High resolution images of the 12 micron and 25 micron IRAS survey data from each HCON crossing the Galactic Plane are being created for those regions that the original IRAS processing labeled as confused. This encompasses the area within 100 deg longitude of the Galactic Center and within 3 deg to 10 deg of the Plane. The procedures used to create the images preserve the spatial resolution inherent in the IRAS instrument. The images are separated into diffuse and point source components and candidate sources are extracted from the point source image after non-linear spatial sharpening. Fluxes are estimated by convolving the candidate sources with the point response function and cross-correlating with the original point source image. A source is considered real if it is seen on at least two HCON's with a rather generous flux match but a stringent position criterion. A number of fields spanning a range of source densities from low to high have been examined. Initial analysis indicates that the imaging and extraction works quite well up to a source density of about 100 sources per square degree or down to roughly 0.8 Janskys

Gonsalves, Robert A.

Kennealy, John P.

Korte, Rose M.

Price, Stephan D.

Sample, Rebecca S.

English

NASA Technical Reports Server

JN95-21755 /
45
A HIGH RESOLUTION ATLAS OF THE GALACTIC
PLANE AT 12 /_m AND 25 #m
STEPHAN D. PRICE
(;eophy_ics Directorate, Phillips Laboratory
ROSE M. KORTE, REBECCA S. SAMPLE, AND JOHN P. KENNEALY
Mi_ion Research Corporation
ROBER!/' A. GONSALVES
Electlv-Optics Center Tuft_ University
ABSTRACT High resolution images of tile 12/tin and 25/Lm IRAS
survey data fi'om each HCON crossing the Galactic Plane are being cre-
ated for those regions that the original IRAS processing labeled as con-
fused. This encompasses the area within 100 ° longitude of the Galactic
Center ant[ within 3 ° to 10° of the Plane. The procedures used to create
the images preserve the spatial resolution inherent in the 1RAS instru-
ment. The images are separated into diffuse and point source components
and candidate sources are extracted from the point source image after
non-linear spatial sharl)ening. Fluxes are estimated by convolving the
candidate sources with the point response function and cross-correlating
with the original point source image. A source is considered real if it
is seen on at least two H(?ONs with a rather generous llux match but a
stringent position criterion. A number of tields spanning a range of source
densities from low to high have been examined. Initial analysis indicates
that the imaging and extraction works quite well u 1) to a source density
of about 100 sources per square degree or down to roughly 0.8 Janskys.
INTRODUCTION
TIle present effort to improve the resolution of the IRAS data products arises
from an interest in using such observations to study the structure of the Galaxy.
Chester (1986) has shown that at a 12 pm fimiting sensitivity of 0.,1 Jy, IRAS
could detect the moderately bright infiared beacons at least to the Galactic
Center. However, previous studies of the properties of the inner C,alaxy using
the 1RAS data (e.g., the shape of the bulge and distribution of AGB stars by
Habing et al. (1985)and Habing (1986) and the warl)ing of the l)lane derived
by Djorgovsky and Sosin (198_9)) have discarded the 1RAS Point Source Catalog
(PSC) (Version 2 19_8) data along the Galactic Plane as um'eliable due to confu-
sion, precisely in the region most sensitive to the distribution parameters sought.
Weinberg (1992a, 1992b) argued that a color-selected sample of objects could be
chosen fi'om the PSC which were both bright enough that the PSC completely
S. 'ferebey mid J. Ma'zzarella (eds.), Science with High-SpatiM Re_olutiotl Far lnfi'ared Det_a, 45-54,
1994, Jet Propulsion Laboratory, Pa._adena, CA.
https://ntrs.nasa.gov/search.jsp?R=19950015338 2020-06-16T08:24:31+00:00Z
46 PRICE ET AL.
sampled tlmm and of sufficiently uniform luminosity to trace the mass distri-
bution. From this sample, Weinberg concluded that (1992a) the inner Galaxy
was barred rather than having a 4 Kpc ring and (1992b) there was no evidence
