802 research outputs found
The Evolution of Cluster Early-Type Galaxies over the Past 8 Gyr
We present the Fundamental Plane (FP) of early-type galaxies in the clusters
of galaxies RXJ1415.1+3612 at z=1.013. This is the first detailed FP
investigation of cluster early-type galaxies at redshift z=1. The distant
cluster galaxies follow a steeper FP relation compared to the local FP. The
change in the slope of the FP can be interpreted as a mass-dependent evolution.
To analyse in more detail the galaxy population in high redshift galaxy
clusters at 0.8<z<1, we combine our sample with a previous detailed
spectroscopic study of 38 early-type galaxies in two distant galaxy clusters,
RXJ0152.7-1357 at z=0.83 and RXJ1226.9+3332 at z=0.89. For all clusters
Gemini/GMOS spectroscopy with high signal-to-noise and intermediate-resolution
has been acquired to measure the internal kinematics and stellar populations of
the galaxies. From HST/ACS imaging, surface brightness profiles, morphologies
and structural parameters were derived for the galaxy sample. The least massive
galaxies (M=2x10^{10}M_{\sun}) in our sample have experienced their most recent
major star formation burst at z_{form}~1.1. For massive galaxies
(M>2x10^{11}M_{\sun}) the bulk of their stellar populations have been formed
earlier z_{form}>~1.6. Our results confirm previous findings by Jorgensen et
al. This suggests that the less massive galaxies in the distant clusters have
much younger stellar populations than their more massive counterparts. One
explanation is that low-mass cluster galaxies have experienced more extended
star formation histories with more frequent bursts of star formation with
shorter duration compared to the formation history of high-mass cluster
galaxies.Comment: 6 pages, 2 figures, Talk for "Matter Cycles of Galaxies in Clusters",
presented at JENAM 2008, Vienna, to be published in Astronomische Nachrichten
in Nov 2009 (proceedings of Symposium 6 of the JENAM 2008, Vienna
Uniqueness Results for Second Order Bellman-Isaacs Equations under Quadratic Growth Assumptions and Applications
In this paper, we prove a comparison result between semicontinuous viscosity
sub and supersolutions growing at most quadratically of second-order degenerate
parabolic Hamilton-Jacobi-Bellman and Isaacs equations. As an application, we
characterize the value function of a finite horizon stochastic control problem
with unbounded controls as the unique viscosity solution of the corresponding
dynamic programming equation
Obscuration in extremely luminous quasars
The spectral energy distributions and infrared (IR) spectra of a sample of
obscured AGNs selected in the mid-IR are modeled with recent clumpy torus
models to investigate the nature of the sources, the properties of the
obscuring matter, and dependencies on luminosity. The sample contains 21
obscured AGNs at z=1.3-3 discovered in the largest Spitzer surveys (SWIRE,
NDWFS, & FLS) by means of their extremely red IR to optical colors. All sources
show the 9.7micron silicate feature in absorption and have extreme mid-IR
luminosities (L(6micron)~10^46 erg/s). The IR SEDs and spectra of 12 sources
are well reproduced with a simple torus model, while the remaining 9 sources
require foreground extinction from a cold dust component to reproduce both the
depth of the silicate feature and the near-IR emission from hot dust. The
best-fit torus models show a broad range of inclinations, with no preference
for the edge-on torus expected in obscured AGNs. Based on the unobscured QSO
mid-IR luminosity function, and on a color-selected sample of obscured and
unobscured IR sources, we estimate the surface densities of obscured and
unobscured QSOs at L(6micron)>10^12 Lsun, and z=1.3-3.0 to be about 17-22
deg^-2, and 11.7 deg^-2, respectively. Overall we find that ~35-41% of luminous
QSOs are unobscured, 37-40% are obscured by the torus, and 23-25% are obscured
by a cold absorber detached from the torus. These fractions constrain the torus
half opening angle to be ~67 deg. This value is significantly larger than found
for FIR selected samples of AGN at lower luminosity (~46 deg), supporting the
receding torus scenario. A far-IR component is observed in 8 objects. The
estimated far-IR luminosities associated with this component all exceed
3.3x10^12 Lsun, implying SFRs of 600-3000 Msun/yr. (Abridged)Comment: ApJ accepte
AGN Dusty Tori: II. Observational Implications of Clumpiness
From extensive radiative transfer calculations we find that clumpy torus
models with \No \about 5--15 dusty clouds along radial equatorial rays
successfully explain AGN infrared observations. The dust has standard Galactic
composition, with individual cloud optical depth \tV \about 30--100 at visual.
