arXiv subjects

C. M. Gutierrez

Publications and source records attributed to C. M. Gutierrez.

At least 55 records · Page 3Linked to original sources

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

Quantitative Morphology of Galaxies in the Core of the Coma Cluster

We present a quantitative morphological analysis of 187 galaxies in a region covering the central 0.28 square degrees of the Coma cluster. Structural parameters from the best-fitting Sersic r^{1/n} bulge plus, where appropriate, exponential disc model, are tabulated here. This sample is complete down to a magnitude of R=17 mag. By examining the Edwards et al. (2002) compilation of galaxy redshifts in the direction of Coma, we find that 163 of the 187 galaxies are Coma cluster members, and the rest are foreground and background objects. For the Coma cluster members, we have studied differences in the structural and kinematic properties between early- and late-type galaxies, and between the dwarf and giant galaxies. Analysis of the elliptical galaxies reveals correlations among the structural parameters similar to those previously found in the Virgo and Fornax clusters. Comparing the structural properties of the Coma cluster disc galaxies with disc galaxies in the field, we find evidence for an environmental dependence: the scale lengths of the disc galaxies in Coma are 30% smaller. A kinematical analysis shows marginal differences between the velocity distributions of ellipticals with Sersic index n<2 (dwarfs) and those with n>2 (giants); the dwarf galaxies having a greater (cluster) velocity dispersion. Finally, our analysis of all 421 background galaxies reveals a non-uniform distribution in redshift with contrasts in density ~3, characterized by a void extending from ~10,000 to ~20,000 km s^{-1}, and two dense and extended structures centred at ~20,000 and ~47,000 km s^{-1}.

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arXiv2002

A Correlation between Light Concentration and Cluster Local Density for Elliptical Galaxies

Using photometric and redshift data for the Virgo and Coma clusters, we present evidence for a correlation between the light concentration of elliptical galaxies (including dwarf ellipticals) and the local 3-D (i.e. non-projected) density of the clusters: more concentrated ellipticals are located in denser regions. The null hypothesis (i.e. the absence of any relation) is rejected at a significance level better than 99.9%. In order to explain the observed relation, a power law relating the galaxy light concentration and the cluster 3-D density is proposed. We study how the projection effects affect the form and dispersion of the data-points in the light concentration-projected density diagram. The agreement between our model and the observed data suggests that there is a paucity of dwarf elliptical galaxies in the cluster central regions.

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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

Triaxial stellar systems following the r^{1/n} luminosity law: an analytical mass-density expression, gravitational torques and the bulge/disc interplay

We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the r^{1/n} luminosity law - extending the analysis of Ciotti (1991) who explored the properties of spherical r^{1/n} systems. A new `analytical' expression that accurately reproduces the spatial (i.e. deprojected) luminosity density profiles (error < 0.1%) is presented for detailed modelling of the Sersic family of luminosity profiles. We evaluate both the symmetric and the non--axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component. We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n) is found to heavily reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for nonsymmetric structures in the disc. Using seeing-convolved r^{1/n}-bulge plus exponential-disc fits to the K-band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sersic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K-band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, although not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker.

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arXiv2002

The Properties of Satellite Galaxies in External Systems. I. Morphology and Structural Parameters

We present the first results of an ongoing project to study the morphological, kinematical, dynamical, and chemical properties of satellite galaxies of external giant spiral galaxies. The sample of objects has been selected from the catalogue by Zaritsky et al. (1997). The paper analyzes the morphology and structural parameters of a subsample of 60 such objects. The satellites span a great variety of morphologies and surface brightness profiles. About two thirds of the sample are spirals and irregulars, the remaining third being early-types. Some cases showing interaction between pairs of satellites are presented and briefly discussed.

