arXiv subjects

Diego G. Lambas

Publications and source records attributed to Diego G. Lambas.

At least 19 recordsLinked to original sources

arXiv2025

Quasar Pairs as Large--Scale Structure tracers

Quasars are effective tracers of the large-scale distribution of galaxies at high redshift thanks to their high luminosity and dedicated surveys. Previous studies have shown that quasars exhibit a bias similar to that of rich groups, indicating that quasar pairs may be linked to higher density environments, serving as protocluster proxies. In this work, we aim to characterize close quasar pairs within the same halo by identifying them in redshift space. We analyze pair-quasar cross correlations and CMB-derived lensing convergence profiles centered in these systems. We have identified 2777 pairs of quasars in the redshift range from 1.2 to 2.8. Quasar pairs exhibit a distribution of relative luminosities that differs from that of random pairs with the same redshift distribution, indicating that quasars in these systems are distinct from isolated ones. The cross-correlation between pairs and quasars shows a larger amplitude than the auto-correlation function of quasars, suggesting these systems are more strongly biased toward the large-scale mass distribution and reside in more massive halos. This is further supported by higher convergence CMB lensing profiles of pairs compared to isolated quasars with a similar redshift distribution. Our results indicate that quasar pairs are suitable precursors to present-day clusters of galaxies, unlike isolated quasars, which are associated with less dense environments.

astro-ph.CO↗

arXiv2021

AGNs in Small Galaxy Systems: comparing the main properties of active objects in pairs, triplets and groups

We perform a comparative study of AGNs in pairs, triplets and groups. To this end we use the Duplancic et al. catalogue of small galaxy systems and consider BPT and WHAN diagnostic diagrams to select optical AGNs. Also we identify mid-IR AGNs by using WISE data. We performed a comparison between the different AGN classification methodologies and study the AGN fraction in pairs, triplets, and groups with four to six members. We also analyse the main properties of Optical and mid-IR AGN hosts and the influence of environment on the active nuclei phenomena in these small galaxy systems. Our results show that, regardless the specifically adopted classification scheme, the fraction of AGN in pairs and triplets is always higher than the corresponding fraction in groups. Moreover, the fraction of powerful AGNs in pair and triplets is about twice the fraction of regular AGNs. We also find a remarkable difference between Optical and mid-IR AGNs in groups, where host galaxies of WISE AGNs are less massive and concentrated, with young stellar populations and blue colours. Also all WISE AGNs in groups have a very close companions and reside in an intermediate global density environment. Galaxy triplets show a larger AGN fraction for galaxies with a close nearest neighbours, while pairs present a nearly constant AGN fraction regardless the distance to the nearest companion. Our studies highlight the important role of interactions, besides the global environment dependence, in the activation of the AGN phenomenon in small galaxy systems.

astro-ph.GA↗

arXiv2021

Modelling H$_2$ and its effects on star formation using a joint implementation of GADGET-3 and KROME

We present P-GADGET3-K, an updated version of GADGET3, that incorporates the chemistry package KROME. P-GADGET3-K follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H$_2$ and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H$_2$ dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of SFR and H$_2$ are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H$_2$ as a function of gas density and temperature. A SF algorithm that takes into account the H$_2$ fraction together with a treatment for the local stellar radiation field improves the agreement with observed H$_2$ abundances over a wide range of gas densities and with the molecular Kennicutt-Schmidt law, implying a more realistic modelling of the star formation process.

astro-ph.GA↗

arXiv2019

TOROS Optical follow-up of the Advanced LIGO-VIRGO O2 second observational campaign

