The empirical connection between gravitational and collisional interactions among galaxies and enhanced activity has been well-documented. However, the physical mechanisms which are responsible for triggering the various forms of activity have not been determined. The author presents the preliminary results of a study of the nuclear and integrated infrared properties of galaxies chosen from the Catalog of Isolated Pairs of Galaxies in the Northern Hemisphere (Karachentsev 1972; hereafter CPG) and the Catalog of Isolated Galaxies (Karachentseva 1973; hereafter KI). Observations of these large, unbiased samples of paired and isolated galaxies are analyzed with the hope of identifying which aspects of galaxy encounters are most closely coupled to the presence of activity

Cutri, Roc M.

English

NASA Technical Reports Server

Y - 1  1 
NUCLEAR AND EXTENDED INFRARED EMISSION IN PAIRED AND 
ISOLATED GALAXIES 
Roc M. Cutri 
Steward Observatory 
University of Arizona 
I. INTRODUCTION 
The empirical connection between gravitational and collisional interactions among 
galaxies and enhanced activity has been well-documented. However, the physical mech- 
anisms which are responsible for triggering the various forms of activity have not been 
determined. We present the preliminary results of a study of the nuclear and integrated 
infrared properties of galaxies chosen from the Catalog of Isolated Pairs of Galades in 
the Northern Hemisphere (Karachentsev 1972; hereafter CPG) and the Catalog of Isolated 
Galazies (Karachentseva 1973; hereafter KI) . Observations of these large, unbiased sam- 
ples of paired and isolated galaxies are analyzed with the hope of identifying which aspects 
of galaxy encounters are most closely coupled to the presence of activity. 
11. NUCLEAR PROPERTIES 
Cutri and McAlary (1985) reported that the 10 pm luminosity distribution of a sample 
of CPG galaxies exhibited a high luminosity tail not present in the distribution of a control 
sample of bright spiral galaxies and Virgo spirals. Although the CPG and control samples 
had very similar absolute B magnitude distributions, the CPG samQle spanned a larger 
range in redshift space than the non-interacting samples, and it was felt that the result 
could suffer from a Malmquist bias. Therefore, we have begun to re-examine this relation- 
ship by using the excellent performance of the new Multiple Mirror Telescope Bolometer 
system to obtain sensitive broadband 10.4 pm measurements of a sample of KI galaxies 
which better match the redshift range of the CPG sample. 
The subsets of the CPG and KI for this study were chosen to have m,, <_ 14.0 or 
mtot 5 13.3 for close pairs, and Oo 5 6 3 7 O .  For the CPG sample, Cutri and McAlary 
obtained data for pairs with LIN, DIS or ATM classifications (i.e. showing some sign of 
disturbed morphology). We have begun to carry out new photometry of the non-disturbed 
(SEP) pairs, as well. To date, approximately 2/3 of the new KI sample has been observed, 
and the 10 pm luminosity distributions of the CPG and KI samples are shown in Figure 1. 
As before, the CPG sample exhibits a distribution essentially similar to the non-interacting 
KI sample, except for a population of sources with Llo > ~ O ~ L ~ .  The M I distribution shows 
several galaxies with higher luminosities than the earlier control samples, but still < iOgLQ. 
It should be noted that although they satisfy the isolation criteria of the KI, the two most 
41 5 
https://ntrs.nasa.gov/search.jsp?R=19910007604 2020-03-19T19:50:04+00:00Z
luminous galaxies in the sample, KI 359 (=NGC 2960) and KI 1004 (=NGC 7479), both 
appear disturbed on POSS plates. The statistical significance of the difference between 
the two distributions is difficult to asdess since the CPG galaxies exhibit a base population 
similar to that of the KI sample. However, a Gehan two-sample test does reject the 
