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Using the Parkes Multibeam to Search for HVC Analogs
D.J. Pisano (ATNF)
with David Barnes (Melbourne), Brad Gibson (Swinburne), Lister Staveley-Smith (ATNF), Ken Freeman (RSAA/ANU)


Possible analogs to Local Group HVCs

courtesy B. Wakker

Blitz et al. (1999) and Braun & Burton (1999) suggest that some HVCs have median distances of 500 kpc ­ 1 Mpc and HI masses of 106-7 M0. We need comparable sensitivity and spatial coverage to find potential analogs, if HVCs are associated with the Local Group.


Satellites in Loose Groups
Models of galaxy formation predict large numbers of satellites in Local Group analogs, particularly with velocity widths less than 20 km/s. Need high velocity resolution! These could be associated with some of the HVCs as suggested by Blitz et al. (1999) and Braun & Burton (1999).

from Klypin et al. (1999)


What is a Loose Group?
A working definition is: A grouping of a few large galaxies and tens of smaller ones, with the large galaxies typically separated by ~ 100-200 kpc. They are of order 1 Mpc in total extent. The Local Group of galaxies is a loose group. Of particular interest are analogs to the Local Group which are dominated by spiral galaxies.


Multibeam Observations of LGG 93, 180, & 478
Group Galaxies Velocity Area Vel. Range dV 14ґ = # beams MHI (3.3 km/s) LGG 93 5 Spirals 750 km/s 25 deg2 1 Mpc
2

LGG 180 3 S, 6 Irr 725 11.1 25 1 1700 1.65 45 7 8x105

LGG 478 3 S, 1 Irr 692 10.6 35 1.7 3400 3.3 43 13 5x105

Dist (H=65) 11.5 Mpc

1700 km/s 1.65 km/s 47 kpc 7 8x105 MO


New Detections in LGG 93


LGG 93 ­ Detection 1

Dec (2000)

Velocity Velocity

RA (2000)


LGG 93 ­ Detection 2

Dec (2000)

Velocity Velocity

RA (2000)


ATCA Follow-Up

LGG 93-1 AM 0311-492 LGG 93-2 LSBG F200-023 IC 1914


Detection Statistics

10 5 3


How can ALFA help?
tobs (Tsys/G)2 * n * Assuming T
sys -1 bm

~ 30 K, Gain = 8 K/Jy, n=7:

(for PKS: Tsys ~ 21 K, Gain = 0.67 K/Jy, n=13)

ALFA can map the same area 2x faster than PKS ! map more groups, more distant groups, ! get better statistics D < 20 Mpc in same amount of time as D < 15 Mpc D < 50 Mpc with same resolution as D < 10 Mpc


ALFA can map the same area 2x deeper than Parkes !lower mass limits can better constrain HVC models at D = 10 Mpc for FWHM = 30 km/s at 5 MHI(PKS) = 6.4 x 106 MO MHI(ALFA) = 4.6 x 106 MO D
HVC

drops from 540 kpc 450 kpc (Braun & Burton 2001)

Easier to map more area than to go deeper! Resolution is Arecibo's big advantage over Parkes.