3,303 research outputs found
The confluence of Gaussian process emulation and wavelets
We discuss two thriving research areas, emulation (in the statistical sense) and wavelet analysis, and explore ways in which the two areas can complement each other to tackle problems that both areas face. The Gaussian process, which is the popular choice in emulation, is used due to its ability to be a surrogate for a function when we are only able to make a limited number of observations from the function. The Gaussian process, however, does not perform well when the underlying function contains a discontinuity. Wavelet analysis, on the other hand, is known for its ability to model and analyse functions that contain discontinuities. Wavelet analysis tends to require a large number of datapoints to be able to model functions accurately, tending to struggle when the amount of data is limited.
As it appears that one area’s strength is the other area’s weakness, this thesis is aimed at exploring the possible overlaps between the two methods, and the ways in which they could benefit each other. Particular attention in the thesis is paid to the challenges that are faced when the function that we are attempting to model contains discontinuities, or, areas of space in which there is a sharp increase/decrease in the value of our observations. We develop methods to select the location of additional design points after we have observed the function at our original design points with the objective of better defining the location of the discontinuity. We also develop novel methods to model the unknown function that we believe contains discontinuities, and look to accurately find our uncertainty in this function
Starburst or AGN Dominance in Submillimetre-Luminous Candidate AGN?
It is widely believed that ultraluminous infrared (IR) galaxies and active
galactic nuclei (AGN) activity are triggered by galaxy interactions and
merging, with the peak of activity occurring at z~2, where submillimetre
galaxies are thousands of times more numerous than local ULIRGs. In this
evolutionary picture, submillimetre galaxies (SMGs) would host an AGN, which
would eventually grow a black hole (BH) strong enough to blow off all of the
gas and dust leaving an optically luminous QSO. To probe this evolutionary
sequence we have focussed on the 'missing link' sources, which demonstrate both
strong starburst (SB) and AGN signatures, in order to determine if the SB is
the main power source even in SMGs when we have evidence that an AGN is present
from their IRAC colours. The best way to determine if a dominant AGN is present
is to look for their signatures in the mid-infrared with the Spitzer IRS, since
often even deep X-ray observations miss identifying the presence of AGN in
heavily dust-obscured SMGs. We present the results of our audit of the energy
balance between star-formation and AGN within this special sub-population of
SMGs -- where the BH has grown appreciably to begin heating the dust emission.Comment: 2 pages, 1 figure. To appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and
C.C. Popescu, AIP Conf. Ser., in pres
The works of Alexander Pope Esq. containing his miscellaneous pieces in verse and prose
Signatura : B-O¹²Procedencia: Biblioteca del Real Colegio de Cirugía de la Armada de Cádiz, 1748-183
California Property Tax Exemptions, Exclusions, Immunities, and Restrictions on Fair Market Valuation--Or, Whatever Became of Full Value Assessment?
The Clustering of AGN in the Sloan Digital Sky Survey
We present the two--point correlation function (2PCF) of narrow-line active
galactic nuclei (AGN) selected within the First Data Release of the Sloan
Digital Sky Survey. Using a sample of 13605 AGN in the redshift range 0.055 < z
< 0.2, we find that the AGN auto--correlation function is consistent with the
observed galaxy auto--correlation function on scales 0.2h^{-1}Mpc to
>100h^{-1}Mpc. The AGN hosts trace an intermediate population of galaxies and
are not detected in either the bluest (youngest) disk--dominated galaxies or
many of the reddest (oldest) galaxies. We show that the AGN 2PCF is dependent
on the luminosity of the narrow [OIII] emission line (L_{[OIII]}), with low
L_{[OIII]} AGN having a higher clustering amplitude than high L_{[OIII]} AGN.
This is consistent with lower activity AGN residing in more massive galaxies
than higher activity AGN, and L_{[OIII]} providing a good indicator of the
fueling rate. Using a model relating halo mass to black hole mass in
cosmological simulations, we show that AGN hosted by ~ 10^{12} M_{odot} dark
matter halos have a 2PCF that matches that of the observed sample. This mass
scale implies a mean black hole mass for the sample of M_{BH} ~ 10^8 M_{odot}.Comment: 5 pages, 4 figures. Accepted for publication in ApJ
On the X-ray properties of submm-selected galaxies
We present an analysis of the X-ray properties of 35 submm galaxies(SMGs) in
the CDF-N. Using a sample of robust 850micron-selected galaxies, with accurate
positions from Spitzer and/or radio counterparts, we find 16 objects (45+/-8%)
with significant X-ray detections in the 2Ms Chandra data. 6 of these SMGs
(~17+/-6%) have measured X-ray luminosities or upper limits consistent with
those expected based on the far-infrared (FIR) or radio-derived star formation
rate (SFR), and hence with the X-rays coming solely from star formation. In
another 7 sources (20+/-7%) a dominant AGN contribution to the X-ray emission
is required, while in 3 more it is unclear whether stellar process or accretion
are responsible. Stacking of the X-ray undetected SMGs reveals a highly
significant detection. If due to star formation, this corresponds to an average
X-ray derived SFR of ~150 Msun/yr. We deduce that the AGN fraction in SMGs
based on X-ray observations is 20-29 (+/-7) %, which is towards the lower limit
of previous estimates. Spectral analysis shows that in general the SMGs are not
heavily obscured in the X-ray but most of the SMGs classfied as AGN show
absorption with N_H in excess of 10^22 cm^-2. Of the secure AGN, the bolometric
luminosity appears to be dominated by the AGN in only 3 cases. In ~85% of the
SMGs, the X-ray spectrum effectively rules out an AGN contribution that
dominates the bolometric emission, even if the AGN is Compton thick. The
evidence therefore suggests that intense star formation accounts for both the
FIR and X-ray emission in most SMGs. We argue that, rather than having an
especially high AGN fraction or duty cycle, SMGs have a high X-ray detection
rate at very faint fluxes partly because of their high star formation rates
and, in rarer cases, because the submm emission is from an AGN.(abridged)Comment: 12 pages, 5 figures, accepted for publication in MNRA
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