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 …