261 research outputs found
Calculating the infrared central charges for perturbed minimal models: improving the RG perturbation
We illustrate a method for improving Renormalisation Group improved perturbation theory by calculating the infrared central charge of a perturbed conformal field theory. The additional input is a dispersion relation that exploits analyticity of the energy-momentum tensor correlator
Deep rest-frame far-UV spectroscopy of the giant Lyman-alpha emitter 'Himiko'
We present deep 10h VLT/XSHOOTER spectroscopy for an extraordinarily luminous
and extended Lya emitter at z=6.595 referred to as Himiko and first discussed
by Ouchi et al. (2009), with the purpose of constraining the mechanisms
powering its strong emission. Complementary to the spectrum, we discuss NIR
imaging data from the CANDELS survey. We find neither for HeII nor any metal
line a significant excess, with 3 sigma upper limits of 6.8, 3.1, and
5.8x10^{-18} erg/s/cm^2 for CIV 1549, HeII 1640, CIII]
1909, respectively, assuming apertures with 200 km/s widths and offset
by -250 km/s w.r.t to the peak Lya redshift. These limits provide strong
evidence that an AGN is not a major contribution to Himiko's Lya flux. Strong
conclusions about the presence of PopIII star-formation or gravitational
cooling radiation are not possible based on the obtained HeII upper limit. Our
Lya spectrum confirms both spatial extent and flux (8.8+/-0.5x10^{-17}
erg/s/cm^2) of previous measurements. In addition, we can unambiguously exclude
any remaining chance of it being a lower redshift interloper by significantly
detecting a continuum redwards of Lya, while being undetected bluewards
On the use of scaling relations for the Tolman test
The use of relations between structural parameters of early type galaxies to
perform the Tolman test is reconsidered. Scaling relations such as the FP or
the Kormendy relation, require the transformation from angular to metric sizes,
to compare the relation at different z values. This transformation depends on
the assumed world model: galaxies of a given angular size, at a given z, are
larger (in kpc) in a non-expanding universe than in an expanding one.
Furthermore, the luminosities of galaxies are expected to evolve with z in an
expanding model. These effects are shown to conspire to reduce the difference
between the predicted SB change with redshift in the expanding and non
expanding cases. We find that the predictions for the visible photometric bands
of the expanding models with passive luminosity evolution are very similar to
those of the static model till z about 1, and therefore, the test cannot
distinguish between the two world models. Recent good quality data are
consistent with the predictions from both models. In the K-band, where the
expected (model) luminosity evolutionary corrections are smaller, the
differences between the xpanding and static models amount to about 0.4 (0.8)
magnitudes at z = 0.4 (1). It is shown that, due to that small difference
between the predictions in the covered z-range, and to the paucity and
uncertainties of the relevant SB photometry, the existing K-band data is not
adequate to distinguish between the different world metrics, and cannot be yet
used to discard the static case. It is pointed out that the scaling relations
could still be used to rule out the non-evolving case if it could be shown that
the coefficients change with the redshift.Comment: Latex, 15 pages with 2 figures. To be published in ApJ Letter
Non-Destructive Probing of Rabi Oscillations on the Cesium Clock Transition near the Standard Quantum Limit
We report on non-destructive observation of Rabi oscillations on the Cs clock
transition. The internal atomic state evolution of a dipole-trapped ensemble of
cold atoms is inferred from the phase shift of a probe laser beam as measured
using a Mach-Zehnder interferometer. We describe a single color as well as a
two-color probing scheme. Using the latter, measurements of the collective
pseudo-spin projection of atoms in a superposition of the clock states are
performed and the observed spin fluctuations are shown to be close to the
standard quantum limit.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
The mass and age of the first SONG target: the red giant 46 LMi
Context. The Stellar Observation Network Group (SONG) is an initiative to build a worldwide network of 1m telescopes with high-precision radial-velocity spectrographs. Here we analyse the first radial-velocity time series of a red-giant star measured by the SONG
telescope at Tenerife. The asteroseismic results demonstrate a major increase in the achievable precision of the parameters for red-giant
stars obtainable from ground-based observations. Reliable tests of the validity of these results are needed, however, before the accuracy
of the parameters can be trusted.
Aims. We analyse the first SONG time series for the star 46 LMi, which has a precise parallax and an angular diameter measured from interferometry, and therefore a good determination of the stellar radius. We use asteroseismic scaling relations to obtain an accurate mass, and modelling to determine the age.
Methods. A 55-day time series of high-resolution, high S/N spectra were obtained with the first SONG telescope. We derive the asteroseismic parameters by analysing the power spectrum. To give a best guess on the large separation of modes in the power spectrum, we have applied a new method which uses the scaling of Kepler red-giant stars to 46 LMi.
Results. Several methods have been applied: classical estimates, seismic methods using the observed time series, and model calculations to derive the fundamental parameters of 46 LMi. Parameters determined using the different methods are consistent within the uncertainties. We find the following values for the mass M (scaling), radius R (classical), age (modelling), and surface gravity (combining mass and radius): M = 1.09 ± 0.04 M⊙, R = 7.95 ± 0.11 R⊙ age t = 8.2 ± 1.9 Gy, and log g = 2.674 ± 0.013.
Conclusions. The exciting possibilities for ground-based asteroseismology of solar-like oscillations with a fully robotic network have been illustrated with the results obtained from just a single site of the SONG network. The window function is still a severe problem which will be solved when there are more nodes in the network
The scaling relations of early--type galaxies in clusters I. Surface photometry in seven nearby clusters
This is the first paper of a series investigating the scaling relations of
early-type galaxies in clusters. Here we illustrate the multi-band imagery and
the image reduction and calibration procedures relative to the whole sample of
22 clusters at 0.05 < z < 0.25. We also present the detailed surface photometry
of 312 early-type galaxies in 7 clusters in the first redshift bin,
z~0.025-0.075. We give for each galaxy the complete set of luminosity and
geometrical profiles, and and a number of global, photometric and morphological
parameters. They have been evaluated taking into account the effects of seeing.
Internal consistency checks and comparisons with data in the literature confirm
the quality of our analysis. These data, together with the spectroscopic ones
presented in the second paper of the series, will provide the local calibration
of the scaling relations.Comment: 36 pages, 13 figures, 7 tables, accepted for publication in A&
The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters
AIMS: We present in this work low and intermediate resolution spectroscopic
data collected for 152 early type galaxies in 8 nearby clusters with z
0.10.
METHODS: We use low resolution data to produce the redshift and the
K-correction for every individual galaxy, as well as to give their overall
spectral energy distribution, and some spectral indicators, including the
4000\AA break, the Mg strength, and the NaD equivalent width.We have also
obtained higher resolution data for early type galaxies in three of the
clusters, to determine their central velocity dispersion.
RESULTS: The effect of the resolution on the measured parameters is
discussed.
CONCLUSIONS: New accurate systemic redshift and velocity dispersion is
presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39.
We have found that the K-correction values for E/S0 bright galaxies in a given
nearby clusters are very similar. We also find that the distribution of the
line indicators significantly differ from cluster to cluster.Comment: 16 pages, 9 figures, Accepted in A&
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