arXiv subjects

L. E. Campusano

Publications and source records attributed to L. E. Campusano.

15 recordsLinked to original sources

arXiv2023

Correlation of structure growth index with current cosmic acceleration: constraints on dark energy models

We study dynamical dark energy models within Einstein's theory by means of matter perturbations and the growth index $γ$. Within four-dimensional General Relativity, we assume that dark energy does not cluster, and we adopt a linear ansatz for the growth index to investigate its impact on the deceleration parameter, $q$, and on the dark energy equation-of-state parameter, $w$. Following this approach, we identify a relationship between $q_0$ (today's value of $q$) and $γ$, which to the best of our knowledge is new. For $w(z)$, we find that in most of the cases considered it crosses the -1 line (quintom) ending at a present day value $w_0 > -1$. Furthermore, we show that an analytic expression for $w(z)$ may be obtained in the form of order (4,4) (or higher) Pad{é} parameterizations.

gr-qc↗

arXiv2022

Solar Anti-Hale Bipolar Magnetic Regions: A Distinct Population with Systematic Properties

Besides their causal connection with long and short-term magnetic variability, solar bipolar magnetic regions are our chief source of insight into the location, size, and properties of large-scale toroidal magnetic structures in the solar interior. The great majority of these regions (~95%) follow a systematic east-west polarity orientation (Hale's law) that reverses in opposite hemispheres and across even and odd cycles. These regions also present a systematic north-south polarity orientation (Joy's law) that helps build the poloidal field that seeds the new cycle. Exceptions to Hale's law are rare and difficult to study due to their low numbers. Here, we present a statistical analysis of the inclination (tilt) with respect to the equator of Hale versus anti-Hale regions spanning four solar cycles, considering two complementary tilt definitions adopted in previous studies. Our results show that anti-Hale regions belong to a separate population than Hale regions, suggesting a different originating mechanism. However, we find that anti-Hale region tilts present similar systematic tilt properties and similar latitudinal distributions to Hale regions, implying a strong connection between the two. We see this as evidence that they belong to a common toroidal flux system. We speculate that anti-Hale regions originate from poloidal field sheared and strengthened on the spot after the emergence of Hale regions with very strong poloidal contribution. Thus, they are not in contradiction with the idea of largely coherent toroidal flux systems inside the solar interior.

astro-ph.SR↗

arXiv2017

LoCuSS: The infall of X-ray groups onto massive clusters

Galaxy clusters are expected to form hierarchically in a LCDM universe, growing primarily through mergers with lower mass clusters and the continual accretion of group-mass halos. Galaxy clusters assemble late, doubling their masses since z~0.5, and so the outer regions of clusters should be replete with infalling group-mass systems. We present an XMM-Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters at z~0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2x10^13-7x10^14Msun, and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is ~25x higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2x10^14Msun, or 19% of the mass within the primary cluster itself. We estimate that ~10^15Msun clusters increase their masses by 16% between z=0.223 and the present day due to the accretion of groups with M200>10^13.2Msun. This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound in halos. The mass function of the infalling X-ray groups appears significantly top-heavy with respect to that of field X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter halos being biased tracers of the underlying large-scale density distribution.

astro-ph.CO↗

arXiv2017

Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?

Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density profiles for galaxy central regions. While simulations suggest a cuspy and universal density profile (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by \protect{\citep{13}}. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy profile is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequence of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.

astro-ph.GA↗

arXiv2016

Strong Lensing In The Inner Halo Of Galaxy Clusters

We present an axially symmetric formula to calculate the probability of finding gravitational arcs in galaxy clusters, being induced by their massive dark matter haloes, as a function of clusters redshifts and virial masses. The formula includes the ellipticity of the clusters dark matter potential by using a pseudo-elliptical approximation. The probabilities are calculated and compared for two dark-matter halo profiles, the Navarro, Frenk and White (NFW) and the Non-Singular-Isothermal-Sphere (NSIS). We demonstrate the power of our formulation through a Kolmogorov-Smirnov (KS) test on the strong lensing statistics of an X-ray bright sample of low redshift Abell clusters. This KS test allows to establish limits on the values of the concentration parameter for the NFW profile ($c_Δ$) and the core radius for the NSIS profile (\rc), which are related to the lowest cluster redshift ($z_{\rm cut}$) where strong arcs can be observed. For NFW dark matter profiles, we infer cluster haloes with concentrations that are consistent to those predicted by $Λ$CDM simulations. As for NSIS dark matter profiles, we find only upper limits for the clusters core radii and thus do not rule out a purely SIS model. For alternative mass profiles, our formulation provides constraints through $z_{\rm cut}$ on the parameters that control the concentration of mass in the inner region of the clusters haloes. We find that $z_{\rm cut}$ is expected to lie in the 0.0--0.2 redshift, highlighting the need to include very low-$z$ clusters in samples to study the clusters mass profiles.

