12,381 research outputs found
Half Cycle Pulse Train Induced State Redistribution of Rydberg Atoms
Population transfer between low lying Rydberg states independent of the
initial state is realized using a train of half-cycle pulses with pulse
durations much less than the classical orbit period. We demonstrate
experimentally the transfer of population from initial states around n=50 down
to n<40 as well as up to the continuum. The measured population transfer
matches well to a model of the process for 1D atoms.Comment: V2: discussion extended, version accepted for publication in Physical
Review
Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976
It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.Comment: 16 page
Cosmic Pathways for Compact Groups in the Milli-Millennium Simulation
We detected 10 compact galaxy groups (CGs) at in the semi-analytic
galaxy catalog of Guo et al. (2011) for the milli-Millennium Cosmological
Simulation (sCGs in mGuo2010a). We aimed to identify potential canonical
pathways for compact group evolution and thus illuminate the history of
observed nearby compact groups. By constructing merger trees for sCG
galaxies, we studied the cosmological evolution of key properties, and compared
them with Hickson CGs (HCGs). We found that, once sCG galaxies come
within 1 (0.5) Mpc of their most massive galaxy, they remain within that
distance until , suggesting sCG "birth redshifts". At stellar masses
of sCG most-massive galaxies are within . In several cases, especially in the two 4- and 5-member
systems, the amount of cold gas mass anti-correlates with stellar mass, which
in turn correlates with hot gas mass. We define the angular difference between
group members' 3D velocity vectors, , and note that
many of the groups are long-lived because their small values of
indicate a significant parallel component. For
triplets in particular, values range between
and so that galaxies are coming together along
roughly parallel paths, and pairwise separations do not show large pronounced
changes after close encounters. The best agreement between sCG and HCG physical
properties is for galaxy values, but HCG values are higher overall,
including for SFRs. Unlike HCGs, due to a tail at low SFR and , and a
lack of galaxies, only a few sCG galaxies
are on the star-forming main sequence.Comment: Style fixes to better match ApJ published version. Uses likeapj1.1
style files: 17 pages, 13 figures, 2 tables. LaTex style files available at
https://github.com/qtast/likeapj/releases/lates
A review of small cetaceans from waters off the Arabian Peninsula. Scientific Committee document SC/50/SM6, International Whaling Commission, Muscat, Oman
Available data on small cetacean species in coastal and offshore waters off peninsula Arabia are reviewed. Species accounts are presented for a total of 16 small cetaceans, including information on the date and source of first records in the region, distribution, stock identity, abundance, external appearance, migrations or local movements, status, incidental takes, directed catches and other threats, ecology, life history and disease/parasites. In addition the origin and present location of all curated specimens are listed. Anecdotal information, such as that obtained from local fishermen and other observers, is also presented
Chemical composition of a sample of bright solar-metallicity stars
We present a detailed analysis of seven young stars observed with the
spectrograph SOPHIE at the Observatoire de Haute-Provence for which the
chemical composition was incomplete or absent in the literature. For five
stars, we derived the stellar parameters and chemical compositions using our
automatic pipeline optimized for F, G, and K stars, while for the other two
stars with high rotational velocity, we derived the stellar parameters by using
other information (parallax), and performed a line-by-line analysis.
Chromospheric emission-line fluxes from CaII are obtained for all targets. The
stellar parameters we derive are generally in good agreement with what is
available in the literature. We provide a chemical analysis of two of the stars
for the first time. The star HIP 80124 shows a strong Li feature at 670.8 nm
implying a high lithium abundance. Its chemical pattern is not consistent with
it being a solar sibling, as has been suggested.Comment: To be published on A
Deep ALMA imaging of the merger NGC1614 - Is CO tracing a massive inflow of non-starforming gas?
Observations of the molecular gas over scales of 0.5 to several kpc provide
crucial information on how gas moves through galaxies, especially in mergers
and interacting systems, where it ultimately reaches the galaxy center,
accumulates, and feeds nuclear activity. Studying the processes involved in the
gas transport is an important step forward to understand galaxy evolution.
12CO, 13CO and C18O1-0 high-sensitivity ALMA observations were used to assess
properties of the large-scale molecular gas reservoir and its connection to the
circumnuclear molecular ring in NGC1614. The role of excitation and abundances
were studied in this context. Spatial distributions of the 12CO and 13CO
emission show significant differences. 12CO traces the large-scale molecular
gas reservoir, associated with a dust lane that harbors infalling gas. 13CO
emission is - for the first time - detected in the large-scale dust lane. Its
emission peaks between dust lane and circumnuclear molecular ring. A
12CO-to-13CO1-0 intensity ratio map shows high values in the ring region (~30)
typical for the centers of luminous galaxy mergers and even more extreme values
in the dust lane (>45). This drop in ratio is consistent with molecular gas in
the dust lane being in a diffuse, unbound state while being funneled towards
the nucleus. We find a high 16O-to-18O abundance ratio in the starburst region
(>900), typical of quiescent disk gas - by now, the starburst is expected to
have enriched the nuclear ISM in 18O relative to 16O. The massive inflow of gas
may be partially responsible for the low 18O/16O abundance since it will dilute
the starburst enrichment with unprocessed gas from greater radii. The
12CO-to-13CO abundance is consistent with this scenario. It suggests that the
nucleus of NGC1614 is in a transient phase of evolution where starburst and
nuclear growth are fuelled by returning gas from the minor merger event.Comment: 10 pages, 9 figures, accepted for publication in A&
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