65 research outputs found
Ammonia (J,K) = (1,1) to (4,4) and (6,6) inversion lines detected in the Seyfert 2 galaxy NGC 1068
We present the detection of the ammonia (NH3) (J,K) = (1,1) to (4,4) and
(6,6) inversion lines toward the prototypical Seyfert 2 galaxy NGC 1068, made
with the Green Bank Telescope (GBT). This is the first detection of ammonia in
a Seyfert galaxy. The ortho-to-para-NH3 abundance ratio suggests that the
molecule was formed in a warm medium of at least 20 K. For the NH3 column
density and fractional abundance, we find (1.09\pm0.23)\times10^14 cm^-2 and
(2.9\pm0.6)\times10^-8, respectively, from the inner 1.2 kpc of NGC 1068. The
kinetic temperature can be constrained to 80\pm20 K for the bulk of the
molecular gas, while some fraction has an even higher temperature of 140\pm30
K.Comment: 5 pages, 3 figures, accepted by A&
Dense Gas in Nearby Galaxies: XVII. The Distribution of Ammonia in NGC253, Maffei2 and IC342
The central few 100 pc of galaxies often contain large amounts of molecular
gas. The chemical and physical properties of these extragalactic star formation
regions differ from those in galactic disks, but are poorly constrained. This
study aims to develop a better knowledge of the spatial distribution and
kinetic temperature of the dense neutral gas associated with the nuclear
regions of three prototypical spiral galaxies, NGC253, IC342, and Maffei2. VLA
CnD and D configuration measurements have been made of three ammonia (NH3)
inversion transitions. The (J,K)=(1,1) and (2,2) transitions of NH3 were imaged
toward IC342 and Maffei2. The (3,3) transition was imaged toward NGC253. The
entire flux obtained from single-antenna measurements is recovered for all
three galaxies observed. Derived lower limits to the kinetic temperatures
determined for the giant molecular clouds in the centers of these galaxies are
between 25 and 50K. There is good agreement between the distributions of NH3
and other H2 tracers, such as rare CO isotopologues or HCN, suggesting that NH3
is representative of the distribution of dense gas. The "Western Peak" in IC342
is seen in the (6,6) line but not in lower transitions, suggesting maser
emission in the (6,6) transition.Comment: 13 pages, 8 figures, latex format, accepted by A&
Quantum Dynamics of Atomic Coherence in a Spin-1 Condensate: Mean-Field versus Many-Body Simulation
We analyse and numerically simulate the full many-body quantum dynamics of a
spin-1 condensate in the single spatial mode approximation. Initially, the
condensate is in a ``ferromagnetic'' state with all spins aligned along the
axis and the magnetic field pointing along the z axis. In the course of
evolution the spinor condensate undergoes a characteristic change of symmetry,
which in a real experiment could be a signature of spin-mixing many-body
interactions. The results of our simulations are conveniently visualised within
the picture of irreducible tensor operators.Comment: Accepted for publication for the special issue of "Optics
Communications" on Quantum Control of Light and Matte
Dust Obscuration in Lyman Break Galaxies at z~4
Measuring star formation rates (SFRs) in high-z galaxies with their
rest-frame ultraviolet (UV) continuum can be uncertain because of dust
obscuration. Prior studies had used the submillimeter emission at 850 um to
determine the intrinsic SFRs of rest-frame UV selected galaxies, but the
results suffered from the low sensitivity and poor resolution (~15''). Here, we
use ultradeep Very Large Array 1.4 GHz images with ~1''-2'' resolutions to
measure the intrinsic SFRs. We perform stacking analyses in the radio images
centered on ~3500 Lyman break galaxies (LBGs) at z~4 in the Great Observatories
Origins Deep Survey-North and South fields selected with Hubble Space
Telescope/Advanced Camera for Surveys data. The stacked radio flux is very low,
0.08+/-0.15 uJy, implying a mean SFR of 6+/-11 M/yr. This is comparable to the
uncorrected mean UV SFRs of 5 M/yr, implying that the z~4 LBGs have little dust
extinction. The low SFR and dust extinction support the previous results that
z~4 LBGs are in general not submillimeter galaxies. We further show that there
is no statistically significant excess of dust-hidden star-forming components
within ~22 kpc from the LBGs.Comment: 6 pages, 3 figures, and 2 tables. Accepted to the Astrophysical
Journal (ApJ
High-resolution mapping of the physical conditions in two nearby active galaxies based on 12CO(1-0), (2-1) and (3-2) lines
We present a detailed analysis of high resolution observations of the three
lowest CO transitions in two nearby active galaxies, NGC4569 and NGC4826. The
CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer
and the CO(3-2) line with the Submillimeter Array. Combining these data allows
us to compare the emission in the three lines and to map the line ratios,
R21=I_{CO(2-1)}/I_{CO(1-0)} and R32=I_{CO(3-2)}/I_{CO(1-0)} at a resolution of
~2", i.e., a linear resolution of 160 pc for NGC4569 and 40 pc for NGC4826. In
both galaxies the emission in the three lines is similarly distributed
spatially and in velocity, and CO is less excited (R32<0.6) than in the
Galactic Center or the centers of other active galaxies studied so far.
According to a pseudo-LTE model the molecular gas in NGC4569 is cold and mainly
optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is
optically thin in the CO(3-2) line. LVG modeling suggests the presence of an
elongated ring of cold and dense gas coinciding with the ILR of the stellar
bar. More excited gas is resolved in the circumnuclear disk of NGC4826.
