The M96 group of galaxies

This conspicuous group of galaxies

contains 3 Messier objects

(M95, M96,

and M105), plus a larger number of fainter

galaxies (including NGCs 3299, 3377, 3384, 3412 and 3489 as well as

UGC 5889, which is also called NGC 3377A in the Sky Catalogue 2000.0).

The Sc galaxy NGC 3389, which is in the same field and close to M105,

is probably a background galaxy, as its redshift corresponds to a receding

velocity of 1138 km/sec, whereas the members of the Leo I group have

radial velocities of only 449..766 km/sec.

In our image on the right hand side, M95 is in the lower right corner,

while M96 is in the lower middle, and M105 is the bright elliptical galaxy

above and left of the picture’s center, together with its fainter neighbors

NGC 3384 and faint NGC 3889.

Nial R. Tanvir of the

Cambridge Astronomy group has investigated this

group of galaxies with the Hubble Space Telescope. He and his coworkers

found 8 Delta Cephei variable stars in the brightest galaxy of the group,

M96, and were able to derive its distance

from the Cepheid period-luminosity relation: M96 is 231+/-13 times more

remote from us than the Large Magellanic Cloud, thus 12.7+/-0.8 Mpc

(41+/-2 million light years).

An improvement of this value is hoped to be obtained from ongoing HST

observations of Cepheid variables in the group galaxies

M95 and UGC 5889 (both spirals).

A first result was obtained for M95 in 1996-97 by the HST H0 Key Project

Team,

J.A. Graham et.al., The Extragalactic Distance Scale Key Project VII.

The Discovery of Cepheids in the Leo I Group Galaxy NGC 3351.

They obtained a distance of 10.05+-0.88 Mpc (32.8+-2.9 million light years),

which after correction for the new Cepheid distance scale becomes

10.90+-0.95 Mpc (35.5+-3.1 million light years).

As a mean value of the two distances obtained in the work of Tanvir and the

H0 key project team, we will use a distance of 38 million light years here.

From the distance derived here, it is possible to gauge a

diameter-velocity dispersion-relation for elliptical galaxies, namely by

using the galaxies M105 and NGC 3377.

By the relation obtained for this, the distance of the

Virgo and Coma clusters of galaxies could be

estimated; one obtains a distance of 18.3+/-2.0 Mpc (60+/-6 million

light years) for the Virgo cluster, and of 105+/-11 Mpc (~340 million

light years) for the Coma cluster of galaxies. (The Virgo cluster distance

may be estimated from that of the M96 group also by other methods,

yielding about the same value).

The Coma distance then allows to estimate the value of the current Hubble

constant (H0, “Hnaught”) to be

H0 = 69+/-8 km/(s*Mpc)

which is again (after the M100 result) intermediate between the

rivaling values of H0=50 and H0=100

(the values given here are corrected for the new Hipparcos results of

February, 1997).

The M96 group may be physically related to the

M66 group which is roughly at the same distance

and situated rather nearby in the sky.

The following table lists some data of the M96 or Leo I group members

listed above (most data from the Sky Catalogue 2000.0):

Name	RA(h:m)	Dec(d:m)	type	m_v	dim	RV
NGC 3299	10:36.4	+12:42	SABdm	13.29p	2.1×1.7	465
M95	10:44.0	+11:42	SBb	9.71	7.4×5.1	649
M96	10:46.8	+11:49	Sbp	9.24	7.1×5.1	766
UGC 5889	10:47.4	+14:04	SABm	14.15p	2.0×1.9	449
NGC 3377	10:47.7	+13:59	E5	10.21	4.4×2.7	595
M105	10:47.8	+12:35	E1	9.26	4.5×4.0	752
NGC 3384	10:48.3	+12:38	E7	9.96	5.9×2.6	641
NGC 3412	10:50.9	+13:25	E5	10.55	3.6×2.0	737
NGC 3489	11:00.3	+13:54	E6	10.33	3.7×2.1	576