We present the results of the optical follow-up, conducted by the TOROS collaboration, of gravitational wave events detected during the Advanced LIGO-Virgo second observing run (Nov 2016 -- Aug 2017). Given the limited field of view ($\sim100\arcmin$) of our observational instrumentation we targeted galaxies within the area of high localization probability that were observable from our sites. We analyzed the observations using difference imaging, followed by a Random Forest algorithm to discriminate between real and bogus transients. For all three events that we respond to, except GW170817, we did not find any bona fide optical transient that was plausibly linked with the observed gravitational wave event. Our observations were conducted using telescopes at Estación Astrof\'ısica de Bosque Alegre, Cerro Tololo Inter-American Observatory, and the Dr. Cristina V. Torres Memorial Astronomical Observatory. Our results are consistent with the LIGO-Virgo detections of a binary black hole merger (GW170104) for which no electromagnetic counterparts were expected, as well as a binary neutron star merger (GW170817) for which an optical transient was found as expected.

astro-ph.HE↗

arXiv2018

The impact of bars and interactions on optically selected AGNs in spiral galaxies

Aims. With the aim of performing a suitable comparison of the internal process of galactic bars with respect to the external effect of interactions on driving gas toward the inner most region of the galaxies, we explored the efficiency of both mechanisms on central nuclear activity in active galactic nuclei (AGN) in spiral galaxies. Methods. We selected samples of barred AGN and active objects residing in pair systems, derived from the Sloan Digital Sky Survey (SDSS). In order to carry out a reliable comparison of both samples (AGNs in barred hosts in isolation and in galaxy pairs), we selected spiral AGN galaxies with similar distributions of redshift, magnitude, stellar mass, color and stellar age population from both catalogs. With the goal of providing an appropriate quantification of the influence of bars and interactions on nuclear activity, we also constructed a suitable control sample of unbarred spiral AGNs with similar host properties than the other two samples. Results. We found that barred AGNs show an excess of nuclear activity (as derived from the $Lum[OIII]$) and accretion rate ($\cal R$) with respect to AGN in pairs. In addition, both samples show an excess of high values of $Lum[OIII]$ and $\cal R$ with respect to unbarred AGNs in the control sample. We also found that the fractions of AGNs with powerful nuclear activity and high accretion rates increase toward more massive hosts with bluer colors and younger stellar populations. Moreover, AGNs with bars exhibit a higher fraction of galaxies with powerful $Lum[OIII]$ and efficient $\cal R$ with respect to AGNs inhabiting pair systems. Regarding to AGN belonging to pair systems, we found that the central nuclear activity is remarkably dependent on the galaxy pair companion features.

astro-ph.GA↗

arXiv2018

The orientation of galaxy pairs with filamentary structures: dependence on morphology

Aims. With the aim of performing an analysis of the orientations of galaxy pair systems with respect to the underlying large-scale structure, we study the alignment between the axis connecting the pair galaxies and the host cosmic filament where the pair resides. In addition, we analyze the dependence of the amplitude of the alignment on the morphology of pair members as well as filament properties. Methods. We build a galaxy pair catalog requiring $r_p < 100\kpc$ and $ΔV < 500 \kms $ within redshift $z<0.1$ from the Sloan Digital Sky Survey (SDSS). We divided the galaxy pair catalog taking into account the morphological classification by defining three pair categories composed by elliptical-elliptical (E-E), elliptical-spiral (E-S) and spiral-spiral (S-S) galaxies. We use a previously defined catalog of filaments obtained from SDSS and we select pairs located closer than $1\mpc$ from the filament spine, which are considered as members of filaments. For these pairs, we calculate the relative angle between the axis connecting each galaxy, and the direction defined by the spine of the parent filament. Results. We find a statistically significant alignment signal between the pair axes and the spine of the host filaments consistent with a relative excess of $ \sim$ 15\% aligned pairs. We obtain that pairs composed by elliptical galaxies exhibit a stronger alignment, showing a higher alignment signal for pairs closer than 200 $\kpc$ to the filament spine. In addition, we find that the aligned pairs are associated with luminous host filaments populated with a high fraction of elliptical galaxies. The findings of this work show that large scale structures play a fundamental role in driving galactic anisotropic accretion as induced by galaxy pairs exhibiting a preferred alignment along the filament direction.

