1,363 research outputs found
Does the proton-to-electron mass ratio vary in the course of cosmological evolution?
The possible cosmological variation of the proton-to-electron mass ratio was
estimated by measuring the H_2 wavelengths in the high-resolution spectrum of
the quasar Q~0347-382. Our analysis yielded an estimate for the possible
deviation of \mu value in the past, 10 Gyr ago: for the unweighted value
; for the weighted value Since the significance of the both
results does not exceed 3, further observations are needed to increase
the statistical significance. In any case, this result may be considered as the
most stringent estimate on an upper limit of a possible variation of \mu (95%
C.L.): This value serves as an
effective tool for selection of models determining a relation between possible
cosmological deviations of the fine-structure constant \alpha and the
elementary particle masses (m, m, etc.).Comment: 6 pages, 1 figure. Talk presented at the JENAM 2002 Workshop on
Varying Fundamental Constants, Porto, 4th September 2002. To be published in
the Conference Proceeding
Testing Cosmological Models With A \lya Forest Statistic: The High End Of The Optical Depth Distribution
We pay particular attention to the high end of the \lya optical depth
distribution of a quasar spectrum. Based on the flux distribution
(Miralda-Escud\'e et al 1996), a simple yet seemingly cosmological model
-differentiating statistic, -- the cumulative probability of
a quasar spectrum with \lya optical depth greater than a high value
-- is emphasized. It is shown that two different models -- the cold dark matter
model with a cosmological constant and the mixed hot and cold dark matter
model, both normalized to COBE and local galaxy cluster abundance -- yield
quite different values of : 0.13 of the former versus 0.058 of
the latter for at . Moreover, it is argued that
may be fairly robust to compute theoretically because it does
not seem to depend sensitively on small variations of simulations parameters
such as radiation field, cooling, feedback process, radiative transfer,
resolution and simulation volume within the plausible ranges of the concerned
quantities. Furthermore, it is illustrated that can be
obtained sufficiently accurately from currently available observed quasar
spectra for , when observational noise is properly taken
into account. We anticipate that analyses of observations of quasar \lya
absorption spectra over a range of redshift may be able to constrain the
redshift evolution of the amplitude of the density fluctuations on
small-to-intermediate scales, therefore providing an independent constraint on
, and .Comment: ApJ Letters, in press, substantial changes have been made from the
last versio
Detecting cold gas at intermediate redshifts: GMRT survey using Mg II systems
Intervening HI 21-cm absorption systems at z > 1.0 are very rare and only 4
confirmed detections have been reported in the literature. Despite their
scarcity, they provide interesting and unique insights into the physical
conditions in the interstellar medium of high-z galaxies. Moreover, they can
provide independent constraints on the variation of fundamental constants. We
report 3 new detections based on our ongoing Giant Metrewave Radio Telescope
(GMRT) survey for 21-cm absorbers at 1.10< z_abs< 1.45 from candidate damped
Lyman_alpha systems. The 21-cm lines are narrow for the z_abs = 1.3710 system
towards SDSS J0108-0037 and z_abs = 1.1726 system toward SDSS J2358-1020. Based
on line full-width at half maximum, the kinetic temperatures are <= 5200 K and
<=800 K, respectively. The 21-cm absorption profile of the third system, z_abs
=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex,
extending up to 100 km/s. The centroids of the 21-cm lines are found to be
shifted with respect to the corresponding centroids of the metal lines derived
from SDSS spectra. This may mean that the 21-cm absorption is not associated
with the strongest metal line component.Comment: 13 pages with 5 figures. Accepted for publication in ApJ
Large-Scale Correlations in the Lyman-alpha Forest at z = 3-4
We present a study of the spatial coherence of the intergalactic medium
toward two pairs of high-redshift quasars with moderate angular separations
observed with Keck/ESI, Q1422+2309A/Q1424+2255 (z_em = 3.63, theta = 39") and
Q1439-0034A/B (z_em = 4.25, theta = 33"). The crosscorrelation of transmitted
flux in the Lyman-alpha forest shows a 5-7 sigma peak at zero velocity lag for
both pairs. This strongly suggests that at least some of the absorbing
structures span the 230-300/h_70 proper kpc transverse separation between
sightlines. We also statistically examine the similarity between paired spectra
as a function of transmitted flux, a measure which may be useful for comparison
with numerical simulations. In investigating the dependence of the correlation
functions on spectral characteristics, we find that photon noise has little
impact for S/N >~ 10 per resolution element. However, the agreement between the
autocorrelation along the line sight and the crosscorrelation between
sightlines, a potential test of cosmological geometry, depends significantly on
instrumental resolution. Finally, we present an inventory of metal lines. These
include a a pair of strong C IV systems at z ~ 3.4 appearing only toward
Q1439B, and a Mg II + Fe II system present toward Q1439 A and B at z = 1.68.Comment: 33 pages, 13 figures, submitted to Ap
High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO J2233-606 with UVES at the ESO VLT
We report on high-resolution observations () of the Hubble
Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle
Spectrograph (UVES). We present spectral data for the wavelength region \AA. The ratio of the final spectrum is about 50 per
resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA.
