1,329 research outputs found
No Evidence for [O III] Variability in Mrk 142
Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng
(2016) claimed to find evidence for flux variations in the narrow [O III]
emission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If
correct, this would imply a surprisingly compact size for the narrow-line
region. We show that the claimed [O III] variations are merely the result of
random errors in the overall flux calibration of the spectra. The data do not
provide any support for the hypothesis that the [O III] flux was variable
during the 2008 monitoring period.Comment: Response to Zhang & Feng 2016, MNRAS Letters, 457, L64
(arXiv:1512.07673). Accepted for publication in MNRAS Letters. 5 pages, 2
figure
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Block co-polyMOFs: morphology control of polymer-MOF hybrid materials.
The hybridization of block copolymers and metal-organic frameworks (MOFs) to create novel materials (block co-polyMOFs, BCPMOFs) with controlled morphologies is reported. In this study, block copolymers containing poly(1,4-benzenedicarboxylic acid, H2bdc) and morphology directing poly(ethylene glycol) (PEG) or poly(cyclooctadiene) (poly(COD)) blocks were synthesized for the preparation of BCPMOFs. Block copolymer architecture and weight fractions were found to have a significant impact on the resulting morphology, mediated through the assembly of polymer precursors prior to MOF formation, as determined through dynamic light scattering. Simple modification of block copolymer weight fraction allowed for tuning of particle size and morphology with either faceted and spherical features. Modification of polymer block architecture represents a simple and powerful method to direct morphology in highly crystalline polyMOF materials. Furthermore, the BCPMOFs could be prepared from both Zr4+ and Zn2+ MOFs, yielding hybrid materials with appreciable surface areas and tuneable porosities. The resulting Zn2+ BCPMOF yielded materials with very narrow size distributions and uniform cubic morphologies. The use of topology in BCPMOFs to direct morphology in block copolymer assemblies may open new methodologies to access complex materials far from thermodynamic equilibrium
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Multicomponent metal-organic framework membranes for advanced functional composites.
The diverse chemical and structural properties of metal-organic frameworks (MOFs) make them attractive for myriad applications, but their native powder form is limiting for industrial implementation. Composite materials of MOFs hold promise as a means of exploiting MOF properties in engineered forms for real-world applications. While interest in MOF composites is growing, research to date has largely focused on utilization of single MOF systems. The vast number of different MOF structures provides ample opportunity to mix and match distinct MOF species in a single composite to prepare multifunctional systems. In this work, we describe the preparation of three types of multi-MOF composites with poly(vinylidene fluoride) (PVDF): (1) co-cast MOF MMMs, (2) mixed MOF MMMs, and (3) multilayer MOF MMMs. Finally, MOF MMMs are explored as catalytic membrane reactors for chemical transformations
An Alternative Approach To Measuring Reverberation Lags in Active Galactic Nuclei
Motivated by recent progress in the statistical modeling of quasar
variability, we develop a new approach to measuring emission-line reverberation
lags to estimate the size of broad-line regions (BLRs) in active galactic
nuclei. Assuming that all emission-line light curves are scaled, smoothed, and
displaced versions of the continuum, this alternative approach fits the light
curves directly using a damped random walk model and aligns them to recover the
time lag and its statistical confidence limits. We introduce the mathematical
formalism of this approach and demonstrate its ability to cope with some of the
problems for traditional methods, such as irregular sampling, correlated
errors, and seasonal gaps. We redetermine the lags for 87 emission lines in 31
quasars and reassess the BLR size--luminosity relationship using 60 H-beta
lags. We confirm the general results from the traditional cross-correlation
methods, with a few exceptions. Our method, however, also supports a broad
range of extensions. In particular, it can simultaneously fit multiple lines
and continuum light curves which improves the lag estimate for the lines and
provides estimates of the error correlations between them. Determining these
correlations is of particular importance for interpreting emission-line
velocity--delay maps. We can also include parameters for luminosity-dependent
lags or line responses. We use this to detect the scaling of the BLR size with
continuum luminosity in NGC 5548.Comment: match to the version accepted to ApJ. New code release available at
http://www.astronomy.ohio-state.edu/~yingzu/spear.htm
Swift/UVOT grism monitoring of NGC 5548 in 2013: an attempt at MgII reverberation mapping
Reverberation-mapping-based scaling relations are often used to estimate the
masses of black holes from single-epoch spectra of AGN. While the
radius-luminosity relation that is the basis of these scaling relations is
determined using reverberation mapping of the H line in nearby AGN, the
scaling relations are often extended to use other broad emission lines, such as
MgII, in order to get black hole masses at higher redshifts when H is
redshifted out of the optical waveband. However, there is no radius-luminosity
relation determined directly from MgII. Here, we present an attempt to perform
reverberation mapping using MgII in the well-studied nearby Seyfert 1, NGC
5548. We used Swift to obtain UV grism spectra of NGC 5548 once every two days
from April to September 2013. Concurrent photometric UV monitoring with Swift
provides a well determined continuum lightcurve that shows strong variability.
