10.02.2013 Views

Max Planck Institute for Astronomy - Annual Report 2005

Max Planck Institute for Astronomy - Annual Report 2005

Max Planck Institute for Astronomy - Annual Report 2005

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

84 III. Scientific Work<br />

Fig. III.4.4: The spiral galaxy NGC 2403 as an example. Left:<br />

integrated HI column density map (similar to the map shown<br />

in Fig. III.4.2). Middle: velocity field of NGC 2403 – the different<br />

colors indicate different velocities: Red colors indicate<br />

emission moving away from the Earth, blue colors represent<br />

approaching material (relative to the center of mass). This<br />

in<strong>for</strong>mation can be used to derive rotation curves and to study<br />

the fine-scale kinematics in galaxies. Right: the velocity dispersion<br />

map of NGC 2403. Red colors indicate high dispersion<br />

in the atomic ISM; blue colors indicate more quiescent<br />

regions. Such maps are used to study the energy input of star<br />

<strong>for</strong>mation into to the ISM.<br />

Fig. III.4.5: The spiral galaxy M 81 in different wavebands:<br />

The distribution of atomic hydrogen from the Things project<br />

is shown in blue in all panels. The other wavebands were observed<br />

with spiTzer and the colors are explained in each panel.<br />

The 3.6 micron emission is dominated by the contribution of<br />

old stars in the bulge, the 8 micron map contains emission from<br />

stars, hot dust and so-called PAH emission features. Such comparisons<br />

provide important clues about the processes leading to<br />

star <strong>for</strong>mation in galaxies of the Things sample.<br />

atomic hydrogen: blue<br />

3.6 �m: green<br />

24 �m: red<br />

atomic hydrogen: blue<br />

3.6 �m: red<br />

8 �m: green<br />

velocity at which the gas is moving. This is illustrated<br />

in Fig. III.4.3, where we show so-called channel maps<br />

<strong>for</strong> one of Things targets (M 101). In each panel, only<br />

HI emission measured at a given velocity (as labeled<br />

in the upper right in each panel) is shown. This clearly<br />

demonstrates that the different parts of the galaxy have<br />

different velocities – the »movement« from the upper<br />

left to the lower right (with increasing channel number)<br />

is due to the rotation of the galaxy (the receding side is<br />

seen in the first channels, the approaching side is in the<br />

last channels, and the systemic velocity of the galaxy is<br />

at around 240 km/s). In addition to this global rotation,<br />

the channel maps also reveal a rich degree of fine structure<br />

in the ISM.<br />

For each of the Things galaxies, these channel maps<br />

are then used to create 1) the integrated HI maps (by<br />

simply adding the channels seen in the channel maps),<br />

2) a map of the average velocity <strong>for</strong> each pixel (so-called<br />

velocity fields) and 3) a velocity dispersion map. As<br />

an example, we present these three maps <strong>for</strong> the galaxy<br />

NGC 2403 in Fig. III.4.4. The left hand panel shows the<br />

atomic hydrogen: blue<br />

8 �m: green<br />

24 �m: red

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!