astro-ph.GA↗

arXiv2018

Non-parametric Morphologies of Mergers in the Illustris Simulation

We study non-parametric morphologies of mergers events in a cosmological context, using the Illustris project. We produce mock g-band images comparable to observational surveys from the publicly available Illustris simulation idealized mock images at $z=0$. We then measure non parametric indicators: asymmetry, Gini, $M_{20}$, clumpiness and concentration for a set of galaxies with $M_* >10^{10}$ M$_\odot$. We correlate these automatic statistics with the recent merger history of galaxies and with the presence of close companions. Our main contribution is to assess in a cosmological framework, the empirically derived non-parametric demarcation line and average time-scales used to determine the merger rate observationally. We found that 98 per cent of galaxies above the demarcation line have a close companion or have experienced a recent merger event. On average, merger signatures obtained from the $G-M_{20}$ criteria anticorrelate clearly with the elapsing time to the last merger event. We also find that the asymmetry correlates with galaxy pair separation and relative velocity, exhibiting the larger enhancements for those systems with pair separations $d < 50$ h$^{-1}$ kpc and relative velocities $V < 350$ km s$^{-1}$. We find that the $G-M_{20}$ is most sensitive to recent mergers ($\sim0.14$ Gyr) and to ongoing mergers with stellar mass ratios greater than 0.1. For this indicator, we compute a merger average observability time-scale of $\sim0.2$ Gyr, in agreement with previous results and demonstrate that the morphologically derived merger rate recovers the intrinsic total merger rate of the simulation and the merger rate as a function of stellar mass.

astro-ph.GA↗

arXiv2017

The evolution of the metallicity gradient and the star formation efficiency in disc galaxies

We study the oxygen abundance profiles of the gas-phase components in hydrodynamical simulations of pre-prepared disc galaxies including major mergers, close encounters and isolated configurations. We analyse the evolution of the slope of oxygen abundance profiles and the specific star formation rate (sSFR) along their evolution. We find that galaxy-galaxy interactions could generate either positive and negative gas-phase oxygen profiles depending on the state of evolution. Along the interaction, galaxies are found to have metallicity gradients and sSFR consistent with observations, on average. Strong gas inflows produced during galaxy-galaxy interactions or as a result of strong local instabilities in gas-rich discs are able to produce both a quick dilution of the central gas-phase metallicity and a sudden increase of the sSFR. Our simulations show that, during these events, a correlation between the metallicity gradients and the sSFR can be set up if strong gas inflows are triggered in the central regions in short timescales. Simulated galaxies without experiencing strong disturbances evolve smoothly without modifying the metallicity gradients. Gas-rich systems show large dispersion along the correlation. The dispersion in the observed relation could be interpreted as produced by the combination of galaxies with different gas-richness and/or experiencing different types of interactions. Hence, our findings suggest that the observed relation might be the smoking gun of galaxies forming in a hierarchical clustering scenario.

astro-ph.GA↗

arXiv2016

A Wide-Field Survey for Transiting Hot Jupiters and Eclipsing Pre-Main-Sequence Binaries in Young Stellar Associations

The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (< 20 cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consist of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (< 50 Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well-characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of 3 nearby (< 150 pc) and young (< 50 Myr) moving groups with a small aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study.

astro-ph.SR↗

arXiv2015

The sparkling Universe: the coherent motions of cosmic voids

We compute the bulk motions of cosmic voids, using a $Λ$CDM numerical simulation considering the mean velocities of the dark matter inside the void itself and that of the haloes in the surrounding shell. We find coincident values of these two measures in the range $\sim$ 300-400 km/s, not far from the expected mean peculiar velocities of groups and galaxy clusters. When analysing the distribution of the pairwise relative velocities of voids, we find a remarkable bimodal behaviour consistent with an excess of both systematically approaching and receding voids. We determine that the origin of this bimodality resides in the void large scale environment, since once voids are classified into void-in-void (R-type) or void-in-cloud (S-type), R-types are found mutually receding away, while S-types approach each other. The magnitude of these systematic relative velocities account for more than 100 km/s, reaching large coherence lengths of up to 200 h$^{-1}$ Mpc . We have used samples of voids from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) and the peculiar velocity field inferred from linear theory, finding fully consistent results with the simulation predictions. Thus, their relative motion suggests a scenario of a sparkling Universe, with approaching and receding voids according to their local environment.

