New 8 to 13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8 to 13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central regions of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet induced star formation in NGC 1068

Fazio, G. G.

Gezari, D. Y.

Hoffmann, W. F.

Lamb, G. M.

Mccreight, C. R.

Shu, P. K.

Tresch-Fienberg, R.

English

NASA Technical Reports Server

N87- 2437 0
STRUCTURE IN THE NUCLEUS OF NGC 1068 AT i0 MICRONS
R. Tresch-Fienberg I, G. G. Fazio I, D. Y. Gezarl 2 W. F Hoffmann 3
G. M. Lamb 2, P. K. Shu 2, and C. R. McCreight 4
New 8 - 13 #m array camera images of the central kiloparsec of Seyfert 2
galaxy NGC 1068 resolve infrared source structure which is extended and
asymmetric (2.1 x 0.7 arcsec FWHM), with its long axis oriented at position
angle 33 °. Infrared emission 1-2 arcsec to the northeast of the very center of
the galaxy appears coincident with a weak, barely resolved, discrete source in
the kiloparsec-scale Jet detected in published radio continuum maps of the
galaxy•
Very Large Array (VLA) observations show a linear, clumpy structure some
10-15 arcsec (N 1 kpc) long, extending to the NE and SW of the nucleus. This
feature is usually described as a jet (Wilson and Ulvestad 1982, 1983; Pedlar
et al. 1983) though at sub-arcsec resolution the emission nearest the center of
the galaxy is asymmetric in position angle (van der Hulst, Hummel, and Dickey
1982; Wilson and Ulvestad 1983). Condonet al. (1982) reject the jet
hypothesis altogether, arguing instead that the radio emission arises from
supernovae in regions of intense star formation.
There is clear evidence of star formation in the disk of NGC 1068. The
infrared (IR) spectrum of NGC 1068 resembles thermal IR spectra seen in
galactic HII regions and molecular clouds. About 98% of the galaxy's
bolometric luminosity is emitted between 1.5 #m and 3 nan (Rieke and Low 1975;
Telesco, Harper, and Loewenstein 1976; Hildebrand et al. 1977; Telesco and
Harper 1980). A I0 #m map and far-IR aperture photometry (Telesco et al. 1984)
show that about 10% of the flux density at A < 20 #m, and virtually all of the
longer wavelength IR radiation, arises principally from the galactic disk at
3 < r < 18 arcsec, in a region where CO emission also has been detected
(Rickard et al. 1977; Scoville, Young, and Lucy 1983).
The infrared images of NGC 1068 (Figure !) were used to derive maps of the
spatial distribution of 8 - 13 #m color temperature (Figure 2) and warm dust
opacity (Figure 3). The results suggest that there exist two point-like
luminosity sources in the central region of NGC 1068, with the brighter source
at the nucleus and the fainter one some i00 parsecs to the northeast. This
geometry strengthens the possibility that the i0 #m emission observed from
grains in the nucleus is powered by a non-thermal source. In the context of
earlier visible and radio studies, these results considerably strengthen the
case for jet-induced star formation in NGC 1068.
_Harvard-Smithsonian Center for Astrophysics
_NASA Goddard Space Flight Center
_Steward Observatory, University of Arizona
NASA Ames Research Center
Carol J. Lonsdale Persson (Editor)
Star Formation in Galaxies 717 F,_.._c_.,G pAGE BLANK NOT FILMED
https://ntrs.nasa.gov/search.jsp?R=19870014937 2020-03-20T11:07:09+00:00Z
R. TRESCH-FIENBERG ET AL.
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Right Ascension (1950) Right Ascension (1950)
Figure 1--Calibrated isophotes for the array came, a images of NGC 1068.
In each case, the lowest contour level is 3a above the mean background
intensity in the periphery of the field of view, which has been subtracted from the map.
The hatched square represents one 0.78 × 0.78 arcsec IR CID pixel. The contour level
spacing is 1.5a at all wavelengths: 8.3 /zm (upper left), g.8 x l0 g Jy ster-1; 9.7 #m
(upper right), g.1 x 109 Jy ster-1; 11.2 #m (lower left), 1.3 x 101° Jy ster-1; and 12.4
