907 research outputs found
A Lyman-alpha blob in the GOODS South field: evidence for cold accretion onto a dark matter halo
We report on the discovery of a z = 3.16 Lyman-alpha emitting blob in the
GOODS South field. The blob has a total Ly-alpha luminosity of ~ 10^(43) erg
s^(-1) and a diameter larger than 60 kpc. The available multi-wavelength data
in the GOODS field consists of 13 bands from X-rays (Chandra) to infrared
(Spitzer). Unlike other discovered Ly-alpha blobs, this blob shows no obvious
continuum counter-part in any of the broad-bands. In particular, no optical
counter-parts are found in the deep HST/ACS imaging available. For previously
published blobs, AGN (Active Galactic Nuclei) or 'superwind' models have been
found to provide the best match with the data. We here argue that the most
probable origin of the extended Ly-alpha emission from the blob in the GOODS
South field is cold accretion onto a dark matter halo.Comment: 4 pages, 2 tables, 2 figures, Accepted to A&A Letters, minor changes
to tex
X-ray variability patterns in blazars
We study the expected variability patterns of blazars within the two-zone
acceleration model putting special emphasis on flare shapes and spectral lags.
We solve semi-analytically the kinetic equations which describe the particle
evolution in the acceleration and radiation zone. We then perturb the solutions
by introducing Lorentzian variations in its key parameters and examine the
flaring behavior of the system. We apply the above to the X-ray observations of
blazar 1ES 1218+304 which exhibited a hard lag behavior during a flaring
episode and discuss possibilities of producing it within the context of our
model. The steady-state radio to X-rays emission of 1ES 1218+304 can be
reproduced with parameters which lie well within the ones generally accepted
from blazar modeling. Additionally, we find that the best way to explain its
flaring behavior is by varying the rate of particles injected in the
acceleration zone.Comment: accepted by A&
Extended Lyman alpha emission around bright quasars
Quasars trace the most massive structures at high redshifts and their
presence may influence the evolution of the massive host galaxies. We study the
extended Lyman alpha emission line regions (EELRs) around seven bright, mostly
radio-quiet quasars (QSOs) at 2.7<z<4.5, and compare luminosities with EELRs
around radio-loud QSOs reported in the literature. Using integral field
spectroscopy, we analyse the morphology and kinematics of the quiescent Lya
EELRs around the QSOs. We find evidence for the presence of EELRs around four
radio-quiet and one radio-loud QSO. All EELRs appear asymmetric and the
optically brightest QSOs also have the brightest Lya nebulae. For the two
brightest nebulae we find velocities between ~600 km s^-1 at the QSO position
to ~200 km s^-1 at a distance of 3-4 arcsec from the QSO and surface flux
densities up to 2-3*10^{-16} erg cm^-2 s^-1 arcsec^-2. The five EELRs have
total Lya luminosities which correspond to ~0.5% of the luminosities from the
QSOs broad Lya emission lines. This fraction is an order of magnitude smaller
than found for EELRs around radio-loud, steep spectrum QSOs reported in the
literature. While the nebulae luminosities are correlated with the QSO Lya
luminosities, we find that nebulae luminosities are not correlated with the
central QSO ionising fluxes. The presence of gas in the EELRs can be
interpreted based on two competing scenarios: either from quasar feedback
mechanisms, or from infalling matter. Apart from these two effects, the Lya
flux around radio-loud objects can be enhanced due to interactions with the
radio jets. The relatively fainter nebulae around radio-quiet QSOs compared to
lobe-dominated radio-loud QSOs can be ascribed to this effect, or to
significant differences in the environments between the two classes.Comment: 15 pages, A&A accepted. Section 4 revise
Muoniated radical states in the organic semiconductor phthalocyanine
Phthalocyanine samples of ZnPc, H2Pc and CuPc were investigated by the muon spin rotation amp; 956;SR technique. In ZnPc and H2Pc, three muoniated radical states of paramagnetic origin were identified, two of which having hyperfine interactions in the range 110 150 MHz and correspondign to muonium addition at the outer benzene rings. The third state presents a smaller hyperfine interaction about 25 MHz , and is tentatively assigned to addition at bridging nitrogen atoms. CuPc has an unpaired electron from the Cu atom, which originates a diamagnetic like signal upon muonium addition. The signal exhibits two components with very different relaxation rates, corresponding to two different spatial couplings of the Cu electron with the muonium s electro
Deer reduce habitat quality for a woodland songbird: evidence from settlement patterns, demographic parameters, and body condition.
Understanding avian responses to ungulate-induced habitat modification is important because deer populations are increasing across much of temperate Europe and North America. Our experimental study examined whether habitat quality for Blackcaps (Sylvia atricapilla) in young woodland in eastern England was affected by deer, by comparing Blackcap behavior, abundance, and condition between paired plots (half of each pair protected from deer). The vegetation in each pair of plots was the same age. The Blackcap is an ideal model species for testing effects of deer on avian habitat quality because it is dependent on dense understory vegetation and is abundant throughout much of Europe. We compared timing of settlement, abundance, age structure (second-year vs. after-second-year), and phenotypic quality (measured as a body condition index, body mass divided by tarsus length) between experimental and control plots. We used point counts to examine Blackcap distribution, and standardized mist netting to collect demographic and biometric data. Incidence of singing Blackcaps was higher in nonbrowsed than in browsed plots, and singing males were recorded in nonbrowsed plots earlier in the season, indicating earlier and preferential territory establishment. Most Blackcaps, both males and females, were captured in vegetation prior to canopy closure (2–4 years of regrowth). Body condition was superior for male Blackcaps captured in nonbrowsed plots; for second-year males this was most marked in vegetation prior to canopy closure. We conclude that deer browsing in young woodland can alter habitat quality for understory-dependent species, with potential consequences for individual fitness and population productivity beyond the more obvious effects on population density
Quantum description of light pulse scattering on a single atom in waveguides
We present a time dependent quantum calculation of the scattering of a
few-photon pulse on a single atom. The photon wave packet is assumed to
propagate in a transversely strongly confined geometry, which ensures strong
atom-light coupling and allows a quasi 1D treatment. The amplitude and phase of
the transmitted, reflected and transversely scattered part of the wave packet
strongly depend on the pulse length (bandwidth) and energy. For a transverse
mode size of the order of , we find nonlinear behavior for a few
photons already, or even for a single photon. In a second step we study the
collision of two such wave packets at the atomic site and find striking
differences between Fock state and coherent state wave packets of the same
photon number.Comment: to appear in Phys. Rev.
A jet-cloud interaction in the 3C 196 environment
Powerful radio galaxies and radio-loud quasars at high redshifts are
frequently associated with extended emission-line regions (EELRs). Here we
investigate the [O II] EELR around the quasar 3C 196 at z=0.871 using integral
field spectroscopy. We also detect extended [Ne II] emission at a distance of
about 30 kpc from the core. The emission is aligned with the radio hot spots
and shows a redshifted and a blueshifted component with a velocity difference
of ~800 km s^-1. The alignment effect and large velocities support the
hypothesis that the EELR is caused by a jet-cloud interaction, which is
furthermore indicated by the presence of a pronounced bend in the radio
emission at the location of the radio hot spots. We also report observations of
two other systems which do not show as clear indications of interactions. We
find a weaker alignment of an [O II] EELR from the z=0.927 quasar 3C 336, while
no EELR is found around the core-dominated quasar OI 363 at z=0.63.Comment: 7 pages, accepted for publication in A&
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