419 research outputs found
The Kast Ground Based UV Spectral Survey of 79 QSOs at Redshift 2 for Lyman Alpha Forest and Metal Absorption
We present a moderate resolution (~1.15 Angstroms/pixel) survey of 79 quasars
obtained using the Kast spectrograph on the Shane 3m telescope at Lick
observatory. The spectra span the wavelength range of 3175-5880 Angstroms, and
have typical signal to noise of 6-20 in the regions of the spectra showing
Lyman alpha forest absorption. The quasars have a mean emission redshift of
z=2.17, and nearly all cover the entire Lyman alpha forest between Lyman alpha
and Lyman beta. Although the quasars were selected to avoid BAL, two quasars in
the survey are BAL, one of which is a new discovery. We list the HI and metal
ions observed in a total of 140 absorption systems. We also identify 526
emission lines, and list their observed wavelengths, along with new redshifts
of the quasars. We determine the rest wavelengths of 3 emission lines or line
blends in the forest to be 1070.95 +/- 1.00, 1123.13 +/- 0.51, and 1175.88 +/-
0.30 Angstroms.Comment: Submitted to the Astronomical Journa
QSOs and Absorption Line Systems Surrounding the Hubble Deep Field
We have imaged a 45x45 sq. arcmin. area centered on the Hubble Deep Field
(HDF) in UBVRI passbands, down to respective limiting magnitudes of
approximately 21.5, 22.5, 22.2, 22.2, and 21.2. The principal goals of the
survey are to identify QSOs and to map structure traced by luminous galaxies
and QSO absorption line systems in a wide volume containing the HDF. We have
selected QSO candidates from color space, and identified 4 QSOs and 2 narrow
emission-line galaxies (NELGs) which have not previously been discovered,
bringing the total number of known QSOs in the area to 19. The bright z=1.305
QSO only 12 arcmin. away from the HDF raises the northern HDF to nearly the
same status as the HDF-S, which was selected to be proximate to a bright QSO.
About half of the QSO candidates remain for spectroscopic verification.
Absorption line spectroscopy has been obtained for 3 bright QSOs in the field,
using the Keck 10m, ARC 3.5m, and MDM 2.4m telescopes. Five heavy-element
absorption line systems have been identified, 4 of which overlap the
well-explored redshift range covered by deep galaxy redshift surveys towards
the HDF. The two absorbers at z=0.5565 and z=0.5621 occur at the same redshift
as the second most populated redshift peak in the galaxy distribution, but each
is more than 7Mpc/h (comoving, Omega_M=1, Omega_L=0) away from the HDF line of
sight in the transverse dimension. This supports more indirect evidence that
the galaxy redshift peaks are contained within large sheet-like structures
which traverse the HDF, and may be precursors to large-scale ``pancake''
structures seen in the present-day galaxy distribution.Comment: 36 pages, including 9 figures and 8 tables. Accepted for publication
in the Astronomical Journa
Intrinsic Properties of the <z>=2.7 Lyman Alpha Forest from Keck Spectra of QSO HS 1946+7658
We present the highest quality Lyman Alpha forest spectra published to date,
from the QSO HS 1946+7658. The distribution of H I column densities is a power
law of slope -1.5 from Log N = 12.1 - 14. This power law can extend to N = 0,
because lines weaker than Log N = 12.1 do not have a large H I optical depth.
Low column lines with Log N > 9 could account for all observed He II
absorption, but lines with Log N > 12 alone are unlikely to do so. The b
distribution between 20 and 60 km/sec is a Gaussian with a mean of 23 km/sec
(less than reported in past at this z), and a sigma b of 14 km/sec. We report
no evolution in the Lyman alpha forest (except the number of lines), because Lu
et al. (1997) found the same N and b distributions at = 3.7. We see lines
with 14 80 km/sec that cannot be accounted for by noise
or blending effects. We discover that the lower cutoff in the b distribution
varies with N, from b = 14 km/sec at Log N = 12.5 to b = 22 km/sec at Log N =
14.0, but otherwise b and N are not correlated. We see no Lyman Alpha line
clustering above 50 \kms, in disagreement with previous results from lower
signal to noise data, but we do see a 3 sigma clustering signal at 25 - 50
km/sec among lines with Log N > 13.6Comment: (Minor changes including new identifications for two weak lines) 46
pages including 16 Figures, Latex Table 1 Available at
http://nately.ucsd.edu/~david . To appear in Ap
Bacteriological Quality of Fresh Vegetables and Peeled Sugar-Cane Obtained from Selected Markets in Zaria, Nigeria
Fresh vegetables and peeled sugar-cane serves as an essential component of a healthy diet, but despite their benefit they are prompt to bacterial contamination. The bacteriological quality of four types of fresh vegetables and peeled sugar-cane obtained from selected markets in Zaria, Nigeria was determined using standard microbiological method. The fresh vegetables, peeled sugar-cane, water and hand-swab samples were collected from four different locations namely; Samaru, Sabon-gari, Tudun-wada and Zaria-city. The total bacteria plate counts ranged from 3.3 x 106 cfu/g to 1.6 x 107 cfu/g with Tudu-wada having the highest bacteria load in lettuce. The coliform count of fresh vegetables and peeled sugar-cane varies from 1.3 x 104 to 8.6 x 105 cfu/g in the entire markets with Tudu-wada having the highest value in cucumber, the counts were obviously above specified Standard of 105 cfu/g and 103 cfu/g (ICMSF, 1978). Pathogenic bacteria isolated include; Citrobacter fruendii, Escherichia coli, Enterobacter spp., Klebsiella. spp., Shigella spp., Serratia spp., Cronobacter sakazaki, Staphylococcus aureus, Pseudomonas spp., and others Staphylococci spp.. This study showed that, fresh vegetables and peeled sugar-cane are contaminated with pathogenic bacteria making them unsafe for human consumption; hence fresh produce should be pre- treated thoroughly, so as to reduce the risk of food- borne outbreaks. Keywords: Pathogenic bacteria · Bacteriological quality, Microbiological method, Coliform counts and food- borne outbreaks. DOI: 10.7176/JNSR/12-8-02 Publication date: April 30th 202
A Composite HST Spectrum of Quasars
We construct a composite quasar spectrum from 284 HST FOS spectra of 101
quasars with redshifts z > 0.33. The spectrum covers the wavelengths between
350 and 3000 A in the rest frame. There is a significant steepening of the
continuum slope around 1050 A. The continuum between 1050 and 2200 A can be
modeled as a power law with alpha = -0.99. For the full sample the power-law
index in the extreme ultraviolet (EUV) between 350 and 1050 A is alpha = -1.96.
