arXiv subjects

C. J. Cesarsky

Publications and source records attributed to C. J. Cesarsky.

29 records · Page 2Linked to original sources

arXiv1999

Element mixing in the Cassiopeia A supernova

Thanks to mid-infrared observations, we provide new clues to the element mixing during a supernova explosion by probing the mixing between three adjacent layers: the oxygen burning products layer (sulfur, argon,...), the silicate layer and the neon layer. The silicate and neon layers are both contaminated by sulfur and argon in a macroscopic way, but appear segregated, so that the mixing is heterogeneous. This finding complements the microscopic mixing information deduced from presolar grains found in meteorites and implies that, at present time, supernovae are probably not the main dust factory in the Galaxy. The mixing is often interpreted in terms of hydrodynamical instabilities driven by the outward shock following the implosion of the supernova core. Testing whether such instabilities can lead to the injection of material from a layer into upper layers without complete mixing, as suggested by the observations presented in this paper, should be possible with the intense lasers which are starting to be used to simulate astrophysical plasmas.

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arXiv1999

Source Counts from the 15 microns ISOCAM Deep Surveys

We present the results of the five mid-IR 15 microns (12-18 microns LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field. The roughly 1000 sources detected, 600 of which have a flux above the 80 % completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to 5 mJy. By adding the ISOCAM surveys of the HDF-North and South (plus flanking fields) and the lensing cluster A2390 at low fluxes and IRAS at high fluxes, we cover four decades in flux from 50 microJy to 0.3 Jy. The slope of the differential counts is very steep (alpha =-3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of alpha =-2.5. When compared with no-evolution models based on IRAS, our counts show a factor of 10 excess at 400 microJy, and a fast convergence, with alpha =-1.6 at lower fluxes.

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arXiv1999

ISO observations of the environment of the soft gamma-ray repeater SGR 1806-20

Observations at near and mid-infrared wavelengths (1-18 micron) of SGR 1806-20 suggest that it is associated with a cluster of giant massive stars which are enshrouded in a dense cloud of dust. The centre of the best sky position of the gamma-ray source (Hurley et al. 1999) lies on top of the dust cloud at only 7 arcsec (~0.5 pc at a distance of 14.5 kpc) from the star cluster, and 12 arcsec (~0.85 pc) from a Luminous Blue Variable Star (LBV) which had been proposed to be associated with the SGR (Kulkarni et al. 1995). The bright cloud of interstellar gas and dust observed with ISO (Infrared Space Observatory) is probably the birth site of the cluster of massive stars, the LBV star, and the progenitor of the soft gamma-ray repeater pulsar. The presence of such a young star formation region is compatible with the current interpretation of soft gamma-ray repeaters as young neutron stars. The SGR 1806-20 compact source is unlikely to form a bound binary system with any of the infrared luminous massive stars, since no flux variations in the near-infrared were detected from the latter in an interval of 4 years.The ISO observations were made over two epochs, 11 days before and 2 hours after a soft gamma-ray burst detected with the Interplanetary Network, and they show no enhanced mid-infrared emission associated to the high energy activity of the SGR.

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arXiv1999

A Mid-Infrared and Far-Infrared View of Galaxies

From the disk of normal galaxies to the nucleus of prototype active sources, we review the wealth of results and new understanding provided by recent infrared probes and, in particular, the four instruments on-board of ISO.

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arXiv1999

Isocam Extragalactic Mid-Infrared Deep Surveys Unveiling Dust-Enshrouded Star Formation In The Universe

ISOCAM extragalactic mid-infrared deep surveys have detected a population of strong IR emitters ten times more numerous than expected if there were no evolution from z<0.2 (IRAS) up to the maximum redshift of these galaxies (z=1.5). The mid-IR cosmic background produced by these galaxies (2.35+/-0.8 nW m^-2 sr^-1, at 15 microns above 50 microJy) is larger than 30 per cent of the energy radiated in the I band by the optical galaxies detected in the HDF, which are two orders of magnitude more numerous. This fraction is much higher than in the local universe (z<0.2) as probed by IRAS, where all integrated IR emission from 8 to 1000 microns makes 30 per cent of the optical starlight. Even assuming a conservative SED, they produce a major contribution to the 140 mu m DIRBE background measured by Hauser et al. (1998, 25.1+/-7 nW m^-2 sr^-1) and Lagache et al. (1999, 15.3+/-9.5 nW m^ -2 sr^-1). This is both a confirmation of the strong IR cosmic background that was first detected by Puget et al. (1996) and the first identification of the galaxies responsible for a large fraction of this background at 140 microns. We find that these bright (several 10^11 Lsol) and massive ( = 1.5x10^11 Msol) IR galaxies have a typical redshift of z=0.7 and optical colors similar to field galaxies. The fraction of galaxies with morphological signs of interactions is larger at higher redshift. This is consistent with the nature of local luminous IR galaxies found by IRAS, which often exhibit evidence of galaxy interaction or merging and indicates that interactions should play a crucial role in the evolution of galaxies as expected from bottom-up scenarios.

