The I-GALFA science goal is to map all the inner-Galaxy H I 21cm line emission that the Arecibo 305m telescope can see within 10 degrees of the Galactic plane. The telescope is constrained to point within about 19.7 degrees of vertical. Given the observatory's latitude, this limits observations to declinations between -1.33 and +38.03 degrees.
Most I-GALFA fields are observed by ``nodding'' the telescope north and south along the meridian to trace out a zig-zag pattern on the sky as the Earth rotates. Nodding observations from many days with different starting positions will cover the entire field and can be ``basket-woven'' into a map (see the image gallery and daily position plots for illustrations). Nodding is not possible near the zenith, but here the telescope can instead be ``wagged'' in azimuth at a fixed angular offset east or west of the meridian to achieve a similar scan pattern.
Below is an RA+DEC map of H I line peak brightness in the Leiden-Dwingeloo sky survey, with curved lines marking Galactic latitudes every 10 degrees and longitudes every 30 degrees. I-GALFA observations, designed to cover the area within 10 degrees of the Galactic plane (the gray line), are marked in red and blue. Click on the image for a larger version.
The I-GALFA fields fill the AO DEC range and overlap with each other by 20', with one field 3 degrees wide at the zenith and four others 9.3 degrees wide covering the rest of the survey. The fields shown here are have the minimum RA range needed to cover |GLAT| <= 10 deg. The LST range of each field is shown in blue. This includes a 15m block at the start for Least-Squares Frequency Switching (LSFS) spectral baseline calibration, as well as the two possible versions of Field Z (only one of which is being observed). Fields A, B, C, and D are observed on the meridian where RA = LST, but Field Z uses LST = RA + dHA, where dHA = +0.85h for ZE (observed east of the meridian), and dHA = -0.85h for ZW (observed west of the meridian).
|min RA rangea,b|
|full DEC rangeb|
|min LST range|
|A||18.0628 19.9022||-01.2667 +08.1167||31.51 42.03||17.8128 19.9022||1.8394+0.25||26+3|
|B||18.3713 20.2741||+07.7833 +17.1667||41.68 52.26||18.1213 20.2741||1.9028+0.25||26+3|
|ZEe||18.6707 20.3967||+16.8333 +19.8333||51.92 55.30||17.5707 19.5467||1.7260+0.25||12+2|
|ZWe||18.6707 20.3967||+16.8333 +19.8333||51.92 55.30||19.2707 21.2467||1.7260+0.25||12+2|
|C||18.7597 20.8814||+19.5000 +28.8833||54.94 65.75||18.5097 20.8814||2.1217+0.25||26+3|
|D||19.0737 21.5435||+28.5500 +37.9333||65.40 76.56||18.8237 21.5435||2.4698+0.25||26+3|
|aThis RA range is the absolute minimum needed to cover |b| <= 10o.|
|bRA+DEC are in current equinox for LST compatibility; observations use J2000.|
|cExtra 0.25 hrs is for Least-Squares Frequency Switching calibration (LSFS; Heiles 2007).|
|dMinimum days required to map field + 10% overhead for telescope problems, etc.|
|eZE and ZW are 2 versions of the same field; only one (ZW) is being observed.|
For more information on the observation of these fields, see the schedule and status pages.
The I-GALFA fields are shown in Galactic coordinates below. The CGPS I+II, VGPS, and SGPS I+II synthesis surveys are marked in green. These maps can also be compared to one of the entire Arecibo sky.