116 research outputs found
The Galaxy Structure-Redshift Relationship
There exists a gradual, but persistent, evolutionary effect in the galaxy
population such that galaxy structure and morphology change with redshift. This
galaxy structure-redshift relationship is such that an increasingly large
fraction of all bright and massive galaxies at redshifts 2 < z < 3 are
morphologically peculiar at wavelengths from rest-frame ultraviolet to
rest-frame optical. There are however examples of morphologically selected
spirals and ellipticals at all redshifts up to z ~ 3. At lower redshift, the
bright galaxy population smoothly transforms into normal ellipticals and
spirals. The rate of this transformation strongly depends on redshift, with the
swiftest evolution occurring between 1 < z < 2. This review characterizes the
galaxy structure-redshift relationship, discusses its various physical causes,
and how these are revealing the mechanisms responsible for galaxy formation.Comment: 20 pages, 8 figures. Invited Review to appear in "Penetrating Bars
Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes A New Note", ed.
D. Block et a
Supermassive black holes do not correlate with galaxy disks or pseudobulges
The masses of supermassive black holes are known to correlate with the
properties of the bulge components of their host galaxies. In contrast, they
appear not to correlate with galaxy disks. Disk-grown pseudobulges are
intermediate in properties between bulges and disks. It has been unclear
whether they do or do not correlate with black holes in the same way that
bulges do, because too few pseudobulges were classified to provide a clear
result. At stake are conclusions about which parts of galaxies coevolve with
black holes, possibly by being regulated by energy feedback from black holes.
Here we report pseudobulge classifications for galaxies with dynamically
detected black holes and combine them with recent measurements of velocity
dispersions in the biggest bulgeless galaxies. These data confirm that black
holes do not correlate with disks and show that they correlate little or not at
all with pseudobulges. We suggest that there are two different modes of black
hole feeding. Black holes in bulges grow rapidly to high masses when mergers
drive gas infall that feeds quasar-like events. In contrast, small black holes
in bulgeless galaxies and galaxies with pseudobulges grow as low-level
Seyferts. Growth of the former is driven by global processes, so the biggest
black holes coevolve with bulges, but growth of the latter is driven locally
and stochastically, and they do not coevolve with disks and pseudobulges.Comment: 6 pages, 3 Postscript figures, 1 table; to appear in Nature (20
January 2011
X-ray Absorption and Reflection in Active Galactic Nuclei
X-ray spectroscopy offers an opportunity to study the complex mixture of
emitting and absorbing components in the circumnuclear regions of active
galactic nuclei, and to learn about the accretion process that fuels AGN and
the feedback of material to their host galaxies. We describe the spectral
signatures that may be studied and review the X-ray spectra and spectral
variability of active galaxies, concentrating on progress from recent Chandra,
XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for
absorption covering a wide range of column densities, ionization and dynamics,
and discuss the growing evidence for partial-covering absorption from data at
energies > 10 keV. Such absorption can also explain the observed X-ray spectral
curvature and variability in AGN at lower energies and is likely an important
factor in shaping the observed properties of this class of source.