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arXiv1998

Medium-distant clusters of galaxies seen by ISO

We present a comprehensive study of ISO cluster galaxies in connection with other wavelengths. First results show that infrared galaxies detected by ISOCAM concentrate on the edge of clusters. Surprisingly, they are not emission lines galaxies but very luminous elliptical, merging or interacting ones, which suggests non-trivial connections between star formation rate, optical and mid-IR properties. However, no correlation has been found between the MIR/optical star formation properties of the galaxies, so that the exact origin of the IR emission remains unclear.

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arXiv1998

ISOCAM observations of the Hubble Deep Field reduced with the PRETI method

We have developed a new ISOCAM data reduction technique based on wavelet analysis, especially designed for the detection of faint sources in mid-infrared surveys. This method, the Pattern REcognition Technique for Isocam data (PRETI) has been used to reduce the observations of the Hubble Deep Field (HDF) and flanking fields with ISOCAM at 6.75 (LW2) and 15 microns (LW3). Simulations of ISOCAM data allow us to test the photometric accuracy and completeness of the reduction. We detect 49 objects in the ISO-HDF at high confidence level, 42 in the LW3 filter, 3 in the LW2 filter, and 4 in both filters. An additional, less secure, list of 100 sources is presented, of which 89 are detected at 15 microns only, 7 at 6.75 microns only and 4 in both filters. Number counts derived from our results show an excess by a factor of 10 with respect to the prediction of a no evolution model (Franceschini 1998) in the LW3 band. On the contrary, the number of sources in the LW2 band is compatible with the prediction of such a model, but with greater uncertainties, given the small number of detections.

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arXiv1998

A classical approach to faint extragalactic source extraction from ISOCAM deep surveys. Application to the Hubble Deep Field

We have developed a general data reduction technique for ISOCAM data coming from various deep surveys of faint galaxies. In order to reach the fundamental limits of the camera (due to the background photon noise and the readout noise), we have devised several steps in the reduction processes that transform the raw data to a sky map which is then used for point source and sligthly extended source extraction. We show illustrative examples of our present scheme by using data taken from the publicly available Hubble Deep Field ISOCAM survey in order to demonstrate its characteristics. More than thirty sources down to the 60 (resp. 100) microJy level are clearly detected above 4 sigma at wavelengths of 7 (resp. 15) micron, the vast majority at 15 micron. A large fraction of these sources can be identified with visible objects of median magnitude 22 and K-band magnitude of 17.5 and redshifts between 0.5 and 1 (when available). A few very red objects could be at larger redshifts.

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arXiv1998

Isocam deep surveys unveiling star formation in the mid-infrared

Before having exhausted the helium in its tank on April 8, 1998, the Infrared Space Observatory had time to perform several complementary surveys at various depths and areas within selected regions of the sky. We present the results of some of the surveys done with the mid-infrared camera, ISOCAM, on-board ISO, and more specifically those surveys which were performed using the broad-band filter LW3 (12-18 microns). We show that mid-infrared allows to discriminate starburst and post-starburst galaxies among galaxies which present similar optical-UV morphological and colour signatures. Furthermore, the strong evolution found in the surveys indicates that more star formation is hidden in the infrared at higher redshifts.

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arXiv1998

Deep ISOCAM view of the core of the lensing cluster A2390

We have imaged the inner square arcminute of the well known lensing and cooling flow cluster A2390 (z = 0.23) down to a sensitivity of 65 and 130 microJy at 6.75 and 15 micronmetre, respectively. We report the first evidence of an active star-forming region in a cooling flow (at those wavelengths) and strong emission in the mid-IR from lensed galaxies located at z=0.9.

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arXiv1997

Source Counts and Background Radiation

Our present understanding of the extragalactic source counts and background radiation at infrared and sub-mm wavelengths is reviewed. Available count data are used to constrain evolutionary models of galaxies and Active Nuclei. The CIRB, on the other hand, provides crucial information on the integrated past IR emissivity, including sources so faint to be never accessible. The near-IR and sub-mm are suited to search for the CIRB. These cosmological windows are ideal to detect redshifted photons from the two most prominent broad emission features in galaxy spectra: the stellar photospheric 1 micron peak and the one at 100 micron due to dust re-radiation. The recently claimed detection of an isotropic diffuse component at 100-200 microns would support the evidence for strong cosmic evolution from $z=0$ to $z\sim 2$ of faint gas-rich late-type galaxies, as inferred from direct long-$λ$ counts. Furthermore, an equally intense CIRB flux measured in the wavelength range 200 to 500 $μm$ may be in support of models envisaging a dust-enshrouded phase during formation of spheroidal galaxies (e.g. Franceschini et al., 1994): the background spectrum at such long wavelengths would indicate an high redshift ($z>2-3$) for this active phase of star formation, implying a relevant constraint on structure formation scenarios. We argue that, given the difficulties for sky surveys in this spectral domain, only sporadic tests of these ideas will be achieved in the next several years. Only a mission like FIRST, in combination with large mm arrays and optical telescopes, will allow to thoroughly investigate, via photometric and spectroscopic surveys, these IR-bright early phases in the evolution of galaxies and AGNs.

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