for a mid-infrared Galactic Bulge. Canterna et al. (private communication), on
tile other hand, found several different populations of objects in tile direction of
l = 30 ° based upon color and apparent scale height and concluded that major
constituents of tile inner Galaxy were inadequately sampled due to confusion.
We have processed the IRAS survey data to obtain 12 tim and 25 tzm images
along the Galactic Plane which preserve the inherent spatial resolution of the
IRAS instrument. Sources are extracted from each HCON image ba_ed on a
signal-to-noise criterion. The source fists from the three HCONs are matched
with a rather loose tlux criterion and a more stringent position criterion. Based
on the dLogN/dLog S vs Log S plots, tile current processing seems to work well
up to source densities of about 100 per square degree. This is some two to four
times higher than the practical limit to the PSC. For two moderate density lid(Is,
one ill the Plane at l, b _ (35 °, -0.,1°), tile other at tile edge of the Galactic Bulge(t,b~ 335.,1o,2.4 °) tile "conlpleteness" of the source counts were extended t'ronl
2.5 .]y in the I'SC to 0.6-0.8 Jy. While the flux agreement between the 1)SC and
tile current processing is, in general, quite good, some notable exceptions exist
where we have resolved sources that tile I)SC processing has combined into a
single object.
PROCESSING
Initially, our intent was to super-resolve the IRAS survey data on tile Galac-
tic Plane with tile Filtered Entropy Restoration described by Kennealy et al.
( 987), Korte et al. (1989) and Gonsalves et al. (1990). Since this apl, roach
uses Fourier transform multiplications tbr the filtering required by the restora-
tion, it is much faster than the equivalent matrix multit)lications used by IPAC's
YORI(: or Gull and Skilling's MEIvlSYS. The Filtered Entropy Restoration pro-
duces comt)aral)le resolution and intensity distributions as the more complex
algorithms and is comt)utationally much faster, an important factor given the
vohune of data to be processed. However, in order tbr the Fourier Transform
based procedure to work at best fidelity, the IRAS "footprint" data has to be
projected onto a rectilinear grid with a routine that "wtfitens" the image result-
ing ill an isoplanatic response function.
Since the primary objective of this effort is to enumerate and quantify tile
discrete sources down to relatively low signal-to-noise in the high density regions
along tile Galactic t)lane, we subsequently decided it best to extract sources at
tile regrklded stage and use the multil)le images from the different HCONs to
improve reliability of the flux estimates and confidence ill the derived source
lists. Sources are extracted front each of the three HCON grids and a two-out-
of- three conlirmation is used. In contrast, all tile data have to be used together
to fully realize the resolution enhancement of tile maximunl entropy l)rocedure.
l"urtllermore, the additional sources we expect to detect are at a signal-to-noise
of live to 15 and the resolution of nlaxilllUln entropy enhancenmnt is known to
vary as an inverse function of signal-to-noise (Narayan and Nityananda, 1986).
GALACTIC PLANEATLAS AT 12proAND 25pro 47
IMAGE GENERATION
IPAC hasprovidedus with IRAS surveyfootprint datacoveringthe Galactic
Planein roughly6° x 6° fields.Eachplate of theseregionsis dividedinto four
overlappingquadrantscovering3.5° x 3.5°. Scandata in thesefieldsaresorted
by scanangleandSOPinto threegroups.Scanswith nearlythesamescanangle
and SOPscloselyspacedin time form a groupwhichusually,but not always,
correspondsto an HCON. Noiseis estimatedfor eachdetectorby high-pass
filteringthedata, theniterativelyadjustingthermsvaluebyrejectingdeviations
greaterthan2.8a.Thehigh-passfilter isa Wienerfilter whichextractsthehigh-
frequencynoisecoml)onentfrom the data streamof eachdetectorscan. The
resultingnoisecomparesfavorablywith that determinedwith other methods
suchastimzerosumfilterdescribedin the1RAS Explanatory Supplement (1988).
The data from each detector scan are separated into a low frequency or
background component and a point or smMl extended source component. The
in-scan background is estimated by a lower bound numerical fitting procedure
