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Register a new userQuasar clustering in a galaxy and quasar formation model based on ultra high-resolution N-body simulations
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Taira Oogi
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We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z=4 (a few 1e+11 Msun) to z=1 (a few 1e+12 Msun), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar--galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.
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We present the most precise estimate to date of the clustering of quasars on very small scales, based on a sample of 47 binary quasars with magnitudes of $g<20.85$ and proper transverse separations of $sim 25,h^{-1}$,kpc. Our sample of binary quasars, which is about 6 times larger than any previous spectroscopically confirmed sample on these scales, is targeted using a Kernel Density Estimation technique (KDE) applied to Sloan Digital Sky Survey (SDSS) imaging over most of the SDSS area. Our sample is complete in that all of the KDE target pairs with $17.0 lesssim R lesssim 36.2,h^{-1}$,kpc in our area of interest have been spectroscopically confirmed from a combination of previous surveys and our own long-slit observational campaign. We catalogue 230 candidate quasar pairs with angular separations of $<8arcsec$, from which our binary quasars were identified. We determine the projected correlation function of quasars ($bar W_{rm p}$) in four bins of proper transverse scale over the range $17.0 lesssim R lesssim 36.2,h^{-1}$,kpc. The implied small-scale quasar clustering amplitude from the projected correlation function, integrated across our entire redshift range, is $A=24.1pm3.6$ at $sim 26.6 ~h^{-1}$,kpc. Our sample is the first spectroscopically confirmed sample of quasar pairs that is sufficiently large to study how quasar clustering evolves with redshift at $sim 25 ~h^{-1}$ kpc. We find that empirical descriptions of how quasar clustering evolves with redshift at $sim 25 ~h^{-1}$ Mpc also adequately describe the evolution of quasar clustering at $sim 25 ~h^{-1}$ kpc.
Recent observations have found that many $zsim 6$ quasar fields lack galaxies. This unexpected lack of galaxies may potentially be explained by quasar radiation feedback. In this paper I present a suite of 3D radiative transfer cosmological simulations of quasar fields. I find that quasar radiation suppresses star formation in low mass galaxies, mainly by photo-dissociating their molecular hydrogen. Photo-heating also plays a role, but only after $sim$100 Myr. However, galaxies which already have stellar mass above $10^5 M_odot$ when the quasar turns on will not be suppressed significantly. Quasar radiative feedback suppresses the faint end of the galaxy luminosity function (LF) within $1$ pMpc, but to a far lesser degree than the field-to-field variation of the LF. My study also suggests that by using the number of bright galaxies ($M_{1500}<-16$) around quasars, we can potentially recover the underlying mass overdensity, which allows us to put reliable constraints on quasar environments.
Aims. We have searched for temporal variations of narrow absorption lines in high resolution quasar spectra. A sample of 5 distant sources have been assembled, for which 2 spectra - VLT/UVES or Keck/HIRES - taken several years apart are available. Methods. We first investigate under which conditions variations in absorption line profiles can be detected reliably from high resolution spectra, and discuss the implications of changes in terms of small-scale structure within the intervening gas or intrinsic origin. The targets selected allow us to investigate the time behavior of a broad variety of absorption line systems, sampling diverse environments: the vicinity of active nuclei, galaxy halos, molecular-rich galaxy disks associated with damped Lya systems, as well as neutral gas within our own Galaxy. Results. Absorption lines from MgII, FeII or proxy species with lines of lower opacity tracing the same kind of gas appear to be remarkably stable (1 sigma upper limits as low as 10 % for some components on scales in the range 10 - 100 au), even for systems at z_abs ~ z_e. Marginal variations are observed for MgII lines toward PKS 1229-021 at z_abs = 0.83032; however, we detect no systems displaying changes as large as those reported in low resolution SDSS spectra. In neutral or diffuse molecular media, clear changes are seen for Galactic NaI lines toward PKS 1229-02 (decrease of N by a factor of four for one of the five components over 9.7 yr), corresponding to structure at a scale of about 35 au, in good agreement with known properties of the Galactic interstellar medium. Tentative variations are detected for H2 J=3 lines toward FBQS J2340-0053 at z_abs =2.05454 (~35% change in column density), suggesting the existence of structure at the 10 au-scale for this warm gas. A marginal change is also seen in CI from another velocity component (~70% variation in N(CI)).
We study the density structures of dark matter subhalos for both cold dark matter and self-interacting dark matter models using high-resolution cosmological $N$-body simulations. We quantify subhalos central density at 150 pc from the center of each subhalo at the classical dwarf spheroidal and ultrafaint dwarf scales. By comparing them with observations, we find that the self-interacting scattering cross-section of $sigma/m<3 rm{cm^{2}g^{-1}}$ is favored. Due to the combination of hosts tide and self-interactions, the central density of subhalos with small pericenter shows a noticeable difference between the cold and the self-interacting models, indicating that dwarf satellites with small pericenter are ideal sites to further constrain the nature of dark matter by future large spectroscopic surveys.
Super-Eddington mass accretion has been suggested as an efficient mechanism to grow supermassive black holes (SMBHs). We investigate the imprint left by the radiative efficiency of the super-Eddington accretion process on the clustering of quasars using a new semi-analytic model of galaxy and quasar formation based on large-volume cosmological $N$-body simulations. Our model includes a simple model for the radiative efficiency of a quasar, which imitates the effect of photon trapping for a high mass accretion rate. We find that the model of radiative efficiency affects the relation between the quasar luminosity and the quasar host halo mass. The quasar host halo mass has only weak dependence on quasar luminosity when there is no upper limit for quasar luminosity. On the other hand, it has significant dependence on quasar luminosity when the quasar luminosity is limited by its Eddington luminosity. In the latter case, the quasar bias also depends on the quasar luminosity, and the quasar bias of bright quasars is in agreement with observations. Our results suggest that the quasar clustering studies can provide a constraint on the accretion disc model.
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