528 research outputs found
The Optical and Radio Properties of a Low-Redshift Sample of Broad-lined Active Galactic Nuclei
The question as to whether the distribution of radio loudness in active galactic nuclei (AGN) is actually bimodal has been discussed extensively in the literature. Furthermore, there have been claims that radio loudness depends on black hole mass and Eddington ratio. We investigate these claims using the low redshift broad line AGN sample of Greene & Ho 2007, which consists of 8434 objects at z \u3c 0.35 from the Sloan Digital Sky Survey (SDSS) Fourth Data Release. We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGN, 846 have radio emission within 4 of the optical counterpart and are considered to be core emission. We also perform a systematic search for extended emission in FIRST that can be positively associated with the optical counterparts and find 51 out of the 846 previously detected core sources have extended emission that must be taken into account when calculating the total radio luminosity. Further, we find an additional 12 objects that have extended radio emission but no detectable radio core and have classic FR II type morphologies. Using these data, the question of radio bimodality and the dependence of radio-loudness on physical parameters are investigated for different subsets of the total sample. We find modest trends in the radio-loud fraction as a function of black hole mass and Eddington ratio, where the fraction of RL AGN increases for the largest black hole mass group and decreases with increasing Eddington ratio. With extended emission taken into account, we find strong evidence for a bimodal distribution in radio-loudness, where the lower radio luminosity core-only sources appear as a population separate from the extended sources with a dividing line at log(R) = 1.75. This dividing line is interesting in that it requires the radio luminosity to be 50 times the optical luminosity, ensuring that these are indeed the most RL AGN, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio quiet AGN in this sample
Radio Properties of Low Redshift Broad Line Active Galactic Nuclei Including Extended Radio Sources
We present a study of the extended radio emission in a sample of 8434 low
redshift (z < 0.35) broad line active galactic nuclei (AGN) from the Sloan
Digital Sky Survey (SDSS). To calculate the jet and lobe contributions to the
total radio luminosity, we have taken the 846 radio core sources detected in
our previous study of this sample and performed a systematic search in the
Faint Images of the Radio Sky at Twenty-centimeters (FIRST) database for
extended radio emission that is likely associated with the optical
counterparts. We found 51 out of 846 radio core sources have extended emission
(> 4" from the optical AGN) that is positively associated with the AGN, and we
have identified an additional 12 AGN with extended radio emission but no
detectable radio core emission. Among these 63 AGN, we found 6 giant radio
galaxies (GRGs), with projected emission exceeding 750 kpc in length, and
several other AGN with unusual radio morphologies also seen in higher redshift
surveys. The optical spectra of many of the extended sources are similar to
that of typical broad line radio galaxy spectra, having broad H
emission lines with boxy profiles and large M_BH. With extended emission taken
into account, we find strong evidence for a bimodal distribution in the
radio-loudness parameter R, where the lower radio luminosity core-only sources
appear as a population separate from the extended sources, with a dividing line
at log(R) . This dividing line ensures that these are indeed the
most radio-loud AGN, which may have different or extreme physical conditions in
their central engines when compared to the more numerous radio quiet AGN.Comment: 25 pages, 6 figures, accepted to A
The development of structural adhesive systems suitable for use with liquid oxygen Annual summary report, 1 Jul. 1964 - 30 Jun. 1965
Preparation and testing of adhesive polyurethanes, polycarbonates, and other highy halogenated polymers for liquid oxygen compatibilit
Broad Band Photometric Reverberation Mapping of NGC 4395
We present results of broad band photometric reverberation mapping (RM) to
measure the radius of the broad line region, and subsequently the black hole
mass (M), in the nearby, low luminosity active galactic nuclei (AGN)
NGC 4395. Using the Wise Observatory's 1m telescope equipped with the SDSS
g, r and i broad band filters, we monitored NGC 4395 for 9 consecutive
nights and obtained 3 light curves each with over 250 data points. The g and
r bands include time variable contributions from H and H
(respectively) plus continuum. The i band is free of broad lines and covers
exclusively continuum. We show that by looking for a peak in the difference
between the cross-correlation and the auto-correlation functions for all
