We measure the cosmological bias factor of damped Ly α absorbers (DLAs) from their crosscorrelation with the Ly α forest absorption, as a function of the DLA metal strength, defined from an average ...of equivalent widths of the strongest detectable low-ionization metal lines. A clear increase of the bias factor with metal strength is detected, as expected from a relation of metallicity and velocity dispersion with host halo mass. The relation is stronger after the metal strength is corrected for the H I column density, to make it more related to metallicity instead of metal column density. After correcting for the effects of measurement errors of the metal strength parameter, we find that the bias factor of DLAs with the weakest metal lines is close to unity, consistent with an origin in dwarf galaxies with host halo masses ∼1010 M, whereas the most metal rich DLAs have a bias factor as large as bDLA ∼ 3, indicative of massive galaxies or galaxy groups in host haloes with masses ∼1012 M. Our result confirms the physical origin of the relation of bias factors measured from cross-correlation studies to the host haloes of the absorbers.
We measure the two-point clustering of spectroscopically confirmed quasars from the final sample of the Baryon Oscillation Spectroscopic Survey (BOSS) on comoving scales of 4 ≲ s ≲ 22 h
−1 Mpc. The ...sample covers 6950 deg2 ∼ 19 (h
− 1Gpc)3 and, over the redshift range 2.2 ≤ z ≤ 2.8, contains 55 826 homogeneously selected quasars, which is twice as many as in any similar work. We deduce b
Q = 3.54 ± 0.10; the most precise measurement of quasar bias to date at these redshifts. This corresponds to a host halo mass of ∼2 × 1012 h
−1 M⊙ with an implied quasar duty cycle of ∼1 per cent. The real-space projected correlation function is well fitted by a power law of index 2 and correlation length r
0 = (8.12 ± 0.22) h
− 1 Mpc over scales of 4 ≲ r
p ≲ 25 h
−1 Mpc. To better study the evolution of quasar clustering at moderate redshift, we extend the redshift range of our study to z ∼ 3.4 and measure the bias and correlation length of three subsamples over 2.2 ≤ z ≤ 3.4. We find no significant evolution of r
0 or bias over this range, implying that the host halo mass of quasars decreases somewhat with increasing redshift. We find quasar clustering remains similar over a decade in luminosity, contradicting a scenario in which quasar luminosity is monotonically related to halo mass at z ≈ 2.5. Our results are broadly consistent with previous BOSS measurements, but they yield more precise constraints based upon a larger and more uniform data set.
Abstract
Observations of the Lyman-
α
forest from spectroscopic surveys such as the Baryon Oscillation Spectroscopic Survey or its extension, eBOSS, or the ongoing Dark Energy Spectroscopic ...Instrument (DESI) survey offer a unique window to study the growth of structure on megaparsec scales. Interpretation of these measurements is a complicated task, requiring hydrodynamical simulations to model and marginalize over the thermal and ionization state of the intergalactic medium. This complexity has limited the use of Ly
α
clustering measurements in joint cosmological analyses. In this work we show that the cosmological information content of the one-dimensional power spectrum (
P
1D
) of the Lyman-
α
forest can be compressed into a simple two-parameter likelihood without any significant loss of constraining power. We simulate
P
1D
measurements from DESI using hydrodynamical simulations and show that the compressed likelihood is model independent and lossless, recovering unbiased results even in the presence of massive neutrinos or running of the primordial power spectrum.
The initial conditions of cosmological simulations are commonly drawn from a Gaussian ensemble. The limited number of modes inside simulations gives rise to sample variance: statistical fluctuations ...that limit the accuracy of the simulation predictions. Fixed fields offer an alternative initialization strategy; they have the same power spectrum as Gaussian fields but no intrinsic amplitude scatter. Paired fixed fields consist of two fixed fields with opposite phases that cancel phase correlations. We study the statistical properties of those fields for 19 different quantities at different redshifts through a large set of 600 N-body and 530 state-of-the-art magnetohydrodynamic simulations. We find that paired fixed simulations do not introduce a bias on any of the examined quantities. We quantify the statistical improvement brought by these simulations on different power spectra-matter, halos, cold dark matter, gas, stars, galaxies, and magnetic fields-finding that they can reduce their variance by factors as large as 106. We quantify the improvement achieved by fixing and by pairing, showing that sample variance can be highly suppressed by pairing after fixing. Paired fixed simulations do not change the scatter in quantities such as the probability distribution function or the halo, void, or stellar mass functions. We argue that procedures aiming at reducing the sample variance of those quantities are unlikely to work. Our results show that paired fixed simulations do not affect either mean relations or scatter of galaxy properties and suggest that the information embedded in one-point statistics is highly complementary to that in clustering.
