170 research outputs found
Stellar indices and kinematics in Seyfert 1 nuclei
No full textThis is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Jiménez-Benito, L., Díza, A.I., Terlevich, R. and E. Terlevich. Stellar indices and kinematics in Seyfert 1 nuclei. Monthly Notices of the Royal Astronomical Society 317 (2000): 907-92
A spectroscopic search for red supergiants in the M33 giant H II region NGC 604
No full textThis is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Terlevich, E., Díaz, A.I., Terlevich, R., González-Delgado, R.M., Pérez, E. and M.L. García Vargas. A spectroscopic search for red supergiants in the M33 giant H II region NGC 604. Monthly Notices of the Royal Astronomical Society 279 (1996): 1219-123
Design and Cahracterization of a 10-Gb/s Dual Drive Z-Cut Ti:LiNbO3 Electrooptical modulator
No full textAbundance determination of multiple star-forming regions in the H II galaxy SDSS J165712.75+321141.4
No full textThis is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Hägele, G.F., García-Benito, R., Pérez-Montero, E., Díaz, Á.I., Cardaci, M.V., Firpo, V., Terlevich, E. and R. Terlevich. Abundance determination of multiple star-forming regions in the H II galaxy SDSS J165712.75+321141.4. Monthly Notices of the Royal Astronomical Society 414 (2011): 272-28
Integral field spectroscopy of H II region complexes: the outer disc of NGC 6946
No full textThis is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. García-Benito, R., Díaz, A., Hägele, G.F., Pérez-Montero, E., López, J., Vílchez, J.M., Pérez, E., Terlevich, E., Terlevich, R., D. Rosa-González. Integral field spectroscopy of H II region complexes: the outer disc of NGC 6946. Monthly Notices of the Royal Astronomical Society 408 (2010): 2234-225
Probing the star formation history of early-type galaxies in clusters
No full textIn this thesis, we present a new photometric catalogue of the local Coma galaxy cluster in the Johnson U- and V- bands. We cover an area of 3360arcmin(^2) of sky, to a depth of V = 20mag in a 13 arcsec diameter aperture, and produce magnitudes for ~ 1400 extended objects in metric apertures from 8.8 to 26arcsec diameters. The mean internal RMS scatter in the photometry is 0.014mag in V, and 0.026mag in U, for Via(_13) < 17mag.We use this photometric catalogue to place limits on the levels of scatter in the colour- magnitude relation (CMR) in the Coma cluster. We subdivide the galaxy population by morphology, luminosity and position on the sky, and analyse the CMR in each of them. The lowest levels of scatter are found in the elliptical galaxies, and the late type galaxies have the highest numbers of galaxies blue-wards of the CMR. We finds signs of decreased scatter and systematically bluer galaxy colours with increasing projected radius from the center of the cluster, and attribute it to a mean galactic age gradient. We find that the typical mass of galaxies within clusters can increase by a factor of two through dissipationless merging without destroying the CMR. We compare the spectral line indices of galaxies in the Coma cluster with their deviation from the mean colour-magnitude relation (CMR). We find that the CMR in Coma is driven primarily by a luminosity-metallicity correlation, however we cannot rule out a contribution from age effects. Colour deviations blue-ward of the mean relation are strongly correlated with the Hydrogen Baimer line series absorption, indicating the presence of a young stellar population in these blue galaxies. We use a wavelet code to suggest an association between X-ray cluster substructure and 'E+A' galaxy activity in high redshift clusters
Correlated X-ray/ultraviolet/optical variability in the very low mass AGN NGC 4395
No full textWe report the results of a 1-yr Swift X-ray/ultraviolet (UV)/optical programme monitoring the dwarf Seyfert nucleus in NGC4395 in 2008-2009. The UV/optical flux from the nucleus was found to vary dramatically over the monitoring period, with a similar pattern of variation in each of the observed UV/optical bands (spanning 1900-5500 Å). In particular, the luminosity of NGC4395 in the 1900 Å band changed by more than a factor of 8 over the monitoring period. The fractional variability was smaller in the UV/optical bands than that seen in the X-rays, with the X-ray/optical ratio increasing with increasing flux. Pseudo-instantaneous flux measurements in the X-ray and each UV/optical band were well correlated, with cross-correlation coefficients of ≥0.7, significant at 99.9per cent confidence. Archival Swift observations from 2006 sample the intra-day X-ray/optical variability on NGC4395. These archival data show a very strong correlation between the X-ray and b bands, with a cross-correlation coefficient of 0.84 (significant at >99per cent confidence). The peak in the cross-correlation function is marginally resolved and asymmetric, suggesting that X-rays lead the b band, but by ≤1h. In response to recent (2011 August) very high X-ray flux levels from NGC4395 we triggered Swift target of opportunity observations, which sample the intra-hour X-ray/UV variability. These observations indicate, albeit with large uncertainties, a lag of the 1900 Å band behind the X-ray flux of ∼400s. The tight correlation between the X-ray and UV/optical lightcurves, together with the constraints we place on the lag time-scale, is consistent with the UV/optical variability of NGC4395 being primarily due to reprocessing of X-ray photons by the accretion disc
Constraining the dark energy equation of state using alternative cosmic tracers
No full textWe propose to use the H II galaxies redshift-distance relation, measured by means of
their L(Hβ) −δ correlation, in order to determine the Hubble function to intermediate
and high redshifts, in an attempt to constrain the dark energy equation of state parameters
solution space, as an alternative to the cosmological use of type Ia supernovae.