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arXiv2001

The effects of seeing on Sersic profiles. II. The Moffat PSF

The effects of seeing on Sersic r^{1/n} profile parameters are extensively studied using a Moffat function. This analytical approximation to the point spread function (PSF) is shown to provide the best fit to the PSF predicted from atmospheric turbulence theory when beta=4.765. The Moffat PSF is additionally shown to contain the Gaussian PSF as a limiting case beta->infinity. The Moffat function is also shown to be numerically well behaved when modelling narrow PSFs in HST images. Seeing effects are computed for elliptically symmetric surface brightness distributions. The widely used assumption of circular symmetry when studying the effects of seeing on intrinsically elliptical sources is shown to produce significant discrepancies with respect to the true effects of seeing on these sources. A prescription to correct raw (observed) central intensities, effective radii, index n and mean effective surface brightness is given.

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arXiv2001

COSMOSOMAS: A Circular Scanning Instrument to Map the Sky at Centimetric Wavelengths

We describe the first instrument of a Cosmic Microwave Background experiment for mapping cosmological structures on medium angular scales (the COSMOSOMAS experiment) and diffuse Galactic emission. The instrument is located at Teide Observatory (Tenerife) and is based on a circular scanning sky strategy. It consists of a 1 Hz spinning flat mirror directing the sky radiation into a 1.8 m off-axis paraboloidal antenna which focuses it on to a cryogenically cooled HEMT-based receiver operating in the frequency range 12--18 GHz. The signal is split by a set of three filters, allowing simultaneous observations at 13, 15 and 17 GHz, each with a 1 GHz bandpass. A 1-5 degree resolution sky map complete in RA and covering 20 degrees in declination is obtained each day at these frequencies. The observations presented here correspond to the first months of operation, which have provided a map of ~9000 square degrees on the sky centred at DEC = +31 degrees with sensitivities of 140, 150 and 250 microK per beam area in the channels at 13, 15 and 17 GHz respectively. We discuss the design and performance of the instrument, the atmospheric effects, the reliability of the data obtained and prospects of achieving a sensitivity of 30 microK per beam in two years of operation.

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arXiv2001

Quantitative Morphology of the Intermediate-Redshift Galaxy Cluster Abell 2443 from Ground-Based Imaging -- Evidence for a galaxy concentration index correlation with cluster density

We present broad-band photometry and provide a quantitative analysis of the structure of galaxies in the inner region of the Abell Cluster 2443 (z~0.1). The galaxy parameters have been derived by fitting a two-component model (Sersic r^{1/n} bulge and exponential disk) to a magnitude-limited sample. Using a new method of analysis which takes into account the effects of seeing on the structural parameters and considers the ellipticity as an active parameter, we avoid systematic errors arising from assumptions of circular symmetry. 76% of the sample galaxies were classified with these models, the rest were morphologically peculiar. For the spiral galaxies, the relation between n and B/D is consistent with the trend observed in nearby field galaxy samples. The Sersic index n (which can be considered as a concentration index) of the elliptical galaxies is correlated with the local surface density of the cluster. Monte Carlo simulations were used to check the reliability of the method and determine the magnitude selection criteria.

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arXiv2000

The effects of seeing on Sersic profiles

The effects of seeing on the parameters of the Sèrsic profile are studied in an analytical form using a Gaussian point spread function. The surface brightness of Sèrsic profiles is proportional (in magnitudes) to $r^{1/n}$. The parameter $n$ serves to classify the type of profile and is related to the central luminosity concentration. It is the parameter most affected by seeing; furthermore, the value of $n$ that can be measured is always smaller than the real one. It is shown that the luminosity density of the Sèrsic profile with $n$ less than 0.5 has a central depression, which is physically unlikely. Also, the intrinsic ellipticity of the sources has been taken into account and we show that the parameters are dependent when the effects of seeing are non-negligible. Finally, a prescription for correcting raw effective radii, central intensities and $n$ parameters is given.

