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Register a new userCosmology with the submillimetre galaxies magnification bias: Proof of concept
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Context. As recently demonstrated, high-z submillimetre galaxies (SMGs) are the perfect background sample for tracing the mass density profiles of galaxies and clusters (baryonic and dark matter) and their time-evolution through gravitational lensing. Their magnification bias, a weak gravitational lensing effect, is a powerful tool for constraining the free parameters of a halo occupation distribution (HOD) model and potentially also some of the main cosmological parameters. Aims. The aim of this work is to test the capability of the magnification bias produced on high-z SMGs as a cosmological probe. We exploit cross-correlation data to constrain not only astrophysical parameters ($M_{min}$, $M_1$, and $alpha$), but also some of the cosmological ones ($Omega_m$, $sigma_8$, and $H_0$) for this proof of concept. Methods. The measured cross-correlation function between a foreground sample of GAMA galaxies with spectroscopic redshifts in the range 0.2 < z < 0.8 and a background sample of H-ATLAS galaxies with photometric redshifts >1.2 is modelled using the traditional halo model description that depends on HOD and cosmological parameters. These parameters are then estimated by performing a Markov chain Monte Carlo analysis using different sets of priors to test the robustness of the results and to study the performance of this novel observable with the current set of data Results. With our current results, $Omega_m$ and $H_0$ cannot be well constrained. However, we can set a lower limit of >0.24 at 95% confidence level (CL) on $Omega_m$ and we see a slight trend towards $H_0>70$ values. For our constraints on $sigma_8$ we obtain only a tentative peak around 0.75, but an interesting upper limit of $sigma_8lesssim 1$ at 95% CL. We also study the possibility to derive better constraints by imposing more restrictive priors on the astrophysical parameters.
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Aims. The main purpose of this work is to provide a method to derive tabulated observational constraints on the halo mass function (HMF) by studying the magnification bias effect on high-redshift submillimeter galaxies. Under the assumption of universality, we parametrize the HMF according to two traditional models, namely the Sheth and Tormen (ST) and Tinker fits and assess their performance in explaining the measured data within the {Lambda} cold dark matter ({Lambda}CDM) model. We also study the potential influence of the halo occupation distribution (HOD) parameters in this analysis and discuss two important aspects regarding the HMF parametrization. Methods. We measure the cross-correlation function between a foreground sample of GAMA galaxies with redshifts in the range $0.2<z<0.8$ and a background sample of H-ATLAS galaxies with redshifts in the range $1.2<z<4.0$ and carry out an MCMC algorithm to check this observable against its mathematical prediction within the halo model formalism. Results. If all HMF parameters are assumed to be positive, the ST fit only seems to fully explain the measurements by forcing the mean number of satellite galaxies in a halo to increase substantially from its prior mean value. The Tinker fit, on the other hand, provides a robust description of the data without relevant changes in the HOD parameters, but with some dependence on the prior range of two of its parameters. When the normalization condition for the HMF is dropped and we allow negative values of the $p_1$ parameter in the ST fit, all the involved parameters are better determined, unlike the previous models, thus deriving the most general HMF constraints. While all cases are in agreement with the traditional fits within the uncertainties, the last one hints at a slightly higher number of halos at intermediate and high masses, raising the important point of the allowed parameter range.
The study of the magnification bias produced on high-redshift sub-millimetre galaxies by foreground galaxies through the analysis of the cross-correlation function was recently demonstrated as an interesting independent alternative to the weak-lensing shear as a cosmological probe. In the case of the proposed observable, most of the cosmological constraints mainly depend on the largest angular separation measurements. Therefore, we aim to study and correct the main large-scale biases that affect foreground and background galaxy samples to produce a robust estimation of the cross-correlation function. Then we analyse the corrected signal to derive updated cosmological constraintsWe measured the large-scale, bias-corrected cross-correlation functions using a background sample of H-ATLAS galaxies with photometric redshifts > 1.2 and two different foreground samples (GAMA galaxies with spectroscopic redshifts or SDSS galaxies with photometric ones, both in the range 0.2 < z < 0.8). These measurements are modelled using the traditional halo model description that depends on both halo occupation distribution and cosmological parameters. We then estimated these parameters by performing a Markov chain Monte Carlo under multiple scenarios to study the performance of this observable and how to improve its results. After the large-scale bias corrections, we obtain only minor improvements with respect to the previous magnification bias results, mainly confirming their conclusions: a lower bound on $Omega_m > 0.22$ at $95%$ C.L. and an upper bound $sigma_8 < 0.97$ at $95%$ C.L. (results from the $z_{spec}$ sample). However, by combining both foreground samples into a simplified tomographic analysis, we were able to obtain interesting constraints on the $Omega_m$-$sigma_8$ plane as follows: $Omega_m= 0.50_{- 0.20}^{+ 0.14}$ and $sigma_8= 0.75_{- 0.10}^{+ 0.07}$ at 68% CL.
Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an `orientation bias in the selection and analysis of such galaxies in flux-limited cosmological surveys? We investigate these questions using the Simba cosmological simulation paired with the dust radiative transfer code Powderday. We select eight simulated SMGs ($S_{850}gtrsim2$ mJy) at $z = 2$, and measure the variance of their `observed emission over 50 random orientations. Each galaxy exhibits significant scatter in its emission close to the peak of the thermal dust emission, with variation in flux density of up to $sim$50 mJy at the peak. This results in an appreciable dispersion in the inferred dust temperatures and infrared luminosities ($16^{mathrm{th}}-84^{mathrm{th}}$ percentile ranges of 5 K and 0.1 dex, respectively) and therefore a fundamental uncertainty in derived parameters such as dust mass and star formation rate ($sim$30% for the latter using simple calibrations). Using a Monte Carlo simulation we also assess the impact of orientation on flux-limited surveys, finding a bias in the selection of SMGs towards those with face-on orientations, as well as those at lower redshifts. We predict that the orientation bias will affect flux-limited single-dish surveys, most significantly at THz frequencies, and this bias should be taken into account when placing the results of targeted follow-up studies in a statistical context.
A recent comparison of the massive galaxy cluster Abell 2744 with the Millennium XXL (MXXL) N-body simulation has hinted at a tension between the observed substructure distribution and the predictions of LambdaCDM. Follow-up investigations indicated that this could be due to the contribution from the host halo and the subhalo finding algorithm used. To be independent of any subhalo finding algorithm, we therefore investigate the particle data of the MXXL simulation directly. We propose a new method to find substructures in 2D mass maps using a wavelet transform, which treats the simulation and observations equally. Using the same criteria to define a subhalo in observations and simulated data, we find three Abell 2744 analogues in the MXXL simulation. Thus the observations in Abell 2744 are in agreement with the predictions of LambdaCDM. We investigate the reasons for the discrepancy between the results obtained from the SUBFIND and full particle data analyses. We find that this is due to incompatible substructure definitions in observations and SUBFIND.
Gravitational lensing magnification modifies the observed spatial distribution of galaxies and can severely bias cosmological probes of large-scale structure if not accurately modelled. Standard approaches to modelling this magnification bias may not be applicable in practice as many galaxy samples have complex, often implicit, selection functions. We propose and test a procedure to quantify the magnification bias induced in clustering and galaxy-galaxy lensing (GGL) signals in galaxy samples subject to a selection function beyond a simple flux limit. The method employs realistic mock data to calibrate an effective luminosity function slope, $alpha_{rm{obs}}$, from observed galaxy counts, which can then be used with the standard formalism. We demonstrate this method for two galaxy samples derived from the Baryon Oscillation Spectroscopic Survey (BOSS) in the redshift ranges $0.2 < z leq 0.5$ and $0.5 < z leq 0.75$, complemented by mock data built from the MICE2 simulation. We obtain $alpha_{rm{obs}} = 1.93 pm 0.05$ and $alpha_{rm{obs}} = 2.62 pm 0.28$ for the two BOSS samples. For BOSS-like lenses, we forecast a contribution of the magnification bias to the GGL signal between the multipole moments, $ell$, of 100 and 4600 with a cumulative signal-to-noise ratio between 0.1 and 1.1 for sources from the Kilo-Degree Survey (KiDS), between 0.4 and 2.0 for sources from the Hyper Suprime-Cam survey (HSC), and between 0.3 and 2.8 for ESA Euclid-like source samples. These contributions are significant enough to require explicit modelling in future analyses of these and similar surveys. Our code is publicly available within the textsc{MagBEt} module (url{https://github.com/mwiet/MAGBET}).
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