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Papers by rosa delgado

Astrophysical Journal, 2004

In a recently completed survey of the stellar populations properties of LINERS and LINER/HII Tran... more In a recently completed survey of the stellar populations properties of LINERS and LINER/HII Transition Objects (TOs), we have identified a numerous class of galactic nuclei which stand out because of their conspicuous 10 8−9 yr populations, traced by high order Balmer absorption lines and other stellar indices. These objects were called "Young-TOs", since they all have TO-like emission line ratios. In this paper we extend this previous work, which concentrated on the nuclear properties, by investigating the radial variations of spectral properties in Low Luminosity Active Galactic Nuclei (LLAGN). Our analysis is based on high signal to noise long-slit spectra in the 3500-5500Å interval for a sample of 47 galaxies. The data probe distances of typically up to 850 pc from the nucleus with a resolution of ∼ 100 pc (∼ 1 ′′ ) and S/N ∼ 30. Stellar population gradients are mapped by the radial profiles of absorption line equivalent widths and continuum colours along the slit. These variations are further analyzed by means of a decomposition of each spectrum in terms of template galaxies representative of very young (≤ 10 7 yr), intermediate age (10 8−9 yr) and old (10 10 yr) stellar populations.

Astrophysical Journal Supplement Series, 1999

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related proper... more Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by . We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by . Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 10 6 to 10 9 yr.

Astronomical Journal, 2008

In several studies of Low Luminosity Active Galactic Nuclei (LLAGNs), we have characterized the p... more In several studies of Low Luminosity Active Galactic Nuclei (LLAGNs), we have characterized the properties of the stellar populations in LINERs and LINER/HII Transition Objects (TOs). We have found a numerous class of galactic nuclei which stand out because of their conspicuous 0.1-1 Gyr populations. These nuclei were called "Young-TOs" since they all have TO-like emission line ratios. To advance our knowledge of the nature of the central source in LLAGNs and its relation with stellar clusters, we are carrying out several imaging projects with the Hubble Space Telescope (HST) at near-UV, optical and near-IR wavelengths. In this paper, we present the first results obtained with observations of the central regions of 57 LLAGNs imaged with the WFPC2 through any of the V (F555W, F547M, F614W) and I (F791W, F814W) filters that are available in the HST archive. The sample contains 34% of the LINERs and 36% of the TOs in the Palomar sample. The mean spatial resolution of these images is 10 pc. With these data we have built an atlas that includes structural maps for all the galaxies, useful to identify compact nuclear sources and, additionally, to characterize the circumnuclear environment of LLAGNs, determining the frequency of dust and its morphology. The main results obtained are: 1) We have not found any correlation between the presence of nuclear compact sources and emission-line type. Thus, nucleated LINERs are as frequent as nucleated TOs. 2) The nuclei of "Young-TOs" are brighter than the nuclei of "Old-TOs" and LINERs. These results confirm our previous results that Young-TOs are separated from other LLAGNs classes in terms of their central stellar population properties and brightness. 3) Circumnuclear dust is detected in 88% of the LLAGNs, being almost ubiquitous in TOs. 4) The dust morphology is complex and varied, from nuclear spiral lanes to chaotic filaments and nuclear disk-like structures. Chaotic filaments are as frequent as dust spirals; but nuclear disks are mainly seen in LINERs. These results suggest an evolutionary sequence of the dust in LLAGNs, LINERs being the more evolved systems and Young-TOs the youngest.

Monthly Notices of The Royal Astronomical Society, 2005

Astrophysical Journal, 1997

... GR J. HECKMAN,2,3,4 GONZAçLEZ-DELGADO,2,5 LEITHERER,2,5 MEURER,2, 3 KROLIK,2,3 AS A. AND A. W... more ... GR J. HECKMAN,2,3,4 GONZAçLEZ-DELGADO,2,5 LEITHERER,2,5 MEURER,2, 3 KROLIK,2,3 AS A. AND A. WILSON,2,4,6 KORATKAR,2,5 KINNEY2,5 Received 1996 October 9 ; accepted 1997 January 6 ABSTRACT There ...

