1509.02833
Shadow of a Colussus: A z=2.45 galaxy protocluster detected in 3D Ly-a forest tomographic mapping of the COSMOS field
Lee, Hennawi, White, PRochaska, Font-Ribera, Schlegel, Rich, Suzuki, Strk, Le Fevre, Nugent, Salvato, Zamorani
Using moderate-resolution optical spectra from 58 BG Ly-break galaxies and quasars at z~2.3-3 within a 11.5'x13.5' area of the COSMOS field (~1200 deg2 projected are density or ~2.4 Mpc/h mean transverse separation), reconstruct a 3d tomographic map of the FG Lya forest absorption at 2.2<z<2.5 with an effective smoothing scale of sigma_3d~3.5 Mpc/h comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, find that the galaxy positions are clearly biased towards regions with enhanced IGM absorption in the tomographic map. Find an extended IGM overdensity with deep absorption troughs at z=2.45 associated with a recently-discovered galaxy protocluster at the same redshift. Based on simulations matched to the data, estimate the enclosed DM mass within this IGM overdensity to be M_dm(z=2.45)=(9±4)e13 Msun/h, and argue based on this mass and absorption strength that it will form at least one z~0 galaxy cluster with M(z=0)=(3±2)e14Msun/h, although its elongated nature suggests that it will likely collapse into two separate clusters. Also point out a compact overdensity of six MOSDEF galaxies at z=2.30 within a r~1Mpc/h radius and Delta z~0.006, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Lya forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM over densities associated with protoclusters and other features of LSS.
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