using a ten sample support. Thus, variations with coherency spanning a width
of three detectors or greater than 2_ are included in the background file; more
rapid variations are put into a high frequency file. Residual striping is estimated
by comparing the in-scan averages in the background file with the cross scan
profiles. These baselines are removed. Since a lower bound is used (a few
negative points are allowed) the result is biased for the noisy channels; the high
frequency values are slightly too large and the background is somewhat too low.
The bias adjustment in the background image coml)ensates for the bias in this
file.
A background and a source image is created for each quadrant by interl)o-
lating the data to an 876 × 876 point grid of 1,1.,t arc-second pixels. At each
grid point, ira, the brightness, fg, is calculated by a nfinimum mean square error
interpolation of the nearest twelve data values, dk, from the irregularly spaced
scans. The weights used ilk the interpolation are such that the resulting im-
age is "whitened" to a uniform model isoplanatic response function, h,,_ . The
model response is an average of the response fimctions of the largest detectors
in the array, made even aim symmetric by reflecting the leading response about
the median peak to eliminate the tails, then averaging the result of folding the
mean response function about the in-scan and cross-scan axes centered on the
function. The end product is symmetric about any line drawn through the cen-
ter of the function. The calculation of the interpolation weights requires the
solution of a twelfth-order matrix equation involving the statistical averages of
dkdj an([ dki,_, ht essence each scan is convolved with the transl)ose of tile ap-
pficable t)oint source response function centered on the cross-scan offset of the
grid point in question. The detector response functions, h_l, are those of Moshir
(private communication) which are described in the Expltmatory Supplement to
the IRAS Faint Source Survey (Moshir et al. 1992). Weights are assigned to
the result proportional to the inverse of the noise of the detector that generated
the data l)oint. This 3 × ,1 matrix is multiplied by the inverse matrix of the de-
tector rest)onse centered on a data l)oint and the transpose centered on the grid
point (both suitably weighted by the noise) convolved with a model response.
48 PRICEET AL.
Mathematically:
fg = (hdhtd + NSR)-lhmhtdFd,
where NSR is a local noise-to-signal ratio and Fa is the vector of twelve data
values. There is a slight amount of smoothing to the extent that hm is slightly
larger than h d for some of the detectors.
The background and source images are added to produce the total image
for the quadrant field. A noise grid is also generated based oil the weighted
averages of the noises multiplied by the whitening matrix.
SOURCE EXTRACTION
An iterative mean square error (mse) gradient linage enhancement routine with
a positivity constraint is used to sharpen or increase the resolution of the source
image. If the stellar fluxes of amplitude ai are distributed with a position variable
xi such that
4x) : _._(x - x_)
which is related to the observed source map by
d(x) = _(_) • i,(x) + n(x)
then the sharpening Mgorithm is
3,_ = n th estimate of_(x)
= _,_-1+ cW(x) > 0
a = stepsize = fv(x)e(x)dx
g(x) = rose gradient = -2e(x),p(x)
e(x) = error = d(x)- _n-l(x)*p(x)
Potential sources are at the positions of the peaks of positive excursions from
the local background in the sharpened source image. The source lists are sub-
sequently thresholded to be greater than a local signal-to-noise ratio of 4.5.
The SNR value was empirically chosen based on eliminating spurious sources in
severM tields of moderately high source density.
Fluxes are estimated by cross-correlating the positions of the extracted
source convolved with the model response function and the match-filtered source
image.
d(_)
.-(:_)
: match-filtered source image = d(x), p(x)
_(x) * p(x) (plus noise)
4x) • v(x), _,(-x) = _(_), ,,(x)
GALACTIC PLANE ATLAS AT 12#m AND 25#m 49
where r(x) is the autocorrelation function of p(x). Since
