171 research outputs found
Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies
Using Voigt-profile-fitting procedures on Keck HIRES spectra of nine QSOs we
identify 1099 CIV absorber components clumped in 201 systems outside the Lyman
forest over 1.6 < z < 4.4. With associated SiIV, CII, SiII and NV where
available we investigate bulk statistical and ionization properties of the
components and systems and find no significant change in redshift for CIV and
SiIV while CII, SiII and NV change substantially. The CIV components exhibit
strong clustering but no clustering is detected for systems on scales from 150
km/s out to 50000 km/s. We conclude the clustering is due entirely to the
peculiar velocities of gas present in the circumgalactic media of galaxies.
Using specific combinations of ionic ratios we compare our observations with
model ionization predictions for absorbers exposed to the metagalactic ionizing
radiation background augmented by proximity radiation from their associated
galaxies and find the generally accepted means of radiative escape by
transparent channels from the internal star-forming sites is spectrally not
viable for our stronger absorbers. We develop an active scenario based on
runaway stars with resulting changes in the efflux of radiation that naturally
enable the needed spectral convergence and in turn provide empirical indicators
of morphological evolution in the associated galaxies. Together with a
coexisting population of relatively compact galaxies indicated by the weaker
absorbers in our sample the collective escape of radiation is sufficient to
maintain the IGM ionized over the full range 1.9 < z < 4.4.Comment: 131 pages including 46 pages of figures and 33 pages of tables.
Accepted for publication by the Astrophysical Journal (Supplement). arXiv
admin note: text overlap with arXiv:astro-ph/030755
Interview with Wallace L. W. Sargent
An interview in two sessions in July 1991 with Dr. Wallace L. W. Sargent, Ira S. Bowen Professor of Astronomy in the Division of Physics, Mathematics, and Astronomy (PMA). Dr. Sargent received his BS (1956), MS (1957) and PhD in physics (1959) from the University of Manchester, U.K. He became a research fellow at Caltech, working on quasar absorption lines, from 1959 to 1962. In 1966, he joined the Caltech faculty as an assistant professor of astronomy, becoming associate professor two years later, full professor in 1971, and Bowen Professor in 1981. He served as executive officer for astronomy 1975-1981 and 1996-1997 and director of Palomar 1997-2000. In this interview, he discusses his involvement with the origins, in the early 1980s, of the first of the Keck Foundation telescopes on Mauna Kea, known as Keck I.
He recalls the initial plans for a big telescope in partnership either with the Carnegie Institution, the University of Arizona, or the University of California, and the circumstances leading to eventually joining with UC on Keck I; the problematic relationship with Carnegie; and his involvement, along with Rochus Vogt, Gerry Neugebauer, and Edward Stone, in raising money from the Keck Foundation.
He discusses the design competition for the proposed 10-meter telescope; the contributions of Jerry Nelson, then at Lawrence Berkeley Laboratory; and the difficulties encountered in designing and building the telescope. He concludes with an account of the decision to build Keck II
The Lyman-alpha Forest at z~4: Keck HIRES Observations of Q 0000-26
This paper describes a study of the Lyman-alpha forest absorption clouds
along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with
the High Resolution Spectrometer on the 10m Keck telescope. We derive accurate
H I column density and Doppler width distributions for the clouds from Voigt
profile fitting. We also analyze simulated Lyman-alpha forest spectra of
matching characteristics in order to gauge the effects of line
blending/blanketing and noise in the data. The results are compared with
similar studies at lower redshifts in order to study any possible evolution in
the clouds' properties. We also estimate the mean intensity of the UV
background at z=4 from an analysis of the proximity effect.Comment: plain TeX containing 23 PS pages, 3 PS tables, and 9 PS figures, ApJ,
Dec 1, 1996 issue replacing an earlier version which contains an corrupted
table
Discovery of excess O I absorption towards the z = 6.42 QSO SDSS J1148+5251
We present a search for O I in the spectra of nine 4.9 < z_qso < 6.4 QSOs
taken with Keck/HIRES. We detect six systems with N(O I) > 10^13.7 cm^{-2} in
the redshift intervals where O I 1302 falls redward of the Ly-alpha forest.
Four of these lie towards SDSS J1148+5251 (z_qso = 6.42). This imbalance is
unlikely to arise from variations in sensitivity among our data or from a
statistical fluctuation. The excess O I occurs over a redshift interval that
also contains transmission in Ly-alpha and Ly-beta. Therefore, if these O I
systems represent pockets of neutral gas, then they must occur within or near
regions of the IGM that are highly ionized. In contrast, no O I is detected
towards SDSS J1030+0524 (z_qso = 6.30), whose spectrum shows complete
absorption in Ly-alpha and Ly-beta over \Delta z ~ 0.2. Assuming no ionization
corrections, we measure mean abundance ratios = -0.04 +/- 0.06,
= -0.31 +/- 0.09, and = -0.34 +/- 0.07 (2 sigma), which are
consistent with enrichment dominated by Type II supernovae. The O/Si ratio
limits the fraction of silicon in these systems contributed by metal-free very
massive stars to < 30%, a result which is insensitive to ionization
corrections. The ionic comoving mass densities along the z_qso > 6.2
sightlines, including only the detected systems, are \Omega(O I) = (7.0 +/-
0.6) * 10^{-8}, \Omega(Si II) = (9.6 +/- 0.9) * 10^{-9}, and \Omega(C II) =
(1.5 +/- 0.2) * 10^{-8}.Comment: Submitted to ApJ, with changes to reflect referee's comment
The Distribution of Metallicity in the IGM at z~2.5: OVI and CIV Absorption in the Spectra of 7 QSOs
We present a direct measurement of the metallicity distribution function for
the high redshift intergalactic medium. We determine the shape of this function
using survival statistics, which account for both detections and non-detections
of OVI and CIV associated with HI absorption in quasar spectra. Our OVI sample
probes the metal content of ~50% of all baryons at z~2.5. We find a median
intergalactic abundance of [O,C/H]=-2.82; the differential abundance
distribution is approximately lognormal with mean ~-2.85 and
\sigma=0.75 dex. Some 60-70% the Lya forest lines are enriched to observable
levels ([O,C/H]>-3.5) while the remaining ~30% of the lines have even lower
abundances. Thus we have not detected a universal metallicity floor as has been
suggested for some Population III enrichment scenaria. In fact, we argue that
the bulk of the intergalactic metals formed later than the first stars that are
thought to have triggered reionization. We do not observe a significant trend
of decreasing metallicity toward the lower density IGM, at least within regions
that would be characterized as filaments in numerical simulations. However, an
[O/H] enhancement may be present at somewhat high densities. We estimate that
roughly half of all baryons at these redshifts have been enriched to
[O/H]>=-3.5. We develop a simple model for the metallicity evolution of the
IGM, to estimate the chemical yield of galaxies formed prior to z~2.5. We find
that the typical galaxy recycled 0.1-0.4% of its mass back into the IGM as
heavy elements in the first 3 Gyr after the Big Bang.Comment: 23 pages in emulateapj, 19 figures. Accepted to ApJ, pending review
of new changes. Revised comparison between our results and Schaye et al
(2003
- …