arXiv subjects

C. Cesarsky

Publications and source records attributed to C. Cesarsky.

44 records · Page 3Linked to original sources

arXiv1999

A Deep 12 Micron Survey with ISO

We present the first results of a study of faint 12 micron sources detected with the Infrared Space Observatory (ISO) in four deep, high galactic latitude fields. The sample includes 50 such sources in an area of 0.1 square degrees down to a 5 sigma flux limit of about 500 microJy. From optical identifications based on the US Naval Observatory (USNO) catalogue and analysis of the optical/IR colours and Digital Sky Survey (DSS) images, we conclude that 37 of these objects are galaxies and 13 are stars. We derive galaxy number counts and compare them with existing IRAS counts at 12 microns, and with models of the 12 micron source population. In particular, we find evidence for significant evolution in the galaxy population, with the no-evolution case excluded at the 3.5 sigma level. The stellar population is well matched by existing models. Two of the objects detected at 12 micron are associated with known galaxies. One of these is an IRAS galaxy at z=0.11 with a luminosity of 10^11 L_sun.

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arXiv1998

A 1.4 GHz Survey of the Southern ELAIS Region

A deep survey of the European Large Area ISO Survey (ELAIS) field in the southern celestial hemisphere (hereinafter S1) has been carried out with the Australia Telescope Compact Array (ATCA) at 1.4 GHz. The S1 region, covering about 4 square degrees, has been also surveyed in the mid- and far-infrared (5-200 micron) with the Infrared Space Observatory (ISO). The radio survey provides uniform coverage of the entire S1 region, with a sensitivity (5 sigma) of 0.4 mJy over the whole area and 0.2 mJy in the center. To this sensitivity, virtually all the radio counterparts of the far-infrared extragalactic ISO sources should be detected. This paper presents a radio sample - complete at the 5 sigma level - consisting of 581 sources detected at 1.4 GHz. Of these radio sources, 349 have peak flux density in the range 0.2-1 mJy, forming a new homogeneous sample of sub-mJy radio sources. Due to its size, depth and multi-waveband coverage, the sample will allow us to study in greater detail the sub-mJy radio source population. The full catalogue will be available from http://athena.ph.ac.uk/

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arXiv1998

FIRBACK: I. A deep survey at 175 $μ$m with ISO, preliminary results

FIRBACK is a deep survey conducted with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) at an effective wavelength of 175 $μ$m. We present here results we have obtained on the first field, the so-called Marano1 which covers around 0.25 square degree. We find that the source density for objects with a flux above 200 mJy exceeds the counts expected for sources found in the IRAS deep surveys with a similar flux by about an order of magnitude. Such an excess was expected on the basis of the high far infrared background detected with the FIRAS and DIRBE instruments aboard the Cosmic Background Explorer (COBE). These sources are likely to be redshifted infrared galaxies. The steep number counts indicate strong cosmological evolution in this population. The detected sources account for only 10 % of the cosmic IR background. An extrapolation of the counts down to about 10 mJy would be needeed to account for the whole background at this wavelength.

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arXiv1998

A barred spiral at the centre of the giant elliptical radio galaxy Centaurus A

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (CenA, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of CenA reveals a bisymmetric structure with a diameter of 5' (5 kpc), centred at the AGN. This structure is remarkably similar to that of a barred spiral galaxy, with the bar lying in a plane that is tilted ~18 degrees from the line of sight. The true nature of the distribution of dust in the inner regions of CenA is noticeably displaced from the more chaotic and widespread optical obscuration. The barred spiral is a quasi-stable structure formed at the center of the giant elliptical from the tidal debris of a gas-rich object(s) accreted in the past 10^9 years. The total size and mass of interstellar gas in the barred spiral at the center of CenA is comparable to the small Local Group spiral galaxy Messier 33. The observation of this remarkable structure opens the more general question on whether the dusty hosts of giant radio galaxies like CenA, are "symbiotic" galaxies composed of a barred spiral inside an elliptical, where the bar serves to funnel gas toward the AGN.

