Intergalactic plasmas were investigated from both an observational and theoretical point of view. A multiobject spectrometer, the MX spectrograph was used to obtain detailed dynamical information on clusters of galaxies; this information was then compared with X ray emission from hot gas in these clusters. Several spectra of galaxies are presented, and data reduction of the spectra was discussed. The existence of quasar winds in Seyfert galaxies and the interaction between such a wind and the interstellar medium also were considered

Scott, J. S.

English

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https://ntrs.nasa.gov/search.jsp?R=19840022998 2020-03-20T22:42:46+00:00Z
a(NASA-CR-173825) STUDIES GF X-RAY CLUSTERS
	 N84-31008
OF GALAXIES/INTERGALACTIC PLASMAS Final
	 xr,
Report (Arizona Univ. , Tucson.)
	 16 p
JC A02/MF A01
	 CSCL 038	 Unclas
63/90 20116
FINAL REPORT
PREPARED FOR THE
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
GRANT NUMBER
NAGN - 124
STUDIES OF X-RAY CLUSTERS OF GALAXIES/
INTERGALACTIC PLASMAS
i
PRINCIPAL INVESTIGATOR:
Dr. John S. Scott
Steward Observatory
University of Arizona
Tucson, Arizona 85721^^
^	 ^ G
REPORT SUBMITTED BY:
Yh .a L g,
Dr. John T. Stocke
	 ^p
DATE:
	
	 L
August 22, 1984
I&
I. PURPOSE
The purpose of this NASA SRT grant was to study intergalactic
plasmas from both an observational and a theoretical point of view.
The observational work focussed on the development of a unique new
spectroscopic technique designed to simultaneously obtain the spectra
of 44 galaxies in a cluster of gelaxies. This automated multi-object
spectrometer, the "MX Spectrograph", now ma!-es it possible to obtain
detailed dynamical information on clusters of galaxies that can be
compared with X-ray emission from hot gas in these clusters.
The theoretical portion of the grant involved the study of QSO
winds and their effects on the interstellar and intergalactic
environment.
The principal investigator, Dr. John S. Scott, left Steward
Observatory and the astronomical community to accept a job in private
industry during the course of this grant (August 1983). Dr. Scott
L
chose to no longer be associated with this research or this research
grant after his departure. Therefore, this final report has been	 j
prepared by Dr. John T. Stocke who has been associated with the grant I
only since Dr. Scott's departure. I
Prep ^'.:- • a and reprints supported by this grant are attached.
t
j	 ^ ,
(+)
E
II. OBSERVATIONAL STUDIES OF CLUSTERS OF GALAXIES
Progress on observations of clusters of galaxies with the MX
Spectrometer has been slow, but steady. The MX mobile fiber
spectrometer is now in the construction phase, and should be
operational by the winter (1984-85) observing season. Earlier
observations of 250 galaxies with the Medusa aperture plate system and
an intensified CCD detector are now in the reduction stages.
Preliminary results are outlined in Section A below in excerpts from
Dr. John Hill's Ph.D. dissertation (1984). A major activ.ty since the
departure of Dr. John Scott has been the development of an efficient
data reduction system capable of handling the large amounts of
spectrescopic data produced by multiple fiber spectrometers. The
system we have developed is described in another section of Dr. Hill's
dissertation (see Section B below). NASA funds have been used to pay
student programmers and to purchase a pair of removable disk packs for
the VICOM image processor with which the multi-object spectra will be
reduced.
A. Observations wW the Medusa Spectrograph
Figure 3 shows a set of galaxy spectra from a 3 hour
exposure on A576 taken in December 1980. The dispersion was 250 A
mm- 1
 from a 300 1 mm- 1
 grating with a resolution of 12A. Velocities
were measured from this N2 baked 11IaJ photographic plate and several
others to an accuracy of 90 km 9 -1 by Hintzen, et al. (1982). The
2
3
ifA..^b• ./ r:- is •.^-Jr_ ...
ORIGINAL' PAC7
OF POOR QUALiVY
A578A-1 plate ♦3005 12/1/80
HAK H9
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— —
•--
•	 0: to - -
	
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i cma-•	 HMr3 40 •. .	 .• .	 .
n 1
a
n
►+.Ar :	 .	 .	 .	 ..IP. .
W2	 -	 •
H•Ari	 •	 I	
I
400nm	 450nm	 500nm	 550nm
Figure 3. Photograph of 37 Spectra from A576
This figure shows intensified photographic spectra of 37 objects
in the cluster of galaxies Abell 576. A three hour exposure at the 2.3m
telescope, December 1980. The spectra are identified by galaxy number
and blue is to the left.
	
