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M. Lopez-Corredoira

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

At least 55 records · Page 3Linked to original sources
arXiv2008

The long Galactic bar as seen by UKIDSS Galactic Plane Survey

Over the last decade there have been a series of results supporting the hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45 deg. This is apparently a very different structure from the triaxial bulge of the Galaxy, which is thicker and shorter and dominates the star counts at |l|<10 deg. In this paper, we analyse the stellar distribution in the inner Galaxy to see if there is clear evidence for two triaxial or bar-like structures in the Milky Way. By using the red-clump population as a tracer of Galactic structure, we determine the apparent morphology of the inner Galaxy. Deeper and higher spatial resolution NIR photometry from the UKIDSS Galactic Plane Survey allows us to use in-plane data even at the innermost Galactic longitudes, a region where the source confusion is a dominant effect that makes it impossible to use other NIR databases such as 2MASS or TCS-CAIN. We show that results previously obtained with using the red-clump giants are confirmed with the in-plane data from UKIDSS GPS. There are two different structures coexisting in the inner Galactic plane: one with a position angle of 23.60+-2.19 deg that can be traced from the Galactic Centre up to l=10 deg (the Galactic bulge), and other with a larger position angle of 42.44+-2.14 deg, that ends around l=28 deg (the long Galactic bar).

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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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arXiv2008

Analysis of possible anomalies in the QSO distribution of the Flesch & Hardcastle catalogue

AIMS. A recent catalogue by Flesch & Hardcastle presents two major anomalies in the spatial distribution of QSO candidates: i/ an apparent excess of such objects near bright galaxies, and ii/ an excess of very bright QSO candidates compared to random background expectations in several regions of the sky. Because anyone of these anomalies would be relevant in a cosmological context, we carried out an extensive analysis of the probabilities quoted in that catalogue. METHODS. We determine the nature and redshift of a subsample of 30 sources in that catalogue by analysing their optical spectra (another 11 candidates were identified from existing public databases). These have allowed us to statistically check the reliability of the probabilities QSO status quoted by Flesch & Hardcastle for their candidates. RESULTS. Only 12 of the 41 candidates turned out QSOs (7 of which have been identified here for the first time). CONCLUSIONS. The probabilities of the QSOs' being the candidates given by Flesch & Hardcastle are overestimated for m_B<17 and for objects projected near (<1 arcmin) bright galaxies. This is the cause of the anomalies mentioned above.

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arXiv2007

Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies

The Galactic foreground contamination in CMBR anisotropies, especially from the dust component, is not easily separable from the cosmological or extragalactic component. In this paper, some doubts will be raised concerning the validity of the methods used to date to remove Galactic dust emission in order to show that none of them achieves its goal. First, I review the recent bibliography on the topic and discuss critically the methods of foreground subtraction: the cross-correlation with templates, analysis assuming the spectral shape of the Galactic components, the "maximum entropy method", "internal linear combination", and "wavelet-based high resolution fitting of internal templates". Second, I analyse the galactic latitude dependence from WMAP data. The frequency dependence is discussed with the data in the available literature. The result is that all methods of subtracting the Galactic contamination are inaccurate. The galactic latitude dependence analysis or the frequency dependence of the anisotropies in the range 50-250 GHz put a constraint on the maximum Galactic contribution in the power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and possibly higher for larger scales. The origin of most of the signal in the CMBR anisotropies is not Galactic. In any case, the subtraction of the Galaxy is not accurate enough to allow a "precision Cosmology"; other sources of contamination (extragalactic, solar system) are also present.

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arXiv2007

Galactic disc warps due to intergalactic accretion flows onto the disc

The accretion of the intergalactic medium onto the gaseous disc is used to explain the generation of galactic warps. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small for most incident inflow angles and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shaped warp. The torque produced by a flow of velocity ~100 km/s and baryon density ~10^{-25} kg/m^3, which is within the possible values for the intergalactic medium, is enough to generate the observed warps and this mechanism offers quite a plausible explanation. The inferred rate of infall of matter, ~1 M_sun/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of chemical evolution resolving key issues, notably the G-dwarf problem. Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because it would produce a dependence of the scaleheight of the disc with the Galactocentric azimuth in the outer disc, but rather than being an objection this is another argument in favour of the mechanism because this dependence is actually observed in our Galaxy.

