arXiv subjects

Martin Lopez-Corredoira

Publications and source records attributed to Martin Lopez-Corredoira.

At least 37 records · Page 2Linked to original sources

arXiv2017

Tests and problems of the standard model in Cosmology

The main foundations of the standard $Λ$CDM model of cosmology are that: 1) The redshifts of the galaxies are due to the expansion of the Universe plus peculiar motions; 2) The cosmic microwave background radiation and its anisotropies derive from the high energy primordial Universe when matter and radiation became decoupled; 3) The abundance pattern of the light elements is explained in terms of primordial nucleosynthesis; and 4) The formation and evolution of galaxies can be explained only in terms of gravitation within a inflation+dark matter+dark energy scenario. Numerous tests have been carried out on these ideas and, although the standard model works pretty well in fitting many observations, there are also many data that present apparent caveats to be understood with it. In this paper, I offer a review of these tests and problems, as well as some examples of alternative models.

astro-ph.CO↗

arXiv2016

Against free will in the contemporary natural sciences

The claim of the freedom of the will (understood as an individual who is transcendent to Nature) in the name of XXth century scientific knowledge, against the perspective of XVIIIth-XIXth century scientific materialism, is analysed and refuted in the present paper. The hypothesis of reductionism finds no obstacle within contemporary natural sciences. Determinism in classical physics is irrefutable, unless classical physics is itself refuted. From quantum mechanics, some authors 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, here I defend the opposite thesis because indeterminism does not imply free will, and because the considerations about an autonomous mind sending orders to the body is against neuroscience or evolutionary theories about human beings. The quantum theory of measurement can be interpreted without the intervention of human minds, but other fields of science cannot contemplate the mentalist scenario. A fatalistic or materialist view, which denies the possibility of a free will, makes much more sense in scientific terms.

physics.hist-ph↗

arXiv2016

Alcock-Paczynski Test with Model-independent BAO Data

Cosmological tests based on the statistical analysis of galaxy distributions usually depend on source evolution. An exception is the Alcock-Paczynski (AP) test, which is based on the changing ratio of angular to spatial/redshift size of (presumed) spherically-symmetric source distributions with distance. Intrinsic redshift distortions due to gravitational effects may also have an influence, but they can now be overcome with the inclusion of a sharp feature, such as the Baryonic Acoustic Oscillation (BAO) peak. Redshift distortions affect the amplitude of the peak, but impact its position only negligibly. As we shall show here, the use of this diagnostic, with new BAO peaks from SDSS-III/BOSS at average redshifts =0.38, 0.61 and 2.34, disfavors the current concordance (LCDM) model at 2.3 sigma. Within the context of expanding Friedmann-Robertson-Walker (FRW) cosmologies, these data instead favor the zero active mass equation-of-state, rho+3p=0, where rho and p are, respectively, the total density and pressure of the cosmic fluid, the basis for the R_h=ct universe.

astro-ph.CO↗

arXiv2016

A case against an X-shaped structure in the Milky Way young bulge

CONTEXT. A number of recent papers have claimed the discovery of an X-shape structure in the bulge of our Galaxy in the population of the red clumps. AIMS. We endeavor to analyze the stellar density of bulge stars in the same regions using a different stellar population that is characteristic of the young bulge ($\lesssim 5$ Gyr). Particularly, we use F0-F5 main-sequence stars with distances derived through photometric parallax. METHODS. We extract these stars from extinction-corrected color-magnitude diagrams in the near-infrared of VISTA-VVV data in some bulge regions and calculate the densities along the line of sight. We take the uncertaintity in the photometric parallax and the contamination of other sources into account, and we see that these errors do not avoid the detection of a possible double peak along some lines of sight as expected for a X-shape bulge if it existed. RESULTS. Only a single peak in the density distribution along the line of sight is observed, so apparently there is no X-shape structure for this population of stars. Nonetheless, the effects of the dispersion of absolute magnitudes in the selected population might be an alternative explanation, although in principle these effects are insufficient to explain this lack of double peak according to our calculations. CONCLUSIONS. The results of the present paper do not demonstrate that previous claims of X-shaped bulge using only red clump stars are incorrect, but there are apparently some puzzling questions if we want to maintain the validity of both the red-clump results and the results of this paper.

