Lister Staveley-Smith – X-ALFA March 15, 2003 1
HIPASS – RESULTS & LESSONSA HIPASS result
– Bright Galaxies and the HIMFThe ALFA advantage
– Speed, depth, resolutionThings to get right
– On-line & reduction software, obs strategiesThings to think about
– INTMIT, deconvolution
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)
New HIPASS bright galaxies Ryan-Weber et al. (2002)
•87/1000 previously uncatalogued galaxies
•138 new redshifts
BGC 2DSWML joint HI mass-velocity function
Zwaan et al. (2003);
astro-ph/0302440
BGC HI mass function
Lister Staveley-Smith – X-ALFA March 15, 2003 5
Comparison with previous work (see also Steve Schneider’s talk)
Lister Staveley-Smith – X-ALFA March 15, 2003 6
The ALFA advantage - ISpeed
– e.g. 7 days would complete Decl. range 25o-38o to HIPASS sensitivity!
26.02
ALFA
PKS
ALFA
PKS
PKS
ALFA
PKS
ALFA
n
n
S
S
Time required to survey a given region to a given sensitivity (see also D.J. Pisano’s talk)
2
6'.3
3'.14
7
132
1
1
.9
28
21
.64.0
JyK
K
K
JyK
sensitivity #beams
beam area
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 to cz<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 - IIIResolution N.B. for a filled aperture,
linear resolution always the same at the max survey depth dmax (A/T )1/2.
Parkes beam
HIPASS J0620-57 = ESO161-G001/NGC 2222/NGC 2221 (ATCA observation)
HIPASS spectrum
Arecibo beam
Lister Staveley-Smith – X-ALFA March 15, 2003 9
The ALFA advantage – an example Cosmic variance for HIPASS BGC dwarfs
Dwarf galaxies
#10 Mpc cells
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)
A BABRaw multibeam spectra near
1499 MHzPost-correlation RFI
cancellation with reference horns
t
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 …
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