298 research outputs found
Eigengalaxies: describing galaxy morphology using principal components in image space
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyWe demonstrate how galaxy morphologies can be represented by weighted sums of "eigengalaxies" and how eigengalaxies can be used in a probabilistic framework to enable principled and simplified approaches in a variety of applications. Eigengalaxies can be derived from a Principal Component Analysis (PCA) of sets of single- or multi-band images. They encode the image space equivalent of basis vectors that can be combined to describe the structural properties of large samples of galaxies in a massively reduced manner. As an illustration, we show how a sample of 10,243 galaxies in the Hubble Space Telescope CANDELS survey can be represented by just 12 eigengalaxies. We show in some detail how this image space may be derived and tested. We also describe a probabilistic extension to PCA (PPCA) which enables the eigengalaxy framework to assign probabilities to galaxies. We present four practical applications of the probabilistic eigengalaxy framework that are particularly relevant for the next generation of large imaging surveys: we (i) show how low likelihood galaxies make for natural candidates for outlier detection (ii) demonstrate how missing data can be predicted (iii) show how a similarity search can be performed on exemplars (iv) demonstrate how unsupervised clustering of objects can be implemented.Peer reviewe
Mapping the CgrA regulon of Rhodospirillum centenum reveals a hierarchal network controlling Gram-negative cyst development
Table S2. A table of all called CgrA ChIP-seq peaks and their locations on the genome. (PDF 286 kb
Effects of tin phosphate nanosheet addition on proton-conducting properties of sulfonated poly(ether sulfone) membranes
Organic/inorganic composite membranes were prepared by dispersing nanosheets of layered tin phosphate
hydrate [Sn(HPO4)2·nH2O (SnP)] in sulfonated poly(ether sulfone) (SPES) at SnP contents of 0–40 vol.%.
The stabilities and proton conductivities of SPES/SnP nanosheet (SnP-NS) composite membraneswere investigated
and comparedwith those of SPES/SnP particle (SnP-P) composite membranes. The chemical stabilities as evaluated
by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier-transform infrared spectroscopy
were improved in both composite membranes. The improvement in the structural stability of SPES/SnP-NS composite
membranes was more evident than that in SPES/SnP-P. The results suggest that exfoliation of SnP increases
the area of the SPES–SnP interface and extends the connectivity of the network of hydrogen bonds. A composite
membrane containing 10 vol.% SnP-NS (SPES/SnP-NS10vol.%) showed a high conductivity of 5.9×10−2 S cm−1
at 150 °C under saturated water vapor pressure. Although less water was present in SPES/SnP-NS10vol.% than in
SPES/SnP-P10vol.% or pure SPES, the conductivity of SnP-NS10vol.% was the highest among these samples at
130 °C under a high relative humidity (RH). However at a low RH, the proton-conducting property was not
improved by changing the composition of the SnP-NS. These results suggest that the hydrogen-bond network
operates effectively for proton conduction at a high RH, but at a low RH, the network fails to conduct as a result
of a decrease in water content accompanied by structural stabilization
The elliptical colour-magnitude relation as a discriminant between the monolithic and merger paradigms: the importance of progenitor bias
The colour-magnitude relation (CMR) of cluster ellipticals has been widely
used to constrain their star formation histories (SFHs) and to discriminate
between the monolithic and merger paradigms of elliptical galaxy formation. We
investigate the elliptical CMR predicted in the merger paradigm by using a LCDM
hierarchical merger model. We first highlight sections of the literature which
indicate that the traditional use of fixed apertures to derive colours gives a
distorted view of the CMR due to the presence of colour gradients in galaxies.
Fixed aperture observations make the CMR steeper and tighter than it really is.
We then show that the star formation history (SFH) of cluster ellipticals
predicted by the model is quasi-monolithic, with over 95 percent of the total
stellar mass formed before a redshift of 1. The quasi-monolithic SFH produces a
predicted CMR that agrees well at all redshifts with its observed counterpart
once the fixed aperture effect is removed. More importantly, we present
arguments to show that the elliptical-only CMR can be used to constrain the
SFHs of present-day cluster ellipticals only if we believe a priori in the
monolithic collapse model. It is not a meaningful tool for constraining the SFH
in the merger paradigm, because a progressively larger fraction of the
progenitor set of present-day cluster ellipticals is contained in late-type
star forming systems at higher redshift, which cannot be ignored when deriving
the SFHs. Hence, the elliptical-only CMR is not a useful discriminant between
the two competing theories of elliptical galaxy evolution.Comment: replaced with accepted versio
The morphological mix of dwarf galaxies in the nearby Universe
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We use a complete, unbiased sample of 257 dwarf (10 8 M < M < 10 9.5 M) galaxies at z < 0.08, in the COSMOS field, to study the morphological mix of the dwarf population in low-density environments. Visual inspection of extremely deep optical images and their unsharp-masked counterparts reveals three principal dwarf morphological classes. 43 per cent and 45 per cent of dwarfs exhibit the traditional ‘early-type’ (elliptical/S0) and ‘late-type’ (spiral) morphologies, respectively. However, 10 per cent populate a ‘featureless’ class, that lacks both the central light concentration seen in early-types and any spiral structure – this class is missing in the massive-galaxy regime. 14 per cent, 27 per cent, and 19 per cent of early-type, late-type, and featureless dwarfs respectively show evidence for interactions, which drive around 20 per cent of the overall star formation activity in the dwarf population. Compared to their massive counterparts, dwarf early-types show a much lower incidence of interactions, are significantly less concentrated and share similar rest-frame colours as dwarf late-types. This suggests that the formation histories of dwarf and massive early-types are different, with dwarf early-types being shaped less by interactions and more by secular processes. The lack of large groups or clusters in COSMOS at z < 0.08, and the fact that our dwarf morphological classes show similar local density, suggests that featureless dwarfs in low-density environments are created via internal baryonic feedback, rather than by environmental processes. Finally, while interacting dwarfs can be identified using the asymmetry parameter, it is challenging to cleanly separate early and late-type dwarfs using traditional morphological parameters, such as ‘CAS’, M 20, and the Gini coefficient (unlike in the massive-galaxy regime).Peer reviewe
Relaxed blue ellipticals: accretion-driven stellar growth is a key evolutionary channel for low mass elliptical galaxies
How elliptical galaxies form is a key question in observational cosmology.
