The author discusses the morphology of luminous Infrared Astronomy Satellite (IRAS) galaxies. A few comments are made about the direction to be taken in future observations of luminous IRAS galaxies

Becklin, E. E.

English

NASA Technical Reports Server

MORPHOLOGY OF LUMINOUS IRAS GALAXIES:
SUMMARY TALK
N87- 24376
E. E. Becklin
University of Hawaii, Institute for Astronomy
Honolulu, Hawaii 96822 USA
As my part of the summary I will discuss the morphology of luminous IRAS
galaxies and make a few comments about where we go from here in our
understanding.
MORPHOLOGY OF LUMINOUS IRAS GALAXIES
I will define a luminous IRAS galaxy as one with a luminosity of
>3 x I0 I0 Le, corresponding to the break in the galaxy luminosity function
(Soifer et al. 1986). I will discuss the morphological properties of three
subgroups, each separated in luminosity by about a factor of ten.
For galaxies just above the break at L ~ 3 x i0 I0 to i0 II Le, there appear
to be two dominant types. First, there are luminous Sc galaxies in which most
of the emission is coming from the disk of the galaxy. Significant infrared
emission is seen both from interstellar grains and grains in giant molecular
clouds (Persson and Helou 1986; Mezger et al. 1986). For these galaxies the
infrared to blue luminosity ratio is similar to galaxies of a lower luminosity.
Second, there appears to be a class of optically barred galaxies (~10% of all
barred galaxies) that show significant infrared emission in this luminosity
range (Hawarden et al. 1986). The galaxies have been discovered by their
strong 25-_m emission, but also show a blue (hot) 60- to 100-_m color.
Devereux (1986) has shown that these "hot" barred galaxies appear predominantly
in earlier types. Observations by Devereux (1986) and Hawarden et al. (1986)
indicate that the emission is nuclear in origin and probably from a burst of
star formation. The galaxies NGC 253 and M82 may be nearby examples. Very
interesting results on M82 indicate a ring structure and an outflow (Sofue
1986; Lo et ai.1986).
For galaxies with luminosities at L ~ I0 II Lo to 5 x I0 II Le, we find
that galaxy interactions and mergers become much more important (Joseph and Wright
1986; Cutri 1986; Lonsdale et al. 1984). It appears from previous work and
papers presented here by Keel (1986); Rodriguez-Espinosa et ai.(198_; Wilson
0986); as well as the review by Rieke d98_, that we see both nuclear star forma-
tion and an active nucleus in the form of Seyfert-type activity. Surprisingly,
the amount of luminosity seen in star formation and a Seyfert-type nucleus
appear almost equal. This occurs collectively in a sample of galaxies and also
in many individual galaxies such as NGC 1068. At this point we do not know
which phenomenon is more fundamental. Put simply, we do not know the relation-
ship between star formation and an active compact nucleus. The results pre-
sented certainly indicate that there must in fact be an important connection.
Is it as simple as the fact that both are fed by interstellar material?
Carol J. Lonsdale Persson (Editor)
Star Formation in Galaxies 753
https://ntrs.nasa.gov/search.jsp?R=19870014943 2020-03-20T11:05:56+00:00Z
E.E. BECKLIN
At a luminosity at or greater than 1012 Le we find the following
properties.
I) Infrared selected galaxies have as high or a higher space density, at
a given luminosity than objects selected from optical, x-ray, or radio
surveys (Solfer et el. 1986, and references therein).
2) Most or all of the galaxies have a high LIR/LB(>I0). These are true
infrared galaxies.
3) Most or all are interacting or merging.
4)
5)
There is evidence for great amounts of interstellar material from the
interstellar reddening, CO llne observations (Young 1986; Sanders et
al. 1986) and submilllmeter continuum measurements (Emerson et al.
1984; Chini et al. 1986). Most interesting, the region of strong CO
emission is, in some galaxies, very compact (Sargent et al. 1986).
I would speculate based on a few nearby galaxies (Becklln and
Wynn-Willlams 1986) that most of the infrared radiation from this
class of galaxy comes from an active compact nucleus.
Finally, at a luminosity of > 1013 Le, we do not presently know the space
density of infrared objects, although a few appear to have been found
(Klelnmann and Keel 1986).
COMMENTS ON FUTURE OBSERVATIONS OF LUMINOUS IRAS GALAXIES
I would llke to make some points about observations of hlgh-lumlnoslty
infrared galaxies llke Arp 220.
I) Understanding of these objects will probably be critical in solving
QS0-Seyfert-energy source problem. The explanation of these phenomena
may require an understanding of new physical processes (for example
Harwlt et al. 1986).
2) We will be better off if we study a moderate number of galaxies in
great detail rather than gathering large quantities of statistics.
3) The objects will be difficult to study at optical, near infrared, and
x-ray wavelengths because the optical depth in dust is too large.
This was nicely pointed out by Rieke in his review.