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arXiv2007

Bar-driven injection of intergalactic matter into galactic halos

AIMS. The non-conservative gravitational potential of barred galaxies, or of any other non-axisymmetric structure, produces a loss of energy in infalling particles of the intergalactic medium into the galaxy, which are trapped in its potential. This dynamical friction can contribute towards increasing the total mass of barred galaxies. METHODS. Analytical calculations of the energy loss are carried out using the orbits of the particles derived numerically. Theoretical predictions are compared with observations through the statistical analysis of the rotation curves of barred and non-barred galaxies, either in cluster or field galaxies. RESULTS. There is a net effect of accretion, but it is normally very low in relative terms. It is only significant (>10% of the total mass of the dark matter halo in the life of the galaxy) if the density of the intergalactic medium is higher than ~3e13 Msun/Mpc^3 (or considerably lower in cases of motions of the galaxies close to the IGM average motion, or perpendicular to the plane of the galaxy, or when the halo mass is low). Data on rotation curves do not show clear trends towards higher halo mass for barred galaxies, only slight trends for early-type spiral galaxies. In any case, the statistical uncertainties are limited to the detection of differences in masses >~20%, so the effect of bar-driven injection of intergalactic matter into galactic halos might be present with relative contributions to the average mass of these barred galaxies lower than 20%.

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arXiv2007

Tracing the long bar with red-clump giants

Over the last decade a series of results have lent support to the hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45 deg. This is apparently a very different structure from the triaxial bulge of the Galaxy. In this paper, we analyse the stellar distribution in the inner 4 kpc of the Galaxy to see if there is clear evidence for two triaxial or barlike structures, or whether there is only one. By using the red-clump population as a tracer of the structure of the inner Galaxy we determine the apparent morphology of the inner Galaxy. Star counts from 2MASS are used to provide additional support for this analysis. We show that there are two very different large-scale triaxial structures coexisting in the inner Galaxy: a long thin stellar bar constrained to the Galactic plane (|b|<2 deg) with a position angle of 43.1 +- 1.8 deg, and a distinct triaxial bulge that extends to at least |b|<7.5 deg with a position angle of 12.6 +- 3.2 deg. The scale height of the bar source distribution is around 100 pc, whereas for the bulge the value of this parameter is five times larger.

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arXiv2007

International Workshop on Redshift Mechanisms in Astrophysics and Cosmology

An extraordinary event took place recently in Ireland. A group of independent and professional researchers met to discuss an old heterodox topic with important consequences in astrophysics and, especially, in cosmology: possible causes of the redshifts in the spectra of astrophysical objects other than a Doppler or expanding universe mechanism. Many decades of work have been devoted to this kind of research, most of it forgotten by the greater part of the astrophysical community nowadays. But the question is still open, the debate is still alive, as was shown by the participants in the present Workshop. There is no smoke without fire, and the existence of many facts and theories on alternative origins of redshifts may point to some new pathways in physics that deserve further attention. This was precisely the aim of this meeting. (...)

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arXiv2006

Estimation of Galactic model parameters in high latitudes with 2MASS

In this paper, we try to find any dependence of the Galactic structural parameters with the Galactic longitude for either the thin disc or the thick disc of the Milky Way, that would indicate to possible inhomogeneities or asymmetries in those Galactic components. Galactic model parameters obtained using a set of 36 high-latitude fields with 2MASS photometry for the different fields show that, effectively, they are Galactic longitude-dependent. The thick disc scaleheight changes from 800 pc at 150 deg < l < 230 deg to 1050 pc at |l| < 30 deg. A plausible explanation for this finding might be the effect of the flare in this Galactic component that changes the scaleheight with Galactocentric distance

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arXiv2006

First tentative detection of anisotropy in the QSO distribution around nearby edge-on spiral galaxies

