68 research outputs found
An online student portfolio for the development and assessment of engineering graduate attributes
An online student portfolio was evaluated as a means for engaging students with the concept of graduate attributes, and for documenting student attainment of graduate attributes. Students rated the portfolio system as easy to use, and indicated that it helped them to appreciate the skills and knowledge they had developed.<br /
Cold and Warm Gas Outflows in Radio AGN
The study of the conditions and the kinematics of the gas in the central
region of AGN provides important information on the relevance of feedback
effects connected to the nuclear activity. Quantifying these effects is key for
constraining galaxy evolution models. Here we present a short summary of our
recent efforts to study the occurrence and the impact of gas outflows in
radio-loud AGN that are in their first phase of their evolution. Clear evidence
for AGN-induced outflows have been found for the majority of these young radio
sources. The outflows are detected both in (warm) ionized as well in (cold)
atomic neutral gas and they are likely to be driven (at least in most of the
cases) by the interaction between the expanding jet and the medium. The mass
outflow rates of the cold gas (HI) appear to be systematically higher than
those of the ionized gas. The former reach up to ~50 Msun/yr, and are in the
same range as "mild" starburst-driven superwinds in ULIRGs, whilst the latter
are currently estimated to be a few solar masses per year. However, the kinetic
powers associated with these gaseous outflow are a relatively small fraction (a
few x 10^-4) of the Eddington luminosity of the galaxy. Thus, they do not
appear to match the requirements of the galaxy evolution feedback models.Comment: Invited talk, to appear in the Proceedings of the IAU Symposium 267,
"Co-Evolution of Central Black Holes and Galaxies", B.M. Peterson, R.S.
Somerville, T. Storchi-Bergmann, eds., in pres
Fast neutral outflows in nearby radio galaxies: a major source of feedback
Fast (~1000 km/s) outflows of neutral gas (from 21-cm HI absorption) are
detected in strong radio sources. The outflows occur, at least in some cases,
at distances from the radio core that range between few hundred parsecs and
kpc. These HI outflows likely originate from the interaction between radio jets
and the dense surrounding medium. The estimated mass outflow rates are
comparable to those of moderate starburst-driven superwinds. The impact on the
evolution of the host galaxies is discussed.Comment: 4 pages, 2 figures. Conference proceedings to appear in "The Central
Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San
Francisco: ASP
An online student portfolio for the development and assessment of engineering graduate attributes
An online student portfolio was evaluated as a means for engaging students
with the concept of graduate attributes, and for documenting student
attainment of graduate attributes. Students rated the portfolio system as easy
to use, and indicated that it helped them to appreciate the skills and
knowledge they had developed
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
In order to identify the dominant nuclear outflow mechanisms in Active
Galactic Nuclei, we have undertaken deep, high resolution observations of two
compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera
for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets
known to have powerful emission line outflows, but they also contain all the
potential drivers for the outflows: relativistic jets, quasar nuclei and
starbursts. ACS allows the compact nature (<0.15") of these radio sources to be
optically resolved for the first time. Through comparison with existing radio
maps we have seen consistency in the nuclear position angles of both the
optical emission line and radio data. There is no evidence for bi-conical
emission line features on the large-scale and there is a divergance in the
relative position angles of the optical and radio structure. This enables us to
exclude starburst driven outflows. However, we are unable to clearly
distinguish between radiative AGN wind driven outflows and outflows powered by
relativistic radio jets. The small scale bi-conical features, indicative of
such mechanisms could be below the resolution limit of ACS, especially if
aligned close to the line of sight. In addition, there may be offsets between
the radio and optical nuclei induced by heavy dust obscuration, nebular
continuum or scattered light from the AGN.Comment: 9 pages, 8 figures, emulateapj, ApJ Accepte
Starburst radio galaxies: General properties, evolutionary histories and triggering
In this paper we discuss the results of a programme of spectral synthesis modelling of a sample of starburst radio galaxies in the context of scenarios for the triggering of the activity and the evolution of the host galaxies. New optical spectra are also presented for a subset of the objects discussed. The starburst radio galaxies - comprising ∼15-25 per cent of all powerful extragalactic radio sources - frequently show disturbed morphologies at optical wavelengths, and unusual radio structures, although their stellar masses are typical of radio galaxies as a class. In terms of the characteristic ages of their young stellar populations (YSPs), the objects can be divided into two groups: those with YSP ages tYSP≤ 0.1 Gyr, in which the radio source has been triggered quasi-simultaneously with the main starburst episode, and those with older YSP in which the radio source has been triggered or re-triggered a significant period after the starburst episode. Most of the former group are associated with a large mid- to far-IR (MFIR) continuum and [Oiii] emission-line luminosities (LIR > 1011L⊙, W), while most of the latter have lower luminosities. Combining the information on the YSP with that on the optical morphologies of the host galaxies, we deduce that the majority of the starburst radio galaxies have been triggered in galaxy mergers in which at least one of the galaxies is gas rich. However, the triggering (or re-triggering) of the radio jets can occur immediately before, around or a significant period after the final coalescence of the merging nuclei, reflecting the complex gas infall histories of the merger events. Although ∼25 per cent of starburst radio galaxies are sufficiently bright at MFIR wavelengths to be classified as ultraluminous infrared galaxies (ULIRGs), we show that only the most massive ULIRGs are capable of evolving into radio galaxies. Finally, for a small subset of starburst radio galaxies in rich clusters of galaxies, cooling flows associated with the hot X-ray haloes offer a viable alternative to mergers as a trigger for the radio jet activity. Overall, our results provide further evidence that a powerful radio jet activity can be triggered via a variety of mechanisms, including different evolutionary stages of major galaxy mergers; clearly, radio-loud AGN activity is not solely associated with a particular stage of a unique type of gas accretion event. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.This research has made use of the NASA/IPAC Extragalactic Data base (NED) which is operated by the Jet Propulsion Laboratory. Based on observations made with ESO Telescopes at the La Silla and Paranal observatories under programmes 70.B-0663(A), 71.B-0320(A), 078B-0660(A).Peer Reviewe
Coastally Trapped Wind Reversals: Progress toward Understanding
Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of
fog or stratus, are an important warm-season forecast problem due to their impact on coastal maritime activities and
airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for producing
these events, yet observational and modeling limitations at the time left these competing interpretations open for
debate. In an effort to improve our physical understanding, and ultimately the prediction, of these events, the Office of
Naval Research sponsored an Accelerated Research Initiative in Coastal Meteorology during the years 1993â 98 to study
these and other related coastal meteorological phenomena. This effort included two field programs to study coastally
trapped disturbances as well as numerous modeling studies to explore key dynamic mechanisms. This paper describes
the various efforts that occurred under this program to provide an advancement in our understanding of these disturbances.
While not all issues have been solved, the synoptic and mesoscale aspects of these events are considerably better understood.Most of the authors were supported through the Office of Naval Research Coastal Meteorology Accelerated Research Initiative, one of the authors (WTT) was supported by Program Element 0601153N, Naval Research Laboratory
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
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