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Elliptical galaxies

Elliptical galaxies

Rough subdivision
· Normal ellipticals. Giant ellipticals (gE's), intermediate luminosity (E's), and compact ellipticals (cE's), covering a range of luminosities from MB -23m to MB -15m . · Dwarf ellipticals (dE's). These differ from the cE's in that they have a significantly smaller surface brightness and a lower metallicity. · cD galaxies. Extremely luminous (up to MB -25m ) and large (up to 1 Mpc) galaxies near centers of rich clusters of galaxies. · Blue compact dwarf galaxies (BCD's). BCD's are clearly bluer (B - V 0.0 - 0.3) and contain an appreciable amount of gas in comparison with other E's. · Dwarf spheroidals (dSph's). Low luminosity and surface brightness (they have been observed down to MB -8m ).

Elliptical galaxies

Elliptical galaxies

Characteristic values for E's (Schneider 2006).
Type MB ­22m to ­25m ­15 to ­23 ­13 to ­19 ­14 to ­17 ­8 to ­15 M(M ) D25 (kpc) M/LB

cD E dE BCD dSph

1013 - 1014 108 - 1013 107 - 109 109 107 - 108

300-1000 1-200 1-10 <3 0.1­0.5

>100 10­100 1­10 0.1­10 5­100


Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Shapes of elliptical galaxies


Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Shapes of elliptical galaxies

Some results:

Isophote twisting

Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Shapes of elliptical galaxies

Fine structures


Elliptical galaxies
Shapes of elliptical galaxies

Elliptical galaxies
Photometric profiles

Fine structures: Virgo E/S0 galaxy NGC 4382 Kormendy et al. (2008):

Elliptical galaxies
Kormendy relation

Elliptical galaxies
Kormendy relation

Kormendy (1977) demonstrated that a correlation exists berween re and µe in the sense that larger galaxieshave fainter effective surface brightnesses. Thick solid line ­ µe = A lg re + const, A 3 (Kormendy relation). Thin solid line ­ a line of constant luminosity: MVauc = µe - 5 lg re - 39.96, so µe 5 lg re .
Capaccioli et al. (1992) Kormendy et al. (2008)

Applications of the KR: surface brightness evolution, Tolmen's test for expansion.


Elliptical galaxies
Faber-Jackson relation

Elliptical galaxies
Fundamental plane

A relation for elliptical galaxies, analogous to the TFR, was found by Sandra Faber and Roger Jackson (1976). They discovered that the velocity dispersion in the center of ellipticals, 0 , scales with luminosity,
B L 0 ,

The fundamental plane (FP) is a relation that combines surface photometry with spectroscopy. The FP was discovered independently and simultaneously by Djorgovski & Davis (1987) and Dressler et al. (1987).

where B 4.

The dispersion of ellipticals about this relation is larger than that of spirals about the TFR. The FJR can be used to estimate a galaxy's distance from its measured velocity dispersion.

Elliptical galaxies
Fundamental plane

Elliptical galaxies
Fundamental plane

Standard presentation of the FP is lg re = lg 0 + lg I The FP is a relation between re , , and µe and is linear in logarithmic space. Since 2 L Ie re , the FP can also be expressed as a relation between L, , and µe or between re , , and L. or re
0 e

+ const

I . e

1.3 in the B , 1.7 in the K passband; -0.8. The Kormendy (µe - re ) and the Faber­Jackson (L - ) relations are diferent projections of the FP. Applications: galaxy distances, evolution of E.
Pahre et al. (1998) ­ 301 galaxy, K band.


Elliptical galaxies
Fundamental plane

Elliptical galaxies
Fundamental plane

Observational data on the FP coefficients

Bender et al. (1992) introduced a new or thogonal coordinate system for the FP known as the -space, defined by the following independent variables:

which relate to galaxian total mass, M , average effective surface brightness, I e , and mass-to-light ratio, M /L, respectively.

Elliptical galaxies
Fundamental plane

Elliptical galaxies
Fundamental plane

Simple interpretation of the FP
Such parametrization is useful for a number of reasons: (1) -variables are expressed only in terms of observables, (2) the 1 - 3 plane represents an edge-on view of the FP and provides a direct view of the tilt, (3) the 1 - 2 plane almost represents a face-on view of the FP.
9000 galaxies from the SDSS, g band.

For a bound system GM =k R
E

V2 , 2 to the

where kE = 2 for a virialized system. We relate the observable quantities re , 0 and I physical quantities through re = kR R ,
2 0 = k V

e

V2 ,

2 L = kL I e re .

The parameters kR , kV , and kL reflect the density structure, kinematical structure, and luminosity structure of the given galaxy. If these parameters are constant, the galaxies constitute a homologous family.


Elliptical galaxies
Fundamental plane

Elliptical galaxies
Fundamental plane

Therefore, assuming kE = 2 we obtain re = kS (M/L)-1
2 0

I

-1 e

, A non-constant kS (M/L)-1 product can be explained by a systematic deviation from homology (kS varies), or a systematic variations of the M/L ratios, or both. The interpretation of the FP is still a matter of debate. There are some evidences in favour of M/L variations (M/L L0.2-0.3 ) and of non-homology (e.g. n L).

where M/L ­ global mass-to-luminosity ratio and kS = (GkR kV kL )-1 . For homology kS will be constant. (Homology means that structure of small and big galaxies is the same.) When this relation is compared to the observed FP, re
1.4 0

I

- 0.8 e

,

it is seen that the coefficients of the FP are not 2 and -1 as expected from homology and constant mass-to-light ratios. The product kS (M/L)-1 cannot be constant, but has to be a function of 0 and I e .

Elliptical galaxies
Dn - 0 correlation

Elliptical galaxies
Dn - 0 correlation

Dressler et al. (1987) have defined a readily measured photometric parameter that has a tight correlation with 0 by vir tue of the FP. This parameter, Dn , is the diameter within which the mean surface brightness is In = 20.75 in the B band. If we assume that all ellipticals half a self-similar brightness profile, I (r ) = Ie f (r /re ), with f (1) = 1, then the mean surface brightness In can be written as In = 2 I
Dn /2 e0 1 4

For a de Vaucouleurs profile we have approximately f (x ) x with 1.2 in the relevant range of radius. Using this approximation to evaluate the integral, we obtain Dn re Ie
1/

-

re I

0.8 e

.
e

dr r f (r /re )
2 Dn

=

Replacing re by the FP and taking into account that I we finally find 1 0 Dn 0 .4 Ie .05 .

Ie ,

8 Ie (

re 2 ) Dn

Dn /2re

dx x f (x ).
0

This implies that Dn is nearly independent of Ie and only depends on 0 . The Dn - relation describes the proper ties of ellipticals considerably better than the FJR and, in contrast to the FP, it is relation between only two observables.


Elliptical galaxies
Dn - 0 correlation

Elliptical galaxies
Disky vs. boxy

Empirically, ellipticals follow the normalized Dn - relation Dn 0 = 2.05 ( )1.33 , kpc 100 km/s and they scatter around this relation with a relative width of about 15% (Dressler et al. 1987).

Elliptical galaxies
Disky vs. boxy

Elliptical galaxies
Stellar populations


Elliptical galaxies
Stellar populations

Elliptical galaxies
Mass-metallicity relation

Zaritsky et al. (1994): ellipticals ­ open circles

Dressler et al. (1987)