combinations of filters, we can get a reliable estimate of the time lag
necessary to compute M. We measure the time lag for H to be
hours, comparable to previous studies using the line resolved
spectroscopic RM method. We argue that this lag implies a black hole mass of
M \Msun
Recent increases in water column denitrification in the seasonally suboxic bottom waters of the Santa Barbara Basin
Author Posting. Ā© American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(12), (2019): 6786-6795, doi:10.1029/2019GL082075.Denitrification in the anoxic sediments of the Santa Barbara Basin has been well documented in the historic and modern record, but the regulation of and frequency with which denitrification occurs in the overlying water column are less understood. Since 2004, the magnitude and speciation of redox active nitrogen species in bottom waters have changed markedly. Most notable are periods of decreased nitrate and increased nitrite concentrations. Here we examine these changes in nitrogen cycling as recorded by the stable isotopes of dissolved nitrate from 2010ā2016. When compared to previous studies, our data identify an increase in water column denitrification in the bottom waters of the basin. Observations from inside the basin as well as data from the wider California Current Ecosystem implicate a longāterm trend of decreasing oxygen concentrations as the driver for these observed changes, with ramifications for local benthic communities and regional nitrogen loss.We thank CalCOFI and Shonna Dovel for sample collection and two anonymous reviewers for improving the manuscript. Thanks also to Daniel Sigman for useful discussions, and Zoe Sandwith and Jen Karolewski for help with sample analysis. Data sets presented here were supported in part by CCEāLTER augmented funding (NSF grant OCEā1026607). Additional funding came from the Edna Bailey Sussman Foundation and the San Diego Foundation Blasker Environment grant. All data can be accessed at http://calcofi.org and https://oceaninformatics.ucsd.edu/datazoo/catalogs/ccelter/datasets. SDW acknowledges the support of a fellowship through the HanseāWissenschaftskolleg (Institute for Advanced Studies).2019-12-1
Radio Properties of Low Redshift Broad Line Active Galactic Nuclei
The question as to whether the distribution of radio-loudness in active
galactic nuclei (AGN) is actually bimodal has been discussed extensively in the
literature. Futhermore, there have been claims that radio-loudness depends on
black hole mass and Eddington ratio. We investigate these claims using the low
redshift broad line AGN sample of Greene & Ho (2007), which consists of 8434
objects at z < 0.35 from the Sloan Digital Sky Survey Fourth Data Release (SDSS
DR4). We obtained radio fluxes from the Very Large Array Faint Images of the
Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the
8434 SDSS AGN, 821 have corresponding observed radio fluxes in the FIRST
survey. We calculated the radio-loudness parameter (R) for all objects above
the FIRST detection limit (1 mJy), and an upper limit to R for the undetected
objects. Using these data, the question of radio bimodality is investigated for
different subsets of the total sample. We find no clear demarcation between the
radio-loud (RL, R > 10) and radio-quiet (RQ, R < 10) objects, but instead fill
in a more radio-intermediate population in a continuous fashion for all
subsamples. We find that 4.7% of the AGN in the flux-limited subsample are RL
based on core radio emission alone. We calculate the radio-loud fraction (RLF)
as both a function of black hole mass and Eddington ratio. The RLF decreases
(from 13% to 2%) as Eddington ratio increases over 2.5 order of magnitude. The
RLF is nearly constant (~5%) over 4 decades in black hole mass, except for an
increase at masses greater than 10^8 solar masses. We find for the FIRST
detected subsample that 367 of the RL AGN have black hole masses less than 10^8
solar masses, a large enough number to indicate that RL AGN are not a product
of only the most massive black holes in the local universe.Comment: 28 pages, 14 figures, accepted to A
1995 General Correspondence Related to Proposals, DWC Awards Nominations, and other Memorandums.
Primarily correspondence between DWC chairs and members of the Executive Board, Committees and Task Force
Advancing Evaluation Practices in Philanthropy
In recent years, the philanthropic sector has neared consensus on the need to improve measurement and evaluation of its work. Although the philanthropies they lead use different methods, members of the Aspen Philanthropy Group (APG) have agreed that basic principles and practices can inform efforts to monitor performance, track progress, and assess the impact of foundation strategies, initiatives, and grants. They hope to build a culture of learning in the process
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