138 research outputs found
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
When two become one: an apparent QSO pair turns out to be a single quasar
We report on our serendipitous discovery that the objects Q 01323-4037 and Q
0132-4037, listed in the V\'eron-Cetty & V\'eron catalog (2006) as two
different quasars, are actually a quasar and a star. We briefly discuss the
origin of the misidentification, and provide a refined measurement of the
quasar redshift.Comment: 3 pages, 2 figures; accepted for publication in A&
Measuring the Cosmological Geometry from the Lyman Alpha Forest along Parallel Lines of Sight
We discuss the feasibility of measuring the cosmological metric using the
redshift space correlation function of the Lya forest in multiple lines of
sight, as a function of angular and velocity separation. The geometric
parameter that is measured is f(z) = H(z) D(z)/c, where H(z) is the Hubble
constant and D(z) the angular diameter distance at redshift z. The correlation
function is computed in linear theory. We describe a method to measure it from
observations with the Gaussianization procedure of Croft et al (1998) to map
the Lya forest transmitted flux to an approximation of the linear density
field. The effect of peculiar velocities on the shape of the recovered power
spectrum is pointed out. We estimate the error in recovering the f(z) factor
from observations due to the variance in the Lya absorbers. We show that ~ 20
pairs of quasars (separations < 3') are needed to distinguish a flat \Omega_0=1
universe from a universe with \Omega_0=0.2, \Omega_\Lambda=0.8. A second
parameter that is obtained from the correlation function of the Lya forest is
\beta \simeq \Omega(z)^{0.6}/b (affecting the magnitude of the peculiar
velocities), where b is a linear theory bias of the Lya forest. The statistical
error of f(z) is reduced if b can be determined independently from numerical
simulations, reducing the number of quasar pairs needed for constraining
cosmology to approximately six. On small scales, where the correlation function
is higher, f(z) should be measurable with fewer quasars, but non-linear effects
must then be taken into account. The anisotropy of the non-linear redshift
space correlation function as a function of scale should also provide a precise
quantitative test of the gravitational instability theory of the Lya forest.Comment: submitted to Ap
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
Toward a Measurement of the Cosmological Geometry at z~2: Predicting Lyman-alpha Forest Correlation in Three Dimensions, and the Potential of Future Data Sets
The correlation between Lyman-alpha absorption in the spectra of quasar pairs
can be used to measure the transverse distance scale at z~2, which is sensitive
to the cosmological constant (Omega_Lambda) or other forms of vacuum energy.
Using Hydro-PM simulations, I compute the three-dimensional power spectrum of
the Lyman-alpha forest flux, P_F(k,mu), from which the redshift-space
anisotropy of the correlation can be obtained. I find that box size ~40 Mpc/h
and resolution ~40 Kpc/h are necessary for convergence of the calculations to
<5% on all relevant scales, although somewhat poorer resolution can be used for
large scales. I compute directly the linear theory bias parameters of the
Lyman-alpha forest, potentially allowing simulation results to be extended to
arbitrarily large scales. I investigate the dependence of P_F(k,mu) on the
primordial power spectrum, the temperature-density relation of the gas, and the
mean flux decrement, finding that the redshift-space anisotropy is relatively
insensitive to these parameters. A table of results is provided for different
parameter variations. I investigate the constraint that can be obtained on
Omega_Lambda using quasars from a large survey. Assuming 13 (theta/1')^2 pairs
at separation <theta, and including separations <10', a measurement to <5% can
be made if simulations can predict the redshift-space anisotropy with <5%
accuracy, or to <10% if the anisotropy must be measured from the data. The
Sloan Digital Sky Survey (SDSS) will obtain spectra for a factor ~5 fewer pairs
than this, so followup observations of fainter pair candidates will be
necessary. I discuss the requirements on spectral resolution and
signal-to-noise ratio (SDSS-quality spectra are sufficient).Comment: Submitted to ApJ, 47 page
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the Damped Ly-alpha galaxy at z_abs=3.3901
Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.Comment: Accepted by Ap
The Asiago-ESO/RASS QSO Survey. I.The Catalog and the Local QSO Luminosity Function
This paper presents the first results of a survey for bright quasars (V <
14.5 and R30.
The photometric database is derived from the GSC and USNO catalogs. Quasars are
identified on the basis of their X-ray emission measured in the ROSAT All Sky
Survey. The surface density of quasars brighter than 15.5 mag turns out to be
, about 3 times higher than that estimated by
the PG survey. The quasar optical Luminosity Function (LF) at is computed and shown to be consistent with a Luminosity Dependent
Luminosity Evolution of the type derived by La Franca and Cristiani (1997) in
the range . The predictions of semi-analytical models of
hierarchical structure formation agree remarkably well with the present
observations.Comment: 54 pages Latex, with 7 PostScript figures. Some minor changes.
