1,091 research outputs found
On the spectroastrometric separation of binary point-source fluxes
Spectroastrometry is a technique which has the potential to resolve flux
distributions on scales of milliarcseconds. In this study, we examine the
application of spectroastrometry to binary point sources which are spatially
unresolved due to the observational point spread function convolution. The
technique uses measurements with sub-pixel accuracy of the position centroid of
high signal-to-noise long-slit spectrum observations. With the objects in the
binary contributing fractionally more or less at different wavelengths
(particularly across spectral lines), the variation of the position centroid
with wavelength provides some information on the spatial distribution of the
flux. We examine the width of the flux distribution in the spatial direction,
and present its relation to the ratio of the fluxes of the two components of
the binary. Measurement of three observables (total flux, position centroid and
flux distribution width) at each wavelength allows a unique separation of the
total flux into its component parts even though the angular separation of the
binary is smaller than the observations' point-spread function. This is because
we have three relevant observables for three unknowns (the two fluxes, and the
angular separation of the binary), which therefore generates a closed problem.
This is a wholly different technique than conventional deconvolution methods,
which produce information on angular sizes of the sampling scale.
Spectroastrometry can produce information on smaller scales than conventional
deconvolution, and is successful in separating fluxes in a binary object with a
separation of less than one pixel. We present an analysis of the errors
involved in making binary object spectroastrometric measurements and the
separation method, and highlight necessary observing methodology.Comment: 11 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Spatial decomposition of on-nucleus spectra of quasar host galaxies
In order to study the host galaxies of type 1 (broad-line) quasars, we
present a semi-analytic modelling method to decompose the on-nucleus spectra of
quasars into nuclear and host galaxy channels. The method uses the spatial
information contained in long-slit or slitlet spectra. A routine determines the
best fitting combination of the spatial distribution of the point like nucleus
and extended host galaxy. Inputs are a simultaneously observed PSF, and
external constraints on galaxy morphology from imaging. We demonstrate the
capabilities of the method to two samples of a total of 18 quasars observed
with EFOSC at the ESO 3.6m telescope and FORS1 at the ESO VLT.
~50% of the host galaxies with sucessful decomposition show distortions in
their rotation curves or peculiar gas velocities above normal maximum
velocities for disks. This is consistent with the fraction from optical
imaging. All host galaxies have quite young stellar populations, typically 1-2
Gyr. For the disk dominated hosts these are consistent with their inactive
counterparts, the luminosity weighted stellar ages are much younger for the
bulge dominated hosts, compared to inactive early type galaxies. While this
presents further evidence for a connection of galaxy interaction and AGN
activity for half of the sample, this is not clear for the other half: These
are often undistorted disk dominated host galaxies, and interaction on a
smaller level might be detected in deeper high-resolution images or deeper
spectroscopic data. The velocity information does not show obvious signs for
large scale outflows triggered by AGN feedback - the data is consistent with
velocity fields created by galaxy interaction.Comment: Accepted for publication in MNRAS; 19 pages, 12 figure
A Multi-wavelength Study of the Sunyaev-Zel'dovich Effect in the Triple-Merger Cluster MACS J0717.5+3745 with MUSTANG and Bolocam
We present 90, 140, and 268GHz sub-arcminute resolution imaging of the
Sunyaev-Zel'dovich effect (SZE) in MACSJ0717.5+3745. Our 90GHz SZE data result
in a sensitive, 34uJy/bm map at 13" resolution using MUSTANG. Our 140 and
268GHz SZE imaging, with resolutions of 58" and 31" and sensitivities of 1.8
and 3.3mJy/beam respectively, was obtained using Bolocam. We compare these maps
to a 2-dimensional pressure map derived from Chandra X-ray observations. Our
MUSTANG data confirm previous indications from Chandra of a pressure
enhancement due to shock-heated, >20keV gas immediately adjacent to extended
radio emission seen in low-frequency radio maps. The MUSTANG data also detect
pressure substructure that is not well-constrained by the X-ray data in the
remnant core of a merging subcluster. We find that the small-scale pressure
enhancements in the MUSTANG data amount to ~2% of the total pressure measured
in the 140GHz Bolocam observations. The X-ray template also fails on larger
scales to accurately describe the Bolocam data, particularly at the location of
a subcluster known to have a high line of sight optical velocity (~3200km/s).
Our Bolocam data are adequately described when we add an additional component -
not described by a thermal SZE spectrum - coincident with this subcluster.
Using flux densities extracted from our model fits, and marginalizing over the
temperature constraints for the region, we fit a thermal+kinetic SZE spectrum
to our data and find the subcluster has a best-fit line of sight proper
velocity of 3600+3440/-2160km/s. This agrees with the optical velocity
estimates for the subcluster. The probability of velocity<0 given our
measurements is 2.1%. Repeating this analysis using flux densities measured
non-parametrically results in a 3.4% probability of a velocity<=0. We note that
this tantalizing result for the kinetic SZE is on resolved, subcluster scales.Comment: 10 Figures, 18 pages. this version corrects issues with the previous
arXiv versio
Spectroscopic Transit Search: a self-calibrating method for detecting planets around bright stars
We search for transiting exoplanets around the star Pictoris using
high resolution spectroscopy and Doppler imaging that removes the need for
standard star observations. These data were obtained on the VLT with UVES
during the course of an observing campaign throughout 2017 that monitored the
Hill sphere transit of the exoplanet Pictoris b. We utilize line
profile tomography as a method for the discovery of transiting exoplanets. By
measuring the exoplanet distortion of the stellar line profile, we remove the
need for reference star measurements. We demonstrate the method with white
noise simulations, and then look at the case of Pictoris, which is a
Scuti pulsator. We describe a method to remove the stellar pulsations
and perform a search for any transiting exoplanets in the resultant data set.
