265 research outputs found
An Unbiassed Census of Active Galactic Nuclei in the Two Micron All Sky Survey
(Abridged) We present an unbiassed near-IR selected AGN sample, covering
12.56 square degrees down to K ~ 15.5, selected from the Two Micron All Sky
Survey (2MASS). Our only selection effect is a moderate color cut (J-K>1.2)
designed to reduce contamination from galactic stars. We observed both
point-like and extended sources. Using the brute-force capabilities of the 2dF
multi-fiber spectrograph on the Anglo-Australian Telescope, we obtained spectra
of 65% of the target list: an unbiassed sub-sample of 1526 sources.
80% of the 2MASS sources in our fields are galaxies, with a median redshift
of 0.15. The remainder are K- and M-dwarf stars.
Seyfert-2 Galaxies are roughly three times more common in this sample than in
optically selected galaxy samples (once corrections have been made for the
equivalent width limit and for different aperture sizes).
We find 14 broad-line (Type-1) AGNs, giving a surface density down to K<15
comparable to that of optical samples down to B=18.5. Half of our Type-1 AGNs
could not have been found by normal color selection techniques. In all cases
this was due host galaxy light contamination rather than intrinsically red
colors.
We conclude that the Type-1 AGN population found in the near-IR is not
dramatically different from that found in optical samples. There is no evidence
for a large population of AGNs that could not be found at optical wavelengths,
though we can only place very weak constraints on any population of dusty
high-redshift QSOs.Comment: AJ in pres
Active Control of Solar Array Dynamics During Spacecraft Maneuvers
Recent NASA mission plans require spacecraft to undergo potentially significant maneuvers (or dynamic loading events) with large solar arrays deployed. Therefore there is an increased need to understand and possibly control the nonlinear dynamics in the spacecraft system during such maneuvers. The development of a nonlinear controller is described. The utility of using a nonlinear controller to reduce forces and motion in a solar array wing during a loading event is demonstrated. The result is dramatic reductions in system forces and motion during a 10 second loading event. A motion curve derived from the simulation with the closed loop controller is used to obtain similar benefits with a simpler motion control approach
An Unbiassed Census of Active Galactic Nuclei in the Two Micron All Sky Survey
(Abridged) We present an unbiassed near-IR selected AGN sample, covering
12.56 square degrees down to K ~ 15.5, selected from the Two Micron All Sky
Survey (2MASS). Our only selection effect is a moderate color cut (J-K>1.2)
designed to reduce contamination from galactic stars. We observed both
point-like and extended sources. Using the brute-force capabilities of the 2dF
multi-fiber spectrograph on the Anglo-Australian Telescope, we obtained spectra
of 65% of the target list: an unbiassed sub-sample of 1526 sources.
80% of the 2MASS sources in our fields are galaxies, with a median redshift
of 0.15. The remainder are K- and M-dwarf stars.
Seyfert-2 Galaxies are roughly three times more common in this sample than in
optically selected galaxy samples (once corrections have been made for the
equivalent width limit and for different aperture sizes).
We find 14 broad-line (Type-1) AGNs, giving a surface density down to K<15
comparable to that of optical samples down to B=18.5. Half of our Type-1 AGNs
could not have been found by normal color selection techniques. In all cases
this was due host galaxy light contamination rather than intrinsically red
colors.
We conclude that the Type-1 AGN population found in the near-IR is not
dramatically different from that found in optical samples. There is no evidence
for a large population of AGNs that could not be found at optical wavelengths,
though we can only place very weak constraints on any population of dusty
high-redshift QSOs.Comment: AJ in pres
The Southern 2MASS AGN Survey: spectroscopic follow-up with 6dF
The Two Micron All-Sky Survey (2MASS) has provided a uniform photometric
catalog to search for previously unknown red AGN and QSOs. We have extended the
search to the southern equatorial sky by obtaining spectra for 1182 AGN
candidates using the 6dF multifibre spectrograph on the UK Schmidt Telescope.
These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey.
The candidates were selected using a single color cut of J - Ks > 2 to Ks ~
15.5 and a galactic latitude of |b|>30 deg. 432 spectra were of sufficient
quality to enable a reliable classification. 116 sources (or ~27%) were
securely classified as type 1 AGN, 20 as probable type 1s, and 57 as probable
type 2 AGN. Most of them span the redshift range 0.05<z<0.5 and only 8 (or ~6%)
were previously identified as AGN or QSOs. Our selection leads to a
significantly higher AGN identification rate amongst local galaxies (>20%) than
in any previous galaxy survey. A small fraction of the type 1 AGN could have
their optical colors reddened by optically thin dust with A_V<2 mag relative to
optically selected QSOs. A handful show evidence for excess far-IR emission.
