205 research outputs found
Metal abundances and kinematics of quasar absorbers.- I. Absorption systems toward J2233-606
The metal line profiles of different ions observed in high HI column density
systems [N(HI) > 10^{16} cm^{-2}] in quasar spectra can be used to constrain
the ionization structure and kinematic characteristics of the absorbers. For
these purposes, a modified Monte Carlo Inversion (MCI) procedure was applied to
the study of three absorption systems in the spectrum of the HDF-South quasar
J2233-606 obtained with the UVES spectrograph at the VLT/Kueyen telescope. The
MCI does not confirm variations of metal abundances within separate systems
which were discussed in the literature. Instead, we found that an assumption of
a homogeneous metal content and a unique photoionizing background is sufficient
to describe the observed complex metal profiles. It was also found that the
linear size L and the line-of-sight velocity dispersion sigma_v measured within
the absorbers obey a scaling relation, namely, sigma_v increases with
increasing L, and that metal abundance is inversely proportional to the linear
size of the system: the highest metallicity was measured in the system with the
smallest L.Comment: 10 pages, 7 ps figures, accepted to A&
Sensitivity of the H3O+ inversion-rotational spectrum to changes in m_e/m_p
Quantum mechanical tunneling inversion transition in ammonia NH3 is actively
used as a sensitive tool to study possible variations of the electron-to-proton
mass ratio, mu = m_e/m_p. The molecule H3O+ has the inversion barrier
significantly lower than that of NH3. Consequently, its tunneling transition
occurs in the far-infrared (FIR) region and mixes with rotational transitions.
Several such FIR and submillimiter transitions are observed from the
interstellar medium in the Milky Way and in nearby galaxies. We show that the
rest-frame frequencies of these transitions are very sensitive to the variation
of mu, and that their sensitivity coefficients have different signs. Thus, H3O+
can be used as an independent target to test hypothetical changes in mu
measured at different ambient conditions of high (terrestrial) and low
(interstellar medium) matter densities. The environmental dependence of mu and
coupling constants is suggested in a class of chameleon-type scalar field
models - candidates to dark energy carrier.Comment: 8 pages, 2 figures, accepted to ApJ; v2: reformatted for ApJ and
discussion of systematics significantly extende
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
Molecular hydrogen, deuterium and metal abundances in the damped Ly-alpha system at z = 3.025 toward QSO 0347-3819
We have detected in high resolution spectra of the quasar Q0347--3819
obtained with the UVES spectrograph at the VLT/Kueyen telescope over 80
absorption features in the Lyman and Werner H2 bands at the redshift of a
damped Ly-alpha system at z = 3.025. The z = 3.025 system spans over 80 km/s
and exhibits a multicomponent velocity structure in the metal lines. The main
component at z = 3.024855 shows a total H2 column density N(H2) =
(4.10\pm0.21)*10^{14} cm^{-2} and a fractional molecular abundance f(H2) =
(1.94\pm0.10)*10^{-6} derived from the H2 lines arising from J=0 to 5
rotational levels of the ground electronic-vibrational state. For the first
time we unambiguously reveal a pronounced [alpha-element/iron-peak] enhancement
of [O,Si/Zn] = 0.6\pm0.1 (6 sigma c.l.) at high redshift. The simultaneous
analysis of metal and hydrogen lines leads to D/H = (3.75\pm0.25)*10^{-5}. This
value is consistent with standard big bang nucleosynthesis if the
baryon-to-photon ratio, eta, lies within the range 4.37*10^{-10} <= eta <=
5.32*10^{-10}, implying 0.016 <= Omega_b h^2_100 <= 0.020.Comment: 32 pages, 16 ps figures, accepted to Ap
QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time
The variation of the dimensionless fundamental physical constant mu = m_p/m_e
(the proton to electron mass ratio) can be constrained via observation of Lyman
and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha
systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high
resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis
yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for
the observed offsets between discrete spectra and for the first time we find
indications for inter-order distortions. Current analyses tend to underestimate
the impact of systematic errors. Based on the scatter of the measured redshifts
and the corresponding low significance of the redshift-sensitivity correlation
we estimate the limit of accuracy of line position measurements to about 220
m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption
line fit and about 150 m/s allocated to systematics related to instrumentation
and calibration.Comment: 9 pages, 9 figures, accepted for publication in A&
Relativistic corrections to isotope shift in light ions
We calculate isotope mass shift for several light ions using Dirac wave
functions and mass shift operator with relativistic corrections of the order of
. Calculated relativistic corrections to the specific mass shift
vary from a fraction of a percent for Carbon, to 2% for Magnesium. Relativistic
corrections to the normal mass shift are typically smaller. Interestingly, the
final relativistic mass shifts for the levels of one multiplet appear to be
even closer than for non-relativistic operator. That can be important for the
astrophysical search for possible -variation, where isotope shift is a
source of important systematic error. Our calculations show that for levels of
the same multiplet this systematics is negligible and they can be used as
probes for -variation.Comment: 7 pages, 5 tables, revtex
Star-forming regions of the Aquila rift cloud complex. II. Turbulence in molecular cores probed by NH3 emission
(Abridged) Aims. We intend to derive statistical properties of stochastic gas
motion inside the dense low mass star forming molecular cores traced by
NH3(1,1) and (2,2) emission lines. Methods. We use the spatial two-point
autocorrelation (ACF) and structure functions calculated from maps of the
radial velocity fields. Results. We find oscillating ACFs which eventually
decay to zero with increasing lags on scales of 0.04 <= l <= 0.5 pc. The
current paradigm supposes that the star formation process is controlled by the
interplay between gravitation and turbulence, the latter preventing molecular
cores from a rapid collapse due to their own gravity. Thus, oscillating ACFs
may indicate a damping of the developed turbulent flows surrounding the dense
but less turbulent core - a transition to dominating gravitational forces and,
hence, to gravitational collapse.Comment: 11 pages, 16 figures, 3 tables, to be published in Astronomy and
Astrophysic
The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619
We report the measurement of the primordial D/H abundance ratio towards QSO
\object. The column density of the hydrogen in the Lyman limit
system is high, \lnhi \cmm, allowing for the deuterium to
be seen in 5 Lyman series transitions. The measured value of the D/H ratio
towards QSO \object is found to be D/H. The
metallicity of the system showing D/H is found to be solar,
indicating that the measured D/H is the primordial D/H within the measurement
errors. The gas which shows D/H is neutral, unlike previous D/H systems which
were more highly ionized. Thus, the determination of the D/H ratio becomes more
secure since we are measuring it in different astrophysical environments, but
the error is larger because we now see more dispersion between measurements.
Combined with prior measurements of D/H, the best D/H ratio is now D/H, which is 10% lower than the previous value. The new
values for the baryon to photon ratio, and baryonic matter density derived from
D/H are and \ob
respectively.Comment: Minor text and reference changes. To appear in the May 10, 2001 issue
of the Astrophysical Journa
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