We study the case of a bright (L > L
) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z = 0.05) undergoing ram-pressure stripping. Integral-field spectroscopy with ...Wide Field Spectrograph (WiFeS) at the 2.3-m Australian National University telescope, complemented by imaging in ultraviolet (GALEX), B and R European Southern Observatory (ESO) 2.2-m WFI, Hα (Magellan), K (United Kingdom Infrared Telescope), 24 and 70 μm (Spitzer), allows us to reveal the impact of ram pressure on the interstellar medium. With these data we study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc, extending ∼13 kpc in projection from it. Narrow-band Hα imaging resolves this outflow into a complex of knots and filaments, similar to those seen in other cluster galaxies undergoing ram-pressure stripping. The gas velocity field is complex with the extraplanar gas showing signature of rotation, while the stellar velocity field is regular and the K-band image shows a symmetric stellar distribution. We use line-ratio diagnostics to ascertain the origin of the observed emission. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust (A
v
= 1.5-2.3 mag). All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc south-west (SW) from the centre. These two regions account for half of the total star formation in the galaxy, which overall amounts to 7.2 ± 2.2 M yr−1. In the SW region we identify a starburst characterized by a ∼5× increase in the star formation rate over the last ∼100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t ∼ 60 Myr ago, and an angle between the galaxy rotation axis and the intracluster medium wind of ∼45°. The ram pressure is therefore acting at an intermediate angle between face-on and edge-on. Taking into account that the galaxy is found ∼1 Mpc from the cluster centre in a relatively low density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores, as also recently observed in the Virgo cluster.
Aims. We investigate the influence of stellar bulges on the star formation and morphology of disc galaxies that suffer from ram pressure. Several tree-SPH (smoothed particle hydrodynamics) ...simulations have been carried out to study the dependence of the star formation rate on the mass and size of a stellar bulge. In addition, different strengths of ram pressure and different alignments of the disc with respect to the intra-cluster medium (ICM) are applied. Methods. The simulations were carried out with the combined N-body/hydrodynamic code GADGET-2 with radiative cooling and a recipe for star formation. The same galaxy with different bulge sizes was used to accomplish 31 simulations with varying inclination angles and surrounding gas densities of 10-27g cm-3 and 10-28g cm-3. For all the simulations a relative velocity of 1000 km s-1 for the galaxies and an initial gas temperature for the ICM of 107K were applied. Besides galaxies flying edge-on and face-on through the surrounding gas, various disc tilt angles in between were used. To allow a comparison, the galaxies with the different bulges were also evolved in isolation to contrast the star formation rates. Furthermore, the influence of different disc gas mass fractions has been investigated. Results. As claimed in previous works, when ram pressure is acting on a galaxy, the star formation rate (SFR) is enhanced and rises up to four times with increasing ICM density compared to galaxies that evolve in isolation. However, a bulge suppresses the SFR when the same ram pressure is applied. Consequently, fewer new stars are formed because the SFR can be lowered by up to 2M⊙ yr-1. Furthermore, the denser the surrounding gas, the more interstellar medium (ISM) is stripped. While at an ICM density of 10-28g cm-3 about 30% of the ISM is stripped, the galaxy is almost completely (more than 90%) stripped when an ICM density of 10-27g cm-3 is applied. But again, a bulge prevents the stripping of the ISM and reduces the amount being stripped by up to 10%. Thereby, fewer stars are formed in the wake if the galaxy contains a bulge. The dependence of the SFR on the disc tilt angle is not very pronounced. Merely a slight trend of decreasing star formation with increasing inclination angle can be determined. Furthermore, with increasing disc tilt angles, less gas is stripped and therefore fewer stars are formed in the wake. Reducing the disc gas mass fraction results in a lower SFR when the galaxies evolve in vacuum. On the other hand, the enhancement of the SFR in case of acting ram pressure is less pronounced with increasing gas mass fraction. Moreover, the fractional amount of stripped gas does not depend on the gas mass fraction.
GMD@CSB.DB: the Golm Metabolome Database Kopka, Joachim; Schauer, Nicolas; Krueger, Stephan ...
Bioinformatics,
04/2005, Letnik:
21, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Metabolomics, in particular gas chromatography–mass spectrometry (GC–MS) based metabolite profiling of biological extracts, is rapidly becoming one of the cornerstones of functional genomics and ...systems biology. Metabolite profiling has profound applications in discovering the mode of action of drugs or herbicides, and in unravelling the effect of altered gene expression on metabolism and organism performance in biotechnological applications. As such the technology needs to be available to many laboratories. For this, an open exchange of information is required, like that already achieved for transcript and protein data. One of the key-steps in metabolite profiling is the unambiguous identification of metabolites in highly complex metabolite preparations from biological samples. Collections of mass spectra, which comprise frequently observed metabolites of either known or unknown exact chemical structure, represent the most effective means to pool the identification efforts currently performed in many laboratories around the world. Here we present GMD, The Golm Metabolome Database, an open access metabolome database, which should enable these processes. GMD provides public access to custom mass spectral libraries, metabolite profiling experiments as well as additional information and tools, e.g. with regard to methods, spectral information or compounds. The main goal will be the representation of an exchange platform for experimental research activities and bioinformatics to develop and improve metabolomics by multidisciplinary cooperation. Availability: http://csbdb.mpimp-golm.mpg.de/gmd.html Contact: Steinhauser@mpimp-golm.mpg.de Supplementary information: http://csbdb.mpimp-golm.mpg.de/
We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (
$\mathcal {M}_{\star }\sim 0.4\text{--}1\times 10^{10}$
M⊙) galaxies are members ...of the two clusters SC 1329−313 (z ∼ 0.045) and SC 1327−312 (z ∼ 0.049). Integral-field spectroscopy complemented by imaging in the ugriK bands and in Hα narrow band is used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS 61086 and SOS 90630, we observe one-sided extraplanar ionized gas extending respectively ∼30 and ∼41 kpc in projection from their discs. The galaxies' gaseous discs are truncated, and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS 61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting ∼250 Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster–cluster interaction experienced by SC 1329−313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS 90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster–cluster merger on RPS.