14
1i
3
wavelength scale is labelled on the spectra along with galaxy ID
numbers. The position of the redshifted calcium H and K lines is also
indicated. The heliocentric redshift of A576 is 0.0381 ± 0.0005. The
global radial velocity dispersion derived from measurements o' 47
galaxies in A576 was found to be 914 ( + 113, -83) km s -1 . Since the
cluster gas density varies with the square of the velocity dispersion,
our observations imply that the gas density is only 2/3 the value
adopted by White and Silk (1980). This strengthened their conclusions
from X-ray data, that there was too little hot gas to account for the
observed microwave decrement. More recent microwave observations at 6
cm by Lasenby and Davies (1982) have failed to show any significant
microwave decrement in A576. Rothenflug, et al. (1983) report Solid
State Spectrometer observations showing in the center of the cluster a
lower X-ray temperature which is consistent with the observed galaxy
velocities. They suggest that the lower X-ray temperature may be due
to a cooling flow in the X-ray gas or to the emission of individual
cluster galaxies. Neither X-ray nor optical data are able to
distinguish between these two modes. Birkinshaw and Gull (1984)
describe the state of recent microwave decrement observations in
serveral cluster.
The results above assume that both the gas and the galaxies are in
equilibrium, and that their distributions reflect the same symmetric
potential. Our sample of velocities in A576 provides no evidence for
large-scale cluster rotation. Therefore, the line-of-sight velocity
dispersion is a good measure of the gravitational potential of the
ti7
4system. The radial velocity dispersion shows only a slow decrease
with increasing radius from the cluster center. This seems to confirm
the conclusion, which White and Silk draw from X-ray observations,
that the binding mass of the cluster is distributed over a region
significatly larger than the "cluster core". Additional studies are
underway to provide more data on the velocity structure of the
galaxies in A576.
The Medusa spectrograph has collected about 800 spectra of galaxies
as of Febreary, 1983. The major portion of these (200 redshifts) will
be published by Hill, et al. (1984) . Figure 4 shows plots of raw
spectra of five galaxies in the cluster Abell 2151 obtained with the
intensified CCD detector at the 2.3m telescope. This single ?0-minute
exposure includes galaxies with visual magnitudes from 15.0 to 17.5.
Additional exposures were taken to measure the redshifts of the
fainter galaxies. The spectral resolution is 12 Q FWHM. The CCD
allows more sophisticated data reduction including subtraction of the
sky background obtained with fibers looking at empty areas of the
field. Except for flexure, the fixed format of the CCD allows direct
velocity calibration of each fiber by taking full-field comparison
lamp exposures. This added complexity also requires more time spent
at the computer to obtain a radial velocity.
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u)
F-
Z
O
U
-^.M
^W^
380	 400	 420	 440	 480	 480	 600	 820	 840	 680	 880
WAVELENGTH (nm)
Figure 4. Plots of CCD Spectra from Abell 2151.
This figure shows raw Medusa spectra of galaxies in the cluster
Abell 2151 (Hercules) were taken on 14 June 82 at the Steward 2.3m
telescope (exp A2151-1.G6). These spectra are 5 of 31 which were
extracted frow a single 20-minute intensified CCD exposure. All galaxy
spectra are plotted on the same scale with a vertical offset added.
[41	
. _
	
