HIPASS and HIJASS cover the same area of sky that is visible at Arecibo, HIPASS south of Dec.= +25°, and HIJASS further to the north. However, in addition to the large increase in sensitivity, ALFA surveys provide 2 direct benefits over the other two: improved angular and velocity resolution. The significant higher angular resolution (FWHM ~3.5arcmin for ALFA versus 12 arcmin for HIJASS and 15.5 arcmin for HIPASS) will help to limit the confusion of sources that plagued those other surveys. The HIPASS follow-up needed is enormous and therefore has been limited to the highest flux sources. It will be years before the sources are followed-up (if ever). An ALFA survey will be able to do science with the survey data directly, without time consuming interferometric follow-up. Additionally, the higher velocity resolution of ALFA will be useful in several ways: First, detecting edge-on galaxies with peak fluxes near the noise limit. The edge of a double peak spectrum is much sharper at higher velocity resolution which should make it easier to automatically detect these sources. Second, the higher velocity resolution will allow more accurate velocity and velocity width measurements, without the need for follow-up. Even the narrowest sources will be detected over several channels. Third, since most rfi is narrow band, the higher frequency resolution will be extremely useful in identifying and excising rfi.
The HIJASS survey has a further serious limitation. Very bad rfi in the frequency band corresponding to cz ~ 4500 - 7500 km/s (within the range of much of the interesting large scale structure e.g., Pisces-Perseus, A1367-Coma-Great Wall). In addition, HIJASS is not scheduled to do any more observing in the Arecibo range (a 4° × 4° region in Virgo and a few other areas have been covered at this point) for the next few years.
The principal advantage that an Arecibo survey will have over previous surveys is depth and the number of independent volumes surveyed. Table B.1 below includes a comparison of the major surveys, including those discussed here. For comparative purposes, the rms noise per beam quoted for each survey has been scaled to a velocity resolution of 18 km/s, the resolution of HIPASS.
|Survey||Area||Beam||Vmax||Vresa||ts||rmsb||Ndet||min MHI c||Ref|
| ||(deg2)||(arcmin)||(km/s)||(km/s)||(s)||(mJy)|| ||(Msun)|| |
|AHISS||65||3.3||-700 - 7400||16||var||0.7||65||1.9x106||1|
|ADBS||430||3.3||-650 - 7980||34||12||3.6||265||9.9x106||2|
|WSRT||1800||49.||-1000 - 6500||17||60||18||155||4.9x107||3|
|Nancay CVn||800||4 x 20||-350 - 2350||10||80||7.5||33||2.0x107||4|
|HIJASS||1115||12.||-1000 - 10000d||18||400||13||222||3.6x107||5|
|HIJASS-VIR||32||12.||500 - 2500||18||3500||4.||31||1.1x107||6|
|HIDEEP||60||15.5||-1280 - 12700||18||9000||3.2||173||8.8x106||7|
|HIZSS||1840||15.5||-1280 - 12700||27||200||15.||110||4.1x107||8|
|HICAT||21341||15.5||300 - 12700||18||450||13.||4315||3.6x107||9|
|HIPASS|| ||15.5||300 - 12700||18||450||13.||(6000)||3.6x107||10|
|AUDS||0.4||3.5||-960 - 47000e||TBD||70 × 3600||0.02||(40)||0.6x10 6||11|
|AGES||TBD||3.5||-960 - 47000e||TBD||300||0.5||TBD||1.4x106||12|
|ALFALFA||7000||3.5||-2000 - 18000||11||28||1.6||(30000)||4.4x106|