38 research outputs found
The Kinematic Evolution of Strong MgII Absorbers
We consider the evolution of strong (W_r(2796) > 0.3A) MgII absorbers, most
of which are closely related to luminous galaxies. Using 20 high resolution
quasar spectra from the VLT/UVES public archive, we examine 33 strong MgII
absorbers in the redshift range 0.3 < z < 2.5. We compare and supplement this
sample with 23 strong MgII absorbers at 0.4 < z < 1.4 observed previously with
HIRES/Keck. We find that neither equivalent width nor kinematic spread (the
optical depth weighted second moment of velocity) of MgII2796 evolve. However,
the kinematic spread is sensitive to the highest velocity component, and
therefore not as sensitive to additional weak components at intermediate
velocities relative to the profile center. The fraction of absorbing pixels
within the full velocity range of the system does show a trend of decreasing
with decreasing redshift. Most high redshift systems (14/20) exhibit absorption
over the entire system velocity range, which differs from the result for low
redshift systems (18/36) at the 95% level. This leads to a smaller number of
separate subsystems for high redshift systems because weak absorping components
tend to connect the stronger regions of absorption. We hypothesize that low
redshift MgII profiles are more likely to represent well formed galaxies, many
of which have kinematics consistent with a disk/halo structure. High redshift
MgII profiles are more likely to show evidence of complex protogalactic
structures, with multiple accretion or outflow events. Although these results
are derived from measurements of gas kinematics, they are consistent with
hierarchical galaxy formation evidenced by deep galaxy surveys.Comment: Accepted to the Astrophysical Journa
A Bare Molecular Cloud at \u3cem\u3ez\u3c/em\u3e ~ 0.45*
Several neutral species (Mg I, Si I, Ca I, Fe I) have been detected in a weak Mg II absorption line system (Wr (2796) ~ 0.15 Ă
) at z ~ 0.45 along the sightline toward HE0001-2340. These observations require extreme physical conditions, as noted in D\u27Odorico. We place further constraints on the properties of this system by running a wide grid of photoionization models, determining that the absorbing cloud that produces the neutral absorption is extremely dense (~100-1000 cm-3), cold (\u3c 100 K), and has significant molecular content (~72%-94%). Structures of this size and temperature have been detected in Milky Way CO surveys and have been predicted in hydrodynamic simulations of turbulent gas. In order to explain the observed line profiles in all neutral and singly ionized chemical transitions, the lines must suffer from unresolved saturation and/or the absorber must partially cover the broad emission line region of the background quasar. In addition to this highly unusual cloud, three other ordinary weak Mg II clouds (within densities of ~0.005 cm-3 and temperatures of ~10, 000 K) lie within 500 km s-1 along the same sightline. We suggest that the \u27\u27bare molecular cloud,\u27\u27 which appears to reside outside of a galaxy disk, may have had in situ star formation and may evolve into an ordinary weak Mg II absorbing cloud. Based on public data obtained from the ESO archive of observations from the UVES spectrograph at the VLT, Paranal, Chile
Gram-positive Rod Surveillance for Early Anthrax Detection
Connecticut established telephone-based gram-positive rod (GPR) reporting primarily to detect inhalational anthrax cases more quickly. From March to December 2003, annualized incidence of blood isolates was 21.3/100,000 persons; reports included 293 Corynebacterium spp., 193 Bacillus spp., 73 Clostridium spp., 26 Lactobacillus spp., and 49 other genera. Around-the-clock GPR reporting has described GPR epidemiology and enhanced rapid communication with clinical laboratories
Evolution of the Population of Very Strong MgII Absorbers
We present a study of the evolution of several classes of MgII absorbers, and
their corresponding FeII absorption, over a large fraction of cosmic history:
2.3 to 8.7 Gyrs from the Big Bang. Our sample consists of 87 strong
(Wr(MgII)>0.3 A) MgII absorbers, with redshifts 0.2<z<2.5, measured in 81
quasar spectra obtained from the Very Large Telescope(VLT)/Ultraviolet and
Visual Echelle Spectrograph(UVES) archives of high-resolution spectra (R \sim
45,000). No evolutionary trend in Wr(FeII)/Wr(MgII) is found for moderately
strong MgII absorbers (0.3<Wr(MgII)<1.0 A). However, at lower z we find an
absence of very strong MgII absorbers (those with Wr(MgII)>1 A) with small
ratios of equivalent widths of FeII to MgII. At high z, very strong MgII
absorbers with both small and large Wr(FeII)/Wr(MgII) values are present. We
compare our findings to a sample of 100 weak MgII absorbers (Wr(MgII)<0.3 A)
found in the same quasar spectra by Narayanan et al. (2007).
