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a deep blind HI survey with the Parkes telescope

HIDEEP:

R. Minchin M. Disney Q. Parker P. Boyce E. de Blok G. Banks

K. Freeman D. Garcia M. Grossi R. Haynes P. Knezek R. Lang6 Mar 2003

D. Malin R. Price M. Putman I. Stewart A. Wright


Background
! HI surveys were until a few years ago limited by single beam and correlator velocity range ! New Multibeam instruments and correlators have now made large surveys possible
o HIPASS ­ all sky up to dec +22 (450s per beam) o HIJASS ­ northern sky down to +22 (350s per beam)

! Parallel to HIPASS: o HIDEEP: "The HI

equivalent of the Hubble Deep Field" ­ (9000s per beam)


HIDEEP: The Basics
! 4 by 8 degrees region in Centaurus ! centered on = 13h40m00s, = -30o00'00" ! velocity range: -1280 to 12,7000 km/s, 1024 ch at 13.2 km/s spacing ! velocity resolution 18 km/s ! beam size ~14', pixel size 4' ! includes Cen A group and outer parts Cen cluster ! not instrumentation noise limited: noise ~ 1/t ! noise = 3.2 ± 0.2 mJy


HIDEEP: The Detections
! Data cube searched 3 times:
o 2 humans and 1 computer o only objects detected 2 out of 3 times retained

! 173 detections ! profiles and positions extracted and quantified ! selection limits:
o peak flux and velocity width limited o limits are 9.6 mJy and 4 ch = 52.8 km/s o completeness limit at ~18 mJy
5 optim.smooth limit 3 peak flux limit


HIDEEP: Optical Follow-Up
! HIDEEP field imaged with UK Schmidt telescope at Siding Spring, Australia ! 8 1hr exposures in R-band on Tech-Pan plates ! Digitised using SUPERCOSMOS ! 6 by 4 degrees overlap with HI field ! limiting surface brightness is 26.5 R (27 to 28 B) ! 96 HI sources in field
o o o o 59% known galaxies, z known 24% known galaxies, z unknown 17% uncatalogued galaxies no HI without optical....


HIDEEP: Galaxy Properties
(a personal and biased selection)

Large Scale Structure:
! HIDEEP lies in the super galactic plane ! For z<10,000 km/s good correlation between optical LSS and HI LSS ! Beyond 10,000 km/s HI sources appear to populate void
o real or HI/optical selection effects?
x NED HIDEEP


HIDEEP: Galaxy Properties
(a personal and biased selection)

Surface Brightnesses:
! Large fraction of sample has LSB ! KS test: late-type ESO-LV and HIDEEP surface brightness parent distribution differ at 99% ! Galaxies in HIDEEP are more gas-rich
observed corrected


HIDEEP: Column Densities - Theory
TB =
! Column density sensitivity of radio-telescope ! HIDEEP: Tsys = 26K, tobs=9000s, V =13.2 km/s

2k

2 S

TA


Tsys tobs
-2
(c) j sarkissian

! NHI > 2.1 1016 V cm
! For V = 200 km/s, NHI ~ 4 1018 cm-2

-2



= 1.8 1018 V cm
Tsys
tobs Vch

N

HI

2.75 10

17

V

5


HIDEEP: Column Densities
Salpeter & Hoffman (1996): rHI = (2.34 ± 0.14) r25 ESO-LV: r25 = (2.15 ± 0.67) re
limit ness lete o mp Jy c 18 m

! What is distribution of HI column densities? ! No resolved imaging yet, so use mean column densities ! Have HI mass, need HI size ! Cut-off in distribution of column densities ! Need systematic underestimate of rHI of factor 3

N

HI

= 10

20.1

M HI cm 2 RHI

-2


HIDEEP: Column Density Cut-off?
! There don't appear to be any low-column density galaxies in HIDEEP ! Distribution is consistent with constant column density log = 20.65 ± 0.38 ! But previous surveys indicate ~ µ .... ! Open questions:
o selection effects? o why would HIDEEP field be different? o KS test of resampled ISIB96 inconclusive

(c) j sarkissian

! But low column density galaxies still absent from both data sets


HIDEEP: Conclusions and Questions
! HIDEEP shows that deep HI surveys are feasible and not limited by instrumental problems ! All HI sources are associated with optical counterpart ­ no "dark galaxies"...? ! There is a lack of lowcolumn density galaxies in HIDEEP ! If real, what causes this lack? Why different from some other surveys?
o ionisation? o "frozen disks" (T o environment?
spin

~TCMB)?