1,458 research outputs found
The absorption spectrum of the QSO PKS 2126-158 (z_em = 3.27) at high resolution
Spectra of the z_em = 3.268 quasar PKS 2126-158 have been obtained in the
range lambda lambda 4300-6620 A with a resolution R = 27000 and an average
signal-to-noise ratio s/n = 25 per resolution element. The list of the
identified absorption lines is given together with their fitted column
densities and Doppler widths. The modal value of the Doppler parameter
distribution for the Ly-alpha lines is = 25 km/s. The column density
distribution can be described by a power-law dn/dN \propto N^{-beta} with beta
= 1.5. 12 metal systems have been identified, two of which were previously
unknown. In order to make the column densities of the intervening systems
compatible with realistic assumptions about the cloud sizes and the silicon to
carbon overabundance, it is necessary to assume a jump beyond the He II edge in
the spectrum of the UV ionizing background at z = 3 a factor 10 larger than the
standard predictions for the integrated quasar contribution. An enlarged sample
of C IV absorptions (71 doublets) has been used to analyze the statistical
properties of this class of absorbers strictly related to galaxies. The column
density distribution is well described by a single power-law, with beta=1.64
and the Doppler parameter distribution shows a modal value b = 14 km/s. The two
point correlation function has been computed in the velocity space for the
individual components of C IV features. A significant signal is obtained for
scales smaller than 200-300 km/s, xi(30< Delta v < 90 km/s) = 32.71 +- 2.89. A
trend of decreasing clustering amplitude with decreasing column density is
apparent, analogously to what has been observed for Ly-alpha lines.Comment: 16 pages, LaTeX (l-aa.sty), 13 ps figures, included in text with
epsf, Fig. 1 can be retrieved at http://www.sissa.it/~dodorico/paper.html,
accepted by Astronomy and Astrophysic
Inhomogeneous metal enrichment at z \sim 1.9: the Lyman limit systems in the spectrum of the HDF-S quasar
We present a detailed analysis of three metal absorption systems observed in
the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage
of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda
3050-10000 \AA). Three main components, spanning about 300 km/s, can be
individuated in the Lyman limit system at z~1.92. They show a surprisingly
large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The
large value found for the second component at z=1.9259, suggests that the line
of sight crosses a star-forming region. In addition, there is a definite
correlation between velocity position and ionisation state in this component,
which we interpret as a possible signature of an expanding H II region. The
systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We
find that photoionisation and collisional ionisation are equal alternatives to
explain the high excitation phase revealed by O VI absorption, seen in these
two systems. From the width of the Si IV, C IV, Si III and C III lines in the
system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7,
excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for
all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2.
The values show a dispersion of more than an order of magnitude and most of
them are much larger than what is observed for weaker systems. This is probably
an indication that high column density systems preferably originate in galactic
halos and are mostly influenced by local ionising sources.Comment: 11 pages, 11 figures, accepted by A&A main journa
Functional and Local Renormalization Groups
We discuss the relation between functional renormalization group (FRG) and
local renormalization group (LRG), focussing on the two dimensional case as an
example. We show that away from criticality the Wess-Zumino action is described
by a derivative expansion with coefficients naturally related to RG quantities.
We then demonstrate that the Weyl consistency conditions derived in the LRG
approach are equivalent to the RG equation for the -function available in
the FRG scheme. This allows us to give an explicit FRG representation of the
Zamolodchikov-Osborn metric, which in principle can be used for computations.Comment: 19 pages, 1 figur
Asymptotic freedom in Horava-Lifshitz gravity
We use the Wetterich equation for foliated spacetimes to study the RG flow of
projectable Horava-Lifshitz gravity coupled to n Lifshitz scalars. Using novel
results for anisotropic heat kernels, the matter-induced beta functions for the
gravitational couplings are computed explicitly. The RG flow exhibits an UV
attractive anisotropic Gaussian fixed point where Newton's constant vanishes
and the extra scalar mode decouples. This fixed point ensures that the theory
is asymptotically free in the large-n expansion, indicating that projectable
Horava-Lifshitz gravity is perturbatively renormalizable. Notably, the
fundamental fixed point action does not obey detailed balance.Comment: 4 pages, 2 figure
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