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M. Lopez-Corredoira

Publications and source records attributed to M. Lopez-Corredoira.

At least 73 records · Page 4Linked to original sources
arXiv2004

The field surrounding NGC 7603: cosmological or non-cosmological redshifts?

We present new observations of the field surrounding the Seyfert galaxy NGC 7603, where four galaxies with different redshifts--NGC 7603 (z=0.029), NGC 7603B (z=0.057) and two fainter emission line galaxies (z=0.245 and z=0.394)--are apparently connected by a narrow filament, leading to a possible case of anomalous redshift. The observations comprise broad and narrow band imaging and intermediate resolution spectroscopy of some of the objects in the field. The new data confirm the redshift of the two emission-line objects found within the filament connecting NGC 7603 and NGC 7603B, and settles their type with better accuracy. Although both objects are point-like in ground based images, using HST archive images we show that the objects have structure with a FWHM=0.3-0.4 arcsec. This and the relative strength and width of the main spectral lines allow us to classify these as HII galaxies with very vigorous star formation, while the rest of the filament and NGC 7603B lack star formation. We delineate the halo of NGC 7603 out to 26.2 mag/square arcsec in the Sloan r band filter and find evidence for strong internal distortions. New narrow emission line galaxies at z=0.246, 0.117 and 0.401 are also found at respectively 0.8, 1.5 and 1.7 arcmin to the West of the filament within the fainter contour of this halo. The probability of three background galaxies of any type with apparent B-magnitudes up to 16.6, 21.1 and 22.1 (the observed magnitudes, extinction correction included) being randomly projected on the filament of the fourth galaxy (NGC 7603) is computed resulting ~ 3 x 10^(-9).

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arXiv2004

New optical spectra and general discussion on the nature of ULX's

We present spectroscopic observations of three Ultra Luminous X-ray sources (ULX's). Two of them are very close to the active galaxy NGC 720 and the other is near NGC 1073. The two around NGC 720 turn out to be quasars at z=0.964 and z= 2.216, the one near NGC 1073 seems to be associated to an HII region at the redshift of NGC 1073. We concentrate our analysis on the two quasars and analyze them in conjunction with a set of 20 additional X-ray sources close to nearby galaxies which also fit the criteria of ULX's and which also have been identified as quasars of medium to high redshift. This sample shows an unusually large fraction of rare BL Lac type objects. The high redshifts of these ULX's and their close proximity to their low redshift, supposedly parent galaxies is a surprising result in the light of standard models. We describe the main properties of each of these objects and their parent galaxy, and briefly discuss possible interpretations.

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arXiv2003

Fluctuations of K-band galaxy counts

We measure the variance in the distribution of off-plane (|b|>20 deg.) galaxies with m_K<13.5 from the 2MASS K-band survey in circles of diameter between 0.344 deg. and 57.2 deg. The use of a near-infrared survey makes negligible the contribution of Galactic extinction to these fluctuations. We calculate these variances within the standard Lambda-CDM model assuming that the sources are distributed like halos of the corresponding mass, and it reproduces qualitatively the galaxy counts variance. Therefore, we test that the counts can be basically explained in terms only of the large scale structure. A second result of this paper is a new method to determine the two point correlation function obtained by forcing agreement between model and data. This method does not need the knowledge of the two-point angular correlation function, allows an estimation of the errors (which are low with this method), and can be used even with incomplete surveys. Using this method we get xi(z=0, r<10 h^{-1}Mpc)=(29.8+/-0.3) (r/h^{-1}Mpc)^{-1.79+/-0.02}, which is the first measure of the amplitude of xi in the local Universe for the K-band. It is more or less in agreement with those obtained through red optical filters selected samples, but it is larger than the amplitude obtained for blue optical filters selected samples.