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arXiv1998

Dust in the Wheel: The Cartwheel Galaxy in the Mid-IR

We present mid-infrared images at $6.7 μm$ and $15 μm$ of ``The Cartwheel'' (AM~0035-33), the prototypical collisional ring galaxy. The observations, taken with ISOCAM, reveal the distribution of hot dust in the galaxy and its two companions in the north-east. The intensity of the mid-IR emission from the outer star forming ring of the Cartwheel shows considerable azimuthal variation and peaks at the most active H$α$ region of the ring. The 15 $μm$ to 6.7 $μm$ flux ratio of 5.2 is the highest among all the galaxies of our sample. A surprising result of our observations is the discovery of significant emission from the inner regions of the galaxy, including the inner ring, spokes and nucleus, where previously only low level H$α$ emission had been reported. At 6.7 $μm$, this emission is stronger than the one from the outer star forming ring, and at 15 $μm$, it represents 40% of the emission from the outer ring. The H$α$ to mid-IR flux ratios from the inner regions are consistent with the heating of grains from weak star formation activity.

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arXiv1998

The FIRBACK 175 micron Survey

The FIRBACK project is a collaboration of eight institutes aimed at using long wavelength surveys with ISO to uncover the nature of the Cosmic Far-Infrared Background. We have surveyed nearly 4 sq. deg. in three regions in the northern and southern hemispheres with the ISOPHOT instrument on ISO, using the 175 micron filter. As reported by Puget et al. (1998) and Reach et al. (these proceedings), the first 0.25 sq. deg. region studied in this programme contains many more 175 micron sources than expected. Initial reduction of the remaining survey areas appears to confirm this result. The area surveyed by FIRBACK represents the largest and deepest long wavelength far-IR survey available before the launch of SIRTF.

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arXiv1998

A Deep VLA survey at 20cm of the ISO ELAIS survey regions

We have used the Very Large Array(VLA) in C configuration to carry out a sensitive 20cm radio survey of regions of sky that have been surveyed in the Far Infra-Red over the wavelength range 5-200 microns with ISO as part of the European Large Area ISO Survey(ELAIS). As usual in surveys based on a relatively small number of overlapping VLA pointings the flux limit varies over the area surveyed. The survey has a flux limit that varies from a 5$σ$ limit of 0.135mJy over an area of 0.12deg$^2$ to a 5$σ$ limit of 1.15mJy or better over the whole region covered of 4.22 deg$^2$. In this paper we present the radio catalogue of 867 sources. These regions of sky have previously been surveyed to shallow flux limits at 20cm with the VLA as part of the VLA D configuration NVSS(FWHM=45 arcsec) and VLA B configuration FIRST(FWHM=5 arcsec) surveys. We have carried out a a detailed comparison of the reliability of our own survey and these two independent surveys in order to assess the reliability and completeness of each survey.

astro-ph↗

arXiv1998

The dark side of star formation in the Antennae galaxies

We compare mid-infrared images of the Antennae galaxies (NGC 4038/39) from the Infrared Space Observatory, with optical images from the Hubble Space Telescope. The mid-infrared observations show that the most intense starburst in this colliding system of galaxies takes place in an off-nucleus reg ion that is inconspicuous at optical wavelengths. The analyses of the mid-infrar ed spectra indicate that the most massive stars are being formed in an optically obscured knot of 50 pc radius, which produces about 15% of the total luminosity from the Antennae galaxies between 12.5 microns and 18 microns. The mid-infrared observations reported here demonstrate that the interpretation of star formation properties in colliding/merging systems based on visible wavelengths alone can be profoundly biased due to dust obscuration. The multiwavelength view of this nearby prototype merging system suggests caution in deriving scenarios of early evolution of high redshift galaxies using only observations in the narrow rest-frame ultraviolet wavelength range.

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