DOUBLE GALAXY CLUSTERS

Gary A. Wegner Department of Physics & Astronomy Dartmouth College

KIAS 5 November 2014 OUTLINE

1. Examples of some double clusters

2. Simulations

3. What we can hope to learn

4. Star formation in mergers

5. Abell 2465

6. Conclusions

Best known case: the “Bullet” cluster Clowe etal. 2006, ApJ, 648, 109 Separation of X-ray, galaxies, matter profile from strong and weak lensing

Two more examples, RX J 1347.5-1145 (Bradac et al. 2006, ApJ, 681, 187) MACS J0025.4-1222, “Baby bullet” (Bradac et al. 2008, ApJ, 687, 959) Abell 2744, Owers et al. 2011, ApJ, 728, 27 Abell 2146 Russell et al 2012 MNRAS, 423, 236 DLSCL J00916.2+2951 (Musket ball cluster) Dawson et al. 2012, ApJ, 747, L42 (See also for many further examples.) Abell 2744: Example of a more complicated merging Merten et al. 2011, MNRAS, 417, 33

Sloshing: Markevitch & Vikhlinin 2007, Phys. Rep., 443, 1 Abell 1644, Johnson et al. 710, 1776 Radio relics MACS J1752+4440 More examples see Merging cluster collaboration http://www.mergingclustercollaboration.org/ Radial infall model Simplest method used by many for estimate Beers, Geller & Huchra 1982, ApJ, 257, 23 (Abell 98)

(See also Dawson 2013, ApJ, 772, 131) Early merger models, Roettiger et al. 1997, ApJS, 109, 307 2:1 mass ratio Left: gas density ; Right: gas density and dark matter evolution Off-centre collisions showing dark matter and gas densities. Ricker & Sarazin 2001, ApJ, 561, 621

m1:m2 = 1:1

m1:m2 = 1:3 X-ray emission for the 1:1 case (left)

LX and TX (right) Gas surface density (top) for 1:1 mass ratio Projected temperature (below) Poole et al. 2006, MNRAS, 373, 881 X-ray surface brightness off centre mergers (Takizawa 2000, ApJ, 532, 183) 15 15 m1:m2 (10 M0) = 0.5:0.5 m1:m2(10 M0) = 0.5:0.125 WHAT CAN WE LEARN?

1. Large scale gravitational interaction

2. Baryonic - darkmatter interactions

3. Limits on self-interacting darkmatter cross sections

4. Star formation processes in different environment Merging clusters with & without SF Hwang & Lee 2009, MNRAS, 397, 2111 Cluster integrated & normalized star formation rate relations Bai et al. 2009, ApJ, 693, 1840; Koyama et al. 2010, MNRAS, 403, 1611

Note: General SFR and gas depletion, cf. Vijayaragharan & Ricker 2013, MNRAS, 435, 2713 Cluster integrated and normalized SFR Shim et al. 2011, ApJ, 727, 14; Popesso et al., 2012, A&A, 537, 58 (groups > clusters)

Σ SFR/M = 1.2(1 + z)5.3 cl Biviano et al. 2011, A&A, 532, 77

SFR vs. number of subcomponents Cohen, Hickox, Wegner, Einasto, Vennik 2014, ApJ, 783, 186

Other studies include: Rines & Diaferio 2010 AJ, 139, 580 and 2006 AJ, 132, 1275 Park & Hwang 2009, ApJ, 699, 1595 + others Cohen, Hickox, & Wegner 2014, preprint, from WISE data

(Wen & Han 3013, MNRAS, 436, 275 Γ - relaxation factor)

Abell 2465 showing NE and SW subclusters Wegner 2011, MNRAS, 413, 1333 z = 0.245 14 14 M200 (NE) =4.1± 0.8 x 10 M0 ; M200(SW) = 3.8± 0.8x 10 M0 Δ R = 5.5 Mpc Abell 2465 – two subclusters SW NE Abell 2465 Spectroscopic sample, XMM, NVSS Abell 2465 I-band light contours

MI < -20 -16 > MI > -20 Star formation in Abell 2465 Wegner, Chu, Hwang Narrow and broad-band filters. Redshifts in hatched histogram Selection of Hα sources showing cuts Top – cluster field Below – background field Abell 2465 Comparison photometric & spectroscopic

Hα equivalent widths & locations Hα sources inside R200 of SW and NE clumps and whole cluster Abell 2465 Hα and WISE IR luminosity functions Abell 2465

In the ΣSFR/Mcl diagrams Abell 2465 Hα galaxies in the cluster Abell 2465 Cluster members with strong WISE IR Abell 2465 – blue fraction Spectroscopic sample, most red sequence

UB sample, fb = 0.53 ± 0.02 (0.2 typical)

(Line: Wilmer et al. 2006) Abell 2465 Cumulative SFR densities Hα and IR compared with NFW (Left) Chandra X-ray image (right) CONCLUSIONS FROM ABELL 2465

1. Abell 2465 higher Σ(SFR)/Mcl mass normalized SFR in z and Mcl relations.

2. U and B data indicate higher fb, blue fraction.

3. Hα and IR SFR less concentrated to cluster centre than NFW.

4. Hα and IR sources interacting galaxies, harassment?

5. Shallow distribution SF and X-ray may indicate subclusters not yet collided .

6. SFR higher in double clusters before passing through centres.