#m (lower right), 1.6 × 101° Jy ster -1.
718
10#mNUCLEARSTRUCTUREINNGC1068
The imaging observations of NGC 1068 were made at the Infrared Telescope
Facility (IRTF) on Mauna Kea, Hawaii, on 1983 August 16 using the Goddard
infrared array camera system, which is based on a 16 x 16 pixel Si:Bi charge
injection device (CID) array (Lamb et al. 1984; Gezari et al. 1985; Tresch-
Fienberg 1985). The images were obtained in four bandpasses, with effective
wavelengths of 8.3, 9.7, 11.2, and 12.4 _m and bandwidths of about 10% (Figure
i). The field of view of the array for these observations was 12.5 x 12.5
arcsec, corresponding to approximately 0.9 x 0.9 kpc.
Atmospheric conditions during the observations were very favorable; visual
seeing was better than i arcsec. At the IRTF, the optical plate scale at the
detector is 0.78 arcsec/pixel, and the diffraction-limited FWHM instrumental
profile of a point source ranges from 0.9 to i.I arcsec between 8.3 and 12.4 _m
(compared with A/D = 0.7 arcsec at I0 _m). The actual spatial resolution of
the camera system, determined from the size (FWHM) of point source calibration
images, was 2.3 arcsec in R.A. and 1.3 arcsec in Dec. at all wavelengths.
The presence of a distinct IR source NE of the nucleus was tested by
subtracting an instrumental point spread function (obtained from images of the
reference star p Peg, c.f. Figure 5) from the array camera images and examining
the remaining emission. This is appropriate because the galaxy is known to
contain a compact source at its very center, based on speckle interferometry
(Meaburn et al. 1982, McCarthy et al. 1982) and radio mapping (van der Hulst,
Hummel, and Dickey 1982; Wilson and Ulvestad 1983).
All the images of NGC 1068 show substantial residual emission following
the subtraction of a point source from the nucleus. This emission is
concentrated in a small region 1.7 + 0.4 arcsec to the NE of the nucleus at
position angle 39" _ 3". Within th_ uncertainties of measurement, this region
coincides with the apparent extranuclear color temperature peak; it appears to
be the IR counterpart of the weak radio feature described above. This new IR
source emits 35% + 10% of the total i0 #m flux density within the central 7
arcsec of the gal_xy, or 7.3 + 2.1Jy. This demonstrates that a substantial
fraction of the I0 _m emission from the central region of NGC 1068 is
associated wih the radio Jet outside the galaxy's core.
Close inspection of the 6 cm maps of Condonet al. (1982) and Wilson and
Ulvestad (1983), as well as the 18 cm map of Pedlar et al. (1983), reveals a
weak but clearly present peak in the radio continuum jet, 1.4 + 0.2 arcsec NE
of the nucleus at position angle 41" + 9°. The i0 _m emission-NE of the
nucleus extends to the position of th_s faint radio peak, and the new color
temperature and dust density maps described above indicate that there is a
luminosity source there.
The existence of the NE source may be further confirmed by comparing the 8
- 13 _m appearance of the nuclear region of NGC 1068 with a simple model.
Figure 4 shows a contour diagram of an IR array camera image that could result
at the IRTF when observing two point sources separated by 1.6 arcsec at a
position angle of 35", with the NE source 54% as luminous as the primary
source. Comparison of the real and synthetic galaxy images shows that the
i0 _m morphology is reproduced quite well by this model.
719
R. TRESCH-FIENBERG ET AL.
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NGC 1068
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8.3/12.4 pm Tc
I I I 1
I I I I I I
7:3 7.'0 8.'7
02 h 40 m
Right Ascension (1950)
Figure 2 -Map of the mid.IR color temperature neax the nucleus of NGC 1068, derived
from the 8.3 amd 12.4 pm array camera images. Contours are plotted at 2,_K int411rv_s
between 300 and 425K, with the peak temperature in the NE of the map.
O_
o