Monthly Notices of The Royal Astronomical Society, 2005

We present a spectroscopic atlas of active galactic nuclei covering the region around the λλ8498,... more We present a spectroscopic atlas of active galactic nuclei covering the region around the λλ8498, 8542, 8662 Calcium triplet (CaT). The sample comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst and 6 normal galaxies. The spectra pertain to the inner ∼ 300 pc in radius, and thus sample the central kinematics and stellar populations of active galaxies. The data are used to measure stellar velocity dispersions (σ ⋆ ) both with cross-correlation and direct fitting methods. These measurements are found to be in good agreement with each-other and with those in previous studies for objects in common. The CaT equivalent width is also measured. We find average values and sample dispersions of W CaT of 4.6 ± 2.0, 7.0± and 7.7±1.0 A for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We further present an atlas of [SIII]λ9069 emission line profiles for a subset of 40 galaxies. These data are analyzed in a companion paper which addresses the connection between stellar and Narrow Line Region kinematics, the behaviour of the CaT equivalent width as a function of σ ⋆ , activity type and stellar population properties.

Astrophysical Journal, 2001

We report the results of a spectroscopic investigation of a sample of 20 of the brightest type 2 ... more We report the results of a spectroscopic investigation of a sample of 20 of the brightest type 2 Seyfert nuclei. Our goal is to search for the direct spectroscopic signature of massive stars and thereby probe the role of circumnuclear starbursts in the Seyfert phenomenon. The method used is based on the detection of the higher order Balmer lines and He I lines in absorption and the Wolf-Rayet feature at ~4680 Å in emission. These lines are strong indicators of the presence of young (a few Myr) and intermediate-age (a few 100 Myr) stellar populations. In over half the sample, we have detected He I and/or strong stellar absorption features in the high-order (near-UV) Balmer series together with relatively weak lines from an old stellar population. In three others we detect a broad emission feature near 4680 Å that is most plausibly ascribed to a population of Wolf-Rayet stars (the evolved descendants of the most massive stars). We therefore conclude that the blue and near-UV light of over half of the sample is dominated by young and/or intermediate age stars. The ``young'' Seyfert 2 galaxies have larger far-IR luminosities, cooler mid/far-IR colors, and smaller [O III]/Hβ flux ratios than the ``old'' ones. These differences are consistent with a starburst playing a significant energetic role in the former class. We consider the possibility that there may be two distinct subclasses of Seyfert 2 nuclei (``starbursts'' and ``hidden broadline regions'' [BLRs]). However, the fact that hidden BLRs have been found in three of the ``young'' nuclei argues against this and suggests that nuclear starbursts may be a more general part of the Seyfert phenomenon.

Astrophysical Journal, 2004

We present a study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). ... more We present a study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). Our goal is to search for spectroscopic signatures of young and intermediate-age stars and to investigate their relationship with the ionization mechanism in LLAGNs. The method used is based on the stellar population synthesis of the optical continuum of the innermost (20-100 pc) regions in these galaxies. For this purpose, we have collected high spatial resolution optical (2900-5700 Å) STIS spectra of 28 nearby LLAGNs that are available in the Hubble Space Telescope archive. The analysis of these data is compared with a similar analysis also presented here for 51 ground-based spectra of LLAGNs. Our main findings are as follows: (1) No features due to Wolf-Rayet stars were convincingly detected in the STIS spectra. (2) Young stars contribute very little to the optical continuum in the ground-based aperture. However, the fraction of light provided by these stars is higher than 10% in most of the weak-[O I] ([OI]/Hα<=0.25) LLAGN STIS spectra. (3) Intermediate-age stars contribute significantly to the optical continuum of these nuclei. This population is more frequent in objects with weak than with strong [O I]. Weak-[O I] LLAGNs that have young stars stand out for their intermediate-age population. (4) Most of the strong-[O I] LLAGNs have predominantly old stellar population. A few of these objects also show a featureless continuum that contributes significantly to the optical continuum. These results suggest that young and intermediate-age stars do not play a significant role in the ionization of LLAGNs with strong [O I]. However, the ionization in weak-[O I] LLAGNs with young and/or intermediate-age populations could be due to stellar processes. A comparison of the properties of these objects with Seyfert 2 galaxies that harbor a nuclear starburst suggests that weak-[O I] LLAGNs are the lower luminosity counterparts of the Seyfert 2 composite nuclei. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based on observations made with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.