The main effect driving the evolution of very strong MgII systems is the
difference between the kinematic profiles at low and high redshifts. At high z,
we observe that, among the very strong MgII absorbers, all of the systems with
small ratios of Wr(FeII)/Wr(MgII) have relatively large velocity spreads,
resulting in less saturated profiles. At low z, such kinematically spread
systems are absent, and both FeII and MgII are saturated, leading to
Wr(FeII)/Wr(MgII) values that are all close to 1. The high redshift, small
Wr(FeII)/Wr(MgII) systems could correspond to sub-DLA systems, many of which
have large velocity spreads and are possibly linked to superwinds in star
forming galaxies. In addition to the change in saturation due to kinematic
evolution, the smaller Wr(FeII)/Wr(MgII) values could be due to a lower
abundance of Fe at high z, which would indicate relatively early stages of star
formation in those environments.Comment: 20 pages, 14 figures (figure 1 is a set of 87 figures, which is
available on the online version), accepted for publication in the MNRA
Deer Meat as the Source for a Sporadic Case of Escherichia coli O157:H7 Infection, Connecticut1
We report a case of Escherichia coli O157:H7, which was acquired by eating wild White-Tailed deer (Odocoileus virginianus). DNA fingerprint analysis verified venison as the source of infection. This pediatric case emphasizes the need for dissemination of information to hunters regarding the safe handling and processing of venison
A Bare Molecular Cloud at z~0.45
Several neutral species (MgI, SiI, CaI, FeI) have been detected in a weak
MgII absorption line system (W_r(2796)~0.15 Angstroms) at z~0.45 along the
sightline toward HE0001-2340. These observations require extreme physical
conditions, as noted in D'Odorico (2007). We place further constraints on the
properties of this system by running a wide grid of photoionization models,
determining that the absorbing cloud that produces the neutral absorption is
extremely dense (~100-1000/cm^3), cold (<100 K), and has significant molecular
content (~72-94%). Structures of this size and temperature have been detected
in Milky Way CO surveys, and have been predicted in hydrodynamic simulations of
turbulent gas. In order to explain the observed line profiles in all neutral
and singly ionized chemical transitions, the lines must suffer from unresolved
saturation and/or the absorber must partially cover the broad emission line
region of the background quasar. In addition to this highly unusual cloud,
three other ordinary weak MgII clouds (within densities of ~0.005/cm^3 and
temperatures of ~10000K) lie within 500 km/s along the same sightline. We
suggest that the "bare molecular cloud", which appears to reside outside of a
galaxy disk, may have had in situ star formation and may evolve into an
ordinary weak MgII absorbing cloud.Comment: 15 pages, 4 figures, 4 tables, ApJ accepte
A Groundbased Imaging Study of Galaxies Causing DLA, subDLA, and LLS Absorption in Quasar Spectra
We present results from a search for galaxies that give rise to damped Lyman
alpha (DLA), subDLA, and Lyman limit system (LLS) absorption at redshifts 0.1
~< z ~< 1 in the spectra of background quasars. The sample was formed from a
larger sample of strong MgII absorbers (W_0^(2796) >= 0.3 A) whose HI column
densities were determined by measuring the Ly-alpha line in HST UV spectra.
