534 research outputs found
The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-type galaxies
with the presence of optical morphological peculiarities, as measured by the
fine-structure index (Sigma). HI mapping observations from the literature are
used to track the cold-gas content, and archival ROSAT PSPC data are used to
quantify the hot-gas content. We find that E and S0 galaxies with a high
incidence of optical peculiarities are exclusively X-ray underluminous and,
therefore, deficient in hot gas. In contrast, more relaxed galaxies with little
or no signs of optical peculiarities span a wide range of X-ray luminosities.
That is, the X-ray excess anticorrelates with Sigma. There appears to be no
similar trend of cold-gas content with either fine-structure index or X-ray
content. The fact that only apparently relaxed E and S0 galaxies are strong
X-ray emitters is consistent with the hypothesis that after strong disturbances
such as a merger hot-gas halos build up over a time scale of several gigayears.
This is consistent with the expected mass loss from stars.Comment: 12 pages, latex, 5 figures. Accepted for publication in A
Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
We study dust and associated molecular gas in 352 nearby early-type galaxies
(ETGs) with prominent dust lanes. 65% of these `dusty ETGs' (D-ETGs) are
morphologically disturbed, suggesting a merger origin. This is consistent with
the D-ETGs residing in lower density environments compared to the controls
drawn from the general ETG population. 80% of D-ETGs inhabit the field
(compared to 60% of the controls) and <2% inhabit clusters (compared to 10% of
the controls). Compared to the controls, D-ETGs exhibit bluer UV-optical
colours (indicating enhanced star formation) and an AGN fraction that is more
than an order of magnitude greater (indicating higher incidence of nuclear
activity). The clumpy dust mass residing in large-scale features is estimated,
using the SDSS r-band images, to be 10^{4.5}-10^{6.5} MSun. A comparison to the
total (clumpy + diffuse) dust masses- calculated using the far-IR fluxes of 15%
of the D-ETGs that are detected by the IRAS- indicates that only ~20% of the
dust resides in these large-scale features. The dust masses are several times
larger than the maximum value expected from stellar mass loss, ruling out an
internal origin. The dust content shows no correlation with the blue
luminosity, indicating that it is not related to a galactic scale cooling flow.
No correlation is found with the age of the recent starburst, suggesting that
the dust is accreted directly in the merger rather than being produced in situ
by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in
the literature we estimate that the median current and initial molecular gas
fraction are ~1.3% and ~4%, respectively. Recent work suggests that the merger
activity in nearby ETGs largely involves minor mergers (mass ratios between
1:10 and 1:4). If the IRAS-detected D-ETGs form via this channel, then the
original gas fractions of the accreted satellites are 20%-44%. [Abridged]Comment: 11 pages, 18 figures, 1 table, MNRAS (Accepted for publication- 2012
March 19
Dynamical mean-field study of ferromagnetism in the periodic Anderson model
The ferromagnetic phase diagram of the periodic Anderson model is calculated
using dynamical mean-field theory in combination with the modified perturbation
theory. Concentrating on the intermediate valence regime, the phase boundaries
are established as function of the total electron density, the position of the
atomic level and the hybridization strength. The main contribution to the
magnetic moment stems from the f-electrons. The conduction band polarization
is, depending on the system parameters either parallel or antiparallel to the
f-magnetization. By investigating the densities of states, one observes that
the change of sign of the conduction band polarization is closely connected to
the hybridization gap, which is only apparent in the case of almost complete
polarization of the f-electrons. Finite-temperature calculations are also
performed, the Curie temperature as function of electron density and f-level
position are determined. In the intermediate-valence regime, the phase
transitions are found to be of second order.Comment: 12 pages, 11 figures, accepted by Phys. Rev.
The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years
We combine deep UBVRIzJK photometry from the Multiwavelength Survey by
Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a
large-scale study of the rest-frame ultraviolet (UV) properties of 674
high-redshift (0.5<z<1) early-type galaxies, drawn from the Extended Chandra
Deep Field South (E-CDFS). Galaxy morphologies are determined through visual
inspection of Hubble Space Telescope (HST) images taken from the GEMS survey.
We harness the sensitivity of the UV to young (<1 Gyr old) stars to quantify
the recent star formation history of early-type galaxies across a range of
luminosities (-23.5 < M(V) < -18). Comparisons to simple stellar populations
forming at high redshift indicate that only ~1.1 percent of early-types in this
sample are consistent with purely passive ageing since z=2. Parametrising the
recent star formation (RSF) in terms of the mass fraction of stars less than a
Gyr old, we find that the early-type population as a whole shows a typical RSF
between 5 and 13% in the redshift range 0.5<z<1. Early-types on the UV red
sequence show RSF values less than 5% while the reddest early-types are
virtually quiescent with RSF values of ~1%. We find compelling evidence that
early-types of all luminosities form stars over the lifetime of the Universe,
although the bulk of their star formation is already complete at high redshift.