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arXiv2003

A three-dimensional Galactic extinction model

A large-scale three-dimensional model of Galactic extinction is presented based on the Galactic dust distribution model of Drimmel and Spergel (2001). The extinction A_V to any point within the Galactic disk can be quickly deduced using a set of three-dimensional cartesian grids. Extinctions from the model are compared to empirical extinction measures, including lines-of-sight in and near the Galactic plane using optical and NIR extinction measures; in particular we show how extinction can be derived from NIR color-magnitude diagrams in the Galactic plane to a distance of 8 kiloparsec.

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arXiv2002

A catalog of warps in spiral and lenticular galaxies in the Southern hemisphere

A catalog of optical warps of galaxies is presented. This can be considered complementary to that reported by Sanchez-Saavedra et al., with 42 galaxies in the northern hemisphere, and to that by Reshetnikov & Combes, with 60 optical warps. The limits of the present catalog are: logr25 > 0.60, B_{t} < 14.5, delta(2000) < 0, -2.5 < t < 7. Therefore, lenticular galaxies have also been considered. This catalog lists 150 warped galaxies out of a sample of 276 edge-on galaxies and covers the whole southern hemisphere, except the Avoidance Zone. It is therefore very suitable for statistical studies of warps. It also provides a source guide for detailed particular observations. We confirm the large frequency of warped spirals: nearly all galaxies are warped. The frequency and warp angle do not present important differences for the different types of spirals. However, no lenticular warped galaxy has been found within the specified limits. This finding constitutes an important restriction for theoretical models.

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arXiv2002

Quantum mechanics and free will: counter-arguments

Since quantum mechanics (QM) was formulated, many voices have claimed this to be the basis of free will in the human beings. Basically, they argue that free will is possible because there is an ontological indeterminism in the natural laws, and that the mind is responsible for the wave function collapse of matter, which leads to a choice among the different possibilities for the body. However, I defend the opposite thesis, that free will cannot be defended in terms of QM. First, because indeterminism does not imply free will, it is merely a necessary condition but not enough to defend it. Second, because all considerations about an autonomous mind sending orders to the body is against our scientific knowledge about human beings; in particular, neither neurological nor evolutionary theory can admit dualism. The quantum theory of measurement can be interpreted without the intervention of human minds, but other fields of science cannot contemplate the mentalist scenario, so it is concluded that QM has nothing to say about the mind or free will, and its scientific explanation is more related to biology than to physics. A fatalistic or materialist view, which denies the possibility of a free will, makes much more sense in scientific terms.

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arXiv2002

Old stellar Galactic disc in near-plane regions according to 2MASS: scales, cut-off, flare and warp

We have pursued two different methods to analyze the old stellar population near the Galactic plane, using data from the 2MASS survey. The first method is based on the isolation of the red clump giant population in the color-magnitude diagrams and the inversion of its star counts to obtain directly the density distribution along the line of sight. The second method fits the parameters of a disc model to the star counts in 820 regions. Results from both independent methods are consistent with each other. The qualitative conclusions are that the disc is well fitted by an exponential distribution in both the galactocentric distance and height. There is not an abrupt cut-off in the stellar disc (at least within R<15 kpc). There is a strong flare (i.e. an increase of scale-height towards the outer Galaxy) which begins well inside the solar circle, and hence there is a decrease of the scale-height towards the inner Galaxy. Another notable feature is the existence of a warp in the old stellar population whose amplitude is coincident with the amplitude of the gas warp. It is shown for low latitude stars (mean height: |z|~300 pc) in the outer disc (galactocentric radius R>6 kpc) that: the scale-height in the solar circle is h_z(R_sun)=3.6e-2 R_sun, the scale-length of the surface density is h_R=0.42 R_sun and the scale-length of the space density in the plane (i.e. including the effect of the flare) is H=0.25 R_sun. The variation of the scale-height due to the flare follows roughly a law h_z(R) =~ h_z(R_sun) exp [(R-R_\odot)/([12-0.6R(kpc)] kpc)] (for R<~15 kpc; R_sun=7.9 kpc). The warp moves the mean position of the disc to a height z_w=1.2e-3 R(kpc)^5.25 sin(phi+(5 deg.)) pc (for R<~13 kpc; R_sun=7.9 kpc).

