Preliminary results from a program to map the thermal far-infrared emission from cool dust in elliptical galaxies using the Yerkes 60-Channel Camera on the Kuiper Airborne Observatory (KAO) are presented. The 160 micron emission from the elliptical NGC 6542 is apparently extended over the optical galaxy whereas the 100 micron emission is unresolved. This implies a dust temperature gradient consistent with that expected for dust with Galactic properties exposed to the general interstellar radiation field of the elliptical galaxy. Observations of the elliptical NGC 5666 and the NGC 7463/4/5 compact group (consisting of the elliptical NGC 7464, the S0 NGC 7465, and the spiral NGC 7463) are also discussed

Harper, D. A.

Knapp, G. R.

Lees, Joanna F.

Rupen, Michael P.

English

NASA Technical Reports Server

FAR-INFRARED MAPPING
GALAXIES
OF DUSTY
5/-/--
N95- 21763
101 )
/-
ELLIPTICAL
<¢
/
/
JOANNA F. LEES AND D. A. HARPER
Dept. of Astron. and Astroph., the University of Chicago, 5640 S. Ellis
Ave., 571icago, IL 60637
iVI. P. RUPEN
National Radio AstTvn. Obs., P.O. Box 0 SocorTv, NM 87801
G. R. KNAPP
Dept. of A_troph. Sci. Princeton University, Princeton, NJ 08544
ABSTRACT Prdiminary results fi'om a program to map the ther-
mal far-infrared emission fi'om cool (lust in elliptical galaxies using the
Yerkcs 60-Channel CaInera on the Kuipcr Airborne Observatory (KAO)
are presented. The 160 tml emission from the elliptical NGC 6524 is ap-
l)arently extended over the opticM galaxy whereas the 100 pm emission
is tmresolved. This implies a (lust temf)erature gradient consistent with
that expected tbr (lust with Galactic prol)erties exposed to the general
interstellar radiation lield of the elliptical galaxy. Observations of the
elliptical NC, C 5666 and the NGC 7463/4/5 compact groul) (consisting
of the elliptical NG(_.' 746,1, the SO NGC 7,165, and the spiral NGC 7463)
are also discussed.
INTRODUCTION
Early-type galaxies generally are dominated by an old stellar population and
contain little gas and dust compared to the typical late-type spiral. However,
since the launch of the II/AS satellite in the mid-t980's, it has been known that
many of these systems contain small quantities of cold interstellar matter: ,15%
of all elliptical galaxies show thermal dust emission at 60 - 100ttm (Knat)p et al.
1989) with teml)eratures apparently similar to dust in spiral galaxies. Ratios of
global gas quantities (such as CO and HI 21 Cln emission) to the far-infrared
emission are also indistinguishable from those tbr spirals (Lees et al. 1991).
However, before last }'ear, only one dusty elliptical galaxy (NGC 5128; Cen
A) was close enough to be fully mapped 1)y II(AS (Eckart e t al. 1990) and at
higher resolution with the KAO (Joy et al. 1988; see also Lcster 1993, these
proceedings). Only two dusty ellipticals, both strong radio sources (Cen A and
Per A), had been observed at all at wavelengths between 100 tim and 2 ram.
S. "ferebey asld J. Mazzmella (edb.), Science with High-Spa{ial Re_olution Far Infrared Data, 101-106,
1994, Jet Pl'opulbion Laboratory, Pabadena, CA.
https://ntrs.nasa.gov/search.jsp?R=19950015346 2020-06-16T08:24:46+00:00Z
102 LEES ET AL.
. 1 0 _0 30 40 50 60 '70 £0 90 3oq "i] It
11ol ... /1J_o
"::-: 111
,ol ff/t(ltu B/ .... ,,o
•._.-'_{i'.,_,_ --.., ;, I:;7,I ' Q k %.__[;']..;...... I• , .., _'_ - .,, ;..-',_;_-;'
so | \ _ :_:_;}:'-'-'.-":' I so
Z"2 I
<'o/ Fo
10 20 30 40 50 60 70 80 90 lO0 110
FIG U RE I The 160 tLm KAO map of NGC 6524. The positive contours show
the ON beam (see text) at 1.5rr, 2.1c,, 2.7a, 3.3a, etc. The negative (dashed)
contours show the OFF beams. Each pixel in the image is :l".5 and the resolution,
shown in the upper right, is ,1,1".
OBSERVATIONS
