Rotation and Mass of the Magellanic-Type Galaxy NGC 4631.
Abstract
e edgewise Magellanic-type galaxy NGC 4631 was derived from five long-exposure spectrograms taken in April 1961 with the B-spectrograph at the prime focus of the 82-inch reflector. Measurements were made in 395 points of Ha and six other emission lines at intervals of 50~ = 7"45 extending over a total length of 10' along the major axis of the object. The velocity range is from +530 km sec-1 about 6' west to +740 km sec-' about 4' east of the center; the adopted mean rotational velocities are Vr= 57 km sec-1 at r=2'0 and Vr=97 km sec-1 at r=4'0. If the distance is A=4.4 Mpc (Astrophys. J. Suppl. No. 48, 270, 1961), these velocities give for the total mass of a model made up of two inhomogeneons spheroids (Astrophys. J. 131, 265, 1960) of radii 5' and 10' and axis ratio c/a=0.2, ~ = (2.4~0.4) X 1010 solar masses the central density is Pc 5.5 X 10-24 g cm-3 and the mean density ~p>~1.0X 10-24 g cm-3. With the total magnitude ~~=9.7 (pg) measured by Holmberg (Lund Medd. II, No. 136, 1958) and the apparent modulus m-M=28.4, MT -18.7, and the apparent mass-luminosity ratio is ~Th/ = 5.1; if the internal absorption is ~m~0.5 mag. the corrected ratio is (~/ ) o~3.2. Systematic departures of up to t40 km sec-1 from a regular rotation curve are tentatively interpreted as evidence of large-scale streaming motions of the gas in the central regions of the system, in particular of a flow away from the center and along the bar. e edgewise Magellanic-type galaxy NGC 4631 was derived from five long-exposure spectrograms taken in April 1961 with the B-spectrograph at the prime focus of the 82-inch reflector. Measurements were made in 395 points of Ha and six other emission lines at intervals of 50~ = 7"45 extending over a total length of 10' along the major axis of the object. The velocity range is from +530 km sec-1 about 6' west to +740 km sec-' about 4' east of the center; the adopted mean rotational velocities are Vr= 57 km sec-1 at r=2'0 and Vr=97 km sec-1 at r=4'0. If the distance is A=4.4 Mpc (Astrophys. J. Suppl. No. 48, 270, 1961), these velocities give for the total mass of a model made up of two inhomogeneons spheroids (Astrophys. J. 131, 265, 1960) of radii 5' and 10' and axis ratio c/a=0.2, ~ = (2.4~0.4) X 1010 solar masses the central density is Pc 5.5 X 10-24 g cm-3 and the mean density ~p>~1.0X 10-24 g cm-3. With the total magnitude ~~=9.7 (pg) measured by Holmberg (Lund Medd. II, No. 136, 1958) and the apparent modulus m-M=28.4, MT -18.7, and the apparent mass-luminosity ratio is ~Th/ = 5.1; if the internal absorption is ~m~0.5 mag. the corrected ratio is (~/ ) o~3.2. Systematic departures of up to t40 km sec-1 from a regular rotation curve are tentatively interpreted as evidence of large-scale streaming motions of the gas in the central regions of the system, in particular of a flow away from the center and along the bar.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 1962
- DOI:
- 10.1086/108614
- Bibcode:
- 1962AJ.....67..113D