857 research outputs found
X-ray Ionization of Heavy Elements Applied to Protoplanetary Disks
The consequences of the Auger effect on the population of heavy-element ions are analyzed for the case of relatively cool gas irradiated by keV X-rays with intended applications to the accretion disks of young stellar objects. Highly charged ions are rapidly reduced to the doubly charged state in neutral gas, so the aim here is to derive the production rates for these singly and doubly charged ions and to specify their transformation by recombination, charge transfer, and molecular reactions. The theory is illustrated by calculations of the abundance
Molecular gas heating in Arp 299
Understanding the heating and cooling mechanisms in nearby (Ultra) luminous
infrared galaxies can give us insight into the driving mechanisms in their more
distant counterparts. Molecular emission lines play a crucial role in cooling
excited gas, and recently, with Herschel Space Observatory we have been able to
observe the rich molecular spectrum. CO is the most abundant and one of the
brightest molecules in the Herschel wavelength range. CO transitions are
observed with Herschel, and together, these lines trace the excitation of CO.
We study Arp 299, a colliding galaxy group, with one component harboring an AGN
and two more undergoing intense star formation. For Arp 299 A, we present PACS
spectrometer observations of high-J CO lines up to J=20-19 and JCMT
observations of CO and HCN to discern between UV heating and alternative
heating mechanisms. There is an immediately noticeable difference in the
spectra of Arp 299 A and Arp 299 B+C, with source A having brighter high-J CO
transitions. This is reflected in their respective spectral energy line
distributions. We find that photon-dominated regions (PDRs) are unlikely to
heat all the gas since a very extreme PDR is necessary to fit the high-J CO
lines. In addition, this extreme PDR does not fit the HCN observations, and the
dust spectral energy distribution shows that there is not enough hot dust to
match the amount expected from such an extreme PDR. Therefore, we determine
that the high-J CO and HCN transitions are heated by an additional mechanism,
namely cosmic ray heating, mechanical heating, or X-ray heating. We find that
mechanical heating, in combination with UV heating, is the only mechanism that
fits all molecular transitions. We also constrain the molecular gas mass of Arp
299 A to 3e9 Msun and find that we need 4% of the total heating to be
mechanical heating, with the rest UV heating
How Dutch Institutions Enhance the Adaptive Capacity of Society
This report examines the adaptive capacity of the institutional framework of the Netherlands to cope with the impacts of climate change. Historically, institutions have evolved incrementally to deal with existing social problems. They provide norms and rules for collective action and create continuity rather than change. However, the nature of societal problems is changing as a result of the processes of globalization and development. With the progress made in the natural sciences, we are able to predict in advance, to a certain extent, the potential environmental impacts of various human actions on society, for example, climate change. This raises some key questions: Are our institutions capable of dealing with this new knowledge about future impacts and, more importantly, with the impacts themselves? Are our institutions capable of dealing with the inherent uncertainty of the predictions
Low loss, high contrast optical waveguides based on CMOS compatible LPCVD processing
A new class of integrated optical waveguide structures is presented, based on low cost CMOS compatible LPCVD processing. This technology allows for medium and high index contrast waveguides with very low channel attenuation. The geometry is basically formed by a rectangular cross-section silicon nitride filled with and encapsulated by silicon dioxide . The birefringence and minimal bend radius of the waveguide is completely controlled by the geometry of the waveguide layer structures. Experiments on typical geometries will be presented, showing excellent characteristics (channel attenuation â€0.06 dB/cm, IL â€0.6 dB, PDL â€0.2 dB, Bg «1 x , bend radius â€500 ÎŒm)
Persistence of Methicillin-resistant Staphylococcus aureus (MRSA) in pig herds over a two year period
Aim of this study was to determine if a known MRSA contamination within a pig herd could persist for a period of two years. Material and Methods: 16 pig herds with a known MRSA contamination were asked to participate in this study. Per herd, five dust swabs (SodiboxÂź) were collected every two months for a period of two years. Samples were tested for presence of MRSA by culture and two PCRâs for confirmation of MRSA. Isolates were typed by spa- en MLVA-typing
Black hole accretion and star formation as drivers of gas excitation and chemistry in Mrk231
We present a full high resolution SPIRE FTS spectrum of the nearby
ultraluminous infrared galaxy Mrk231. In total 25 lines are detected, including
CO J=5-4 through J=13-12, 7 rotational lines of H2O, 3 of OH+ and one line each
of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels
up to J=8 can be accounted for by UV radiation from star formation. However,
the approximately flat luminosity distribution of the CO lines over the
rotational ladder above J=8 requires the presence of a separate source of
excitation for the highest CO lines. We explore X-ray heating by the accreting
supermassive black hole in Mrk231 as a source of excitation for these lines,
and find that it can reproduce the observed luminosities. We also consider a
model with dense gas in a strong UV radiation field to produce the highest CO
lines, but find that this model strongly overpredicts the hot dust mass in
Mrk231. Our favoured model consists of a star forming disk of radius 560 pc,
containing clumps of dense gas exposed to strong UV radiation, dominating the
emission of CO lines up to J=8. X-rays from the accreting supermassive black
hole in Mrk231 dominate the excitation and chemistry of the inner disk out to a
radius of 160 pc, consistent with the X-ray power of the AGN in Mrk231. The
extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of
X-ray driven excitation and chemistry in this region.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics Special Issue on Herschel first result
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
Fine-Structure Line Emission from the Outflows of Young Stellar Objects
The flux and line shape of the fine-structure transitions of \NeII\ and
\NeIII\ at 12.8 and 15.55\,m and of the forbidden transitions of \OI\
are calculated for young stellar objects with a range of
mass-loss rates and X-ray luminosities using the X-wind model of jets and the
associated wide-angle winds. For moderate and high accretion rates, the
calculated \NeII\ line luminosity is comparable to or much larger than produced
in X-ray irradiated disk models. All of the line luminosities correlate well
with the main parameter in the X-wind model, the mass-loss rate, and also with
the assumed X-ray luminosity --- and with one another. The line shapes of an
approaching jet are broad and have strong blue-shifted peaks near the effective
terminal velocity of the jet. They serve as a characteristic and testable
aspect of jet production of the neon fine-structure lines and the \OI\
forbidden transitions.Comment: 8 pages, 5 figures, published in Ap
Molecular gas around low-luminosity AGN in late-type spirals
We have studied the molecular gas in the vicinity of low-luminosity active
galactic nuclei (AGNs) in three bulge-less spiral galaxies: NGC 1042, NGC 4178,
and NGC 4395. The (1-0) and (2-1) transitions of gaseous carbon monoxide (CO)
are clearly detected within the central kpc of all three galaxies. In the case
of NGC 4395, this constitutes the first reported detection of CO. In general,
the CO emission is faint, as may be expected from their less-than-spectacular
star formation activity. Interestingly, however, both face-on galaxies in our
sample (which allow an unimpeded view of their nucleus) show an elevated
intensity ratio CO(2-1)/CO(1-0) when compared to similar late-type spirals
without an AGN. We discuss that this is unlikely due to a very compact CO
source. Instead, we speculate that even energetically weak AGN can impact the
physical state of the surrounding gas. We do not detect any tracers of dense
molecular gas such as HCN or HCO+, but the sensitivity of our observations
allows us to establish upper limits that lie at the low end of the range
observed in more energetic AGN. The derived gas density is less than
n(H2)\approx 2e03 cm^-3 which is significantly lower than in most other nearby
galaxies. The scarcity of dense gas suggests that the conditions for star
formation are poor in these nuclei.Comment: Accepted for publication in A&A. 8 pages, 5 figure
- âŠ