Luminosity Dependence

Dividing our sample with respect to luminosity at Mr = −21.49 in two groups of equal num-ber with each sub–sample containing 48 galax-ies, the offsets of the FJR from the local FJR

Figure 7.1: Offsets of the Faber–Jackson relation in Gunnr for the early-type cluster galaxies in A 2390 and A 2218 from the local FJR by the J99 Coma sam-ple as a function of luminosityMr. Filled symbols de-note brighter galaxies withMr<−21.49, open sym-bols fainter galaxies withMr>−21.49. The dashed line indicates a zero offset.

are explored. Fig. 7.1 shows the offsets of the FJR in Gunn r for the early-type galaxies in the clusters A 2390 and A 2218 from the local FJR as defined by the J99 Coma sample as a function of luminosity M_r. Brighter galaxies with Mr < −21.49 are indicated as solid sym-bols, fainter objects with M_r >−21.49 as open symbols. Subdividing the total sample with re-spect to their luminosity Mr at Mr = −21.49 (0.2 mag brighter thanL^∗_r) into two sub-samples of equal number, the brighter cluster galaxies (Mr < −21.49) show on average an evolution with ∆Mr =−0.39±0.13^m. Fainter objects in the rich cluster sample (M_r>−21.49) are on av-erage more luminous by ∆Mr=−0.25±0.18^m. Table 7.1 gives a comparison between the two groups of early-type galaxies with different lumi-nosities. The difference in mean luminosity be-tween lower-luminous and higher-luminous gal-axies is within their 1σ error and therefore

neg-Chapter 7: Environmental Effects on Galaxy Properties 157

Figure 7.2: Offsets of the Faber–Jackson relation in Gunnrfor the morphologically classified elliptical and S0 galaxies in A 2390 and A 2218 from the local FJR by the J99 Coma sample as a function of M_r. Ellipticals are indicated as solid circles, S0s as open circles. The vertical line denotes the border between brighter and fainter galaxies atM_r=−21.49 and the dashed line a zero offset. Lenticulars show on average a stronger evolution than ellipticals.

ligible.

For the offsets from the local FJR in Fig.7.1, the errors of the offsets on the absolute magnitudes were computed as

δ(∆FJR)² =δM_{r clus}² +δM_{r J99}² . (7.2) The first term on the right hand side corresponds to the total error in absolute r magnitude as given in Eq.4.14on page91and the second term are the errors in absolute r magnitude for the Coma J99 data. Individual errors for the J99 data were adopted as published by the authors with mean errors of δM_r = 0.09^m on the pho-tometry.

The galaxy samples with fainter and brighter luminosities exhibit different mean velocity dis-persions (log σ = 2.18, and 2.31, respec-tively). For this reason, a two-dimensional

Table 7.1: Evolution of the Faber–Jackson relation in Gunn r derived for various rich cluster samples.

N is the number of galaxies and ∆Mrindicates the mean luminosity evolution. The fourth column de-notes the±1σdeviation in the mean luminosity evo-lution and the last column ∆hM_rigives the median evolution.

Sample N ∆Mr σMr ∆hMri

[mag] [mag]

(1) (2) (3) (4) (5)

A 2218 48 −0.31 0.15 −0.29 A 2390 48 −0.32 0.29 −0.35 A 2218+A 2390 96 −0.32 0.22 −0.35 low L^a 48 −0.25 0.18 −0.29 high L 48 −0.39 0.13 −0.44 low mass^b 48 −0.62 0.34 −0.63 high mass 48 −0.02 0.16 −0.01

in^c 48 −0.26 0.20 −0.24

out 48 −0.35 0.20 −0.40

a fainter: M_r >−21.49, brighter: M_r <−21.49.

b less-massive: logσ <2.231, more-massive: logσ >2.231.

c in: only core sample R <455.6 kpc,

out: only outer region sample R >455.6 kpc.

Kolmogorov-Smirnov (KS) test is not the ap-propriate statistical method for a comparison.

Instead, bootstrap-bisector fits to the individ-ual sub–samples of lower and higher luminosi-ties are performed. A bootstrap bisector fit to the lower-luminosity cluster galaxies restricted toMr >−21.49 gives

M_r =−(2.65±0.46) logσ−(15.21±1.00), (7.3) whereas the same fitting method to the higher-luminosity ones with Mr<−21.49 yields

M_r =−(2.85±0.53) logσ−(15.47±1.23). (7.4) Fainter and brighter galaxies have slightly dif-ferent slopes but the difference is not statisti-cally significant. An insignificant slope change

Table 7.2: Evolution of the Faber–Jackson relation in Gunnrderived for various Low–LXsamples. N is the number of galaxies and ∆Mrindicates the mean luminosity evolution. (4) denotes the ±1σ deviation in the mean luminosity evolution and the last column

∆hM_rigives the median evolution.

