134 research outputs found
Maps of the number of HI clouds along the line of sight at high galactic latitude
Characterizing the structure of the Galactic Interstellar Medium (ISM) in
three dimensions is of high importance for accurate modeling of dust emission
as a foreground to the Cosmic Microwave Background (CMB). At high Galactic
latitude, where the total dust content is low, accurate maps of the 3D
structure of the ISM are lacking. We develop a method to quantify the
complexity of the distribution of dust along the line of sight with the use of
HI line emission. The method relies on a Gaussian decomposition of the HI
spectra to disentangle the emission from overlapping components in velocity. We
use this information to create maps of the number of clouds along the line of
sight. We apply the method to: (a) the high-galactic latitude sky and (b) the
region targeted by the BICEP/Keck experiment. In the North Galactic Cap pixels
are occupied by 3 clouds on average, while in the South the number falls to
2.5. The statistics of the number of clouds are affected by
Intermediate-Velocity Clouds (IVCs), primarily in the North. The presence of
IVCs results in detectable features in the dust emission measured by
\textit{Planck}. We investigate the complexity of HI spectra in the BICEP/Keck
region and find evidence for the existence of multiple components along the
line of sight. The data and software are made publicly available, and can be
used to inform CMB foreground modeling and 3D dust mapping.Comment: 28 pages (including appendices), 19 figures, submitted to AAS
journals, comments welcom
Maps of the Number of H I Clouds along the Line of Sight at High Galactic Latitude
Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H i line emission. The method relies on a Gaussian decomposition of the H i spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H i spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping
Extreme Starlight Polarization in a Region with Highly Polarized Dust Emission
Galactic dust emission is polarized at unexpectedly high levels, as revealed
by Planck. The origin of the observed polarization fractions can
be identified by characterizing the properties of optical starlight
polarization in a region with maximally polarized dust emission. We measure the
R-band linear polarization of 22 stars in a region with a submillimeter
polarization fraction of . A subset of 6 stars is also measured in
the B, V and I bands to investigate the wavelength dependence of polarization.
We find that starlight is polarized at correspondingly high levels. Through
multiband polarimetry we find that the high polarization fractions are unlikely
to arise from unusual dust properties, such as enhanced grain alignment.
Instead, a favorable magnetic field geometry is the most likely explanation,
and is supported by observational probes of the magnetic field morphology. The
observed starlight polarization exceeds the classical upper limit of
%mag and is at least
as high as 13%mag that was inferred from a joint analysis of Planck
data, starlight polarization and reddening measurements. Thus, we confirm that
the intrinsic polarizing ability of dust grains at optical wavelengths has long
been underestimated.Comment: Accepted by A&AL, data to appear on CDS after publication. 6 page
Velocity models inferred from p-waves travel time curves in south Aegean
Με σκοπό τη δημιουργία μοντέλων ταχύτητας στην περιοχή του νοτίου Αιγαίου, χρησιμοποιούμε τις καταγραφές σεισμών κατά τη χρονική περίοδο από 1η Ιανουαρίου έως 3Ιη Αυγούστου 2005 από ένα νέο τηλεμετρικό δίκτυο που εγκαταστάθηκε και λειτουργεί στην περιοχή της Κρήτης. Τα μοντέλα ταχύτητας κατασκευάζονται από τις καμπύλες χρόνων διαδρομής των επιμηκών κυμάτων και χρησιμοποιούνται σε συνδυασμό με τις χρονικές διορθώσεις στο χρόνο άφιξης των σεισμικών κυμάτων σε κάθε σεισμολογικό σταθμό του δικτύου για τον ακριβή προσδιορισμό των εστιακών παραμέτρων των σεισμών που έχουν καταγραφεί στην περιοχή του νοτίου Αιγαίου με τη χρήση του προγράμματος HYPOINVERSE. Συνδυάζοντας όλες τις διαθέσιμες πληροφορίες από τη βιβλιογραφία και τα αποτελέσματα της παρούσας μελέτης προσδοκούμε να συμβάλουμε στην αποσαφήνιση του σεισμοτεκτονικού προτύπου της περιοχής καθώς και της γεωμετρίας της καταδυόμενης λιθόσφαιρας της ανατολικής Μεσογείου.The seismicity recorded during Ist January to 31st August 2005 from a new telemetry network installed and operating on the island of Crete, is used in an effort to obtain new velocity models for the area of south Aegean. The models are constructed from the P-waves travel time curves and are later used for the events relocation with the HYPOINVERSE algorithm and station delays calculation. Furthermore, results are discussed and compared with the ones derived from other significant previous works presented the last years. We anticipate by combining all the available information from the literature and the analysis of our data set to contribute to the seismotectonic modeling of the study area and to construct a most complete image of the geometry of the subducted plate
Eliminating artefacts in polarimetric images using deep learning
Polarization measurements done using Imaging Polarimeters such as the Robotic Polarimeter are very sensitive to the presence of artefacts in images. Artefacts can range from internal reflections in a telescope to satellite trails that could contaminate an area of interest in the image. With the advent of wide-field polarimetry surveys, it is imperative to develop methods that automatically flag artefacts in images. In this paper, we implement a Convolutional Neural Network to identify the most dominant artefacts in the images. We find that our model can successfully classify sources with 98 per cent true positive and 97 per cent true negative rates. Such models, combined with transfer learning, will give us a running start in artefact elimination for near-future surveys like WALOP
Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique
The third Fermi-LAT catalog (3FGL) presented the data of the first four years
of observations from the Fermi Gamma-ray Space Telescope mission. There are
3034 sources, 1010 of which still remain unidentified. Identifying and
classifying gamma-ray emitters is of high significance with regard to studying
high-energy astrophysics. We demonstrate that optical polarimetry can be an
advantageous and practical tool in the hunt for counterparts of the
unidentified gamma-ray sources (UGSs). Using data from the RoboPol project, we
validated that a significant fraction of active galactic nuclei (AGN)
associated with 3FGL sources can be identified due to their high optical
polarization exceeding that of the field stars. We performed an optical
polarimetric survey within uncertainties of four unidentified 3FGL
sources. We discovered a previously unknown extragalactic object within the
positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and
measured a redshift of . Using these measurements and
archival data we demonstrate that this source is a candidate counterpart for
3FGL J0221.2+2518 and most probably is a composite object: a star-forming
galaxy accompanied by AGN. We conclude that polarimetry can be a powerful asset
in the search for AGN candidate counterparts for unidentified Fermi sources.
Future extensive polarimetric surveys at high galactic latitudes (e.g.,
PASIPHAE) will allow the association of a significant fraction of currently
unidentified gamma-ray sources.Comment: accepted to A&
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