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arXiv2002

Warps and correlations with intrinsic parameters of galaxies in the visible and radio

From a comparison of the different parameters of warped galaxies in the radio, and especially in the visible, we find that: a) No large galaxy (large mass or radius) has been found to have high amplitude in the warp, and there is no correlation of size/mass with the degree of asymmetry of the warp. b) The disc density and the ratio of dark to luminous mass show an opposing trend: smaller values give more asymmetric warps in the inner radii (optical warps) but show no correlation with the amplitude of the warp; however, in the external radii neither is there any correlation with the asymmetry. c) A third anticorrelation arises from a comparison of the amplitude and degree of asymmetry in the warped galaxies. Hence, it seems that very massive dark matter haloes have nothing to do with the formation of warps but only with the degree of symmetry in the inner radii, and are unrelated to the warp shape for the outermost radii. Denser discs show up the same dependence.

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arXiv2002

Two emission line objects with z>0.2 in the optical filament apparently connecting the Seyfert galaxy NGC 7603 to its companion

We present new spectroscopic observations of an old case of anomalous redshift--NGC 7603 and its companion. The redshifts of the two galaxies which are apparently connected by a luminous filament are z=0.029 and z=0.057 respectively. We show that in the luminous filament there are two compact emission line objects with z=0.243 and z=0.391. They lie exactly on the line traced by the filament connecting the galaxies. As far as we are aware, this is the most impressive case of a system of anomalous redshifts discovered so far.

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arXiv2002

New light and shadows on Stephan's Quintet

We present deep broad-band R and narrow-band Halpha images of Stephan's Quintet. The observations in the R band show that the diffuse halo of the Stephan's Quintet is larger than previously thought and extends out to NGC 7320C. However, we have not found emission connecting NGC 7331 and NGC 7320 to R ~ 26.7 mag/arcsec^2 (at more than 3-sigma level), so there is no direct evidence up to this limiting magnitude of a relation between the peculiar kinematical structure found in NGC 7331 and an ongoing or past interaction between this galaxy and NGC 7320. The Halpha emission at high-velocity (6000-7000 km/s) is distributed in a diffuse structure running NS between NGC 7319 and NGC 7318B and in some other more concentrated features. Some of these are located in the tidal tails produced by the interaction between the galaxies of the group. With the Halpha images we have made a two-dimensional velocity map which helps to identify the origin of each structure detected. This map does not show features at intermediate velocities between the high- and low-redshift members of the group. This is in agreement with the standard scenario in which the apparent proximity of NGC 7320 to the rest of the galaxies of the Quintet is merely a projection effect. The only point which is unclear in this interpretation, is an Halpha filament which is seen extending throughout NGC 7320 with velocity at 6500 km/s instead of the 800 km/s expected for this galaxy.

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arXiv2002

Generation of galactic disc warps due to intergalactic accretion flows onto the disc

A new method is developed to calculate the amplitude of the galactic warps generated by a torque due to external forces. This takes into account that the warp is produced as a reorientation of the different rings which constitute the disc in order to compensate the differential precession generated by the external force, yielding a uniform asymptotic precession for all rings. Application of this method to gravitational tidal forces in the Milky Way due to the Magellanic Clouds leads to a very low amplitude of the warp. If the force were due to an extragalactic magnetic field, its intensity would have to be very high, to generate the observed warps. An alternative hypothesis is explored: the accretion of the intergalactic medium over the disk. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shape warp. The torque produced by a flow of velocity ~100 km/s and baryon density \~10^{-25} kg/m^3 is enough to generate the observed warps and this mechanism offers quite a plausible explanation. First, because this order of accretion rate is inferred from other processes observed in the Galaxy, notably its chemical evolution. The inferred rate of infall of matter, ~1 solar-mass/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of this chemical evolution resolving key issues, notably the G-dwarf problem. Second, because the required density of the intergalactic medium is within the range of values compatible with observation. By this mechanism, we can explain the warp phenomenon in terms of intergalactic accretion flows onto the disk of the galaxy.

