Up: Abell 1451 and 1RXS J131423.6-251521: A galaxies

5 Discussion

5.1 Abell 1451

The dynamical state of Abell 1451 is very similar to that of Abell 665 (Gomèz et al. 2000) and to the more distant Abell 1300 (Lémonon et al. 1997; Reid et al. 1998), suggesting that it may also be in the final stage of establishing equilibrium after a merger event.

$\begin{figure} \par\includegraphics[width=13cm,clip]{aa2550f9.eps} \end{figure}$

Figure 9: Abell 1451: circularly averaged surface brightness profile in the energy band [0.1-2.4] keV. Bin size is $15\hbox {$^{\prime \prime }$ }$ and the solid line is the King profile fit (Eq. (1)) with parameters in Table 8.

$\begin{figure} \par\includegraphics[width=13cm,clip]{aa2550f10.eps} \end{figure}$

Figure 10: RXJ1314-25: circularly averaged surface brightness profile in the [0.1-2.4] keV energy band. Bin size is $7.5\hbox {$^{\prime \prime }$ }$ and the solid line is the King profile fit (Eq. (1)). The deviation of the inner two points from the model is due to the irregular morphology in the cluster centre.

Table 8: $\beta$ -profile best-fit parameters with the corresponding 95% confidence intervals.
Parameter Abell 1451 RXJ1314-25

$r_{\rm c}$ (arcsec) $59\pm20$ $81\pm 28$

$r_{\rm c}$ (kpc) $240\pm90$ $400\pm140$

$\beta$ $0.50\pm0.08$ $0.77\pm0.23$

**Table 8:** $\beta$ -profile best-fit parameters with the corresponding 95% confidence intervals.
Parameter	Abell 1451	RXJ1314-25
$r_{\rm c}$ (arcsec)	$59\pm20$	$81\pm 28$
$r_{\rm c}$ (kpc)	$240\pm90$	$400\pm140$
$\beta$	$0.50\pm0.08$	$0.77\pm0.23$

Table 9: X-ray data for both clusters. $N_{\rm H}$ is taken from Dickey & Lockman (1990). ASCA data for $T_{\rm X}$ and $L_{\rm X}$ in the [2-10] keV band (Matsumoto et al. 2001) are indicated correspondingly. The count-rate C is in [0.1-2.4] keV band. The luminosities in [0.5-2], [2-10] keV and bolometric bands were obtained by extrapolation of the King profile out to $5\hbox {$^\prime $ }$ .
Parameter Abell 1451 RXJ1314-25

$r_{\rm lim} = 5\hbox{$^\prime$ }$ (Mpc) 1.3 1.5

$N_{\rm H}$ (10²⁰ cm^-2) 4.5 6.7

$T_{\rm X}$ (keV) ASCA 13.4^+1.9_-1.5 8.7^+0.7_-0.6

Count-rate $C(r < r_{\rm lim})$ (cts s^-1) 0.126 0.083

$F_{\rm X}\ [$ 0.5-2] keV (10^-12 erg cm^-2 s^-1) 4.4 3.2

$F_{\rm X}\ [$ 2-10] keV (10^-12 erg cm^-2 s^-1) 11.2 6.8

$L_{\rm X}\ [$ 0.5-2] keV (10⁴⁴ erg s^-1) 6.8 7.4

$L_{\rm X}\ [$ 2-10] keV (10⁴⁴ erg s^-1) 17.2 16.0

$L_{\rm X}\ [$ 2-10] keV (10⁴⁴ erg s^-1) ASCA 15.0 $^\dag$ 18.0 $^\ddag$

$L_{{\rm bol}}\ (10^{44}$ erg s^-1) 39.8 34.0

n_p(0) (10^-3 cm^-3) 5.09 5.31

$M_{\rm tot}(<r_{\rm lim})$ (10 $^{14}~M_{\odot}$ )^* 8.6 9.7

$M_{\rm gas}(<r_{\rm lim})$ (10 $^{14}~M_{\odot}$ )^* 2.2 2.6

$M_{\rm gas}/M_{\rm tot}(< r_{\rm lim})$ 0.25 0.27

**Table 9:** X-ray data for both clusters. $N_{\rm H}$ is taken from Dickey & Lockman (1990). ASCA data for $T_{\rm X}$ and $L_{\rm X}$ in the [2-10] keV band (Matsumoto et al. 2001) are indicated correspondingly. The count-rate C is in [0.1-2.4] keV band. The luminosities in [0.5-2], [2-10] keV and bolometric bands were obtained by extrapolation of the King profile out to $5\hbox {$^\prime $ }$ .
Parameter	Abell 1451	RXJ1314-25

