The Bright and the Dark Side of Malin 1

Malin 1 has long been considered a prototype giant, dark matter dominated Low Surface Brightness galaxy. Two recent studies, one based on a re-analysis of VLA HI observations and the other on an archival Hubble I-band image, throw a new light on this enigmatic galaxy and on its dark/luminous matter properties.Comment: 4 pages, 3 figures, to appear in the Proceedings of the 41st ESLAB Symposium "The Impact of HST on European Astronomy", 29 May to 1 June 2007, ESTEC, Noordwijk, N

Estimation of the occurrence, severity, and volume of heartwood rot using airborne laser scanning and optical satellite data

Rot in commercial timber reduces the value of the wood substantially and estimating the occurrence, severity, and volume of heartwood rot would be a useful tool in decision-making to minimize economic losses. Remotely sensed data has recently been used for mapping rot on a single-tree level, and although the results have been relatively poor, some potential has been shown. This study applied area-based approaches to predict rot occurrence, rot severity, and rot volume , at an area level. Ground reference data were collected from harvester operations in 2019–2021. Predictor variables were calculated from multi-temporal remotely sensed data together with environmental variables. Response variables from the harvester data and predictor variables from remotely sensed data were aggregated to grid cells and to forest stands. Random Forest models were built for the different combinations of response variables and predictor subsets, and validated with both random- and spatial cross-validation. The results showed that it was not possible to estimate rot occurrence and rot severity with the applied modeling procedure (pR2: 0.00–0.16), without spatially close training data. The better performance of rot volume models (pR2: 0.12–0.37) was mainly due to the correlation between timber volume and rot volum

Testing the nature of S0 galaxies using planetary nebula kinematics in NGC 1023

We investigate the manner in which lenticular galaxies are formed by studying their stellar kinematics: an S0 formed from a fading spiral galaxy should display similar cold outer disc kinematics to its progenitor, while an S0 formed in a minor merger should be more dominated by random motions. In a pilot study to attempt to distinguish between these scenarios, we have measured the planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the Planetary Nebula Spectrograph, we have detected and measured the line-of-sight velocities of 204 candidate PNe in the field of this galaxy. Out to intermediate radii, the system displays the kinematics of a normal rotationally-supported disc system. After correction of its rotational velocities for asymmetric drift, the galaxy lies just below the spiral galaxy Tully-Fisher relation, as one would expect for a fading system. However, at larger radii the kinematics undergo a gradual but major transition to random motion with little rotation. This transition does not seem to reflect a change in the viewing geometry or the presence of a distinct halo component, since the number counts of PNe follow the same simple exponential decline as the stellar continuum with the same projected disc ellipticity out to large radii. The galaxy's small companion, NGC 1023A, does not seem to be large enough to have caused the observed modification either. This combination of properties would seem to indicate a complex evolutionary history in either the transition to form an S0 or in the past life of the spiral galaxy from which the S0 formed. More data sets of this type from both spirals and S0s are needed in order to definitively determine the relationship between these types of system.Comment: Accepted for publication in MNRAS. Version with full resolution figure 1 can be found at http://www.nottingham.ac.uk/~ppzmrm/N1023_PNS.accepted.pd

Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae

We examine the dark matter properties of nearby early-type galaxies using planetary nebulae (PNe) as mass probes. We have designed a specialised instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William Herschel telescope, with the purpose of measuring PN velocities with best efficiency. The primary scientific objective of this custom-built instrument is the study of the PN kinematics in 12 ordinary round galaxies. Preliminary results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al. 2003) are now confirmed by the first complete PN.S datasets. On the other hand early-type galaxies with a "regular" dark matter content are starting to be observed among the brighter PN.S target sample, thus confirming a correlation between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and the galaxy luminosity and mass.Comment: 5 pages, 2 figures. To appear in the proceedings of the IAU Symposium 244 "Dark Galaxies and Lost Baryons", Cardiff 25-29 June 2007, eds. J.I. Davies & M.J. Disne

