arXiv subjects

E. Florido

Publications and source records attributed to E. Florido.

51 records · Page 3Linked to original sources

arXiv2010

Near-infrared and optical observations of galactic warps: A common, unexplained feature of most discs

Context: Warps occurring in galactic discs have been studied extensively in HI and in the optical, but rarely in the near-infrared (NIR) bands that trace the older stellar populations. Aims: We provide NIR data of nearby edge-on galaxies, combined with optical observations, for direct comparison of the properties of galactic warps as a function of wavelength, and calculate warp curves for each galaxy and obtain the characteristic warp parameters. We discuss these properties as possible constraints to the different mechanisms that have been proposed for the development and persistence of galactic warps. Methods: We observed 20 galaxies that were selected from a statistically complete diameter-limited subsample of edge-on disc galaxies. We used the Cerro Tololo Infrared Imager (CIRIM) at the CTIO 1.5m Ritchey-Chretien telescope to acquire the NIR data. We used the 1.54m Danish and 0.92m Dutch telescopes at the European Southern Observatory's La Silla site for our optical observations. Results: Our results show that 13 of our 20 sample galaxies are warped, with the warp more pronounced in the optical than at NIR wavelengths. In the remaining seven galaxies, no warp is apparent within the limitations of our automated detection method. The transition between the unperturbed inner disc and the outer, warped region is rather abrupt. S0 galaxies exhibit very small or no warps. The magnetic model remains one of a number of interesting formation scenarios.

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arXiv2008

Probing IGM large-scale flows: warps in galaxies at shells of voids

CONTEXT. Hydrodynamical cosmological simulations predict flows of the intergalactic medium along the radial vector of the voids, approximately in the direction of the infall of matter at the early stages of the galaxy formation. AIMS. These flows might be detected by analysing the dependence of the warp amplitude on the inclination of the galaxies at the shells of the voids with respect to the radial vector of the voids. This analysis will be the topic of this paper. METHODS. We develop a statistical method of analysing the correlation of the amplitude of the warp and the inclination of the galaxy at the void surface. This is applied to a sample of 97 edge-on galaxies from the Sloan Digital Sky Survey. Our results are compared with the theoretical expectations, which are also derived in this paper. RESULTS. Our results allow us to reject the null hypothesis (i.e., the non-correlation of the warp amplitude and the inclination of the galaxy with respect to the void surface) at 94.4% C. L., which is not conclusive. The absence of the radial flows cannot be excluded at present, although we can put a constraint on the maximum average density of baryonic matter of the radial flows of <~ 4 Omega_b rho_crit.

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arXiv2006

Truncated stellar disks in the near infrared. I. Observations

We present NIR surface photometry of 11 edge-on galaxies obtained in the course of a long term project aimed at analysing the occurrence and type of the truncation of the outer disks. Observations were carried out at the 1.5 m CST (Carlos Sánchez Telescope) in Tenerife (Spain) using the CAIN infrared camera. 7 galaxies exhibit clear truncation on their disk profiles and 4 galaxies were observed to be clearly untruncated within observational limits. We describe the truncations as real, smooth and complete (as suggested by extrapolation and in the sense that the measured truncation curve goes into the noise at a truncation radius $R_{tr}$), following a decline proportional to $(R_{tr} -R)^{-n}$ (where $R$ is the radius). Despite its deep photometric reach, the data presented do not permit a detailed exploration of the region where optical data show a second slope. Special care was taken concerning the surface brightness deprojection of edge-on galaxies, which was carried out by two methods, one comprising the inversion of Abel's integral equation and the other following a numerical method. These methods gave nearly identical results. NIR observations of truncations could differ from observations in the optical, since the two domains trace different stellar populations.

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arXiv2006

Truncated stellar discs in the near infrared. II. Statistical properties and interpretation

The results obtained in paper I are used to study possible relationships between the truncation radius of stellar discs in the NIR and structural parameters of the galaxies. The NIR truncation radius is larger for brighter galaxies, being proportional to $V_m^c$ with $c \approx 3/2$, and with $V_m$ being the asymptotic rotation velocity at large radii (when the rotation curve becomes flat), and is lower for higher wavelengths. When it is normalized to the scalelength, the truncation is an increasing function of the central surface brightness and is lower for late type galaxies, although these correlations are weaker. These relations are in agreement with the scenario of magnetically driven truncations.