$r_{\rm lim} = 5\hbox{$^\prime$ }$ (Mpc)	1.3	1.5
$N_{\rm H}$ (10²⁰ cm^-2)	4.5	6.7
$T_{\rm X}$ (keV) ASCA	13.4^+1.9_-1.5	8.7^+0.7_-0.6
Count-rate $C(r < r_{\rm lim})$ (cts s^-1)	0.126	0.083
$F_{\rm X}\ [$ 0.5-2] keV (10^-12 erg cm^-2 s^-1)	4.4	3.2
$F_{\rm X}\ [$ 2-10] keV (10^-12 erg cm^-2 s^-1)	11.2	6.8
$L_{\rm X}\ [$ 0.5-2] keV (10⁴⁴ erg s^-1)	6.8	7.4
$L_{\rm X}\ [$ 2-10] keV (10⁴⁴ erg s^-1)	17.2	16.0
$L_{\rm X}\ [$ 2-10] keV (10⁴⁴ erg s^-1) ASCA	15.0 $^\dag$	18.0 $^\ddag$
$L_{{\rm bol}}\ (10^{44}$ erg s^-1)	39.8	34.0
n_p(0) (10^-3 cm^-3)	5.09	5.31
$M_{\rm tot}(<r_{\rm lim})$ (10 $^{14}~M_{\odot}$ )^*	8.6	9.7
$M_{\rm gas}(<r_{\rm lim})$ (10 $^{14}~M_{\odot}$ )^*	2.2	2.6
$M_{\rm gas}/M_{\rm tot}(< r_{\rm lim})$	0.25	0.27

$^\dag$ ASCA/GIS luminosity out to $4\hbox{$^\prime$ }$ , including the contribution from the QSO $\sim 1\hbox{$^\prime$ }30\hbox{$^{\prime\prime}$ }$ south of the centre.
$^\ddag$ ASCA/GIS luminosity out to $4\hbox{$^\prime$ }$ , including the contribution from the Sy1 galaxy $\sim$ $3\hbox{$^\prime$ }15\hbox{$^{\prime\prime}$ }$ south-east of the centre.
^* Assuming hydrostatic equilibrium.

Table 10: Details of the ATCA radio observations of the two clusters.
Restoring Beam

Cluster Frequency RMS Noise $b_{\rm maj}$ $b_{\rm min}$ PA

(Obs. Date) (GHz) mJy/beam ('') ('') (deg)

Abell 1451 1.384 0.08 27.8 9.4 -0.5

(1999 Feb. 25) 2.496 0.06 15.4 5.2 -0.5

RXJ1314-25 1.384 0.09 23.8 9.4 0.9

(1999 Feb. 26) 2.496 0.06 13.2 5.2 0.8

**Table 10:** Details of the ATCA radio observations of the two clusters.
			Restoring Beam
Cluster	Frequency	RMS Noise	$b_{\rm maj}$	$b_{\rm min}$	PA
(Obs. Date)	(GHz)	mJy/beam	('')	('')	(deg)
Abell 1451	1.384	0.08	27.8	9.4	-0.5
(1999 Feb. 25)	2.496	0.06	15.4	5.2	-0.5
RXJ1314-25	1.384	0.09	23.8	9.4	0.9
(1999 Feb. 26)	2.496	0.06	13.2	5.2	0.8

Support for the merger scenario comes from different morphological and physical reasons which are summarized below:

Table 11: Radio sources for Abell 1451 and RXJ1314-25 within 1 Abell radius of the cluster centre. Source coordinates are from VSAD. The peak ( $S_{\rm peak}$ ) and integrated ( $S_{\rm int}$ ) flux densities were measured using either VSAD or kview as described in the text. For Abell 1451 we adopt the X-ray emission peak as the centre.
N RA (err s) Dec (err $\hbox{$^{\prime\prime}$ }$ ) $\nu$ $S_{\rm peak}$ (err) $S_{\rm int}$ (err)

(J2000) GHz mJy/bm mJy

Abell 1451

R1 12:02:51.67(0.04) -21:26:35.8(1.0) 1.384 3.9 12.1

2.496 1.6 9.6

R2 12:02:56.73(0.06) -21:28:46.7(1.9) 1.384 0.60(0.06) 1.10(0.19)

