Extragalactic abstracts - IRSA - California Institute of Technology

Spitzer_Approved_Extragalactic
Mar 25, 10 16:24 Page 713/742
Spitzer Space Telescope − General Observer Proposal #20016
Search for Very Thick Disks Around NGC 891 and NGC 5907 with the IRS PUI
Principal Investigator: Martin Burgdorf
Institution: John Moores University
Technical Contact: Martin Burgdorf, John Moores University
Co−Investigators:
Matthew Ashby, Harvard/Smithsonian Center for Astrophysics
Science Category: dark matter
Observing Modes: IrsPeakupImage
Hours Approved: 2.1
Abstract:
Flat galaxy rotation curves routinely observed out to large radii in HI and in
optical emission lines are convincing evidence for the existence of dark matter.
As yet, we know very little about the nature of this dark matter. An intriguing
possibility is that a population of very cool objects − extreme brown dwarfs or
"Jupiters’’ − accounts for a significant part of its mass. Their intrinsic
faintness at visible wavelengths would explain why they have not yet been
clearly detected. IRAC GTO observations of two famous edge−on galaxies (NGC 891
and 5907) have yielded good evidence for such a very red, thick disk component
that could comprise some of this "missing mass", but the mid−infrared colors as
yet offer no clear discriminant of the thick disks’ makeup. We propose to use
the IRS PUI mode for follow−up observations of the thick disks seen in the two
edge−on IRAC GTO program galaxies. By measuring the thick disk fluxes at 16
microns we can obtain crucial information for example about the temperature of
the objects in these disks and hence get a better idea of their nature. As the
expected signal is much smaller than the foreground emission from the zodiacal
light, we propose to execute raster maps perpendicular to the midplanes of these
galaxies without touching the regions of strong emission. The radiation from the
thick disks will then appear as a surface brightness gradient measured as a
function of distance on both sides of the galactic midplanes. Previous attempts
to detect halo or thick disk material around edge−on galaxies concentrated on
the near infrared; the observations proposed here would be the first ones at
longer wavelengths which are aimed only at regions outside the visible disks.
In addition to the proposed 16 micron images, we will obtain 22 micron images in
parallel, from the other IRS peak−up array at similar positions relative to the
galaxies. We request 2.1 hours to carry out this program.
Spitzer_Approved_Extragalactic
Printed_by_SSC
Mar 25, 10 16:24 Page 714/742
Spitzer Space Telescope − General Observer Proposal #40125
Are LMC/SMC microlensing events due to dark matter?
Principal Investigator: Andrew Gould
Institution: Ohio State University
Technical Contact: William Reach, Spitzer Science Center
Co−Investigators:
William Reach, Spitzer Science Center, California Institute of Te
Andrzej Udalski, Warsaw University Observatory
Kim Griest, Department of Physics, Unversity of California, Sa
Subo Dong, Department of Astronomy, Ohio State University
David Bennett, Department of Physics, Notre Dame University
Andrew Boden, Michelson Science Center, California Institute of
Science Category: dark matter
Observing Modes: IracMap
Hours Approved: 25.5
Abstract:
The outstanding question in the interpretation of microlensing events observed
toward the Magellanic Clouds (MC) is the location and nature of the lens
population. Because Earth−based photometric observations are ambiguous in
inferring the lens distance, existing MC survey events can be explained by
lenses in the Galactic halo, the Galactic disk, the clouds themselves, or a
combination of all three. By virtue of its orbit, Spitzer offers a literally
unique perspective on MC microlensing events. Here we propose to continue our
program of target−of−opportunity Spitzer/IRAC photometric observations of MC
microlensing events detected in an ongoing ground−based survey, and to combine
the Spitzer and ground−based datasets to unambiguously determine the lens
"microlens parallax", which strongly constrains the host population of
individual lenses. The first such Spitzer observations constrained
OGLE−2005−SMC−001 to lie in the Galactic halo at 95% conficence. A handful of
additional determinations will unambiguously settle the lens location
controversy and associated uncertainty in interpreting MC microlensing
surveys,and allow the determination of whether the putative halo lenses comprise
a significant component of Galactic dark matter.
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