The clustering of baryonic matter. I: a halo-model approach

In this paper I generalize the halo model for the clustering of dark matter in order to produce the power spectra of the two main baryonic matter components in the Universe: stars and hot gas. As a natural extension, this can be also used to describe the clustering of all mass. According to the design of the halo model, the large-scale power spectra of the various matter components are physically connected with the distribution of each component within bound structures and thus, ultimately, with the complete set of physical processes that drive the formation of galaxies and galaxy clusters. Besides being practical for cosmological and parametric studies, the semi-analytic model presented here has also other advantages. Most importantly, it allows one to understand on physical ground what is the relative contribution of each matter component to the total clustering of mass as a function of scale, and thus it opens an interesting new window to infer the distribution of baryons through high precision cosmic shear measurements. This is particularly relevant for future wide-field photometric surveys such as Euclid. In this work the concept of the model and its uncertainties are illustrated in detail, while in a companion paper we use a set of numerical hydrodynamic simulations to show a practical application and to investigate where the model itself needs to be improved.Comment: 25 pages, 9 figures. Accepted for publication by JCA

Lensing dispersion of supernova flux: a probe of nonlinear structure growth

The scatter in the apparent magnitude of type Ia supernovae induced by stochastic gravitational lensing is highly dependent on the nonlinear growth of cosmological structure. In this paper, we show that such a dependence can potentially be employed to gain significant information about the mass clustering at small scales. While the mass clustering ultimately hinges on cosmology, here we demonstrate that, upon obtaining more precise observational measurements through future cosmological surveys, the lensing dispersion can very effectively be used to gain information on the poorly understood astrophysical aspects of structure formation, such as the clumpiness of dark matter halos and the importance of gas physics and star formation into shaping the large-scale structure. In order to illustrate this point we verify that even the tentative current measurements of the lensing dispersion performed on the Supernova Legacy Survey sample favor a scenario where virialized structures are somewhat less compact than predicted by $n-$body cosmological simulations. Moreover, we are also able to put lower limits on the slope of the concentration-mass relation. By artificially reducing the statistical observational error we argue that with forthcoming data the stochastic lensing dispersion will allow one to importantly improve constraints on the baryonic physics at work during the assembly of cosmological structure.Comment: 13 pages, 6 figures. Accepted for publication by MNRA

Comparison of weak lensing by NFW and Einasto halos and systematic errors

Recent N-body simulations have shown that Einasto radial profiles provide the most accurate description of dark matter halos. Predictions based on the traditional NFW functional form may fail to describe the structural properties of cosmic objects at the percent level required by precision cosmology. We computed the systematic errors expected for weak lensing analyses of clusters of galaxies if one wrongly models the lens density profile. Even though the NFW fits of observed tangential shear profiles can be excellent, viral masses and concentrations of very massive halos (>~ 10^{15}M_Sun/h) can be over- and underestimated by ~10 per cent, respectively. Misfitting effects also steepen the observed mass-concentration relation, as observed in multi-wavelength observations of galaxy groups and clusters. Based on shear analyses, Einasto and NFW halos can be set apart either with deep observations of exceptionally massive structures (>~ 2\times10^{15}M_Sun/h) or by stacking the shear profiles of thousands of group-sized lenses (>~ 10^{14}M_Sun/h).Comment: 12 pages, 4 figures, in press on JCAP; v02: cosmic noise include

