1,808 research outputs found
Associated Absorption Lines in the Radio-Loud Quasar 3C 351: Far-Ultraviolet Echelle Spectroscopy from the Hubble Space Telescope
As one of the most luminous radio-loud quasars showing intrinsic ultraviolet
(UV) and X-ray absorption, 3C 351 provides a laboratory for studying the
kinematics and physical conditions of such ionized absorbers. We present an
analysis of the intrinsic absorption lines in the high-resolution ( 7
km/s) far-UV spectrum which was obtained from observations with the Space
Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope
(HST). The spectrum spans wavelengths from 1150 \AA to 1710 \AA, and shows
strong emission lines from O VI and Ly. Associated absorption lines are
present on the blue wings of the high-ionization emission doublets O VI
1032,1038 and N V 1238,1242, as well as the
Lyman lines through Ly. These intrinsic absorption features are
resolved into several distinct kinematic components, covering rest-frame
velocities from -40 to -2800 km/s, with respect to the systemic redshift of
. For the majority of these absorption line regions, strong
evidence of partial covering of both the background continuum source and the
BELR is found, which supports the intrinsic absorption origin and rules out the
possibility that the absorption arises in some associated cluster of galaxies.
The relationship between the far-UV absorbers and X-ray `warm' absorbers are
studied with the assistance of photoionization models. Most of the UV
associated absorption components have low values of the ionization parameter
and total hydrogen column densities, which is inconsistent with previous claims
that the UV and X-ray absorption arises in the same material. Analysis of these
components supports a picture with a wide range of ionization parameters,
temperatures, and column densities in AGN outflows.Comment: 27 pages with 5 figures, accepted by Ap
QSO Absorption Systems Detected in Ne VIII: High-Metallicity Clouds with a Large Effective Cross Section
Using high resolution, high signal-to-noise ultraviolet spectra of the z =
0.9754 quasar PG1148+549 obtained with the Cosmic Origins Spectrograph (COS) on
the Hubble Space Telescope, we study the physical conditions and abundances of
NeVIII+OVI absorption line systems at z(abs) =0.68381, 0.70152, 0.72478. In
addition to NeVIII and OVI, absorption lines from multiple ionization stages of
oxygen (OII, OIII, OIV) are detected and are well-aligned with the more highly
ionized species. We show that these absorbers are multiphase systems including
hot gas (T ~ 10^{5.7} K) that produces NeVIII and OVI, and the gas metallicity
of the cool phase ranges from Z = 0.3 Z_{solar} to supersolar. The cool
(~10^{4} K) phases have densities n_{H} ~ 10^{-4} cm^{-3} and small sizes (<
4kpc); these cool clouds are likely to expand and dissipate, and the NeVIII may
be within a transition layer between the cool gas and a surrounding, much
hotter medium. The NeVIII redshift density, dN/dz = 7^{+7}_{-3}, requires a
large number of these clouds for every L > 0.1L* galaxy and a large effective
absorption cross section (>~ 100 kpc), and indeed, we find a star forming ~L*
galaxy at the redshift of the z(abs)=0.72478 system, at an impact parameter of
217 kpc. Multiphase absorbers like these NeVIII systems are likely to be an
important reservoir of baryons and metals in the circumgalactic media of
galaxies.Comment: Final published version (Astrophysical Journal
The Role of a Hot Gas Environment on the Evolution of Galaxies
Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres
The Heavy Element Enrichment of Lyman alpha Clouds in the Virgo Supercluster
Using high S/N STIS echelle spectra (FWHM=7 km/s) of 3C 273, we constrain the
metallicities of two Lya clouds in the vicinity of the Virgo cluster. We detect
C II, Si II, and Si III absorption lines in the Lya absorber at z = 0.00530.
Previous observations with FUSE have revealed Ly beta - Ly theta lines at this
redshift, thereby accurately constraining N(H I). We model the ionization of
the gas and derive [C/H] = -1.2^{+0.3}_{-0.2}, [Si/C] = 0.2+/-0.1, and log
n_{H} = -2.8+/-0.3. The model implies a small absorber thickness, ~70 pc, and
thermal pressure p/k ~ 40 cm^{-3} K. It is most likely that the absorber is
pressure confined by an external medium because gravitational confinement would
require a very high ratio of dark matter to baryonic matter. Based on Milky Way
sight lines in which carbon and silicon abundances have been reliably measured
in the same interstellar cloud (including new measurements presented herein),
we argue that the overabundance of Si relative to C is not due to dust
depletion. Instead, this probably indicates that the gas has been predominately
enriched by Type II supernovae. Such enrichment is most plausibly provided by
an unbound galactic wind, given the absence of galaxies within a projected
distance of 100 kpc and the presence of galaxies capable of driving a wind at
larger distances. We also constrain the metallicity and physical conditions of
the Virgo absorber at z = 0.00337 based on detections of O VI and H I and an
upper limit on C IV. If this absorber is collisionally ionized, the O VI/C IV
limit requires T > 10^{5.3} K. For either collisional ionization or
photoionization, we find that [O/H] > -2.0 at z = 0.00337.Comment: Final Ap.J. versio
Evaluation of a Prototype Ultrasonic Detection System for Quantifying Fish Movement in the Upper Mississippi River
Growing random sequences
We consider the random sequence x[n] = x[n-1] + yxq, with y > 0, where q = 0, 1,..., n - 1 is chosen randomly from a probability distribution P[n] (q). When all q are chosen with equal probability, i.e. P[n](q) = 1/n, we obtain an exact solution for the mean and the divergence of the second moment as functions of n and y. For y = 1 we examine the divergence of the mean value of x[n], as a function of n, for the random sequences generated by power law and exponential P[n](q) and for the non-random sequence P[n](q) = δ[q,β(n-1)]
Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward delta Orionis by the Interstellar Medium Absorption Profile Spectrograph
Studies of the abundances of deuterium in different astrophysical sites are
of fundamental importance to answering the question about how much deuterium
was produced during big bang nucleosynthesis and what fraction of it was
destroyed later. With this in mind, we used the Interstellar Medium Absorption
Profile Spectrograph (IMAPS) on the ORFEUS-SPAS II mission to observe at a
wavelength resolution of 4 km/s (FWHM) the L-delta and L-epsilon absorption
features produced by interstellar atomic deuterium in the spectrum of delta Ori
A. A chi-square analysis indicated that 0.96 < N(D I)< 1.45e15 cm^{-2} at a 90%
level of confidence, and the gas is at a temperature of about 6000K. To obtain
an accurate value of N(H I) needed for a determination of the atomic ratio of D
to H, we measured the L-alpha absorption features in 57 spectra of delta Ori in
the IUE archive. From our measurement of N(H I)= 1.56e20 cm^{-2}, we found that
N(D I)/N(H I)= 7.4(+1.9,-1.3)e-6 (90% confidence). Our result for D/H contrasts
with the more general finding along other lines of sight that D/H is
approximately 1.5e-5. The underabundance of D toward delta Ori A is not
accompanied by an overabundance of N or O relative to H, as one might expect if
the gas were subjected to more stellar processing than usual.Comment: 37 pages, 6 figures. Submitted to the Astrophysical Journa
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
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