arXiv subjects

D. Garcia Lambas

Publications and source records attributed to D. Garcia Lambas.

7 recordsLinked to original sources

arXiv2026

On the astrophysical origin of cosmic rays: Constraining the Ultra-High-Energy Cosmic Ray Horizon through Nearby Galaxy Distributions

The origin of ultra-high-energy cosmic rays (UHECR) remains a central open problem in astroparticle physics. The observed large-scale anisotropy of UHECR arrival directions above several EeV, together with the spectral suppression at the highest energies, suggests extragalactic sources confined to a limited volume of the nearby Universe, though the effective spatial scale of this contribution remains poorly constrained. We aim to constrain the effective propagation horizon of UHECR with energies E >= 8 EeV by studying how well the observed large-scale anisotropy is reproduced by the distribution of nearby galaxies at different distances, accounting for Galactic magnetic-field deflections. We construct volume-limited galaxy samples from the GLADE+ catalogue extending to 10000 km/s (~150 Mpc) and use both dipole comparisons and angular cross-correlation analyses with the Pierre Auger Observatory UHECR flux map (E >= 8 EeV) to characterize the distance dependence of the anisotropy signal, further weighting the galaxy-UHECR correlations using deflection maps derived from a Galactic magnetic field model. We find that the angular separation between the galaxy and UHECR dipoles is minimized for galaxies within cz < 4000 km/s (< 60 Mpc), where the galaxy dipole amplitude is also maximal. The galaxy-UHECR cross-correlation signal is dominated by this nearby population and weakens rapidly at larger distances. Accounting for Galactic magnetic field deflections enhances the correlation amplitude by more than a factor of two, indicating that magnetic effects significantly shape the observed anisotropy. Our results indicate that the observed anisotropy of UHECR of 8 EeV and above is primarily driven by sources within ~50-60 Mpc, consistent with expectations from energy losses and magnetic deflections, retaining a measurable imprint of the nearby extragalactic matter distribution.

astro-ph.HE↗

arXiv2022

Spin alignment around TNG300-1 voids

Using a new statistical approach we study the alignment signal of galactic spins with respect to the center of voids identified in the TNG-300 simulation. We explore this signal in different samples of galaxies, varying their distance from the void center, mass, spin norm, local density, and velocity. We find a strong tendency (>9 sigma) of massive, high-spin, and low radial velocity galaxies to be aligned perpendicularly to the void-centric direction in a wide range of distances corresponding to 0.9 to 1.4 void radii. Furthermore, we find that in these subdense environments, local density is irrelevant in the amplitude of spin alignment, while the largest impact is associated to the galaxy void-centric radial velocity in the sense that those at the lowest expansion rate are more strongly aligned perpendicularly to the center of the void. Our results suggest that further analysis at understanding intrinsic alignments and their relation to large scale structures may probe key for weak lensing studies in upcoming large surveys such as Euclid and LSST.

astro-ph.GA↗

arXiv2022

Satellite galaxies in groups in the CIELO Project I. Gas removal from galaxies and its re-distribution in the intragroup medium

We study the impact of the environment on galaxies as they fall in and orbit in the potential well of a Local Group (LG) analogue, following them with high cadence. The analysis is performed on eight disc satellite galaxies from the CIELO suite of hydrodynamical simulations. All galaxies have stellar masses within the range $[10^{8.1} - 10^{9.56}] M_{\sun} $h$^{-1}$. We measure tidal torques, ram pressure and specific star formation rates (sSFR) as a function of time, and correlate them with the amount of gas lost by satellites along their orbits. Stronger removal episodes occur when the disc plane is oriented perpendicular to the direction of motion. More than one peripassage is required to significantly modify the orientations of the discs with respect to the orbital plane. The gas removed during the interaction with the central galaxies may be also found opposite to the direction of motion, depending on the orbital configuration. Satellites are not totally quenched when the galaxies reach their first peripassage, and continue forming about $10\%$ of the final stellar mass after this event. The fraction of removed gas is found to be the product of the joint action of tidal torque and ram pressure, which can also trigger new star formation activity and subsequent supernova feedback.

