268 research outputs found
To the center of cold spot with Planck
The structure of the cold spot, of a non-Gaussian anomaly in the cosmic
microwave background (CMB) sky first detected by Vielva et al. is studied using
the data by Planck satellite. The obtained map of the degree of stochasticity
(K-map) of CMB for the cold spot, reveals, most clearly in 100 GHz band, a
shell-type structure with a center coinciding with the minima of the
temperature distribution. The shell structure is non-Gaussian at a 4\sigma
confidence level. Such behavior of the K-map supports the void nature of the
cold spot. The applied method can be used for tracing voids that have no
signatures in redshift surveys.Comment: A & A (in press), 4 pages, 5 figures; to match the published versio
Star Formation Rates from [C II] 158 μm and Mid-infrared Emission Lines for Starbursts and Active Galactic Nuclei
A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)]) - 7.0, for SFR in M ⊙ yr-1 and L([C II]) in L ⊙. We conclude that L([C II]) can be used to measure SFR in any source to a precision of ~50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL ν(158 μm) - 42.8 for SFR in M ⊙ yr-1 and νL ν(158 μm) in erg s-1
Triangulum galaxy viewed by Planck
We used Planck data to study the M33 galaxy and find a substantial
temperature asymmetry with respect to its minor axis projected onto the sky
plane. This temperature asymmetry correlates well with the HI velocity field at
21 cm, at least within a galactocentric distance of 0.5 degree, and it is found
to extend up to about 3 degrees from the galaxy center. We conclude that the
revealed effect, that is, the temperature asymmetry and its extension, implies
that we detected the differential rotation of the M33 galaxy and of its
extended baryonic halo.Comment: 8 pages, 8 figures, in press on Astronomy and Astrophysics, main
journa
Experimental study of photon beam polarimeter based on nuclear e+e- pair production in an amorphous target
The experimental method of the linearly polarized photons polarimetry,using
incoherent e+e- pair production process has been investigated on the beam of
coherent bremsstrahlung (CB) photons in the energy range of 0.9-1.1 GeV at the
Yerevan synchrotron.Comment: 6 pages (text),10 figure
Planck view of the M82 galaxy
Planck data towards the galaxy M82 are analyzed in the 70, 100 and 143 GHz
bands. A substantial north-south and East-West temperature asymmetry is found,
extending up to 1 degree from the galactic center. Being almost
frequency-independent, these temperature asymmetries are indicative of a
Doppler-induced effect regarding the line-of-sight dynamics on the halo scale,
the ejections from the galactic center and, possibly, even the tidal
interaction with M81 galaxy. The temperature asymmetry thus acts as a
model-independent tool to reveal the bulk dynamics in nearby edge-on spiral
galaxies, like the Sunyaev-Zeldovich effect for clusters of galaxies.Comment: 4 pages, 3 figures, in press on A&
[CII] 158 micron Luminosities and Star Formation Rate in Dusty Starbursts and AGN
Results are presented for [CII] 158 micron line fluxes observed with the
Herschel PACS instrument in 112 sources with both starburst and AGN
classifications, of which 102 sources have confident detections. Results are
compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and
with L(IR) from IRAS fluxes; AGN/starburst classifications are determined from
equivalent width of the 6.2 micron PAH feature. It is found that the [CII] line
flux correlates closely with the flux of the 11.3 micron PAH feature
independent of AGN/starburst classification, log [f([CII] 158 micron)/f(11.3
micron PAH)] = -0.22 +- 0.25. It is concluded that [CII] line flux measures the
photodissociation region associated with starbursts in the same fashion as the
PAH feature. A calibration of star formation rate for the starburst component
in any source having [CII] is derived comparing [CII] luminosity L([CII]) to
L(IR) with the result that log SFR = log L([CII)]) - 7.08 +- 0.3, for SFR in
solar masses per year and L([CII]) in solar luminosities. The decreasing ratio
of L([CII]) to L(IR) in more luminous sources (the "[CII] deficit") is shown to
be a consequence of the dominant contribution to L(IR) arising from a luminous
AGN component because the sources with largest L(IR) and smallest
L([CII])/L(IR) are AGN.Comment: Accepted for publication in The Astrophysical Journa
CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II. High-resolution observations
The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope observed about 15,000 objects during the cryogenic mission lifetime. Observations provided low-resolution (R~60-127) spectra over ~5-38um and high-resolution (R~600) spectra over ~10-37um. The Cornell Atlas of Spitzer/IRS Sources (CASSIS) was created to provide publishable quality spectra to the community. Low-resolution spectra have been available in CASSIS since 2011, and we present here the addition of the high-resolution spectra. The high-resolution observations represent approximately one third of all staring observations performed with the IRS instrument. While low-resolution observations are adapted to faint objects and/or broad spectral features (e.g., dust continuum, molecular bands), high-resolution observations allow more accurate measurements of narrow features (e.g., ionic emission lines) as well as a better sampling of the spectral profile of various features. Given the narrow aperture of the two high-resolution modules, cosmic ray hits and spurious features usually plague the spectra. Our pipeline is designed to minimize these effects through various improvements. A super sampled point-spread function was created in order to enable the optimal extraction in addition to the full aperture extraction. The pipeline selects the best extraction method based on the spatial extent of the object. For unresolved sources, the optimal extraction provides a significant improvement in signal-to-noise ratio over a full aperture extraction. We have developed several techniques for optimal extraction, including a differential method that eliminates low-level rogue pixels (even when no dedicated background observation was performed). The updated CASSIS repository now includes all the spectra ever taken by the IRS, with the exception of mapping observations
Peculiarities of electromagnetic field oscillations of a charged particle rotating about a conductive ball
The paper investigates some characteristic features of the electromagnetic field of a relativistic charged particle that uniformly rotatesabout a conductive ball in its equatorial plane. It is assumed that the braking of the particle due to radiation is compensatedby an external influence (e.g. the electric force) that compels the particle to turn uniformly in a circle. The magnetic permittivityof the ball is assumed to be one. The work is based on the corresponding exact analytic solutions of Maxwell’s equations. The generalizedDrude-Lorentz-Sommerfeld formula for the dielectric function of the conductive ball is used in numerical calculations.It is shown that localized oscillations of a high-amplitude electromagnetic field can be generated at a given harmonic inside the ballat a certain (resonant) particle rotation frequency at a small distance from the surface of the ball. Herewith, at large distances fromthe trajectory of the particle, these localized oscillations are accompanied by intense radiation at the same harmonic, which is manytimes more intense than the analogous radiation in the case when the ball is absent.The possibilities of using this phenomenon to develop sources of quasi-monochromatic electromagnetic radiation in the range fromgiga- to terra hertz frequencies are discussed
Correlation Effects in Nuclear Transparency
The Glauber approximation is used to calculate the contribution of nucleon
correlations in high-energy reactions. When the excitation energy of
the residual nucleus is small, the increase of the nuclear transparency due to
correlations between the struck nucleon and the other nucleons is mostly
compensated by a decrease of the transparency due to the correlations between
non detected nucleons. We derive Glauber model predictions for nuclear
transparency for the differential cross section when nuclear shell level
excitations are measured. The role of correlations in color transparency is
briefly discussed.Comment: 24 pages revtex, 4 uuencoded PostScript Figures as separate fil
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