277 research outputs found
A Herschel and CARMA view of CO and [C II] in Hickson Compact groups
Understanding the evolution of galaxies from the starforming blue cloud to
the quiescent red sequence has been revolutionized by observations taken with
Herschel Space Observatory, and the onset of the era of sensitive millimeter
interferometers, allowing astronomers to probe both cold dust as well as the
cool interstellar medium in a large set of galaxies with unprecedented
sensitivity. Recent Herschel observations of of H2-bright Hickson Compact
Groups of galaxies (HCGs) has shown that [CII] may be boosted in diffuse
shocked gas. CARMA CO(1-0) observations of these [CII]-bright HCGs has shown
that these turbulent systems also can show suppression of SF. Here we present
preliminary results from observations of HCGs with Herschel and CARMA, and
their [CII] and CO(1-0) properties to discuss how shocks influence galaxy
transitions and star formation.Comment: 4 pages, 3 figures, Proceedings for IAU Symposium 309, Galaxies in 3D
across the Univers
The search for extended infrared emission near interacting and active galaxies
The following subject areas are covered: the search for extended far IR emission; the search for extended emission in galaxy groups; a brief review of the flattening algorithm; the target groups; extended emission from groups and intergalactic HI clouds; and morphological image processing
Jet-ISM Interaction in the Radio Galaxy 3C293: Jet-driven Shocks Heat ISM to Power X-ray and Molecular H2 emission
We present a 70ks Chandra observation of the radio galaxy 3C293. This galaxy
belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have
very luminous emission from warm molecular hydrogen. In radio galaxies, the
molecular gas appears to be heated by jet-driven shocks, but exactly how this
mechanism works is still poorly understood. With Chandra, we observe X-ray
emission from the jets within the host galaxy and along the 100 kpc radio jets.
We model the X-ray spectra of the nucleus, the inner jets, and the X-ray
features along the extended radio jets. Both the nucleus and the inner jets
show evidence of 10^7 K shock-heated gas. The kinetic power of the jets is more
than sufficient to heat the X-ray emitting gas within the host galaxy. The
thermal X-ray and warm H2 luminosities of 3C293 are similar, indicating similar
masses of X-ray hot gas and warm molecular gas. This is consistent with a
picture where both derive from a multiphase, shocked interstellar medium (ISM).
We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs),
like 3C293, typically have LH2/LX~1 and MH2/MX~1, whereas MOHEGs that are BCGs
have LH2/LX~0.01 and MH2/MX~0.01. The more massive, virialized, hot atmosphere
in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction.
On the other hand, LH2/LX~1 in the Spiderweb BCG at z=2, which resides in an
unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM
interaction may contribute to the establishment of a hot atmosphere in BCGs and
other massive elliptical galaxies.Comment: Accepted by ApJ 21 pages in ApJ format, 9 figures, 8 table
Blood pressure management in acute stroke
Blood pressure (BP) is elevated in 75% or more of patients with acute stroke and is associated with poor outcomes. Whether to modulate BP in acute stroke has long been debated. With the loss of normal cerebral autoregulation, theoretical concerns are twofold: high BP can lead to cerebral oedema, haematoma expansion or haemorrhagic transformation; and low BP can lead to increased cerebral infarction or perihaematomal ischaemia. Published evidence from multiple large, high-quality, randomised trials is increasing our understanding of this challenging area, such that BP lowering is recommended in acute intracerebral haemorrhage and is safe in ischaemic stroke. Here we review the evidence for BP modulation in acute stroke, discuss the issues raised and look to on-going and future research to identify patient subgroups who are most likely to benefit
The role of glyceryl trinitrate, a nitric oxide donor, in acute stroke
Nitric oxide donors (e.g. glyceryl trinitrate (GTN)) are candidate treatments for acute stroke with haemodynamic, reperfusion, and neuroprotective properties. In order to establish the safety and efficacy of NO donors in acute stroke a Cochrane systematic review and meta-analysis was performed. Transdermal GTN was assessed in 5 trials (n=4197) in acute stroke. Overall, GTN was safe and lowered blood pressure but did not influence clinical outcome. However, early treatment with GTN within 6 hours (n=312) improved clinical outcomes across a variety of domains (death and dependency, death, disability, cognition, mood, and quality of life).
Using data from the large Efficacy of Nitric Oxide in Stroke (ENOS) trial, the haemodynamic properties of GTN were explored. GTN lowered BP and its derivatives including BP variability. Further, increased BP variability was associated with poor functional and cognitive outcomes and increased death at day 90.
