arXiv subjects

A. Diaz-Sanchez

Publications and source records attributed to A. Diaz-Sanchez.

16 recordsLinked to original sources

arXiv2020

Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5

Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the Universe. Key aspects to these processes are the gas heating and cooling mechanisms. Although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the \textit{Planck} satellite (LPs) at z ~ 1.1 - 3.5. We analyze 162 CO rotational transitions (ranging from Jupper = 1 - 12) and 37 atomic carbon fine-structure lines ([CI]) in order to characterize the physical conditions of the gas in sample of LPs. We simultaneously fit the CO and [CI] lines, and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two component gas density, while the second assumes a turbulence driven log-normal gas density distribution. These LPs are among the most gas-rich, infrared (IR) luminous galaxies ever observed ($μ_{\rm L}$L$_{\rm IR(8-1000μm) } \sim 10^{13-14.6} $\Lsun; $< μ_{\rm L}$M$_{\rm ISM}> = 2.7 \pm 1.2 \times 10^{12}$ \Msun, with $μ_{\rm L} \sim 10-30$ the average lens magnification factor). Our results suggest that the turbulent ISM present in the LPs can be well-characterized by a high turbulent velocity dispersion ($<ΔV_{\rm turb}> \sim 100 $ \kms) and gas kinetic temperature to dust temperature ratios $ \sim 2.5$, sustained on scales larger than a few kpc. We speculate that the average surface density of the molecular gas mass and IR luminosity $Σ_{\rm M_{\rm ISM}}$ $\sim 10^{3 - 4}$ \Msun pc$^{-2}$ and $Σ_{\rm L_{\rm IR}}$ $\sim 10^{11 - 12}$ \Lsun kpc$^{-2}$, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.

astro-ph.GA↗

arXiv2017

A near/mid infrared search for ultra-bright submillimetre galaxies: Searching for Cosmic Eyelash Analogues

We present results from a near/mid IR search for submillimetre galaxies over a region of 6230 sq deg. of the southern sky. We used a cross-correlation of the VISTA Hemispheric Survey (VHS) and the WISE database to identify bright galaxies (K_s <= 18.2) with near/mid IR colours similar to those of the high redshift lensed sub-mm galaxy SMM J2135-0102. We find 7 galaxies which fulfill all five adopted near/mid IR colour (NMIRQC) criteria and resemble the SED of the reference galaxy at these wavelengths. For these galaxies, which are broadly distributed in the sky, we determined photometric redshifts in the range z=1.6-3.2. We searched the VHS for clusters of galaxies, which may be acting as gravitational lenses, and found that 6 out of the 7 galaxies are located within 3.5 arcmin of a cluster/group of galaxies. Using the J-K_s vs J sequences we determine photometric redshifts for these clusters/groups in the range z=0.2-0.9. We propose the newly identified sources are ultra-bright high redshift lensed SMG candidates. Follow-up observations in the sub-mm and mm are key to determine the ultimate nature of these objects.

astro-ph.GA↗

arXiv2010

High contrast optical imaging of companions: the case of the brown dwarf binary HD-130948BC

High contrast imaging at optical wavelengths is limited by the modest correction of conventional near-IR optimized AO systems.We take advantage of new fast and low-readout-noise detectors to explore the potential of fast imaging coupled to post-processing techniques to detect faint companions to stars at small separations. We have focused on I-band direct imaging of the previously detected brown dwarf binary HD130948BC,attempting to spatially resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited images of HD130948 with ~0.1" resolution.In order to improve the detectability of the faint binary in the vicinity of a bright (I=5.19 \pm 0.03) solar-type star,we implemented a post-processing technique based on wavelet transform filtering of the image which allows us to strongly enhance the presence of point-like sources in regions where the primary halo dominates. We detect for the first time the BD binary HD130948BC in the optical band I with a SNR~9 at 2.561"\pm 0.007" (46.5 AU) from HD130948A and confirm in two independent dataset that the object is real,as opposed to time-varying residual speckles.We do not resolve the binary, which can be explained by astrometric results posterior to our observations that predict a separation below the NOT resolution.We reach at this distance a contrast of dI = 11.30 \pm 0.11, and estimate a combined magnitude for this binary to I = 16.49 \pm 0.11 and a I-J colour 3.29 \pm 0.13. At 1", we reach a detectability 10.5 mag fainter than the primary after image post-processing. We obtain on-sky validation of a technique based on speckle imaging and wavelet-transform processing,which improves the high contrast capabilities of speckle imaging.The I-J colour measured for the BD companion is slightly bluer, but still consistent with what typically found for L2 dwarfs(~3.4-3.6).

