35 research outputs found
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 15m 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 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
( 2, 1--4), observed by
ISOCAM at 7 and 15 . In combination with near-infrared (I, J, K) 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
are AGB stars above the RGB tip, a number of them show an excess in
([7]-[15]) and (K-[15]) colours, characteristic
of mass-loss. The latter, especially (K-[15]), provide
estimates of the mass-loss rates and show their distribution in the range
10 to 10 M/yr.Comment: 16 pages, accepted for publication in Astronomy and Astrophysic