Star formation in the massive cluster merger Abell 2744

July 2014 • 2014MNRAS.442..196R

Authors • Rawle, T. D. • Altieri, B. • Egami, E. • Pérez-González, P. G. • Richard, J. • Santos, J. S. • Valtchanov, I. • Walth, G. • Bouy, H. • Haines, C. P. • Okabe, N.

Abstract • We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope (HST) Frontier Field recent cluster merger A2744 (z = 0.308). Wide-field, ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFR_UV+IR = 343 ± 10 M_⊙ yr^-1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFR_UV+IR = 201 ± 9 M_⊙ yr^-1. Focusing on obscured star formation, this core region exhibits a total SFR_IR = 138 ± 8 M_⊙ yr^-1, a mass-normalized SFR_IR of Σ_SFR = 11.2 ± 0.7 M_⊙ yr^-1 per 10¹⁴ M_⊙ and a fraction of IR-detected SF galaxies f_SF = 0.080^{+0.010}_{-0.037}. Overall, the cluster population at z ∼ 0.3 exhibits significant intrinsic scatter in IR properties (total SFR_IR, T_dust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFR_UV/SFR_IR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.

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Greg Walth

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