In 1992 we began a l)rogram to study the infrared properties of IRAS-bright
elliptical galaxies. In April and July 1992 we mapped three ellipticals in the
far-infrared using the Yerkes 60-channel camera on the Kuiper Airborne Ob-
servatory. The camera is an 8 x 8 bolometer array (without the corner pixels)
operating at the diffraction limit of the KAO telescope with pixel sizes of 16",
25", ,l,l", and ,1,1" at wavelengths of 60, t00,160, and 200 #m respectively (results
from an earlier version of the camera with 32 pixels are presented in Engargiola
1991).
We are also involved in projects to obtain JHK images of dusty ellipticals
using the G I/IM near-infi'ared camera on the ARC telescope at Apache Point,
New Mexico and to detine the 350-1100 #m submillimeter spectra of these galax-
ies using the James (_?lark Maxwell Telescope in Hawaii. Our ultintate goal is
to use the stellar radiation tield derived from the near-infl'ared images and the
far-infi'ared and submillimeter photonmtry of the thermal dust emission to ac-
curately model the equilibrium dust emission from elliptical galaxies.
FIR MAPPING OF DUSTY ELLIPTICAL GALAXIES 103
Ii0
i00
90
8O
70
60
5O
4O
30
2O
I0
10 20 _0 40 50 60 70 _0
@
:< .i81:i 
". -. '4 i.
• .-/ ,Ip -. v
ol io | "2
.i 0
,_|11 • • h .10.
• Ol. i I-I1 i
e, Ja o • • .,,a.j_
.i_'." r. .... ,_,:: ";X::_
I-" . .| _i
' |'.|o ;.tso_
_;.'¢r _ :;.i_ _. .'..,_;m |. i .-. _
_,1. ...'._.
.,,-..... _-_-.,_,¢.__ ..
•',. :._
:,: ,.:
lle • ,|
•! ,:,
;.,,;
='..'.-'.
i0 20 30 40 50 60 70 80 90 i00 1
Ii0
i00
9O
8O
70
6O
50
4O
3O
2O
I0
FIGU RE 2 The 100/ml KAO real) of NGC 652,h The positive contours show
the ON beam (see text) at 2(7, 2.5a, 3.1a, 3.6a, etc. The negative (dashed)
contours show the OH" beams. Each pixel in the image is 2" and the resolution,
shown in the upper right, is 25".
RESULTS
In Figures 1-3 we show tile far-infrared mal)s of NGC 652,1 (at I60 and 100
lira) and of NGC 5666 (at 160 ;Lm) obtained from the KAO. At 160 #m our
resolution is 44" and the area plotted in Figures 1 and 3 is about 6'.4 on a side.
At 100 tLm tile resolution is 25" and the lield of Figure 2 is about 3'.7 x 3'.7.
lit order to maximize the integration time on these relatively faint objects
we used a small chop throw of about 2'which meant the source was on the array
on both ON and OI"F beams. The result of doing the background subtraction
(ON-OFF) produces two negative half-intensity images of the source oil either
side of the positive image. This can be seen clearly in I,'igures 1-3.
NGC 6524 is classiiied as E/S0 in the UC, C catalog. It is quite isolated,
with the nearest neighbor being ahnost a degree away, and has a weak active
nucleus with broad emission lines (ivlerighi et al. 1991). It has the distinction
of being the second-brightest elliptical at far-infrared wavelengths (after Cen A)
with tlux densities measured by IRAS of 7.9 Jy at 100 tmi and 3.9 Jy at 60 #m
(Knapp et al. 1989).
The most striking result froin our KAO observations of NGC 6524 shown in
Figures 1 and 2 is that the galaxy appears to be clearly resolved perpendicular
104 LEESET AL.
ii0
I00
90
80
70
6O
40
30
20
I0
I0 20 so 40 _o tiff 70 flO 90 10011
•_ ;.I=-I_0. • a.il
|.e,b| .i t !- "llJ
i. I i I i. •. _ iII Is l.Ilk. I• _" . °l I
'-"':r--_;:.--("_ ....."_--
• •..,,_. _"- "T_FI"
. :-:..
_'° =p
i I i ° =_. i
i • l, ii..o
-..*-.=.....;.
II0
I00
90
8O
70
6O
5O
40
30
10
I0 20 30 40 50 60 70 80 90 i00 ii0
HGURE 3 Tile 160 #m KAO real) of NGC 5666. The positive contours show
tile ON beam (see text) at 2or, 2.,la, 2.8(r, 3.2a, etc. The negative (dashed)
COlltours show tile OFF beams. Each pixel in the image is 3".5 and tile resolution,
shown in the ul)per right, is 44".
.75
.5
.25
I • . I
50 1 O0
Column (pixels)
FI(;UI{E ,1 Cut through tile NGC 6524 160 #m peak, l)erpendicular to the
