Clustering and Environment of Quasars at High Redshift Michael A. Strauss, Princeton University

Joe HennawiJenny Greene Xin Liu Nic Ross

The Clustering of High- Redshift Objects The clustering of dark matter with time (and thus redshift) is well-understood. Galaxies and quasars live in dark matter halos, which are biased relative to the dark matter. The strength of that biasing, which determines the clustering strength at any epoch, depends on the mass of the dark matter halos.

The peaks of the highest mountains are strongly clustered. Similarly, the most massive dark matter halos will be strongly correlated.

The comoving clustering length of luminous galaxies is roughly independent of z at least to z ~ 5 (although the clustering strength depends on luminosity and color). The comoving clustering length of luminous galaxies is roughly independent of z at least to z ~ 5 (although the clustering strength depends on luminosity and color). Therefore, the distribution of galaxies must be increasingly biased relative to the dark matter at high redshift,  galaxies =b  dark matter Therefore, the distribution of galaxies must be increasingly biased relative to the dark matter at high redshift,  galaxies =b  dark matter Ouchi et al. 2004

How about quasars? Quasars are powered by the ubiquitous supermassive black holes in the cores of ordinary massive galaxies. Therefore, we’d expect that the clustering of quasars should be similar to that of luminous galaxies, at the same redshift. Bahcall, Kirhakos, Schneider

SDSS Quasar Sample Courtesy Xiaohui Fan

Comoving Correlation Length of Quasars as Function of Redshift Ross et al. 2009

The correlation length is insensitive to: Quasar color Virial black hole mass (as measured from spectrum) Redshift (at least to z~2.5) Luminosity (except for most luminous 10%) Clustering is a measure of dark matter halo mass. None of these quantities correlate strongly enough with halo mass to have a measurable effect. This suggests that luminosity is not closely tied to halo (and thus black hole?) mass in this redshift range (at least over the small dynamic range in L explored to date).

What happens at higher redshift? z>3 is before the peak of quasar activity. Higher-redshift quasars (in flux-limited samples) are very luminous, and therefore are powered by very massive black holes. If very massive black holes are associated with very massive dark-matter halos, then high-redshift quasars should sit in very rare, many  peaks in the density field. We already know higher-redshift quasars are rare! Rare peaks are very strongly biased relative to the overall density field. So we expect high-redshift quasars to be more strongly clustered than are ordinary galaxies.

Let’s measure this with the SDSS high-z quasar sample z>2.9 quasars in a uniformly selected sample over 4000 deg 2 from DR5. Mean spacing between quasars is 150 h -1 Mpc. This is a sparse sample! Shen et al. 2007

Projected distance on the sky Projected correlation function Equivalent to  (r) = (r/r 0 ) -  r 0 =15.2±2.7 Mpc/h  = 2.0±0.3 A bias of 10! Measured correlation function for 2.9 < z < 5 quasar sample At these redshifts, ordinary galaxies have r 0 ~5 Mpc/h Shen et al. 2007

So the clustering was larger in the past For 2.9 < z < 3.5: r 0 =16.9±1.7 Mpc/h b~10 For z > 3.5: r 0 =24.3±2.4 Mpc/h b~15

Evolution of quasar correlation length with redshift

What mass halos do high- redshift quasars live in? Observed clustering strength suggests a halo mass of >several  solar masses, essentially independent of redshift. The correlation between luminosity and halo mass must be quite good (White et al. 2008). This interpretation may be affected by merger bias (Wyithe & Loeb 2009) if quasars are triggered by mergers, but Bonoli et al. (2010) argue that the effect is small. There are still substantial uncertainties in the relationship between halo mass and bias at the high-bias, high-z end, giving factors of ~few uncertainty in the inferred mass.

Model of Shen (2009; see his poster!). The predicted bias of quasars as a function of redshift. Smaller error bars from the full SDSS DR7 sample will be an important test of models like this.