Large scale nested stellar discs in NGC 7217

NGC7217 is an unbarred early-type spiral galaxy having a multi-segment exponential light profile and a system of starforming rings of the unknown origin; it also possesses a circumnuclear gaseous polar disc. We analysed new long slit spectroscopic data for NGC7217 and derived the radial distributions of its stellar population parameters and stellar and gaseous kinematics up to the radius of r~100 arcsec (~8 kpc). We performed the dynamical analysis of the galaxy by recovering its velocity ellipsoid at different radii, and estimated the scaleheights of its two exponential discs. The inner exponential stellar disc of NGC7217 appears to be thin and harbours intermediate age stars (t(SSP) ~ 5 Gyr). The outer stellar disc seen between the radii of 4 and 7 kpc is very thick (z0 = 1...3 kpc), metal-poor, [Fe/H]<-0.4 dex, and has predominantly young stars, t(SSP) = 2 Gyr. The remnants of minor mergers of gas-rich satellites with an early-type giant disc galaxy available in the GalMer database well resemble different structural components of NGC7217, suggesting two minor merger events in the past responsible for the formation of the inner polar gaseous disc and large outer starforming ring. Another possibility to form the outer ring is the re-accretion of the tidal streams created by the first minor merger.Comment: Accepted to MNRAS, 12 pages, 10 figure

Band - Weg interactie

De huidige infrastructuur van wegen waarover men zich snel en comfortabel kan verplaatsen is niet meer weg te denken uit onze maatschappij. Twee “componenten” die hierbij een belangrijke rol spelen zijn het wegdek en de band. Het contact tussen band en wegdek is mede bepalend voor de veiligheid. De rolweerstand beïnvloedt het brandstofverbruik en dus de uitstoot van uitlaatgassen. De mechanische eigenschappen en geometrie van het wegdek en de band bepalen de geluidproductie (verkeersgeluid) maar ook de mate van slijtage van beide componenten (fijn stof). Er wordt onderzoek gedaan om de veiligheid, de rolweerstand, de duurzaamheid e.d. van banden en wegdek te verbeteren. In veel gevallen wordt dit door de bandenindustrie en de wegdekproducenten afzonderlijk gedaan. Op deze manier streeft men er naar om te komen tot een optimale band en een optimaal wegdek. Maar wat optimaal is voor de band hoeft nog niet optimaal voor het wegdek te zijn. Vandaar dat voor een echt optimale combinatie van band en wegdek, onderzoek moet worden gedaan naar de gekoppelde situatie of wel naar band-weg interactie. Om dit te realiseren hebben 4 onderzoeksgroepen van de Universiteit Twente met ervaring op het gebied van wegdekken of banden de krachten gebundeld teneinde band-wegdek interactie (modelmatig en experimenteel) integraal te kunnen onderzoeke

Plexin A Is a Neuronal Semaphorin Receptor that Controls Axon Guidance

AbstractThe Semaphorins comprise a large family of secreted and transmembrane proteins, some of which function as repellents during axon guidance. Semaphorins fall into seven subclasses. Neuropilins are neuronal receptors for class III Semaphorins. In the immune system, VESPR, a member of the Plexin family, is a receptor for a viral-encoded Semaphorin. Here, we identify two Drosophila Plexins, both of which are expressed in the developing nervous system. We present evidence that Plexin A is a neuronal receptor for class I Semaphorins (Sema 1a and Sema 1b) and show that Plexin A controls motor and CNS axon guidance. Plexins, which themselves contain complete Semaphorin domains, may be both the ancestors of classical Semaphorins and binding partners for Semaphorins

Evolutionary paths to and from the red sequence: Star formation and HI properties of transition galaxies at z~0

(Abridged) We investigate the properties of galaxies between the blue and the red sequence (i.e., the transition region) by combining UV and NIR imaging to HI line observations for a volume-limited sample of nearby galaxies. We confirm the existence of a tight relation between colour and HI-fraction across all the range of colours, although outside the blue cloud this trend becomes gradually weaker. Transition galaxies are divided into two different families, according to their atomic hydrogen content. HI-deficient galaxies are the majority of transition galaxies in our sample. They are found in high density environments and all their properties are consistent with a quenching of the star formation via gas stripping. However, while the migration from the blue cloud is relatively quick (i.e., <=1 Gyr), a longer amount of time (a few Gyr at least) seems required to completely suppress the star formation and reach the red sequence. At all masses, migrating HI-deficient galaxies are mainly disks, implying that the mechanism responsible for today's migration in clusters cannot have played a significant role in the creation of the red sequence at high-redshift. Conversely, HI-normal transition galaxies are a more heterogeneous population. A fraction of these objects show evidence for accretion/minor-merging events suggesting that at least part of the HI reservoir has an external origin. The detailed evolution of such systems is still unclear, but our analysis suggests that some galaxies might have migrated back from the red sequence after accretion events. Our study clearly shows the variety of evolutionary paths leading to the transition region and suggests that the transition galaxies may not be always associated with systems quickly migrating from the blue to the red sequence.Comment: 19 pages, 11 Figures, 1 Table. MNRAS in press. High resolution version available at http://www.astro.cardiff.ac.uk/pub/Luca.Cortese/papers/mnras09_1159_hires.p