704 research outputs found
Tracing star formation in galaxies with molecular line and continuum observations
We report our recent progress on extragalactic spectroscopic and continuum
observations, including HCN(J=1-0), HCO(J=1-0), and CN(N=1-0) imaging
surveys of local Seyfert and starburst galaxies using the Nobeyama Millimeter
Array, high-J CO observations (J=3-2 observations using the Atacama
Submillimeter Telescope Experiment (ASTE) and J=2-1 observations with the
Submillimeter Array) of galaxies, and 1.1 mm continuum observations
of high-z violent starburst galaxies using the bolometer camera AzTEC mounted
on ASTE.Comment: 6 pages, 5 figures, To appear in proceedings of "Far-Infrared and
Submillimeter Emission of the Interstellar Medium", EAS Publication Series,
Bad Honnef, November 2007, Eds. C. Kramer, S. Aalto, R. Simon. See
http://www.nro.nao.ac.jp/~f0212kk/FIR07/kk-ver20.pdf for a version with high
resolution figure
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
High-resolution HNC 3-2 SMA observations of Arp220
We present high resolution (0."4) observations of HNC J=3-2 with the
SubMillimeter Array (SMA). We find luminous HNC 3-2 line emission in the
western part of Arp220, centered on the western nucleus, while the eastern side
of the merger shows relatively faint emission. A bright (36 K), narrow (60
km/s) emission feature emerges from the western nucleus, superposed on a
broader spectral component. A possible explanation is weak maser emission
through line-of-sight amplification of the background continuum source. There
is also a more extended HNC 3-2 emission feature north and south of the
nucleus. This feature resembles the bipolar OH maser morphology around the
western nucleus. Substantial HNC abundances are required to explain the bright
line emission from this warm environment. We discuss this briefly in the
context of an X-ray chemistry and radiative excitation. We conclude that the
luminous and possibly amplified HNC emission of the western nucleus of the
Arp220 merger reflects the unusual, and perhaps transient, environment of the
starburst/AGN activity there. The faint HNC line emission towards Arp220-east
reveals a real difference in physical conditions between the two merger nuclei.Comment: 7 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Atomic Diagnostics of X-ray Irradiated Protoplanetary Disks
We study atomic line diagnostics of the inner regions of protoplanetary disks
with our model of X-ray irradiated disk atmospheres which was previously used
to predict observable levels of the NeII and NeIII fine-structure transitions
at 12.81 and 15.55mum. We extend the X-ray ionization theory to sulfur and
calculate the fraction of sulfur in S, S+, S2+ and sulfur molecules. For the
D'Alessio generic T Tauri star disk, we find that the SI fine-structure line at
25.55mum is below the detection level of the Spitzer Infrared Spectrometer
(IRS), in large part due to X-ray ionization of atomic S at the top of the
atmosphere and to its incorporation into molecules close to the mid-plane. We
predict that observable fluxes of the SII 6718/6732AA forbidden transitions are
produced in the upper atmosphere at somewhat shallower depths and smaller radii
than the neon fine-structure lines. This and other forbidden line transitions,
such as the OI 6300/6363AA and the CI 9826/9852AA lines, serve as complementary
diagnostics of X-ray irradiated disk atmospheres. We have also analyzed the
potential role of the low-excitation fine-structure lines of CI, CII, and OI,
which should be observable by SOFIA and Herschel.Comment: Accepted by Ap
A Spitzer Survey of Mid-Infrared Molecular Emission from Protoplanetary Disks II: Correlations and LTE Models
We present an analysis of Spitzer-IRS observations of H2O, OH, HCN, C2H2, and
CO2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse
sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections
and strengths of most mid-IR molecular emission features are correlated with
each other, suggesting a common origin and similar excitation conditions. We
note that the line detection efficiency is anti-correlated with the 13/30 um
SED spectral slope, which is a measure of the degree of grain settling in the
disk atmosphere. We also note a correlation between detection efficiency and
H-alpha equivalent width, and tentatively with accretion rate, suggesting that
accretional heating contributes to line excitation. If detected, H2O line
fluxes are correlated with the mid-IR continuum flux, and other co-varying
system parameters, such as L_star. However, significant sample variation,
especially in molecular line ratios, remains. LTE models of the H2O emission
show that line strength is primarily related to the best-fit emitting area, and
this accounts for most source-to-source variation in H2O emitted flux. Best-fit
temperatures and column densities cover only a small range of parameter space,
near 10^{18} cm-2 and 450 K for all sources, suggesting a high abundance of H2O
in many planet-forming regions. Other molecules have a range of excitation
temperatures from ~500-1500 K, also consistent with an origin in planet-forming
regions. We find molecular ratios relative to water of ~10^{-3} for all
molecules, with the exception of CO, for which n(CO)/n(H2O)~1. However, LTE
fitting caveats and differences in the way thermo-chemical modeling results are
reported make comparisons with such models difficult, and highlight the need
for additional observations coupled with the use of line-generating radiative
transfer codes
Radiative transfer models of mid-infrared H2O lines in the Planet-forming Region of Circumstellar Disks
The study of warm molecular gas in the inner regions of protoplanetary disks
is of key importance for the study of planet formation and especially for the
