arXiv subjects

E. Martinez-Gonzalez

Publications and source records attributed to E. Martinez-Gonzalez.

103 records · Page 6Linked to original sources

arXiv1998

Imaging around PC1643+4631A at the Lyman limit

We present a list of candidates for high redshift late-type galaxies in the field around the z=3.79 quasar PC1643+4631A. Deep U,V and R imaging has been used to search for objects with a strong Lyman break between U and V, characteristic of galaxies with high hydrogen column densities at $z\sim 3$. A further study of the red objects detected by Hu & Ridgway (1994) has been done, allowing the temptative identification of many of them as low redshift ($z\sim 0.4$) elliptical galaxies.

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arXiv1997

Correlation of Excursion Sets for Non-Gaussian CMB Temperature Distributions

We present a method, based on the correlation function of excursion sets above a given threshold, to test the Gaussianity of the CMB temperature fluctuations in the sky. In particular, this method can be applied to discriminate between standard inflationary scenarios and those producing non-Gaussianity such as topological defects. We have obtained the normalized correlation of excursion sets, including different levels of noise, for 2-point probability density functions constructed from the Gaussian, χ_n^2 and Laplace 1-point probability density functions in two different ways. Considering subdegree angular scales, we find that this method can distinguish between different distributions even if the corresponding marginal probability density functions and/or the radiation power spectra are the same.

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arXiv1997

Are optically-selected QSO catalogs biased ?

A thorough study of QSO-galaxy correlations has been done on a region close to the North Galactic Pole using a complete subsample of the optically selected CFHT/MMT QSO survey and the galaxy catalog of Odewahn and Aldering (1995). Although a positive correlation between bright QSOs and galaxies is expected because of the magnification bias effect, none is detected. On the contrary, there is a significant (>99.6%) anticorrelation between z<1.6 QSOs and red galaxies on rather large angular distances. This anticorrelation is much less pronounced for high redshift z>1.6 QSOs, which seems to exclude dust as a cause of the QSO underdensity. This result suggests that the selection process employed in the CFHT/MMT QSO survey is losing up to 50% of low redshift z<1.6 QSOs in regions of high galaxy density. The incompleteness in the whole z<1.6 QSO sample may reach 10% and have important consequences in the estimation of QSO evolution and the QSO autocorrelation function.

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arXiv1997

Weak lensing correlations in open and flat universes

Correlations between the magnification or polarization of background sources, induced by gravitational lensing due to the large-scale structure, and the positions of foreground galaxies are investigated. We found that their amplitude is enhanced with respect to correlations for a single population. We analize the dependence of the correlations with the density parameter Ωconsidering a nonlinear evolution of the matter power spectrum. The contribution of the linear evolution is negligible at scales below several arcminutes. Detailed results on the dependence of the correlations on the redshift of the foreground and background populations for different cosmological models are presented. The effect reaches its maximum amplitude for foreground populations with relatively small redshifts due to the fast increase of the nonlinear matter power spectrum at recent times.

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arXiv1997

Statistical excess of foreground galaxies around high-z radiogalaxies

K-band imaging of a sample of 21 radiogalaxies with z \sim 1.5 reveals the existence of a statistical association of foreground galaxies with the positions of the radiosources. The excess is detected within a 1' radius at a high significance level (>99.8%). K-band light is a good tracer of stellar mass, so this result indicates the existence of an association between foreground mass perturbations and background radiosources, as expected from the magnification bias effect, and confirms previous results obtained for other high-z radio-loud AGN.

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arXiv1996

Peaks in the Cosmic Microwave Background: flat versus open models

We present properties of the peaks (maxima) of the CMB anisotropies expected in flat and open CDM models. We obtain analytical expressions of several topological descriptors: mean number of maxima and the probability distribution of the gaussian curvature and the eccentricity of the peaks. These quantities are calculated as functions of the radiation power spectrum, assuming a gaussian distribution of temperature anisotropies. We present results for angular resolutions ranging from 5' to 20' (antenna FWHM), scales that are relevant for the MAP and COBRAS/SAMBA space missions and the ground-based interferometer experiments. Our analysis also includes the effects of noise. We find that the number of peaks can discriminate between standard CDM models, and that the gaussian curvature distribution provides a useful test for these various models, whereas the eccentricity distribution can not distinguish between them.

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arXiv1996

The absorbers towards Q0836+113

We have performed RIJHK_S imaging of the field around the z=2.67 quasar Q0836+113, which presents several metal line and a damped Lyαabsorption systems in its spectrum. The images reveal the existence of a red K_S=18.9 object \approx 11 arcsec from the quasar. On the basis of the empirical relationships between absorption radius and luminosity we conclude that this object may be the CIV absorber at z=1.82. This could be the first detection of a high redshift galaxy causing high-ionisation absorption. After carefully subtracting the QSO, we do not detect, up to a 3σlimiting magnitude for extended objects of K_S=20.8, the damped Lyαabsorber apparently detected as a Lyαemitter at z=2.47. It is also suggested, that object ``SW'' from Wolfe et al. (1992) could be the galaxy responsible for the claimed MgII absorption at z=0.37.