The equivalent width (EW) and color distributions of the type 1 and 2 AGN are
consistent with AGN unified models. In particular, the EW of the [OIII]
emission line weakly correlates with optical--near-IR color in each class of
AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the
optical properties of the 2MASS red AGN are not dramatically different from
those of optically-selected QSOs. Our near-IR selection appears to detect the
most near-IR luminous QSOs in the local universe to z~0.6 and provides
incentive to extend the search to deeper near-IR surveys.Comment: 57 pages, 12 figures, 4 tables, to appear in vol.27/4 of Publications
of the Astronomical Society of Australia (PASA
An HST/WFPC2 Snapshot Survey of 2MASS-Selected Red QSOs
Using simple infrared color selection, 2MASS has found a large number of red,
previously unidentified, radio-quiet QSOs. Although missed by UV/optical
surveys, the 2MASS QSOs have K-band luminosities that are comparable to
"classical" QSOs. This suggests the possible discovery of a previously
predicted large population of dust-obscured radio-quiet QSOs. We present the
results of an imaging survey of 29 2MASS QSOs observed with WFPC2 onboard the
Hubble Space Telescope. I-band images, which benefit from the relative
faintness of the nuclei at optical wavelengths, are used to characterize the
host galaxies, measure the nuclear contribution to the total observed I-band
emission, and to survey the surrounding environments. The 2MASS QSOs are found
to lie in galaxies with a variety of morphologies, luminosities, and dynamical
states, not unlike those hosting radio-quiet PG QSOs. Our analysis suggests
that the extraordinary red colors of the 2MASS QSOs are caused by extinction of
an otherwise typical QSO spectrum due to dust near the nucleus.Comment: 23 pages including 9 figures and 7 tables, accepted for publication
in ApJ, higher resolution HST images at:
http://shapley.as.arizona.edu/~amarble/papers/twomq
Understanding Air Transportation Market Dynamics Using a Search Algorithm for Calibrating Travel Demand and Price
This paper presents a search algorithm based framework to calibrate origin-destination (O-D) market specific airline ticket demands and prices for the Air Transportation System (ATS). This framework is used for calibrating an agent based model of the air ticket buy-sell process - Airline Evolutionary Simulation (Airline EVOS) -that has fidelity of detail that accounts for airline and consumer behaviors and the interdependencies they share between themselves and the NAS. More specificially, this algorithm simultaneous calibrates demand and airfares for each O-D market, to within specified threshold of a pre-specified target value. The proposed algorithm is illustrated with market data targets provided by the Transportation System Analysis Model (TSAM) and Airline Origin and Destination Survey (DB1B). Although we specify these models and datasources for this calibration exercise, the methods described in this paper are applicable to calibrating any low-level model of the ATS to some other demand forecast model-based data. We argue that using a calibration algorithm such as the one we present here to synchronize ATS models with specialized forecast demand models, is a powerful tool for establishing credible baseline conditions in experiments analyzing the effects of proposed policy changes to the ATS
An Integrated Framework for Modeling Air Carrier Behavior, Policy, and Impacts in the U.S. Air Transportation System
The implementation of the Next Generation Air Transportation System (NextGen) in the United States is an ongoing challenge for policymakers due to the complexity of the air transportation system (ATS) with its broad array of stakeholders and dynamic interdependencies between them. The successful implementation of NextGen has a hard dependency on the active participation of U.S. commercial airlines. To assist policymakers in identifying potential policy designs that facilitate the implementation of NextGen, the National Aeronautics and Space Administration (NASA) and LMI developed a research framework called the Air Transportation System Evolutionary Simulation (ATS-EVOS). This framework integrates large empirical data sets with multiple specialized models to simulate the evolution of the airline response to potential future policies and explore consequential impacts on ATS performance and market dynamics. In the ATS-EVOS configuration presented here, we leverage the Transportation Systems Analysis Model (TSAM), the Airline Evolutionary Simulation (AIRLINE-EVOS), the Airspace Concept Evaluation System (ACES), and the Aviation Environmental Design Tool (AEDT), all of which enable this research to comprehensively represent the complex facets of the ATS and its participants. We validated this baseline configuration of ATS-EVOS against Airline Origin and Destination Survey (DB1B) data and subject matter expert opinion, and we verified the ATS-EVOS framework and agent behavior logic through scenario-based experiments that explored potential implementations of a carbon tax, congestion pricing policy, and the dynamics for equipage of new technology by airlines. These experiments demonstrated ATS-EVOS's capabilities in responding to a wide range of potential NextGen-related policies and utility for decision makers to gain insights for effective policy design
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