2.496 -- --

R3 12:02:58.94(0.04) -21:38:35.8(0.5) 1.384 25.8(0.08) 28.3(0.15)

2.496 12.2(0.06) 14.4(0.12)

R4 12:03:06.66(0.05) -21:39:29.8(0.5) 1.384 18.6(0.08) 18.6(0.14)

2.496 7.80(0.06) 8.27(0.11)

R5 12:03:08.65(0.05) -21:39:40.6(0.6) 1.384 3.75(0.08) 4.24(0.15)

2.496 1.95(0.06) 2.31(0.12)

R6 12:03:10.59(0.04) -21:29:54.4(0.7) 1.384 1.90(0.08) 1.97(0.14)

2.496 0.98(0.06) 1.02(0.11)

R7 12:03:17.35(0.04) -21:32:31.3(0.5) 1.384 11.4(0.07) 15.4

2.496 5.51(0.06) 7.2

R8 12:03:26.97(0.04) -21:30:49.9(0.7) 1.384 2.21(0.07) 2.65(0.15)

2.496 1.19(0.06) 1.36(0.11)

R9 12:03:32.53(0.04) -21:33:09.1(0.5) 1.384 6.11(0.07) 9.7

2.496 2.56(0.04) 6.2

R10 12:03:32.85(0.05) -21:36:26.2(1.6) 1.384 0.73(0.08) 0.73(0.10)

2.496 0.36(0.06) 0.40(0.11)

R11 12:03:33.84(0.05) -21:30:22.1(1.7) 1.384 0.39(0.08) 0.36(0.13)

2.496 0.30(0.05) 0.47(0.13)

R12 12:03:45.47(0.07) -21:36:11.7(2.1) 1.384 0.52(0.07) 0.80(0.17)

2.496 -- --

R13 12:03:47.24(0.05) -21:36:15.1(1.3) 1.384 0.78(0.07) 1.01(0.16)

2.496 0.31(0.05) 1.09(0.19)

R14 12:03:47.91(0.04) -21:28:33.1(0.5) 1.384 5.53(0.08) 5.32(0.14)

2.496 2.70(0.06) 2.79(0.12)

RXJ1314-25

R1
13:14:00.90(0.04) -25:16:53.7(0.7) 1.384 2.09(0.09) 2.38(0.1)

2.496 0.84(0.06) 1.13(0.1)

R2 13:14:18.62(0.05) -25:15:47.0(1.0) 1.384 1.16(0.03) 13.0

2.496 -- --

R3 13:14:30.31(0.04) -25:17:14.2(0.7) 1.384 1.93(0.08) 4.4

2.496 0.54(0.04) 1.7

R4 13:14:34.31(0.06) -25:11:59.9(1.6) 1.384 0.69(0.09) 0.64(0.2)

2.496 0.62(0.07) 0.57(0.1)

R5 13:14:45.90(0.05) -25:15:05.5(0.7) 1.384 1.57(0.04) 6.8

2.496 0.48(0.04) 1.5

R6 13:14:48.64(0.04) -25:16:18.3(0.6) 1.384 3.20(0.09) 3.65(0.2)

2.496 1.47(0.05) 2.20(0.1)

**Table 11:** Radio sources for Abell 1451 and RXJ1314-25 within 1 Abell radius of the cluster centre. Source coordinates are from `VSAD`. The peak ( $S_{\rm peak}$ ) and integrated ( $S_{\rm int}$ ) flux densities were measured using either `VSAD` or `kview` as described in the text. For Abell 1451 we adopt the X-ray emission peak as the centre.
N	RA (err s)	Dec (err $\hbox{$^{\prime\prime}$ }$ )	$\nu$	$S_{\rm peak}$ (err)	$S_{\rm int}$ (err)
	(J2000)	GHz	mJy/bm	mJy