astro-ph.GA↗

arXiv2015

The number of tidal dwarf satellite galaxies in dependence of bulge index

We show that a significant correlation (up to 5sigma) emerges between the bulge index, defined to be larger for larger bulge/disk ratio, in spiral galaxies with similar luminosities in the Galaxy Zoo 2 of SDSS and the number of tidal-dwarf galaxies in the catalogue by Kaviraj et al. (2012). In the standard cold or warm dark-matter cosmological models the number of satellite galaxies correlates with the circular velocity of the dark matter host halo. In generalized-gravity models without cold or warm dark matter such a correlation does not exist, because host galaxies cannot capture in-falling dwarf galaxies due to the absence of dark-matter-induced dynamical friction. However, in such models a correlation is expected to exist between the bulge mass and the number of satellite galaxies, because bulges and tidal-dwarf satellite galaxies form in encounters between host galaxies. This is not predicted by dark matter models in which bulge mass and the number of satellites are a priori uncorrelated because higher bulge/disk ratios do not imply higher dark/luminous ratios. Hence, our correlation reproduces the prediction of scenarios without dark matter, whereas an explanation is not found readily from the a priori predictions of the standard scenario with dark matter. Further research is needed to explore whether some application of the standard theory may explain this correlation.

astro-ph.CO↗

arXiv2015

Tests for the Expansion of the Universe

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock--Paczyński test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock--Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.

astro-ph.CO↗

arXiv2014

Milky Way rotation curve from proper motions of red clump giants

We derive the stellar rotation curve of the Galaxy in the range of Galactocentric radii of R=4-16 kpc at different vertical heights from the Galactic plane of z between -2 and +2 kpc. We used the PPMXL survey, which contains the USNO-B1 proper motions catalog cross-correlated with the astrometry and near-infrared photometry of the 2MASS Point Source Catalog. To improve the accuracy of the proper motions, we calculated the average proper motions of quasars to know their systematic shift from zero in this PPMXL survey, and we applied the corresponding correction to the proper motions of the whole survey, which reduces the systematic error. We selected from the CM diagram K vs. (J-K) the red clump giants and used the information of their proper motions to build a map of the rotation speed of our Galaxy. We obtain an almost flat rotation curve with a slight decrease for higher values of R or |z|. The most puzzling result is obtained for the farthest removed and most off-plane regions, where a significant deviation from a null average proper motion (~4 mas/yr) in the Galactic longitude direction for the anticenter regions can be directly translated into a rotation speed much lower than in the solar Galactocentric radius: an average speed of 82+/-5(stat.)+/-58(syst.) km/s. A scenario with a rotation speed lower than 150 km/s in these regions of our explored zone is intriguing, and invites one to reconsider different possibilities for the dark matter distribution. However, given the high systematic errors, we cannot conclude about this. Hence, more measurements of the proper motions at high R and |z| are necessary to validate the exotic scenario that would arise if this low speed were confirmed.

astro-ph.GA↗

arXiv2013

Non-standard Models and the Sociology of Cosmology

I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.

physics.hist-ph↗

arXiv2013

Alcock-Paczynski cosmological test

In order to test the expansion of the universe and its geometry, we carry out an Alcock & Paczynski cosmological test, that is, an evaluation of the ratio of observed angular size to radial/redshift size. The main advantage of this test is that it does not depend on the evolution of the galaxies, but only on the geometry of the universe. However, the redshift distortions produced by the peculiar velocities of the gravitational infall do also have an influence, which should be separated from the cosmological effect. We derive the anisotropic correlation function of sources in three surveys within the Sloan Digital Sky Survey (SDSS): galaxies from SDSS-III/Baryon Oscillation Spectroscopy Survey-Data Release 10 (BOSS-DR10), and QSOs from SDSS-II and SDSS-III/BOSS-DR10. From these, we are able to disentangle the dynamic and geometric distortions and thus derive the ratio of observed angular size to radial/redshift size at different redshifts. We also add some other values available in the literature. Then, we use the data to evaluate which cosmological model fits them. We used six different models: concordance Lambda-CDM, Einstein-de Sitter, open-Friedman Cosmology without dark energy, flat quasi-steady state cosmology, a static universe with a linear Hubble law, and a static universe with tired-light redshift. Only two of the six models above fit the data of the Alcock & Paczynski test: concordance Lambda-CDM and static universe with tired-light redshift; whereas the rest of them are excluded at a >95% confidence level. If we assume that Lambda-CDM is the correct one, the best fit with a free Omega_m is produced for Omega_m=0.24^{+0.10}_{-0.07}.

