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HIPASS – RESULTS & LESSONS

HIPASS – RESULTS & LESSONS. A HIPASS result Bright Galaxies and the HIMF The ALFA advantage Speed, depth, resolution Things to get right On-line & reduction software, obs strategies Things to think about INTMIT, deconvolution. HIPASS Bright Galaxy Catalog (BGC) Koribalski et al. (2003).

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HIPASS – RESULTS & LESSONS

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  1. HIPASS – RESULTS & LESSONS • A HIPASS result • Bright Galaxies and the HIMF • The ALFA advantage • Speed, depth, resolution • Things to get right • On-line & reduction software, obs strategies • Things to think about • INTMIT, deconvolution Lister Staveley-Smith – X-ALFA March 15, 2003

  2. HIPASS Bright Galaxy Catalog (BGC)Koribalski et al. (2003) • HIPASS has detected ~7000 galaxies with Decl.<25o • Bright Galaxy Catalog defined to contain the 1000 HI-brightest galaxies with Decl.<0o(S>116mJy)

  3. 87/1000 previously uncatalogued galaxies • 138 new redshifts New HIPASS bright galaxies Ryan-Weber et al. (2002)

  4. BGC 2DSWML joint HI mass-velocity function Zwaan et al. (2003); astro-ph/0302440 BGC HI mass function

  5. Comparison with previous work (see also Steve Schneider’s talk) Lister Staveley-Smith – X-ALFA March 15, 2003

  6. The ALFA advantage - I • Speed • e.g. 7 days would complete Decl. range 25o-38o to HIPASS sensitivity! sensitivity #beams beam area Time required to survey a given region to a given sensitivity (see also D.J. Pisano’s talk) Lister Staveley-Smith – X-ALFA March 15, 2003

  7. The ALFA advantage - II • Sensitivity • HIPASS (=250 sec/pix) is complete for M* galaxies only for cz<4000 km s-1. • ALFA (same ) would be complete tocz<15,000 km s-1 ! • Deep ALFA (=few hrs) should be able to detect M* galaxies to z=0.1-0.16 (the max ALFA redshift) • Don’t forget single-object `MX’ mode (object always in a beam) which is up to 4 TIMES FASTER than for single-beams HI at z=0.18 in a A2218 spiral with WSRT (Zwaan et al. 2001) Lister Staveley-Smith – X-ALFA March 15, 2003

  8. The ALFA advantage - III • Resolution N.B. for a filled aperture, linear resolution always the same at the max survey depth dmax (A/T )1/2. Arecibo beam Parkes beam HIPASS spectrum HIPASS J0620-57 = ESO161-G001/NGC 2222/NGC 2221 (ATCA observation) Lister Staveley-Smith – X-ALFA March 15, 2003

  9. The ALFA advantage – an example • Cosmic variance for HIPASS BGC dwarfs #10 Mpc cells Dwarf galaxies Lister Staveley-Smith – X-ALFA March 15, 2003

  10. Cosmic Variance in HIPASS BGC Zwaan et al. (2003) Lister Staveley-Smith – X-ALFA March 15, 2003

  11. Things to get right… • Correlator • Ideal would be 4-8 bits x 200 MHz x 8192 channels x 2 polarisations x 7 beams + INTMIT [present plan 1.5 bits x 100 MHz x 4096 channels x 2 polarisations x 7 beams] • On-line software • Hide complexity (parallactification, scanning schemes, calibration …) • Allow flexibility (allow users to experiment) • Schedulable or interactive observing • Reduction software • As above! • Needs to be able to run in real-time Lister Staveley-Smith – X-ALFA March 15, 2003

  12. Example • Let ALFA re-map a 64 deg2 HIPASS field • Use HIPASS sensitivity (13 mJy/beam) • Require Nyquist sampling of sky with all 7 beams • Bandwidth 100 MHz, 7x2x4096 channels • Integration time = 1 sec/beam; Total time = 2.6 hrs • Drive rate = 20 deg/min [IMPOSSIBLE IN ZA] • Correlator integration period = 60 ms [OUTSIDE SPECS] • Minimum data volume = 36 GB • Minimum data rate = 4 MB/s (=200xHIPASS) • The Parkes LiveData processor will NOT handle this • The JCMT/DRAO ACSIS 32-processor linux cluster might Lister Staveley-Smith – X-ALFA March 15, 2003

  13. Things to think about - I • Interference mitigation(Briggs, Bell & Kesteven 2001) t A B A B  Raw multibeam spectra near 1499 MHz Post-correlation RFI cancellation with reference horns Lister Staveley-Smith – X-ALFA March 15, 2003

  14. Things to think about - II • Deconvolution Nearby extended sources, or confused regions will need deconvolution. Complicated by a PSF which varies with time, frequency, position and beam number. Cortes-Medellin (2002) Lister Staveley-Smith – X-ALFA March 15, 2003

  15. Summary • HIMF possibilities (faint-end, cosmic variance, density dependence…) • Large-scale, shallow ALFA surveys not possible. • Correlator capability a bit low for surveys and INTMIT requirements • Data reduction bottleneck? • Deconvolution methods … Lister Staveley-Smith – X-ALFA March 15, 2003

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