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arXiv2001

Probability distribution of density fluctuations in the non-linear regime

We present a general procedure for obtaining the present density fluctuation probability distribution given the statistics of the initial conditions. The main difficulties faced with regard to this problem are those related to the non-linear evolution of the density fluctuations and those posed by the fact that the fields we are interested in are the result of filtering an underlying field with structure down to scales much smaller than that of filtering. The solution to the latter problem is discussed here in detail and the solution to the former is taken from a previous work. We have checked the procedure for values of the rms density fluctuation as large as 3/2 and several power spectra and found that it leads to results in excellent agreement with those obtained in numerical simulations. We also recover all available exact results from perturbation theory.

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arXiv2001

Searching for the in-plane Galactic bar and ring in DENIS

New evidence for a long thin Galactic bar (in contradistinction to the bulge), as well as for the existence of the ring and the truncation of the inner disc, are sought in the DENIS survey. First, we examine DENIS and Two Micron Galactic Survey star counts for the characteristic signatures of an in-plane bar and ring. The star counts in the plane for 30 deg.>l>-30 deg. are shown to be highly asymmetric with considerably more sources at positive than at negative longitudes. At |b|\approx 1.5 deg., however, the counts are nearly symmetric. Therefore, the asymmetry is not due to the disc, which is shown to have an inner truncation, or to the bulge, so there has to be another major component in the inner Galaxy that is causing the asymmetries. This component provides up to 50% of the detected sources in the plane between the bulge and l=27 deg. or l=-14 deg. This component is shown to be consistent with an in-plane bar with a position angle of 40 deg. and half-length of 3.9 kpc. However, there is also a major peak in the counts at l=-22 deg., which coincides with the tangential point of the so-called 3 kpc arm. This is shown to be most probably a ring or a pseudo-ring. The extinction in the plane is also shown to be asymmetric with more extinction at negative than at positive longitudes. For l<8 deg. the extinction is shown to be slightly tilted with respect to b=0 deg. in the same manner as the HI disc. We conclude that the Galaxy is a fairly typical ringed barred spiral galaxy.

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arXiv2000

An excess of very bright stars in the inner bulge

From an analysis of the stars remaining in central regions of the Galaxy after subtracting those belonging to the disc and the bulge, we deduce that the inner bulge must have an extra young population with respect the rest of the bulge. It is shown that there is a higher ratio of very bright stars in the central bulge than than there is in the outer bulge. This is interpreted as being an additional young component due to the presence of star formation regions near the Galactic Centre which is absent in the outer bulge.

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arXiv2000

Detection of the old stellar component of the major Galactic bar

We present near-IR colour--magnitude diagrams and star counts for a number of regions along the Galactic plane. It is shown that along the l=27 b=0 line of sight there is a feature at 5.7 +-0.7kpc with a density of stars at least a factor two and probably more than a factor five times that of the disc at the same position. This feature forms a distinct clump on an H vs. J-H diagram and is seen at all longitudes from the bulge to about l=28, but at no longitude greater than this. The distance to the feature at l=20 is about 0.5kpc further than at l=27 and by l=10 it has merged with, or has become, the bulge. Given that at l=27 and l=21 there is also a clustering of very young stars, the only component that can reasonably explain what is seen is a bar with half length of around 4kpc and a position angle of about 43+-7.

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arXiv2000

Complete Zeldovich approximation

We have developed a generalization of the Zeldovich approximation (ZA) that is exact in a wide variety of situations, including plannar, spherical and cilyndrical symmetries. We have shown that this generalization, that we call complete Zeldovich approximation (CZA), is exact to second order at an arbitrary point within any field. For gaussian fields, the third order error have been obtained and shown to be very small. For statistical purposes, the CZA leads to results exact to the third order.

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