astro-ph.IM↗

arXiv2010

High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM

In this paper, we present an original observational approach, which combines, for the first time, traditional speckle imaging with image post-processing to obtain in the optical domain diffraction-limited images with high contrast (1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing step is based on wavelet filtering an has analogy with edge enhancement and high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope (NOT) and the lucky imaging instrument FASTCAM show that we are able to detect L-type brown dwarf companions around a solar-type star with a contrast DI~12 at 2" and with no use of any coronographic capability, which greatly simplifies the instrumental and hardware approach. This object has been detected from the ground in J and H bands so far only with AO-assisted 8-10 m class telescopes (Gemini, Keck), although more recently detected with small-class telescopes in the K band. Discussing the advantage and disadvantage of the optical regime for the detection of faint intrinsic fluxes close to bright stars, we develop some perspectives for other fields, including the study of dense cores in globular clusters. To the best of our knowledge this is the first time that high contrast considerations are included in optical speckle imaging approach.

astro-ph.IM↗

arXiv2007

Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association

We present the discovery of a companion near the deuterium burning mass limit located at a very wide distance, at an angular separation of 4.6+/-0.1 arcsec (projected distance of ~ 670 AU) from UScoCTIO108, a brown dwarf of the very young Upper Scorpius association. Optical and near-infrared photometry and spectroscopy confirm the cool nature of both objects, with spectral types of M7 and M9.5, respectively, and that they are bona fide members of the association, showing low gravity and features of youth. Their masses, estimated from the comparison of their bolometric luminosities and theoretical models for the age range of the association, are 60+/-20 and 14^{+2}_{-8} MJup, respectively. The existence of this object around a brown dwarf at this wide orbit suggests that the companion is unlikely to have formed in a disk based on current planet formation models. Because this system is rather weakly bound, they did not probably form through dynamical ejection of stellar embryos.

astro-ph↗

arXiv2007

New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster

(Abridged) The nature of S Ori 70, a faint mid-T type object found towards the direction of the young sigma Orionis cluster, is still under debate. We intend to disentangle whether it is a field brown dwarf or a 3-Myr old planetary-mass member of the cluster. We report on near-infrared JHK_s and mid-infrared [3.6] and [4.5] IRAC/Spitzer photometry recently obtained for S Ori 70. The new near-infrared images (taken 3.82 yr after the discovery data) have allowed us to derive a very small proper motion (11.0 +/- 5.9 mas/yr) for this object, which is consistent with the proper motion of the cluster within 1.5 sigma the astrometric uncertainty. The colors (H-K_s), (J-K_s) and K_s-[3.6] appear discrepant when compared to T4-T7 dwarfs in the field. This behavior could be ascribed to a low-gravity atmosphere or alternatively to an atmosphere with a metallicity significantly different than solar. Taking into account the small proper motion of S Ori 70 and its new near- and mid-infrared colors, a low-gravity atmosphere remains as the most likely explanation to account for our observations. This supports S Ori 70's membership in sigma Orionis, with an estimated mass in the interval 2-7 Mjup, in agreement with our previous derivation.