The models naturally explain the observed behavior of the 10\mic silicate
feature, in particular the lack of deep absorption features in AGN of any type.
The weak 10\mic emission feature tentatively detected in type 2 QSO can be
reproduced if in these sources \No drops to \about 2 or \tV exceeds \about 100.
The clouds angular distribution must have a soft-edge, e.g., Gaussian profile,
the radial distribution should decrease as or . Compact tori can
explain all observations, in agreement with the recent interferometric evidence
that the ratio of the torus outer to inner radius is perhaps as small as \about
5--10. Clumpy torus models can produce nearly isotropic IR emission together
with highly anisotropic obscuration, as required by observations. In contrast
with strict variants of unification schemes where the viewing-angle uniquely
determines the classification of an AGN into type 1 or 2, clumpiness implies
that it is only a probabilistic effect; a source can display type 1 properties
even from directions close to the equatorial plane. The fraction of obscured
sources depends not only on the torus angular thickness but also on the cloud
number \No. The observed decrease of this fraction at increasing luminosity can
be explained with a decrease of either torus angular thickness or cloud number,
but only the latter option explains also the possible emergence of a 10\mic
emission feature in QSO2.Comment: To appear in ApJ September 20, 200
Interferometric Astrometry of the Low-mass Binary Gl 791.2 (= HU Del) Using Hubble Space Telescope Fine Guidance Sensor 3: Parallax and Component Masses
With fourteen epochs of fringe tracking data spanning 1.7y from Fine Guidance
Sensor 3 we have obtained a parallax (pi_abs=113.1 +- 0.3 mas) and perturbation
orbit for Gl 791.2A. Contemporaneous fringe scanning observations yield only
three clear detections of the secondary on both interferometer axes. They
provide a mean component magnitude difference, Delta V = 3.27 +- 0.10. The
period (P = 1.4731 yr) from the perturbation orbit and the semi-major axis (a =
0.963 +- 0.007 AU) from the measured component separations with our parallax
provide a total system mass M_A + M_B = 0.412 +- 0.009 M_sun. Component masses
are M_A=0.286 +- 0.006 M_sun and M_B = 0.126 +- 0.003 M_sun. Gl 791.2A and B
are placed in a sparsely populated region of the lower main sequence
mass-luminosity relation where they help define the relation because the masses
have been determined to high accuracy, with errors of only 2%.Comment: 19 pages, 5 figures. The paper is to appear in August 2000 A
Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources
We have measured mid-infrared radiation from an orientation-unbiased sample
of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS
instruments on the Spitzer Space Telescope. Powerful emission (L_24micron >
10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the
Spitzer data as well as other measurements from the literature with synchrotron
and dust components. The IRS data provide powerful constraints on the fits. At
15 microns, quasars are typically four times brighter than radio galaxies with
the same isotropic radio power. Based on our fits, half of this difference can
be attributed to the presence of non-thermal emission in the quasars but not
the radio galaxies. The other half is consistent with dust absorption in the
radio galaxies but not the quasars. Fitted optical depths are anti-correlated
with core dominance, from which we infer an equatorial distribution of dust
around the central engine. The median optical depth at 9.7 microns for objects
with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R <
10^-2, it is 1.1. We have thus addressed a long-standing question in the
unification of FR II quasars and galaxies: quasars are more luminous in the
mid-infrared than galaxies because of a combination of Doppler-boosted
synchrotron emission in quasars and extinction in galaxies, both
orientation-dependent effects.Comment: 42 pages, 14 figures plus two landscape tables. Accepted for
publication in Ap