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arXiv2000

A measurement at the first acoustic peak of the CMB with the 33 GHz interferometer

This paper presents the results from the Jodrell Bank-IAC two-element 33 GHz interferometer operated with an element separation of 32.9 wavelengths and hence sensitive to 1 deg scale structure on the sky. The level of CMB fluctuations, assuming a flat CMB spatial power spectrum over the range of multipoles l = 208 +- 18, was found using a likelihood analysis to be ΔT_l = 63^{+7}_{-6} mu K at the 68% confidence limit, after the subtraction of the contribution of monitored point sources. Other possible foreground contributions have been assessed and are expected to have negligible impact on this result.

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arXiv1999

CMB observations with the Jodrell Bank - IAC interferometer at 33 GHz

The paper presents the first results obtained with the Jodrell Bank - IAC two-element 33 GHz interferometer. The instrument was designed to measure the level of the Cosmic Microwave Background (CMB) fluctuations at angular scales of 1 - 2 degrees. The observations analyzed here were taken in a strip of the sky at Dec = +41 deg with an element separation of 16.7 lambda, which gives a maximum sensitivity to ~1.6 deg structures on the sky. The data processing and calibration of the instrument are described. The sensitivity achieved in each of the two channels is 7 micro K per resolution element. A reconstruction of the sky at Dec = +41 deg using a maximum entropy method shows the presence of structure at a high level of significance. A likelihood analysis, assuming a flat CMB spatial power spectrum, gives a best estimate of the level of CMB fluctuations of Delta Tl = 43 (+13,-12) micro K for the range l = 109 +/- 19; the main uncertainty in this result arises from sample variance. We consider that the contamination from the Galaxy is small. These results represent a new determination of the CMB power spectrum on angular scales where previous results show a large scatter; our new results are in agreement with the theoretical predictions of the standard inflationary cold dark matter models.

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arXiv1999

A 33 GHz interferometer for CMB observations on Tenerife

We describe a new high sensitivity experiment for observing cosmic microwave background (CMB) anisotropies. The instrument is a 2-element interferometer operating at 33 GHz with a ~3 GHz bandwidth. It is installed on the high and dry Teide Observatory site on Tenerife where successful beam-switching observations have been made at this frequency. Two realizations of the interferometer have been tested with element separations of 11.9 lambda and 16.7 lambda. The resulting angular resolution of ~2 deg was chosen to explore the amplitude of CMB structure on the large angular scale side of the Doppler (acoustic) peak. It is found that observations are unaffected by water vapour for more than 70 per cent of the time when the sensitivity is limited by the receiver noise alone. Observations over several months are expected to give an rms noise level of ~10 - 20 micro K covering ~100 resolution elements. Preliminary results show stable operation of the interferometer with the detection of discrete radio sources as well as the Galactic plane at Dec = +41 deg and -29 deg.

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arXiv1999

A counterrotating central component in NGC 5728

We present a detailed study of the stellar kinematics in the barred galaxy NGC 5728 based on I-band photometry and long-slit spectroscopic observations in the region of the near-IR Ca II triplet. The analysis of the stellar line-of-sight velocity distribution (LOSVD) has revealed, in the central regions of the bar, the presence of a cold (v/sigma~2.5) prograde $S$-shaped velocity component that coexists in the central 4 kpc with a fainter and hotter (v/sigma~0.5) counterrotating component. Beyond 4 kpc from the nucleus the LOSVD shows the stellar bar kinematics. The comparison of the radial surface brightness profile of the velocity components with that obtained from an I-band image shows that the counterrotating core follows a r^(1/4) profile, while the S-shaped component does not follows the flat bar surface brightness profile. Several possible scenarios accounting for such kinematic signatures found in the center of the bar in NGC 5728 are discussed.

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arXiv1999

Cosmic Microwave background map making with data between 10 and 90GHz

We use data from the Tenerife 10, 15 and 33 GHz beamswitching experiments along with the COBE 53 and 90 GHz data to separate the cosmic microwave background (CMB) signal from the Galactic signal and create two maps at high Galactic latitude. The new multi-MEM technique is used to obtain the best reconstruction of the two channels. The two maps are presented and known features are identified within each. We find that the Galactic contribution to both the 15 and 33 GHz Tenerife data is small enough to be ignored when compared to the errors in the data and the magnitude of the CMB signal.