This tail-end of star formation is measurable and not negligible, with luminous
(-23<M(V)<-20.5) early-types potentially forming 10-15% of their mass since
z=1, with their less luminous (M(V)>-20.5) counterparts potentially forming
30-60 percent of their mass in the same redshift range. (abridged)Comment: Submitted to MNRA
The GALEX UV emission in shell galaxies: tracing galaxy "rejuvenation" episodes
We present the GALEX far FUV and near NUV ultraviolet imaging of three nearby
shell galaxies, namely NGC 2865, NGC 5018 and NGC 7135. The system of shells
and fine structures visible in the optical is detected in the NUV image of NGC
2865 and in both NUV and FUV images of NGC 7135. The NUV image of NGC 5018 does
not present shell structures. We detect absorption features in the nuclear
region of all three galaxies. NGC 2865 has a nearly flat colour profile with
(FUV-NUV)~2 throughout the whole galaxy. NGC 7135 is blue in the center
(FUV-NUV)~0 and as red as (FUV-NUV)~1.5 in the outskirts, including the faint
shell-like feature. We investigate the ability of the nuclear GALEX (FUV-NUV)
colour to provide information about rejuvenation phenomena in the stellar
populations of the shell galaxies. To this aim, we derive from theory the
relationship between the Mg2, Hbeta, HgammaA, HdeltaA Lick line-strength
indices and the (FUV-NUV) colour. We extend the study to a sample of early-type
galaxies with emission lines in their optical spectra (Annibali et al. 2007).
In the index vs.(FUV-NUV) colour diagrams, most of the galaxies are well
explained by passively evolving SSPs. On the average, ages and metallicities of
the galaxies in our sample estimated from optical line-strength indices are
consistent with those inferred from the (FUV-NUV) colour. In general, all the
colours but for (FUV-NUV) and (FUV-V), become nearly age insensitive when 1-2
Gyr have elapsed from the last star forming event. Considering composite
stellar population models with a recent burst of star formation, we suggest
that the position of the NGC 7135 and NGC 2865 nuclei in the (FUV-NUV)-Hbeta
plane could be explained in term of a recent rejuvenation episode. (Abridged)Comment: Accepted for publication in MNRAS Main Journal, 21 pages, 15 figure
Kondo screening and exhaustion in the periodic Anderson model
We investigate the paramagnetic periodic Anderson model using the dynamical
mean-field theory in combination with the modified perturbation theory which
interpolates between the weak and strong coupling limits. For the symmetric
PAM, the ground state is always a singlet state. However, as function of the
hybridization strength, a crossover from collective to local Kondo screening is
found. Reducing the number of conduction electrons, the local Kondo singlets
remain stable. The unpaired f-electrons dominate the physics of the system. For
very low conduction electron densities, a large increase of the effective mass
of the quasiparticles is visible, which is interpreted as the approach of the
Mott-Hubbard transition.Comment: 10 pages, 8 figures, accepted by Phys. Rev.
Rhomboid family member 2 regulates cytoskeletal stress-associated Keratin 16.
Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad. It can be induced in hyperproliferative states such as wound healing, inflammation and cancer. Here we show that the inactive rhomboid protease RHBDF2 (iRHOM2) regulates thickening of the footpad epidermis through its interaction with K16. K16 expression is absent in the thinned footpads of irhom2-/- mice compared with irhom2+/+mice, due to reduced keratinocyte proliferation. Gain-of-function mutations in iRHOM2 underlie Tylosis with oesophageal cancer (TOC), characterized by palmoplantar thickening, upregulate K16 with robust downregulation of its type II keratin binding partner, K6. By orchestrating the remodelling and turnover of K16, and uncoupling it from K6, iRHOM2 regulates the epithelial response to physical stress. These findings contribute to our understanding of the molecular mechanisms underlying hyperproliferation of the palmoplantar epidermis in both physiological and disease states, and how this 'stress' keratin is regulated
Clues from nearby galaxies to a better theory of cosmic evolution
The great advances in the network of cosmological tests show that the
relativistic Big Bang theory is a good description of our expanding universe.
But the properties of nearby galaxies that can be observed in greatest detail
suggest a still better theory would more rapidly gather matter into galaxies
and groups of galaxies. This happens in theoretical ideas now under discussion.Comment: published in Natur
Future-proofing hydrogeology by revising groundwater monitoring practice
Groundwater is an important global resource and its sustainable use faces major challenges. New methods and advances in computational science could lead to much improved understanding of groundwater processes and subsurface properties. A closer look at current groundwater monitoring practice reveals the need for updates with a special focus on the benefits of high-frequency and high-resolution datasets. To future-proof hydrogeology, this technical note raises awareness about the necessity for improvement, provides initial recommendations and advocates for the development of universal guidelines
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DNA methylation-based classification of central nervous system tumours.
Accurate pathological diagnosis is crucial for optimal management of patients with cancer. For the approximately 100 known tumour types of the central nervous system, standardization of the diagnostic process has been shown to be particularly challenging-with substantial inter-observer variability in the histopathological diagnosis of many tumour types. Here we present a comprehensive approach for the DNA methylation-based classification of central nervous system tumours across all entities and age groups, and demonstrate its application in a routine diagnostic setting. We show that the availability of this method may have a substantial impact on diagnostic precision compared to standard methods, resulting in a change of diagnosis in up to 12% of prospective cases. For broader accessibility, we have designed a free online classifier tool, the use of which does not require any additional onsite data processing. Our results provide a blueprint for the generation of machine-learning-based tumour classifiers across other cancer entities, with the potential to fundamentally transform tumour pathology
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