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arXiv2004

Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033

We present integral field spectroscopy of NGC 5033, a low luminosity Seyfert galaxy. The observations were made with INTEGRAL, a fiber based system operating at the WHT. The intensity map of the H$β$ emission line represents a spiral or ring-like pattern of HII regions. On the contrary, the [OIII] intensity map morphology is markedly anisotropic. The strong morphological differences imply that the [OIII] emitters represent highly ionized gas illuminated by the central source. The [OIII] map morphology is compatible with a biconical structure of ionization induced by strong extinction in the galaxy disc that also obscures half of the spheroidal stellar bulge. We identify the spectrum corresponding to the Seyfert 1 nucleus from the presence of H$β$ broad emission lines. This spectrum is located in a region where strong extinction is expected but exhibits the bluest spectral energy distribution. The Seyfert 1 nucleus seems to be offcenter with respect to the stellar rotation center. This result has been also found in other Seyfert galaxies and interpreted in terms of a past merger. The offcentering could indicate the presence of nonsymmetric departures in the gravitational potential which could be fueling the active nucleus. The kinematics of the [OIII] emitters show important deviations at a kpc scale with respect to the stellar velocity field and show features related to the asymmetrical morphology of the high ionization region.

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arXiv2002

Axisymmetrical Gas Inflow in the Central Region of NGC 7331

New Integral Field Spectroscopy of the central region of NGC 7331 reveals strong H$α$ emission in the well-known CO and HI ring of NGC 7331. The [NII]/H$α$ ratio indicates that a large scale stellar formation process is taken place at the ring in agreement with previous hypothesis about the exhaustion of gas in the inner to the ring region. The dynamics of stars and gas are not coupled. There is a ring of peculiar velocities in the ionized gas velocity map. These peculiar velocities can be well interpreted by the presence of an axisymmetric inflow of 40 km/s at the inner boundary of the large-scale gaseous ring. We infer an inwards total flux of 1.6 M$_{\odot}$yr$^{-1}$. This value is typical of the accretion rates in hypothetical {\bf large} nuclear black holes. Despite the large differences in the scales of the nucleus and the gas ring of NGC 7331, we suggest that this inwards flux is feeding the nucleus.

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arXiv2002

The truncation of stellar discs: the magnetic hypothesis

We propose a hypothesis of the truncation of stellar discs based on the magnetic model of the rotation curve of spiral galaxies. Once the disc had formed and acquired its present structure, approximately, three balanced forces were acting on the initial gas: gravity and magnetic forces, inwards, and centrifugal force. When stars are formed from this gas, the magnetic force is suddenly suppressed. Gravitation alone cannot retain the newly-formed stars and at birth places beyond a certain galactocentric radius they escape to intergalactic space. This radius is the so-called ``truncation radius'', which is predicted to be at about 4-5 disc radial scale lengths, in promising agreement with observations.

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arXiv2000

Magnetic Fields are not ignorable in the dynamics of disks

Magnetic fields are considered to be dominant when $ε_{B}\geqε_{K}$, being $ε_{B}=B^{2}/8π$ the magnetic energy density and $ε_{K}=1/2 ρθ^{2}$ the rotation energy density, for a conventional moderate B= 1 $μ$G. They are considered to be negligible when $ε_{B}<ε_{K}$ for $B\sim 10 μ$G. With no assumption and no theoretical calculation, we show that magnetic fields cannot be ignored in the outer parts of a galaxy like the Milky Way and in the whole disk of a dwarf galaxy.

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arXiv1999

Magnetic fields and the large-scale structure

The large-scale structure of the Universe has been observed to be characterized by long filaments, forming polyhedra, with a remarkable 100-200 Mpc periodicity, suggesting a regular network. The introduction of magnetic fields into the physics of the evolution of structure formation provides some clues to understanding this unexpected lattice structure. A relativistic treatment of the evolution of pre-recombination inhomogeneities, including magnetic fields, is presented to show that equivalent-to-present field strengths of the order of $10^{-8}$ G could have played an important role. Primordial magnetic tubes generated at inflation, at scales larger than the horizon before recombination, could have produced filamentary density structures, with comoving lengths larger than about 10 Mpc. Structures shorter than this would have been destroyed by diffusion due to the small pre-recombination conductivity. If filaments constitute a lattice, the primordial magnetic field structures that produced the post-recombination structures of matter, impose several restrictions on the lattice. The simplest lattice compatible with these restrictions is a network of octahedra contacting at their vertexes, which is indeed identifiable in the observed distribution of superclusters.

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arXiv1998

The egg-carton Universe

The distribution of superclusters in the Local Supercluster neighbourhood presents such a remarkable periodicity that some kind of network must fit the observed large scale structure. A three dimension chessboard has been suggested$^{1}$. The existence of this network is really a challenge for currently-suggested theoretical models. For instance, CDM models of the formation of the large scale structure predict a random distribution of superclusters$^{2}$. If the filaments of matter that are now observed building up the network are fossil relics of over-dense regions of magnetic field energy before Recombination, then it has been shown$^{3}$ that the simplest network compatible with magnetic field constraints is made up of octahedra contacting at their vertexes. This suggests a set of superimposed egg-carton structures. Our aim in this paper is to show that the real large-scale structure is actually fitted by the theoretical octahedron structure.