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arXiv1996

Large Scale QSO-galaxy correlations for radio loud and optically selected QSO samples

We have studied the distribution of $B_J<20.5$ galaxies from the ROE/NRL COSMOS/UKST catalogue around two samples of $z>0.3$ QSOs with similar redshift distributions. The first sample is formed by 144 radio-loud QSOs from the Parkes Catalogue, and the other contains 167 optically selected QSOs extracted from the Large Bright Quasar Survey. It is found that there is a $\approx 99.0%$ significance level excess of COSMOS/UKST galaxies around the PKS QSOs, whereas there is a marginal defect of galaxies around the LBQS QSOs. When the distribution of galaxies around both samples is compared, we found that there is an overdensity of galaxies around the PKS sample with respect to the LBQS sample anticorrelated with the distance from the QSOs at a $99.7%$ significance level. Although this result apparently agrees with the predictions of the double magnification bias, it is difficult to explain by gravitational lensing effects alone; dust in the foreground galaxies and selection effects in the detection of LBQS QSOs should be taken into account. It has been established that the lines of sight to PKS flat-spectrum QSOs go through significatively higher foreground galaxy densities than the directions to LBQS quasars, what may be partially related with the reported reddening of PKS QSOs.

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arXiv1995

Omega from the COBE-DMR anisotropy maps

We have made a likelihood statistical analysis of the angular correlations in the {\it COBE}-DMR two-year sky maps by Monte Carlo simulation of the temperature fluctuations. We assume an open universe and consider as primordial power spectrum the Harrison-Zeldovich one, $P(k)=Ak$. We find that the flatness of the universe is not implied by the data. The quadrupole normalization amplitude, $Q_{rms-PS}$, is related to the density parameter, $Ω$, by $Q_{rms-PS} = 10.67 + 55.81 Ω- 128.59 Ω^2 + 81.26 Ω^3\ μ$K. We have determined the p.d.f. of $Ω$ due to cosmic plus sampling (i.e. $20^\circ$ galactic cut) variance which generically shows a bimodal shape. The uncertainty as given by the r.m.s. is $\approx 0.35$, therefore to better constrain $Ω$ experiments sensitive to higher multipoles ($l>20$) should be considered.

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arXiv1995

High redshift AGNs from the 1Jy catalogue and the magnification bias

We have found a statistically significant (99.1 \%) excess of red ($O-E>2$) galaxies with photographic magnitudes $E<19.5$, $O< 21$ taken from the APM Sky Catalogue around $z \sim 1$ radiosources from the 1Jy catalogue. The amplitude, scale and dependence on galaxy colours of the observed overdensity are consistent with its being a result of the magnification bias caused by the weak gravitational lensing of large scale structures at redshift $z \approx 0.2-0.4$ and are hardly explained by other causes, as obscuration by dust.

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arXiv1995

INTERMEDIATE RESOLUTION SPECTROSCOPY OF THE RADIO GALAXY B2 0902+34 AT $Z\approx 3.4$

We have carried out spectroscopic observations of the high redshift ($z\approx 3.4$) radio galaxy 0902+34 at intermediate resolution with the William Herschel Telescope. The dynamical spectral ranges covered are 4600-5480 Åand 5920-7680 Åwith resolutions of 5.4 Åand 9.5 Å, respectively. We detect a continuum that is almost flat and resolve three emission lines: Ly$α$, C IV $λ$1549 and He II $λ$1640, the last one previously undetected. The line ratios are similar to the typical values found for narrow-line high redshift radio galaxies. Line ratios observed in different regions of the galaxy seem to indicate the presence of strong ionization and/or dust density gradients. We have not detected any Ly$α$ absorption at z=3.3968 (red wing of the Ly$α$ emission line) as might be expected from the absorption found at 21 cm by other authors using the VLA and Arecibo antennas. We discuss possible models for the H I absorbing cloud.

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arXiv1995

Genus and spot density in the COBE DMR first year anisotropy maps

A statistical analysis of texture on the {\it COBE}-DMR first year sky maps based on the genus and spot number is presented. A generalized $χ^2$ statistic is defined in terms of ``observable'' quantities: the genus and spot density that would be measured by different cosmic observers. This strategy together with the use of Monte Carlo simulations of the temperature fluctuations, including all the relevant experimental parameters, represent the main difference with previous analyses. Based on the genus analysis we find a strong anticorrelation between the quadrupole amplitude $Q_{rms-PS}$ and the spectral index $n$ of the density fluctuation power spectrum at recombination of the form $Q_{rms-PS}= 22.2 \pm 1.7 - (4.7 \pm 1.3) \times n\ μ$K for fixed $n$, consistent with previous works. The result obtained based on the spot density is consistent with this $Q_{rms-PS} (n)$ relation. In addition to the previous results we have determined, using Monte Carlo simulations, the minimum uncertainty due to cosmic variance for the determination of the spectral index with the genus analysis. This uncertainty is $δn\approx 0.2$.

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arXiv1994

R-Band Imaging of Fields Around 1<z<2 Radiogalaxies

We have taken deep $R$-band images of fields around five radiogalaxies: 0956+47, 1217+36, 3C256, 3C324 and 3C294 with $1<z<2$ . 0956+47 is found to show a double nucleus. Our data on 1217+36 suggest the revision of its classification as a radiogalaxy. We found a statistically significant excess of bright ($19.5<R<22$) galaxies on scales of 2 arcmin around the radiogalaxies (which have $R \approx 21.4$) in our sample. The excess has been determined empirically to be at $\gtrsim 99.5\%$ level. It is remarkable that this excess is not present for $22<R<23.75$ galaxies within the same area, suggesting that the excess is not physically associated to the galaxies but due to intervening groups and then related to gravitational lensing.

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