The safety and efficacy of transdermal GTN in important subgroups in acute stroke was assessed. GTN was safe in the context of blood markers of dehydration with no precipitous drops in BP seen in such patients. GTN in the context of ipsilateral or bilateral carotid stenosis was safe and may improve outcome in severe ipsilateral carotid stenosis. Although GTN was safe, it did not improve outcome in patients with lacunar syndromes either overall or within 6 hours of onset. Baseline imaging markers of small vessel disease and ‘brain frailty’ were associated with functional and cognitive outcomes 90 days after stroke.
In summary, this thesis has confirmed the safety of transdermal GTN in acute stroke both overall and in important subgroups. Mechanistic data suggest that GTN may reduce BP variability, which seems to be more strongly associated with outcome than absolute BP or trend in BP. Transdermal GTN is safe to be administered in acute stroke patients with elevated BP prior to blood markers of dehydration or carotid stenosis status being known. Baseline imaging markers of SVD and ‘brain frailty’ predict clinical outcome and should be used as minimisation criteria in future acute stroke trials and may help guide future clinical decision-making
Star Formation Suppression Due to Jet Feedback in Radio Galaxies with Shocked Warm Molecular Gas
We present Herschel observations of 22 radio galaxies, selected for the presence of shocked, warm molecular hydrogen emission. We measured and modeled spectral energy distributions in 33 bands from the ultraviolet to the far-infrared to investigate the impact of jet feedback on star formation activity. These galaxies are massive, early-type galaxies with normal gas-to-dust ratios, covering a range of optical and infrared colors. We find that the star formation rate (SFR) is suppressed by a factor of ~3–6, depending on how molecular gas mass is estimated. We suggest that this suppression is due to the shocks driven by the radio jets injecting turbulence into the interstellar medium (ISM), which also powers the luminous warm H_2 line emission. Approximately 25% of the sample shows suppression by more than a factor of 10. However, the degree of SFR suppression does not correlate with indicators of jet feedback including jet power, diffuse X-ray emission, or intensity of warm molecular H_2 emission, suggesting that while injected turbulence likely impacts star formation, the process is not purely parameterized by the amount of mechanical energy dissipated into the ISM. Radio galaxies with shocked warm molecular gas cover a wide range in SFR–stellar mass space, indicating that these galaxies are in a variety of evolutionary states, from actively star-forming and gas-rich to quiescent and gas-poor. SFR suppression appears to have the largest impact on the evolution of galaxies that are moderately gas-rich
Jet-related Excitation of the [CII] Emission in the Active Galaxy NGC 4258 with SOFIA
We detect widespread [CII]157.7um emission from the inner 5 kpc of the active
galaxy NGC 4258 with the SOFIA integral field spectrometer FIFI-LS. The
emission is found associated with warm H2, distributed along and beyond the end
of southern jet, in a zone known to contain shock-excited optical filaments. It
is also associated with soft X-ray hot-spots, which are the counterparts of the
`anomalous radio arms' of NGC~4258, and a 1 kpc-long filament on the minor axis
of the galaxy which contains young star clusters. Palomar-CWI H-alpha integral
field spectroscopy shows that the filament exhibits non-circular motions within
NGC 4258. Many of the [CII] profiles are very broad, with the highest line
width, 455 km/s, observed at the position of the southern jet bow-shock.
Abnormally high ratios of L([CII])/L(FIR) and L([CII])/L(PAH7.7um) are found
along and beyond the southern jet and in the X-ray hotspots. These are the same
regions that exhibit unusually large intrinsic [CII] line widths. This suggests
that the [CII] traces warm molecular gas in shocks and turbulence associated
with the jet. We estimate that as much as 40% (3.8 x 10^39 erg/s) of the total
[CII] luminosity from the inner 5 kpc of NGC 4258 arises in shocks and
turbulence (< 1% bolometric luminosity from the active nucleus), the rest being
consistent with [CII] excitation associated with star formation. We propose
that the highly-inclined jet is colliding with, and being deflected around,
dense irregularities in a thick disk, leading to significant energy dissipation
over a wide area of the galaxy.Comment: Accepted for Publication in the Astrophysical Journal Oct 29 201
VLBI detection of an Infrared-Faint Radio Source
Infrared-Faint Radio Sources represent a new and unexpected class of object
which is bright at radio wavelengths but unusually faint at infrared
wavelengths. If, like most mJy radio sources, they were either conventional
active or star-forming galaxies in the local Universe, we would expect them to
be detectable at infrared wavelengths, and so their non-detection by the
Spitzer Space Telescope is surprising. Here we report the detection of one of
these sources using Very Long Baseline Interferometry, from which we conclude
that the sources are driven by Active Galactic Nuclei. We suggest that these
sources are either normal radio-loud quasars at high redshift or abnormally
obscured radio galaxies.Comment: accepted by MNRA
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