Showing papers by "A. Gil de Paz published in 2002"
TL;DR: In this paper, optical long-slit spectroscopy and imaging of the protoplanetary nebula CRL 618 was presented, which consists of shock-excited gas, which emits many recombination and forbidden lines, and dust, which scatters light from the innermost regions.
Abstract: In this paper we present optical long-slit spectroscopy and imaging of the protoplanetary nebula CRL 618. The optical lobes of CRL 618 consist of shock-excited gas, which emits many recombination and forbidden lines, and dust, which scatters light from the innermost regions.
51 citations
TL;DR: In this article, the authors present optical long-slit spectroscopy and imaging of the protoplanetary nebula CRL618. The optical lobes consist of shock-excited gas, which emits many recombination and forbidden lines, and dust, which scatters light from the innermost regions.
Abstract: In this paper (paper I) we present optical long-slit spectroscopy and imaging of the protoplanetary nebula CRL618. The optical lobes of CRL618 consist of shock-excited gas, which emits many recombination and forbidden lines, and dust, which scatters light from the innermost regions. From the analysis of the scattered Halpha emission, we derive a nebular inclination of i=24+-6 deg. The spectrum of the innermost part of the east lobe (visible as a bright, compact nebulosity close to the star in the Halpha HST image) is remarkably different from that of the shocked lobes but similar to that of the inner HII region, suggesting that this region represents the outermost parts of the latter. We find a non-linear radial variation of the gas velocity along the lobes.
The largest projected LSR velocities (~80 km/s) are measured at the tips of the lobes, where the direct images show the presence of compact bow-shaped structures. The velocity of the shocks in CRL618 is in the range ~75-200 km/s, as derived from diagnostic line ratios and line profiles. We report a brightening (weakening) of [OIII]5007AA ([OI]6300AA) over the last ~10 years that may indicate a recent increase in the speed of the exciting shocks. From the analysis of the spatial variation of the nebular extinction, we find a large density contrast between the material inside the lobes and beyond them: the optical lobes seem to be `cavities' excavated in the AGB envelope by interaction with a more tenuous post-AGB wind. The electron density, with a mean value n_e~5E3-1E4 cm-3, shows significant fluctuations but no systematic decrease along the lobes, in agreement with most line emission arising in a thin shell of shocked material (the lobe walls) rather than in the post-AGB wind filling the interior of the lobes. (...)
49 citations
TL;DR: In this paper, the uncertainties to be expected in the derivation of galaxy physical properties (star formation history, age, metallicity, reddening) when comparing broad-band photometry to the predictions of evolutionary synthesis models are derived.
Abstract: We have derived the uncertainties to be expected in the derivation of galaxy physical properties (star formation history, age, metallicity, reddening) when comparing broad-band photometry to the predictions of evolutionary synthesis models. We have obtained synthetic colors for a large sample (9000) of artificial galaxies assuming different star formation histories, ages, metallicities, reddening values, and redshifts. The colors derived have been perturbed by adopting different observing errors, and compared back to the evolutionary synthesis models grouped in different sets. The comparison has been performed using a combination of Monte Carlo simulations, a Maximum Likelihood Estimator and Principal Component Analysis. After comparing the input and derived output values we have been able to compute the uncertainties and covariant degeneracies between the galaxy physical properties as function of (1) the set of observables available, (2) the observing errors, and (3) the galaxy properties themselves. In this work we have considered different sets of observables, some of them including the standard Johnson/Cousins (UBVRI) and Sloan Digital Sky Survey (SDSS) bands in the optical, the 2 Micron All Sky Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer (GALEX) bands in the UV, at three different redshifts, z=0.0, 0.7, and 1.4. This study is intended to represent a basic tool for the design of future projects on galaxy evolution, allowing an estimate of the optimal band-pass combinations and signal-to-noise ratios required for a given scientific objective.
28 citations
TL;DR: In this article, the uncertainties to be expected in the derivation of galaxy physical properties (star formation history, age, metallicity, and reddening) when comparing broadband photometry to the predictions of evolutionary synthesis models are derived.
Abstract: We have derived the uncertainties to be expected in the derivation of galaxy physical properties (star formation history, age, metallicity, and reddening) when comparing broadband photometry to the predictions of evolutionary synthesis models. We have obtained synthetic colors for a large sample (~9000) of artificial galaxies by assuming different star formation histories, ages, metallicities, reddening values, and redshifts. The colors derived have been perturbed by adopting different observing errors and compared against the evolutionary synthesis models grouped in different sets. The comparison has been performed using a combination of Monte Carlo simulations, a maximum likelihood estimator, and principal component analysis. After comparing the input and derived output values we have been able to compute the uncertainties and covariant degeneracies between the galaxy physical properties as a function of (1) the set of observables available, (2) the observing errors, and (3) the galaxy properties themselves. In this work we have considered different sets of observables, some of them including the standard Johnson-Cousins (UBVRCIC) and Sloan Digital Sky Survey (SDSS) bands in the optical, the Two Micron All-Sky Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer (GALEX) bands in the UV, at three different redshifts, z = 0.0, 0.7, and 1.4. This study is intended to represent a basic tool for the design of future projects on galaxy evolution, allowing an estimate of the optimal bandpass combinations and signal-to-noise ratios required for a given scientific objective.
24 citations
TL;DR: In this article, the authors have mapped the 12CO J = 1-0 and J = 2-1 line emission in Markarian 86, one of the most metal-deficient blue compact dwarf galaxies so far detected in 12CO.
Abstract: We have mapped the 12CO J = 1-0 and J = 2-1 line emission in Markarian 86, one of the most metal-deficient blue compact dwarf galaxies so far detected in 12CO. The 12CO emission is distributed in a horseshoe-like structure that follows the locus of the most recent star formation regions. The minimum in molecular line emission corresponds to the position of an older, massive nuclear starburst. The H2 mass of the galaxy [in the range of (0.4-5) × 107 M☉] and its morphology have been compared with the predictions of hydrodynamic simulations of the evolution of the interstellar medium surrounding a nuclear starburst. These simulations suggest that the physical conditions in the gas swept out by the starburst could have led to the formation of the ring of molecular gas reported here. This result provides an attractive scenario for explaining the propagation (in a galactic scale) of the star formation in dwarf galaxies.
16 citations
TL;DR: In this article, the authors present an analysis of the integrated properties of the stellar populations in the UCM Survey of Halpha-selected galaxies, including the effects of the nebular continuum, line emission and dust attenuation.
Abstract: We present an analysis of the integrated properties of the stellar populations in the Universidad Complutense de Madrid Survey of Halpha-selected galaxies. In this paper, the first of a series, we describe in detail the techniques developed to model star-forming galaxies using a mixture of stellar populations, and taking into account the observational uncertainties. We assume a recent burst of star formation superimposed on a more evolved population. The effects of the nebular continuum, line emission and dust attenuation are taken into account. We also test different model assumptions including the choice of specific evolutionary synthesis model, initial mass function, star formation scenario and the treatment of dust extinction. Quantitative tests are applied to determine how well these models fit our multi-wavelength observations for the UCM sample. Our observations span the optical and near infrared, including both photometric and spectroscopic data. Our results indicate that extinction plays a key role in this kind of studies, revealing that low- and high-extinction objects may require very different extinction laws and must be treated differently. We also demonstrate that the UCM Survey galaxies are best described by a short burst of star formation occurring within a quiescent galaxy, rather than by continuous star formation. A detailed discussion on the inferred parameters, such as the age, burst strength, metallicity, star formation rate, extinction and total stellar mass for individual objects, is presented in paper II of this series.