Autonomy Operating System for UAVs: Pilot-in-a-Box
The Autonomy Operating System (AOS) is an open flight software platform with Artificial Intelligence for smart UAVs. It is built to be extendable with new apps, similar to smartphones, to enable an expanding set of missions and capabilities. AOS has as its foundations NASAs core flight executive and core flight software (cFEcFS). Pilot-in-a-Box (PIB) is an expanding collection of interacting AOS apps that provide the knowledge and intelligence onboard a UAV to safely and autonomously fly in the National Air Space, eventually without a remote human ground crew. Longer-term, the goal of PIB is to provide the capability for pilotless air vehicles such as air taxis that will be key for new transportation concepts such as mobility-on-demand. PIB provides the procedural knowledge, situational awareness, and anticipatory planning (thinking ahead of the plane) that comprises pilot competencies. These competencies together with a natural language interface will enable Pilot-in-a-Box to dialogue directly with Air Traffic Management from takeoff through landing. This paper describes the overall AOS architecture, Artificial Intelligence reasoning engines, Pilot-in-a-box competencies, and selected experimental flight tests to date
Properties of dusty tori in active galactic nuclei - II. Type 2 AGN
(abridged) This paper is the second part of a work investigating the
properties of dusty tori in AGN by means of multi-component SED fitting. It
focuses on low luminosity, low redshift (z < 0.25) AGN selected among emission
line galaxies as well as X-ray, radio and mid-infrared selected type 2 AGN
samples from the literature. The available multi-band photometry covers the
spectral range from the u-band up to 160 um. The observed SED of each object is
fit to a set of multi-component models comprising a stellar component, a high
optical depth torus and cold emission from a starburst (SB). The contribution
of the various components (stars, torus, SB) is reflected in the position of
the objects on the IRAC colour diagram. The comparison of type 1 (as derived
from Hatziminaoglou et al. 2008) and type 2 AGN properties is broadly
consistent with the Unified Scheme. The estimated ratio between type 2 and type
1 objects is about 2-2.5:1. The AGN accretion-to-infrared luminosity ratio is
an indicator of the obscuration of the AGN since it scales down with the
covering factor. We find evidence supporting the receding torus paradigm, with
the estimated fraction of obscured AGN decreasing with increasing optical
luminosity over four orders of magnitude. The average star formation rates are
of ~ 10, 40 and 115 Mo/yr for the low-z, type 2 and quasar samples,
respectively; but this might simply reflect observational biases, as our
quasars are one to two orders of magnitude more luminous than the type 2 AGN.
For the majority of objects with 70 and/or 160 um detections an SB component
was needed in order to reproduce the data points, implying that the
far-infrared emission in AGN arises mostly from star formation; moreover, the
SB-to-AGN luminosity ratio shows a slight trend with increasing luminosity.Comment: 20 pages, 23 figures, accepted for publication in MNRAS; full
versions of tables 1-4 and Figs. 5, 14 and 15 only available as online
materia
When who and how matter: explaining the success of referendums in Europe
This article aims to identify the institutional factors that make a referendum successful. This comparative analysis seeks to explain the success of top-down referendums organized in Europe between 2001 and 2013. It argues and tests for the main effect of three institutional factors (popularity of the initiator, size of parliamentary majority, and political cues during referendum campaigns) and controls for the type of referendum and voter turnout. The analysis uses data collected from referendums and electoral databases, public opinion surveys, and newspaper articles. Results show that referendums proposed by a large parliamentary majority or with clear messages from political parties during campaign are likely to be successful
- …