466 research outputs found
Lick Slit Spectra of Thirty-Eight Objective Prism QSO Candidates and Low Metallicity Halo Stars
We present Lick Observatory slit spectra of 38 objects which were claimed to
have pronounced ultraviolet excess and emission lines by Zhan \& Chen. Most of
our spectra have FWHM spectral resolutions of about 4~\AA , and relatively high
S/N of about 10 -- 50, although some have FWHM ~\AA ~or lower S/N.
We find eleven QSOs, four galaxies at , twenty-two stars and one
unidentified object with a low S/N spectrum. Six of the QSOs show absorption
systems, including Q0000+027A with a relatively strong associated C~IV
absorption system, and Q0008+008 (V) with a damped Ly
system with an H~I column density of cm. The stars include a
wide variety of spectral types. There is one new DA4 white dwarf at 170~pc, one
sdB at 14~kpc, and three M stars. The rest are of types F, G and K. We have
measured the equivalent widths of the Ca~II~K line, the G-band and the Balmer
lines in ten stars with the best spectra, and we derive metallicities. Seven of
them are in the range ~[Fe/H]~, while the others are less
metal poor. If the stars are dwarfs, then they are at distances of 1 to 7~kpc,
but if they are giants, typical distances will be about 10~kpc.Comment: (Plain Tex, 21 pages, including tables. Send email to
'travell_oir%[email protected]' for 12 pages of figures) To appear in the
%%Astronomical Journal, August, 199
Fluctuations of the intergalactic ionization field at redshift z ~ 2
(Abridged) Aims. To probe the spectral energy distribution (SED) of the
ionizing background radiation at z ~ 2 and to specify the sources contributing
to the intergalactic radiation field. Methods. The spectrum of a bright quasar
HS1103+6416 (zem = 2.19) contains five successive metal-line absorption systems
at zabs = 1.1923, 1.7193, 1.8873, 1.8916, and 1.9410. The systems are optically
thin and reveal multiple lines of different metal ions with the ionization
potentials lying in the extreme ultraviolet (EUV) range (1 Ryd to 0.2 keV). For
each system, the EUV SED of the underlying ionization field is reconstructed by
means of a special technique developed for solving the inverse problem in
spectroscopy. For the zabs = 1.8916 system, the analysis also involves the HeI
resonance lines of the Lyman series and the HeI 504 A continuum, which are seen
for the first time in any cosmic object except the Sun. Results. From one
system to another, the SED of the ionizing continuum changes significantly,
indicating that the intergalactic ionization field at z ~ 2 fluctuates at the
scale of at least Delta_z ~ 0.004. This is consistent with Delta_z ~ 0.01
estimated from HeII and HI Lyman-alpha forest measurements between the
redshifts 2 and 3.Comment: 29 pages, 18 figures, 3 tables, accepted for publication in A\&
Lick Optical Spectra of Quasar HS 1946+7658 at 10 km/sec Resolution: Lyman-Alpha Forest and Metal Absorption Systems
We present optical spectra of QSO HS~1946+7658 with either high resolution
(FWHM=10 km/s) or high signal to noise ratio (SNR=40-100). We find 113 Lyman
alpha and six metal line systems. The metal systems at Zabs=2.844 and 3.050
have complex velocity structures. We find that the system at 2.844 is a damped
Ly-a absorption system, with neutral hydrogen column density of
logN(HI)=20.2+/-0.4, and it is the cause of the Lyman limit break at 3520\AA.
The metal abundance in the gas phase of the system is [M/H]=-2.6+/-0.3, with a
best estimate of [M/H]= -2.8, with ionization parameter Gamma=-2.75, from a
photoionization model. We show that the abundance ratios rule out appreciable
dust in this DLA system. We do not see the enhancement of O over C reported in
Nature by Reimers last years. We see CII*(1335) offset by 15 km/s with respect
to CII(1334), presumably because the gas density varies from 2 - 8 cm(-3) with
changing velocity in the DLA system. These densities imply that the damped
component is 6 - 25 pc thick, which is reasonable for a single cloud in a cold
spiral disk. We see a 2.6sigma lack of Ly-a forest lines well away from the QSO
redshift, which may be a chance fluctuation. We also see a correlation between
column density N(HI) and Doppler parameter b for 96 unsaturated Ly-a forest
absorption lines, and although this correlation persists in the 36 Ly-a lines
which lie in regions where SNR=8-16, we agree with Rauch etal (1993) that it is
probably a bogus effect of low SNR. We show that there are few low-b Ly-a
forest lines in moderate SNR data.Comment: (Plain Tex, 46 pages and 21 figures. To get 21 postscript files for
figures ftp to 132.239.146.152 and login as ftp in directory /pub/fan). To
appear in the Astrophysical Journal Supplement
The Evolution of Lyman alpha Absorbers in the Redshift Range 0.5<z<1.9
We investigate the evolution and the statistical properties of the Lya
absorbers of the intergalactic medium (IGM) in the largely unexplored redshift
range z=0.5-1.9. We use high-resolution (R > 30,000) UV (STIS) and optical
(VLT/UVES and Keck/HIRES) spectra of nine bright quasars with z_em < 1.94. The
main results for the combined Lya line sample are summarized as follows: 1. The
evolution of the number density of the absorbers can be described by the power
law dn/dz ~ (1+z)^gamma. The number density of the low column density lines
decreases with decreasing z with gamma=0.74+-0.31 in the interval z=0.7-1.9. A
comparison with results at higher redshifts shows that it is decelerated in the
explored redshift range and turns into a flat evolution for z -> 0. The
stronger absorbers thin out faster (gamma=1.50+-0.45). The break in their
evolution predicted for z=1.5-1.7 cannot be seen down to z=0.7. On the other
hand, a comparison with values from the literature for the local number density
gives a hint that this break occurs at lower redshift. 2. The distribution of
the column densities of the absorbers is complete down to N_HI=10^12.90 cm^-2.
It can be approximated by a single power law with the exponent beta=1.60+-0.03
over almost three orders of magnitude. beta is redshift independent. 3. The Lya
lines with lower column densities as well as the higher column density lines
show marginal clustering with a 2 sigma significance over short distances
(Delta v < 200 km/s and Delta v < 100 km/s, respectively). We do not see any
difference in the clustering with either column density or redshift.Comment: 15 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
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
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