ABSTRACT
Cosmological studies of large-scale structure have relied on two-point statistics, not fully exploiting the rich structure of the cosmic web. In this paper we show how to capture some of ...this cosmic web information by using the minimum spanning tree (MST), for the first time using it to estimate cosmological parameters in simulations. Discrete tracers of dark matter such as galaxies, N-body particles or haloes are used as nodes to construct a unique graph, the MST, that traces skeletal structure. We study the dependence of the MST on cosmological parameters using haloes from a suite of COmoving Lagrangian Acceleration (COLA) simulations with a box size of $250\ h^{-1}\, {\rm Mpc}$, varying the amplitude of scalar fluctuations (As), matter density (Ωm), and neutrino mass (∑mν). The power spectrum P and bispectrum B are measured for wavenumbers between 0.125 and 0.5 $h\, {\rm Mpc}^{-1}$, while a corresponding lower cut of ∼12.6 $h^{-1}\, {\rm Mpc}$ is applied to the MST. The constraints from the individual methods are fairly similar but when combined we see improved 1σ constraints of $\sim 17{{\ \rm per\ cent}}$ ($\sim 12{{\ \rm per\ cent}}$) on Ωm and $\sim 12{{\ \rm per\ cent}}$ ($\sim 10{{\ \rm per\ cent}}$) on As with respect to P (P + B) thus showing the MST is providing additional information. The MST can be applied to current and future spectroscopic surveys (BOSS, DESI, Euclid, PSF, WFIRST, and 4MOST) in 3D and photometric surveys (DES and LSST) in tomographic shells to constrain parameters and/or test systematics.
Abstract
We present the first result in exploring the gaseous halo and galaxy correlation using the Dark Energy Spectroscopic Instrument survey validation data in the Cosmic Evolution Survey (COSMOS) ...and Hyper Suprime-Cam field. We obtain multiphase gaseous halo properties in the circumgalactic medium by using 115 quasar spectra (signal-to-noise ratio > 3). We detect Mg
ii
absorption at redshift 0.6 <
z
< 2.5, C
iv
absorption at 1.6 <
z
< 3.6, and H
i
absorption associated with the Mg
ii
and C
iv
. By crossmatching the COSMOS2020 catalog, we identify the Mg
ii
and C
iv
host galaxies in 10 quasar fields at 0.9<
z
< 3.1. We find that within the impact parameter of 250 kpc, a tight correlation is seen between the strong Mg
ii
equivalent width and the host galaxy star formation rate. The covering fraction
f
c
of the strong Mg
ii
selected galaxies, which is the ratio of the absorbing galaxy in a certain galaxy population, shows significant evolution in the main-sequence galaxies and marginal evolution in all the galaxy populations within 250 kpc at 0.9 <
z
< 2.2. The
f
c
increase in the main-sequence galaxies likely suggests the coevolution of strong Mg
ii
absorbing gas and the main-sequence galaxies at the cosmic noon. Furthermore, Mg
ii
and C
iv
absorbing gas is detected out of the galaxy virial radius, tentatively indicating the feedback produced by the star formation and/or the environmental effects.
ABSTRACT
We propose a new method for fitting the full-shape of the Lyman-α (Ly α) forest 3D correlation function in order to measure the Alcock-Paczynski (AP) effect. Our method preserves the ...robustness of baryon acoustic oscillations (BAO) analyses, while also providing extra cosmological information from a broader range of scales. We compute idealized forecasts for the Dark Energy Spectroscopic Instrument (DESI) using the Ly α autocorrelation and its cross-correlation with quasars, and show how this type of analysis improves cosmological constraints. The DESI Ly α BAO analysis is expected to measure H(zeff)rd and DM(zeff)/rd with a precision of $\sim 0.9{{\ \rm per\ cent}}$, where H is the Hubble parameter, rd is the comoving BAO scale, DM is the comoving angular diameter distance, and the effective redshift of the measurement is zeff ≃ 2.3. By fitting the AP parameter from the full shape of the two correlations, we show that we can obtain a precision of $\sim 0.5-0.6{{\ \rm per\ cent}}$ on each of H(zeff)rd and DM(zeff)/rd. Furthermore, we show that a joint full-shape analysis of the Ly α auto and cross-correlation with quasars can measure the linear growth rate times the amplitude of matter fluctuations in spheres of 8 h−1Mpc, fσ8(zeff). Such an analysis could provide the first ever measurement of fσ8(zeff) at redshift zeff > 2. By combining this with the quasar autocorrelation in a joint analysis of the three high-redshift two-point correlation functions, we show that DESI could be able to measure fσ8(zeff ≃ 2.3) with a precision of $5-12{{\ \rm per\ cent}}$, depending on the smallest scale fitted.
PDF
