Enhancement of galaxy overdensity around quasar pairs at z < 3.6 based on the Hyper Suprime-Cam Subaru Strategic Program Survey

Abstract

We investigate the galaxy overdensity around proto-cluster scale quasar pairs at high (z > 3) and low (z ∼ 1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first-year survey data covering effectively ∼ 121 deg 2 with the 5σ depth of i ∼ 26.4 and the SDSS DR12Q catalog, we find two luminous pairs at z ∼ 3.3 and 3.6 which reside in > 5σ overdense regions of gdropout galaxies at i < 25. The projected separations of the two pairs are R ⊥ = 1.75 and 1.04 proper Mpc, and their velocity offsets are ∆V = 692 and 1448 km s −1 , respectively. This result is in clear contrast to the average z ∼ 4 quasar environments as discussed in Uchiyama et al. (2017) and implies that the quasar activities of the pair members are triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on via non-merger events such as bar and disk instabilities. At z ∼ 1, we find 37 pairs with R ⊥ < 2 pMpc and ∆V < 2300 km s −1 in the current HSC-Wide coverage, including four from Hennawi et al. (2006). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high density (> 4σ) regions. Thanks to the large sample size, we find a statistical evidence that this excess is unique to the pair environments when compared to single quasar and randomly selected galaxy environments at the same redshift range. Moreover, there are nine small-scale (R ⊥ < 1 pMpc) pairs, two of which are found to reside in cluster fields. Our results demonstrate that < 2 pMpc-scale quasar pairs at both redshift range tend to occur in massive haloes, although perhaps not the most massive ones, and that they are useful to search for rare density peaks.

Keck/Palomar Cosmic Web Imagers Reveal an Enormous Lyα Nebula in an Extremely Overdense Quasi-stellar Object Pair Field at z = 2.45

“…Using the Hyper-Suprime-Cam survey and SDSS DR12 QSO database, Onoue et al (2018) found that QSO pairs trace >5σ overdense regions over 15 co-Mpc. These overdense regions could be protoclusters with M z=0 >10 14 M e .…”

“…This has motivated our survey using QSO pairs. In addition, recent studies have suggested that Sloan Digital Sky Survey (SDSS) QSO pairs trace protoclusters (Onoue et al 2018), and thus the extended Lyα, C IV, He II lines traced by QSO pairs can be used to probe cool (T ∼ 10 4 K) and warm (T ∼ 10 5 K) gas in the early intracluster medium (ICM; Valentino et al 2016).…”

The Goldilocks problem of the quasar contribution to reionization

“…Several observations support this hypothesis (e.g. Kim et al 2009;Cantalupo et al 2012;Morselli et al 2014;Ota et al 2018;Onoue et al 2018) although some exceptions have been found (Bañados et al 2013;Fanidakis et al 2013;Mazzucchelli et al 2017). In practice, we consider each DM halo as a potential host of a QSO and sample the associated magnitude at 1450 Å (M AB ) from a Gaussian distribution with mean…”

The Environment of QSOs Triplets at 1 > z > 1.5

“…(2019b)), Hydrogen Alpha Emitters (HAEs) (Hatch et al, 2011b;Hayashi et al, 2012), submillimeter galaxies (Daddi et al, 2009;Capak et al, 2011;Rigby et al, 2014;Dannerbauer et al, 2014), radio galaxies (Venemans et al, 2002(Venemans et al, , 2007Hatch et al, 2011a;Hayashi et al, 2012;Wylezalek et al, 2013;Cooke et al, 2014), isolated QSOs González-Serrano, 1999, 2002;Stott et al, 2020) and systems of QSOs (Boris et al, 2007;Onoue et al, 2018). These are all biased tracers and are useful to find massive systems in formation (Overzier, 2016), since the bias between the distribution of baryonic matter and dark matter haloes in structure formation scenarios (Kaiser, 1984) implies that high-z objects form in large high-z density fluctuations.…”

“…Recently, Stott et al (2020) to protoclusters and others, not (e.g., Boris et al, 2007;Farina et al, 2011;Green et al, 2011;Sandrinelli et al, 2014;Eftekharzadeh et al, 2017;Onoue et al, 2018).…”