363 research outputs found
A Global Inventory of Feedback
Feedback from both supermassive black holes and massive stars plays a fundamental role in the evolution of galaxies and the inter-galactic medium. In this paper, we use available data to estimate the total amount of kinetic energy and momentum created per co-moving volume element over the history of the universe from three sources: massive stars and supernovae, radiation pressure and winds driven by supermassive black holes, and radio jets driven by supermassive black holes. Kinetic energy and momentum injection from jets peaks at z ≈ 1, while the other two sources peak at z ≈ 2. Massive stars are the dominant global source of momentum injection. For supermassive black holes, we find that the amount of kinetic energy from jets is about an order-of-magnitude larger than that from winds. We also find that the amount of kinetic energy created by massive stars is about 2.5 εstar times that carried by jets (where εstar is the fraction of injected energy not lost to radiative cooling). We discuss the implications of these results for the evolution of galaxies and IGM. Because the ratio of the black hole mass to galaxy mass is a steeply increasing function of mass, we show that the relative importance of black hole feedback to stellar feedback likewise increases with mass. We show that there is a trend in the present-day universe which, in the simplest picture, is consistent with galaxies that have been dominated by black hole feedback being generally quenched, while galaxies that have been dominated by stellar feedback are star-forming. We also note that the amount of kinetic energy carried by jets and winds appears to be sufficient to explain the properties of hot gas in massive halos (>1013 Mʘ)
Paediatric drowning: a standard operating procedure to aid the prehospital management of paediatric cardiac arrest resulting from submersion
Objectives: Drowning is one of the leading causes of death in children. Resuscitating a child following submersion is a highpressure situation, and standard operating procedures can reduce error. Currently, the Resuscitation Council UK guidance does not include a standard operating procedure on paediatric drowning. The objective of this project was to design a standard operating procedure to improve outcomes of drowned children. Methods: A literature review on the management of paediatric drowning was conducted. Relevant publications were used to develop a standard operating procedure for management of paediatric drowning. Results: A concise standard operating procedure was developed for resuscitation following paediatric submersion. Specific recommendations include: the Heimlich manoeuvre should not be used in this context; however, prolonged resuscitation and therapeutic hypothermia are recommended. Conclusions: This standard operating procedure is a potentially useful adjunct to the Resuscitation Council UK guidance and should be considered for incorporation into its next iteration
HiZELS: the High Redshift Emission Line Survey with UKIRT
In these proceedings we report on HiZELS, the High-z Emission Line Survey,
our successful panoramic narrow-band Campaign Survey using WFCAM on UKIRT to
detect and study emission line galaxies at z~1-9. HiZELS employs the H2(S1)
narrow-band filter together with custom-made narrow-band filters in the J and
H-bands, with the primary aim of delivering large, identically-selected samples
of H-alpha emitting galaxies at redshifts of 0.84, 1.47 and 2.23. Comparisons
between the luminosity function, the host galaxy properties, the clustering,
and the variation with environment of these H-alpha-selected samples are
yielding unique constraints on the nature and evolution of star-forming
galaxies, across the peak epoch of star-formation activity in the Universe. We
provide a summary of the project status, and detail the main scientific results
obtained so far: the measurement of the evolution of the cosmic star-formation
rate density out to z > 2 using a single star-formation indicator,
determination of the morphologies, environments and dust-content of the
star-forming galaxies, and a detailed investigation of the evolution of their
clustering properties. We also summarise the on-going work and future goals of
the project.Comment: To appear in proceedings of "UKIRT at 30: A British Success Story"
Radio Jets in Galaxies with Actively Accreting Black Holes: new insights from the SDSS
The majority of nearby radio-loud AGN are found in massive, old elliptical
galaxies with weak emission lines. At high redshifts,however, most known radio
AGN have strong emission lines. In this paper, we examine a subset of radio AGN
with emission lines selected from the Sloan Digital Sky Survey. The probability
for a nearby radio AGN to have emission lines is a strongly decreasing function
of galaxy mass and an increasing function of radio luminosity above 10^25 W/Hz.
Emission line and radio luminosities are correlated, but with large dispersion.
At a given radio power, AGN with small black holes have higher [OIII]
luminosities (which we interpret as higher accretion rates) than AGN with big
black holes. However, if we scale both radio and emission line luminosities by
the black hole mass, we find a correlation between normalized radio power and
accretion rate in Eddington units that is independent of black hole mass. There
is also a clear correlation between normalized radio power and the age of the
stellar population in the galaxy. Present-day AGN with the highest normalized
radio powers are confined to galaxies with small black holes. High-redshift,
high radio-luminosity AGN could be explained if big black holes were similarly
active at earlier cosmic epochs. To investigate why only a small fraction of
emission line AGN become radio loud, we create matched samples of radio-loud
and radio-quiet AGN and compare their host galaxy properties and environments.
