is approximately 165
solar masses/yr, which agrees with the estimate of the star formation rate from
broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to
harbor one of most profoundly disrupted low entropy cores observed in a
cluster, and offers new insights into the survivability of cool cores in the
context of hierarchical structure formation.Comment: 19 pages, 15 figures, 5 tables. Accepted by MNRAS for publication
September 30 201
The Fermi Bubbles: Supersonic Active Galactic Nucleus Jets with Anisotropic Cosmic-Ray Diffusion
The Fermi Gamma-Ray Space Telescope reveals two large bubbles in the Galaxy, which extend nearly symmetrically ~50° above and below the Galactic center. Using three-dimensional (3D) magnetohydrodynamic simulations that self-consistently include the dynamical interaction between cosmic rays (CRs) and thermal gas and anisotropic CR diffusion along the magnetic field lines, we show that the key characteristics of the observed gamma-ray bubbles and the spatially correlated X-ray features in the ROSAT 1.5 keV map can be successfully reproduced by recent jet activity from the central active galactic nucleus. We find that after taking into account the projection of the 3D bubbles onto the sky the physical heights of the bubbles can be much smaller than previously thought, greatly reducing the formation time of the bubbles to about a Myr. This relatively small bubble age is needed to reconcile the simulations with the upper limit of bubble ages estimated from the cooling time of high-energy electrons. No additional physical mechanisms are required to suppress large-scale hydrodynamic instabilities because the evolution time is too short for them to develop. The simulated CR bubbles are edge-brightened, which is consistent with the observed projected flat surface brightness distribution. Furthermore, we demonstrate that the sharp edges of the observed bubbles can be due to anisotropic CR diffusion along magnetic field lines that drape around the bubbles during their supersonic expansion, with suppressed perpendicular diffusion across the bubble surface. Possible causes of the slight bends of the Fermi bubbles to the west are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98587/1/0004-637X_761_2_185.pd
Synthesis, characterization and thermal behaviour of solid state compounds of 2-chlorobenzylidenepyruvate with trivalent aluminium, gallium, indium and scandium metals
Alterações radiográficas e ultra-sonográficas iniciais em osteoartrite experimental eqüina
Desenvolvimento do self e processos de hiperindividualização: interrogações à Psicologia Dialógica
Preparation and thermal decomposition of solid state chelates of ethylenediaminetetraacetic acid with manganese
Solid state of general formula H2[Mn(EDTA)].3,5H2O, where EDTA is ethylenediaminetetraacetate, were
prepared. Thermogravimetry derivative thermogravimetry (TG-DTG), differential scanning calorimetry (DSC) and other
methods of analysis have been used to characterize and to study the thermal stability and thermal decomposition of this
complex
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