AIMS. To check whether the polar angle distribution of QSOs around nearby spiral galaxies is isotropic or not. METHODS. A statistical analysis of the polar angle distribution of large samples of QSOs from the SDSS survey and Monte Carlo simulations to calculate their significance are carried out. RESULTS. There is a clear excess of QSOs near the minor axis with respect to the major axis of nearby edge-on spiral galaxies, significant at a level 3.5-sigma up to angular distances of 3 deg. (or ~1.7 Mpc) from the centre of each galaxy. The significance is increased to 3.9-sigma with the z>0.5 QSOs, and it reaches 4.8-sigma if we include galaxies whose circles of radius 3 degrees are covered by the SDSS in more than 98% (instead of 100%) of the area. CONCLUSIONS. Gravitational lensing in the halo of nearby galaxies or extinction seem insufficient to explain the observed anisotropic distribution of QSOs. The anisotropic distribution agrees qualitatively with the predictions of Arp's models, which claim that QSOs are ejected by galaxies along the rotation axis, although Arp's prediction give a distance of the QSOs ~3 times smaller than that found here. In any case, a chance fluctuation, although highly improbable, might be a possibility rather than a true anisotropy, and the present results should be corroborated by other groups and samples, so we prefer to consider it as just a first tentative detection.

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arXiv2006

The Long Bar in the Milky Way. Corroboration of an old hypothesis

Recent GLIMPSE data have further confirmed the hypothesis of the existence of an in-plane long bar different from the bulge of the Milky Way with the same characteristics as emphasized some years ago by our team. In this paper, we present two new analyses that corroborate recent and earlier claims concerning the existence in our Galaxy of a long flat bar with approximate dimensions 7.8 kpc x 1.2 kpc x 0.2 kpc and a position angle of approximately 43 deg.: 1) star counts with 2MASS All-Sky Release and MSX data, which give an excess in the plane region along 0<l<30 deg. compared with -30 deg.<l<0, and which cannot be due to the bulge, spiral arms, a ring, or extinction; 2) new data on the distance of the long bar using the red clump method, together with recent observations of our own that are compared with our model, and that are in agreement with the long-bar scenario.

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arXiv2006

Galactic Warp in the overdensity of the Canis Major Region

Bellazzini et al. (2006b) claim that Lopez-Corredoira et al.'s (2002) warp model is totally unable to reproduce the Canis Major structure in the red clump stars. However, slight variations in the azimuth of the Lopez-Corredoira et al. (2002) warp model, justified by the uncertainties in the parameter as well as the local irregularities with respect to the average model, derive a result much closer to the observations of the overdensity south/north. The bump of red clump stars with m_K=13-13.5 around l=241 deg., b=-8.5 deg. and the depth of the Canis Major structure are also explainable in terms of the warp with an appropriate extrapolation of constant height between galactocentric radii of 13 and 16 kpc, as observed roughly in the southern warp, instead of a monotonically increasing height like the northern warp; and the observed velocity distribution of stars cannot exclude the warp possibility. A warp model is therefore still a possible explanation of the Canis Major overdensity, and the hypothesis of the existence of a dwarf galaxy is unnecessary, although still a possibility too.

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arXiv2006

Toward a Clean Sample of Ultra-Luminous X-ray Sources

CONTEXT. Observational follow-up programmes for the characterization of ultra-luminous X-ray sources (ULXs) require the construction of clean samples of such sources in which the contamination by foreground/background sources is minimum. AIMS. In this article we calculate the degree of foreground/background contaminants among the ULX sample candidates in the Colbert & Ptak (2002) catalogue and compare these computations with available spectroscopical identifications. METHODS. We use statistics based on known densities of X-ray sources and AGN/QSOs selected in the optical. The analysis is done individually for each parent galaxy. The existing identifications of the optical counterparts are compiled from the literature. RESULTS. More than a half of the ULXs, within twice the distance of the major axis of the 25 mag/arcsec$^2$ isophote from RC3 nearby galaxies and with X-ray luminosities $L_X$[2-10 keV] $\ge 10^{39}$ erg/s, are expected to be high redshift background QSOs. A list of 25 objects (clean sample) confirmed to be real ULXs or to have a low probability of being contaminant foreground/background objects is provided.