i	 y	 1
[q	 5
B. Data Reduction
A series of programs and CLIs (macros) designated MARS = Multi
Aperture Reduction System have been written by J. Eisenhamer, D.
Silva, and M. Wenz, under the guidance of J. Hill with occasional
assistance by A. Koski. The major features of MARS not seen in other
spectral reduction systems include: a program that locates the
indivudual spectra on a CCD frame and extracts them into a
one-dimensional format, and a program that automatically fits
dispersion curves to a series of similar HeAr spectra when supplied
with an initial guess at the dispersion curve and a catalog of
measurable lines. The MARS driver routines and all 1-D spectra
manipulations run on the Data General Eclipse (S-250) computer under
AOS. The two-dimensional erica manipulations such as flat fields,
frame alignment and defect removal are presently being implemented on
a VICOM image processing system recently purchased by Steward
Observatory. The VICOM can perform pipeline arithmetic and lookup
table operations at 8 MHz pixel rates to process an entire image in
one video frame time. A simple array processor can be used to operate
at video rates on an image with a 3 x 3 small generating kernel.
After collection of the spectral and calibration CCD frames
described in Table 2, each frame must be corrected for the flat field
response and bias of the CCD detector. These operations will be done
on the VICOM image processing system a:'ter we have modified it to
retain 16 bit data for all operations. Because it was designed for
C
M.
^►^ .a ./s ^= ^^'.. s a.^ --	 - _'--^,fir.. n c..^.^:
^	 ^-.. 1 .,	 -a 	»	 .^^ .. • ,,,.- ^^-Y'^M^ _	 - .,r^^..^..,_- . _ _..--_.	 .^f	 /=-1711
6
visual image processing, the standard mode of VICOM operation uses 12
bit planes of memory for the image and 4 bit planes for eight-color
graphics. Eleven bit signed integers ( ± 4K) are fine for picture
processing but are not adequate for astronomical data reduction
involving multiple frame spectral images. Present Medusa data
requires alignment of individual CCD exposures to remove
flexure in the detector chain before further processing can occur.
Individual frames are shifted by integer and fractional pixel amounts
with the pipeline processor, so that the interlaced HeAr spectra
between the galaxy spectra all coincide. Fractional pixel shifts in
two dimensions can be performed by operation on the images with a 3 x 3
small generating kernel (SGK). The kernel performs bilinear
interpolation of the pixels onto a displaced grid. Larger kernelR
could be used for more complicated interpolation schemes, but the 	 3
linear term preserves most of the infomation in the sampled spectral	 3
image, while minimizing the blurring which occurs. We have not yet
approached the problem of cosmic ray removal in a serious fashion, but
it will ultimately be necessary to remove them from the data at this
stage of the reduction processing.
After Cle indivudual frames have be ^n refined and aligned, they
are coadded to form the final spectral and calibration lamp images.
To locate the individual spectra on the CCD frame, a copy of the
coaddition result is filtered on the VICOM with a 5 x 5 kernel to
smooth the data on pixel to pixel scales and to enhance features with
the characteristic size of the spectra. This smooth frame is then
a^
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7
searched for local maxima at the interfiber spacing to identify the
individual spectra. Ten cuts are made transverse to the dispersion
direction and a parabolic fit is used to locate the maximum position
of each spectrum across the chip. These data points are then used to
generate becond-order polynomials which describe the locations of the
spectra on the image frame. This set of polynomials is used as a map
to direct the program which extracts the individual spectra from the
original, not smoothed, data frames into one-dimensional files. Other
parameters for the extraction process such as the width of spectrum to
extract are entered by the user.
The one-dimensional tiles can be formatted to work on either
of the spectral reduction systems now in use at Stewart:: IRS by C.
Foltz, or CZWT by W. Tifft. In order to avoid the tedium of measuring
the positions of thousands of helium and argon lines by hand, we have
written an automatic routine to find dispersion curves for all of the
comparison spectra on a given calibration frame. The program uses a
rough dispersion curve of the first fiber spectrum on a frame to
predict line positions on the next spectrum. The process continues
across the entire length ^ F the slit. With an accurate prediction,
the program is able to find the center of the emission lines by
fitting a parabola to the local maxima in the spectra. This program
has been quite successful and usually produces a better dispersion
curve than manual measurement while taking only 5% of the time
previously required. I should point out thRt this routine is fas: and
t
i
?I
eefficient but not magic. If the calibration frame is of poor quality
It will produce meaningless dispersion curves. Care must be taken to
be sure that the data and the wavelength catalog are similar enough to
prevent the prediction algorithm from becoming unstable.
Measurement of lines in galaxy spectra is currently done
manually with IRS. Figure 21 shows one of 30 spectra extracted from a
series of exposures in Abell 993B. Both the raw sum and the
sky-subtracted sum of nine 20-minute exposures are shown. The raw
extraction of a single 20-minute exposure is also shown. No flat
field correction has been applied in :his preliminary reduction. Large
cosmic ray events were removed manually. The redshift measured from
six absorption lines in galaxy 225 is 11720 km s -I . At some time in
the future we expect to use a cross correlation routine to automate
the galaxy measurement process. When combined with manual 	 t
verification, the cross correlation procedure should be faster and
more reliable than manually measuring line positions. The major
problems are expected to be creating templates, and removing cosmic
rays and emission lines which would give false correlation peaks.
k
-. J
?l
. ,
	
s	
&,
A993 Galaxy 255
sky subtracted sum
v
=	 c	 o
o
Y	 ° LL	 °r	 =	 v
ro	 c7
U
V	 I
sum of 9 exposures
a	 o	 a ro
x	 °
^	 i	 =	 °	
= z
	
