Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe

Abstract

All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-α emission at redshift z ≈ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ∼10(-7), implying a physical connection between Lyman-α nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (≃10(11) solar masses) of cool dense (volume density ≃ 1 cm(-3)) gas, which is in conflict with current cosmological simulations.

UBIQUITOUS GIANT Lyα NEBULAE AROUND THE BRIGHTEST QUASARS AT z ∼ 3.5 REVEALED WITH MUSE∗

“…The three giant nebulae discovered hitherto with NB imaging (Cantalupo et al 2014;Martin et al 2014;Hennawi et al 2015) are all characterized by bright extended emission with surface brightness values larger than 10 −17 erg s −1 cm −2 arcsec −2 , a value that is easily reachable within 1 hr of integration time with MUSE. Therefore, for this exploratory survey (094.A-0396, 095.A-0708, 096.A-0345), we use a total exposure time of 1 hr for each quasar split into 4×900 s exposures.…”

“…This result seems to be in stark contrast with previous narrow-band and spectroscopic surveys for bright radio-quiet quasars at highredshift. These studies have found detection rates of giant nebula less than 10% using NB imaging at < < z 2 3 (Cantalupo et al 2014;Martin et al 2014;Hennawi et al 2015;Arrigoni Battaia et al 2016), while spectroscopic surveys at any redshift have found exclusively smaller nebulae (<60 pkpc) and only in about 50% of the cases (North et al 2012;Fathivavsari et al 2015). Because all these surveys-including our MUSE observations-reached a similar depth, the origin of this discrepancy must be searched for somewhere else.…”

“…To date, the two giant nebulae detected by Cantalupo et al (2014; the "Slug" Nebula) and Hennawi et al (2015; the "Jackpot" Nebula) and the extended emission reported by Martin et al (2014) are the only radio-quiet a Ly nebulae with sizes significantly larger than 100 pkpc. Other NB surveys (e.g., Hu et al 1991;Arrigoni Battaia et al 2016) and spectroscopic observations (e.g., Christensen et al 2006;North et al 2012;Herenz et al 2015) have either not detected any extended emission at all or detected emission on much smaller scales (50-60 pkpc), which was found in about 50% of the cases.…”

“…Filter losses could be particularly relevant for kinematically narrow nebulae while broader nebulae, such as radio-loud systems, would be less affected. Long-slit spectroscopic surveys, on the other hand, can only cover a small part of the area around the quasars (i.e., they suffer from slit losses) and all giant nebulae discovered so far are clearly asymmetric (Cantalupo et al 2014;Martin et al 2014;Hennawi et al 2015). Moreover, in order to discover faint and extended nebulosities, it is necessary to properly remove the point-spread function (PSF) associated with the hyper-luminous quasars, a task that is particularly difficult for some instruments (e.g., LRIS/Keck) and in general for NB imaging (PSF losses).…”

“…Following the early predictions of Hogan & Weymann (1987), Gould & Weinberg (1996), andHaiman & Rees (2001, and more detailed radiative transfer studies focusing also on quasar illumination (Cantalupo et al 2005;Kollmeier et al 2010), fluorescent a Ly surveys were successfully carried out using custom-built narrow-band (NB) filters on 8 m class telescopes and ultradeep integration on hyper-luminous and radio-quiet quasars at z 2 (Cantalupo et al 2012(Cantalupo et al , 2014Hennawi et al 2015). These surveys have revealed dense and compact intergalactic clouds with very little star formation ("dark galaxies"), circumgalactic streams around star forming galaxies (Cantalupo et al 2012), and two giant nebulae with sizes of about 460 physical kiloparsecs (pkpc; Cantalupo et al 2014) and 350 pkpc (Hennawi et al 2015) in proximity of the quasars. The typical detection rate of giant nebulae (i.e., with projected sizes larger than 100 pkpc) around radio-quiet quasars in these NB surveys is less than 10% considering both deep LRIS/Keck data (S. Cantalupo et al 2016, in preparation) and shallower surveys using GMOS (Arrigoni Battaia et al 2016).…”