544 research outputs found
A Lower Limit to the Universal Density of Metals at z \sim 3
Column density distribution functions of CIV with 12.05 < log (N) < 14.35 and
SiIV with 11.70 < log (N) < 13.93 have been obtained using 81 CIV absorbers and
35 SiIV absorbers redward of the Ly alpha forest in the lines of sight to seven
quasars with 2.518 < z(em) < 3.78. These distribution functions have been
directly integrated to yield ion densities at z = 3 to 3.5 of Omega(CIV) = (2.0
\pm 0.5) x 10(-8) and Omega(SiIV) = (7.0 \pm 2.6) x 10(-9) with H0 = 65
km/s/Mpc and q0 = 0.02 (1 sigma errors). A larger sample of 11 quasar lines of
sight was used to measure CII/CIV, SiIII/SiIV, and NV/CIV ratios, which suggest
that CIV and SiIV are the dominant ionization stages and that corrections to
Omega(Carbon) and Omega(Silicon) are no more than a factor of two. Normalizing
the alpha-process elements to silicon and the Fe-coproduction elements to
carbon gives a density of heavy elements in these forest clouds of
Omega(metals) = (3.3 \pm 0.8) x 10(-7) (H0 = 65, q0 = 0.02). The implications
for the amount of star formation and for the ionization of the IGM prior to z =
3 are discussed.Comment: 12 pages LaTeX (aaspp4.sty) with 3 encapsulated postscript figures.
To be published in ApJ Letters (accepted September 3, 1997
The Carbon Content of Intergalactic Gas at z=4.25 and its Evolution Toward z=2.4
This paper presents ionization-corrected measurements of the carbon abundance
in intergalactic gas at 4.0 < z < 4.5, using spectra of three bright quasars
obtained with the MIKE spectrograph on Magellan. By measuring the CIV strength
in a sample of 131 discrete HI-selected quasar absorbers with
\rho/\bar{\rho}>1.6, we derive a median carbon abundance of [C/H]=-3.55, with
lognormal scatter of approximately ~0.8 dex. This median value is a factor of
two to three lower than similar measurements made at z~2.4 using CIV and OVI.
The strength of evolution is modestly dependent on the choice of UV background
spectrum used to make ionization corrections, although our detection of an
abundance evolution is generally robust with respect to this model uncertainty.
We present a framework for analyzing the effects of spatial fluctuations in the
UV ionizing background at frequencies relevant for CIV production. We also
explore the effects of reduced flux between 3-4 Rydbergs (as from HeII Lyman
series absorption) on our abundance estimates. At HeII line absorption levels
similar to published estimates the effects are very small, although a larger
optical depth could reduce the strength of the abundance evolution. Our results
imply that ~50% of the heavy elements seen in the IGM at z~2.4 were deposited
in the 1.3 Gyr between z~4.3 and z~2.4. The total implied mass flux of carbon
into the Lyman alpha forest would constitute ~30% of the IMF-weighted carbon
yield from known star forming populations over this period.Comment: Accepted for publication in the Astrophysical Journal. 23 pages, 24
figures, 2 table
Faintest Galaxy Morphologies from WFPC2 Imaging of the Hawaii Survey Fields
We present very deep WFPC2 images in the F814W filter of two Hawaii
Survey fields, SSA13 and SSA22. Using these data with previous ground-based
imaging and spectroscopy, we compare the colors, star-forming properties and
morphologies of the faintest galaxies with a reference sample of bright nearby
galaxies and analyze the changes in field galaxy morphology with magnitude. Our
principal result is the identification of a new morphological class of
``chain'' galaxies at the faintest magnitudes. Based on limited spectroscopy,
we tentatively conclude that these are linearly organized giant star-forming
regions at and, if this is correct, that these are large galaxies
in the process of formation.Comment: 18 pages + 1 table of text as 1 LaTeX file (uses aastex style macros:
aaspp.sty, flushrt.sty) plus 1 uuencoded compressed tar file of 12 PostScript
figures (Figs. 3-9, 16-17, and 21-23). The remaining gray-scale plots are
available by anonymous ftp at
ftp://hubble.ifa.hawaii.edu/pub/preprints/plates To appear in the October
1995 Astronomical Journa
The Minimum Universal Metal Density Between Redshifts of 1.5 and 5.5
It appears that the Lyman alpha forest is becoming thick at a redshift of
about 5.5, cutting off the higher redshift intergalactic medium from view in
neutral hydrogen. However, the effects of star formation at higher redshift are
still readable in the intergalactic metal lines. In this paper I use
observations of 32 quasars with emission redshifts in the range 2.31 to 5.86 to
study the evolution of the intergalactic metal density from z = 1.5 to z = 5.5.
The C IV column density distribution function is consistent with being
invariant throughout this redshift range. From direct integration, I determine
Omega_CIV to be in the range (2.5 - 7) \times 10^{-8} and Omega_SiIV in the
range (0.9 - 3) \times 10^{-8} between z = 1.5 and z = 5. The metallicity at z
= 5 exceeds 3.5 \times 10^{-4}, which in turn implies that this fraction of the
universal massive star formation took place beyond this redshift. This is
sufficient to have ionized the intergalactic medium.Comment: This posting (v3) adds a factor of (1/c) in equation (1), and also
the definition of Delta X, both omitted from v2. This is a typographical
error and there is no impact on the published values of Omega_ion in the text
and figures. v2: Revised to correct an error in equation (1) in the published
version. This was a typographical error only and all values of Omega_ion in
the text and figures of the published version were correctly computed with
H_0 = 65 km/s/Mpc and Omega_m = 1. (5 pages including 4 figures.
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