481 research outputs found
Lensed Quasar Hosts
Gravitational lensing assists in the detection of quasar hosts by amplifying
and distorting the host light away from the unresolved quasar core images. We
present the results of HST observations of 30 quasar hosts at redshifts 1 < z <
4.5. The hosts are small in size (r_e <~ 6 kpc), and span a range of
morphologies consistent with early-types (though smaller in mass) to
disky/late-type. The ratio of the black hole mass (MBH, from the virial
technique) to the bulge mass (M_bulge, from the stellar luminosity) at 1<z<1.7
is broadly consistent with the local value; while MBH/M_bulge at z>1.7 is a
factor of 3--6 higher than the local value. But, depending on the stellar
content the ratio may decline at z>4 (if E/S0-like), flatten off to 6--10 times
the local value (if Sbc-like), or continue to rise (if Im-like). We infer that
galaxy bulge masses must have grown by a factor of 3--6 over the redshift range
3>z>1, and then changed little since z~1. This suggests that the peak epoch of
galaxy formation for massive galaxies is above z~1. We also estimate the duty
cycle of luminous AGNs at z>1 to be ~1%, or 10^7 yrs, with sizable scatter.Comment: 8 pages, 6 figures, review article with C. Impey at the conference on
"QSO Host Galaxies: Evolution and Environment", Aug. 29-Sep. 2, 2005, Lorentz
Center, Leiden, The Netherland
Probing the Coevolution of Supermassive Black Holes and Quasar Host Galaxies
At low redshift, there are fundamental correlations between the mass of
supermassive black holes (MBH) and the mass (Mbulge) and luminosity of the host
galaxy bulge. We investigate the same relation at z>=1. Using virial mass
estimates for 11 quasars at z >~2 to measure their black hole mass, we find
that black holes at high z fall nearly on the same MBH versus R-band magnitude
(MR) relation (to ~0.3 mag) as low-redshift active and inactive galaxies,
without making any correction for luminosity evolution. Using a set of
conservative assumptions about the host galaxy stellar population, we show that
at z>~2 (10 Gyrs ago) the ratio of MBH/Mbulge was 3--6 times larger than today.
Barring unknown systematic errors on the measurement of MBH, we also rule out
scenarios in which moderately luminous quasar hosts at z>~2 were fully formed
bulges that passively fade to the present epoch. On the other hand, 5 quasar
hosts at z~1 are consistent with current day MBH-MR relationship after taking
into account evolution, appropriate for that of E/S0 galaxies. Therefore, z~1
host galaxies appear to fit the hypothesis they are fully formed early-type
galaxies. We also find that most quasar hosts with absolute magnitudes brighter
than MR = -23 cannot fade below L* galaxies today, regardless of their stellar
population makeup, because their black hole masses are too high and they must
arrive at the local MBH-MR relationship by z=0.Comment: 16 pages, 3 figures, 2 tables. ApJ in press. Corrected for minor
typographical error
Influence of Pretransplant Restrictive Lung Disease on Allogeneic Hematopoietic Cell Transplantation Outcomes
We conducted a 15-year retrospective cohort study to determine the prevalence of restrictive lung disease prior to allogeneic hematopoietic cell transplant (HCT), and to assess whether this was a risk factor for poor outcomes. 2545 patients were eligible for the analysis. Restrictive lung disease was defined as a total lung capacity (TLC) <80% of predicted normal. Chest x-rays and /or computed tomography scans were reviewed for all restricted patients to determine whether lung parenchymal abnormalities were unlikely or highly likely to cause restriction. Multivariate Cox-proportional hazard and sensitivity analyses were performed to assess the relationship between restriction and early respiratory failure and nonrelapse mortality. Restrictive lung disease was present in 194 subjects (7.6%) prior to transplantation. Among these cases, radiographically apparent abnormalities were unlikely to be the cause of the restriction in 149 (77%) subjects. In unadjusted and adjusted analyses, the presence of pulmonary restriction was significantly associated with a 2-fold increase in risk for early respiratory failure and nonrelapse mortality, suggesting that these outcomes occurring in the absence of radiographically apparent abnormalities may be related to respiratory muscle weakness. These findings suggest that pulmonary restriction should be considered as a risk factor for poor outcomes after transplant
LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234
We present rest-frame optical images and spectra of the gravitationally
lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were
performed with the newly commissioned LUCIFER1 near-infrared instrument mounted
on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame
optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc
with a lens magnification factor of about 5 for the A and B components. We also
discovered a new arc belonging to another lensed high-z source galaxy, which
makes this lens system a potential double Einstein ring system. Using the high
S/N rest-frame optical spectra covering H+K band, we detected Hbeta, OIII,
Halpha, NII and SII emission lines. Detailed physical properties of this high-z
galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V))
is computed from the flux ratio of Halpha and Hbeta and appears to be much
higher than that towards stellar continuum (E_s(B-V)), derived from the optical
and NIR broad band photometry fitting. The metallicity was estimated using N2
and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much
lower than the typical z~2 star-forming galaxies. From the flux ratio of SII
6717 and 6732, we found that the electron number density of the HII regions in
the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much
higher than that in local HII regions. The star-formation rate was estimated
via the Halpha luminosity, after correction for the lens magnification, to be
about 365\pm69 Msun/yr. Combining the FWHM of Halpha emission lines and the
half-light radius, we found the dynamical mass of the lensed galaxy is
5.8\pm0.9x10^10 Msun. The gas mass is 5.1\pm1.1x10^10~Msun from the H\alpha
flux surface density by using global Kennicutt-Schmidt Law, indicating a very
