Showing papers by "Rosa M. González Delgado published in 2001"
TL;DR: In this paper, the authors used the stellar features in the HST/GHRS ultraviolet spectrum and the optical emission lines to identify an ~5 Myr old, very little reddened stellar population as the main source of UV light in the central regions of the starburst galaxy NGC 7714, and they found that the young burst responsible for the UV light represents only a small part of an extended episode of enhanced star formation initiated a few times 108 yr ago.
Abstract: We combine existing multiwavelength data (including an HST/GHRS UV spectrum and a ground-based optical spectrum) with unpublished HST/WFPC2 images, near-IR photometry, and K-band spectroscopy. We use these data to constrain the young, the intermediate-age, and the old stellar populations in the central regions of the starburst galaxy NGC 7714. In a previous paper the stellar features in the HST/GHRS ultraviolet (UV) spectrum and the optical emission lines were used to identify an ~5 Myr old, very little reddened stellar population as the main source of UV light in the central ~330 pc. The optical data indicated the existence of an older population. The nature of the latter is investigated here. Stellar absorption features in the optical and the near-IR are used to break partly the strong degeneracy between the effects of aging and those of the inhomogeneous dust distribution on the UV-optical-IR colors. Consistency with far-IR, X-ray, and radio data is also addressed. The successful models have essential features in common. We find that the young burst responsible for the UV light represents only a small part of an extended episode of enhanced star formation, initiated a few times 108 yr ago. The star formation rate is likely to have varied on this timescale, averaging about 1 M☉ yr-1. The mass of young and intermediate-age stars thus formed equals at least 10% of the mass locked in preexisting stars of the underlying spiral galaxy nucleus, and fractions around 25% are favored. The spectrophotometric star formation timescale is long compared to the ~110 Myr elapsed since closest contact with the neighboring NGC 7715, according to the 1992 dynamical models of Smith & Wallin. The initial trigger of the starburst thus remains elusive. NGC 7714 owes its brightness in the UV to a few low extinction lines of sight toward young stars. Our results based on the integrated spectrophotometry of the central ~330 pc are supported by high-resolution images of this area. The different extinction values obtained when different spectral indicators are used result naturally from the coexistence of populations with various ages and obscurations. The near-IR continuum image looks smoothest, as a consequence of lower sensitivity to extinction and of a larger contribution of old stars. We compare the nuclear properties of NGC 7714 with results from studies in larger apertures. We emphasize that the global properties of starburst galaxies are the result of the averaging over many lines of sight with very diverse properties in terms of obscuration and stellar ages. The overall picture is strongly reminiscent of the other nearby "prototypical" starburst, M82.
43 citations
TL;DR: In this article, a radial corrugation in the velocity field of the spiral galaxy NGC 5427 was detected, in Hα emission, showing that the maximum amplitude of the sinusoidal line variations are displaced some 500 pc from the central part of spiral arms, whereas the peak redshifted velocities are located some 500pc downstream of the arm.
Abstract: Here we report the detection, in Hα emission, of a radial corrugation in the velocity field of the spiral galaxy NGC 5427. The central velocity of the Hα line displays coherent, wavy-like variations in the vicinity of the spiral arms. The spectra along three different arm segments show that the maximum amplitude of the sinusoidal line variations are displaced some 500 pc from the central part of the spiral arms. The peak blueshifted velocities appear some 500 pc upstream of the arm, whereas the peak redshifted velocities are located some 500 pc downstream of the arm. This kinematical behavior is similar to the one expected in a galactic bore generated by the interaction of a spiral density wave with a thick gaseous disk, as recently modeled by Martos & Cox.
21 citations
01 Jan 2001
TL;DR: In this article, a simple population synthesis scheme was proposed to recognize composite starburst+Seyfert 2 nuclei from a few easy-to-obtain optical measurements.
Abstract: We present a simple population synthesis scheme which recognizes composite starburst+Seyfert 2 nuclei from a few easy-to-obtain optical measurements. Composite systems seem to evolve towards less luminous Seyfert 2's which do not harbor detectable circum-nuclear starbursts. We encourage applications of this cheap diagnostic tool to large samples of Seyfert 2's, as well as its extension to other activity classes, in order to test and refine this evolutionary scenario.
2 citations
Posted Content•
TL;DR: In this article, a simple population synthesis scheme was proposed to recognize composite starburst+Seyfert 2 nuclei from a few easy-to-obtain optical measurements.
Abstract: We present a simple population synthesis scheme which recognizes composite starburst+Seyfert 2 nuclei from a few easy-to-obtain optical measurements. Composite systems seem to evolve towards less luminous Seyfert 2's which do not harbor detectable circum-nuclear starbursts. We encourage applications of this cheap diagnostic tool to large samples of Seyfert 2's, as well as its extension to other activity classes, in order to test and refine this evolutionary scenario.
1 citations
Posted Content•
TL;DR: In this paper, the authors discuss evidence in favor of the Starburst-AGN connection, as well as possible differences in terms of star formation activity between Sy1 and Sy2, that suggest an alternative interpretation of the Seyfert classification to that proposed by the standard unification model.
Abstract: Observations at ultraviolet, optical and near-infrared wavelengths have shown the existence of recent star formation in the nuclear regions of Seyfert 2 (Sy2) galaxies that suggest a connection between the Starburst and the Seyfert phenomenon. According with the standard unified models of AGN circumnuclear starbursts also have to be present (and in the same numbers) in Sy1 as in Sy2 galaxies. This review discuss evidence in favor of the Starburst-AGN connection, as well as possible differences in terms of star formation activity between Sy1 and Sy2, that suggest an alternative interpretation of the Seyfert classification to that proposed by the standard unification model.
Posted Content•
TL;DR: In this paper, a review deals with properties of very young stellar clusters which are in the nebular phase and are embedded in photoionized regions (classical extragalactic HII regions (RHIIs) or starburst galaxies).
Abstract: This review deals with properties of very young (< 10-20 Myr) stellar clusters which are in the nebular phase and are embedded in photoionized regions (classical extragalactic HII regions (RHIIs) or starburst galaxies). Based on the analysis of the integrated light of these clusters at the UV and optical wavelengths, different techniques are discussed that allow to estimate in consistent the stellar content and the evolutionary state of the ionizing clusters.