We present an isolated Milky-Way-like simulation in the gadget2
N-body smoothed particle hydrodynamics (SPH) code. The Galactic disc star formation rate (SFR) surface densities and a stellar mass ...indicative of the Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life-friendly environments. SFR and stellar component density are calculated by averaging the gadget2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from 10 to 15 kpc cylindrical galactocentric distance in a 10-Gyr simulated time span. At 10 Gyr, the simulation results imply the following. Stellar particles that have spent almost all of their lifetime in habitable-friendly conditions typically reside at ∼16 kpc from the Galactic Centre and are ∼3 Gyr old. Stellar particles that have spent ≥90 per cent of their 4–5 Gyr long lifetime in habitable-friendly conditions are also predominantly found in the outskirts of the Galactic disc. Fewer than 1 per cent of these particles can be found at a typical Solar system galactocentric distance of 8–10 kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disc around stellar hosts younger than the Sun.
Aims. We investigate the effect of ram pressure stripping (RPS) on several simulations of merging pairs of gas-rich spiral galaxies. We are concerned with the changes in stripping efficiency and the ...time evolution of the star formation rate. Our goal is to provide an estimate of the combined effect of merging and RPS compared to the influence of the individual processes. Methods. We make use of the combined N-body/hydrodynamic code GADGET-2. The code features a threshold-based statistical recipe for star formation, as well as radiative cooling and modeling of galactic winds. In our simulations, we vary mass ratios between 1:4 and 1:8 in a binary merger. We sample different geometric configurations of the merging systems (edge-on and face-on mergers, different impact parameters). Furthermore, we vary the properties of the intracluster medium (ICM) in rough steps: the speed of the merging system relative to the ICM between 500 and 1000 km s-1, the ICM density between 10-29 and 10-27 g cm-3, and the ICM direction relative to the mergers’ orbital plane. Ram pressure is kept constant within a simulation time period, as is the ICM temperature of 107 K. Each simulation in the ICM is compared to simulations of the merger in vacuum and the non-merging galaxies with acting ram pressure. Results. Averaged over the simulation time (1 Gyr) the merging pairs show a negligible 5% enhancement in SFR, when compared to single galaxies under the same environmental conditions. The SFRs peak at the time of the galaxies first fly-through. There, our simulations show SFRs of up to 20 M⊙ yr-1 (compared to 3 M⊙ yr-1 of the non-merging galaxies in vacuum). In the most extreme case, this constitutes a short-term (<50 Myr) SFR increase of 50 % over the non-merging galaxies experiencing ram pressure. The wake of merging galaxies in the ICM typically has a third to half the star mass seen in the non-merging galaxies and 5% to 10% less gas mass. The joint effect of RPS and merging, according to our simulations, is not significantly different from pure ram pressure effects.
Electrowetting is a versatile tool to reduce the apparent contact angle of partially wetting conductive liquids by several tens of degrees via an externally applied voltage. We studied various ...fundamental and applied aspects of equilibrium liquid surface morphologies both theoretically and experimentally. Our theoretical analysis showed that surface profiles on homogeneous surfaces display a diverging curvature in the vicinity of the three phase contact line. The asymptotic contact angle at the contact line is equal to Young's angle, independent of the applied voltage. With respect to the morphology of the liquid surface, contact angle variations achieved by electrowetting are equivalent to those achieved by varying the chemical nature of the substrates, except for electric field-induced distortions in a region close to the contact line. Experimentally, we studied the (global) morphology of liquid microstructure substrates with stripe-shaped electrodes. As the local contact angle is reduced by increasing the applied voltage, liquid droplets elongate along the stripe axis as expected. For droplets on a single surface with a stripe electrode, there is a discontinuous morphological transition where elongated droplets transform into translationally invariant cylinder segments with the contact line pinned along the stripe edge and vice versa. If the liquid is confined between two parallel surfaces with parallel stripe electrodes, the elongation of the droplet and its transformation into a translationally invariant morphology with pinned contact lines is continuous. Experimental results are compared to analytical and numerical models.
The influence of an imidazolium type ionic liquid (IL) on the relaxation behavior of carbon-nanotube (CNT) based polychloroprene nanocomposites prepared by melt mixing has been investigated by ...broadband dielectric spectroscopy. It is demonstrated that the presence of the ionic liquid modifies the relaxation behavior of the pure rubber matrix and leads to a significant increase of the conductivity for the CNT/rubber composites. For the unfilled rubber, a distinct glass transition of the IL is observed for high concentrations demonstrating that the IL forms a separate phase. The increased conductivity of the CNT-filled rubber composites is related to a physical coupling between CNTs and rubber matrix mediated by IL leading to a better dispersion of the CNTs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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