x z
i	
N
	 Z	 z
z	 N	 z	 a	 z \	 z Z
	
z	 z
night sky
20-minute exposure
_	 1	 1
380
	
400	 440
	
480	 520	 560	 600
WAVELENOTFS (nm)
Figure 21. Spectrum of A9938.2.G255
This figure shows the spectrum of galaxy 255 in the cluster
A993. The Medusa spectrograph with an intensified CCD detector was used
on the 2.3m telescope. A single 20-minute exposure is plotted at the
same scale as the raw and sky-subtracted sum of nine 20-minute frames.
The spectral resolution is 12 R,
N
z
Z)
OU
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..:. J
III. THEORETICAL STUDIES OF QSO WINDS
In order to test the existence of "quasar-winds" (Weymann et al.
1982) in active galaxies and QSOs, the interaction between such a wine'
and the interstellar medium (ISM) has been investigated by A. V. R.
Schieno as part of his doctoral dissertation (A. V. R. Schiano 1984a
and b) . This study concentrates on Seyfert galaxies since some
effects of this interaction may be directly observable in nearby
objects. In particular, certain properties of the Narrow Emission
Line Regions (NELRa) of Seyfert galaxies ma y be due to the interaction
of the ISM with such a wind.
Since Seyfert galaxies are predominantly spiral galaxies, the
propagation of the wind into a flattened disk distribution of gas was
investigated. The model interstellar medium environment (density,
temperature, pressure, cloud sizes, etc.) was based on observed
properties of the Milky Way and nearby spiral galaxies. Given the low
number density of clouds in the ISM. it is possible to separate the
r±nd-gas and wind-cloud interactions based on cloud density alone
(Sgro 1975). At low mechanical wind luminosity (log Liwind) < log
Liphoton} = 42 to 44 cgs) the wind fails to propagate to large enough
distances in the galactic disk, and hence does not encounter enough
clouds to require a more complicated analysis of the difference
between gas and clouds in the model. However, at higher Liwindi
(appropriate for QSOs) the grind-cloud effects dominate the propagation
of the wind.
9
i
A10
The Kompaneets approximation (Kompaneets 1959) along with the
stellar wind similarity solutions of Weaver et al. 1975 were used to
Investigate the propagation of the wind "bubble" in a flattened disk
geometry. Since the bubble travels fastest in the lowest density gas,
the bubble progresses rapidly along the galactic pole with a timescale
of a few million years. In the disk the higher ISM gas density and
pressure tends to slow the bubble's motion and eventually stops the
wind near a point where the wind ram pressure equals the ISM Ras
pressure. This occurs at about 5 - 10 million years after wind
turn-on. The stability of the solution is studied as well as the
nature of the steady-state solution. The maximum distance that the
wind reaches in the plane is of order 5 to 10 Kpc for log L{wind} = 44
cgs. The observational effects of the wind-gas interaction are
determined and found to be probably unobservable at present.
The interaction between the wind and interstellar clouds was also
investigated. Due to the high ram pressure of the wind, interstellar
clouds would be compressed to much higher than normal pressures and
densities. Combining this with the effects of the photons from the
active nucleus produces clouds with properties not unlike NELR clouds.
The win i :am pressure is capable of accelerating large clouds ( > 100
solar masses) to velocities comparable to those seen in NELR line
profiles. It is also shown that under the conditions inferred for the
regions between NELR clouds (log Temperature = 8 to 9 cgs), i
significant thermal evaporation of clouds occurs. Thus only large
16
11
clouds can survive for a NELR crossing time. Such large clouds are
incapable of being accelerated to high velocities (1000 kms) by photons
alone. It is thus proposed that NELR clouds are normal interstellar
clouds being accelerated and confined by a powerful quasar wind.
Because of the relatively large size (1 to 10 Kpc) of the wind's
extent, it may be possible to directly observe the wind in nearby,
bright, Seyfert galaxies and hence prove or disprove the existence of
the wind itself.
1
is
t^l ;r
REFERENCES
Birkinshaw, M. and Gull, S. 1984, M.N.R.A.S., 206, 359.
Hill, J. 1984, unpublished Ph.D. Dissertation, University of Arizona.
Hill, J. Eisenhammer, J . , Silva, D. and Woenz, M. 1984,  in
preparation.
Hinzen, P., Hill, J., Lindley, D., Scott, J., and Angel, J. 1982,
A.J., 87, 1656.
Lasenby, A. and Davis, R., 1982, M.N.R.A.S., 203, 1137.
Rothenfliwg, R., Vigrour., L., Mushotzky, R., and Holt, S. 1983, NASA
Tech Memo #85103 (Ap. J. in press 1984).
Schiano, A. V. R. 1984a, in preparation.
Schiano, A. V. R. 1984b, in preparation.
Sgro, A. G. 1975, Ap. J., 197, 621.
Weaver, R., McCray, R., Castor, J., Shapiro, P., Moore, R., 1977, Ap. J.,
218, 377.
Weymann, R. J., Scott, J., Schiano, A. V. R., and Christiansen, W.
1982, Ap. J. 262, 497.
White, S. and Silk, J. 1980, Ap. J. 241, 864.
4
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Studies of X-ray clusters of galaxies/intergalactic plasmas

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