high gas fraction of 0.79\pm0.19 in J0900+2234.Comment: 11 pages, 6 figures accepted by ApJ, revised based on referee repor
Strategic Optimization of Water Reuse in Wafer Fabs via Multi-Constraint Linear Programming Technique
The risk of water shortage has been posing as a threat to water demanding industries in Taiwan, including the high-tech industries where ultrapure water is needed for the production of microchips. Such risks are especially unpredictable in the age of climate change, where more frequent extreme climate events such as prolonged droughts have sent these industries scrambling for securing water supply at a very high cost. The national policy also mandates strict water recycling standards for these high-tech plants, while the risk of water supply shortage also forces the industry to be water-conscious. However, most plants set their water recycling strategies based on experience or âârules of thumbâ practices, without implementing optimization tools that can help making decisions in a more scientific approach. In this study we applied linear programming technique to optimize the water recovery path for a microchip assembly plant. A water balance diagram was formulated and completed to determine the existing water recycling performance, and the data was converted to a water flow network. The water flow network was then derived with a mathematical model to formulate a linear optimization problem. The proposed linear programming model is composed of mass balance constraints, unit specification constraints, capacity constraints as well as water quality constraints (discharge limits). The linear programming method was effectively applied to improve the efficiency of water reuse. With the installation of the regeneration units, an increase of 40.1% in the volume of reused water was predicted. The results from water cost structure also indicated that, at higher water tariff, water reuses through reclaiming and generating spent effluents can alleviate the overall water consumption costs
GEMS Survey Data and Catalog
We describe the data reduction and object cataloging for the GEMS survey, a large-area (800 arcmin(2)) two-band (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on the Hubble Space Telescope, centered on the Chandra Deep Field-South.STScI HST-GO-9500.01NASA GO-9500, NAS5-26555, NAG5-13063, NAG5-13102European Communityâs Human Potential Programunder contractHPRN-CT-2002-00316, HPRN-CT-2002-00305McDonald Observator
Dry Mergers in GEMS: The Dynamical Evolution of Massive Early-Type Galaxies
We have used the 28'x 28' HST image mosaic from the GEMS (Galaxy Evolution
from Morphology and SEDs) survey in conjunction with the COMBO-17 photometric
redshift survey to constrain the incidence of major mergers between
spheroid-dominated galaxies with little cold gas (dry mergers) since z = 0.7. A
set of N-body merger simulations was used to explore the morphological
signatures of such interactions: they are recognizable either as < 5kpc
separation close pairs or because of broad, low surface brightness tidal
features and asymmetries. Data with the depth and resolution of GEMS are
sensitive to dry mergers between galaxies with M_V < -20.5 for z < 0.7; dry
mergers at higher redshifts are not easily recovered in single-orbit HST
imaging. Six dry mergers (12 galaxies) with luminosity ratios between 1:1 and
4:1 were found from a sample of 379 red early-type galaxies with M_V < -20.5
and 0.1 < z < 0.7. The simulations suggest that the morphological signatures of
dry merging are visible for ~250Myr and we use this timescale to convert the
observed merger incidence into a rate. On this basis we find that present day
spheroidal galaxies with M_V < -20.5 on average have undergone between 0.5 and
2 major dry mergers since z ~ 0.7. We have compared this result with the
predictions of a Cold Dark Matter based semi-analytic galaxy formation model.
The model reproduces the observed declining major merger fraction of bright
galaxies and the space density of luminous early-type galaxies reasonably well.
The predicted dry merger fraction is consistent with our observational result.
Hence, hierarchical models predict and observations now show that major dry
mergers are an important driver of the evolution of massive early-type galaxies
in recent epochs.Comment: ApJ, in press. The paper has been extensively modified, detailing the
automated+visual selection and dry merger classification. 11 pages emulateapj
with 9 reduced-quality figures. A high quality copy is available at
http://www.mpia-hd.mpg.de/homes/bell/papers/dry.ps.g
An Explanation for the Observed Weak Size Evolution of Disk Galaxies
Surveys of distant galaxies with the Hubble Space Telescope and from the
ground have shown that there is only mild evolution in the relationship between
radial size and stellar mass for galactic disks from z~1 to the present day.
Using a sample of nearby disk-dominated galaxies from the Sloan Digital Sky
Survey (SDSS), and high redshift data from the GEMS (Galaxy Evolution from
Morphology and SEDs) survey, we investigate whether this result is consistent
with theoretical expectations within the hierarchical paradigm of structure
formation. The relationship between virial radius and mass for dark matter
halos in the LCDM model evolves by about a factor of two over this interval.
However, N-body simulations have shown that halos of a given mass have less
centrally concentrated mass profiles at high redshift. When we compute the
expected disk size-stellar mass distribution, accounting for this evolution in
the internal structure of dark matter halos and the adiabatic contraction of
the dark matter by the self-gravity of the collapsing baryons, we find that the
predicted evolution in the mean size at fixed stellar mass since z~1 is about
15-20 percent, in good agreement with the observational constraints from GEMS.
At redshift z~2, the model predicts that disks at fixed stellar mass were on
average only 60% as large as they are today. Similarly, we predict that the
rotation velocity at a given stellar mass (essentially the zero-point of the
Tully-Fisher relation) is only about 10 percent larger at z~1 (20 percent at
z~2) than at the present day.Comment: 13 pages, 6 figures, accepted for publication in ApJ. Revised in
response to referee's comments to improve clariry. Results are unchange
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