Redshifts, column densities and Doppler widths of the absorption features have
been determined with Voigt-profile fitting. A total of 621 lines have been
measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems
containing metal lines have been identified. Together with other data in the
literature, the present spectrum confirms that the evolution of the number
density of Ly-alpha lines with \huno has an upturn at .Comment: 34 pages Latex, with 3 PostScript figures. Astronomical Journal, in
press. A few revised upper limit
Temperature and Kinematics of CIV Absorption Systems
We use Keck HIRES spectra of three intermediate redshift QSOs to study the
physical state and kinematics of the individual components of CIV selected
heavy element absorption systems. Fewer than 8 % of all CIV lines with column
densities greater than 10^{12.5} cm^{-2} have Doppler parameters b < 6 km/s. A
formal decomposition into thermal and non-thermal motion using the simultaneous
presence of SiIV gives a mean thermal Doppler parameter b_{therm}(CIV) = 7.2
km/s, corresponding to a temperature of 38,000 K although temperatures possibly
in excess of 300,000 K occur occasionally. We also find tentative evidence for
a mild increase of temperature with HI column density. Non-thermal motions
within components are typically small (< 10 km/s) for most systems, indicative
of a quiescent environment. The two-point correlation function (TPCF) of CIV
systems on scales up to 500 km/s suggests that there is more than one source of
velocity dispersion. The shape of the TPCF can be understood if the CIV systems
are caused by ensembles of objects with the kinematics of dwarf galaxies on a
small scale, while following the Hubble flow on a larger scale. Individual high
redshift CIV components may be the building blocks of future normal galaxies in
a hierarchical structure formation scenario.Comment: submitted to the ApJ Letters, March 16, 1996 (in press); (13 Latex
pages, 4 Postscript figures, and psfig.sty included
The Nature of Associated Absorption and the UV-X-ray Connection in 3C 288.1
We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar,
3C 288.1. The data cover ~590 A to ~1610 A in the quasar rest frame. They
reveal a wealth of associated absorption lines (AALs) with no accompanying
Lyman-limit absorption. The metallic AALs range in ionization from C III and N
III to Ne VIII and Mg X. We use these data and photoionization models to derive
the following properties of the AAL gas: 1) There are multiple ionization zones
within the AAL region, spanning a factor of at least ~50 in ionization
parameter. 2) The overall ionization is consistent with the ``warm'' X-ray
continuum absorbers measured in Seyfert 1 nuclei and other QSOs. However, 3)
the column densities implied by the AALs in 3C 288.1 are too low to produce
significant bound-free absorption at any UV-X-ray wavelengths. Substantial
X-ray absorption would require yet another zone, having a much higher
ionization or a much lower velocity dispersion than the main AAL region. 4) The
total hydrogen column density in the AAL gas is log N_H (cm-2)= 20.2. 5) The
metallicity is roughly half solar. 6) The AALs have deconvolved widths of ~900
km/s and their centroids are consistent with no shift from the quasar systemic
velocity (conservatively within +/-1000 km/s). 7) There are no direct
indicators of the absorber's location in our data, but the high ionization and
high metallicity both suggest a close physical relationship to the quasar/host
galaxy environment. Finally, the UV continuum shape gives no indication of a
``blue bump'' at higher energies. There is a distinct break of unknown origin
at ~1030 A, and the decline toward higher energies (with spectral index alpha =
-1.73, for f_nu ~ nu^alpha) is even steeper than a single power-law
interpolation from 1030 A to soft X-rays.Comment: 27 pages with figures and tables, in press with Ap
High resolution study of associated C IV absorption systems in NGC 5548
We present the results of a careful analysis of associated absorption systems