astro-ph.CO↗

arXiv2013

Interacting galaxies: co-rotating and counter-rotating systems with tidal tails

We analyse interacting galaxy pairs with evidence of tidal features in the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). The pairs were selected within $z<0.1$ by requiring a projected separation $r_p < 50 \kpc$ and relative radial velocity $ΔV < 500 \kms$. We complete spectroscopic pairs using galaxies with photometric redshifts considering $ΔV_{phot} < 6800 \kms$, taking into account the mean photometric redshift uncertainty. We classify by visual inspection pairs of spirals into co-rotating and counter-rotating systems. For a subsample of non-AGN galaxies, counter-rotating pairs have larger star formation rates, and a higher fraction of young, star-forming galaxies. These effects are enhanced by restricting to $r_p < 12 \kpc$. The distributions of $C$, $D_n(4000)$ and $(M_u-M_r)$ for AGN galaxies show that counter-rotating hosts have bluer colours and younger stellar population than the co-rotating galaxies although the relative fractions of Seyfert, Liner, Composite and Ambiguous AGN are similar. Also, counter-rotating hosts have more powerful AGN as revealed by enhanced $Lum[OIII]$ values. The number of co-rotating systems is approximately twice the number of counter-rotating pairs which could be owed to a more rapid evolution of counter-rotating systems, besides possible different initial conditions of these interacting pairs.

astro-ph.GA↗

arXiv2013

On the relation between Seyfert 2 accretion rate and environment at z < 0.1

We analyse different properties of the small scale environment of Seyfert 2 for two samples selected according to the accretion rate parameter, R, from the DR7-SDSS survey. We compare the results with two control samples of non-active galaxies that cover the same redshift range, luminosity, colours, morphology, age and stellar mass content. Our study shows that both high and low accretion rate subsamples reside in bluer and lower density environments than the control samples. However, we find that this difference is at least two times stronger for the low accretion rate Seyferts. In the vicinity of Seyfert 2, red galaxies have systematically lower values of stellar-mass as compared with corresponding control samples. The lower values of stellar mass for red neighbours is more significant at higher density environments and it is more evident for low accretion rate Seyfert. We also find that this effect is independent of the host's stellar mass. Our results are consistent with a scenario where AGN occurrence is higher in lower/medium density environments with a higher merger rate and a lack of a dense intergalactic medium (that can strip gas from these systems) that provide suitable conditions for the central black hole feeding. We find this particularly evident for the low accretion rate Seyferts that could compensate through the intergalactic medium the lack of gas of their hosts.

astro-ph.CO↗

arXiv2013

Galaxy triplets in Sloan Digital Sky Survey Data Release 7: II. A connection with compact groups?