transport of H2O and organic molecules to the surfaces of rocky
planets/satellites. Recent Spitzer observations have shown that the
mid-infrared spectra of protoplanetary disks are covered in emission lines due
to water and other molecules. Here, we present a non-LTE 2D radiative transfer
model of water lines in the 10-36 mum range that can be used to constrain the
abundance structure of water vapor, given an observed spectrum, and show that
an assumption of local thermodynamic equilibrium (LTE) does not accurately
estimate the physical conditions of the water vapor emission zones. By applying
the model to published Spitzer spectra we find that: 1) most water lines are
subthermally excited, 2) the gas-to-dust ratio must be one to two orders of
magnitude higher than the canonical interstellar medium ratio of 100-200, and
3) the gas temperature must be higher than the dust temperature, and 4) the
water vapor abundance in the disk surface must be truncated beyond ~ 1 AU. A
low efficiency of water formation below ~ 300 K may naturally result in a lower
water abundance beyond a certain radius. However, we find that chemistry, may
not be sufficient to produce an abundance drop of many orders of magnitude and
speculate that the depletion may also be caused by vertical turbulent diffusion
of water vapor from the superheated surface to regions below the snow line,
where the water can freeze out and be transported to the midplane as part of
the general dust settling. Such a vertical cold finger effect is likely to be
efficient due to the lack of a replenishment mechanism of large, water-ice
coated dust grains to the disk surface.Comment: 12 pages, accepted for publication in Ap
ALMA Observations of Warm Molecular Gas and Cold Dust in NGC 34
We present ALMA Cycle-0 observations of the CO (6-5) line emission
(rest-frame frequency = 691.473 GHz) and of the 435 dust continuum
emission in the nuclear region of NGC 34, a local luminous infrared galaxy
(LIRG) at a distance of 84 Mpc (1" = 407 pc) which contains a Seyfert 2 active
galactic nucleus (AGN) and a nuclear starburst. The CO emission is well
resolved by the ALMA beam (), with an integrated flux of
. Both the morphology
and kinematics of the CO (6-5) emission are rather regular, consistent with a
compact rotating disk with a size of 200 pc. A significant emission feature is
detected on the red-shifted wing of the line profile at the frequency of the
line, with an integrated flux of . However, it cannot be ruled out
that the feature is due to an outflow of warm dense gas with a mean velocity of
. The continuum is resolved into an elongated
configuration, and the observed flux corresponds to a dust mass of . An unresolved central core () contributes of the continuum flux and of
the CO (6-5) flux, consistent with insignificant contributions of the AGN to
both emissions. Both the CO (6-5) and continuum spatial distributions suggest a
very high gas column density () in the nuclear
region at .Comment: 10 pages, 13 figures, accepted for publication in Astrophysical
Journa
Voedselprijzen en speculatie op agrarische termijnmarkten : literatuurstudie en interviews
Het LEI heeft informatie over kapitaalstromen op financiële termijnmarkten voor agrarische goederen bij elkaar gebracht. Daarnaast heeft het een literatuuronderzoek gedaan waarbij zowel kwantitatieve (21) als kwalitatieve (19) studies en opiniestukken zijn meegenomen. Het LEI heeft de literatuur zowel inhoudelijk samengevat als beoordeeld op kwaliteit. Daarnaast heeft het LEI op basis van beschikbare bronnen een overzicht gegeven van de mogelijke effecten van het beperken van derivatenhandel door middel van positielimieten. Profundo heeft een aantal pensioenfondsen en andere vermogensbeheerders (zoals banken) geïnterviewd om inzicht te krijgen over hun beleid en hun visie over financiële derivaten markten en voedselprijzen
Herschel observations of water vapour in Markarian 231
The Ultra Luminous InfraRed Galaxy Mrk 231 reveals up to seven rotational
lines of water (H2O) in emission, including a very high-lying (E_{upper}=640 K)
line detected at a 4sigma level, within the Herschel/SPIRE wavelength range,
whereas PACS observations show one H2O line at 78 microns in absorption, as
found for other H2O lines previously detected by ISO. The absorption/emission
dichotomy is caused by the pumping of the rotational levels by far-infrared
radiation emitted by dust, and subsequent relaxation through lines at longer
wavelengths, which allows us to estimate both the column density of H2O and the
general characteristics of the underlying far-infrared continuum source.
Radiative transfer models including excitation through both absorption of
far-infrared radiation emitted by dust and collisions are used to calculate the
equilibrium level populations of H2O and the corresponding line fluxes. The
highest-lying H2O lines detected in emission, with levels at 300-640 K above
the ground state, indicate that the source of far-infrared radiation
responsible for the pumping is compact (radius=110-180 pc) and warm
(T_{dust}=85-95 K), accounting for at least 45% of the bolometric luminosity.
The high column density, N(H2O)~5x10^{17} cm^{-2}, found in this nuclear
component, is most probably the consequence of shocks/cosmic rays, an XDR
chemistry, and/or an "undepleted chemistry" where grain mantles are evaporated.
A more extended region, presumably the inner region of the 1-kpc disk observed
in other molecular species, could contribute to the flux observed in low-lying
H2O lines through dense hot cores, and/or shocks. The H2O 78 micron line
observed with PACS shows hints of a blue-shifted wing seen in absorption,
possibly indicating the occurrence of H2O in the prominent outflow detected in
OH (Fischer et al., this volume).Comment: 5 pages, 3 figure
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