83 research outputs found
Clear detection of dusty torus signatures in a Weak-Line Radio Galaxy: the case of PKS 0043-42
We report the clearest detection to date of dusty torus signatures in a
Weak-Line Radio Galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS)
rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 0043-42 (z=0.116) shows
a clear spectral turnover at wavelengths longer than ~20 micron suggestive of
warm dust, as well as a 9.7 micron silicate absorption feature. In addition,
the hard X-ray results, based on Chandra data, strongly support a picture in
which PKS 0043-42 has a torus and accretion disc more typical of Strong-Line
Radio Galaxies (SLRGs). The MIR and X-ray spectra are markedly different from
those of other WLRGs at similar redshifts, and here we show that the former can
be successfully fitted with clumpy torus models with parameters characteristic
of Type-2 AGN tori: close to edge-on (i=74 deg) and relatively broad (torus
angular width=60 deg), with an outer radius of 2 pc, hydrogen column density
~1.6x10^(23) cm^(-2), and AGN bolometric luminosity ~1.6x10^(44) erg s^(-1).
The presence of a compact torus in PKS 0043-42 provides evidence that this WLRG
is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a
diverse population, and PKS 0043-42 may represent a type of radio galaxy in
which the AGN activity has been recently re-triggered as a consequence of
intermittent gas supply, or in which the covering factor of the Narrow-Line
Region (NLR) clouds is relatively low.Comment: 7 pages, 6 figures, 1 table. Accepted by MNRA
An independent analysis of the Spitzer/IRAC phase curves of WASP43 b
We present here a reanalysis of the Spitzer Space Telescope phase curves of
the hot Jupiter WASP43 b, using the wavelet pixel-Independent Component
Analysis, a blind signal-source separation method. The data analyzed were
recorded with the InfraRed Array Camera and consisted of two visits at 3.6
m, and one visit at 4.5 m, each visit covering one transit and two
eclipse events. To test the robustness of our technique we repeated the
analysis on smaller portions of the phase curves, and by employing different
instrument ramp models. Our reanalysis presents significant updates of the
planetary parameters compared to those reported in the original phase curve
study of WASP43 b. In particular, we found (1) higher nightside temperatures,
(2) smaller hotspot offsets, (3) a greater consistency (1 )
between the two 3.6~m visits, and (4) a greater similarity with the
predictions of the atmospheric circulation models. Our parameter results are
consistent within 1 with those reported by a recent reanalysis of the
same data sets. For each visit we studied the variation of the retrieved
transit parameters as a function of various sets of stellar limb-darkening
coefficients, finding significant degeneracy between the limb-darkening models
and the analysis output. Furthermore, we performed the analysis of the single
transit and eclipse events, and we examined the differences between these
results with the ones obtained with the whole phase curve. Finally we provide a
formula useful to optimize the trade-off between precision and duration of
observations of transiting exoplanets.Comment: published on A
Star Formation in Quasar Hosts and the Origin of Radio Emission in Radio-Quiet Quasars
Radio emission from radio-quiet quasars may be due to star formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively-driven outflow. In this paper we examine whether radio emission from radio-quiet quasars is a byproduct of star formation in their hosts. To this end we use infrared spectroscopy and photometry from Spitzer and Herschel to estimate or place upper limits on star formation rates in hosts of ~300 obscured and unobscured quasars at z\u3c1. We find that low-ionization forbidden emission lines such as [NeII] and [NeIII] are likely dominated by quasar ionization and do not provide reliable star formation diagnostics in quasar hosts, while PAH emission features may be suppressed due to the destruction of PAH molecules by the quasar radiation field. While the bolometric luminosities of our sources are dominated by the quasars, the 160 micron fluxes are likely dominated by star formation, but they too should be used with caution. We estimate median star formation rates to be 6-29 Msun/year, with obscured quasars at the high end of this range. This star formation rate is insufficient to explain the observed radio emission from quasars by an order of magnitude, with log(L_radio, observed/L_radio, SF)=0.6-1.3 depending on quasar type and star formation estimator. Although radio-quiet quasars in our sample lie close to the 8-1000 micron infrared / radio correlation characteristic of the star-forming galaxies, both their infrared emission and their radio emission are dominated by the quasar activity, not by the host galaxy
Conical shell illumination incorporating a moving aperture for depth-resolved high-energy X-ray diffraction
In many applications, the main limitation of X-ray absorption methods is that the signals measured are a function of the attenuation coefficient, which tells us almost nothing about the chemical or crystallographic nature of objects under inspection. To calculate fundamental crystallographic parameters requires the measurement of diffracted photons from a sample. Standard laboratory diffraction methods have been refined for well over a century and provide ‘gold standard’ structural models for well-prepared samples and single crystals but have little applicability for thick heterogeneous samples as demanded by many screening applications. We present a new high-energy X-ray diffraction probe, which in comparison with previous depth-resolving hollow beam techniques, requires a single beam, point detector and a simple swept aperture to resolve sample signatures at unknown locations within an inspection space. We perform Monte Carlo simulations to support experiments on both single- and multiple-material localisation and identification. The new probe is configured and tested using low-cost commercial components to provide a rapid and cost-effective solution for applications including explosives detection, process control and diagnostics.The Royal Society and The Wolfson Foundation RSWF\R1\180012.