According to our pseudo-LTE model this corresponds to warmer gas with a ~50% of
the CO(3-2) emission being optically thin. LVG modeling indicates the presence
of a semicircular arc of dense and cold gas centered on the dynamical center
and ~70 pc in radius. The gas temperature increases and its density decreases
toward the center. A near side/far side asymmetry noticeable in the CO, R32 and
Pa-alpha maps suggests that opacity effects play a role. Examining published CO
maps of nearby active galaxies we find similar asymmetries suggesting that this
could be a common phenomenon in active galaxies. These mainly qualitative
results open new perspectives for the study of active galaxies with the future
Atacama Large Millimeter/submillimeter Array.Comment: accepted for publication in A&
Submillimetre observations of RX J1856.5--3754
We report on submillimetre bolometer observations of the isolated neutron
star RX J1856.5--3754 using the LABOCA bolometer array on the Atacama
Pathfinder Experiment (APEX) Telescope. No cold dust continuum emission peak at
the position of RX J1856.5--3754 was detected. The 3 sigma flux density upper
limit of 5 mJy translates into a cold dust mass limit of a few earth masses. We
use the new submillimetre limit, together with a previously obtained H-band
limit, to constrain the presence of a gaseous, circumpulsar disc. Adopting a
simple irradiated-disc model, we obtain a mass accretion limit of dM/dt less
than 10^{14} g/s, and a maximum outer disc radius of around 10^{14} cm. By
examining the projected proper motion of RX J1856.5--3754, we speculate about a
possible encounter of the neutron star with a dense fragment of the CrA
molecular cloud a few thousand years ago.Comment: 6 pages, 3 figures, 1 table; accepted by MNRA
Locating the Youngest HII Regions in M82 with 7 mm Continuum Maps
We present 7mm Very Large Array continuum images of the starburst galaxy M82.
On arcsecond scales, two-thirds of the 7mm continuum consists of free-free
emission from HII regions. In the subarcsecond resolution map, we identify 14
compact sources, including 9 bright HII regions with N_Lyc > 10^51 sec^-1. Four
of the HII regions have rising spectra, implying emission measures > 10^8 cm^-6
pc. Except for one compact source with peculiar features, all other compact
radio sources are found in dust lanes and do not have optical or near-infrared
continuum counterparts. Four regions of extended, high brightness (EM > 10^7
cm-6 pc) radio emission are found in our high resolution map, including some as
large as ~2", or 30 pc, representing either associations of small HII regions,
or sheetlike structures of denser gas. The good correlation between 7 mm
emission and Spitzer IRAC 8 micron continuum-removed PAH feature suggests that
PAH emission may track the recently formed OB stars. We find an excellent
correlation between molecular gas and star formation, particularly dense gas
traced by HCN, down to the ~ 45 pc scale in M82. We also find star formation
efficiencies (SFEs) of 1-10% on the same scale, based on CO maps. The highest
SFE are found in regions with the highest dense gas fractions.Comment: 18 pages, 10 figures. Accepted for publication in A
Precise Identifications of Submillimeter Galaxies: Measuring the History of Massive Star-Forming Galaxies to z>5
We carried out extremely sensitive Submillimeter Array (SMA) 340 GHz (860
micron) continuum imaging of a complete sample of SCUBA 850 micron sources (>4
sigma) with fluxes >3 mJy in the GOODS-N. Using these data and new SCUBA-2
data, we do not detect 4 of the 16 SCUBA sources, and we rule out the original
SCUBA fluxes at the 4 sigma level. Three more resolve into multiple fainter SMA
galaxies, suggesting that our understanding of the most luminous high-redshift
dusty galaxies may not be as reliable as we thought. 10 of the 16 independent
SMA sources have spectroscopic redshifts (optical/infrared or CO) to z=5.18.
Using a new, ultradeep 20 cm image obtained with the Karl G. Jansky Very Large
Array (rms of 2.5 microJy), we find that all 16 of the SMA sources are detected
at >5 sigma. Using Herschel far-infrared (FIR) data, we show that the five
isolated SMA sources with Herschel detections are well described by an Arp 220
spectral energy distribution template in the FIR. They also closely obey the
local FIR-radio correlation, a result that does not suffer from a radio bias.
We compute the contribution from the 16 SMA sources to the universal star
formation rate (SFR) per comoving volume. With individual SFRs in the range
700-5000 solar masses per year, they contribute ~30% of the
extinction-corrected ultraviolet-selected SFR density from z=1 to at least z=5.
Star formation histories determined from extinction-corrected ultraviolet
populations and from submillimeter galaxy populations only partially overlap,
due to the extreme ultraviolet faintness of some submillimeter galaxies.Comment: 26 pages, minor changes to match published versio
A new approach for testing variations of fundamental constants over cosmic epochs using FIR fine-structure lines
Aims. To obtain limits on the variation of the fine-structure constant alpha
and the electron-to-proton mass ratio mu over different cosmological epochs.
Methods. A new approach based on the comparison of redshifts of far infrared
(FIR) fine-structure lines and low-lying rotational transitions in CO is
proposed which is in principle more sensitive by a factor of 10 compared to QSO
metal absorption lines. Results. Estimations of the quotient F = alpha^2/mu
obtained for two distant quasars J1148+5251 (z = 6.42) and BR1202-0725 (z =
4.69) provide Delta F/F = (0.1+/-1.0)10^{-4} and (1.4+/-1.5)10^{-4},
respectively. The obtained limits are consistent with no variation of physical
constants at the level of 0.01% over a period of 13 Gyr. Conclusions. Upcoming
observations of quasars and distant galaxies in FIR fine-structure lines of
different species and in CO low rotational lines at the SOFIA, HSO, and ALMA
are expected to improve the current limit by, at least, an order of magnitude.Comment: 5 pages, to appear in A&A main journa
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