<=== observer ===>
"DLEMKE",\
"Lemke, D.",\
"",\
"Max-PLanck-Institut fuer Astronomie",\
"Koenigstuhl 17",\
"",\
"D-69117",\
"Heidelberg",\
"Germany",\
"49 6221 528259",\
"49 6221 528246",\
"lemke@mpiahd.mpi-hd.mpg.de"
<=== proposal ===>
"DLBDHALO",1,5,\
{"brown dwarfs","dark matter","normal galaxies"},\
{"U. Klaas","C. Telesco"}
<=== title ===>
Search for Brown Dwarf Halos in Edge-on Galaxies
<=== abstract ===>
SCIENTIFIC ABSTRACT
We propose to use ISOPHOT at 20 micron to search for a suspected halo composed
of Brown Dwarfs in a nearby edge-on galaxy. Halos of Brown Dwarfs may
constitute much of the "missing mass" in galaxies. We select a galaxy that has
a flat rotation curve indicative of the presence of dark matter. BD cooling
curves imply typical temperatures of ~400 K after 10 Gyr, so spectral
bandpasses in the 10 - 20 micron region are most appropriate. Because halos of
dark matter are expected to be of very low surface brightness (0.03 - 0.07
microJy per sq.arcsec) initial discovery attempts can only be made with very
large beams. This requires the most sensitive instruments onboard a He-cooled
S/C. As the possible BD halo emission sits on top of a huge foreground
emission, careful target candidate selection and application of an appropriate
observing mode are necessary.
Since this program is rather time consuming, and colour information is
essential for disentangling different emission components, we have co-ordinated
these observations with the ISOCAM team. The selected spatial resolution of
ISOCAM (6 arcsec per pixel) will also help to recognize discrete objects in the
beam.
A program aiming at the ultimate surface brightness sensitivity limit of
ISOPHOT will highly depend on the actual performance and stability of the
detectors in space. Therefore, the feasibility of the program can only be
confirmed after the ISO Performance Verification Phase.
OBSERVATION SUMMARY
We select the P_20 micron filter which is close to the wavelength of maximum
intensity of a possible BD component. This spectrally complements the ISOCAM
observations at 6.75 micron. We select the largest ISOPHOT beam diameter which
is the 180 arcsec aperture. We will perform very long staring observations in
order to achieve the highest photometric accuracy. The required on-source
integration time to detect the estimated BD emission is about 6 hours. The
same amount of time will be spent on a background reference position. The
longest staring mode observation time with ISOPHOT in one filter is 2048 s,
which means that we have to split our observation into several parts. We will
use a CONCATENATION of the PHT-P sparse map modules P17 and P19 measuring
alternately on-source and off-source. This is equivalent to very slow chopping.
After each 2048 s exposure a measurement with the internal reference source
for detector responsivity monitoring is included.
The halo position of NGC 5907 is located 180 arcsec southwest of the nucleus
(RA offset: -62", DEC offset: -169") and that of IC 2531 130 arcsec southeast
of the nucleus (RA offset: +34", DEC offset: -126"), both in fields with a
minimum number of stars. The distances of the background positions from the
galaxy centres are larger than the galaxy semi-major axes (NGC 5907 - RA
offset: -450", DEC offset: -257", distance to halo position 342"; IC 2531 -
RA offset: +278", DEC offset: -194", distance to halo position 221"). Like the
on-source positions they are located in fields having a minimum star density.
<=== scientific_justification ===>
Time distribution for autumn launch targets
Team top 40% second 30% last 30%
PHT : 0 0 43930
Time distribution for spring launch targets
Team top 40% second 30% last 30%
PHT : 0 0 43930
object selection criteria:
In co-ordination with the ISOCAM team we have selected one galaxy per launch
season, NGC 5907 for the autumn launch (88% visibility) and IC 2531 for the
spring launch (26% visibility).
The objects should be late-type spirals (small bulge) and have a flat rotation
curve and a high rotation velocity. Both galaxies are Sc type, and HI
measurements indicate v<rot,max> ~250 km s**-1.
The objects should be nearly edge-on in order to avoid disk emission being in
the beam and to position the measurement beam as close as possible to the
plane to have a high column density; inclination angles are:
NGC 5907: i = 87 - 90 deg
IC 2531 : i = 90 deg
In order to minimize extended foreground components the objects should be
located at high galactic and ecliptic latitudes:
NGC 5907: b = 51 deg beta = 68 deg
IC 2531: b = 20 deg beta = -38 deg
On ISSA 100 micron plates NGC 5907 has a clean and low 100 micron background.
Around IC 2531 the 100 micron background is somewhat higher and more structured.
Due to its relatively low galactic latitude, the environment of IC 2531 shows
a higher star density than NGC 5907.
<=== autumn_launch_targets ===>
1, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2357, 2
2, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 3
3, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2197, 4
4, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 0
5, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2357, 6
6, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 7
7, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2197, 8
8, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 0
9, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2357, 10
10, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 11
11, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2197, 12
12, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 0
13, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2357, 14
14, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 15
15, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2197, 16
16, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 0
17, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2357, 18
18, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 19
19, "PHT17", 3.0, "N", "NGC 5907 halo", 15.23794, +56.48944, 1950, 0., 0., 2197, 20
20, "PHT19", 3.0, "N", "NGC 5907 back", 15.22853, +56.43528, 1950, 0., 0., 2116, 0
<=== spring_launch_targets ===>
1, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2357, 2
2, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 3
3, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2197, 4
4, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 0
5, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2357, 6
6, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 7
7, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2197, 8
8, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 0
9, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2357, 10
10, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 11
11, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2197, 12
12, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 0
13, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2357, 14
14, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 15
15, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2197, 16
16, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 0
17, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2357, 18
18, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 19
19, "PHT17", 3.0, "N", "IC 2531 halo ", 9.96211, -29.41000, 1950, 0., 0., 2197, 20
20, "PHT19", 3.0, "N", "IC 2531 back ", 9.96550, -29.45222, 1950, 0., 0., 2116, 0