The MgII emission line, however, is not strongly correlated with the continuum
variability, and there is no significant lag between the two. We discuss these
results in the context of using MgII scaling relations to estimate
high-redshift black hole masses.Comment: 8 pages, 7 figures, accepted for publication in Ap
The Black Hole Mass-Bulge Luminosity Relationship for Active Galactic Nuclei from Reverberation Mapping and Hubble Space Telescope Imaging
We investigate the relationship between black hole mass and bulge luminosity
for AGNs with reverberation-based black hole mass measurements and bulge
luminosities from two-dimensional decompositions of Hubble Space Telescope host
galaxy images. We find that the slope of the relationship for AGNs is 0.76-0.85
with an uncertainty of ~0.1, somewhat shallower than the M_BH \propto
L^{1.0+/-0.1} relationship that has been fit to nearby quiescent galaxies with
dynamical black hole mass measurements. This is somewhat perplexing, as the AGN
black hole masses include an overall scaling factor that brings the AGN
M_BH-sigma relationship into agreement with that of quiescent galaxies. We
discuss biases that may be inherent to the AGN and quiescent galaxy samples and
could cause the apparent inconsistency in the forms of their M_BH-L_bulge
relationships.Comment: 5 pages, 3 figures and 2 tables, submitted to ApJ Letter
Nucleate pool boiling in the long duration low gravity environment of the Space Shuttle
The results are presented of an experimental study of nucleate pool boiling performed in the low gravity environment of the space shuttle. Photographic observations of pool boiling in Freon 113 were obtained during the 'Tank Pressure Control Experiment,' flown on the Space Transportation System, STS-43 in August 1991. Nucleate boiling data from large (relative to bubble size) flat heating surfaces (0.1046 by 0.0742 m) was obtained at very low heat fluxes (0.22 to 1.19 kW/sq m). The system pressure and the bulk liquid subcooling varied in the range of 40 to 60 kPa and 3 to 5 C respectively. Thirty-eight boiling tests, each of 10-min duration for a given heat flux, were conducted. Measurements included the heater power, heater surface temperature, the liquid temperature and the system pressure as functions of heating time. Video data of the first 2 min of heating was recorded for each test. In some tests the video clearly shows the inception of boiling and the growth and departure of bubbles from the surface during the first 2 min of heating. In the absence of video data, the heater temperature variation during heating shows the inception of boiling and stable nucleate boiling. During the stable nucleate boiling, the wall superheat varied between 2.8 to 3.8 C for heat fluxes in the range of 0.95 to 1.19 kW/sq m. The wall superheat at the inception of boiling varied between 2 to 13 C
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
Stellar Velocity Dispersion Measurements in High-Luminosity Quasar Hosts and Implications for the AGN Black Hole Mass Scale
We present new stellar velocity dispersion measurements for four luminous
quasars with the NIFS instrument and the ALTAIR laser guide star adaptive
optics system on the Gemini North 8-m telescope. Stellar velocity dispersion
measurements and measurements of the supermassive black hole masses in luminous
quasars are necessary to investigate the coevolution of black holes and
galaxies, trace the details of accretion, and probe the nature of feedback. We
find that higher-luminosity quasars with higher-mass black holes are not offset
with respect to the MBH-sigma relation exhibited by lower-luminosity AGNs with
lower-mass black holes, nor do we see correlations with galaxy morphology. As
part of this analysis, we have recalculated the virial products for the entire
sample of reverberation-mapped AGNs and used these data to redetermine the mean
virial factor hfi that places the reverberation data on the quiescent
M_BH-sigma relation. With our updated measurements and new additions to the AGN
sample, we obtain = 4.31 +/- 1.05, which is slightly lower than, but
consistent with, most previous determinations.Comment: Accepted for publication in ApJ. For a brief video highlighting the
results of this paper, see: http://www.youtube.com/watch?v=Mxx80aOVw1
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