4,312 research outputs found
Molecular Gas and Star Formation in the SAURON Early-type Galaxies
We present the results of a survey of CO emission in 43 of the 48
representative E/S0 galaxies observed in the optical with the SAURON
integral-field spectrograph. The CO detection rate is 12/43 or 28%. This is
lower than previous studies of early-types but can probably be attributed to
different sample selection criteria. As expected, earlier type, more luminous
and massive galaxies have a relatively lower molecular gas content. We find
that CO-rich galaxies tend to have higher H\beta but lower Fe5015 and Mgb
absorption indices than CO-poor galaxies. Those trends appear primarily driven
by the age of the stars, an hypothesis supported by the fact that the galaxies
with the strongest evidence of star formation are also the most CO-rich. In
fact, the early-type galaxies from the current sample appear to extend the
well-known correlations between FIR luminosity, dust mass and molecular mass of
other galaxy types. The star formation interpretation is also consistent with
the SAURON galaxies' radio continuum and FIR flux ratios, and their inferred
star formation efficiencies are similar to those in spiral galaxies. It thus
appears that we have identified the material fueling (residual) star formation
in early-type galaxies, and have demonstrated that it is actively being
transformed. Nevertheless, the lack of strong correlations between the CO
content and most stellar parameters is compatible with the idea that, in a
significant number of sample galaxies, the molecular gas has been accreted from
the outside and has properties rather independent from the old, pre-existing
stellar component.Comment: 14 pages, 9 figures, accepted in MNRA
Quantum feedback for rapid state preparation in the presence of control imperfections
Quantum feedback control protocols can improve the operation of quantum
devices. Here we examine the performance of a purification protocol when there
are imperfections in the controls. The ideal feedback protocol produces an
eigenstate from a mixed state in the minimum time, and is known as rapid state
preparation. The imperfections we examine include time delays in the feedback
loop, finite strength feedback, calibration errors, and inefficient detection.
We analyse these imperfections using the Wiseman-Milburn feedback master
equation and related formalism. We find that the protocol is most sensitive to
time delays in the feedback loop. For systems with slow dynamics, however, our
analysis suggests that inefficient detection would be the bigger problem. We
also show how system imperfections, such as dephasing and damping, can be
included in model via the feedback master equation.Comment: 15 pages, 6 figures and 2 tables. V2 the published version, fig. 1
corrected and some minor changes to the tex
Maximum information gain in weak or continuous measurements of qudits: complementarity is not enough
To maximize average information gain for a classical measurement, all
outcomes of an observation must be equally likely. The condition of equally
likely outcomes may be enforced in quantum theory by ensuring that one's state
is maximally different, or complementary, to the measured observable.
This requires the ability to perform unitary operations on the state,
conditioned on the results of prior measurements. We consider the case of
measurement of a component of angular momentum for a qudit (a -dimensional
system, with ). For weak or continuous-in-time (i.e. repeated weak)
measurements, we show that the complementarity condition ensures an average
improvement, in the rate of purification, of only 2. However, we show that by
choosing the optimal control protocol of this type, one can attain the best
possible scaling, , for the average improvement. For this protocol
the acquisition of information is nearly deterministic. Finally we contrast
these results with those for complementarity-based protocols in a register of
qbits.Comment: 21 pages, 21 figures. V2 published versio
The overmassive black hole in NGC 1277: new constraints from molecular gas kinematics
We report the detection of CO(1-0) emission from NGC 1277, a lenticular
galaxy in the Perseus Cluster. NGC 1277 has previously been proposed to host an
overmassive black hole (BH) compared to the galaxy bulge luminosity (mass),
based on stellar-kinematic measurements. The CO(1-0) emission, observed with
the IRAM Plateau de Bure Interferometer (PdBI) using both, a more compact
(2.9-arcsec resolution) and a more extended (1-arcsec resolution)
configuration, is likely to originate from the dust lane encompassing the
galaxy nucleus at a distance of 0.9 arcsec (~320 pc). The double-horned CO(1-0)
profile found at 2.9-arcsec resolution traces of
molecular gas, likely orbiting in the dust lane at $\sim 550\ \mathrm{km\
s^{-1}}\sim 2\times 10^{10}\
M_\odot\sim
1.7\times 10^{10}\ M_\odotM/L_V=6.3\sim 5\times 10^{9}\ M_\odotM/L_V=10$. While the molecular gas reservoir
may be associated with a low level of star formation activity, the extended
2.6-mm continuum emission is likely to originate from a weak AGN, possibly
characterized by an inverted radio-to-millimetre spectral energy distribution.
