HI cubes were calibrated and constructed for each azimuth at a
resolution of 3.9 arcminutes. Each cell is 30 arcsec square
and the RA, DEC size is 201 x 110 pixels constituting a complete areal
coverage of 1.54 square degrees. The velocity spacing is 1.29 km/s and
800 velocity pixels have been extracted from the original cubes (to avoid Galactic
emission as well as edge problems) for a total velocity coverage of 1034 km/s.
The cubes were then cleaned with the beam corresponding to the azimuth
of the cube and for the pixel being
considered. (Beams are here .) Some cleaning artifacts remain (beams were not characterized
as well as we would have liked) and therefore negative values
below -3sigma were clipped. Also, in a few areas,
the 'wandering birdie' created regions
in which blanking was required. The emission has been interpolated over
those blanked regions.
The 12 cubes corresponding to each individual azimuth can be
downloaded
here (file = N2903_AZCUBE_n.FITS), where n is a number from 1 to 12
corresponding to the various azimuths (n = 1 => az = 104 ... n = 12 =>
az = 255 -- for a complete list, see the beams).
All 12 azimuths were then averaged together to make the final cube. The final cube, as described above, is in fits format and can be downloaded here (file = N2903_FINAL_CUBE.FITS) The rms of the cube is about 1.1 mJy/beam and the peak emission is 586 mJy/beam, for a dynamic range of 533. A MOM0 (file = N2903_MOM0.FITS) and MOM1 (file = N2903_MOM1.FITS) map can also be downloaded.
Since some calibration and cleaning artifacts do remain, we then smoothed each cube at each azimuth to 4.5 arcminute resolution (no clipping in this case). The smoothed cubes for each azimuth can also be downloaded here (file = N2903_AZCUBE_SMOOTHED_n.FITS) where, again, n refers to the azimuth. The final cube was then remade as before. The final smoothed cube can also be downloaded here (file = N2903_FINAL_CUBE_SMOOTHED.FITS) The rms of the cube is about 0.7 mJy/beam and the peak emission is 666 mJy/beam, for a dynamic range of 951. The HI mass of N2903 is 4.2E9 Msun. This compares with some new Westerbork results (Braun et al. 2007, A&A, 461, 455) who find 4.0E9 Msun. A MOM0 (file = N2903_MOM0_SMOOTHED.FITS) and MOM1 (file = N2903_MOM1_SMOOTHED.FITS) map can also be downloaded.
A proper analysis of the minimum detectable emission still needs to be done (note that some rows of the cube have a lower rms than others since there are sometimes several scans at a point and sometimes not).
I include below gif images of the mom0 map of the smoothed data. The left image shows the emission normally and the right image accentuates the lowest levels. You can see that there is one companion at (preliminary) coordinates: RA, DEC = 09 30 38.45, 21 43 7.9, Vel = 582.8 km/s (velocity profile not made yet). This emission is at the location of a 2MASS galaxy: 2MASX J09303320+2140099.
Here is the
global profile of the companion. **Preliminary**
results: From the global profile, we find M_HI = 1.5E6 Msun.
From the Bell et al. (2003) conversion of stellar K-band
flux to stellar mass, we find a stellar mass of 4E7 Msun. From the
line width, we find M_tot = 1E8 M_sun. The latter value has uncertainties
because the galaxy appear to be unresolved (so R was just taken as 1/2 the
3.9 arcmin beam) and we also don't know the inclination (so sin i was taken
as 1). A closer inspection might improve these values. Taking the mass
as between 5E7 and 1E8 M_sun, we can compare the number of expected
companions from Diemand, Kuhlen, & Madau's 2006 paper (Their Fig. 5).
We have fully sampled a region 308 kpc X 138 kpc in size around NGC2903.
Diemand et al. let the virial radius of the Milky Way be 389 kpc. NGC2903
has very similar properties to the MW so we expect there to be a similar
number of companions. We have also sampled (effectively) about 0.3 of
their virial radius. So interpolating from their curve (this is *very*
rough) we might have expected to see 20 or 30 companions, whereas we see
only one.