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Register a new userCosmological constraints with the sub-millimetre galaxies Magnification Bias after large scale bias corrections
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Joaquin Gonzalez-Nuevo
Publication date
2020
fields
Physics
and research's language is
English
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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.
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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.
Dust emission at sub-millimetre wavelengths allows us to trace the early phases of star formation in the Universe. In order to understand the physical processes involved in this mode of star formation, it is essential to gain knowledge about the dark matter structures - most importantly their masses - that sub-millimetre galaxies live in. Here we use the magnification effect of gravitational lensing to determine the average mass and dust content of sub-millimetre galaxies with 250mu flux densities of S_250>15mJy selected using data from the Herschel Multi-tiered Extragalactic Survey. The positions of hundreds of sub-millimetre foreground lenses are cross-correlated with the positions of background Lyman-break galaxies at z~3-5 selected using optical data from the Canada-France Hawaii Telescope Legacy Survey. We detect a cross-correlation signal at the 7-sigma level over a sky area of one square degree, with ~80% of this signal being due to magnification, whereas the remaining ~20% comes from dust extinction. Adopting some simple assumptions for the dark matter and dust profiles and the redshift distribution enables us to estimate the average mass of the halos hosting the sub-millimetre galaxies to be log(M_200/M_sun)=13.17+0.05-0.08(stat.) and their average dust mass fraction (at radii of >10kpc) to be M_dust/M_200~6x10^-5. This supports the picture that sub-millimetre galaxies are dusty, forming stars at a high rate, reside in massive group-sized halos, and are a crucial phase in the assembly and evolution of structure in the Universe.
We study the nature of rapidly star-forming galaxies at z=2 in cosmological hydrodynamic simulations, and compare their properties to observations of sub-millimetre galaxies (SMGs). We identify simulated SMGs as the most rapidly star-forming systems that match the observed number density of SMGs. In our models, SMGs are massive galaxies sitting at the centres of large potential wells, being fed by smooth infall and gas-rich satellites at rates comparable to their star formation rates (SFR). They are not typically undergoing major mergers that significantly boost their quiescent SFR, but they still often show complex gas morphologies and kinematics. Our simulated SMGs have stellar masses of log M*/Mo~11-11.7, SFRs of ~180-500 Mo/yr, a clustering length of 10 Mpc/h, and solar metallicities. The SFRs are lower than those inferred from far-IR data by a factor of 3, which we suggest may owe to one or more systematic effects in the SFR calibrations. SMGs at z=2 live in ~10^13 Mo halos, and by z=0 they mostly end up as brightest group galaxies in ~10^14 Mo halos. We predict that higher-M* SMGs should have on average lower specific SFRs, less disturbed morphologies, and higher clustering. We also predict that deeper far-IR surveys will smoothly join SMGs onto the massive end of the SFR-M* relationship defined by lower-mass z=2 galaxies. Overall, our simulated rapid star-formers provide as good a match to available SMG data as merger-based scenarios, offering an alternative scenario that emerges naturally from cosmological simulations.
We analyse the surface density of very faint galaxies at the limit of the sky background noise in the field of the cluster of galaxies Cl0024+1654. The radial variation of their number density in the magnitude bins $B=26-28$ and $I=24-26.5$ displays an (anti)bias magnification effect for $I < 24$ which provides the redshift range of the populations seen in $B$ and $I$. The depletion curve can be reproduced with two redshift populations with $60% pm 10%$ of the $B$ galaxies between $z=0.9$ and $z=1.1$ and the remaining at a redshift close to $z=3$. The $I$ selected population is similar but with a minimum extending from the $B$ inner critical line to $R_I=60$. Whatever the cosmological model, the $I$-selected galaxies spread up to a larger redshift with about 20% above $z > 4$. Using a model for the gravitational potential, the locations of the two extreme critical lines for the B and I galaxies favour $Omega_{Lambda}$-dominated flat universes with a cosmological constant ranging from 0.6 to 0.9. The result is confirmed by a preliminary investigation of A370. We discuss the method to search the last critical line and the various biases.
We present a mitigation strategy to reduce the impact of non-linear galaxy bias on the joint `$3 times 2 $pt cosmological analysis of weak lensing and galaxy surveys. The $Psi$-statistics that we adopt are based on Complete Orthogonal Sets of E/B Integrals (COSEBIs). As such they are designed to minimise the contributions to the observable from the smallest physical scales where models are highly uncertain. We demonstrate that $Psi$-statistics carry the same constraining power as the standard two-point galaxy clustering and galaxy-galaxy lensing statistics, but are significantly less sensitive to scale-dependent galaxy bias. Using two galaxy bias models, motivated by halo-model fits to data and simulations, we quantify the error in a standard $3 times 2$pt analysis where constant galaxy bias is assumed. Even when adopting conservative angular scale cuts, that degrade the overall cosmological parameter constraints, we find of order $1 sigma$ biases for Stage III surveys on the cosmological parameter $S_8 = sigma_8(Omega_{rm m}/0.3)^{alpha}$. This arises from a leakage of the smallest physical scales to all angular scales in the standard two-point correlation functions. In contrast, when analysing $Psi$-statistics under the same approximation of constant galaxy bias, we show that the bias on the recovered value for $S_8$ can be decreased by a factor of $sim 2$, with less conservative scale cuts. Given the challenges in determining accurate galaxy bias models in the highly non-linear regime, we argue that $3 times 2$pt analyses should move towards new statistics that are less sensitive to the smallest physical scales.
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