which is tile flux-weighted sum of tile autocorrelation functions centered on the
positions of the extracted sources. We evaluate z(x) at the locations, xk, and
solve
z(xk)= a,T( k- forthe (1)
In crowded regions, the flux errors for overlapping sources couple with the
position errors. We combine these errors by calculating a multiple-parameter
Cramer-Rao bound using the Fisher information matrix. The errors are bounded
in that they can be no smaller than the Cramer-Rao bound. The local signal-
to-noise is increased by the ratio of the square root of the maximum in the
autocorrelated response function to the peak input value. In the present case,
the gain is about 6.7 for well-isolated sources. Part of this gain comes from
smoothing the source image with a matched filter. The rest arises from the fact
that the autocorrelation function used in the parameter estimation spans three
to four samples of in-scan data from four to live detectors in all HCON. The
autocorrelation is a weighted co-addition of these data points which, if the noise
is uncorrelated, will improve the signal-to-noise. The "noise" due to confusion
decreases this gain by an inverse function of the area common to overlapping
sources.
A flux criterion and the distance between candidate sources were used in
matching sources from different HCONs. Tile position uncertainties are well
represented by Gaussian distributions; tile procedures used to image sharpen
the uncertainty distribution from tile convolution of a Gaussian with a unit
response (CGU) described in the IRAS Explatuttory Supplement (1988) and by
Fowler and RolD (1982). A source was included in tile Galactic Plane catalog
if a position match was found for at least two of the three HCONs and the
flux measured on HCON1 was within a factor of two of that from HCON2; no
tlux criterion was used for matches with ItCON3 sources. The output from
tile matches are positions, thxes, the errors in these quantities, the SNR, and
correlation coetficients derived from the match. The 12 pm and 25 pm lists are
band-merged using a position criterion similar to that for the 1-1CON matching.
The individual HCON lists are examined for possible matches in the missing
color if no band inerge has occurred. If such a match is found, it is included in
the tinal source list and appropriately annotated.
RELIABILITY AND COMPLETENESS
It is ditficult to estimate tile reliability and completeness of the sources detected
by these procedures, as comparisons with internal and external source lists are
limited. Tile source selection criteria on tlux and number of times observed are
certainly less restrictive than those used to create the PSC. On the other hand,
50 PRICEET AL.
the t)ositionmatchingis significantlytighter in the cross-scandirection.At the
moment,our bestestimatesareinferentialand qualitative.Thereliability and
comt)letenessshouldbeacceptablyhigh because:
tbr 2,13.5° x 3.5°tields wedetect>95%of tile I)SCFQAL=3 sources,and
morethanhalf thesefieldshave>98%associationrate in the highdensity
regions. Thereareno significantdifferencesbetweenour positionsand
thosefrom the PSC.The linear regressionbetweenour fluxesandthose
fromthe PSChavea slopeof 1 andan interceptof 0 within therespective
errors.The standarddeviationin the fit tendsto behigherthan the 5%
calibrationaccuracygivenin the ExplanatorySupplement.This is traced
to a broadeningof the distributionat the fainterendof theregressionand
a fewoutlierswhereweresolvewhat the PSCclassifiesasa singlesource.
the log N vslog S plots to fainterlevelsareconsistentwith the brighter
countsh'omthePSC.Timslopesofthe logNvslogSplotsaresteeper,with
physicallymoreplausiblevaluesthan that derivedfromthe PSCalone.A
typical setof ttux vsdensitydiagramsis shownin Figure1. Figurela is
tim resultderivedfromthe PSC,whileFigurelb is that front thepresent
study'sGalacticPlaneCatalog(GPC)for thesamefield.
the differentialtluxvs densityplotsturn oversharplybelowtheestimated
completenesslevel,asseenbelowin Figure2. A cursoryexaminatioIlof
a few fieldsindicatesthat the sourcelists may be reliableand complete
up to a sourcedensityof about 100objectspersquaredegreeor downto