chop direction (solid line), and through a point source observed oil the same
night (dashed line). The abscissa is cohunn number in pixel_ (each l)ixel is 3".5
and the ordinate is far-infrared flux density relative to the peak. The resolution
is ,1.1" or about 13 pixels.
FIR MAPPINGOF DUSTYELLIPTICAL GALAXIES 105
to the chopdirectionat 160tim (Fig. 1). A one-dimensional cut through tile
KAO 160 jtnt map is compared to that for a point source observed on the same
night in Figure 4. The NGC 6524 profile resembles a point source superposed
on lower-level extended emission. This extended emission is at about the 4a
level in our data, and we intend to reobserve this galaxy in 1993 to confirm this
result. The 100 ttm mat) in Figure 2, in contrast, shows no such extent, even
though the resolution and map scale are almost twice as high. The FWHM of
the 160 t,m emission is about 2_ (the optical size is V.7), but at 100 #m the
FWItM is less than 25".
The 160 and 100 #m KAO data imply a radial dust temperature gradient
in NGC 6524. 1,br a dust emissivity (u = 2) and grain parameters like those
in our Galaxy, the central dust temperature is 29°K, in agreement with the
observed IRAS 60 and 100 #m ttux densities (Knapp et al. 1989) and our recent
submillimeter photometry at the JCMT (Knapp, Lees & Rupen, in preparation).
In the outer parts of the galaxy (r _ V) the dust temperature must be less than
22°K. A simple model for optically thin dust in equilibrium in the old stellar
radiation field delined by recent H and K band photometry by us at Apache
Point predicts a (lust temperature gradient of 29°K in the inner KAO beam
to 20°K in the outer parts, in excellent agreement with our data. We hol)e to
acquire additional observations of NGC 6524 this year on the KAO to actually
measure the dust temperature in the outer parts of the galaxy.
Figure 3 shows our 160 #m KAO map of the isolated, gas-rich compact
elliptical NGC 5666. NGC 5666 aI)pears to be unresolved at this wavelength,
which is not surprising considering the fact that its optical size is less than an
arcminute. Its CO emission is also probably very compact (Lees et al. 1991) as
is the central H(_ and thermal radio emission (Wrobel & Heeschen 1988), but
it has an extended, rotating H1 disk over :¥ (Lake, Schommer & van Gorkom
1987) which apparently does not emit strongly at 160 #m. Like NGC 652,1, the
1RAS 60-100 #m measurements, our 160 #m data point, and our recent JCMT
submillimeter photometry indicate a central dust temperature of about 27°K.
The compact interacting system NGC 7463/,1/5 was also mapped at 160
#m, but unfortunately the data were of poor quality due to telescope stability
problems on the KAO last July. The SO NGC 7465 and the spiral NGC 7463
were both apparently detected, with NGC 7,16::1having significantly cooler dust
emission. This is also evident in the II/AS CPC images of this group (van Driel
et al. 1993).
ACKNOWLEDGMENTS
This research was supported by NASA grant NGR 14-001-227.
REFERENCES
Eckart, A., et al. 1990, ApJ, 363,451
Engargiola, G. 1991, ApJS, 76,875
Joy, M., Lester, D. F., Harvey, P. M., & Ellis, H. B. 1988, ApJ, 326,662
106 LEES ET AL.
Knapp, G. R., Guhathakurta, P., Kim, D.-W., & Jura, M. 1989, ApJS, 70, 329
Lake, G., Schommer, R.A., & van Gorkom, J.H. 1987, Apd, 314, 57
Lees, J.F., Knapp, G.R., Rupen, M.P., & Phillips, T.G. 1991, Apd, 379, 177
Merighi, R., Basso, L., Vigotti, M., Lahulla, J.F., & Lopez-Arroyo, M. 1991,
ANAS, 89, 225
Wrobel, J.M., & Heesehen, D.S. 1988, ApJ, 335,677
Van Driel, W., de Graauw, Th., de Jong, T., & Wesselius, P.R. 1993, A_AS, in
press


Far-infrared mapping of dusty elliptical galaxies

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server