162 research outputs found
The X-ray Evolution of Merging Galaxies
From a Chandra survey of nine interacting galaxy systems the evolution of
X-ray emission during the merger process has been investigated. From comparing
Lx/Lk and Lfir/Lb it is found that the X-ray luminosity peaks around 300 Myr
before nuclear coalescence, even though we know that rapid and increasing star
formation is still taking place at this time. It is likely that this drop in
X-ray luminosity is a consequence of outflows breaking out of the galactic
discs of these systems. At a time around 1 Gyr after coalescence, the
merger-remnants in our sample are X-ray dim when compared to typical X-ray
luminosities of mature elliptical galaxies. However, we do see evidence that
these systems will start to resemble typical elliptical galaxies at a greater
dynamical age, given the properties of the 3 Gyr system within our sample,
indicating that halo regeneration will take place within low Lx
merger-remnants.Comment: 4 pages, 1 figure, to appear in the Proceedings of the IAU Symposium
No. 23
Low-mass X-ray binaries and globular clusters streamers and ARCS in NGC 4278
We report significant inhomogeneities in the projected two-dimensional spatial distributions of low-mass X-ray binaries (LMXBs) and globular clusters (GCs) of the intermediate mass elliptical galaxy NGC 4278. In the inner region of NGC 4278, a significant arc-like excess of LMXBs extending south of the center at ∼50″ in the western side of the galaxy can be associated with a similar overdensity of the spatial distribution of red GCs from Brassington et al. Using a recent catalog of GCs produced by Usher et al. and covering the whole field of the NGC 4278 galaxy, we have discovered two other significant density structures outside the D 25 isophote to the W and E of the center of NGC 4278, associated with an overdensity and an underdensity, respectively. We discuss the nature of these structures in the context of the similar spatial inhomogeneities discovered in the LMXBs and GCs populations of NGC 4649 and NGC 4261, respectively. These features suggest streamers from disrupted and accreted dwarf companions.Peer reviewe
AGN activity and the misaligned hot ISM in the compact radio elliptical NGC4278
The analysis of a deep (579 ks) Chandra ACIS pointing of the elliptical
galaxy NGC4278, which hosts a low luminosity AGN and compact radio emission,
allowed us to detect extended emission from hot gas out to a radius of \sim 5
kpc, with a 0.5--8 keV luminosity of 2.4x10^{39} erg/s. The emission is
elongated in the NE-SW direction, misaligned with respect to the stellar body,
and aligned with the ionized gas, and with the Spitzer IRAC 8\mum non-stellar
emission. The nuclear X-ray luminosity decreased by a factor of \sim 18 since
the first Chandra observation in 2005, a dimming that enabled the detection of
hot gas even at the position of the nucleus. Both in the projected and
deprojected profiles, the gas shows a significantly larger temperature (kT=0.75
keV) in the inner \sim 300 pc than in the surrounding region, where it stays at
\sim 0.3 keV, a value lower than expected from standard gas heating
assumptions. The nuclear X-ray emission is consistent with that of a low
radiative efficiency accretion flow, accreting mass at a rate close to the
Bondi one; estimates of the power of the nuclear jets require that the
accretion rate is not largely reduced with respect to the Bondi rate. Among
possibile origins for the central large hot gas temperature, such as
gravitational heating from the central massive black hole and a recent AGN
outburst, the interaction with the nuclear jets seems more likely, especially
if the latter remain confined, and heat the nuclear region frequently. The
unusual hot gas distribution on the galactic scale could be due to the
accreting cold gas triggering the cooling of the hot phase, a process also
contributing to the observed line emission from ionize gas, and to the hot gas
temperature being lower than expected; alternatively, the latter could be due
to an efficiency of the type Ia supernova energy mixing lower than usually
adopted.Comment: 48 pages, submitted to Ap
Immunosuppressive and immunomodulatory therapies for idiopathic inflammatory myopathies
Objectives: This is a protocol for a Cochrane Review (intervention). The objectives are as follows:. This protocol is for two separate reviews to assess the effects (benefits and harms) of immunosuppressant and immunomodulatory treatments for the idiopathic inflammatory myopathies.
Targeted treatments: To assess the effects (benefits and harms) of targeted immunosuppressant and immunomodulatory treatments for the idiopathic inflammatory myopathies: dermatomyositis (DM, including juvenile dermatomyositis, jDM), immune mediated necrotising myopathy (IMNM), anti-synthetase syndrome (ASS), overlap-myositis (OM) and polymyositis (PM). We will also include cancer-related myositis and amyopathic dermatomyositis.
