830 research outputs found
First CO J=6-5, 4-3 detections in local ULIRGs: the dense gas in Mrk231, and its colling budget
We report on detections of the high-excitation CO J=6-5, J=4-3 lines in
Mrk231, a prototypical Ultra Luminous Infrared Galaxy (ULIRG) and Seyfert 1
QSO. These observations are combined with CO J=3-2, HCN J=4-3 (this work), and
CO J=2-1, J=1-0, 13CO J=2-1, HCN J=1-0 measurements taken from the literature
to provide better constraints on the properties of the molecular gas in an
extreme starburst/QSO in the local Universe. We find that the CO J=4-3 and
J=6-5 transitions trace a different gas phase from that dominating the lower
three CO transitions, with n(H_2) ~ (1-3)x10^4 cm-3 and Tk ~ (40-70) K. This
phase is responsible for the luminous HCN emission, and contains most of the H2
gas mass of this galaxy. The total CO line cooling emanating from this dense
phase is found similar to that of the [CII] line at 158 micron, suggesting a
very different thermal balance to that seen in lower IR-luminosity galaxies,
and one likely dominated by dense photon-dominated regions. Our dense
"sampling" of the CO rotational ladder and the HCN lines enables us to produce
well-constrained Spectral Line Energy Distributions (SLEDs) for the dense
molecular gas in Mrk231 and compare them to those of high redshift starbursts,
many of which have SLEDs that may be affected by strong lensing. Finally, we
use our local molecular line excitation template to assess the capabilities of
future cm and mm/sub-mm arrays in detecting CO and HCN transitions in similar
systems throughout the local and distant universe.Comment: accepted for publication in The Astrophysical Journal; 37 pages,
preprint format; 5 figures (2 in color
The SCUBA Bright Quasar Survey II: unveiling the quasar epoch at submillimetre wavelengths
We present results of the first systematic search for submillimetre continuum emission from z=2, radio-quiet, optically-luminous quasars, using the SCUBA/JCMT. We have observed a homogeneous sample of 57 quasars in the redshift range 1.54) redshift. The target sensitivity of the survey (3sigma=10mJy at 850um) was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. 9 targets are detected, with fluxes in the range 7-17mJy. Although there is a suggestion of variation of submm detectability between z=2 and z=4, this is consistent with the K-correction of a characteristic far-infrared spectrum. Additionally, the weighted mean fluxes of non-detections at z=2 and z>4 are comparable
Climate change effects on stream and river temperatures across the northwest U.S. from 1980â2009 and implications for salmonid fishes
Radio Observations of Infrared Luminous High Redshift QSOs
We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a
sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were
selected as the brightest sources at 250 GHz from the recent survey of Omont et
al. (2001). We detect seven sources at 1.4 GHz with flux densities, S_{1.4} >
50 microJy. These centimeter (cm) wavelength observations imply that the
millimeter (mm) emission is most likely thermal dust emission. The
radio-through-optical spectral energy distributions for these sources are
within the broad range defined by lower redshift, lower optical luminosity
QSOs. For two sources the radio continuum luminosities and morphologies
indicate steep spectrum, radio loud emission from a jet-driven radio source.
For the remaining 10 sources the 1.4 GHz flux densities, or limits, are
consistent with those expected for active star forming galaxies. If the radio
emission is powered by star formation in these systems, then the implied star
formation rates are of order 1e3 M_solar/year. We discuss the angular sizes and
spatial distributions of the radio emitting regions, and we consider briefly
these results in the context of co-eval black hole and stellar bulge formation
in galaxies.Comment: to appear in the A
Thermoelastic Properties of Ringwoodite [Fe_x,Mg_(1-x)]_2SiO_4: Its Relationship to the 520 km Seismic Discontinuity
We combine density functional theory (DFT) within the local density
approximation (LDA), the quasiharmonic approximation (QHA), and a model
vibrational density of states (VDoS) to calculate elastic moduli and sound
velocities of gamma-[Fe_x,Mg_(1-x)]_2SiO_4 (ringwoodite), the most abundant
mineral of the lower Earth's transition zone (TZ). Comparison with experimental
values at room-temperature and high pressure or ambient-pressure and high
temperature shows good agreement with our first-principles findings. Then, we
investigate the contrasts associated with the
beta-to-gamma-[Fe_x,Mg_(1-x)]_2SiO_4 transformation at pressures and
temperatures relevant to the TZ. This information offers clearly defined
reference values to advance the understanding of the nature of the 520 km
seismic discontinuity.Comment: 29 pages, 6 figures, 2 tables. Under Revie
XMM-Newton Observations of High Redshift Quasars
We report on our XMM observations of the high redshift quasars BR 2237--0607
(z=4.558) and BR 0351--1034 (z=4.351), together with 14 other z>4 objects found
in the XMM public archive. Contrary to former reports, we do not find high
redshift radio-loud quasars to be more absorbed than their radio-quiet
counterparts. We find that the optical to X-ray spectral index alpha-ox is
correlated with the luminosity density at 2500 A, but does not show a
correlation with redshift. The mean 2-10 keV power-law slope of the 9 high
redshift radio-quiet quasars in our sample for which a spectral analysis can be
performed is alpha-x1.23+-0.48, similar to alpha-x=1.19 found from the ASCA
observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), and
significantly different from alpha-x=0.78 found for low redshift Broad-Line
Seyfert galaxies. While the optical/UV spectra of low to high redshift quasars
look remarkably similar, we find a first indication of a difference in their
X-ray spectrum. The steep X-ray spectral index suggests high Eddington ratios
L/L_Edd. These observations give credence to the hypothesis of Mathur (2000)
that NLS1s are low luminosity cousins of high redshift quasars, both likely to
be in their early evolutionary stage.Comment: 25 pages, AJ, in press (Jan 2006
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