Magnification bias as a novel probe for primordial magnetic fields

In this paper we investigate magnetic fields generated in the early Universe. These fields are important candidates at explaining the origin of astrophysical magnetism observed in galaxies and galaxy clusters, whose genesis is still by and large unclear. Compared to the standard inflationary power spectrum, intermediate to small scales would experience further substantial matter clustering, were a cosmological magnetic field present prior to recombination. As a consequence, the bias and redshift distribution of galaxies would also be modified. Hitherto, primordial magnetic fields (PMFs) have been tested and constrained with a number of cosmological observables, e.g. the cosmic microwave background radiation, galaxy clustering and, more recently, weak gravitational lensing. Here, we explore the constraining potential of the density fluctuation bias induced by gravitational lensing magnification onto the galaxy-galaxy angular power spectrum. Such an effect is known as magnification bias. Compared to the usual galaxy clustering approach, magnification bias helps in lifting the pathological degeneracy present amongst power spectrum normalisation and galaxy bias. This is because magnification bias cross-correlates galaxy number density fluctuations of nearby objects with weak lensing distortions of high-redshift sources. Thus, it takes advantage of the gravitational deflection of light, which is insensitive to galaxy bias but powerful in constraining the density fluctuation amplitude. To scrutinise the potentiality of this method, we adopt a deep and wide-field spectroscopic galaxy survey. We show that magnification bias does contain important information on primordial magnetism, which will be useful in combination with galaxy clustering and shear. We find we shall be able to rule out at 95.4% CL amplitudes of PMFs larger than 0.0005 nG for values of the PMF power spectral index ~0.Comment: 21 pages, 9 figures; published on JCA

On Strong Lensing by Galaxy Clusters

Wir stellen eine neue, semi-analytische Methode vor, um die Effizienz des starken Linseneffekts in Galaxienhaufen zu berechnen. Sie reproduziert die Ergebnisse vollständig numerischer Simulationen, ist aber wesentlich schneller. Wir wenden sie auf eine Galaxienhaufenpopulation an und zeigen, dass Verschmelzungsprozesse die Wahrscheinlichkeit für starke Linseneffekte erheblich erhöhen. Eine Analyse des starken Linseneffekts in kosmologischen Modellen mit verschiedenen Arten dynamischer dunkler Energie zeigt, dass die Anzahl stark verzerrter Bilder beträchtlich zunimmt, wenn frühe dunkle Energie zugelassen wird. Wir untersuchen die starken Gravitationslinseneigenschaften und die Röntgenemission von Galaxienhaufen, um Auswahleffekte zu quantifizieren. Wir berechnen optische Tiefen von Galaxienhaufen als Funktion der Beobachtungszeit und untersuchen, wie sich die Konzentrationsverteilung der Dichteprofile darauf auswirkt. Wir stellen fest, dass die Profilkonzentration einen Auswahleffekt auf die Linseneffizienz und die Röntgenleuchtkraft erzeugt. Schließlich zeigen wir, dass das Arc-Statistik-Problem in einem Universum mit realistisch normierten Schwankungen der Materiedichte auch dann fortbesteht, wenn die Rotverschiebungsverteilung der Quellen und Wechselwirkungen zwischen Galaxienhaufen angemessen berücksichtigt werden. Eine abschließende Untersuchung des starken Linseneffekts in der TeVeS-Theorie bestätigt, dass zusätzliche unsichtbare Masse notwendig ist, um die beobachteten Linseneffekte im verschmelzenden Galaxienhaufen 1E0657-558 zu sehen

Neglecting Primordial non-Gaussianity Threatens Future Cosmological Experiment Accuracy

Future galaxy redshift surveys aim at probing the clustering of the cosmic large-scale structure with unprecedented accuracy, thus complementing cosmic microwave background experiments in the quest to deliver the most precise and accurate picture ever of our Universe. Analyses of such measurements are usually performed within the context of the so-called vanilla LCDM model - the six-parameter phenomenological model which, for instance, emerges from best fits against the recent data obtained by the Planck satellite. Here, we show that such an approach is prone to subtle systematics when the Gaussianity of primordial fluctuations is concerned. In particular, we demonstrate that, if we neglect even a tiny amount of primordial non-Gaussianity - fully consistent with current limits - we shall introduce spurious biases in the reconstruction of cosmological parameters. This is a serious issue that must be properly accounted for in view of accurate (as well as precise) cosmology.Comment: 8 pages, 4 figures, 2 table

The clustering of galaxies and galaxy clusters: constraints on primordial non-Gaussianity from future wide-field surveys