astro-ph.CO↗

arXiv2015

Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate

The Atacama B-Mode Search (ABS) instrument is a cryogenic ($\sim$10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the Cosmic Microwave Background (CMB) at large angular scales ($40<\ell<500$) to limit the B-mode polarization spectrum around the primordial B-mode peak from inflationary gravity waves at $\ell \sim100$. The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers. They are coupled to orthogonal polarizations from a planar ortho-mode transducer (OMT) and observe at 145 GHz. ABS employs an ambient-temperature, rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move the signal band away from atmospheric $1/f$ noise, allowing for the recovery of large angular scales. We discuss how the signal at the second harmonic of the HWP rotation frequency can be used for data selection and for monitoring the detector responsivities.

astro-ph.IM↗

arXiv2009

The Clowes-Campusano Large Quasar Group Survey: I. GALEX selected sample of LBGs at z$\sim$1

The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The SDSS and 2dF galaxy surveys have revealed a number of structures on 40-150 h^-1 Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar populations in large structures at higher redshift, we have investigated two sheet-like structures of galaxies at z=0.8 and 1.3 spanning 150 h^-1 comoving Mpc embedded in large quasar groups extending over at least 200 h^-1 Mpc. We present first results of an analysis of these sheet--like structures using two contiguous 1deg GALEX fields (FUV and NUV) cross-correlated with optical data from the Sloan Digital Sky Survey (SDSS). We derive a sample of 462 Lyman Break Galaxy (LBG) candidates coincident with the sheets. Using the GALEX and SDSS data, we show that the overall average spectral energy distribution of a LBG galaxy at z~1 is flat (in f_lambda) in the rest frame wavelength range from 1500A, to 4000A, implying evolved populations of stars in the LBGs. From the luminosity functions we get indications for overdensities in the two LQGs compared to their foreground regions. Similar conclusions come from the calculation of the 2-point correlation function, showing a 2sigma overdensity for the LBGs in the z~0.8 LQG on scales of 1.6 to 4.8 Mpc, indicating similar correlation scales for our LBG sample as their z~3 counterparts.

astro-ph.CO↗

arXiv2006

The dynamical state of massive galaxy clusters

We study the mass distribution of a sample of 24 X-ray bright Abell clusters through weak gravitational lensing. This method is independent of the dynamical state of the galaxy cluster. Hence, by comparing dynamical and lensing mass estimators, we can access the dynamical state of these clusters. We have found that clusters with ICM temperatures above 8 keV show strong deviations from the relaxation, as well as the presence of prominent sub-structures. For the remaining clusters (the majority of the sample) we have found agreement among the several mass estimators, which indicates that most of the clusters are in or close to a state of dynamical equilibrium.

astro-ph↗

arXiv2004

Detection of 20-30 Mpc-scale Galaxy Structures Embedded in 100 Mpc-scale Structures of Quasars and MgII Absorbers at z~0.8 and z~1.2