We analyse a sample of 71 triplets of luminous galaxies derived from the work of O'Mill et al. (2012). We compare the properties of triplets and their members with those of control samples of compact groups, the ten brightest members of rich clusters, and galaxies in pairs. The triplets are restricted to have members with spectroscopic redshifts in the range 0.01<z<0.14 and Mr<-20.5. We analyse the stellar mass (SM) content, the star formation rates, the Dn(4000) parameter and colour index and also analyse different global properties of these systems as total star formation activity and global colours. We calculate the probability that the properties of galaxies in triplets are strongly correlated. We define the triplet compactness as a measure of the percentage of the system total area that is filled by the light of member galaxies. Our analysis suggest that triplet galaxy members behave similarly to compact group members and galaxies in rich clusters. We also find that systems comprising 3 blue, star-forming, young stellar population galaxies (blue triplets) are most probably real systems and not a chance configuration of interloping galaxies. The same holds for triplets composed by 3 red, non star-forming galaxies, showing the correlation of galaxy properties in these systems. From the analysis of the triplet as a whole, we conclude that, at a given total SM content, triplets show a total star formation activity and global colours similar to compact groups. However, blue triplets show a high total star formation activity with a lower SM content. From an analysis of the compactness parameter of the systems we find that light is even more concentrated in triplets than in compact groups. We propose that triplets composed by 3 luminous galaxies, should not be considered as an analogous of galaxy pairs with an extra member, but rather they are a natural extension of compact groups.

astro-ph.CO↗

arXiv2012

The influence of superstructures on bright galaxy environments: clustering properties

We analyse the dependence of clustering properties of galaxies as a function of their large-scale environment. In order to characterize the environment on large scales, we use the catalogue of future virialized superstructures (FVS) by Luparello et al. and separate samples of luminous galaxies according to whether or not they belong to FVS. In order to avoid biases in the selection of galaxies, we have constructed different subsamples so that the distributions of luminosities and masses are comparable outside and within FVS. As expected, at large scales, there is a strong difference between the clustering of galaxies inside and outside FVS. However, this behaviour changes at scales r < 1 Mpc/h, where the correlations have similar amplitudes. The amplitude of the two-halo term of the correlation function for objects inside FVS does not depend on their mass, but rather on that of the FVS. This is confirmed by comparing this amplitude with that expected from extended Press-Schechter fits. In order to compare these observational results with current models for structure formation, we have performed a similar analysis using a semi-analytic implementation in a LCDM cosmological model. We find that the cross-correlation functions from the mock catalogue depend on the large-scale structures in a similar way to the observations. From our analysis, we conclude that the clustering of galaxies within the typical virialized regions of groups, mainly depends on the halo mass, irrespective of the large-scale environment.

astro-ph.CO↗

arXiv2011

Galaxy interactions I: Major and minor mergers

We study galaxy pair samples selected from the Sloan Digital Sky Survey (SDSS-DR7) and we perform an analysis of minor and major mergers with the aim of investigating the dependence of galaxy properties on interactions. We build a galaxy pair catalog requiring rp < 25 kpc h-1 and Delta V < 350 km s-1 within redshift z<0.1. By visual inspection of SDSS images we removed false identifications and we classify the interactions into three categories: pairs undergoing merging, M; pairs with evident tidal features, T; and non disturbed, N. We also divide the pair sample into minor and major interactions according to the luminosity ratio of the galaxy members. We study star formation activity through colors and star formation rates. We find that 10% of the pairs are classified as M. These systems show an excess of young stellar populations as inferred from the Dn(4000) spectral index, colors, and star formation rates of the member galaxies, an effect which we argue, is directly related to the ongoing merging process. We find 30% of the pairs exhibiting tidal features (T pairs) with member galaxies showing evidence of old stellar populations. Regardless of the color distribution, we find a prominent blue peak in the strongest mergers, while pairs with tidal signs under a minor merger show a strong red peak. Therefore, our results show that galaxy interactions are important in driving the evolution of galaxy bimodality. By adding stellar masses and star formation rates of the two members of the pairs, we explore the global efficiency of star formation of the pairs as a whole. We find that, at a given total stellar mass, major mergers are significantly more efficient (a factor 2) in forming new stars, with respect to both minor mergers or a control sample of non-interacting galaxies.