Literature radio and X-ray data indicate that the BH in NGC 1277 is also
overmassive with respect to the Fundamental Plane of BH activity.Comment: 15 pages, 13 figures; accepted for publication in MNRAS on 20 January
2016; updated version including minor changes and note added in proo
Conductivity and the current-current correlation measure
We review various formulations of conductivity for one-particle Hamiltonians
and relate them to the current-current correlation measure. We prove that the
current-current correlation measure for random Schr\"odinger operators has a
density at coincident energies provided the energy lies in a localization
regime. The density vanishes at such energies and an upper bound on the rate of
vanishing is computed. We also relate the current-current correlation measure
to the localization length
Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs
Radial stellar migration in galactic discs has received much attention in
studies of galactic dynamics and chemical evolution, but remains a dynamical
phenomenon that needs to be fully quantified. In this work, using a Tree-SPH
simulation of an Sb-type disc galaxy, we quantify the effects of blurring
(epicyclic excursions) and churning (change of guiding radius). We quantify
migration (either blurring or churning) both in terms of flux (the number of
migrators passing at a given radius), and by estimating the population of
migrators at a given radius at the end of the simulation compared to
non-migrators, but also by giving the distance over which the migration is
effective at all radii. We confirm that the corotation of the bar is the main
source of migrators by churning in a bar-dominated galaxy, its intensity being
directly linked to the episode of a strong bar, in the first 1-3 Gyr of the
simulation. We show that within the outer Lindblad resonance (OLR), migration
is strongly dominated by churning, while blurring gains progressively more
importance towards the outer disc and at later times. Most importantly, we show
that the OLR limits the exchange of angular momentum, separating the disc in
two distinct parts with minimal or null exchange, except in the transition
zone, which is delimited by the position of the OLR at the epoch of the
formation of the bar, and at the final epoch. We discuss the consequences of
these findings for our understanding of the structure of the Milky Way disc.
Because the Sun is situated slightly outside the OLR, we suggest that the solar
vicinity may have experienced very limited churning from the inner disc.Comment: Accepted for publication in Astronomy and Astrophysics (acceptance
date: 27/04/15), 24 pages, 24 figure
Quantum limits on post-selected, probabilistic quantum metrology
Probabilistic metrology attempts to improve parameter estimation by
occasionally reporting an excellent estimate and the rest of the time either
guessing or doing nothing at all. Here we show that probabilistic metrology can
never improve quantum limits on estimation of a single parameter, both on
average and asymptotically in number of trials, if performance is judged
relative to mean-square estimation error. We extend the result by showing that
for a finite number of trials, the probability of obtaining better estimates
using probabilistic metrology, as measured by mean-square error, decreases
exponentially with the number of trials. To be tight, the performance bounds we
derive require that likelihood functions be approximately normal, which in turn
depends on how rapidly specific distributions converge to a normal distribution
with number of trials.Comment: V1:8 pages, 1 figure. V2: 9 pages, 1 figure, revised text. V3: 11
pages, 1 figure, revised text; V4 published version, revised title ;-
CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M63
Results from the UV satellite GALEX revealed large extensions of disks in
some nearby spiral galaxies, extending out to 3 to 4 times the isophotal
radius, r25. M63 is a remarkable example of a spiral galaxy with one of the
most extended UV disks, so it offers the opportunity to search for the
molecular gas and characterize the star formation in outer disk regions as
revealed by the UV emission. We obtained deep CO(1-0) and CO(2-1) observations
on the IRAM 30 m telescope along the major axis of the M63 disk from the center
out to the galactocentric radius rgal = 1.6 r25 and over a bright UV region at
rgal = 1.36 r25. CO(1-0) is detected all along the M63 major axis out to r25,
and CO(2-1) is confined to rgal = 0.68 r25, which may betray lower excitation
temperatures in the outer disk. CO(1-0) is also detected in the external bright
UV region of M63. The radial profiles of the CO emission and of the Halpha, 24
micron, NUV and FUV star formation tracers and HI taken from the literature
show a severe drop with the galactocentric radius, such that beyond r25 they
are all absent with the exception of a faint UV emission and HI. The CO
emission detection in the external UV region, where the UV flux is higher than
the UV flux observed beyond r25, highlights a tight correlation between the CO
and UV fluxes, namely the amount of molecular gas and the intensity of star
formation. This external UV region is dominated by the atomic gas, suggesting
that HI is more likely the precursor of H2 rather than the product of UV
photodissociation. A broken power law needs to be invoked to describe the
Kennicutt-Schmidt (K-S) relation of M63 from the center of the galaxy out to
rgal = 1.36 r25. While all along the major axis out to r25 the K-S relation is
almost linear, in the external UV region the SFR regime is highly nonlinear and
characterized by a steep K-S relation and very low star formation efficiency.Comment: 12 pages, 8 figures, A&A accepte
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