We report the finding of two large-scale structures of galaxies in a 40'x35' field embedded in a 25deg^2 area where two 100 Mpc-scale structures of quasars and MgII absorbers at z~0.8 and z~1.2 have been previously detected. Using deep optical (V- and I-band) imaging, we are able to select high-redshift (0.5<z<1.3) early-type galaxies as those redder than the cluster red sequence at z=0.5 and having I<23.5. Through comparison with a 35'x35' control field, we find a 30% excess of these red galaxies, corresponding to 563 galaxies across the field. The colour distribution of the excess galaxies shows a coherent peak at 2.7<V-I<3.1 and the magnitude distribution is well described by a Schechter function, showing unambiguously that the galaxy excess is primarily due to a population of early-type galaxies at z=0.83\pm0.08. In follow-up NIR imaging of the four best cluster candidates, we identify three clusters at z=0.8\pm0.1, each having well defined red sequences of ~20 galaxies at I-K~3.4, forming a structure 20 Mpc across. The fourth candidate, corresponding to a previously identified cluster at z=1.2\pm0.1 is confirmed with 28 K<20.5 galaxies having VIJK colours consistent with passively-evolving galaxies at z~1.2 located within 1' of the cluster centre. The results of this study support the presence of two sheet-like large-scale galaxy structures extending across the 20-30 Mpc scales explored by the optical data, one ``sheet'' at z~0.8 with three associated clusters, and a second ``sheet'' at z~1.2 with one embedded cluster. Our results confirm that, at least inside the probed region, the two known 100 Mpc-scale structures at z~1 of quasars and MgII absorbers also mark out volumes with an enhanced density of galaxies.

astro-ph↗

arXiv2002

Large Scale Structure at z=1.2 Outlined by MgII Absorbers

The largest known structure in the high redshift universe is mapped by at least 18 quasars and spans ~5 deg x 2.5 deg on the sky, with a quasar spatial overdensity of 6-10 times above the mean. This large quasar group provides an extraordinary laboratory ~100 x 200 x 200 h^-3 comoving Mpc^3 in size (q0=0.5, Lambda=0, H0=100h km/s/Mpc) covering 1.20<z<1.39 in redshift. One approach to establish how LQGs relate to mass (galaxy) enhancements is to probe their gas content and distribution via background quasars. We have found the large quasar group to be associated with 11 MgII absorption systems at 1.2<z<1.4; 0.02%--2.05% of simulations with random MgII redshifts match or exceed this number in that redshift interval, depending on the normalization method used. The minimal spanning tree test also supports the existence of a structure of MgII absorbers coincident with the LQG, and additionally indicates a foreground structure populated by MgII absorbers and quasars at z~0.8. Finally, we find a tendency for MgII absorbers in general to correlate with field quasars (i.e. quasars both inside and outside of the LQG) at a projected scale length on the sky of 9/h Mpc and a velocity difference |Delta v|=3000 to 4500 km/s. While the correlation is on a scale consistent with observed galaxy-AGN distributions, the nonzero velocity offset could be due to the "periphery effect", in which quasars tend to populate the outskirts of clusters of galaxies and metal absorption systems, or to peculiar velocity effects.

astro-ph↗

arXiv2001

Environments of Quasars in the Context of Large-Scale Structure

We are looking at quasar environment in the context of large-scale structure (LSS) - a new approach, giving a more informed interpretation of quasar-galaxy correlations. This paper presents our first results for a sample of z ~ 0.3 quasars. We are using Voronoi tessellation applied in colour (B_J - R) slices for the detection of galaxy clusters and the minimal spanning tree (MST) to delineate the large-scale structure. This new cluster-detection method allows us to find reliably galaxy clusters at z < 0.3 from SuperCOSMOS measurements of UK Schmidt plates. By reconstructing the large-scale structure in a relatively narrow redshift band (0.2 < z < 0.3), we show that quasars follow the large-scale structure traced by galaxy clusters. None of the quasars in our radio-quiet sample is located in the central area of a galaxy cluster. Two quasars, found in a very rich environment, are actually located between two very close galaxy clusters, consistent with results on z ~ 1 quasars suggesting that cluster merg ers may be involved in one of the quasar formation mechanisms.

astro-ph↗

arXiv2001

VLT Spectroscopy of Galaxies Lensed by Abell AC114: Implication for the Mass Model and the Study of Low-Luminosity Galaxies at High-Redshift

