497 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
VLT/UVES shows no cosmological variability of alpha
The cosmological variability of alpha is probed from individual observations
of pairs of FeII lines. This procedure allows a better control of the
systematics and avoids the influence of the spectral shifts due to ionization
inhomogeneities in the absorbers and/or non-zero offsets between different
exposures. Applied to the FeII lines of the metal absorption systems at zabs =
1.839 in Q1101--264 and at zabs = 1.15 in HE0515--4414 observed by means of
UVES at the ESO-VLT, it provides da/a = 0.4 (+/- 1.5 stat)x10^{-6}. The result
is shifted with respect to the Keck/HIRES mean da/a = -5.7(+/- 1.1
stat})x10^{-6} (Murphy et al. 2004) at a high confidence level (95%). Full
details of this work are given in Levshakov et al (2005)Comment: 3 pages, 1 postscript figur
Simulating cosmic metal enrichment by the first galaxies
We study cosmic metal enrichment via AMR hydrodynamical simulations in a (10
Mpc/h) volume following the Pop III-Pop II transition and for different Pop
III IMFs. We have analyzed the joint evolution of metal enrichment on galactic
and intergalactic scales at z=6 and z=4. Galaxies account for <9% of the
baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e.
regions with extremely low density (<1), (b) the true intergalactic
medium (IGM, 1<<10) and (c) the circumgalactic medium (CGM,
10<), the interface between the IGM and galaxies. By z=6 a
galactic mass-metallicity relation is established. At z=4, galaxies with a
stellar mass show log(O/H)+12=8.19, consistent with
observations. The total amount of heavy elements rises from
at z=6 to 8.05 at z=4. Metals in
galaxies make up to ~0.89 of such budget at z=6; this fraction increases to
~0.95 at z=4. At z=6 (z=4) the remaining metals are distributed in
CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01
(0.03/0.02/0.01). Analogously to galaxies, at z=4 a density-metallicity
(-Z) relation is in place for the diffuse phases: the IGM/voids have a
spatially uniform metallicity, Z~Zsun; in the CGM Z steeply rises
with density up to ~Zsun. In all diffuse phases a considerable
fraction of metals is in a warm/hot (T>K) state. Due to these
physical conditions, CIV absorption line experiments can probe only ~2% of the
total carbon present in the IGM/CGM; however, metal absorption line spectra are
very effective tools to study reionization. Finally, the Pop III star formation
history is almost insensitive to the chosen Pop III IMF. Pop III stars are
preferentially formed in truly pristine (Z=0) gas pockets, well outside
polluted regions created by previous star formation episodes.Comment: 23 pages, 18 figures, 3 tables, Accepted for publication in MNRA
The lithium isotope ratio in the metal-poor halo star G271-162 from VLT/UVES observations
A high resolution (R = 110.000), very high S/N (>600) spectrum of the
metal-poor turnoff star G271-162 has been obtained in connection with the
commissioning of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D
hydrodynamical model atmospheres, the lithium isotope ratio has been estimated
from the LiI 670.8 nm line by means of spectral synthesis. The necessary
stellar line broadening (1D: macroturbulence + rotation, 3D: rotation) has been
determined from unblended KI, CaI and FeI lines. The 3D line profiles agree
very well with the observed profiles, including the characteristic line
asymmetries. Both the 1D and 3D analyses reveal a possible detection of 6Li in
G271-162, 6Li/7Li = 0.02 +-0.01 (one sigma). It is discussed if the smaller
amount of 6Li in G271-162 than in the similar halo star HD84937 could be due to
differences in stellar mass and/or metallicity or whether it may reflect an
intrinsic scatter of the Li isotope ratio in the ISM at a given metallicity.Comment: 5 pages with 6 figures. Accepted as a letter in A&
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