661 research outputs found
Decision-level adaptation in motion perception
Prolonged exposure to visual stimuli causes a bias in observers’ responses to subsequent stimuli. Such adaptation-induced biases are usually explained in terms of changes in the relative activity of sensory neurons in the visual system which respond selectively to the properties of visual stimuli. However, the bias could also be due to a shift in the observer’s criterion for selecting one response rather than the alternative; adaptation at the decision level of processing rather than the sensory level. We investigated whether adaptation to implied motion is best attributed to sensory-level or decision-level bias. Three experiments sought to isolate decision factors by changing the nature of the participants’ task while keeping the sensory stimulus unchanged. Results showed that adaptation-induced bias in reported stimulus direction only occurred when the participant’s task involved a directional judgement, and disappeared when adaptation was measured using a non-directional task (reporting where motion was present in the display, regardless of its direction). We conclude that adaptation to implied motion is due to decision-level bias, and that a propensity towards such biases may be widespread in sensory decision-makin
Dynamics of Inner Galactic Disks: The Striking Case of M100
We investigate gas dynamics in the presence of a double inner Lindblad
resonance within a barred disk galaxy. Using an example of a prominent spiral,
M100, we reproduce the basic central morphology, including four dominant
regions of star formation corresponding to the compression maxima in the gas.
These active star forming sites delineate an inner boundary (so-called nuclear
ring) of a rather broad oval detected in the near infrared. We find that
inclusion of self-gravitational effects in the gas is necessary in order to
understand its behavior in the vicinity of the resonances and its subsequent
evolution. The self-gravity of the gas is also crucial to estimate the effect
of a massive nuclear ring on periodic orbits in the stellar bar.Comment: 11 pages, postscript, compressed, uuencoded. Paper and 4 figures
available at ftp://pa.uky.edu/shlosman/nobel or at
http://www.pa.uky.edu/~shlosman/ . Invited talk at the Centennial Nobel
Symposium on "Barred Galaxies and Circumnuclear Activity," A.Sandquist et al.
(Eds.), Springer-Verlag, in pres
The central region of M83: Massive star formation, kinematics, and the location and origin of the nucleus
We report new near-IR integral field spectroscopy of the central starburst
region of the barred spiral galaxy M83 obtained with CIRPASS on Gemini-S, which
we analyse in conjunction with GHaFaS Fabry-Perot data, an AAT IRIS2 Ks-band
image, and near- and mid-IR imaging from the Hubble and Spitzer space
telescopes. The bulk of the current star formation activity is hidden from
optical view by dust extinction, but is seen in the near- and mid-IR to the
north of the nucleus. This region is being fed by inflow of gas through the bar
of M83, traced by the prominent dust lane entering into the circumnuclear
region from the north. An analysis of stellar ages confirms that the youngest
stars are indeed in the northwest. A gradual age gradient, with older stars
further to the south, characterises the well-known star-forming arc in the
central region of M83. Detailed analyses of the Pa beta ionised gas kinematics
and near-IR imaging confirm that the kinematic centre coincides with the
photometric centre of M83, and that these are offset significantly, by about 3
arcsec or 60 pc, from the visible nucleus of the galaxy. We discuss two
possible options, the first of which postulates that the kinematic and
photometric centre traces a galaxy nucleus hidden by a substantial amount of
dust extinction, in the range A_V=3-10 mag. By combining this information with
kinematic results and using arguments from the literature, we conclude that
such a scenario is, however, unlikely, as is the existence of other "hidden"
nuclei in M83. We thus concur with recent authors and favour a second option,
in which the nucleus of the galaxy is offset from its kinematic and photometric
centre. This is presumably a result of some past interaction, possibly related
to the event which lies at the origin of the disturbance of the outer disk of
the galaxy. (Abridged)Comment: MNRAS, in press; 16 pages latex, 15 figure
An Empirical Relation Between The Large-Scale Magnetic Field And The Dynamical Mass In Galaxies
The origin and evolution of cosmic magnetic fields as well as the influence