Sample N ∆Mr σMr ∆hMri

[mag] [mag]

(1) (2) (3) (4) (5)

Cl 0849 15 −0.30 0.19 −0.36 Cl 1701 5 −0.42 0.19 −0.20 Cl 1702 7 −0.57 0.20 −0.51 Low–L_X 27 −0.44 0.19 −0.38 lowL^a 13 −0.23 0.22 −0.36 highL 14 −0.55 0.13 −0.26 low mass^b 13 −0.69 0.73 −0.71 high mass 14 −0.12 0.15 −0.07 in^c 13 −0.30 0.17 −0.15 out 14 −0.48 0.18 −0.45

a fainter: M_r >−21.77, brighter: M_r<−21.77.

b less-massive: logσ <2.215, more-massive: logσ >2.215.

c in: only core sample R <474.4 kpc,

out: only outer region sample R >474.4 kpc.

of ∆a = 0.2±0.5 between the sub–samples is found.

An analysis of the FP for the rich cluster gal-axies in the previous chapter 6, revealed that the lenticular galaxies show a larger offset from the local FP relation and a stronger evolution than the elliptical galaxies. To verify this re-sult with the FJR, the FJR offsets of early-type cluster galaxies in A 2390 and A 2218 from the local FJR are displayed in Fig. 7.2, similar to Fig. 7.1but now divided into the morphological types of elliptical and S0 galaxies. For this anal-ysis, the total rich cluster sample is restricted to the 33 E+S0 galaxies which enter the FP and where a morphological classification based upon HST images is available. The bright cD

gal-Figure 7.3: Offsets of the Faber–Jackson relation in Gunnrfor the early-type cluster galaxies in the Low–

L_X clusters CL 0849, CL 1701 and CL 1702 from the local FJR by the J99 Coma sample as a function of luminosity M_r. Filled symbols denote brighter gal-axies M_r < −21.77, open symbols fainter galaxies M_r>−21.77. The dashed line corresponds to a zero evolution.

axy of A 2218 was excluded as no counterpart of this galaxy type was observed in A 2390. In Fig.7.2the sample of ellipticals and S0 galaxies is shown as solid and open symbols. The higher-luminosity Es (Mr < −21.49) are brighter by h∆M_{r E}i =−0.14 with a scatterσ_Mr = 0.11^m, lower-luminosity Es (M_r>−21.49) show an evo-lution of h∆Mr Ei = −0.23 with σMr = 0.18^m. The brighter S0s are offset to the local FJR re-lation byh∆M_rS0i=−0.66 withσ_Mr = 0.12^m, fainter S0s byh∆Mr S0i=−0.45 with a scatter ofσ_Mr = 0.13^m. These results confirm the anal-ysis of the FP where also the lenticular galax-ies are more luminous than the ellipticals. Both sub–samples of brighter and fainter S0s show a stronger evolution than the Es. An interesting is-sue would be also if there is a difference between the sub–groups of faint and bright ellipticals and S0 galaxies. Unfortunately the sub–samples are

Chapter 7: Environmental Effects on Galaxy Properties 159

too small to test this in greater detail.

In order to investigate the offsets of the FJR of the Low–L_X clusters from the local FJR with respect to luminosity, the poor cluster sample is divided atMr =−21.77 in two groups with the high-luminosity sub-sample containing 14 galax-ies and the low-luminosity counterpart compris-ing 13 objects. Fig. 7.3 shows the offsets of the FJR in Gunn r for the early-type galaxies in the Low–LX clusters CL 0849, CL 1701 and CL 1702 from the local FJR by the J99 Coma sample as a function of luminosityM_r. Brighter galaxies with Mr < −21.77 are represented as solid symbols, fainter galaxies withMr>−21.77 are denoted as open symbols. Brighter clus-ter galaxies indicate on average an evolution of

∆Mr = −0.55±0.13^m, fainter objects in the poor cluster sample (M_r>−21.77) are on aver-age more luminous by ∆M_r = −0.23±0.22^m. At a first glance, these values suggest an impres-sion of a larger offset for brighter galaxies. How-ever, the scatter of the fainter galaxies is also larger than for the brighter ones and the me-dian offsets are similar for both sub-classes. Ta-ble7.2compares the individual values for the two groups of early-type galaxies with different Mr. As the difference in median luminosity between lower-luminosity and higher-luminosity galaxies is within their 1σ error, the differences in the sub-samples are negligible.

The Low–L_X early-type cluster galaxies were vi-sually classified as nine elliptical galaxies and one S0 galaxy (cf. section 4.4). As the number of galaxies in each sub–class is unbalanced but also too low, a reliable comparison and further anal-ysis as for the rich cluster galaxies cannot be performed.