4) We need infrared diagnostics and tools to make these studies. The
primary diagnostic will be infrared spectroscopy with high angular
resolution. The spectroscopy is important to understand the physical
environment and to get velocity information. High quality observa-
tions will be necessary in conjunction with theoretical and laboratory
studies of molecular and atomic lines.
FACILITIES FOR FUTURE OBSERVATIONS
As regards tools for these studies, ground-based, suborbital, and space-
based platforms will all be important. From the ground, infrared use of the
754
SUMMARY:LUMINOUSIRASGALAXIES
new large telescopes llke the Keck 10-meter will be extremely important. This
is especially true with the use of multl-element detectors at infrared wave-
lengths, both for imaging and spectroscopy. Also the new submillimeter tele-
scopes, presently under construction, will be of extreme importance in studying
these galaxies in the continuum and in spectral lines. Another important tool
will be the proposed 3-meter airplane telescope, SOFIA. This instrument will
provide a large collecting area for spectroscopy above the earth's atmosphere
and will allow high angular resolution for imaging in the far-infrared.
In space, the second generation of instruments on HST will include an
instrument that extends the wavelength coverage to 2.5 Pa. Because of the
extreme high angular resolution possible with HST this instrument will be very
important. This is particularly true for the Pu llne that cannot be seen from
the ground.
The reduced background of a cryogenic telescope in space increases the
sensitivity of an infrared telescope many orders of magnitude. Therefore, ISO
and SIRTF will be critical in studies of these galaxies. I have a political
concern about where these projects are headed. ISO is approved, but is now
making many critical compromises because of funding. These compromises will
seriously jeopardize the science return. SIRTF does not appear to be able to
get in the long NASA queue of approved projects. As an outsider, I have the
following question: Is it not scientifically reasonable to bring the two
projects together and create the best of both projects? It seems especially
relevant to discuss this today at the scientific meeting discussing the results
of the extremely successful European-USA project IRAS.
SUMMARY
A year ago Malcolm Longair reviewed the first IRAS conference and con-
cluded that the most important new result discussed at the conference was the
existence of small grains or large molecules--a discovery that, in fact, was
not made by IRAS. This year I am happy to report that IRAS has brought infra-
red astronomy into the "big league" with respect to luminous phenomena in
galaxies. It now seems clear that in the luminosity range from 1012 to 1013 Le
there is a large density of luminous infrared galaxies. In this luminosity
range, the space density of galaxies selected by their infrared emission
appears larger than the corresponding objects selected on the bases of their
optical, radio, or x-ray emission. More important, I personally believe that
it will be the detailed studies of these infrared galaxies that will give us
the answer to the energy source in all luminous objects such as Seyfert galax-
ies and QSOs.
REFERENCES
Becklln, E. E., and Wynn-Willlams, C. G. 1986, this conference.
Cutrl, R. M. 1986, this conference.
Devereux, N. 1986, this conference.
Emerson, J. P., Clegg, P. E., Gee, G., Cunningham, C. T., Griffin, M. J.,
Brown, L. M. J., Robson, E. I., and Longmore, A. J. 1984, Nature, 311,
237.
Harwlt, M. O., Houck, J. R., Soifer, B. T., and Palumbo, G. G. C. 1986, this
conference.
755
E.E.BECKLIN
Hawarden, T. G., Mountain, C. M., Leggett, S. K., and Puxley, P. J. 1986,
this conference.
Joseph, R. D., and Wright, G. S. 1986, M.N.R.A.S., 214, 87.
Keel, W. C. 1986, this conference.
Kleinmann, S., and Keel, W. C. 1986p late paper this conference.
Krugel, E., Chini, R., Kreysa, E., and Mezger, P. G. 1986, this conference.
Lo, K. Y., Masson, C. R., Phillips, T. G., and Scoville, N. Z. 1986, this
conference.
Lonsdale, C. J., Persson, S. E., and Matthews, K. 1984, Ap. J., 287, 95.
Mezger, P. G., Cox, P., and Krugel, E. 1986, this conference.
Persson, C. G., and Helou, G. 1986, this conference.
Rieke, G. 1986, this conference.
Rodrlguez-Espinosa, J. M., Rudy, R. J., and Jones, B. 1986, this conference.
Sanders, D. B., Scoville, N. Z., Soifer, B. T., Young, J. S., Schloerb, F. P.,
Rice, W. L., Danielson, G. E. 1986, this conference.
Sargent, A. I., Scoville, N. Z., Sanders, D. B. and Soifer, B. T. 1986,
late paper this conference.
Sofue, Y. 1986, this conference.
Solfer, B. T., Sanders, D. B., Neugebauer, G., Danielson, G. E., Persson, C.
J., Madore, B. F., Persson, S. E. 1986, this conference.
Wilson, A. S. 1986, this conference.
Young, J. S. 1986, this conference.
756


Morphology of luminous IRAS galaxies: Summary talk

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server