astro-ph.CO↗

arXiv2013

The Twilight of the Scientific Age

This brief article presents the introduction and draft of the fundamental ideas developed at length in the book of the same title, which gives a challenging point of view about science and its history/philosophy/sociology. Science is in decline. After centuries of great achievements, the exhaustion of new forms and fatigue have reached our culture in all of its manifestations including the pure sciences. Our society is saturated with knowledge which does not offer people any sense in their lives. There is a loss of ideals in the search for great truths and a shift towards an anodyne specialized industry.

physics.hist-ph↗

arXiv2013

Peaks in the CMBR power spectrum. II. Physical interpretation for any cosmological scenario

In a previous paper (part I), the mathematical properties of the cosmic microwave background radiation power spectrum which presents oscillations were discussed. Here, we discuss the physical interpretation: a power spectrum with oscillations is a rather normal characteristic expected from any fluid with clouds of overdensities that emits/absorb radiation or interact gravitationally with the photons, and with a finite range of sizes and distances for those clouds. The standard cosmological interpretation of "acoustic" peaks is just a particular case; peaks in the power spectrum might be generated in scenarios within some alternative cosmological model that have nothing to do with oscillations due to gravitational compression in a fluid. We also calculate the angular correlation function of the anisotropies from the WMAP-7yr and ACT data, in an attempt to derive the minimum number of parameters a polynomial function should have to fit it: a set of polynomial functions with a total of six free parameters, apart from the amplitude, is enough to reproduce the first two peaks. However, the standard model with six tunable free parameters also reproduces higher order peaks, giving the standard model a higher confidence. At present, while no simple function with six free parameters is found to give a fit as good as the one given by the standard cosmological model, we may consider the predictive power of the standard model beyond an instrumentalist approach (such as the Ptolemaic astronomy model of the orbits of the planets).

astro-ph.CO↗

arXiv2012

What do astrophysics and the world's oldest profession have in common?

In the present paper I want to tell of my impressions about the world of research in astrophysics, which I know from close observation. I see with certain pessimism the actual state of astrophysics, as well as of other sciences with similar problems. There are many charms in the profession, as many charms as in love, but not when they are in the service of mercantile aims.

astro-ph↗

arXiv2011

Pending problems in QSOs

Quasars (Quasi Stellar Objects, abbreviated as QSOs) are still nowadays, close to half a century after their discovery, objects which are not completel y understood. In this brief review a description of the pending problems, inconsistencies and caveats in the QSO's research is presented. The standard paradigm model based on the existence of very massive black holes that are responsible for the QSO's huge luminosities, resulting from to their cosmological redshifts, leaves many facts without explanation. There are several observations which lack a clear explanation, for instance: the absence of bright QSOs at low redshifts, a mysterious evolution not properly understood; the inconsistencies of the absorption lines, such as the different structure of the clouds along the QSO's line of sight and their tangential directions; the spatial correlation between QSOs and galaxies; and many others.

astro-ph.CO↗

arXiv2010

Angular size test on the expansion of the Universe

Assuming the standard cosmological model as correct, the average linear size of galaxies with the same luminosity is six times smaller at z=3.2 than at z=0, and their average angular size for a given luminosity is approximately proportional to 1/z. Neither the hypothesis that galaxies which formed earlier have much higher densities nor their luminosity evolution, mergers ratio, or massive outflows due to a quasar feedback mechanism are enough to justify such a strong size evolution. Also, at high redshift, the intrinsic ultraviolet surface brightness would be prohibitively high with this evolution, and the velocity dispersion much higher than observed. We explore here another possibility to overcome this problem by considering different cosmological scenarios that might make the observed angular sizes compatible with a weaker evolution. One of the models explored, a very simple phenomenological extrapolation of the linear Hubble law in a Euclidean static universe, fits the angular size vs. redshift dependence quite well, which is also approximately proportional to 1/z with this cosmological model. There are no free parameters derived ad hoc, although the error bars allow a slight size/luminosity evolution. The type Ia supernovae Hubble diagram can also be explained in terms of this model with no ad hoc fitted parameter. WARNING: I do not argue here that the true Universe is static. My intention is just to discuss which theoretical models provide a better fit to the data of observational cosmology.