astro-ph↗

arXiv2005

Optimization by thermal cycling

An optimization algorithm is presented which consists of cyclically heating and quenching by Metropolis and local search procedures, respectively. It works particularly well when it is applied to an archive of samples instead of to a single one. We demonstrate for the traveling salesman problem that this algorithm is far more efficient than usual simulated annealing; our implementation can compete concerning speed with recent, very fast genetic local search algorithms.

cond-mat.dis-nn↗

arXiv2001

Relaxation properties in a lattice gas model with asymmetrical particles

We study the relaxation process in a two-dimensional lattice gas model, where the interactions come from the excluded volume. In this model particles have three arms with an asymmetrical shape, which results in geometrical frustration that inhibits full packing. A dynamical crossover is found at the arm percolation of the particles, from a dynamical behavior characterized by a single step relaxation above the transition, to a two-step decay below it. Relaxation functions of the self-part of density fluctuations are well fitted by a stretched exponential form, with a $β$ exponent decreasing when the temperature is lowered until the percolation transition is reached, and constant below it. The structural arrest of the model seems to happen only at the maximum density of the model, where both the inverse diffusivity and the relaxation time of density fluctuations diverge with a power law. The dynamical non linear susceptibility, defined as the fluctuations of the self-overlap autocorrelation, exhibits a peak at some characteristic time, which seems to diverge at the maximum density as well.

cond-mat.stat-mech↗

arXiv1999

A review of growing interfaces in quenched disordered media

We make a review of the two principal models that allows to explain the imbibition of fluid in porous media. These models, that belong to the directed percolation depinning (DPD) universality class, where introduced simultaneously by the Tang and Leschhorn [Phys. Rev A 45, R8309 (1992)] and Buldyrev et al. [Phys. Rev. A 45, R8313 (1992)] and reviewed by Braunstein et al. [J. Phys. A 32, 1801 (1999); Phys. Rev. E 59, 4243 (1999)]. Even these models have been classified in the same universality class than the Kardar-Parisi-Zhang equation [Phys. Rev. Lett. 56, 889, (1986)] with quenched noise (QKPZ), the contributions to the growing mechanisms are quite different. The lateral contribution in the DPD models, leads to an increasing of the roughness near the criticality while in the QKPZ equation this contribution always flattens the roughness. These results suggest that the QKPZ equation does not describe properly the DPD models even when the exponents derived from this equation are similar to the one obtained from the simulations of these models. This fact is confirmed trough the deduced analytical equation for the Tang and Leschhorn model. This equation has the same symmetries than the QKPZ one but its coefficients depend on the balance between the driving force and the quenched noise.

cond-mat.stat-mech↗

arXiv1999

Does the Quenched Kardar-Parisi-Zhang Equation Describe the Directed Percolation Depinning Models?

The roughening of interfaces moving in inhomogeneous media is investigated by numerical integration of the phenomenological stochastic differential equation proposed by Kardar, Parisi, and Zhang [Phys. Rev. Lett. 56, 889, (1986)] with quenched noise (QKPZ). We express the evolution equations for the mean height and the roughness into two contributions: the local and the lateral one. We compare this two contributions with the ones obtained for two directed percolation deppining models (DPD): the Tang and Leschhorn model [Phys. Rev A 45, R8309 (1992)] and the Buldyrev et al. model [Phys. Rev. A 45, R8313 (1992)] by Braunstein al. [J. Phys. A 32, 1801 (1999); Phys. Rev. E 59, 4243 (1999)]. Even these models have being classified in the same universality class that the QKPZ the contributions to the growing mechanisms are quite different. The lateral contribution in the DPD models, leads to an increasing of the roughness near the criticality while in the QKPZ equation this contribution always flattens the roughness. These results suggest that the QKPZ equation does not describe properly the DPD models even when the exponents derived from this equation are similar to the one obtained from simulations of these models.