hypothesis that the two are drawn from the same parent population at better than the 
98% level. 
shows the ratio of the IRAS 12 pm flux density to the small aperture 10 pm 
ux density for the CPG and KI galaxies, giving a measure of the extent of the mid-infrared 
earing in mind that the IRAS beam sampled roughly 100 times the area of 
our small aperture measurements, these data show that wherever nuclear 10 pm emission 
is detected it is strongly concentrated within a diameter of 1 kpc. This compactness is 
consistent with the characteristic sizes of galactic nuclei at 10 pm measured by Rieke 
(1976). 
The nuclei of the high luminosity sources from the CPG sample all show HI1 region 
or Liner optical spectra, indicating that the elevated luminosities are due to enhanced 
star formation in and around the nuclear regions. The presence of enhanced nuclear 
10 pm emission in the interacting systems suggests that mass transfer between galaxies 
is probably not the mechanism which triggers the activity, because of the difficulty of 
transporting infalling material directly to the nuclei. Such a conclusion was also reached 
by Keel et d. (1985), whose proposed that tidally enhanced fueling of the nuclei might lead 
to the nuclear activity. Finally, we find no obvious dependence in the 10 pm luminosity 
distribution on pair separation, angular size, velocity difference or interaction morphology. 
TENDED PROPERTIES 
We have examined IRAS ADDSCAN data for a large subset of both the CPG and 
I to investigate galaxy-wide emission in interacting and isolated systems. Because the 
DDSCAN processing co-adds all IRAS survey scans covering a source, these data provide 
the most sensitive survey measurements from the IRAS mission, typically 2-3 times better 
int Source Catalog. This enables better assessment to be made of the mid- 
and 25 pm) emission, which can contribute significantly to the total infrared 
luminosity. Furthermore, ADDSCAN source profiles of the CPG galaxies can be examined 
to determine more accurately whether close pairs of galaxies have been resolved. The 
magnitude limit of the samples was mpI I 15.0 or mtot 5 14.3 for close pairs. 
The distributions of the integrated 12-100 pm luminosities of the KI and CPG sample 
galaxies are shown in Figure 3. The CPG pairs have been divided into two sets: the 
first being pairs with projected separations smaller than the IRAS be- size (unresolved 
416 
pairs) and those seRarated widely enough to have been resolved by the satellite. Unlike 
the nuclear 10 pm luminosities, there is no significant difference in the distributions of the 
CPG and KI integrated luminosities. Haynes and Herter (1988) found a similar null result 
when examining the 60 and 100 pm emission from widely separated CPG pairs. 
The presence of a nearby companion does have some influence on the integrated in- 
frared properties of a galaxy, however, as shown in Figure 4. The distribution of the 
ratio of infrared-to-optical luminosities of CPG systems ranges extends nearly an order 
of magnitude higher than for KI galaxies. If the ratio Lir/Lopt can be taken in part as a 
measure of the star formation rate in a galaxy, then on average, close pairs exhibit only 
a slight enhancement in gal^ a;'cy-wide star forming activity. This concurs with the findings 
of Kennicutt et al. (1987) who found only a mild enhancement in disk star formation in 
their sample of interacting pairs. Interestingly, the CPG galaxies with the highest values 
of Lir/Lopt are not the most luminous cases. 
CPG and KI galaxies span a similar range in mid- and far infrared colors, as is shown 
in Figure 5. The CPG source do exhibit a slightly larger scatter in each color, reminiscent 
of the larger scatter in optical colors found in interacting galaxies by Larson and Tinsley 