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arXiv1998

10 GHz Tenerife CMB observations at 8 degree resolution and their analysis using a new maximum entropy method

The complete set of data from the Tenerife 10 GHz (8 degree FWHM) twin-horn, drift scan experiment is described. These data are affected by both long-term atmospheric baseline drifts and short term noise. A new maximum entropy procedure, utilising the time invariance and spatial continuity of the astronomical signal, is used to achieve a clean separation of these effects from the astronomical signal, and to deconvolve the effects of the beam-switching. We use a fully positive/negative algorithm to produce two-dimensional maps of the intrinsic sky fluctuations. Known discrete sources and Galactic features are identified in the deconvolved map. The data from the 10 GHz experiment, after baseline subtraction with MEM, is then analysed using conventional techniques and new constraints on Galactic emission are made.

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arXiv1997

The IAC-Bartol Cosmic Microwave Background Anisotropy Experiment: Results of the 1994 Campaign

We present the results of a Cosmic Microwave Background (CMB) anisotropy ground-based millimetric experiment sensitive to fluctuations on angular scales of $\sim 2\degg$. Four independent bands centered at 3.3, 2.1, 1.3 and 1.1 mm collected $\sim 550$ hours of observation during the Summer of 1994. The instrument was located on the island of Tenerife at an altitude of 2400 m. The low water-vapor content and the atmospheric stability of the site, combined with new techniques to subtract atmospheric noise, result in the reduction of atmospheric contamination in the lowest frequency channel to a level of $\sim 1.5$~times the instrument noise. Detailed estimations of Galactic foreground contamination show that this contribution is negligible at $|b| \stackrel{>}{_\sim} 12\degg$. Two different multipole bands ($\ell=53^{+22}_{-13}$ and $33^{+24}_{-13}$) are analyzed showing that our technique to subtract the atmospheric contribution is more effective in the multipole band at $\ell=53$. A likelihood analysis of these data reveals the presence of a common signal between the channels at 3.3, 2.1 and 1.3 mm corresponding to a band power estimate of $ \sqrt{\lla (\lla+1) C_{\lla}/(2 π)} = 2.0^{+1.0}_{-0.8} \cdot 10^{-5}$ and $\sqrt{\lla (\lla+1) C_{\lla}/(2 π)} = 4.1^{+2.4}_{-2.2} \cdot 10^{-5}$ for the $\ell =53$ and 33 multipole bands respectively. Calibration uncertainty has been treated as a systematic effect. The level of fluctuations in the $\ell =53$ band is in good agreement with our preliminary analysis presented in Piccirillo \et 1997, with measurements by other experiments working at similar angular scales, and with the predictions of standard Cold Dark Matter (CDM) models.

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arXiv1997

Constraints on cosmological parameters from recent measurements of CMB anisotropy

A key prediction of cosmological theories for the origin and evolution of structure in the Universe is the existence of a `Doppler peak' in the angular power spectrum of cosmic microwave background (CMB) fluctuations. We present new results from a study of recent CMB observations which provide the first strong evidence for the existence of a `Doppler Peak' localised in both angular scale and amplitude. This first estimate of the angular position of the peak is used to place a new direct limit on the curvature of the Universe, corresponding to a density of $Ω=0.7^{+0.8}_{-0.5}$, consistent with a flat Universe. Very low density `open' Universe models are inconsistent with this limit unless there is a significant contribution from a cosmological constant. For a flat standard Cold Dark Matter dominated Universe we use our results in conjunction with Big Bang nucleosynthesis constraints to determine the value of the Hubble constant as $\ho=30-70\kmspmpc$ for baryon fractions $Ω_b=0.05$ to 0.2. For $\ho=50\kmspmpc$ we find the primordial spectral index of the fluctuations to be $n=1.1 \pm 0.1$, in close agreement with the inflationary prediction of $n \simeq 1.0$

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