Astrophys. J., 887, 214-214 (2019/December-3)
Planck far-infrared detection of Hyper Suprime-Cam protoclusters at z ∼ 4: hidden AGN and star formation activity.
KUBO M., TOSHIKAWA J., KASHIKAWA N., CHIANG Y.-K., OVERZIER R., UCHIYAMA H., CLEMENTS D.L., ALEXANDER D.M., MATSUDA Y., KODAMA T., ONO Y., GOTO T., CHENG T.-A. and ITO K.
Abstract (from CDS):
We perform a stacking analysis of Planck, AKARI, Infrared Astronomical Satellite, Wide-field Infrared Survey Explorer, and Herschel images of the largest number of (candidate) protoclusters at z ∼ 3.8 selected from the Hyper Suprime-Cam Subaru Strategic Program. Stacking the images of the 179 candidate protoclusters, the combined infrared (IR) emission of the protocluster galaxies in the observed 12-850 µm wavelength range is successfully detected with >5σ significance (at Planck). This is the first time that the average IR spectral energy distribution (SED) of a protocluster has been constrained at z ∼ 4. The observed IR SEDs of the protoclusters exhibit significant excess emission in the mid-IR compared to that expected from typical star-forming galaxies (SFGs). They are reproduced well using SED models of intense starburst galaxies with warm/hot dust heated by young stars, or by a population of active galactic nucleus (AGN)/SFG composites. For the pure star-forming model, a total IR (from 8-1000 µm) luminosity of 19.3–4.2+0.6×1013L☉ and a star formation rate of 16.3–7.8+1.0×103M☉ yr–1 are found, whereas for the AGN/SFG composite model, 5.1–2.5+2.5×1013L☉ and 2.1–1.7+6.3×103M☉ yr–1 are found. Uncertainty remains in the total SFRs; however, the IR luminosities of the most massive protoclusters are likely to continue increasing up to z ∼ 4. Meanwhile, no significant IR flux excess is observed around optically selected QSOs at similar redshifts, which confirms previous results. Our results suggest that the z ∼ 4 protoclusters trace dense, intensely star-forming environments that may also host obscured AGNs missed by the selection in the optical.
© 2019. The American Astronomical Society. All rights reserved.
Galaxy evolution - Protoclusters
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