We inject fake planet transits with varying orbital periods and planet radii
into the spectra and determine the recovery fraction. In the photon noise
limited case we can recover planets down to a Neptune radius with an 80%
success rate, using an 8 m telescope with a spectrograph and 20
minutes of observations per night. The pulsations of Pictoris limit our
sensitivity to Jupiter-sized planets, but a pulsation removal algorithm
improves this limit to Saturn-sized planets. We present two planet candidates,
but argue that their signals are most likely caused by other phenomena. We have
demonstrated a method for searching for transiting exoplanets that (i) does not
require ancillary calibration observations, (ii) can work on any star whose
rotational broadening can be resolved with a high spectral dispersion
spectrograph and (iii) provides the lowest limits so far on the radii of
transiting Jupiter-sized exoplanets around Pictoris with orbital
periods from 15 days to 200 days with >50% coverage.Comment: Accepted for publication in A&A, 8 pages, 8 figures. The Github
repository can be found at
https://github.com/lennartvansluijs/Spectroscopic-Transit-Searc
A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification
We report on the optical spectroscopic analysis of a sample of 99
low-luminosity quasi-stellar objects (LLQSOs) at base the
Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility
of studying the faint end of the QSO population at smaller cosmological
distances and, therefore, in greater detail. A small number of our LLQSO
present no broad component. Two sources show double broad components, whereas
six comply with the classic NLS1 requirements. As expected in NLR of broad line
AGNs, the [S{\sc{ii}}]based electron density values range between 100 and
1000 N/cm. Using the optical characteristics of Populations A and
B, we find that 50\% of our sources with H broad emission are consistent
with the radio-quiet sources definition. The remaining sources could be
interpreted as low-luminosity radio-loud quasar. The BPT-based classification
renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources,
the possible star burst contribution might control the LINER and HII
classification. Finally, we discuss the aperture effect as responsible for the
differences found between data sets, although variability in the BLR could play
a significant role as well.Comment: 22 pages; 5 tables; 17 figures; in press with A&
The Molonglo Reference Catalog 1-Jy radio source survey IV. Optical spectroscopy of a complete quasar sample
Optical spectroscopic data are presented here for quasars from the Molonglo
Quasar Sample (MQS), which forms part of a complete survey of 1-Jy radio
sources from the Molonglo Reference Catalogue. The combination of low-frequency
selection and complete identifications means that the MQS is relatively free
from the orientation biases which affect most other quasar samples. To date,
the sample includes 105 quasars and 6 BL Lac objects, 106 of which have now
been confirmed spectroscopically. This paper presents a homogenous set of
low-resolution optical spectra for 79 MQS quasars, the majority of which have
been obtained at the Anglo-Australian Telescope. Full observational details are
given and redshifts, continuum and emission-line data tabulated for all
confirmed quasars.Comment: 40 pages, ApJS in pres
Milli-arcsecond--scale Spectral Properties and Jet Motions in M87
We have combined high resolution VLBI Space Observatory Programme (VSOP) data
at 1.6 and 4.8 GHz with Very Long Baseline Array (VLBA) data at higher
frequencies and with similar resolutions to study the spectral properties of
the core of M87 with milliarcsecond resolution. The VSOP data allow a more
accurate measurement of the turn-over frequency, and hence more reliable
determination of associated physical parameters of the source. Comparison of
the images with previously published images yields no evidence for significant
motion of components in the parsec-scale jet. In addition, the brightness
temperatures obtained from model-fits to the core are well below the inverse
Compton limit, suggesting the radio emission we are observing is not strongly
Doppler boosted.
Colour version on http://www.vsop.isas.jaxa.jp/survey/publications/m87.ps.gzComment: To appear in PASJ VSOP special issue. Minor correction
Discovery of a Quadruple Lens in CANDELS with a Record Lens Redshift z=1.53
Using spectroscopy from the Large Binocular Telescope and imaging from the
Hubble Space Telescope we discovered the first strong galaxy lens at z(lens)>1.
The lens has a secure photometric redshift of z=1.53+/-0.09 and the source is
spectroscopically confirmed at z=3.417. The Einstein radius (0.35"; 3.0 kpc)
encloses 7.6 x 10^10 Msol, with an upper limit on the dark matter fraction of
60%. The highly magnified (40x) source galaxy has a very small stellar mass
(~10^8 Msol) and shows an extremely strong [OIII]_5007A emission line (EW_0 ~
1000A) bolstering the evidence that intense starbursts among very low-mass
galaxies are common at high redshift.Comment: accepted for publication in ApJ Letter
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