470 research outputs found
Black Hole Masses in Three Seyfert Galaxies
We analyze published reverberation mapping data for three Seyfert galaxies
(NGC 3227, NGC 3516, and NGC 4593) to refine the mass estimate for the
supermassive black hole in the center of each object. Treatment of the data in
a manner more consistent with other large compilations of such masses allows us
to more securely compare our results to wider samples of data, e.g., in the
investigation of the M_bh-sigma relationship for active and quiescent galaxies.Comment: 14 pages, 4 figures. Accepted for publication in Ap
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
Hydrography and circulation west of Sardinia in June 2014
In the frame of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD (conductivity, temperature, depth) instruments, towed devices, and vessel-mounted ADCPs (acoustic doppler current profilers), are presented and compared with previous knowledge. So far, the circulation is not well-known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72<σΘ/(kg m−3) < 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15′ E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s−1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transports of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition
Nitrogen and Phosphorus Uptake in Pearl Millet and Its Relation to Nutrient and Transpiration Efficiency
Depending on soil and rainfall characteristics, pearl millet [Penniseturn glaucum (L.) R. Br.] production in the Sahel can be limited by inefficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared the efficiency with which N, P, and water are used for growth under varied soil P and water availability. Millet was grown outdoors in semiarid West Texas using rain-sheltered pots of low pH, P-deficient sandy soil. Treatments consisted of four P levels (0–56 g−2) and two water treatments (stressed and not). Plant P concentration decreased strongly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and increased with water stress, but decreased with added P. Because of the effects of age, water availability, and P level on organ nutrient concentration, P-use efficiency (PUE) increased with age, decreased with water stress, and decreased with added P. Nitrogen-use efficiency (NUE) also increased with age and decreased with water stress, but tended to increase with added P. Shoot transpiration efficiency (WUFT) increased with water stress and added P, and so varied inversely with PUE throughout the growth cycle. Phosphate root uptake efficiency (PRE) was less sensitive than PUE to age, P availability, and water stress, because of the compensating effect of root growth; PRE was also positively correlated with WUET and yield. For crop improvement programs interested in increasing both P- and water-use efficiency, PRE is probably a better selection index than PUE
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
Five new real-time detections of Fast Radio Bursts with UTMOST
We detail a new fast radio burst (FRB) survey with the Molonglo Radio
Telescope, in which six FRBs were detected between June 2017 and December 2018.
By using a real-time FRB detection system, we captured raw voltages for five of
the six events, which allowed for coherent dedispersion and very high time
resolution (10.24 s) studies of the bursts. Five of the FRBs show temporal
broadening consistent with interstellar and/or intergalactic scattering, with
scattering timescales ranging from 0.16 to 29.1 ms. One burst, FRB181017, shows
remarkable temporal structure, with 3 peaks each separated by 1 ms. We searched
for phase-coherence between the leading and trailing peaks and found none,
ruling out lensing scenarios. Based on this survey, we calculate an all-sky
rate at 843 MHz of events sky day to a fluence
limit of 8 Jy-ms: a factor of 7 below the rates estimated from the Parkes and
ASKAP telescopes at 1.4 GHz assuming the ASKAP-derived spectral index
(). Our results suggest that FRB
spectra may turn over below 1 GHz. Optical, radio and X-ray followup has been
made for most of the reported bursts, with no associated transients found. No
repeat bursts were found in the survey.Comment: 13 pages, 11 figures, submitted to MNRA
Pearl millet growth as affected by phosphorus and water
In outdoor pot trials near Nacogdoches, Texas in 1988, pearl millet was given 0, 1.15, 3.38 or 7.77 g P/m² with or without water stress conditions. Whole plant DM at final harvest, 84 d after emergence (DAE) increased from about 145 g/pot without P to 626 g with 7.77 g P without water stress and from 64 g without P to 220 g with 7.77 g P with water stress. There was a highly significant water treatment × P rate interaction in terms of plant DM at harvests 28-84 DAE. Grain DM at 84 DAE increased with increasing P rate but was negligible without P without water stress and with <3.38 g P under water stress conditions. Maximum whole plant production rates occurred between 42 and 58 DAE without water stress, increased from 5.0 g/d without P to 18.5 g with 7.77 g P, and between 28 and 42 DAE in water stressed plants, increasing from 1.3 g without P to 8.5 g with 7.77 g P. Growth rates of panicles and grain increased with increasing P rate and were greater without than with water stress. There were no clear effects of P rate or water stress on NAR or RGR
Highly Ionized Collimated Outflow from HE 0238 - 1904
We present a detailed analysis of a highly ionized, multiphased and
collimated outflowing gas detected through O V, O VI, Ne VIII and Mg X
absorption associated with the QSO HE 0238 - 1904 (z_em ~ 0.629). Based on the
similarities in the absorption line profiles and estimated covering fractions,
we find that the O VI and Ne VIII absorption trace the same phase of the
absorbing gas. Simple photoionization models can reproduce the observed N(Ne
VIII), N(O VI) and N(Mg X) from a single phase whereas the low ionization
species (e.g. N III, N IV, O IV) originate from a different phase. The measured
N(Ne VIII)/N(O VI) ratio is found to be remarkably similar (within a factor of
~ 2) in several individual absorption components kinematically spread over ~
1800 km/s. Under photoionization this requires a fine tuning between hydrogen
density (nH) and the distance of the absorbing gas from the QSO. Alternatively
this can also be explained by collisional ionization in hot gas with T >
10^{5.7} K. Long-term stability favors the absorbing gas being located outside
the broad line region (BLR). We speculate that the collimated flow of such a
hot gas could possibly be triggered by the radio jet interaction.Comment: Minor revision (accepted for publication in MNRAS letter
The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
We have obtained high resolution images of the central regions of 14
reverberation-mapped active galactic nuclei (AGN) using the Hubble Space
Telescope Advanced Camera for Surveys High Resolution Camera to account for
host-galaxy starlight contamination of measured AGN luminosities. We measure
the host-galaxy starlight contribution to the continuum luminosity at 5100 A
through the typical ground-based slit position and geometry used in the
reverberation-mapping campaigns. We find that removing the starlight
contribution results in a significant correction to the luminosity of each AGN,
both for lower luminosity sources, as expected, but also for the higher
luminosity sources such as the PG quasars. After accounting for the host galaxy
starlight, we revisit the well-known broad-line region radius--luminosity
relationship for nearby AGN. We find the power-law slope of the relationship
for the H beta line to be 0.518 +/- 0.039, shallower than previously reported
and consistent with the slope of 0.5 expected from the naive theoretical
assumption that all AGN have, on average, the same ionizing spectrum and the
same ionization parameter and gas density in the H beta line-emitting region.Comment: 27 pages, 5 tables, 4 figures, accepted to ApJ; full resolution
figures available at
http://www.astronomy.ohio-state.edu/~bentz/astroph0602412.htm
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