The Department of Homeland Security (DHS), Science and Technology Directorate, Homeland Security Advanced Research Projects Agency, Explosives Division through the Advanced X-ray Material Discrimination Program (HSHQDC-15-CB0036).
Engineering and Physical Sciences Research Council: EP/T034238/1
Jet-triggered star formation in young radio galaxies
Emission in the ultraviolet continuum is a salient signature of the hot,
massive and consequently short-lived, stellar population that traces recent or
ongoing star formation. With the aim of mapping star forming regions and
morphologically separating the generic star formation from that associated with
the galaxy-scale jet activity, we obtained high-resolution HST/UV imaging for a
sample of nine compact radio sources. Out of these, seven are known Compact
Steep Spectrum (CSS) galaxies that host young, kpc-scale radio sources and
hence are the best candidates for studying radio-mode feedback on galaxy
scales, while the other two form a control sample of larger sources. Extended
UV emission regions are observed in six of the seven CSS sources showing close
spatial alignment with the radio-jet orientation. If other mechanisms possibly
contributing to the observed UV emission are ruled out, this could be evidence
in support of jet-triggered star formation in the CSS phase of radio galaxy
evolution.Comment: 4 pages, 2 figures, Proceedings of the 6th Workshop on GHz-Peaked
Spectrum (GPS) and Compact Steep Spectrum (CSS) source
The quantum efficiency and diffractive image artifacts of Si:As IBC mid-IR detector arrays at 5 10 m: Implications for the JWST/MIRI detectors
Arsenic doped back illuminated blocked impurity band (BIBIB) silicon
detectors have advanced near and mid-IR astronomy for over thirty years; they
have high quantum efficiency (QE), especially at wavelengths longer than 10
m, and a large spectral range. Their radiation hardness is also an asset
for space based instruments. Three examples of Si:As BIBIB arrays are used in
the Mid-InfraRed Instrument (MIRI) of the James Webb Space Telescope (JWST),
observing between 5 and 28 m. In this paper, we analyze the parameters
leading to high quantum efficiency (up to 60\%) for the MIRI devices
between 5 and 10 m. We also model the cross-shaped artifact that was first
noticed in the 5.7 and 7.8 m Spitzer/IRAC images and has since also been
imaged at shorter wavelength (m) laboratory tests of the MIRI
detectors. The artifact is a result of internal reflective diffraction off the
pixel-defining metallic contacts to the readout detector circuit. The low
absorption in the arrays at the shorter wavelengths enables photons diffracted
to wide angles to cross the detectors and substrates multiple times. This is
related to similar behavior in other back illuminated solid-state detectors
with poor absorption, such as conventional CCDs operating near 1 m. We
investigate the properties of the artifact and its dependence on the detector
architecture with a quantum-electrodynamic (QED) model of the probabilities of
various photon paths. Knowledge of the artifact properties will be especially
important for observations with the MIRI LRS and MRS spectroscopic modes.Comment: 17 pages, 15 figures, accepted for publication in PAS
Optical- & UV-Continuum Morphologies of Compact Radio Source Hosts
We present the first systematic search for UV signatures from radio
source-driven AGN feedback in Compact Steep Spectrum (CSS) radio galaxies.
Owing to their characteristic sub-galactic jets (1-20 kpc projected linear
sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback
via jet-triggered star formation. The sample consists of 7 powerful CSS
galaxies, and 2 galaxies host to radio sources >20 kpc as control, at low to
intermediate redshifts (z<0.6). Our new HST images show extended UV continuum
emission in 6/7 CSS galaxies; with 5 CSS hosts exhibiting UV knots co-spatial
and aligned along the radio-jet axis. Young (5 M)
stellar populations are likely to be the dominant source of the blue excess
emission in radio galaxies at these redshifts. Hence, the radio-aligned UV
regions could be attributed to jet-induced starbursts. Lower near-UV SFRs
compared to other indicators suggests low scattered AGN light contribution to
the observed UV. Dust attenuation of UV emission appears unlikely from high
internal extinction correction estimates in most sources. Comparison with
evolutionary synthesis models shows that our observations are consistent with
recent (~1-8 Myr old) star forming activity likely triggered by current or an
earlier episode of radio emission, or by a confined radio source that has
frustrated growth due to a dense environment. While follow-up spectroscopic and
polarized light observations are needed to constrain the activity-related
components in the observed UV, the detection of jet-induced star formation is a
confirmation of an important prediction of the jet feedback paradigm.Comment: Submitted to Ap
JWST/MIRI coronagraphic performances as measured on-sky
Characterization of directly imaged exoplanets is one of the most eagerly
anticipated science functions of the James Webb Space Telescope. MIRI, the
mid-IR instrument has the capability to provide unique spatially resolved
photometric data points in a spectral range never achieved so far for such
objects. We aim to present the very first on-sky contrast measurements of the
MIRI's coronagraphs. In addition to a classical Lyot coronagraph at the longest
wavelength, this observing mode implements the concept of the four quadrant
phase mask for the very first time in a space telescope. We observed single
stars together with a series of reference stars to measure raw contrasts as
they are delivered on the detector, as well as reference subtracted contrasts.