Photometric redshifts, galaxy colors, and proximity to the quasar sightline, in
decreasing order of importance, were used to identify galaxies responsible for
the absorption. Our sample includes 80 absorption systems for which the
absorbing galaxies have been identified, of which 54 are presented here for the
first time. The main results of this study are: (i) the surface density of
galaxies falls off exponentially with increasing impact parameter, b, from the
quasar sightline relative to a constant background of galaxies, with an
e-folding length of ~46 kpc. Galaxies with b >~ 100 kpc calculated at the
absorption redshift are statistically consistent with being unrelated to the
absorption system. (ii) log N(HI) is inversely correlated with b at the 3.0
sigma level of significance. DLA galaxies are found systematically closer to
the quasar sightline, by a factor of two, than are galaxies which give rise to
subDLAs or LLSs. The median impact parameter is 17.4 kpc for the DLA galaxy
sample, 33.3 kpc for the subDLA sample, and 36.4 kpc for the LLS sample. (iii)
Absorber galaxy luminosity relative to L*, L/L*, is not significantly
correlated with W_0^(2796), log N(HI), or b. (iv) DLA, subDLA, and LLS galaxies
comprise a mix of spectral types, but are inferred to be predominantly late
type galaxies based on their spectral energy distributions. The implications of
these results are discussed. (Abridged)Comment: Accepted for publication in MNRA
Large scale outflows from z ~ 0.7 starburst galaxies identified via ultra-strong MgII quasar absorption lines
(Abridged) Star formation-driven outflows are a critical phenomenon in
theoretical treatments of galaxy evolution, despite the limited ability of
observations to trace them across cosmological timescales. If the strongest
MgII absorption-line systems detected in the spectra of background quasars
arise in such outflows, "ultra-strong" MgII (USMgII) absorbers would identify
significant numbers of galactic winds over a huge baseline in cosmic time, in a
manner independent of the luminous properties of the galaxy. To this end, we
present the first detailed imaging and spectroscopic study of the fields of two
USMgII absorber systems culled from a statistical absorber catalog, with the
goal of understanding the physical processes leading to the large velocity
spreads that define such systems. Each field contains two bright emission-line
galaxies at similar redshift (dv < 300 km/s) to that of the absorption.
Lower-limits on their instantaneous star formation rates (SFR) from the
observed OII and Hb line fluxes, and stellar masses from spectral template
fitting indicate specific SFRs among the highest for their masses at z~0.7.
Additionally, their 4000A break and Balmer absorption strengths imply they have
undergone recent (~0.01 - 1 Gyr) starbursts. The concomitant presence of two
rare phenomena - starbursts and USMgII absorbers - strongly implies a causal
connection. We consider these data and USMgII absorbers in general in the
context of various popular models, and conclude that galactic outflows are
generally necessary to account for the velocity extent of the absorption. We
favour starburst driven outflows over tidally-stripped gas from a major
interaction which triggered the starburst as the energy source for the majority
of systems. Finally, we discuss the implications of these results and speculate
on the overall contribution of such systems to the global SFR density at z~0.7.Comment: 15 pages, 6 figure, accepted for publication by MNRA
Implications of Dramatic Broad Absorption Line Variability in the Quasar FBQS J1408+3054
We have observed a dramatic change in the spectrum of the formerly heavily
absorbed `overlapping-trough' iron low-ionization broad absorption line
(FeLoBAL) quasar FBQS J1408+3054. Over a time span of between 0.6 to 5
rest-frame years, the Mg II trough outflowing at 12,000 km/s decreased in
equivalent width by a factor of two and the Fe II troughs at the same velocity
disappeared. The most likely explanation for the variability is that a
structure in the BAL outflow moved out of our line of sight to the ultraviolet
continuum emitting region of the quasar's accretion disk. Given the size of
that region, this structure must have a transverse velocity of between 2600
km/s and 22,000 km/s. In the context of a simple outflow model, we show that
this BAL structure is located between approximately 5800 and 46,000
Schwarzschild radii from the black hole. That distance corresponds to 1.7 to 14
pc, 11 to 88 times farther from the black hole than the H-beta broad-line
region. The high velocities and the parsec-scale distance for at least this one
FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with
galaxy-scale outflows in ultraluminous infrared galaxies transitioning to
unobscured quasars. The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL
quasar also means that if (some) FeLoBAL quasars have multiwavelength
properties which distinguish them from HiBAL quasars, then some LoBAL quasars
will share those properties. Finally, we extend previous work on how
multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain
the average lifetime of BAL episodes (currently >60 rest-frame years at 90%
confidence).Comment: Final version to appear in MNRAS: references added and factor of 2
underestimate of accretion disk size corrected, resulting in absorber
constrained to be somewhat closer to the black hole. For an animated gif
showing the spectral evolution of the broad absorption line troughs in this
quasar, see http://www.yorku.ca/phall/film19952009.gi