IAO 2006, Практически тур, Група α, английски — Задача 6. NGC 1325.

Practical round. Problems to solve · 10 ноември 2006 г.

Source annotations

In problem 6 the printed “radial” is crossed out and replaced by handwritten “rotational”. The handwritten antenna list A1, A10, A14, A30 is included. The Russian alternate crosses out 7.3; the English edition does not, so its printed 7.3 is retained.

Условие

In the theory problem 4 you answered the question about the spiral galaxy NGC 1325. You estimated that the inclination of the galaxy is $70^\circ$ and its angular diameter is roughly $6'.5$, corresponding to roughly 43 kpc in the physical diameter. This galaxy was observed at GMRT, India during the month of May 2001, to study its rotation profile using the 21 cm wavelength of hydrogen gas in the galaxy. The bottom figure shows distribution of rotational velocities of the gas as a contour map. The image is superimposed on an optical image of the galaxy (not taken by GMRT).

The centre of this galaxy is receding from us. As the galaxy is rotating about itself, one side of the galaxy would appear to recede at a slower speed from us as compared to the other side. In the bottom figure the white contour lines denote velocities slower than the mean velocity and dark contour lines show velocities faster than the mean velocity. Contour lines are drawn for every 10 km/s change in the velocity in the plane of the galaxy (i.e. do not worry about inclination effects).

6.1. Draw the rotation curve of the galaxy (i.e. rotational velocity vs. distance from centre in arcsec).

6.2. From the rotation curve drawn, estimate the total mass of the galaxy (in masses of Sun $M_S$) assuming the circular motion.

Решение

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Оригинал в Архива: alphapract.jpg · допълнителни данни: alphapractdata.jpg