So that we can use effectively high redshift H II galaxies as probes for dark energy
equation of state parameters, we must reassess the L(Hβ) −δ distance estimator,
minimizing the observational uncertainties and taking care of the possible associated
systematics, such as stellar age, gas metallicity, reddening, environment and morphology.
In order to reassess the L(Hβ) −δ distance estimator, we have selected and observed
a sample of 128 H II galaxies from the local universe. From a preliminary analysis,
which does not yet take care of the possible systematic effects, we have obtained a
relation given by log10 L(Hβ) = (3.95 ± 0.10) log10 δ + (34.68 ± 0.17), which has an
associated dispersion, δ log10 L(Hβ) = 0.299, similar to the one obtained in previous
works (Melnick et al., 1988).
The selection of a intermediate and high redshift sample of H II galaxies, its accurate
observation and analysis, using the previously reassessed L(Hβ)−δ distance estimator,
is a crucial task to be accomplished in order to realize our final objectives and it will
realized during my doctoral research.Se propone utilizar la relación corrimiento al rojo - distancia para galaxias H II, medida
mediante su correlación L(Hβ) −δ, con el propósito de determinar la función de Hubble
a corrimientos al rojo intermedios y altos, en un intento para restringir el espacio de
soluciones de los parámetros de la ecuación de estado de la energía oscura; como una
alternativa al uso cosmológico de supernovas de tipo Ia.
De modo que sea posible el uso efectivo de galaxias H II a alto corrimiento al rojo
como trazadores de los parámetros de la ecuación de estado de la energía oscura, se
hace necesario re-evaluar el estimador de distancia L(Hβ) −δ, minimizando las incertidumbres
observacionales y tomando en cuenta los posibles errores sistemáticos asociados,
tales como edad estelar, metalicidad del gas, enrojecimiento, medio ambiente y
morfología.
Con la intención de re-evaluar el estimador de distancia L(Hβ) −δ, se ha seleccionado
y observado una muestra de 128 galaxias H II del universo local. De un análisis
preliminar, que aún no toma en cuenta los posibles efectos sistemáticos, se ha obtenido
una relación dada por log10 L(Hβ) = (3.95 ± 0.10) log10 δ + (34.68 ± 0.17), la cual
tiene una dispersión asociada, δ log10 L(Hβ) = 0.299, similar a la que se ha obtenido
en trabajos previos (Melnick et al., 1988).
La selección de una muestra de galaxias H II a corrimiento al rojo intermedio y alto,
su observación precisa y análisis, utilizando el estimador de distancia L(Hβ) − δ previamente
re-evaluado, es una tarea crucial a llevar a cabo para conseguir los objetivos
planteados y sera efectuada durante la investigación doctoral
Determinación de H0 a partir de regiones y galaxias HII comparando Cefeidas y TRGB como calibradores de distancia
No full textHoy en día existe una importante discrepancia en el valor de H0,la así llamada tensión de Hubble, que reside en la inconsistencia entre los valores obtenidos en el universo cercano usando principalmente supernovas Ia (SNIa) y grandes distancias a partir del análisis de la radiación de fondo de microondas (CMB). Esta tensión ha llevado a dos posibles hipótesis para su explicación: o los métodos directos tiene efectos sistemáticos que no se han tomado en cuenta, como por ejemplo en la calibración de las SNIa a partir de las cefeidas, o bien se necesita nueva física para explicar la discrepancia. En esta tesis exploro la primera posibilidad, es decir, que el esquema de distancias de las SNIa basado en la relación periodo-luminosidad de las cefeidas este afectada por sistemáticos aún no reconocidos. Motivado por esto y con el objetivo de utilizar estimadores de distancia independientes de las SNIa, analizo todos los módulos de distancia de galaxias determinadas por cefeidas y/o la punta de las gigantes rojas (TRGB) publicados en los últimos 20 años, clasificando los datos en cinco conjuntos de calibradores de cefeidas y uno de TRGB, dependiendo del efecto sistemáticos de la metalicidad y sus tipos de error. Estos conjuntos los uso para calibrar 36 regiones gigantes HII y 181 galaxias HII de la relación L − σ, que es la correlación entre la luminosidad y la dispersión de velocidades de la línea Hβ, para los objetos antes mencionados. Para esto, calculo simultáneamente la pendiente y el punto cero de la relación L − σ, y H0 usando un método MCMC llamado Nested Sampling, variando el límite superior en el corrimiento al rojo para analizar posibles cambios en los parámetros asociados con la distancia media de las HIIG. Luego de analizar y discutir los efectos sistemáticos que podrían afectar los resultados, obtuve con la muestra completa del conjunto de cefeidas un valor para H0 de 74.1 ± 3.8 km s−1 Mpc−1 con variaciones del valor central que van de −1.8 a +0.4 kms −1 Mpc−1, dependiendo del conjunto de calibrador. Este valor es consistente con el resultado más actual de SNIa. Por otra parte, usando el conjunto completo de TRGB obtuve un valor de H0 de 67.3 ± 3.8 km s−1 Mpc−1 coincidente con el valor obtenido por colaboración Planck a partir de los