(1978). We do not find evidence for systematically higher color temperatures among close 
pairs, as was reported by Telesco, Wolstencroft and Done (1988) for pairs drawn from the 
Arp Atlas. In addition, we have been unable to find any correlation between the infrared 
luminosity, Lir/Lopt, or infrared color of the CPG pairs and pair separation, relative size 
or relative velocities. If outright collisions or mergers lead to extremely luminous infrared 
emission (e.g. Sanders et al. 1988), our analysis may be expected to miss such sources 
since the CPG is biased against very close pairs and mergers. 
There does appear to be a weak dependence of Li, on interaction morphology, as 
is shown in Figure 6, which is also present in Lk/Lopt (not shown). If the interaction 
morphology can be interpreted aa an approximate age indicator of the encounter through 
comparison with numerical simulations, the SEP systems should be the youngest (no sign 
of disturbance) or possibly the oldest, followed by the disturbed pairs (DIS), the LIN pairs - 
those showing linear bridges or tails, and finally the pairs enshrouded by common envelopes 
(ATM). The median luminosities and colors then show when the induced star formation in 
each class must reach its peak. Considerable dispersion is introduced due to the different 
morphological types involved in the interactions, uncertain viewing geometries, and coarse 
morphological classifications. One means of clarifying this relationship may be to correlate 
the ages of interactions deduced from numerical simulations to ages from starburst models. 
41 7 
REFERENCES 
Cutri, R.M. and McAlary, C.W. 1985, Ap, J., 290,90. 
Haynes, M.P. and Herter, T. 1988, A.J., 90, 504. 
Karachentsev, I.D. 1972, comm.spec.Aatrofiz. Oba., 7 , l .  
Karachentseva, V.E. 1973, Comm.Spec.Aatroliz.Oba,, 8, 1. 
Keel, W.C., Kennicutt, R.C., Hummel, E. and van der Hulst, 3.M. 1985, AJ., 90,708. 
Kennicutt, R.C., Keel, W.C., van der Hulst, J.M., Hummel, E. and Roettiger, K.A. 1987, 
A.J., 93, 1011. 
Larson, R.B. and Tinsley, B.M. 1978, Ap.J., 219,46. 
Rieke, G.H. 1976, Ap.J.(Lettere), 200; Ll5. 
Sanders, D.B., Soifer, B.T., Elias, J.M., Madote, B.B., Neugebauer, G. and Scoville, N.X. 
1988, Ap.J., 32b, 74. 
Telesco, C.M., Wolstencroft, R.D. and Done, C. 1988, ApJ., 329, 174. 
I 
CPG 
6 7 8 9 10 
Figure 1 -The 10 pm luminosity distribution of BC3 
galaxies (top) and IU galaxies (bottom). Open born 
npmsent 30 upper limits to luminosides. 
11 
10 
9 
I 
A s 
v 
.!a 
CJ 
CPC - Unresolved 
a Resolved 
7 I I I I I 
0 1 2 
11 I I I I 1 
rBUx Fig- 2 -The rad0 of larm beam IRAS 12 densities to small aperruFa ground based 10. flux 
densities. Upper and lower limits are denoted by 
Btrow1I. 
418 
80 
80 KI G a l a x h  i 40 
20 
0 
5 8  7 8 0 10 11 12 
Log L i A L O )  
Figwe 3 - The integrated 12-100 pm luminosities for 
CPG and KI 
ADDSCAN P ata Fbr u ~ o l v c d  CPG pairs (center) 
the average luminosity per galaxy is displayed. 
axies calculated using IRAS 
- I  
- I  -.5 1.6 2 
2 I 
tog F:o/Fzl 
1 ' 1 ' 1 '  
1.5 0 
0 
- CPC Unrerolred, , 
-1 I '  I 1 I l l  
-1 -.S 0 .6 1 1.5 
I Log FZdFli 
Figure 5 - The mid- and far-infmed colors of CPG 
and KI galaxies taken &om IRAS ADDSCAN &a. 
0. 
0 
41 9 
Figure 4 - The integrated inftared luminosity of CPG 
and KI pdaxies as a function of infkanzd-to-optical 
luminoslly ratio. 
,'7 48 " " 1 , , , , 1 , , , , 1 , , , ' 1 , ' , ' , ' ,  
e 7 e 10 I2 
e 7 e e 10 11 12 
e 7 e 0 10 I! I2 
W E . ' . .  , . . , I , . , , I , , , , l . , . . l . . . . $  
e 7 e 0 10 I2 
Log L d L )  
Figure 6 -The integrated infrared luminosity 
disaibulion for each class of CPG interaction . Luminosities for resolved pairs are 
////, and unresolved pairs with \\\ 


Nuclear and extended infrared emission in paired and isolated galaxies

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server