The misterious case of the desappeared galaxies ..

Il giorno venerdì 14 ottobre 2016 23:54:00 UTC+2, Steve Willner ha scritto:
In article ,
writes:
In CDS Strasbourg data center , we can access to the catalogue
VII/250 pare= nt , with datas of 420.000 galaxies . The galaxies
number should be the same for different degreesof eccentric= ity (
ecc.= c/a , in ellipse ; with ecc. =0 we see a circle ( 90 degree=
s )

The above has some non-standard terminology, so I'm not sure what you
are doing. If the galaxy has a ratio of minor to major axis of b/a,
eccentricity _probably_ means 1 - (b/a), though I haven't gone back
to the original source to check that. Maximum eccentricity is
probably about 0.8 or so because galaxies have finite vertical height
even if they are seen edge-on. But as I say, you need to verify how
the original authors defined eccentricity.

From axis ratio, you can use the Hubble formula (not the Hubble Law
dealing with redshifts -- Mr. Hubble did lots of other things!) to
estimate inclination, which is the angle of the galaxy pole to the
line of sight. In other words, an edge-on galaxy will have an
inclination of 90 degrees. The Hubble formula, assuming an intrinsic
axis ratio of 0.2, is cos i = sqrt(1.042*(b/a)^2 - 0.042), where b/a
is the axis ratio. You can see that if b/a = 1, i.e., the galaxy is
round, cos i will be 1 implying i = 0 deg. If the quantity inside
the square root comes out negative, it says the galaxy's true b/a is
less than the smallest assumed value, so just set i = 90.

Once you have inclinations, there should be an equal number of them
in equal intervals of cos i _provided the source catalog is
unbiased_. In practice, there is often bias against edge-on galaxies
because they are generally more highly reddened by dust than pole-on
galaxies.

; with ecc. =3D1 we see a line ( for cutting sight , 0 degrees ) ..... =
easily it comes out : ecc. 1-0.865 ( 0-30degrees) =3D nu. galaxies 6.=
330 ; ecc. 0.865- 0.5 (30-60 degrees) =3D nu. galaxies 107.000 ; e=
cc. 0.5 - 0 (60-90 degrees ) =3D nu. galaxies 298.000 ...

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

.....( the calcules that i report , are referred to the galaxies with complete parameters like z, area , ecc ,,,,.. a inferior number than total catalogue )