Relation to highly clustered galaxies? Comoving correlation length of 2<z<3.5 galaxies as function of color; Quadri et al. (2007). See also Foucaud et al. (2010); Hayashi et al. (2007). There are populations of galaxies whose clustering approaches that of the high-redshift quasars. The ratio of number densities is roughly 3  10 -4, within an order of magnitude of the implied duty cycles of the quasars. To do a proper job of this requires large samples of galaxies with the same redshift distribution as the quasars.

What about small scales? Ouchi et al. 2005: Angular clustering of z~4 galaxies shows a dramatic excess at small scales, much more so than at low redshift. See also Quadri et al

Hennawi, Shen et al. 2010: 27 quasar pairs at z>2.9 Pair at z=3.8, separated by 40 kpc Hennawi et al. 2010

Inferred  (r) on small scales in two redshift bins. Completeness correction is quite uncertain. Shen et al. 2010

Sey II galaxies in SDSS that show double emission lines. Could these be merging systems? Bipolar outflows? We’re starting a program of follow-up. Liu, Shen et al. 2010

Four Seyfert galaxies from Liu sample, showing double nuclei in J and K bands. Liu, Greene et al. 2010

Liu, Greene et al. 2010: Spatially resolved spectroscopy for the same four double- nuclei sources: note the wavelength and positional shifts in the strong emission lines. Position Wavelength

The Environments of High- Redshift Quasars If high-redshift quasars live in many-sigma peaks of the density field, they should have many satellite galaxies. Zheng et al. 2006: overdensity of galaxies around a z=5.7 radio quasar. See also Overzier et al Are radio galaxies/quasars in particularly massive halos?

But most searches for protoclusters around high-z quasars have found little… Similarly, Kim et al. (2009) have HST imaging of the field of 5 z~6 quasars, and see nothing. See also Willott et al (2005); Stiavelli et al. (2005). Mean density of galaxies as a function of projected distance from six z~3.8 quasars. Deep (r=25.5) 3-band photometry from VLT. Fried, Rix et al, in preparation. Distance (Mpc) Density of galaxies

Might radiation from quasars actively suppress galaxy formation around them? Kashikawa et al. 2007: z~4.8 quasar lies in an overdensity of Lyman  absorbers, but an underdensity of Lyman  emitters. Understanding this possible suppression requires knowledge of isotropy and lifetime of quasar emission.

SDSS-III: BOSS 150,000 quasars at z>2.2 First commissioning data!.

Redshift histogram from BOSS

Subaru Hyper-Suprime Cam Satoshi Miyazaki is building an imaging camera with 1.77 deg 2 field of view on Subaru. First light late We are collaborating with NAOJ to carry out wide- field surveys (>1000 deg 2 ) in grizy, to r~27.

LSST: 6.7-m survey telescope on Cerro Pachón in Chilean Andes Telescope will be dedicated to the survey, and will operate for ten years.

A dedicated 10-year survey Field of view of LSST is 9.6 deg 2 ; 3.5 billion pixels. Main survey will cover 20,000 square degrees, with over second exposures in each of r, i, z, and y. 5  depth after two exposures: 23.9 (u), 25.0 (g), 24.7 (r), 24.0 (i), 23.3 (z), 22.1 (y) Depth at end of the survey: 26.2 (u), 27.4 (g), 27.6 (r), 26.9 (i), 26.1 (z), 24.8 (y).

Major construction proposal submitted to NSF in February We’re waiting on the Decadal Survey. First light 2016 or 2017?

With LSST, we can: Select quasars to z~7 Measure angular correlations on wide variety of scales, and study luminosity dependence over a wide range of luminosities. Measure quasar-galaxy cross-correlations, and study host clusters, over a wide range of redshifts.

Summary z>3 quasars are highly biased and very strongly clustered; they live in dark matter halos of ~2  M solar. Models predict a strong luminosity dependence to the clustering at high redshift. There is enhanced clustering of quasars at low redshift; not enough pairs at high redshift to be definitive. Binary black holes are starting to be discovered at low redshift. Quasars at high redshift do not seem to live in (proto- )cluster environments. The next generation of surveys (SDSS-III, Subaru, LSST, etc), will explore clustering at lower luminosity, study quasar-galaxy cross-correlations, and perhaps identify host population of high-x luminous quasars.