a flux of about 0.8-1.0Jy at 12pm and 0.6-0.8 Jy at 25 #m. A noise-
dominated distribution increases the slope as observed for the low density
region shown in Figure 3. Scans from two of the HCONs for this field are,
unfortunately, nearly parallel and phased such that the noisy detectors
overlap, producing an overabundance of coincidences on noise peaks.
There are several analyses by which we hope to quantify reliability and
completeness. The University of Wyoming is using MEMSYS-5 to super-resolve
a number of IRAS AO's near the Galactic Plane. We will compare the survey
results with this data set, which is independent both in acquisition att(t the
method of restoration. We will use the mini-survey to compare the results of a
two-out-of-three criterion with that derived from a larger number of images. We
will randomize the l)ositions of two of the HCONs for several fields to estimate
the number of coincidental agreements.
RESULTS
For the 2,'1 fields surveyed, the effort described in this paper produces front
two to four times as many sources as in the PSC. If the qualitative arguments
regarding conqJleteness and reliability are valid, then we have indeed achieved
our objective of improving the source counts along the Galactic Plane. Logm
(lq2/F2s ) plots for an area in the Galactic Platte at l _ 35 ° and at the edge of
the bulge ( l _ -4.6 °, l ,-_ 2.3 °) show a distribution sharply peaked near a vMue
GALACTIC PLANE ATLAS AT 12#mAND 25#m 51
IO00
lOO
10
1
0.1
, ' ' ' ' ''1 . , , , ,,_
Area = 12.4 de92
613 Sources
Slops nt = -1.23-\
\
\\
\
\\
\
O*_OOOOOOO_\ \ \
*****%%
- 3,,. b,- -o,. _++
1 lo
nu_ (Jans_)
Figure la. Distribution of PSC Sources
1 O0
=
o
IOO0
100
1(]
1
0.1
' ' ' ''1 ' ' ' ' ''1
RA o - 2B3,5 =
DC. - 1.5"
"\
\
\
\
00;_\\
-.;,%
ko - 34.9 _ be - -0.4'
i i i i I i ili
1
Figure lb.
Area = 11.9 de9 z
1775 Sources
Slope Fit = -1.35
10
Flux (Jonaky)
Distribution of GPC Sources
, , , , ,
100
O_
e"
_o
0
814 / _.(hxjCS))
oo
l _ * , , lit[
.@.
-@-
.-@-
--@--
0
1 I I I IIIII
o
o
I,a II
o
c io
I I j j Iljll I i I I I I I
o
vw
ml
'-I
lb. ._
0
+
+
+
+
+
0
+
J _ J J iJiJ[
_n / A(Iog(s))
g
, , , i ,r,l I
e
4
+
+
+
e
o
GALACTIC PLANE ATLAS AT 12#m AND 25tim 53
o.
1000
lOO
' ' ' ' ''i
RA=- 297.6 =
DC o - 21.5"
Area = 13.0 deg 2
449 Sources
Slope _t = -1.05
4
0
0
I . - ..0. ,.-=. %+,
/
1 ........ , , , ,,_,,,,
0.1 1 10
Flux (da nlk'y)
Figure 3. Low-density Band 1 data
lOO
of 0. This is similar to what Weinberg (1992b) found for tile variable AGB stars
he used as structure tracers. Unfortunately, this value for tile peak is ahnost
forced by the fact that most of tile stars in a given tield will have ttuxes near the
cutoff and the sensitivities at 12 tim and 25 t,m are nearly the same.
REFERENCES
Chester, T.J. 1986, in Light on Dark Matter, ed. F.I'. Israel, Dordrecht: Reidel,
3
Djorgovski, S., and Sosin, C. 1989, ApJ, 341, L13
Fowler, J.W., and Rolt'e, E.G. 1982, dourlml of Astrolmutical Sci., Vol. XXX,
No. 4, pp. 385-.102
Gonsalves, R.A., Kennealy, J.P., Korte, R.M., and Price, S.D. 1990, in Maximum
Eldropy al_d Bayesian Method_, ed. I'.F l"ougere, Kluweter Academic
Press (Neth), 369
Itabing, H.J. 1986, in Light on Dark Matter, ed. F.I'. Israel, Dordrecht: Reidel,
329
ltabing, H.J., Olnon, I".M., Chester, T. Gillett, F.C., Rowan-Robinson, M., and
Neugebauer, C,. 1985, At!_A, 152, LI
IRAS Catalog._ a_d Atlases: Exphmatory Suppleme_tt. 1988, ed. C.A. Beichman,
G. Neugel)auer, H.J. Habing, I'.E. Clegg, and T.J. Chester (Washington,
DC: GOP)
Kennealy, J.l'., Korte, R.M., Gonsalves, ll.M., Lyons, T.D., Price, S.D., LeVan,
I'.D., and Aumann, It.H. 1987, in it Advances in hnage Processing, Proc.
SPIE, 804, 16
54 PRICEET AL.
Korte, R.M.,Kennealy,J.P.,Gonsalves,R.A.,and Wong,C. 1989,"Analysisof
IR CelestialSurveyExperiments,AF GeophysicsLab. TechnicalReport,
GL- TR -89- 0265
Ivloshir, M., et al. 1989, Explanatory Supplement to the IRAS Faint Source
Survey (Pasadena: JPL)
Narayan, R., and Nityananda, R. 1986, ARA_A, 24 , 127
Weinberg, M. 1992a, ApJ, 384 , 81
Weinberg, M. 1992b, ApJ, 392, L67


A high resolution atlas of the galactic plane at 12 microns and 25 microns

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server