Abell 1451
R1	12:02:51.67(0.04)	-21:26:35.8(1.0)	1.384	3.9	12.1
			2.496	1.6	9.6
R2	12:02:56.73(0.06)	-21:28:46.7(1.9)	1.384	0.60(0.06)	1.10(0.19)
			2.496	--	--
R3	12:02:58.94(0.04)	-21:38:35.8(0.5)	1.384	25.8(0.08)	28.3(0.15)
			2.496	12.2(0.06)	14.4(0.12)
R4	12:03:06.66(0.05)	-21:39:29.8(0.5)	1.384	18.6(0.08)	18.6(0.14)
			2.496	7.80(0.06)	8.27(0.11)
R5	12:03:08.65(0.05)	-21:39:40.6(0.6)	1.384	3.75(0.08)	4.24(0.15)
			2.496	1.95(0.06)	2.31(0.12)
R6	12:03:10.59(0.04)	-21:29:54.4(0.7)	1.384	1.90(0.08)	1.97(0.14)
			2.496	0.98(0.06)	1.02(0.11)
R7	12:03:17.35(0.04)	-21:32:31.3(0.5)	1.384	11.4(0.07)	15.4
			2.496	5.51(0.06)	7.2
R8	12:03:26.97(0.04)	-21:30:49.9(0.7)	1.384	2.21(0.07)	2.65(0.15)
			2.496	1.19(0.06)	1.36(0.11)
R9	12:03:32.53(0.04)	-21:33:09.1(0.5)	1.384	6.11(0.07)	9.7
			2.496	2.56(0.04)	6.2
R10	12:03:32.85(0.05)	-21:36:26.2(1.6)	1.384	0.73(0.08)	0.73(0.10)
			2.496	0.36(0.06)	0.40(0.11)
R11	12:03:33.84(0.05)	-21:30:22.1(1.7)	1.384	0.39(0.08)	0.36(0.13)
			2.496	0.30(0.05)	0.47(0.13)
R12	12:03:45.47(0.07)	-21:36:11.7(2.1)	1.384	0.52(0.07)	0.80(0.17)
			2.496	--	--
R13	12:03:47.24(0.05)	-21:36:15.1(1.3)	1.384	0.78(0.07)	1.01(0.16)
			2.496	0.31(0.05)	1.09(0.19)
R14	12:03:47.91(0.04)	-21:28:33.1(0.5)	1.384	5.53(0.08)	5.32(0.14)
			2.496	2.70(0.06)	2.79(0.12)
RXJ1314-25
R1	13:14:00.90(0.04)	-25:16:53.7(0.7)	1.384	2.09(0.09)	2.38(0.1)
			2.496	0.84(0.06)	1.13(0.1)
R2	13:14:18.62(0.05)	-25:15:47.0(1.0)	1.384	1.16(0.03)	13.0
			2.496	--	--
R3	13:14:30.31(0.04)	-25:17:14.2(0.7)	1.384	1.93(0.08)	4.4
			2.496	0.54(0.04)	1.7
R4	13:14:34.31(0.06)	-25:11:59.9(1.6)	1.384	0.69(0.09)	0.64(0.2)
			2.496	0.62(0.07)	0.57(0.1)
R5	13:14:45.90(0.05)	-25:15:05.5(0.7)	1.384	1.57(0.04)	6.8
			2.496	0.48(0.04)	1.5
R6	13:14:48.64(0.04)	-25:16:18.3(0.6)	1.384	3.20(0.09)	3.65(0.2)
			2.496	1.47(0.05)	2.20(0.1)

Table 12: Radio-optical identifications in Abell 1451 and RXJ1314-25. N refers to the identification number given in Table 11 and $\Delta$ r is the radius-vector offset between radio and SuperCOSMOS optical positions. T refers to the SuperCOSMOS image classification: 1 = galaxy; 2 = star.
N RA Dec B_J $\Delta r$ T

Optical (J2000) (mag) ( $^{\prime\prime}$ )