The main difference lies in their environments; our local density estimates are
a factor 2 larger around the radio-loud AGN. We propose a scenario in which
radio-loud AGN with emission lines are located in galaxies where accretion of
both cold and hot gas can occur simultaneously. (Abridged)Comment: 18 figures, submitted to MNRA
Life History and Status Classifications of Birds Breeding in Iowa
Life history and status classifications were compiled for 145 bird species that breed in Iowa. Species were classified by food type and substrate, nest substrate, susceptibility to cowbird parasitism, migratory status, predominant habitat use and habitat-use specialization, body mass (an index of home range/territory size), area sensitivity, population trend and vulnerability, and beneficial/harmful aspects in relation to agriculture. Such information may be used to make interspecific comparisons, evaluate interrelationships among life history and status characteristics, and provide insights into the interpretation of previous research. This synthesis also can aid those responsible for making conservation and management decisions about Iowa\u27s avifauna
Water saturation effects on P-wave anisotropy in synthetic sandstone with aligned fractures
The seismic properties of rocks are known to be sensitive to partial liquid or gas saturation, and to aligned fractures. P-wave anisotropy is widely used for fracture characterization and is known to be sensitive to the saturating fluid. However, studies combining the effect of multiphase saturation and aligned fractures are limited even though such conditions are common in the subsurface. An understanding of the effects of partial liquid or gas saturation on P-wave anisotropy could help improve seismic characterization of fractured, gas bearing reservoirs. Using octagonal-shaped synthetic sandstone samples, one containing aligned penny-shaped fractures and the other without fractures, we examined the influence of water saturation on P-wave anisotropy in fractured rocks. In the fractured rock, the saturation related stiffening effect at higher water saturation values is larger in the direction across the fractures than along the fractures. Consequently, the anisotropy parameter ‘?’ decreases as a result of this fluid stiffening effect. These effects are frequency dependent as a result of wave-induced fluid flow mechanisms. Our observations can be explained by combining a frequency-dependent fractured rock model and a frequency-dependent partial saturation model
Predicting dust extinction from the stellar mass of a galaxy
We investigate how the typical dust extinction of H-alpha luminosity from a
star-forming galaxy depends upon star formation rate (SFR), metallicity and
stellar mass independently, using a sample of ~90,000 galaxies from Data
Release 7 of the Sloan Digital Sky Survey (SDSS). We measure extinctions
directly from the Balmer decrement of each source, and while higher values of
extinction are associated with an increase in any of the three parameters, we
demonstrate that the fundamental property that governs extinction is stellar
mass. After this mass-dependent relationship is removed, there is very little
systematic dependence of the residual extinctions with either SFR or
metallicity, and no significant improvement is obtained from a more general
parameterisation. In contrast to this, if either a SFR-dependent or
metallicity-dependent extinction relationship is applied, the residual
extinctions show significant trends that correlate with the other parameters.
Using the SDSS data, we present a relationship to predict the median dust
extinction of a sample of galaxies from its stellar mass, which has a scatter
of ~0.3 mag. The relationship was calibrated for H-alpha emission, but can be
more generally applied to radiation emitted at other wavelengths. These results
have important applications for studies of high-redshift galaxies, where
individual extinction measurements are hard to obtain but stellar mass
estimates can be relatively easily estimated from long-wavelength data.Comment: Accepted for publication in MNRAS. 12 pages. Dedicated to the memory
of Timothy Gar
Evolution of the Most Massive Galaxies to z ~ 0.6: II. The link between radio AGN activity and star formation
We analyze the optical spectra of massive (log M*/Msun > 11.4) radio-loud
galaxies at z~0.2 and z~0.6. By comparing stellar population parameters of
these radio-loud samples with radio-quiet control samples, we investigate how
the presence of a radio-emitting jet relates to the recent star formation
history of the host galaxy. We also investigate how the emission-line
properties of the radio galaxies evolve with redshift by stacking their
spectra. Our main results are the following. (1) Both at low and at high
redshift, half as many radio-loud as radio-quiet galaxies have experienced
significant star formation in the past Gyr. (2) The Balmer absorption line
properties of massive galaxies that have experienced recent star formation show
that star formation occurred as a burst in many of these systems. (3) Both the
radio and the emission-line luminosity of radio AGN evolve significantly with
redshift. However, radio galaxies with similar stellar population parameters,
have similar emission-line properties both at high- and at low-redshift. These
results suggest that massive galaxies experience cyclical episodes of gas
accretion, star formation and black hole growth, followed by the production of
a radio jet that shuts down further activity. The behaviour of galaxies with
log M*/Msun > 11.4 is the same at z = 0.6 as it is at z = 0.2, except that
higher redshift galaxies experience more star formation and black hole growth
and produce more luminous radio jets during each accretion cycle.Comment: 14 pages, 12 figures, submitted to MNRA
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