5,119 research outputs found
Skywalking GEMS and UDF
The two large colour mosaics of the GEMS and UDF projects, both obtained with
the Hubble Space Telescope and ACS, consist of large amounts of data. We
present two web application pages (the GEMS and UDF "Skywalker") that allow to
pan around in these mosaics with downloading only small parts at a time.Comment: 1 pag
Seeing the sky through Hubble's eye: The COSMOS SkyWalker
Large, high-resolution space-based imaging surveys produce a volume of data
that is difficult to present to the public in a comprehensible way. While
megapixel-sized images can still be printed out or downloaded via the World
Wide Web, this is no longer feasible for images with 10^9 pixels (e.g., the
Hubble Space Telescope Advanced Camera for Surveys [ACS] images of the Galaxy
Evolution from Morphology and SEDs [GEMS] project) or even 10^10 pixels (for
the ACS Cosmic Evolution Survey [COSMOS]). We present a Web-based utility
called the COSMOS SkyWalker that allows viewing of the huge ACS image data set,
even through slow Internet connections. Using standard HTML and JavaScript, the
application successively loads only those portions of the image at a time that
are currently being viewed on the screen. The user can move within the image by
using the mouse or interacting with an overview image. Using an astrometrically
registered image for the COSMOS SkyWalker allows the display of calibrated
world coordinates for use in science. The SkyWalker "technique" can be applied
to other data sets. This requires some customization, notably the slicing up of
a data set into small (e.g., 256^2 pixel) subimages. An advantage of the
SkyWalker is the use of standard Web browser components; thus, it requires no
installation of any software and can therefore be viewed by anyone across many
operating systems.Comment: 4 pages, 2 figures, accepted for publication in PAS
The properties of the extended warm ionised gas around low-redshift QSOs and the lack of extended high-velocity outflows
(Abridged) We present a detailed analysis of a large sample of 31
low-redshift, mostly radio-quiet type 1 QSOs observed with integral field
spectroscopy to study their extended emission-line regions (EELRs). We focus on
the ionisation state of the gas, size and luminosity of extended narrow line
regions (ENLRs), which corresponds to those parts of the EELR dominated by
ionisation from the QSO, as well as the kinematics of the ionised gas. We
detect EELRs around 19 of our 31 QSOs (61%) after deblending the unresolved QSO
emission and the extended host galaxy light in the integral field data. We
identify 13 EELRs to be entirely ionised by the QSO radiation, 3 EELRs are
composed of HII regions and 3 EELRs display signatures of both ionisation
mechanisms at different locations. The typical size of the ENLR is 10kpc at a
median nuclear [OIII] luminosity of log(L([OIII])/[erg/s])=42.7+-0.15. We show
that the ENLR sizes are least a factor of 2 larger than determined with HST,
but are consistent with those of recently reported type 2 QSOs at matching
[OIII] luminosities. The ENLR of type 1 and type 2 QSOs appear to follow the
same size-luminosity relation. Furthermore, we show for the first time that the
ENLR size is much better correlated with the QSO continuum luminosity than with
the total/nuclear [OIII] luminosity. We show that ENLR luminosity and radio
luminosity are correlated, and argue that radio jets even in radio-quiet QSOs
are important for shaping the properties of the ENLR. Strikingly, the
kinematics of the ionised gas is quiescent and likely gravitationally driven in
the majority of cases and we find only 3 objects with radial gas velocities
exceeding 400km/s in specific regions of the EELR that can be associate with
radio jets. In general, these are significantly lower outflow velocities and
detection rates compared to starburst galaxies or radio-loud QSOs.Comment: 34 page, 22 figures (slightly degraded in resolution), 10 tables,
accepted for publication in A&A, minor corrections to match with the
publisher versio
The low-metallicity QSO HE 2158-0107: A massive galaxy growing by the accretion of nearly pristine gas from its environment?
[abridged] The metallicities of AGN are usually well above solar in their
NLR, often reaching up to several times solar in their broad-line regions.
Low-metallicity AGN are rare objects which have so far always been associated
with low-mass galaxies hosting low-mass BHs (M_BH<10^6Msun). In this paper we
present IFS data of the low-redshift QSO HE 2158-0107 for which we find strong
evidence for sub-solar NLR metallicities associated with a massive BH
(M_BH~3x10^8Msun). The QSO is surrounded by a large extended emission-line
region reaching out to 30kpc from the QSO in a tail-like geometry. We present
optical and near-IR images and investigate the properties of the host galaxy.