Abell 1451

R1 12:02:51.56 -21:26:35.4 19.26 1.6 1

R2 12:02:56.81 -21:28:55.8 18.42 9.1 1

R3 12:02:58.92 -21:38:36.4 18.18 0.7 1

R5 12:03:08.68 -21:39:40.0 20.12 0.7 2

R6 12:03:10.35 -21:29:54.2 19.13 3.4 1

R7 12:03:17.47 -21:32.27.4 19.41 4.2 1

R8 12:03:26.98 -21:30:51.5 18.19 1.6 1

R11 12:03:45.70 -21:36:11.9 18.98 3.5 1

R12 12:03:47.14 -21:36:12.8 20.28 2.8 1

R13 12:03:48.11 -21:28:33.1 20.40 3.2 2

RXJ1314-25

R1 13:14:00.89 -25:16:54.3 19.81 0.6 2

R2 13:14:23.78 -25:07:51.8 21.07 2.9 1

R3 13:14:30.36 -25:17:17.4 21.40 3.3 1

R4 13:14:34.27 -25:11:58.9 20.07 1.1 1

R5 13:14:46.17 -25:15:09.1 21.37 5.1 1

**Table 12:** Radio-optical identifications in Abell 1451 and RXJ1314-25. N refers to the identification number given in Table 11 and $\Delta$ r is the radius-vector offset between radio and SuperCOSMOS optical positions. T refers to the SuperCOSMOS image classification: 1 = galaxy; 2 = star.
N	RA	Dec	B_J	$\Delta r$	T
	Optical (J2000)	(mag)	( $^{\prime\prime}$ )

Abell 1451
R1	12:02:51.56	-21:26:35.4	19.26	1.6	1
R2	12:02:56.81	-21:28:55.8	18.42	9.1	1
R3	12:02:58.92	-21:38:36.4	18.18	0.7	1
R5	12:03:08.68	-21:39:40.0	20.12	0.7	2
R6	12:03:10.35	-21:29:54.2	19.13	3.4	1
R7	12:03:17.47	-21:32.27.4	19.41	4.2	1
R8	12:03:26.98	-21:30:51.5	18.19	1.6	1
R11	12:03:45.70	-21:36:11.9	18.98	3.5	1
R12	12:03:47.14	-21:36:12.8	20.28	2.8	1
R13	12:03:48.11	-21:28:33.1	20.40	3.2	2
RXJ1314-25
R1	13:14:00.89	-25:16:54.3	19.81	0.6	2
R2	13:14:23.78	-25:07:51.8	21.07	2.9	1
R3	13:14:30.36	-25:17:17.4	21.40	3.3	1
R4	13:14:34.27	-25:11:58.9	20.07	1.1	1
R5	13:14:46.17	-25:15:09.1	21.37	5.1	1

There is no single dominant galaxy. The brightest cluster galaxy (#34, Table 3) is $35\hbox{$^{\prime\prime}$ }$ away from the X-ray centroid, and 580 km s^-1 from the cluster mean redshift.
The putative identification for the central radio source (#40, Table 3) is offset by 1300 km s^-1 from the cluster mean redshift;
Nearly regular X-ray emission, without substructures but slightly twisted inner part;
No cooling flow region;
Deviations from the observed scaling relations $L_{\rm X}$ -T and $\sigma _{\rm v}$ -T (Xue & Wu 2000), shown in Table 13. The cluster is significantly less luminous than expected from its measured temperature. The very high observed temperature (13.4 keV) is probably an indication of a shock that occurred in the recent past. We cannot exclude a possible overestimation of the published ASCA temperature due to the presence of the background X-ray point source. However, the small difference (in the wrong sense) between the ASCA luminosity and our estimate with the QSO emission excluded (see Table 9) seems unlikely to account for a temperature overestimate of more than 4 keV. A new and more accurate measurement of the temperature is clearly needed;
Based on numerical simulations (Roettiger et al. 1997; Belsole et al. 2002), the regular X-ray morphology and high X-ray temperature are fully compatible with expectations from a past merger.

We can also determine the dynamical status of the cluster by comparing its kinetic and potential energies. From the measured velocity dispersion we find $\beta_{\rm spec} = \mu m_{\rm p} \sigma_{\rm v}^2/kT = 0.84\pm0.25$ , while from the X-ray emission, with the correction factor from Bahcall & Lubin (1994), we have $\beta^c_{\rm X} = 1.25 \beta_{\rm X} = 0.63\pm0.1$ . These values are consistent within the uncertainties, indicating that the gas and galaxy motions are close to equipartition.

If a merger occurred recently we might expect signatures at radio wavelengths, such as radio halo/relic sources, and possibly tailed sources (e.g. Enßlin et al. 1998; Reid et al. 1998; Röttgering et al. 1994). There is no evidence for a radio halo, although there is a tailed source (R7) near the cluster centre which could have disrupted it (Giovannini 1999; Liang et al. 2000).