II
._=
m
o
-00* 13'26"
-00"13'30"
-00" 13'34"
NGC 1068
I I I
"remtslq©
I I I I
I I I I I I
7:3 7.'o 6:7
02 h 40 m
Right Ascension (1950)
F_ure 3-Map of the emission optical depth (and, by inference, the relative dust den-
slty) near the nucleus of NCC 1068, derived from the 8.3 ,am intensity map and the
¢_k_r tmnper&ture map. Contours are plotted from r = 6.66 × 10 -8 to 2.33 x 10 -4, with
• level spacing of 3.33 x 10 -s.
t_
O_
e=
O
-00"13'26"
-00013'30"
- 00" 13'34"
NGC 1068 (Synthetic) 8.3 pm
i I I I I
I I I I I I
7'3 7:o o.'7
02h 40 =
Right Ascension (1950)
Figure 4 --Contour diagram of a synthetic image generated by computing the IR array
camera's response on the IRTF to a source comprised of two polnt-like objects separated
by 1.6 arcsec at a position angle of 35 °, with the NE source 54% as luminous as the
primary source and.spatial resolution at 10 #m of about 1.8 arcsec (the average of the 2.3
and 1.3 arcsec resolutions in R.A. and Dec. actually achieved during the observations of
NGC 1068 in August 1983). The position of the primary source on the array corresponds
to the Lssumed position of the galaxy's nucleus in the 8.3/_m array camera map (Figure 2) •
I NGC 1068
1.0-
0.9-
0.8-
0.7-
0.6-
0.5-
-_ 0.3-
_=
0.2
0.1
0.0 I I I , _" _
432 101234
Pixels from Peak
(North)
18 Peg
41.
4321 1234
Pixels from Peak
(South) (North) (South)
Figure S-Intenslty profiles of NGC 1068 (left) and /_ Peg (right) at 8.3 .m (circles),
0.? .m (squares), 11.2 .m (triangles), and 12.4 .m (diamonds). These were generated
using a I x 5 pixel (0.78 x 3.9 arcsec) =slit" a.s described in the text to simulate the
declination slit scans of Becklin et al. (1973). All scans have been normalized to 1.0 at
the peak. A sample error bar (representing only the statistical measuring uncertainty) is
shown for NGC 1068; the uncertainties for/_ Peg are smaller than the plotted symbols.
720
10/zm NUCLEAR STRUCTURE IN NGC 1068
The principal conclusions of this work are:
i. Direct images reveal an asymmetric IR source consisting of a bright
peak plus extended emission several arcsec toward the NE at position angle 33 °.
If the IR peak is assumed coincident with the vlslble/radlo nucleus, then the
I0 #m morphology may be interpreted as a superposition of at least two sources
- one at the very center of the galaxy and another some 1.5 arcsec to the NE in
the radio jet, coincident wih a weak radio continuum peak.
2. Maps of 8.3/12.4 #m color temperature and IR emission optical depth
(i.e., dust density) suggest that at least two sources of luminosity are
required in the central few hundred parsecs of the galaxy. The new data are
consistent with the 8 - 13 #m radiation arising from thermal emission by dust
grains, but a compact, non-thermal source may be responsible for some of the
grain heating.
3. These results suggest that the extra-nuclear radlo/IR source could be a
region in which star formation has been triggered by the ejection of matter in
a jet from the Seyfert nucleus.
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Becklin, E. E., Matthews, K., Neugebauer, G., and Wynn-Williams, C. G. 1973,
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Condon, J. J., Condon, M. A., Gisler, G., and Puschell, J. J. 1982, Ap. J.,
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Gezari, D. Y., Tresch-Fienberg, R., Fazio, G. G., Hoffmann, W. F., Gatley, I.,
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Hildebrand, R. H., Whltcomb, S. E., Winston, R., Stienlng, R. F., Harper, D.
A., and Moseley, S. H. 1977, Ap. J., 216, 698.
Lamb, G., Gezari, D., Shu, P., Tresch-Fienberg, R., Fazio, G., Hoffmann, W.,
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Wilson, A. S. and Ulvestad, J. S. 1983, Ap. J., 275, 8.
721


Structure in the nucleus of NGC 1068 at 10 microns

Structure in the nucleus of NGC 1068 at 10 microns

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