From p-v diagrams, we located three other likely regions of outflow.
The maximum velocity of an outflow can be estimated from the extremum of the emission in the p-v diagram, as in Figure 4. The maximum velocities of the three features are listed in Table 1.
We would like to know how much mass is flowing out of these regions. We can estimate this by isolating the pixels in the kink to the side of the main strip of emission (that is, the gas moving faster or slower than the surrounding gas). We then sum up the values of these pixels and convert to mass as before. The outflow masses of the three features are listed in Table 1.
|Feature||Max. outflow vel. (km/s)||Outflow mass (kg)|
|A||32||2 * 10^6|
|B||-26, -35||1 * 10^6|
|C||26||4 * 10^5|
A note: We might expect that a spherical shell would appear as a two-sided kink: one portion of gas moving toward us and another moving away. However, we were unable to find any such features. The one-sided shells could be explained by the gas in front already having been blown away completely, or by the rear of the shell being obscured by the front.
I visually searched these maps for interesting features, keeping a fairly low threshold for feature "believability" in order not to miss small or faint features. I noted the positions of apparent holes in the gas (breaks in the vertical emission strip), shells (kinks in the strip), and regions of increased gas chaos or turbulence (broadening or chaos in the strip). It is likely that I saw many false positives, since when I located the possible features on a moment 1 map, many fell outside the visible gas (see Figure 9).
However, one feature (a bend in the vertical emission strip seen in panels 1073-1161 of this plot; numbered 27 on the large map) falls directly on the dense lower-central cloud of the galaxy.
This seemed like a believable feature, so I investigated it further using a velocity profile (an array of panels containing velocity histograms for each point in space), shown here . The histograms have been smoothed along the velocity axis to decrease noise. The panels are sequenced with an increment of about 5" (10 pixels) in declination and 2s (30 pixels) in right ascension. In such a diagram, the signature of an expanding shell would be a ring of panels with velocity peaks offset from the systemic velocity of the galaxy, with the encircled panels either having peaks at the systemic velocity or having little total emission. In this figure, it does appear that some of the panels near the edge have velocity peaks nearer to -320 km/s than the systemic -345 km/s, but it is difficult to discern a clear shell.
Unfortunately, trying out kshell on some likely shell locations did not produce
any clear shell signatures. Some outputs are below.
output of kshell:
I then created P-V diagrams for small regions (100 pixels on a side) around each of Hunter's clusters, in order to investigate the dynamics of the nearby HI. They are listed below, with comments on each diagram in parentheses. (In defining the regions, I used kvis to match pixel positions with RA/DEC positions and then fed the pixel positions into AIPS to produce the plots.)
1-1 (Hole just below cluster in declination)
1-2 (Hole just below cluster in declination)
1-3 (Slight kink at RA=00 20 24-32, DEC=914-939(pix) [SHELL?]. Small dark spot (negative emission?) right in the middle of the strip of positive emission at RA=00 20 27, DEC=944. Several frames, including DEC=944,949,954,969 have dark spots outside emission strip.) 1-3b is zoomed in on dark spot.
1-4 (No distinct features except dark spot at RA=00 20 27, DEC=945 (visible in 1-3 also).
2-1 (Hole just below cluster in declination)
2-2 (Emission strip looks smooth; some dark dots)
4-1 (Slight kink at RA=00 20 23-28, DEC=927-937(pix) [SHELL?])
4-2 (Dark spot in emission strip at RA=00 20 27, DEC=946)
4-3 (No distinct features, but emission strip is somewhat bent.) 4-3b is zoomed out in RA but shows nothing much more interesting.
4-4 (Emission is somewhat chaotic at DEC=900. Dark spot in emission strip at RA=00 20 27, DEC=945.
4-5 (Very smooth, no features.)
4-6 (No distinct features.)
4-7 (No distinct features.)
There is some uncertainty in the placement of these clusters and the regions of the corresponding p-v diagrams. Hunter's paper gives the locations in hours/minutes/seconds of RA and degrees/arcminutes/arcseconds of DEC, whereas AIPS reckons locations in pixels. There are two possible ways to locate the features on an AIPS-made map of the galaxy. The tool kvis displays the position of the mouse cursor on a loaded image in both RA/DEC and pixel position. Thus, by simply moving the mouse to the correct RA/DEC position, one can read off the corresponding pixel position.
Alternatively, we could convert manually from units of time to units of arc. An hour at a high declination subtends a smaller arc than an hour at a low declination; to convert from seconds of time to seconds of arc, we divide by 15*cos(DEC), where DEC is in hours.
I decided to do the latter in order to check the first method. The
AIPS image header for the data cube claims that the coordinates of the center
of the galaxy are:
|RA||00h 20m 23s||1024|
|DEC||59d 18' 08"||1025|
|Cluster||RA (in time units, from Hunter)||RA (in pixels, calculated)||RA (in pixels, from kvis)||DEC (in arc units, from Hunter)||DEC (in pixels, calculated||DEC (in pixels, from kvis)|
|1-1||00 20 25.13||992||989||59 18 07.81||1023||1019|
|1-2||00 20 24.62||1000||997||59 18 12.53||1033||1028|
|1-3||00 20 24.95||995||991||59 17 39.97||968||964|
|1-4||00 20 23.92||1010||1007||59 17 45.29||978||975|
|2-1||00 20 26.90||964||962||59 18 17.22||1042||1039|
|2-2||00 20 24.28||1005||1002||59 19 10.54||1149||1146|
|4-1||00 20 27.77||951||949||59 17 38.65||965||962|
|4-2||00 20 28.16||943||943||59 17 35.63||959||956|
|4-3||00 20 26.58||969||967||59 17 02.53||893||890|
|4-4||00 20 27.47||959||953||59 17 07.92||904||900|
|4-5||00 20 28.55||939||936||59 17 21.81||931||928|
|4-6||00 20 26.51||970||968||59 16 36.26||840||837|
|4-7||00 20 27.58||954||952||59 16 36.49||841||838|
A region of interest might be cloud #5, which has several small holes.
Other miscellaneous contour maps:
Lower central cloud -- Levels: 10%,25%,40%,55%,70%,85%
Left hand cloud -- Levels: 10%,25%,40%,55%,70%,85%
Upper cloud -- Levels: 10%,25%,40%,55%,70%,85%
Whole galaxy. Levels: 5,20,40,60,75
Whole galaxy. Levels: 5,20,40,50,60,85
Here is a pdf of the poster, which was presented at the January 2007 meeting of the American Astronomical Society.