Consideration of self-consistent models for local AGN indicates that X-ray
spectra likely comprise a combination of absorption and reflection effects from
material originating within a few light days of the black hole as well as on
larger scales. It is likely that AGN X-ray spectra may be strongly affected by
the presence of disk-wind outflows that are expected in systems with high
accretion rates, and we describe models that attempt to predict the effects of
radiative transfer through such winds, and discuss the prospects for new data
to test and address these ideas.Comment: Accepted for publication in the Astronomy and Astrophysics Review. 58
pages, 9 figures. V2 has fixed an error in footnote
On the Origin of S0 Galaxies
I will review the basic properties of S0 galaxies in the local Universe in
relation to both elliptical and spiral galaxies, their neighbours on the Hubble
sequence, and also in relation to dwarf spheroidal (dSph) galaxies. This will
include colours, luminosities, spectral features, information about the age and
metallicity composition of their stellar populations and globular clusters,
about their ISM content, as well as kinematic signatures and their implications
for central black hole masses and past interaction events, and the number
ratios of S0s to other galaxy types in relation to environmental galaxy
density. I will point out some caveats as to their morphological discrimination
against other classes of galaxies, discuss the role of dust and the wavelength
dependence of bulge/disk light ratios. These effects are of importance for
investigations into the redshift evolution of S0 galaxies -- both as individual
objects and as a population. The various formation and transformation scenarios
for S0 and dSph galaxies will be presented and confronted with the available
observations.Comment: Invited Review, 18 pages, ``BARS 2004'' Conference, South Africa,
June 2004, eds.: K. C. Freeman, D. L. Block, I. Puerari, R. Groess, Kluwer,
in pres
Primary Hyperparathyroidism Influences the Expression of Inflammatory and Metabolic Genes in Adipose Tissue
Background: Primary hyperparathyroidism (PHPT) is characterised by increased production of parathyroid hormone (PTH) resulting in elevated serum calcium levels. The influence on bone metabolism with altered bone resorption is the most studied clinical condition in PHPT. In addition to this, patients with PHPT are at increased risk of non-skeletal diseases, such as impaired insulin sensitivity, arterial hypertension and increased risk of death by cardiovascular diseases (CVD), possibly mediated by a chronic low-grade inflammation. The aim of this study was to investigate whether adipose tissue reflects the low-grade inflammation observed in PHPT patients. Methodology/Principal Findings: Subcutaneous fat tissue from the neck was sampled from 16 non-obese patients with PHPT and from 16 patients operated for benign thyroid diseases, serving as weight-matched controls. RNA was extracted and global gene expression was analysed with Illumina BeadArray Technology. We found 608 differentially expressed genes (q-value,0.05), of which 347 were up-regulated and 261 were down-regulated. Gene ontology analysis showed that PHPT patients expressed increased levels of genes involved in immunity and defense (e.g. matrix metallopeptidase 9, S100 calcium binding protein A8 and A9, CD14, folate receptor 2), and reduced levels of genes involved in metabolic processes. Analysis of transcription factor binding sites present in the differentially expressed genes corroborated the up-regulation of inflammatory processes. Conclusions/Significance: Our findings demonstrate that PHPT strongly influences gene regulation in fat tissue, which may result in altered adipose tissue function and release of pathogenic factors that increase the risk of CVD
Facile labelling of an anti-epidermal growth factor receptor Nanobody with 68Ga via a novel bifunctional desferal chelate for immuno-PET
Maladaptive Habitat Selection of a Migratory Passerine Bird in a Human-Modified Landscape
In human-altered environments, organisms may preferentially settle in poor-quality habitats where fitness returns are lower relative to available higher-quality habitats. Such ecological trapping is due to a mismatch between the cues used during habitat selection and the habitat quality. Maladaptive settlement decisions may occur when organisms are time-constrained and have to rapidly evaluate habitat quality based on incomplete knowledge of the resources and conditions that will be available later in the season. During a three-year study, we examined settlement decision-making in the long-distance migratory, open-habitat bird, the Red-backed shrike (Lanius collurio), as a response to recent land-use changes. In Northwest Europe, the shrikes typically breed in open areas under a management regime of extensive farming. In recent decades, Spruce forests have been increasingly managed with large-size cutblocks in even-aged plantations, thereby producing early-successional vegetation areas that are also colonised by the species. Farmland and open areas in forests create mosaics of two different types of habitats that are now occupied by the shrikes. We examined redundant measures of habitat preference (order of settlement after migration and distribution of dominant individuals) and several reproductive performance parameters in both habitat types to investigate whether habitat preference is in line with habitat quality. Territorial males exhibited a clear preference for the recently created open areas in forests with higher-quality males settling in this habitat type earlier. Reproductive performance was, however, higher in farmland, with higher nest success, offspring quantity, and quality compared to open areas in forests. The results showed strong among-year consistency and we can therefore exclude a transient situation. This study demonstrates a case of maladaptive habitat selection in a farmland bird expanding its breeding range to human-created open habitats in plantations. We discuss the reasons that could explain this decision-making and the possible consequences for the population dynamics and persistence
