Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/research/multibeam/papers/Kilborn_iauc171.ps.gz Äàòà èçìåíåíèÿ: Mon Oct 26 03:21:35 1998 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 10:14:32 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

The Low Surface Brightness Galaxy HIPASS1126­72
Virginia Kilborn 1 , Erwin de Blok 1 , Lister Staveley­Smith 2 , Rachel
Webster 1
1. School of Physics, University of Melbourne, Parkville, Vic 3052,
Australia
2. ATNF, PO Box 76, Epping, NSW 2121, Australia
Abstract. The low surface brightness galaxy HIPASS1126­72 was de­
tected in the HI Parkes All Sky Survey (HIPASS). The galaxy was previ­
ously listed in the Southern Galaxy Catalogue under the name SGC1124.8­
7221. This galaxy represents a class of galaxies that we will readily detect
in the HIPASS survey, which have low surface brightness in the optical,
but are easily detectable in neutral hydrogen.
1. Introduction
The HIPASS survey is being conducted at the 64m Parkes Radio­telescope in
Australia, mounted with a 13 beam ``multibeam'' detector (Webster et al 1998,
Barnes et al, 1998). The beam size for the survey is ¸ 14', and the velocity reso­
lution is 18 km s \Gamma1 . HIPASS1126­72 was detected by eye during routine searches
for galaxies in the HIPASS data cubes. The HIPASS detection represents the
first HI observation of this galaxy, and it was selected for higher resolution ob­
servations on the ATCA since its velocity profile was only just resolved in the
HIPASS data. The velocity profile from HIPASS can be seen in Figure 1(a).
Figure 1. HI Spectrum from (a) the HIPASS survey, and (b) the
Compact Array.
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2. Observations
To obtain higher resolution of HIPASS1126­72, about 7 hours of data was taken
in May 1998 at the Australia Telescope Compact Array (ATCA), with a 750m
array. The resultant beam size was ¸ 60 00 \Theta 40 00 , and the velocity resolution
was 3.3 km s \Gamma1 . The data reduction package MIRIAD was used to reduce the
ATCA data. The HI distribution overlaid on the optical image (Fig. 2), shows
a depression in the HI distribution at the optical center of the galaxy, which is
also the brightest star forming region. This suggests the HI has been depleted
in the formation of stars in this region. The ATCA spectrum can be seen in
Figure 1(b).
Figure 2. HI Spectrum overlaid on the DSS image (image size: 6:4 0 \Theta
6 0 ) ­ the contours are 7% contours, starting with the peak flux.
HIPASS1126­72 was observed in B and R­bands at the Siding Spring 40­inch
telescope in January, 1998. The resulting images can be seen in Figure 3. We
can see that the galaxy is more luminous in the B­band, which is a characteristic
common to low surface brightness galaxies (de Blok, 1997). Ellipse fitting to the
B band image gives an inclination of ¸ 25 o , and the central surface brightness
in B was found to be ¸23.8 mag arcsec \Gamma2 . This galaxy lies close to the galactic
plane, and foreground stars partially obscure one side of the galaxy; these are
especially prominent in the R­band image, and have obstructed us from doing
photometry in that band. The galactic extinction at these galactic coordinates
(l=296,b=­10) is 1.42 magnitudes in the B­band (Schlegel et al, 1998).
Figure 3. MSSSO 40' Observations: (a) Image in B­band (3600s);
(b) Image in R­band (1800s).
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Figure 4. (a) Surface Brightness Profile B­band and (b) HI Surface
Brightness Profile.
3. Characteristics of HIPASS1126­72
Position (J2000): RA: 11:26:28 Dec: ­72:37:15 (ATCA)
Central Surface Brightness (B­band): 23.8 mag arcsec \Gamma2
Heliocentric Velocity: 2012 km s \Gamma1 (ATCA)
Velocity Width (20%, 50%): 27 km s \Gamma1 , 16 km s \Gamma1 (ATCA)
HI Mass: 3:4 \Theta 10 9 M fi (HIPASS)
The 20% velocity width is less than twice the velocity resolution of the HIPASS
survey. Thus the survey will detect galaxies unresolved in velocity, making
interference rejection harder. Figure 4. shows the HI emission extends to a much
greater radius (120'') than the optical light (40­50''). The HI surface brightness
is almost constant to the optical radius of the galaxy, then it decreases.
4. Conclusions
HIPASS1126­72 has one of the narrowest integrated profile widths of any known
galaxy. The low velocity width appears to be the result of its low inclination,
low gravitational potential and low surface density of star­formation. In gen­
eral, the HIPASS survey is very sensitive to such low surface brightness, HI­rich
galaxies. Optical and radio follow­up observations of such galaxies will do much
to elucidate their nature.
5. Acknowledgements
We gratefully acknowledge the help of the Multibeam Working Group in making
the HIPASS observations. Thanks are also due to Michael Brown and Helmet
Jerjen for helping with the optical photometry.
References
Barnes D. G. et al 1998, ADASS VII, ASP conference series 145, p89
de Blok W. J. G. 1997, PhD thesis, University of Groningen
Schlegel D. J., Finkbeiner D. P. & Davis M. 1998, ApJ 500, p525
Webster R. L. et al 1998, this issue
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