of the magnetic fields on the evolution of galaxies are unknown. Though not
without challenges, the dynamo theory can explain the large-scale coherent
magnetic fields which govern galaxies, but observational evidence for the
theory is so far very scarce. Putting together the available data of
non-interacting, non-cluster galaxies with known large-scale magnetic fields,
we find a tight correlation between the integrated polarized flux density,
S(PI), and the rotation speed, v(rot), of galaxies. This leads to an almost
linear correlation between the large-scale magnetic field B and v(rot),
assuming that the number of cosmic ray electrons is proportional to the star
formation rate, and a super-linear correlation assuming equipartition between
magnetic fields and cosmic rays. This correlation cannot be attributed to an
active linear alpha-Omega dynamo, as no correlation holds with global shear or
angular speed. It indicates instead a coupling between the large-scale magnetic
field and the dynamical mass of the galaxies, B ~ M^(0.25-0.4). Hence, faster
rotating and/or more massive galaxies have stronger large-scale magnetic
fields. The observed B-v(rot) correlation shows that the anisotropic turbulent
magnetic field dominates B in fast rotating galaxies as the turbulent magnetic
field, coupled with gas, is enhanced and ordered due to the strong gas
compression and/or local shear in these systems. This study supports an
stationary condition for the large-scale magnetic field as long as the
dynamical mass of galaxies is constant.Comment: 23 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
MUSE-AO view of the starburst-AGN connection: NGC 7130
We present the discovery of a small kinematically decoupled core of
0.2 (60 pc) in radius as well as an outflow jet in the
archetypical AGN-starburst "composite" galaxy NGC 7130 from integral field data
obtained with the adaptive optics-assisted MUSE-NFM instrument on the VLT.
Correcting the already good natural seeing at the time of our science
verification observations with the four-laser GALACSI AO system, we reach an
unprecedented spatial resolution at optical wavelengths of around
0.15. We confirm the existence of star-forming knots arranged
in a ring of 0.58 (185 pc) in radius around the nucleus,
previously observed from UV and optical Hubble Space Telescope and CO(6-5) ALMA
imaging. We determine the position of the nucleus as the location of a peak in
gas velocity dispersion. A plume of material extends towards the NE from the
nucleus until at least the edge of our field of view at 2 (640
pc) radius which we interpret as an outflow jet originating in the AGN. The
plume is not visible morphologically, but is clearly characterised in our data
by emission-line ratios characteristic of AGN emission, enhanced gas velocity
dispersion, and distinct non-circular gas velocities. Its orientation is
roughly perpendicular to the line of nodes of the rotating host galaxy disc. A
circumnuclear area of positive and negative velocities of 0.2
in radius indicates a tiny inner disc, which can only be seen after combining
the integral field spectroscopic capabilities of MUSE with adaptive optics.Comment: Accepted for publication in A&A letter
Constraints on Jupiters from Observations of Galactic bulge microlensing events during 2000
Peer reviewe
CocoaSoils data interoperability vision
Data-generative approaches are becoming increasingly common in modern life science research. Agronomy, food, plant sciences, and biodiversity are examples of complementary scientific disciplines that can greatly benefit from the integration and re-sue of the data that they produce. For instance, at WENR ..
Stars and Gas in the Inner Parts of Galaxies seen in SAURON Integral Field Observations
We give two examples of spiral galaxies that show non-circular gas motions in
the inner kiloparsecs, from SAURON integral field spectroscopy. We use harmonic
decomposition of the velocity field of the ionized gas to study the underlying
mass distribution, employing linear theory. The higher order harmonic terms and
the main kinematic features of the observed data are consistent with an
analytically constructed simple bar model. We also present maps of a number of
strong absorption lines in M 100, derive simple stellar populations and
correlate them with features in the gas kinematics.Comment: 7 pages, 3 figures, to be published in 'The Fate of Gas in Galaxies',
editors R. Morganti et al., New Astronomy Review (Elsevier). needs the
elsart.cls style-file. A higher resolution version available at
http://www.astro.rug.nl/~peletier/Research.htm
- …