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arXiv1998

Magnetic fields and rotation of spiral galaxies

We present a simplified model in which we suggest that two important galactic problems -the magnetic field configuration at large scales and the flat rotation curve- may be simultaneously explained. A highly convective disc produces a high turbulent magnetic diffusion in the vertical direction, stablishing a merging of extragalactic and galactic magnetic fields. The outer disc may then adquire a magnetic energy gradient very close to the gradient required to explain the rotation curve, without the hypothesis of galactic dark matter. Our model predicts symmetries of the galactic field in noticeable agreement with the large scale structure of our galaxy.

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arXiv1998

The truncation of stellar discs. A theoretical model

The truncation of stellar discs is not abrupt but characterized by a continuous distancing from the exponential profile. There exists a truncation curve, $t(r)$, ending at a truncation radius, $r_t$. We present here a theoretical model in which it is assumed that the magnetic hypothesis explaining the flat rotation curve also explains the truncation. Once stars are born, the centripetal magnetic force previously acting on the progenitor gas cloud is suddenly interrupted, and stars must move to larger orbits or escape. The agreement between theoretical and observed truncation curves is very satisfactory. Parameters defining the disc gas rotation curve should therefore be related to those defining the truncation. It is predicted that rotation curves that quickly reach the asymptotic value $θ_0 = θ(r=\infty)$ would have small truncation radii. On the contrary, $r_t$ and $θ_0$ itself, would be uncorrelated quantities.

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arXiv1997

Magnetic fields and large-scale structure in a hot universe. II. Magnetic flux tubes and filamentary structure

In paper I, we obtained an equation for the evolution of density inhomogeneities in a radiation dominated universe when they are affected by magnetic fields. In this second paper we apply this equation to the case in which the subjacent magnetic configuration is a flux tube. For scales of the order of 1 Mpc or less the differential equation is elliptical. To solve it, we have used the numerical method based on "Simultaneous Over Relaxation", SOR, with Chebyshev acceleration and we have treated the problem as a boundary value problem, which restricts the prediction ability of the integration. For large-scale flux tubes, much larger than 1 Mpc, the equation can be analytically integrated and no assumption about the final shape or magnitude of the inhomogeneity is required. In both cases we obtain an evolution which does not differ very much from linear in time. The inhomogeneity in the density becomes filamentary. Large scale structures ($\ge$ 10 Mpc) are probably unaffected by damping, non-linear and amplification mechanisms after Equality, so that this model provides a tool to interpret the present observed large scale structure. Filaments are very frequently found in the large-scale structure in the Universe. It is suggested here that they could arise from primordial magnetic flux tubes, thus providing an alternative hypothesis for its interpretation; in particular we consider the case of the Coma-A1367 supercluster, where the magnetic field is known to be high.

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arXiv1997

Magnetic fields and large scale structure in a hot Universe. III. The polyhedric network

We provide a new tool to interpret the large scale structure of the Universe. As suggested in Paper II, energy density filaments could have been produced by subjacent magnetic flux tubes when the Universe was dominated by radiation. In more recent time epochs, small scale filaments have evolved in a complicated way, but large scale filaments have probably survived and should be identified with present observed matter filaments of clusters. A primordial magnetic field lattice made up of magnetic flux tubes would then have originated a matter lattice made up of cluster filaments. Taking into account some restrictions in the magnetic field configuration we speculate what type of matter network this would have generated. The simplest lattice is made up of octohedra connected at their vertexes, reminding us of a structure of superimposed egg cartons. The vertexes would correspond to large superclusters, which would therefore have eight filaments emerging from them. Some observational evidence is found in the Local Supercluster, which is spider-like, with eight legs.

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arXiv1997

Magnetic Fields and Large Scale Structure in a hot Universe. I. General Equations

We consider that no mean magnetic field exists during this epoch, but that there is a mean magnetic energy associated with large-scale magnetic inhomogeneities. We study the evolution of these inhomogeneities and their influence on the large scale density structure, by introducing linear perturbations in Maxwell equations, the conservation of momentum-energy equation, and in Einstein field equations. The primordial magnetic field structure is time independent in the linear approximation, only being diluted by the general expansion, so that $\vec{B}R^2$ is conserved in comoving coordinates. Magnetic fields have a strong influence on the formation of large-scale structure. Firstly, relatively low fields are able to generate density structures even if they were inexistent at earlier times. Second, magnetic fields act anisotropically more recently, modifying the evolution of individual density clouds. Magnetic flux tubes have a tendency to concentrate photons in filamentary patterns.

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