astro-ph.GA↗

arXiv2022

A statistical formalism for alignment analysis

The detection of anisotropies with respect to a given direction in a vector field is a common problem in astronomy. Several methods have been proposed that rely on the distribution of the acute angles between the data and a reference direction. Different approaches use Monte Carlo methods to quantify the statistical significance of a signal, although often lacking an analytical framework. Here we present two methods to detect and quantify alignment signals and test their statistical robustness. The first method considers the deviance of the relative fraction of vector components in the plane perpendicular to a reference direction with respect to an isotropic distribution. We also derive the statistical properties and stability of the resulting estimator, and therefore does not rely on Monte Carlo simulations to assess its statistical significance. The second method is based on a fit over the residuals of the empirical cumulative distribution function with respect to that expected for a uniform distribution, using a small set of harmonic orthogonal functions, which does not rely on any binning scheme. We compare these methods with others commonly used in the literature, using Monte Carlo simulations, finding that the proposed statistics allow the detection of alignment signals with greater significance.

astro-ph.IM↗

arXiv2019

Following the crumbs: Statistical effects of Ram Pressure in Galaxies

We analyse the presence of dust around galaxy group members through the reddening of background quasars. By taking into account quasar colour and their dependence on redshift and angular position, we derive mean quasar colours excess in projected regions around member galaxies and infer the associated dust mass. For disc-like galaxies perpendicular to the plane of the sky, and at group-centric distances of the order of the virial radius, thus likely to reside in the infall regions of groups, we find systematic colour excess values $e \sim 0.009 \pm 0.004$ for $g-r$ colour. Under the hypothesis of Milky Way dust properties we derive dust masses of $5.8 \pm 2.5 \cdot 10^8 M_{\odot}/h$, implying that a large fraction of dust is being stripped from galaxies in their path to groups. We also studied the photometry of member galaxies to derive a colour asymmetry relative to the group centre direction from a given galaxy. We conclude that the regions of galaxies facing the centre are bluer, consistent with the effects of gas compression and star-formation. We also combine these two procedures finding that galaxies with a small colour asymmetry show the largest amounts of dust towards the external regions compared to a control sample. We conclude that dust removal is very efficient in galaxies on infall. The fact that galaxies redder towards groups centres are associated to the strongest reddening of background quasars suggest that gas removal induced by ram pressure stripping plays a key role in galaxy evolution and dust content.

astro-ph.GA↗

arXiv2018

Analysis of interacting and isolated quasars

The main goal of this study was to determine the effects on equivalent widths (EWs) of some spectral lines produced in the quasars by the presence of surrounding galaxies. To carry this out, a sample of 4663 quasars (QSOs) in the redshift range of 0.20 to 0.40 from the Sloan Digital Sky Survey--Data Release 7 was analyzed. Three QSO sub-samples were defined, taking into account the projected separations and radial velocity differences with neighboring galaxies. In this way, we utilized two sub-samples of QSOs with strong and weak galaxy interactions, with projected separations smaller than 70 kpc, and between 70 and 140 kpc, respectively, and with radial velocity differences less than $5000~$\kms. These sub-samples were compared with isolated QSOs defined as having greater projected separations and radial velocity differences to the galaxies. From a statistical study of the EWs of relevant spectral lines in the QSOs, we show an increment of the EWs of about 20\% in the [OIII]4959,5007 lines and 7\% in H$_α$ for QSOs with stronger galaxy interactions relative to the isolated QSOs. These results indicate that some line EWs of QSOs could be marginally influenced by the environment and that they are not affected by the emission of the host galaxy, which was estimated to be around 10\% of the total emission. Furthermore, in order to gain a better understanding of the origin of the H$_α$ emission line, we performed broad and narrow line decomposition in 100 QSOs in the restricted Sint sub-sample and also 100 randomly selected QSOs in the Iso sub-sample. When these QSOs were compared, the narrow component remained constant whereas the broad component was incremented. Our results, which reveal slight differences in EWs of some emission lines, suggest that galaxy interactions with QSOs may affect the QSO activity.

astro-ph.GA↗

arXiv2017

Observations of the first electromagnetic counterpart to a gravitational wave source by the TOROS collaboration

We present the results of prompt optical follow-up of the electromagnetic counterpart of the gravitational-wave event GW170817 by the Transient Optical Robotic Observatory of the South Collaboration (TOROS). We detected highly significant dimming in the light curves of the counterpart (Delta g=0.17+-0.03 mag, Delta r=0.14+-0.02 mag, Delta i=0.10 +- 0.03 mag) over the course of only 80 minutes of observations obtained ~35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ~59 hr after the event with the EABA 1.5m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a "blue kilonova" relatively free of lanthanides.

astro-ph.HE↗