datos del CMB. Estos resultados sugieren que quizás existen sistemáticos en el esquema de las cefeidas que aun no se han explorado.A discrepancy in the H0 value, the so called Hubble tension, resides in the inconsistency between the values obtained in the near Universe mostly using supernovae Ia (SNIa) and at large distances from the analysis of the cosmic microwave background (CMB). This tension has led to two possible hypothesis to explain it: or there are systematic effects on the direct methods that have not been taken into account (for example the SNIa calibration from cepheids), or new physics is needed to explain the discrepancy. In this thesis I explore the first one, is the SNIa distance scheme based on the cepheids period-luminosity relation being affected by unrecognized systematics? Motivated by this, and to use an independent SNIa distance estimator, I analyze all the cepheid or tip of the giant branch (TRGB) distance modulus published in the last 20 years dividing in five cepheid sets and one TRGB set depending on their systematics and their error types. I use these sets to calibrate 36 giant HII regions and 181 HII galaxies (HIIG) in the so called L − σ relation that is the correlation between the luminosity and the velocity dispersion of the Hβ emission line for the aforementioned objects. To do this, I compute the L − σ slope, the zero point and H0 simultaneously using an MCMC method called Nested Sampling, varying the redshift upper limit to analyze possible changes in the parameters associated with the mean HIIG distance. After the systematic analysis and discussion that could affect the results and using all the available cepheid data, I obtained an H0 value of 74.1 ± 3.8 km s−1 Mpc−1 with variations in the central value ranging from −1.8 to +0.4 km s−1 Mpc−1 depending on the set consistent with most recent SNIa results. On the other hand using the complete TRGB set I obtained an H0 value of 67.3 ± 3.8 km s−1 Mpc−1 coincident with Planck collaboration from the CMB data. These results suggest that there may be some systematics in the distance scale determination that have not been explored yet
Implications of the kinematical structure of circumnuclear star-forming regions on their derived properties
No full textWe review the results of high dispersion spectroscopy of 17 circumnuclear star forming regions (CNSFRs) in 3 nearby early spiral galaxies, NGC 2903, NGC 3310 and NGC 3351.We find that single Gaussian fitting to the Hβ and [Oiii]λ5007 ˚A line profiles results in velocity dispersions around 32 km s−1 and 52 km s−1, respectively, while the IR Caii triplet cross-correlation technique provides stellar velocity dispersion values close to 50 km s−1. Even though multiple kinematical components are present, the relation between gas velocity dispersion and Balmer emission line luminosity (L-σ relation) reproduces the correlation for disk giant Hii regions albeit with a larger scatter. The scatter in the L-σ relation is considerably reduced when theoretical evolutionary corrections are applied suggesting that an age range is present in the sample of CNSFRs. To analyse the observed complex profiles, we performed multiple Gaussian component fits to the Hβ and [Oiii]λ5007 ˚A lines obtaining optimal fits with two Gaussians of different width. These best fits indicate that the narrower component has average velocity dispersion close to 23 km s−1 while the broader component shows average values in the range 50-60 km s−1 for both lines, close to the observed stellar velocity dispersions. The fluxes of the broad and narrow Hβ components are similar. This is not the case for [Oiii]λ5007 ˚A for which the broad components have higher fluxes than the narrow ones, thus producing a clear segregation in their [Oiii]/Hβ ratios. We suggest a possible scenario for understanding the behaviour of CNSFRs in the L-σ and σgas-σ∗ diagrams involving an inner gaseous disk responsible for the narrow component of the emission lines. Our main conclusion is that the presence of different kinematical components with similar total fluxes in the emission line spectrum of CNSFRs raises important doubts regarding properties of the ionized gas derived from global line ratios obtained with low resolution spectroscopy in star-forming regions in the central regions of early type galaxies. Given the ubiquity of these star-forming systems, ionized gas analyses should be done preferably from high dispersion spectra with high spatial resolution.Fil: Hägele, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Universidad Autónoma de Madrid; EspañaFil: Díaz, Angeles. Universidad Autónoma de Madrid. Facultad de Ciencias; EspañaFil: Terlevich, Roberto. Instituto Nacional de Astronomía, Óptica y Electrónica; México. University of Cambridge; Reino UnidoFil: Terlevich, Elena. Instituto Nacional de Astronomía, Óptica y Electrónica; MéxicoFil: Bosch, Guillermo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Cardaci, Monica Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Universidad Autónoma de Madrid; Españ
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