We present the first results of a spectroscopic survey of faint lensed galaxie s in the core of the galaxy cluster AC114 (z=0.312) obtained from observations w ith the FORS1 spectrograph mounted on the VLT-Antu. The galaxies were chose n in areas close to the high-z critical lines predicted by the gravitational lens model of Natarajan et al (NKSE, 1998) for this cluster, according to both lensing and photometric redshift criteria. All the target galaxies are found to correspond to background galaxies with redshifts values in the [0.7, 3.5] interval. Our spectroscopic observations confirm the predicted lensing redshifts for 3 of the multiple-image galaxies, and together with predictions of the NKSE model led to the discovery of a new 5-image configuration at redshift z=3.347. A revised NKSE model, compatible with the redshift of this new multiple-image system, was generated and employed to calculate the gravitational amplifications of all the observed galaxies. The galaxies corresponding to the multiple-image systems are found to be intrinsically fainter, between 0.5 and 1.5 magnitudes, than the limiting magnitudes of existing blank field studies. When all the observed background galaxies are considered, the resulting intrinsic absolute magnitudes range from M_B~-22 to -19. Therefore, a large gain in sensitivity towards low luminosity high-z objects can actually be obtained, in agreement with theoretical expectations. This method can be used advantageously to probe the high redshift Universe and, in particular, its application to an ensemble of massive cluster cores could constraint the faint end of luminosity function of high redshift galaxies.

astro-ph↗

arXiv2000

The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group at z~1.3

The Clowes-Campusano Large Quasar Group (LQG) is the largest known structure at high redshifts, with at least 18 quasars at z~1.3 forming a structure ~200 Mpc across. We are conducting an ultra-deep optical and deep NIR study to examine the galaxy environment of quasars in this LQG to determine if, and how, LQGs trace large-scale structure at early epochs. We report significant associated clustering in the field of a z=1.226 quasar from this LQG in the form of a factor ~11 overdensity of I-K>3.75 galaxies, and red sequences of 15-18 galaxies at I-K~4.3,V-K~6.9, indicative of a population of massive ellipticals at the quasar redshift. The quasar is located between two groups of these galaxies, with further clustering extending over 2-3 Mpc. Within 30 arcsec of the quasar we find a concentration of blue (V-I<1) galaxies in a band that bisects the two groups of red sequence galaxies. This band is presumed to correspond to a region of enhanced star-formation. We suggest that the merging of the two groups of red sequence galaxies has triggered both the quasar and the band of star-formation. Quasars at z~1.3 are located in a variety of environments, but those with associated clustering are found on the cluster peripheries.

astro-ph↗

arXiv2000

The Galaxy Environment of a Quasar at z=1.226: A Possible Cluster Merger

We have conducted ultra-deep optical and deep near-infrared observations of a field around the z=1.226 radio-quiet quasar 104420.8+055739 from the Clowes-Campusano LQG of 18 quasars at z~1.3 in search of associated galaxy clustering. Galaxies at these redshifts are distinguished by their extremely-red colours, with I-K>3.75, and we find a factor ~11 overdensity of such galaxies in a 2.25'x2.25' field centred on the quasar. In particular, we find 15-18 galaxies with colours consistent with being a population of passively-evolving massive ellipticals at the quasar redshift. They form `fingers' in the V-K/K, I-K/K colour-magnitude plots at V-K~6.9, I-K~4.3 comparable to the red sequences observed in other z~1.2 clusters. We find suggestive evidence for substructure among the red sequence galaxies in the K image, in the form of two compact groups, 40 arcsec to the north, and 60 arcsec to the south-east of the quasar. An examination of the wider optical images indicates that this substructure is significant, and that the clustering extends to form a large-scale structure 2-3 Mpc across. We find evidence for a high (>50%) fraction of blue galaxies in this system, in the form of 15-20 `red-outlier' galaxies with I-K>3.75 and V-I<2.00, which we suggest are dusty, star-forming galaxies at the quasar redshift. Within 30 arcsec of the quasar we find a concentration of blue (V-I<1) galaxies in a band that bisects the two groups of red sequence galaxies. This band of blue galaxies is presumed to correspond to a region of enhanced star-formation. We explain this distribution of galaxies as the early-stages of a cluster merger which has triggered both the star-formation and the quasar.

astro-ph↗

arXiv2000

The Galaxy Environment of Quasars in the z~1.3 Clowes-Campusano Large Quasar Group

We report significant associated clustering in the field of a z=1.226 quasar from the Clowes-Campusano LQG in the form of both a factor ~11 overdensity of I-K>3.75 galaxies and red sequences of 15-18 galaxies at I-K~4.3, V-K~6.9 indicative of a population of massive ellipticals at the quasar redshift. The quasar is located between two groups of these galaxies, with further clustering extending over 2-3 Mpc. A band of V-I<1 galaxies bisects the two groups of red sequence galaxies, and we suggest that the merging of these two groups has triggered both this band of star-formation and the quasar.

astro-ph↗