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Exploring HI Galaxies with HIPASS: Results and Insights

Discover the outcomes and lessons from using HIPASS, including the detection of bright galaxies, advantages of ALFA, speed, depth, and resolution considerations, essential observatory strategies, and key concepts to focus on. Learn about the HIPASS Bright Galaxy Catalog, ALFA's advantages in speed, sensitivity, and resolution, as well as crucial aspects like the correlator, online reduction software, interference mitigation, and deconvolution techniques. Gain insights into HI mass functions, survey methodologies, and challenges in data processing and analysis. Delve into the world of extragalactic HI surveys and the potential for future research endeavors.

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Exploring HI Galaxies with HIPASS: Results and Insights

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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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