astro-ph.CO↗

arXiv2009

Intrinsic colors and ages of extremely red elliptical galaxies at high redshift

In order to know the formation epoch of the oldest elliptical galaxies as a function of mass and observed redshift, a statistical analysis for 333 extremely red objects (EROs) classified as old galaxies (OGs) at 0.8<z<2.3 is carried out. Once we get M_V and (B-V) at rest for each galaxy, we calculate the average variation of this intrinsic color with redshift and derive the average age through a synthesis model (the code for the calculation of the age has been made publicly available). The average gradient of the (B-V) color at rest of EROs/OGs is 0.07-0.10 Gyr^{-1} for a fixed luminosity. The stars in these extremely red elliptical galaxies were formed when the Universe was ~2 Gyr old on average. We have not found a significant enough dependence on the observed redshift and stellar mass: dt_{formation}/dt_{observed}=-0.46+/-0.32, dt_{formation}/(d log_10 M_*)=-0.81+/-0.98 Gyr. This fits a scenario in which the stellar formation of the objects that we denominate as EROs-OGs is more intense at higher redshifts, at which the stellar populations of the most massive galaxies form earlier than or at the same time as less massive galaxies.

astro-ph.CO↗

arXiv2009

Absence of anti-correlations and of baryon acoustic oscillations in the galaxy correlation function from the Sloan Digital Sky Survey DR7

One of the most striking features predicted by standard models of galaxy formation is the presence of anti-correlations in the matter distribution at large enough scales (r>r_c). Simple arguments show that the location of the length-scale r_c, marking the transition from positive to negative correlations, is the same for any class of objects as for the full matter distribution, i.e. it is invariant under biasing. This scale is predicted by models to be at about the same distance of the scale signaling the baryonic acoustic oscillation scale r_{bao}. We test these predictions in the newest SDSS galaxy samples.We find that, in several MG samples, the correlation function remains positive at scales >250 Mpc/h, while in the concordance LCDM it should be negative beyond r_c\approx 120 Mpc/h. In other samples the correlation function becomes negative at scales <50 Mpc/h. To investigate the origin of these differences we consider in detail the propagation of errors on the sample density into the estimation of the correlation function. We conclude that these are important at large enough separations, and that they are responsible for the observed differences between different estimators and for the measured sample to sample variations of the correlation function. We conclude that, in the newest SDSS samples, the large scale behavior of the galaxy correlation function is affected by intrinsic errors andv olume-dependent systematic effects which make the detection of correlations to be only an estimate of a lower limit of their amplitude, spatial extension and statistical errors. We point out that these results represent an important challenge to LCDM models as they largely differ from its predictions.(Abridged version).

astro-ph.CO↗

arXiv2009

Sociology of Modern Cosmology

Certain results of observational cosmology cast critical doubt on the foundations of standard cosmology but leave most cosmologists untroubled. Alternative cosmological models that differ from the Big Bang have been published and defended by heterodox scientists; however, most cosmologists do not heed these. This may be because standard theory is correct and all other ideas and criticisms are incorrect, but it is also to a great extent due to sociological phenomena such as the "snowball effect" or "groupthink". We might wonder whether cosmology, the study of the Universe as a whole, is a science like other branches of physics or just a dominant ideology.

physics.gen-ph↗

arXiv2009

Apparent discordant redshift QSO-galaxy associations

An "exotic" idea proposed by Viktor Ambartsumian was that new galaxies are formed through the ejection from older active galaxies. Galaxies beget galaxies, instead of the standard scenario in which galaxies stem from the evolution of the seeds derived from fluctuations in the initial density field. This idea is in some way contained in the speculative proposal that some or all QSOs might be objects ejected by nearby galaxies, and that their redshift is not cosmological (Arp, G./M. Burbidge and others). I will discuss some of the arguments for and against this scenario; in particular, I shall talk about the existence of real physical connections in apparently discordant QSO-galaxy redshift associations. On the one hand, there are many statistical correlations of high-redshift QSOs and nearby galaxies that cannot yet be explained in terms of gravitational lensing, biases, or selection effects; and some particular configurations have very low probabilities of being a projection of background objects. Our understanding of QSOs in general is also far from complete. On the other hand, some cases which were claimed to be anomalous in the past have found an explanation in standard terms. As an example, I will show some cases of our own research into this type: statistics of ULXs around nearby galaxies, and the Flesch & Hardcastle candidate QSOs catalog analysis. My own conclusion is neutral.

astro-ph.CO↗