Non-targeted treatments: To assess the effects (benefits and harms) of non-targeted immunosuppressant and immunomodulatory treatments for the idiopathic inflammatory myopathies: dermatomyositis (DM, including juvenile dermatomyositis, jDM), immune mediated necrotising myopathy (IMNM), anti-synthetase syndrome (ASS), overlap-myositis (OM) and polymyositis (PM). We will also include cancer-related myositis and amyopathic dermatomyositis
Probing the X-Ray Binary Populations of the Ring Galaxy NGC 1291
We present Chandra studies of the X-ray binary (XRB) populations in the bulge
and ring regions of the ring galaxy NGC 1291. We detect 169 X-ray point sources
in the galaxy, 75 in the bulge and 71 in the ring, utilizing the four available
Chandra observations totaling an effective exposure of 179 ks. We report
photometric properties of these sources in a point-source catalog. There are
~40% of the bulge sources and ~25% of the ring sources showing >3\sigma
long-term variability in their X-ray count rate. The X-ray colors suggest that
a significant fraction of the bulge (~75%) and ring (~65%) sources are likely
low-mass X-ray binaries (LMXBs). The spectra of the nuclear source indicate
that it is a low-luminosity AGN with moderate obscuration; spectral variability
is observed between individual observations. We construct 0.3-8.0 keV X-ray
luminosity functions (XLFs) for the bulge and ring XRB populations, taking into
account the detection incompleteness and background AGN contamination. We reach
90% completeness limits of ~1.5\times10^{37} and ~2.2\times10^{37} erg/s for
the bulge and ring populations, respectively. Both XLFs can be fit with a
broken power-law model, and the shapes are consistent with those expected for
populations dominated by LMXBs. We perform detailed population synthesis
modeling of the XRB populations in NGC 1291, which suggests that the observed
combined XLF is dominated by an old LMXB population. We compare the bulge and
ring XRB populations, and argue that the ring XRBs are associated with a
younger stellar population than the bulge sources, based on the relative
overdensity of X-ray sources in the ring, the generally harder X-ray color of
the ring sources, the overabundance of luminous sources in the combined XLF,
and the flatter shape of the ring XLF.Comment: 15 pages, 11 figures. Accepted for publication in Ap
The Spitzer Interacting Galaxies Survey: A Mid-infrared Atlas of Star Formation
The Spitzer Interacting Galaxies Survey is a sample of 103 nearby galaxies in 48 systems, selected using association likelihoods and therefore free from disturbed morphology biases. All galaxies have been observed with Infrared Array Camera and MIPS 24 μm bands from the Spitzer Space Telescope. This catalog presents the global flux densities and colors of all systems and correlations between the interacting systems and their specific star formation rate (sSFR). This sample contains a wide variety of galaxy interactions with systems ranging in mass, mass ratios, and gas-content as well as interaction strength. This study seeks to identify the process of triggering star formation in galaxy interactions, therefore, we focus on the non-active galactic nucleus spiral galaxies only. From this subset of 70 spiral galaxies we have determined that this sample has enhanced sSFR compared to a sample of non-interacting field galaxies. Through optical data we have classified each system by "interaction strength"; the strongly interacting (Stage 4) galaxies have higher sSFR values than the weakly (Stage 2) and moderately (Stage 3) interacting systems. However, the Stage 2 and 3 systems have statistically identical sSFR properties, despite the lack of optical interaction signatures exhibited by the Stage 2 galaxies. We suggest that the similarity of sSFR in these stages could be a consequence of some of these Stage 2 systems actually being post-perigalactic and having had sufficient time for their tidal features to fade to undetectable levels. This interpretation is consistent with the correlation of sSFR with separation, which we have determined to have little variation up to 100 kpc
Formation of black-hole X-ray binaries in globular clusters
Inspired by the recent identification of the first candidate BH-WD X-ray
binaries, where the compact accretors may be stellar-mass black hole candidates
in extragalactic globular clusters, we explore how such binaries could be
formed in a dynamical environment. We provide analyses of the formation rates
via well known formation channels like binary exchange and physical collisions
and propose that the only possibility to form BH-WD binaries is via coupling
these usual formation channels with subsequent hardening and/or triple
formation. Indeed, we find that the most important mechanism to make a BH-WD
X-ray binary from an initially dynamically formed BH-WD binary is triple
induced mass transfer via the Kozai mechanism. Even using the most optimistic
estimates for the formation rates, we cannot match the observationally inferred
production rates if black holes undergo significant evaporation from the
cluster or form a completely detached subcluster of black holes. We estimate
that at least 1% of all formed black holes, or presumably 10% of the black
holes present in the core now, must be involved in interactions with the rest
of the core stellar population.Comment: 10 pages, 2 figures, submitted to Ap
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Exploring strategies for coupled 4D-Var data assimilation using an idealised atmosphere-ocean model
Operational forecasting centres are currently developing data assimilation systems for coupled atmosphere-ocean models. Strongly coupled assimilation, in which a single assimilation system is applied to a coupled model, presents significant technical and scientific challenges. Hence weakly coupled assimilation systems are being developed as a first step, in which the coupled model is used to compare the current state estimate with observations, but corrections to the atmosphere and ocean initial conditions are then calculated independently. In this paper we provide a comprehensive description of the different coupled assimilation methodologies in the context of four dimensional variational assimilation (4D-Var) and use an idealised framework to assess the expected benefits of moving towards coupled data assimilation.
We implement an incremental 4D-Var system within an idealised single column atmosphere-ocean model. The system has the capability to run both strongly and weakly coupled assimilations as well as uncoupled atmosphere or ocean only assimilations, thus allowing a systematic comparison of the different strategies for treating the coupled data assimilation problem. We present results from a series of identical twin experiments devised to investigate the behaviour and sensitivities of the different approaches. Overall, our study demonstrates the potential benefits that may be expected from coupled data assimilation. When compared to uncoupled initialisation, coupled assimilation is able to produce more balanced initial analysis fields, thus reducing initialisation shock and its impact on the subsequent forecast. Single observation experiments demonstrate how coupled assimilation systems are able to pass information between the atmosphere and ocean and therefore use near-surface data to greater effect. We show that much of this benefit may also be gained from a weakly coupled assimilation system, but that this can be sensitive to the parameters used in the assimilation
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