MIRI's coronagraphs achieve raw contrasts greater than at the smallest
angular separations (within ) and about further out (beyond
). Subtracting the residual diffracted light left unattenuated by the
coronagraph has the potential to bring the final contrast down to the
background and detector limited noise floor at most angular separations (a few
times at less than ). MIRI coronagraphs behave as expected from
simulations. In particular the raw contrasts for all four coronagraphs are
fully consistent with the diffractive model. Contrasts obtained with
subtracting reference stars also meet expectations and are fully demonstrated
for two four quadrant phase masks (F1065C and F1140C). The worst contrast,
measured at F1550C, is very likely due to a variation of the phase aberrations
at the primary mirror during the observations, and not an issue of the
coronagraph itself. We did not perform reference star subtraction with the Lyot
mask at F2300C, but we anticipate that it would bring the contrast down to the
noise floor.Comment: submitted to A&
JWST MIRI flight performance: The Medium-Resolution Spectrometer
The Medium-Resolution Spectrometer (MRS) provides one of the four operating
modes of the Mid-Infrared Instrument (MIRI) on board the James Webb Space
Telescope (JWST). The MRS is an integral field spectrometer, measuring the
spatial and spectral distributions of light across the 5-28 wavelength
range with a spectral resolving power between 3700-1300. We present the MRS's
optical, spectral, and spectro-photometric performance, as achieved in flight,
and we report on the effects that limit the instrument's ultimate sensitivity.
The MRS flight performance has been quantified using observations of stars,
planetary nebulae, and planets in our Solar System. The precision and accuracy
of this calibration was checked against celestial calibrators with well-known
flux levels and spectral features. We find that the MRS geometric calibration
has a distortion solution accuracy relative to the commanded position of 8 mas
at 5 and 23 mas at 28 . The wavelength calibration is accurate
to within 9 km/sec at 5 and 27 km/sec at 28 . The uncertainty in
the absolute spectro-photometric calibration accuracy was estimated at 5.6 +-
0.7 %. The MIRI calibration pipeline is able to suppress the amplitude of
spectral fringes to below 1.5 % for both extended and point sources across the
entire wavelength range. The MRS point spread function (PSF) is 60 % broader
than the diffraction limit along its long axis at 5 and is 15 % broader
at 28 . The MRS flight performance is found to be better than prelaunch
expectations. The MRS is one of the most subscribed observing modes of JWST and
is yielding many high-profile publications. It is currently humanity's most
powerful instrument for measuring the mid-infrared spectra of celestial sources
and is expected to continue as such for many years to come.Comment: 16 pages, 21 figure
Spectroscopic time series performance of the Mid-Infrared Instrument on the JWST
We present here the first ever mid-infrared spectroscopic time series
observation of the transiting exoplanet \object{L 168-9 b} with the
Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope. The data were
obtained as part of the MIRI commissioning activities, to characterize the
performance of the Low Resolution Spectroscopy (LRS) mode for these challenging
observations. To assess the MIRI LRS performance, we performed two independent
analyses of the data. We find that with a single transit observation we reached
a spectro-photometric precision of 50 ppm in the 7-8 \micron range at
R=50, consistent with 25 ppm systematic noise. The derived band averaged
transit depth is 524 15 ppm and 547 13 ppm for the two applied
analysis methods, respectively, recovering the known transit depth to within 1
. The measured noise in the planet's transmission spectrum is
approximately 15-20 \% higher than random noise simulations over wavelengths
m. \added{We observed an larger excess
noise at the shortest wavelengths of up to a factor of two, for which possible
causes are discussed.} This performance was achieved with limited in-flight
calibration data, demonstrating the future potential of MIRI for the
characterization of exoplanet atmospheres.Comment: Accepted for publishing in PASP, 21 pages, 10 figure
- …