Deregulation of Rab and Rab Effector Genes in Bladder Cancer
Growing evidence indicates that Rab GTPases, key regulators of intracellular transport in eukaryotic cells, play an important role in cancer. We analysed the deregulation at the transcriptional level of the genes encoding Rab proteins and Rab-interacting proteins in bladder cancer pathogenesis, distinguishing between the two main progression pathways so far identified in bladder cancer: the Ta pathway characterized by a high frequency of FGFR3 mutation and the carcinoma in situ pathway where no or infrequent FGFR3 mutations have been identified. A systematic literature search identified 61 genes encoding Rab proteins and 223 genes encoding Rab-interacting proteins. Transcriptomic data were obtained for normal urothelium samples and for two independent bladder cancer data sets corresponding to 152 and 75 tumors. Gene deregulation was analysed with the SAM (significant analysis of microarray) test or the binomial test. Overall, 30 genes were down-regulated, and 13 were up-regulated in the tumor samples. Five of these deregulated genes (LEPRE1, MICAL2, RAB23, STXBP1, SYTL1) were specifically deregulated in FGFR3-non-mutated muscle-invasive tumors. No gene encoding a Rab or Rab-interacting protein was found to be specifically deregulated in FGFR3-mutated tumors. Cluster analysis showed that the RAB27 gene cluster (comprising the genes encoding RAB27 and its interacting partners) was deregulated and that this deregulation was associated with both pathways of bladder cancer pathogenesis. Finally, we found that the expression of KIF20A and ZWINT was associated with that of proliferation markers and that the expression of MLPH, MYO5B, RAB11A, RAB11FIP1, RAB20 and SYTL2 was associated with that of urothelial cell differentiation markers. This systematic analysis of Rab and Rab effector gene deregulation in bladder cancer, taking relevant tumor subgroups into account, provides insight into the possible roles of Rab proteins and their effectors in bladder cancer pathogenesis. This approach is applicable to other group of genes and types of cancer
Computational models in plant-pathogen interactions: the case of Phytophthora infestans
<p>Abstract</p> <p>Background</p> <p><it>Phytophthora infestans </it>is a devastating oomycete pathogen of potato production worldwide. This review explores the use of computational models for studying the molecular interactions between <it>P. infestans </it>and one of its hosts, <it>Solanum tuberosum</it>.</p> <p>Modeling and conclusion</p> <p>Deterministic logistics models have been widely used to study pathogenicity mechanisms since the early 1950s, and have focused on processes at higher biological resolution levels. In recent years, owing to the availability of high throughput biological data and computational resources, interest in stochastic modeling of plant-pathogen interactions has grown. Stochastic models better reflect the behavior of biological systems. Most modern approaches to plant pathology modeling require molecular kinetics information. Unfortunately, this information is not available for many plant pathogens, including <it>P. infestans</it>. Boolean formalism has compensated for the lack of kinetics; this is especially the case where comparative genomics, protein-protein interactions and differential gene expression are the most common data resources.</p
Evolution of active galactic nuclei
[Abriged] Supermassive black holes (SMBH) lurk in the nuclei of most massive
galaxies, perhaps in all of them. The tight observed scaling relations between
SMBH masses and structural properties of their host spheroids likely indicate
that the processes fostering the growth of both components are physically
linked, despite the many orders of magnitude difference in their physical size.
This chapter discusses how we constrain the evolution of SMBH, probed by their
actively growing phases, when they shine as active galactic nuclei (AGN) with
luminosities often in excess of that of the entire stellar population of their
host galaxies. Following loosely the chronological developments of the field,
we begin by discussing early evolutionary studies, when AGN represented beacons
of light probing the most distant reaches of the universe and were used as
tracers of the large scale structure. This early study turned into AGN
"Demography", once it was realized that the strong evolution (in luminosity,
number density) of the AGN population hindered any attempt to derive
cosmological parameters from AGN observations directly. Following a discussion
of the state of the art in the study of AGN luminosity functions, we move on to
discuss the "modern" view of AGN evolution, one in which a bigger emphasis is
given to the physical relationships between the population of growing black
holes and their environment. This includes observational and theoretical
efforts aimed at constraining and understanding the evolution of scaling
relations, as well as the resulting limits on the evolution of the SMBH mass
function. Physical models of AGN feedback and the ongoing efforts to isolate
them observationally are discussed next. Finally, we touch upon the problem of
when and how the first black holes formed and the role of black holes in the
high-redshift universe.Comment: 75 pages, 35 figures. Modified version of the chapter accepted to
appear in "Planets, Stars and Stellar Systems", vol 6, ed W. Keel
(www.springer.com/astronomy/book/978-90-481-8818-5). The number of references
is limited upon request of the editors. Original submission to Springer: June
201
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