cond-mat.stat-mech↗

arXiv1999

Configuration space in electron glasses

We study numerically the configuration space at low energy of electron glasses. We consider systems with Coulomb interactions, short-range interactions and no interactions. First, we calculate the integrated density of configurations as a function of energy. At a given energy, this density is smaller for Coulomb glasses than for short-range systems, which in turn is smaller than for non-interacting systems. We analyze how the site occupancy varies with the number of configurations. Through this study we estimate the number of particles involved in a typical low-energy transition between configurations. This number increases with system size for long range interactions, while it is basically constant for a short-range interaction. Finally we calculate the density of metastable configurations, i.e. valleys, classified according to their degree of stability.

cond-mat.str-el↗

arXiv1999

Directed percolation depinning models: Evolution equations

We present the microscopic equation for the growing interface with quenched noise for the model first presented by Buldyrev et al. [Phys. Rev. A 45, R8313 (1992)]. The evolution equation for the height, the mean height, and the roughness are reached in a simple way. The microscopic equation allows us to express these equations in two contributions: the contact and the local one. We compare this two contributions with the ones obtained for the Tang and Leschhorn model [Phys. Rev A 45, R8309 (1992)] by Braunstein et al. [Physica A 266, 308 (1999)]. Even when the microscopic mechanisms are quiet different in both model, the two contribution are qualitatively similar. An interesting result is that the diffusion contribution, in the Tang and Leschhorn model, and the contact one, in the Buldyrev model, leads to an increase of the roughness near the criticality.

cond-mat.stat-mech↗

arXiv1999

Growing interfaces in quenched disordered media

We present the microscopic equation of growing interface with quenched noise for the Tang and Leschhorn model [{\em Phys. Rev.} {\bf A 45}, R8309 (1992)]. The evolution equations for the mean heigth and the roughness are reached in a simple way. Also, an equation for the interface activity density (i.e. interface density of free sites) as function of time is obtained. The microscopic equation allows us to express these equations in two contributions: the diffusion and the substratum one. All the equation shows the strong interplay between both contributions in the dynamics. A macroscopic evolution equation for the roughness is presented for this model for the critical pressure $p=0.461$. The dynamical exponent $β=0.629$ is analitically obtained in a simple way. Theoretical results are in excellent agreement with the Monte Carlo simulation.

cond-mat.stat-mech↗

arXiv1999

Microscopic equation for growing interfaces in quenched disordered media

We present the microscopic equation of growing interface with quenched noise for the Tang and Leschhorn model [L. H. Tang and H. Leschhorn, Phys. Rev. A {\bf 45}, R8309 (1992)]. The evolution equation for the height, the mean height, and the roughness are reached in a simple way. An equation for the interface activity density (or free sites density) as function of time is obtained. The microscopic equation allows us to express these equations into two contributions: the diffusion and the substratum contributions. All these equations shows the strong interplay between the diffusion and the substratum contribution in the dynamics.

cond-mat.stat-mech↗

arXiv1999

Dielectric susceptibility of the Coulomb-glass

We derive a microscopic expression for the dielectric susceptibility $χ$ of a Coulomb glass, which corresponds to the definition used in classical electrodynamics, the derivative of the polarization with respect to the electric field. The fluctuation-dissipation theorem tells us that $χ$ is a function of the thermal fluctuations of the dipole moment of the system. We calculate $χ$ numerically for three-dimensional Coulomb glasses as a function of temperature and frequency.

cond-mat.dis-nn↗

arXiv1999

Numerical study of relaxation in electron glasses

We perform a numerical simulation of energy relaxation in three-dimensional electron glasses in the strongly localized regime at finite temperatures. We consider systems with no interactions, with long-range Coulomb interactions and with short-range interactions, obtaining a power law relaxation with an exponent of 0.15, which is independent of the parameters of the problem and of the type of interaction. At very long times, we always find an exponential regime whose characteristic time strongly depends on temperature, system size, interaction type and localization radius. We extrapolate the longest relaxation time to macroscopic sizes and, for interacting samples, obtain values much larger than the measuring time. We finally study the number of electrons participating in the relaxation processes of very low energy configurations.

cond-mat.dis-nn↗