toward NGC 5548. Most of the well resolved narrow components in the associated
system, defined by the Lyman alpha, C IV and N V profiles, show velocity
separation similar (to within 10~\kms) to the C IV doublet splitting. We
estimate the chance probability of occurrence of such pairs with velocity
separation equal to C IV doublet splitting to be . Thus it is
more likely that most of the narrow components are line-locked with C IV
doublet splitting. This will mean that the radiative acceleration plays an
important role in the kinematics of the absorbing clouds. We build grids of
photoionization models and estimate the radiative acceleration due to all
possible bound-bound transitions. We show that the clouds producing absorption
have densities less than , and are in the outer regions of the
broad emission line region (BLR). We note that the clouds which are line-locked
cannot produce appreciable optical depths of O VII and O VIII, and hence cannot
be responsible for the observed ionized edges, in the soft X-ray. We discuss
the implications of the presence of optically thin clouds in the outer regions
of the BLR to the models of broad emission lines.Comment: 21 pages, latex (aasms4 style), incluedes 4 ps figures. To appear in
Astrophysical Journa
Semiclassical approach to the ac-conductance of chaotic cavities
We address frequency-dependent quantum transport through mesoscopic
conductors in the semiclassical limit. By generalizing the trajectory-based
semiclassical theory of dc quantum transport to the ac case, we derive the
average screened conductance as well as ac weak-localization corrections for
chaotic conductors. Thereby we confirm respective random matrix results and
generalize them by accounting for Ehrenfest time effects. We consider the case
of a cavity connected through many leads to a macroscopic circuit which
contains ac-sources. In addition to the reservoir the cavity itself is
capacitively coupled to a gate. By incorporating tunnel barriers between cavity
and leads we obtain results for arbitrary tunnel rates. Finally, based on our
findings we investigate the effect of dephasing on the charge relaxation
resistance of a mesoscopic capacitor in the linear low-frequency regime
The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. II. Modelling Anisotropies with Cosmological Hydrodynamic Simulations
The isotropy of the Lyman-alpha forest in real-space uniquely provides a
measurement of cosmic geometry at z > 2. The angular diameter distance for
which the correlation function along the line of sight and in the transverse
direction agree corresponds to the correct cosmological model. However, the
Lyman-alpha forest is observed in redshift-space where distortions due to
Hubble expansion, bulk flows, and thermal broadening introduce anisotropy.
Similarly, a spectrograph's line spread function affects the autocorrelation
and cross-correlation differently. In this the second paper of a series on
using the Lyman-alpha forest observed in pairs of QSOs for a new application of
the Alcock-Paczynski (AP) test, these anisotropies and related sources of
potential systematic error are investigated with cosmological hydrodynamic
simulations. Three prescriptions for galactic outflow were compared and found
to have only a marginal effect on the Lyman-alpha flux correlation (which
changed by at most 7% with use of the currently favored variable-momentum wind
model vs. no winds at all). An approximate solution for obtaining the zero-lag
cross-correlation corresponding to arbitrary spectral resolution directly from
the zero-lag cross-correlation computed at full-resolution (good to within 2%
at the scales of interest) is presented. Uncertainty in the observationally
determined mean flux decrement of the Lyman-alpha forest was found to be the
dominant source of systematic error; however, this is reduced significantly
when considering correlation ratios. We describe a simple scheme for
implementing our results, while mitigating systematic errors, in the context of
a future application of the AP test.Comment: 20 page
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