• We spent about 36 hours mapping regions of the Milky Way.
• The overall goal is to characterize cirrus and source counts in different Galactic environments.
• The parts of this survey are:
• MIPS and IRAC maps (roughly 10' x 2 degrees) across the L1228 molecular cloud.
• MIPS and IRAC maps (each roughly 15' x 1 degree) at (l = 254.4, b = 0, -2, -5, -9, -14) and (l=105.6, b = -1.3, 0.3, 2, 4, 8, 16, 32) with additional small IRAC maps at l=97.5, b = 0, +/-4, 16

• Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey Ingalls, J., et. al., 2004, ApJS, 154, 281

• The Galactic first-look survey with the Spitzer space telescope Burgdorf, M. J., et. al., 2005, AdSpR, 36, 1050

• Spitzer Space Telescope View of Diffuse Near-Infrared Continuum Emission in the Galaxy Lu, N., 2004, ApJS, 154, 286

• An Aggregate of Young Stellar Disks in Lynds 1228 South Padgett, D. L., et. al., 2004, ApJS, 154, 433

Goals of Galactic FLS

• Characterize the cirrus and background source counts at low Galactic latitudes. This will help guide MIPS and IRAC observers who wish to observe close to the Galactic plane.
• Characterize the internal cirrus and background source counts toward a molecular cloud. This will be useful to observers of stars and dust in molecular clouds. How limiting are fluctuations in the internal cirrus and extinction? How well one can distinguish embedded and background populations?

Original Observational Definition of Galactic FLS

• IRAC and MIPS characterization of IR cirrus and source counts at low Galactic latitudes in two "strips", each ~5 arcmin wide to give a broad range of cirrus intensities and source counts with the -10 ≤ b ≤ +10 latitude range most important.
• First strip located at single longitude, with latitudes ranging from -30 ≤ b ≤ 0 deg. Latitudes from -10 ≤ b ≤ 0 have "continuous" coverage; latitudes from -30 ≤ b ≤ 0 have a lower filling factor (50%).
• Second strip located at significantly different longitude and extending over the latitude range from 0 ≤ b < +10 deg.
• IRAC and MIPS characterization of IR cirrus and source counts towards a molecular cloud.
• A 5' x 2 degree strip through a molecular cloud.
• Same MIPS depth as in Galactic strip scans.
• IRAC coverage of same area but depth 10x the Galactic strip scans
• Total Survey Time: ~36 hrs

Observational Constraints

• Observing Window: December 2003.
• MIPS Scan Direction completely constrained by launch/observation date.
• MIPS scans are not perpendicular to Galactic plane, so a single strip along a constant Galactic longitude not possible.
• Non-contiguous observations act to decrease overlap between MIPS scans and IRAC maps due to evolution of position angle with time (~1 deg/day).
• Visibility window rules out outer-galaxy longitudinal "strip" as well as Cham II, our original molecular cloud.
• We found a new cloud and three strips that have differing gas/dust/stellar properties.
• Galactic strip maps now larger than those suggested in "original definition". They provide better contiguous observations of Galactic structures and minimize concerns of MIPS and IRAC data not overlapping due to time delays between observations.
• Want to provide good high quality 160 micron data to community, so we had to find and include longitudes and latitudes that will not saturate 160 micron detector.

