493 research outputs found

    Angular motion of a PAH molecule in interstellar environment

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    Polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important and hitherto undetected component of the Interstellar Medium (ISM). The theory was based on an explanation of the Unidentified IR Emission Bands by Leger et al. It has already led to a verified prediction on extended galactic and extragalactic emissions measured by IRAS, or by a recent balloon borne experiment. The physics that rules the motion of such molecules in the ISM was studied, taking into account their coupling with the ambient gas, the radiation field (absorption and emission) and the static magnetic field. This is important for many implications of the PAH theory such as the radio emission by these molecules or the expected polarization of their IR emission. A reflection nebulae is considered where the situation is rather well known. Every day life of a mean PAH molecule in such a region is as follows: every 3 hrs a UV photon is absorbed heating the molecule to a thousand degs; the temperature decay due to cooling by IR emission follows then within a few seconds. A collision with a molecule of gas occurs typically once a week, while an H atom is ejected or captured at the same rate. A typical cooling cycle after a heat impulse is given. The PAH molecules studied as representative of the family has typically 50 atoms, a radius of 4.5 A, is circular and has a molecular mass of M = 300; its permanent dipole moment is 3 Debye

    How to make CMB maps from huge timelines with small computers

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    We present in this article two different ways to make CMB maps in practice, from large timelines. One is to make a simple destriping, fitting the data and using the scan intercepts to remove the low frequency noise (stripes). The second, optimal, is to resolve linearly the map-making problem, which in case of big timelines must be simplified and changed from matrices to vectors for the calculations. Assuming few conditions on the noise, it is possible to make fast map-making tools.Comment: 1 fig., proceeding of the "Mining the Sky" conference in Garching, Germany, 200

    The 3.3 micron emission feature: Map of the galactic disk, 10 deg less than 1 less than 35 deg, - 6 deg less than b less than 6 deg

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    The 3.3 micron aromatic feature has been detected in the diffuse galactic emission with the AROME balloon-borne instrument. The results are presented in the form of an map of the 3.3 micron feature's intensity. The AROME instrument consists in a Cassegrain telescope with wobbling secondary mirrors and a liquid/solid nitrogen cooled photometer. The instrumental output is modified by the impulse response of the system. So the galactic surface brightness was restored in Fourier space by an inverse optimal filtering. The map of the feature's intensity is presented for a region of galactic coordinates. All the known H II giant molecular cloud complexes are visible in the 3.3 micron feature emission showing a good correlation with the infrared dust emission

    Simulating the impact of dust cooling on the statistical properties of the intracluster medium

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    From the first stages of star and galaxy formation, non-gravitational processes such as ram pressure stripping, SNs, galactic winds, AGNs, galaxy-galaxy mergers, etc... lead to the enrichment of the IGM in stars, metals as well as dust, via the ejection of galactic material into the IGM. We know now that these processes shape, side by side with gravitation, the formation and the evolution of structures. We present here hydrodynamic simulations of structure formation implementing the effect of the cooling by dust on large scale structure formation. We focus on the scale of galaxy clusters and study the statistical properties of clusters. Here we present our results on the TX−MT_X-M and the LX−ML_X-M scaling relations which exhibit changes on both the slope and normalization when adding cooling by dust to the standard radiative cooling model. For example, the normalization of the TX−MT_X-M relation changes only by a maximum of 2% at M=1014M=10^{14} M⊙_\odot whereas the normalization of the LX−TXL_X-T_X changes by as much as 10% at TX=1T_X=1 keV for models that including dust cooling. Our study shows that the dust is an added non-gravitational process that contributes shaping the thermodynamical state of the hot ICM gas.Comment: 11 pages, 4 figures, ASR in pres

    SAFARI optical system architecture and design concept

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    Map-making methods for Cosmic Microwave Background experiments

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    The map-making step of Cosmic Microwave Background data analysis involves linear inversion problems which cannot be performed by a brute force approach for the large timelines of today. We present in this article optimal vector-only map-making methods, which are an iterative COBE method, a Wiener direct filter and a Wiener iterative method. We apply these methods on diverse simulated data, and we show that they produce very well restored maps, by removing nearly completely the correlated noise which appears as intense stripes on the simply pixel-averaged maps. The COBE iterative method can be applied to any signals, assuming the stationarity of the noise in the timeline. The Wiener methods assume both the stationarity of the noise and the sky, which is the case for CMB-only data. We apply the methods to Galactic signals too, and test them on balloon-borne experiment strategies and on a satellite whole sky survey.Comment: 8 pages without the figures, 11 JPEG figures out of the text, MNRAS, in pres
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