astro-ph.CO↗

arXiv2011

Galaxy interactions II: High density environments

With the aim to assess the role of dense environments in galaxy interactions, properties we present an analysis of close galaxy pairs in groups and clusters, obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). We identified pairs that reside in groups by cross-correlating the total galaxy pair catalogue with the SDSS-DR7 group catalogue from Zapata et al. (2009). We classify pair galaxies according to the intensity of interaction. We analysed the effect of high density environments on different classes of galaxy-galaxy interactions and we have also studied the impact of the group global environment on pair galaxies. We find that galaxy pairs are more concentrated towards the group centres with respect to the other group galaxy members, and disturbed pairs show a preference to contain the brightest galaxy in the groups. The color-magnitude relation exhibits significant differences between pair galaxies and the control sample, consisting in color tails with a clear excess of extremely blue and red galaxies for merging systems. In addition, pair galaxies show a significant excess of young stellar populations with respect to galaxies in the control sample; this finding suggests that, in dense environments, strong interactions produce an important effect in modifying galaxy properties. We find that the fraction of star forming galaxies decreases toward the group centre; however, galaxy pairs show a more efficient star formation activity than galaxies without a close companion. We have also found that pair galaxies prefer groups with low density global environments with respect to galaxies of the corresponding control sample. Blue, young stellar population galaxies prefer groups within low density global environments.

astro-ph.CO↗

arXiv2011

Future virialized structures: An analysis of superstructures in SDSS-DR7

We construct catalogues of present superstructures that, according to a LCDM scenario, will evolve into isolated, virialized structures in the future. We use a smoothed luminosity density map derived from galaxies in SDSS-DR7 data and separate high luminosity density peaks. The luminosity density map is obtained from a volume-limited sample of galaxies in the spectroscopic galaxy catalogue, within the SDSS-DR7 footprint area and in the redshift range 0.04 < z < 0.12. Other two samples are constructed for calibration and testing purposes, up to z = 0.10 and z = 0.15. The luminosity of each galaxy is spread using an Epanechnikov kernel of 8Mpc/h radius, and the map is constructed on a 1 Mpc/h cubic cells grid. Future virialized structures (FVS) are identified as regions with overdensity above a given threshold, calibrated using a LCDM numerical simulation, and the criteria presented by Dünner et al. (2006). We assume a constant mass-to-luminosity ratio and impose the further condition of a minimum luminosity of 10^{12}Lsol. According to our calibrations with a numerical simulation, these criteria lead to a negligible contamination by less overdense (non FVS) superstructures.We present a catalogue of superstructures in the SDSS-DR7 area within redshift 0.04 < z < 0.12 and test the reliability of our method by studying different subsamples as well as a mock catalogue.We compute the luminosity and volume distributions of the superstructures finding that about 10% of the luminosity (mass) will end up in future virialized structures. The fraction of groups and X-ray clusters in these superstructures is higher for groups/clusters of higher mass, suggesting that future cluster mergers will involve the most massive systems. We also analyse known structures in the present Universe and compare with our catalogue of FVS.

astro-ph.CO↗

arXiv2010

Large scale anisotropies on halo infall

We perform a statistical analysis of the peculiar velocity field around dark matter haloes in numerical simulations. We examine different properties of the infall of material onto haloes and its relation to central halo shapes and the shape of the large scale surrounding regions (LSSR). We find that the amplitude of the infall velocity field along the halo shape minor axis is larger than that along the major axis. This is consistent for general triaxial haloes, and for both prolate and oblate systems. We also report a strong anisotropy of the velocity field along the principal axes of the LSSR. The infall velocity field around dark matter haloes reaches a maximum value along the direction of the minor axis of the LSSR, whereas along the direction of its major axis, it exhibits the smallest velocities. We also analyse the dependence of the matter velocity field on the local environment. The amplitude of the infall velocity at high local density regions is larger than at low local density regions. The velocity field tends to be more laminar along the direction towards the minor axis of the LSSR, where the mean ratio between flow velocity and velocity dispersion is of order unity and nearly constant up to scales of 15 Mpc/h. We also detect anisotropies in the outflowing component of the velocity field, showing a maximum amplitude along the surrounding LSSR major axis.

astro-ph.CO↗