4.1. ISO Surveys of Galaxies
While ISO was an observatory rather than a survey mission, many surveys
were carried out using various capabilities of its versatile payload.
Some prominent surveys that concern normal galaxies either directly
or indirectly are listed below. This is by no means an exhaustive list,
especially since most ISO data have yet to be published.
- Mid-infrared maps of nearby galaxies were obtained under the ISO-CAM
(C. Césarsky et
guaranteed time (GT) program, targeting large
angular-size galaxies in various categories, such as early-type, spirals
barred and non-barred, dwarf irregulars, and active
There were also surveys of galaxies in Virgo, Coma and other clusters.
All galaxies were surveyed in the LW2 (6.75 µm) and LW3 (15
µm) filters, and some in
other filters within the 3 to 18 µm wavelength range of ISO-CAM. In
addition, several were observed with the Circular Variable Filter (CVF),
which yields images at a spectral resolution of about 20 over most of the
same wavelength range. These data were taken mostly with 3" pixels, with
an effective resolution of 7 to 9" half-maximum width.
- Far-infrared spectral surveys were
carried out under the GT program of the ISO-LWS
(Clegg et al. 1996),
most notably for a sample of infrared-bright galaxies, meaning those
with a flux density greater than 50 Jy at 60 µm, and of
(Fischer et al., 1999).
Most objects were
observed with a LWS low-resolution full spectral scan covering 45 to 195
- Far-infrared maps of well-resolved nearby galaxies were obtained
under the ISO-PHOT
(Lemke et al. 1996)
GT program at 60, 100 and 175
µm, most notably of M31, M33 and M 101.
- Photometry at
60 µm was also carried
out under the
ISO-PHOT GT program for several samples, including 75 bright (B < 12 mag)
galaxies from the Revised Shapley-Ames Catalog, and selected objects in the
Virgo Cluster. These samples were observed (PI R. Joseph)
at 60, 100 and 175 µm, as
well as 12 µm (ISO-CAM filter LW10), with additional data
the ground in the near-infrared and the submm. The purpose was to extend
the spectral energy distribution, look for cold dust, and investigate
- The surveys above were coordinated by J. Lequeux, resulting in several
coherent data sets of great interest to normal galaxy studies.
The imaging with CAM at 6.75 and 15 µm, sampled galaxies at
from the Magellanic Clouds out to the Virgo Cluster, under programs
and ``VIRGO''; program ``CAMSFR'' imaged star-forming
regions at additional wavelengths, and with the CAM-CVF mode. In Virgo,
at least thirty galaxies were imaged with CAM, and measured with PHOT at
while their [CII] 157.7
µm line was targeted with LWS (PI K. Leech).
- Open time projects included several galaxy surveys, such as the
Knapp et al. (1996)
study of early type galaxies, the Lu et al. study of infrared-cold galaxies,
Metcalfe et al. (1996)
- The ISO Key Project on the Interstellar Medium of Normal Galaxies
(Helou et al. 1996)
under NASA GT collected data on a set of sixty galaxies
that explore the full range of morphology, luminosity, infrared-to-blue
ratio and far-infrared color among star-forming galaxies. These sixty
objects were selected to be small in their IRAS emission size compared to
the 80" LWS beam and the 3' ISO-CAM field of view, so as to
allow studies of their global properties. In addition, nine nearby
galaxies were mapped to the extent possible, including NGC 6946, NGC 1313,
IC 10, and parts of M 101. For most galaxies, maps were
obtained at 7 and 15 µm with ISO-CAM, spectro-photometry was
with ISO-PHOT-S between 3 and 12 µm, and far-infrared
fine-structure lines were targeted with ISO-LWS, attempting to measure as
many as possible of the following lines, in the order listed:
[CII] 157.7 µm,
[OI] 63.2 µm,
[NII] 121.9 µm,
[OIII] 88.4 µm,
[NIII] 57.3 µm,
[OIII] 51.8 µm,
[NII] 145 µm.
- The ISO-PHOT Serendipity Survey gathered data during satellite
slews between target observations with the 170 µm
channel. By the end of
the mission, data had been collected over 150,000° of slew track, with
an estimated 4,000 galaxies detected
(Stickel et al. 1998).
This data set
will be a unique source of far-infrared fluxes for thousands of galaxies
with IRAS detections at
f (100 µm)
- By its nature as an observatory-class mission, ISO has generated
a rich archive containing all the observations of individual galaxies,
groups, or clusters of galaxies investigated by various observers for
specific questions. This collection constitutes a de-facto survey of
unique or peculiar objects from which one could learn much about the less
exotic cases (e.g.
Smith & Madden 1997;
Lu et al. 1996;
Jarrett et al. 1999;
Valentijn et al. 1996;
Xu et al. 1999).
Many useful survey samples
can also be constructed after the fact by selecting objects out of the ISO
archive once it becomes available in the summer of 1999.
Though not addressed directly in this review, ground-based infrared surveys
will make fundamental contributions to our view of normal galaxies,
especially the Two-Micron All-Sky Survey (2MASS,
Skrutskie et al. 1999)
and Deep European Near-Infrared Survey (DENIS,
Epchtein et al. 1999),
Apart from these large systematic surveys,
several near-infrared imaging surveys of nearby galaxies are
already revealing some surprising results.
Grauer & Rieke (1998)
for instance demonstrate that spiral arms are almost as contrasted in the K
band as they are in the B band. See also Terndrup et al. (1994).