We investigate the constraints on primordial non-Gaussianity with varied bispectrum shapes that can be derived from the power spectrum of galaxies and clusters of galaxies detected in future wide field optical/near-infrared surveys. Having in mind the proposed ESA space mission \emph{Euclid} as a specific example, we combine the spatial distribution of spectroscopically selected galaxies with that of weak lensing selected clusters. We use the physically motivated halo model in order to represent the correlation function of arbitrary tracers of the Large Scale Structure in the Universe. As naively expected, we find that galaxies are much more effective in jointly constrain the level of primordial non-Gaussianity $f_\mathrm{NL}$ and the amplitude of the matter power spectrum $\sigma_8$ than clusters of galaxies, due to the much lower abundance of the latter that is not adequately compensated by the larger effect on the power spectrum. Nevertheless, combination of the galaxy power spectrum with the cluster-galaxy cross spectrum can decrease the error on the determination of $f_\mathrm{NL}$ by up to a factor of $\sim 2$. This decrement is particularly evident for the less studied non-Gaussian bispectrum shapes, the so-called enfolded and the orthogonal ones. Setting constraints on these models can shed new light on various aspects of the physics of the early Universe, and it is hence of extreme importance. By combining the power spectra of clusters and galaxies with the cluster-galaxy cross spectrum we find constraints on primordial non-Gaussianity of the order $\Delta f_\mathrm{NL} \sim$ a few, competitive and possibly superior to future CMB experiments.Comment: 16 pages, 10 figures, 4 tables. Accepted for publication on MNRA

Substructure lensing in galaxy clusters as a constraint on low-mass sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell 2390

Certain covariant theories of the modified Newtonian dynamics paradigm seem to require an additional hot dark matter (HDM) component - in the form of either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs) with a mass around 11eV - to be relieved of problems ranging from cosmological scales down to intermediate ones relevant for galaxy clusters. Here we suggest using gravitational lensing by galaxy clusters to test such a marriage of neutrino HDM and modified gravity, adopting the framework of tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter (CDM), such HDM is subject to strong phase-space constraints, which allows one to check cluster lens models inferred within the modified framework for consistency. Since the considered HDM particles cannot collapse into arbitrarily dense clumps and only form structures well above the galactic scale, systems which indicate the need for dark substructure are of particular interest. As a first example, we study the cluster lens Abell 2390 and its impressive straight arc with the help of numerical simulations. Based on our results, we outline a general and systematic approach to model cluster lenses in TeVeS which significantly reduces the calculation complexity. We further consider a simple bimodal lens configuration, capable of producing the straight arc, to demonstrate our approach. We find that such a model is marginally consistent with the hypothesis of 11eV SNs. Future work including more detailed and realistic lens models may further constrain the necessary SN distribution and help to conclusively assess this point. Cluster lenses could therefore provide an interesting discriminator between CDM and such modified gravity scenarios supplemented by SNs or other choices of HDM.Comment: 22 pages, 14 figures, 2 tables; minor changes to match accepted versio

IDCS J1426.5+3508: Cosmological implications of a massive, strong lensing cluster at Z = 1.75

The galaxy cluster IDCS J1426.5+3508 at z = 1.75 is the most massive galaxy cluster yet discovered at z > 1.4 and the first cluster at this epoch for which the Sunyaev-Zel'Dovich effect has been observed. In this paper we report on the discovery with HST imaging of a giant arc associated with this cluster. The curvature of the arc suggests that the lensing mass is nearly coincident with the brightest cluster galaxy, and the color is consistent with the arc being a star-forming galaxy. We compare the constraint on M200 based upon strong lensing with Sunyaev-Zel'Dovich results, finding that the two are consistent if the redshift of the arc is z > 3. Finally, we explore the cosmological implications of this system, considering the likelihood of the existence of a strongly lensing galaxy cluster at this epoch in an LCDM universe. While the existence of the cluster itself can potentially be accomodated if one considers the entire volume covered at this redshift by all current high-redshift cluster surveys, the existence of this strongly lensed galaxy greatly exacerbates the long-standing giant arc problem. For standard LCDM structure formation and observed background field galaxy counts this lens system should not exist. Specifically, there should be no giant arcs in the entire sky as bright in F814W as the observed arc for clusters at z \geq 1.75, and only \sim 0.3 as bright in F160W as the observed arc. If we relax the redshift constraint to consider all clusters at z \geq 1.5, the expected number of giant arcs rises to \sim15 in F160W, but the number of giant arcs of this brightness in F814W remains zero. These arc statistic results are independent of the mass of IDCS J1426.5+3508. We consider possible explanations for this discrepancy.Comment: 7 pages, 4 figures, Accepted to The Astrophysical Journa