Table 13: Scaling relations for Abell 1451 and RXJ1314-25. $\sigma _{\rm v}$ -T is from Xue & Wu (2000), while $L_{\rm bol}$ -T is from Arnaud & Evrard (1999). The temperature from ASCA is in keV, $L_{\rm bol}$ in units of 10⁴⁴ erg s^-1 and $\sigma _v$ in km s^-1 are from this paper.
Cluster T $\sigma _{\rm v}$ $\sigma _{\rm v}$ $L_{\rm bol}$ $L_{\rm bol}$

(obs) (obs) ( $\sigma _{\rm v}$ -T) (obs) ( $L_{\rm bol}$ -T)

Abell 1451 13.4 1330 1670 39.8 116

RXJ1314-25 8.7 1100 1261 34.0 33.5

**Table 13:** Scaling relations for Abell 1451 and RXJ1314-25. $\sigma _{\rm v}$ -T is from Xue & Wu (2000), while $L_{\rm bol}$ -T is from Arnaud & Evrard (1999). The temperature from ASCA is in keV, $L_{\rm bol}$ in units of 10⁴⁴ erg s^-1 and $\sigma _v$ in km s^-1 are from this paper.
Cluster	T	$\sigma _{\rm v}$	$\sigma _{\rm v}$	$L_{\rm bol}$	$L_{\rm bol}$
	(obs)	(obs)	( $\sigma _{\rm v}$ -T)	(obs)	( $L_{\rm bol}$ -T)

Abell 1451	13.4	1330	1670	39.8	116
RXJ1314-25	8.7	1100	1261	34.0	33.5

5.2 RXJ1314-25

RXJ1314-25 is morphologically and dynamically very different from Abell 1451. It shows a clear bi-modal structure - there are two groups in velocity space separated by $\sim$ 1700 km s^-1 (cf. Table 6 and Fig. 5) which are also separated in the projected galaxy distribution (cf. Fig. 6). The dominant galaxies of each group are separated by $\sim$ 1000 km s^-1 in redshift space, and $2\hbox{$^\prime$ } 25\hbox{$^{\prime\prime}$ }$ , or $\approx$ 700 kpc, in projected distance.

The X-ray emission is elongated, with the centroid located between the two dominant galaxies. The elongation, however, is rotated by $\approx$ 20 $^{\circ}$ from the axis connecting the two BCGs. This may simply be due to the decoupling between the galaxies and gas during the merger.

There are no cluster radio sources within the X-ray extension, with the possible exception of the weak (uncatalogued) source at the position of galaxy #48. If we are witnessing an interaction between two sub-clusters, we might expect stronger radio activity than observed. However, residual sidelobes from a strong background source $\sim$ $7\hbox{$^\prime$ }$ south of the centre hamper the detection of any very extended emission. In addition, a more compact ATCA antenna configuration is needed to improve sensitivity to low surface brightness emission. There are, however, two extended radio sources, one of which (R2) has a steep radio spectrum and no optical counterpart, and is therefore a plausible candidate for a relic source.

The observed $L_{\rm X}$ , T and $\sigma _{\rm v}$ for RXJ1314-25 are in good agreement with the $L_{\rm X}$ -T and $\sigma _{\rm v}$ -T scaling relationships (Table 13), suggesting that the merger has progressed to the stage where the transient shock heating and radio activity have dissipated. On the other hand, if the cluster is in a pre-merging phase, then it is unusual that the X-ray elongation is not aligned with the group centres and that there is no sign of X-ray substructure around the eastern group, as revealed, for example, in numerical simulations (Roettiger et al. 1997; Takizawa 2000). The scattered appearance of the projected galaxy distribution of the eastern group compared to the western group (Fig. 6) also supports a post-merging scenario.

In conclusion, our observations suggest that neither cluster is relaxed following a recent merger. However, their properties and scaling laws are quite different, illustrating the diversity in the merging and relaxation processes in cluster formation and evolution. The current data for the two clusters are compatible with the expectations from the merger of a small group with a bigger cluster for Abell 1451, and nearly equal mass groups for RXJ1314-25. Deep XMM and Chandra observations, coupled with detailed numerical simulations are needed to assess these hypotheses and better understand the many aspects of the physical processes occurring during accretion and relaxation over the course of a cluster merger.

Acknowledgements

We would like to thank Romain Teyssier, John Hughes and Pierre-Alain Duc for numerous discussions about simulations, data reduction and analysis. We are especially indebted to Hector Flores and Dario Fadda for providing us with the observation of galaxy #48 in RXJ1314-25 (CFHT, June 2001). We thank the referee Reinaldo de Carvalho for valuable comments.

Up: Abell 1451 and 1RXS J131423.6-251521: A galaxies