Observing Strategies Assumed

• Galactic longitudinal Strips.
• As a result of launch slips and other constraints, strips moved several times. l=150 became 67.5, which settled on 105.6, and l=285 became 272.17, then 290.2, and settled on 254.4.
• Individual scans/maps placed at varying Galactic latitudes.
• Latitude spacing of MIPS scan centers increases with latitude.
• IRAC maps of each position with approximately the same width/length as MIPS scans.
• Widened strips (compared to older observing strategy) so as to make larger contiguous maps.
• Request IRAC and MIPS maps to be observed within 4 days of each other (to minimize field rotation between observations and achieve coverage of the same region with both IRAC and MIPS).
• Using HDR mode in IRAC to maximize dynamic range for all positions.
• 60' x15' wide MIPS fast scans at each latitude center consisting of 10 scan legs with 148" forward and 35" return scans.
• 60' x15' IRAC maps (12 rows by 3 columns; 292.8" offsets) using four dithers of 12 seconds in HDR mode to maximize dynamic range at all positions.
• For l=105.6: 15' x 1 degree strips for MIPS and IRAC. Latitudes are: -1.3, 0.35 (ISO), 2, 4, 8, 16, 32 (cirrus)
• For l=254.4: 15'x1 degree strips for MIPS and IRAC. Latitudes are: 0, -2, -5, -9, -14. By chance, part of our strip at -9 will go through the Vela supernova remnant.
• Galactic Cirrus Position
• Created new position at high Galactic latitude specifically designed to better sample cirrus, etc.
• Located at +32d along the 105.6 longitude
• Uses medium-speed MIPS scan legs to fully sample the 160 micron array.
• Same footprint as other Galactic strips
• IRAC covers same area.
• Star Count position
• For l=97.5: small IRAC-only maps to sample the Galactic disk. Latitudes are: 0, -4, +4, +16.
• L1228 Molecular Cloud
• 120' x10' MIPS fast scan across cloud center; second MIPS strip offset by 150'. The final coverage is ~12.5'x2 degrees
• 120'x10' IRAC map (23 rows by 2 columns; 292.8" offsets).
• IRAC maps consist of 4 dithers of 12 seconds at each position operating in HDR mode.
• All of the MIPS scan legs are now offset by 80' (1/4 array).
• The L1228 MIPS observations are now a single pass of 8 scan legs. (It used to be two separate scans separated by 12 hours.)
• Request IRAC and MIPS maps to be observed within 3 days of each other (to minimize field rotation between observations and achieve coverage of the same region with both IRAC and MIPS).

• These are all "high" background estimates.
• The MIPS estimate is for 10 scan legs.
• 5 sigma point source sensitivity for IRAC 4 bands (now is 48 sec only) [3,4,5,8]: 0.020, 0.025, 0.070, 0.100 mJy
• For MIPS fast scans [24,70,160]: 0.620, 3.865, 31.4 mJy
• For MIPS medium scan (cirrus) [24,70,160]: 0.225, 2.46, 28.9 mJy (point source)
• For MIPS medium scan (cirrus) the 1 sigma extended source sensitivity is estimated to be [24,70,160]: 0.0783, 0.0433, 0.145 MJy/ster

• MIPS is very sensitive. All of the 24 um images will probably be unsaturated (except for occasional point sources). At 160 microns, the position most likely not to saturate is the high-latitude cirrus position. At 70 microns:
• some of L1228 will be OK (i.e., not saturated).
• 105: +8,+16, and +32 will be OK.
• 254: mostly unsaturated (except for point srcs) [and for 160 microns, the -9 and -14 latitudes will probably be fine too]

Illustration of effects of non-simultaneous MIPS/IRAC maps along longitudinal strips. This plot also illustrates the different orientations and areas that may be covered by the FLS observations of L1228. The time difference is from the first day of the time window during which the FLS could be observed (Nov 30) to the last day of this window (Dec 15). For this reason we have requested follow on constraints for the IRAC and MIPS maps of only 3 days (for the molecular cloud). (For the Galactic longitude strips, we have requested that the observations be taken within 4 days.) Click for larger image.

Galactic Longitudinal Strip l = 254.4

IRAS 100 micron images with MIPS footprints overlaid for an observation date of 2003 Dec 15. Latitude spacing increases with increasing latitude. MIPS and IRAC observations are comparable. The MIPS footprints are longer than the targeted 1 degree area due to overscan. The maximum area seen by all detectors will in fact be only 1d. Click for larger image.

Galactic Longitudinal Strip l = 105.6

IRAS 100 micron images with MIPS footprints overlaid for an observation date of 2003 Dec 15. Latitude spacing increases with increasing latitude. MIPS and IRAC observations are comparable. The MIPS footprints are longer than the targeted 1 degree area due to overscan. The maximum area seen by all detectors will in fact be only 1d. Click for larger image.

Galactic Cirrus

Galactic Longitudinal Strip IRAC only l = 97.5

IRAS 12 micron images with IRAC footprints overlaid for an observation date of 2003 Dec 15. These IRAC-only observations are designed to assess star counts. Click for larger image.

L1228 Molecular Cloud

Spitzer IRAC maps (cyan and magenta overlays) shown overlayed on IRAS 100 micron maps. Click for larger image.

MIPS scans (pink, blue, green overlays) shown overlayed on IRAS 100 micron maps. Click for larger image.

• ~ 2 degree scan/maps across the cloud center and extending to lower emission regions.
• Maps oriented across the cloud center but exact angle dependent upon observation date.