Deep Galaxy survey at 6.75 micron with the ISO satellite

Deep 6.75um mid-IR ISOCAM observations were obtained of the Canada-France Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The identification of the sources with optical counterparts is described in detail, and a classification scheme is devised which depends on the S/N of the detection and the inverse probability of chance coincidence. 83% of the 54 ISOCAM sources are identified with Iab<23.5 counterparts. The (I-K)ab colors, radio properties, spectrophotometric properties and frequency of nuclear activity of these counterparts differ on average from those of typical CFRS galaxies. CFRS spectra are available for 21 of the sources which have Iab <= 22.5 (including 7 stars). Most of the strongest sources are stars or AGN. Among the non--stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies that display star formation activity and/or significant contributions of A stars. The ISOCAM sources also display an IR excess, even when compared with heavily-reddened local starburst galaxies. An upper limit of 30% of extragalactic ISO sources could be at z>1 of the 44 S6.75um > 150uJy sources which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded)Comment: 13 pages, 12 figures. Accepted for publication in A

Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey

Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane in mainly four infrared bands between 6 and 25 micron. Two of these bands cover several Unidentified Infrared emission Bands (UIBs). With the aim of extracting the spatial distribution of the UIB emission on a large scale, a scheme has been developed to model the MSX data with emission in the UIBs alongwith the underlying thermal continuum from the interstellar dust. In order to test this scheme, a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152, Sh-156, Sh-186; Zavagno & Ducci 2001) for which imaging study in some individual UIBs is available from ISOCAM measurements, has been studied. The results of this comparative study on small angular scale are as follows : (i) the morphological details extracted from our scheme agree very well with those from the superior ISOCAM measurements; (ii) the integrated strength of UIBs extracted from the MSX database correlates extremely well with the sum of the strengths of individual UIBs measured from ISOCAM. This tight correlation is very encouraging and promises the potential of MSX database for study of large scale spatial distribution of UIB emission (and the carriers of UIBs) in the entire Galactic plane.Comment: to be published in Astronomy & Astrophysics; (9 pages including 2 tables & 11 figures

15um ISO observations of a CFRS field: the cosmic SFR as derived from UV, optical, mid-IR and radio photometry

The CFRS 1452+52 field has been deeply imaged with the Infrared Space Observatory (ISO) using ISOCAM through the LW3 filter (12-18um). Careful data analysis and comparison to deep optical and radio data have allowed us to generate a catalog of 78 15um sources with both radio and optical identifications. They are redder and lie at higher redshift than I-band selected galaxies, with most of them being star-forming galaxies. We have considered the galaxies detected at radio and 15$\mu$m wavelengths which potentially include all strong and heavily extincted starbursts, up to z=1. Spectral energy distributions (SED) for each of the sources have been derived using deep radio, mid-IR, near-IR, optical and UV photometry. The sources were then spectrally classified by comparing to SEDs of well known nearby galaxies. By deriving their FIR luminosities by interpolation, we can estimate their Star Formation Rate (SFR) in a way which does not depend sensitively on the extinction. 75% (-40%, +10%) of the star formation at $z \le 1$ is related to IR emission and the global extinction is in the range Av=0.5 -- 0.85. While heavily extincted starbursts, with SFR in excess of 100 Mo/yr constitute less than a percent of all galaxies, they contribute about 18% of the SFR density out to z=1. Their morphologies range from S0 to Sab, and more than a third are interacting systems. The SFR derived by FIR fluxes is likely to be ~2.9 times higher than those previously estimated from UV fluxes. The derived stellar mass formed since the redshift of 1 could be too high when compared to the present day stellar mass density. This might be due to an IMF in distant star-forming galaxies different from the solar neighborhood one, or to an underestimate of the local stellar mass density.Comment: 15 figures and 5 tables (with lower res. fig. 1, 5 & 6). Accepted for publication in Ap

Stellar sources in the ISOGAL intermediate bulge fields

We present a study of ISOGAL sources in the "intermediate" galactic bulge ($|$$l$$|$ $<$ 2$^\circ$, $|$$b$$|$ $\sim$ 1$^\circ$--4$^\circ$), observed by ISOCAM at 7 and 15 $\mu m$. In combination with near-infrared (I, J, K$_{\rm s}$) data of DENIS survey, complemented by 2MASS data, we discuss the nature of the ISOGAL sources, their luminosities, the interstellar extinction and the mass-loss rates. A large fraction of the 1464 detected sources at 15 $\mu m$ are AGB stars above the RGB tip, a number of them show an excess in ([7]-[15])$_{\rm 0}$ and (K$_{\rm s}$-[15])$_{\rm 0}$ colours, characteristic of mass-loss. The latter, especially (K$_{\rm s}$-[15])$_{\rm 0}$, provide estimates of the mass-loss rates and show their distribution in the range 10$^{-8}$ to 10$^{-5}$ M$_{\rm \odot}$/yr.Comment: 16 pages, accepted for publication in Astronomy and Astrophysic