The continuum flux in the wavelengths near the Lyman limit shows a depression
of about 10 percent. The break in the power-law index and the slight depression
of the continuum near the Lyman limit are features expected in Comptonized
accretion-disk spectra.Comment: 10 figures To appear in the February 1, 1997, issue of the Ap.
Ribbons on the CBR Sky: A Powerful Test of a Baryon Symmetric Universe
If the Universe consists of domains of matter and antimatter, annihilations
at domain interfaces leave a distinctive imprint on the Cosmic Background
Radiation (CBR) sky. The signature is anisotropies in the form of long, thin
ribbons of width , separated by angle where L is the characteristic domain size, and
y-distortion parameter . Such a pattern could potentially be
detected by the high-resolution CBR anisotropy experiments planned for the next
decade, and such experiments may finally settle the question of whether or not
our Hubble volume is baryon symmetric.Comment: LaTeX, 10 pages, 4 figures in epsf. Revised version corrects a couple
of relevant mistake
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
HST Photometry and Keck Spectroscopy of the Rich Cluster MS1054-03: Morphologies, Butcher-Oemler Effect and the Color-Magnitude Relation at z=0.83
We present a study of 81 I selected, spectroscopically-confirmed members of
the X-ray cluster MS1054-03 at z=0.83. Redshifts and spectral types were
determined from Keck spectroscopy. Morphologies and accurate colors were
determined from a large mosaic of HST WFPC2 images in F606W and F814W.
Early-type galaxies constitute only 44% of this galaxy population. Thirty-nine
percent are spiral galaxies, and 17% are mergers. The early-type galaxies
follow a tight and well-defined color-magnitude relation, with the exception of
a few outliers. The observed scatter is 0.029 +- 0.005 magnitudes in restframe
U-B. Most of the mergers lie close to the CM relation defined by the early-type
galaxies. They are bluer by only 0.07 +- 0.02 magnitudes, and the scatter in
their colors is 0.07 +- 0.04 magnitudes. Spiral galaxies in MS1054-03 exhibit a
large range in their colors. The bluest spiral galaxies are 0.7 magnitudes
bluer than the early-type galaxies, but the majority is within +- 0.2
magnitudes of the early-type galaxy sequence. The red colors of the mergers and
the majority of the spiral galaxies are reflected in the fairly low
Butcher-Oemler blue fraction of MS1054-03: f_B=0.22 +- 0.05. The slope and
scatter of the CM relation of early-type galaxies are roughly constant with
redshift, confirming previous studies that were based on ground-based color
measurements and very limited membership information. However, the scatter in
the combined sample of early-type galaxies and mergers is twice as high as the
scatter of the early-type galaxies alone. This is a direct demonstration of the
``progenitor bias'': high redshift early-type galaxies seem to form a
homogeneous, old population because the progenitors of the youngest present-day
early-type galaxies are not included in the sample.Comment: Accepted for publication in the ApJ. At
http://astro.caltech.edu/~pgd/cm1054/ color figures can be obtaine
Intergalactic HeII absorption towards QSO 1157+3143
We report the discovery of a further line of sight allowing detection of HeII
Ly alpha absorption by the intergalactic medium. A HST/STIS survey of 32 bright
z ~ 3 quasars selected from the Hamburg Quasar Surveys yielded one detection
toward QSO 1157+3143 (z ~ 3, B ~ 17). A 10 orbit follow-up spectrum reveals a
UV spectrum significantly supressed by two intervening Lyman limit systems at
z=2.77 and 2.94, but with the continuum flux recovering sufficiently shortward
of ~ 1700 A to allow study of the HeII absorption spectrum in the redshift
range 2.75 < z < 2.97. The absorption is characterized by alternating voids and
dense filament structures seen in both HeII and HI. Attempts to model the HeII
opacity in terms of HI Ly alpha forest absorption are not successful in the
voids, suggesting that HeII reionization is not complete between z=2.77 and
2.97 or that an optically thin Lyman limit system with z ~ 0.3 is responsible
for the additional opacity.Comment: 6 pages, 4 figures, accepted by A&
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