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arXiv2005

Research on candidates for non-cosmological redshifts

(Abridged:) The paradox of apparent optical associations of galaxies with very different redshifts, the so-called anomalous redshift problem, is around 35 years old, but is still without a clear solution and is surprisingly ignored by most of the astronomical community. Statistical correlations among the positions of these galaxies have been pointed out by several authors. Gravitational lensing by dark matter has been proposed as the cause of these correlations, although this seems to be insufficient to explain them and does not work at all for correlations with the brightest and nearest galaxies. Some of these cases may be just fortuitous associations in which background objects are close in the sky to a foreground galaxy, although the statistical mean correlations remain to be explained and some lone objects have very small probabilities of being a projection of background objects. The sample of discordant redshift associations given in Arp's atlas is indeed quite large, and most of the objects remain to be analysed thoroughly. For about 5 years, we have been running a project to observe some of these cases in detail, and some new anomalies have been added to those already known; For instance, in some exotic configurations such as NGC 7603 or NEQ3, which can even show bridges connecting four object with very different redshifts. Not only QSOs but also emission-line galaxies in general are found to take part in this kind of event. Other cases are analyzed: MCG 7-25-46, GC 0248+430, B2 1637+29, VV172 and Stephan's Quintet.

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arXiv2005

The Nature of Ultra Luminous X-ray Sources

We present spectroscopic observations of six optical counterparts of intermediate luminosity X-ray sources (ULXs) around nearby galaxies. The spectra of the six objects show the presence of broad emission features. The identification of these allow us to classify all of the objects as quasars at higher redshift than their assigned parent galaxy. This is one of the first and largest identifications of such objects using unambigous optical spectral features. These results, in conjuction with previous similar identifications of other sources, indicate that high redshift quasars represent an important fraction of catalogued ULX sources. We estimate the density of such sources and compare this with expectations for a population of randomly distributed background quasars.

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arXiv2004

Evidence for a deficit of young and old stars in the Milky Way inner in-plane disc

We give independent proof of the deficit of stars in the in-plane central disc with respect to the predictions of a pure exponential density distribution. We use three different methods: 1) the inversion of the red clump giant distribution in near-infrared colour-magnitude diagrams to obtain the star density along the line of sight; 2) the determination of the density distribution of 1612 MHz sources by means of the distance determination of OH/IR sources from their kinematical information; 3) an analysis of near and mid-infrared star counts and comparison with models. All the tests give the same result: a defect of stars in the inner disc with respect to an exponential disc (either with constant scaleheight or extrapolated from the outer disc), but only in near plane regions. This deficit might be interpreted as a flare in the vertical distribution. The in-plane density is almost independent of R and not an exponential law. Further away from the plane, however, the density increases towards the centre due to the increase of the scaleheight. Tests also show that this result cannot be due to extinction. The deficit affects both the young and the old populations, so it is probably a rather stable feature of the disc, and might be due to the existence of an in-plane bar sweeping the near-plane stars.

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arXiv2004

QSO + galaxy association and discrepant redshifts in NEQ3

Spectroscopy and deep imaging of the group NEQ3 are presented. This system is formed by three compact objects with relative separations of ~2.6 and ~2.8 arcsec, and a lenticular galaxy at ~17 arcsec from the geometric centre of the group. A diffuse filament is located on a line joining the three compact objects and the main galaxy. Analysis of these observations confirms the redshift previously known for three of the objects (z=0.1239 for the main galaxy, and z=0.1935 and 0.1939 for two of the compact objects). We have also determined the previously unknown redshift of the third compact object as z=0.2229. Using the relative strength and width of the main spectral lines, we have classified the compact objects as two HII galaxies and one QSO (the object at z=0.1935). With cross-correlation techniques, we have tentatively estimated the redshift of the filament as z=0.19 (although a weaker component also appears at z=0.12) so that it is probably associated with the halo of the two compact objects at this redshift. The two objects at redshift ~0.19 represent possibly one of the more clear examples of starburst (and perhaps QSO activity) driven by interaction. These, and the relation between these two objects and the other two at (~0.12 and ~0.22) make the nature of this system intriguing, being difficult to explain the whole association on conventional scenarios.

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