The SED of the host is rather blue, indicative of a significant young age
stellar population formed within the last 1Gyr. A 3sigma upper limit of
L_bulge<4.5x10^10Lsun for the H band luminosity and a corresponding stellar
mass upper limit of M_bulge<3.4x10^10Msun show that the host is offset from the
local BH-bulge relations. This is independently supported by the kinematics of
the gas. Although the stellar mass of the host galaxy is lower than expected,
it cannot explain the exceptionally low metallicity of the gas. We suggest that
the extended emission-line region and the galaxy growth are caused by the
infall of nearly pristine gas from the environment of the QSO host. Minor
mergers of dwarf galaxies or the theoretically predicted smooth accretion of
cold gas are both potential drivers behind that process. Since the metallicity
of the gas in the NLR is much lower than expected, we suspect that the external
gas has already reached the galaxy centre and may even contribute to the
current feeding of the BH. HE 2158-0107 appears to represent a particular phase
of substantial BH and galaxy growth that can be observationally linked with the
accretion of external material from its environment.Comment: 14 pages, 12 figures, accepted for publication in A&
Ultrafast pump-probe dynamics in ZnSe-based semiconductor quantum-wells
Pump-probe experiments are used as a controllable way to investigate the
properties of photoexcited semiconductors, in particular, the absorption
saturation. We present an experiment-theory comparison for ZnSe quantum wells,
investigating the energy renormalization and bleaching of the excitonic
resonances. Experiments were performed with spin-selective excitation and
above-bandgap pumping. The model, based on the semiconductor Bloch equations in
the screened Hartree-Fock approximation, takes various scattering processes
into account phenomenologically. Comparing numerical results with available
experimental data, we explain the experimental results and find that the
electron spin-flip occurs on a time scale of 30 ps.Comment: 10 pages, 9 figures. Key words: nonlinear and ultrafast optics,
modeling of femtosecond pump-probe experiments, electron spin-flip tim
Collective behavior of heterogeneous neural networks
We investigate a network of integrate-and-fire neurons characterized by a
distribution of spiking frequencies. Upon increasing the coupling strength, the
model exhibits a transition from an asynchronous regime to a nontrivial
collective behavior. At variance with the Kuramoto model, (i) the macroscopic
dynamics is irregular even in the thermodynamic limit, and (ii) the microscopic
(single-neuron) evolution is linearly stable.Comment: 4 pages, 5 figure
Optical properties of self-organized wurtzite InN/GaN quantum dots: A combined atomistic tight-binding and full configuration interaction calculation
In this work we investigate the electronic and optical properties of
self-assembled InN/GaN quantum dots. The one-particle states of the
low-dimensional heterostructures are provided by a tight-binding model that
fully includes the wurtzite crystal structure on an atomistic level. Optical
dipole and Coulomb matrix elements are calculated from these one-particle wave
functions and serve as an input for full configuration interaction
calculations. We present multi-exciton emission spectra and discuss in detail
how Coulomb correlations and oscillator strengths are changed by the
piezoelectric fields present in the structure. Vanishing exciton and biexciton
ground state emission for small lens-shaped dots is predicted.Comment: 3 pages, 2 figure
How pedophilic men think about adult-child sex: effects of child gender and physical maturity
To date, very little research has tackled whether pedophilic men''s attitude towards adult-child sex depends on characteristics of the adult or the child involved in such acts. This study examines the effect of the child''s gender (male vs. female) and physical maturity (pre-pubescent vs. early pubescent) on the moral evaluation of apparently noncoercive adult-child sex in a 2 x 2 factorial online vignette experiment. One hundred eighty-three English-speaking pedophilic men rated their agreement with moral arguments on the Immoral Sex Scale, as well as whether they believed this behavior to be typical for a child. The results revealed considerable inter-individual differences, with about one third showing restrictive moral attitudes. Contrary to our expectations, gender and physical maturity neither affected the perceived morality of the sexual act, nor beliefs about the representativeness of the child''s behavior. However, when controlling for confounds, pedophilic men believed that boys were more likely to willingly engage in adult-child sex. Furthermore, participants with stronger liberal attitudes were found to be more likely to defend the sexual act, as were participants with a preferential interest in pre-pubescents. There was no link between attitudes towards adult-child sex and sexual offending, replicating the non-associations reported in previous community surveys
Gravitational lens candidates in the E-CDFS
We report ten lens candidates in the E-CDFS from the GEMS survey. Nine of the
systems are new detections and only one of the candidates is a known lens
system. For the most promising five systems including the known lens system, we
present results from preliminary lens mass modelling, which tests if the
candidates are plausible lens systems. Photometric redshifts of the candidate
lens galaxies are obtained from the COMBO-17 galaxy catalog. Stellar masses of
the candidate lens galaxies within the Einstein radius are obtained by using
the -band luminosity and the color-based stellar mass-to-light ratios.
As expected, the lensing masses are found to be larger than the stellar masses
of the candidate lens galaxies. These candidates have similar dark matter
fractions as compared to lenses in SLACS and COSMOS. They also roughly follow
the halo mass-stellar mass relation predicted by the subhalo abundance matching
technique. One of the candidate lens galaxies qualifies as a LIRG and may not
be a true lens because the arc-like feature in the system is likely to be an
active region of star formation in the candidate lens galaxy. Amongst the five
best candidates, one is a confirmed lens system, one is a likely lens system,
two are less likely to be lenses and the status of one of the candidates is
ambiguous. Spectroscopic follow-up of these systems is still required to
confirm lensing and/or for more accurate determination of the lens masses and
mass density profiles.Comment: 12 pages, 5 figures, 3 tables, ApJ accepte
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