While the formation of massive ellipticals is strongly linked to mergers, the
low mass (Mstar < 10^9.5 MSun) regime remains less well explored. In
particular, studying elliptical populations when they are blue, and therefore
rapidly building stellar mass, offers strong constraints on their formation.
Here, we study 108 blue, low-mass ellipticals (which have a median stellar mass
of 10^8.7 MSun) at z < 0.3 in the COSMOS field. Visual inspection of extremely
deep optical HSC images indicates that less than 3 per cent of these systems
have visible tidal features, a factor of 2 less than the incidence of tidal
features in a control sample of galaxies with the same distribution of stellar
mass and redshift. This suggests that the star formation activity in these
objects is not driven by mergers or interactions but by secular gas accretion.
We combine accurate physical parameters from the COSMOS2020 catalog, with
measurements of local density and the locations of galaxies in the cosmic web,
to show that our blue ellipticals reside in low-density environments, further
away from nodes and large-scale filaments than other galaxies. At similar
stellar masses and environments, blue ellipticals outnumber their normal (red)
counterparts by a factor of 2. Thus, these systems are likely progenitors of
not only normal ellipticals at similar stellar mass but, given their high star
formation rates, also of ellipticals at higher stellar masses. Secular gas
accretion, therefore, likely plays a significant (and possibly dominant) role
in the stellar assembly of elliptical galaxies in the low mass regime.Comment: Published in MNRA
Glass-like ordering and spatial inhomogeneity of magnetic structure in Ba3FeRu2O9 : The role of Fe/Ru-site disorder
Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9,
have been studied over a significant period of time in order to understand the
unusual magnetism of ruthenium metal. However, among them, the M=Fe compound
appears different since it is observed that unlike others, the 3d Fe ions and
4d Ru ions can easily exchange their crystallographic positions and as a result
many possible magnetic interactions become realizable. The present study
involving several experimental methods on this compound establish that the
magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H
ruthenates. Local structural study reveals that the possible Fe/Ru-site
disorder further extends to create local chemical inhomogeneity, affecting the
high temperature magnetism of this material. There is a gradual decrease of
57Fe M\"ossbauer spectral intensity with decreasing temperature (below 100 K),
which reveals that there is a large spread in the magnetic ordering
temperatures, corresponding to many spatially inhomogeneous regions. However,
finally at about 25 K, the whole compound is found to take up a global
glass-like magnetic ordering.Comment: 24 page, 7 figure
Metabolic flexibility revealed in the genome of the cyst-forming α-1 proteobacterium Rhodospirillum centenum
<p>Abstract</p> <p>Background</p> <p><it>Rhodospirillum centenum </it>is a photosynthetic non-sulfur purple bacterium that favors growth in an anoxygenic, photosynthetic N<sub>2</sub>-fixing environment. It is emerging as a genetically amenable model organism for molecular genetic analysis of cyst formation, photosynthesis, phototaxis, and cellular development. Here, we present an analysis of the genome of this bacterium.</p> <p>Results</p> <p><it>R. centenum </it>contains a singular circular chromosome of 4,355,548 base pairs in size harboring 4,105 genes. It has an intact Calvin cycle with two forms of Rubisco, as well as a gene encoding phosphoenolpyruvate carboxylase (PEPC) for mixotrophic CO<sub>2 </sub>fixation. This dual carbon-fixation system may be required for regulating internal carbon flux to facilitate bacterial nitrogen assimilation. Enzymatic reactions associated with arsenate and mercuric detoxification are rare or unique compared to other purple bacteria. Among numerous newly identified signal transduction proteins, of particular interest is a putative bacteriophytochrome that is phylogenetically distinct from a previously characterized <it>R. centenum </it>phytochrome, Ppr. Genes encoding proteins involved in chemotaxis as well as a sophisticated dual flagellar system have also been mapped.</p> <p>Conclusions</p> <p>Remarkable metabolic versatility and a superior capability for photoautotrophic carbon assimilation is evident in <it>R. centenum</it>.</p
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