Astronomical Journal, in pres
Problems for MOND in Clusters and the Ly-alpha Forest
The observed dynamics of gas and stars on galactic and larger scales cannot
be accounted for by self-gravity, indicating that there are large quantities of
unseen matter, or that gravity is non-Newtonian in these regimes. Milgrom's
MOdified Newtonian Dynamics (MOND) postulates that Newton's laws are modified
at very low acceleration, and can account for the rotation curves of galaxies
and some other astrophysical observations, without dark matter. Here we apply
MOND to two independent physical systems: Ly-alpha absorbers and galaxy
clusters. While physically distinct, both are simple hydrodynamical systems
with characteristic accelerations in the MOND regime. We find that Ly-alpha
absorbers are somewhat smaller than in Newtonian gravity with dark matter, but
the result depends crucially on the (unknown) background acceleration field in
which they are embedded. In clusters MOND appears to explain the observed
(baryonic) mass-temperature relation. However, given observed gas density and
enclosed mass profiles and the assumption of hydrostatic equilibrium, MOND
predicts radial temperature profiles which disagree badly with observations. We
show this explicitly for the Virgo, Abell 2199 and Coma clusters, but the
results are general, and seem very difficult to avoid. If this discrepancy is
to be resolved by positing additional (presumably baryonic) dark matter, then
this dark matter must have ~1-3 times the cluster gas mass within 1 Mpc. This
result strongly disfavors MOND as an alternative to dark matter (Abridged).Comment: Revised version. Important caveat in Ly-alpha calculation discussed;
conclusions weakened. Coma cluster and calculation of dark matter mass
required by MOND added; cluster conclusions strengthened. 11 EmulateApJ pages
with 3 embedded figures. Accepted by Ap
A flash in the dark: UVES/VLT high resolution spectroscopy of GRB afterglows
We present the first high resolution (R=20000--45000, corresponding to 14
km/s at 4200A to 6.6 km/s at 9000A) observations of the optical afterglow of
Gamma Ray Bursts. GRB020813 and GRB021004 were observed by UVES@VLT 22.19 hours
and 13.52 hours after the trigger, respectively. These spectra show that the
inter--stellar matter of the GRB host galaxies is complex, with many components
contributing to each main absorption system, and spanning a total velocity
range of up to about 3000 km/s. Several narrow components are resolved down to
a width of a few tens of km/s. In the case of GRB021004 we detected both low
and high ionization lines. Combined with photoionization results obtained with
CLOUDY, the ionization parameters of the various systems are consistent with a
remarkably narrow range with no clear trend with system velocity. This can be
interpreted as due to density fluctuations on top of a regular R^-2 wind
density profile.Comment: Most figure improved, a few typos corrected, added a new subsection.
ApJ in pres
Extinction law variations and dust excitation in the spiral galaxy NGC 300
We investigate the origin of the strong radial gradient in the
ultraviolet-to-infrared ratio in the spiral galaxy NGC 300, and emphasize the
importance of local variations in the interstellar medium geometry, concluding
that they cannot be neglected with respect to metallicity effects. This
analysis is based upon a combination of maps from GALEX and Spitzer, and from
the ground (UBVRI, Halpha and Hbeta). We select ionizing stellar clusters
associated with HII regions of widely varying morphologies, and derive their
fundamental parameters from population synthesis fitting of their spectral
energy distributions, measured to eliminate local backgrounds accurately. From
these fits, we conclude that the stellar extinction law is highly variable in
the line of sight of young clusters of similar ages. In the particular model
geometry that we consider most appropriate to the sampled regions, we checked
that our findings are not significantly altered by the correct treatment of
radiative transfer effects. The variations are systematic in nature: extinction
laws of the Milky Way or LMC type are associated with compact HII regions (the
compacity being quantified in two different ways), while clusters surrounded by
diffuse HII regions follow extinction laws of the 30 Doradus or SMC type. The
Calzetti starburst attenuation law, although most often degenerate with the 30
Doradus extinction law, overpredicts ionizing photon fluxes by large amounts.
We also find that the extinction law variations are correlated with the column
density of dust species emitting in the near- and mid-infrared. Finally, we
briefly discuss the nebular to stellar extinction ratios, and the excitation of
aromatic band carriers, invalidating their claimed association with cold dust.Comment: accepted for publication in ApJ -- figure 6 abridged her
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