The role of stars and starbursts in AGN has been a recurring issue for nearly as long as AGN have been recognized as hosts of interesting phenomena. The heated “starburst versus monster” controversy of the 80's and 90's was gradually replaced by “starburst plus monster” studies, as observational work in the past decade has firmly established that accretion onto a super-massive black-hole and star-formation coexist in many galactic nuclei. Whereas the physical link between starbursts and AGN remains unclear, there remains no doubt that starbursts affect a number of properties traditionally associated to the AGN alone, such as the so called “featureless continuum”, emission line ratios and luminosities. This contribution glosses over some of the techniques used to diagnose stellar populations in AGN, focusing on recent results and how this type of work can lead us well beyond what became known as the starburst-AGN connection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using adaptive optics on Keck and the VLT in the H- and K-bands, we have begun a project to probe the dynamics and star formation around AGN on scales of 0.1″. The stellar content of the nucleus is traced through the 2.29 µm CO 2-0 and 1.62 µm CO 6-3 absorption bandheads. These features are directly spatially resolved, allowing us to measure the extent and distribution of the nuclear star forming region. The dynamics are traced through the 2.12 µm H2 1-0 S(1) and 1.64 µm [FeII] emission lines, as well as stellar absorption features. Matching disk models to the rotation curves at various position angles allows us to determine the mass of the stellar and gas components, and constrain the mass of the central black hole. In this contribution we summarise results for the two type 1 AGN Mkn 231 and NGC 7469.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

LLAGN that include low-ionization nuclear emission-line regions (LINERs), and transition-type objects (TOs) represent the most common type of nuclear activity. Here, a study of the central stellar population of LLAGN is presented. Our goal is to search for spectroscopic signatures of young and intermediate age stars, and to investigate their relationship with the ionization mechanism in LLAGN. The method used is based on the stellar population synthesis of the UV-optical continuum of the innermost (20-100 pc) regions in these galaxies. Half of the LINERs and TOs of the Palomar catalogue are analysed. It is found that weak-[OI] ([OI]/Hα≤0.25) LLAGN have an intermediate age stellar population that dominates the optical light. But young stellar clusters dominate the UV continuum in these objects. These clusters can co-exist with a black-hole in spatial scales of a few pc. Most of the strong-[OI] LLAGN have a predominantly old stellar population. These results suggest that young and intermediate age stars do not play a significant role in the ionization of LLAGN with strong [OI].To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this paper we report on our recent results connected with the direct environment of the super massive black hole of the Milky Way. The data are obtained using the VLT facilities (ISAAC and NAOS/CONICA instruments) in the near- and mid-infrared wavelength ranges. We provide a calibration of the foreground and local differential (in wavelength and spatially) extinction of the Galactic Center and report on the discovery of a new complex of infrared excess sources (possibly young stars) located at the northern part of the IRS 13 cluster. Finally, we discuss the origin of filamentary structures observed in the L-band images.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the analysis of Hubble Space Telescope blue spectra at intermediate spectral resolution for the nuclei of 23 nearby disk galaxies. These objects were selected to have nebular emission in their nuclei, and span a range of emission-line classifications as well as Hubble types. Here we focus on the stellar population as revealed by the continuum spectral energy distribution measured within the central 0.″13 (∼8 pc) of these galaxies. The data were modeled with linear combinations of single-age stellar population synthesis models. The large majority (∼80%) of the surveyed nuclei have spectra whose features are consistent with a predominantly old ($\gtrsim 5 \times 10^9$ yr) stellar population. Approximately 25% of these nuclei show evidence of a component with age younger than 1 Gyr, with the incidence of these stars related to the nebular classification. Successful model fits imply an average reddening corresponding to AV∼0.4 mag and stellar metallicity of (1–2.5)$Z_\odot$. Our findings reinforce the picture wherein Seyfert nuclei and the majority of low-ionization nuclear emission-line regions (LINERs) are predominantly accretion-powered, and suggest that much of the central star formation in HII nuclei is actually circumnuclear.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

WFPC2 continuum images of the low metallicity Blue Compact Dwarf Galaxy SBS 0335-052 revealed 6 intense point source that were deemed to be super star clusters. Subsequent observations with NICMOS in the infrared continuum and Paschen α reveals that only 2 of the sources have very young stars with the other point sources as clusters that may have ended their episodes of star formation. The optical images show a probable supernova created cavity to the north of the present clusters, while the currently active star forming clusters lie at the southern end of the cluster. This indicates a possible string of induced star formation propagating from the north to the south. The presence of a large number of O stars in a small volume raises the question of whether super star clusters might be the breeding grounds for intermediate mass black holes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Stellar velocity dispersions in AGN are useful indicators of the black-hole mass (through the M[bull ]−σ[sstarf ] relation) and nuclear stellar populations (through the M/L ratio). We have collected near-infrared spectra of ∼40 Seyferts in the CaII triplet range in order to measure σ[sstarf ] and investigate the connection between stellar populations and AGN properties. In this poster we present a comparison between two methods to measure velocity dispersions: (1) direct fitting (DFM) and (2) cross-correlation (CCM). (1) In DFM the spectra in the CaII triplet range is modeled as a combination of a broadened and shifted stellar spectrum (observed through the same instrumental setup) and a featureless continuum. This method has the advantage of making it easy to mask out noisy regions and sky residuals. (2) CCM converts the width of the star-galaxy cross-correlation function onto a velocity dispersion. We find that these methods yield velocity dispersions consistent to within 20 km s−1 on-average. Our results are consistent to within 20 km s−1 with those objects available in the literature.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss results of the mapping of both the stellar and gaseous kinematics of the nuclear region of 4 nearby Seyfert galaxies, on the basis of GMOS IFU observations in the spectral region of the CaII triplet (8500Å). We do not find in any of these galaxies central drops (within the central hundred parsecs or so) in the stellar velocity dispersions, as recently reported in the literature for a number of Seyferts. However, we do conclude that apparent drops are observed when there is contamination of the CaII triplet absorption lines by underlying line emission. When extended gas emission ([SIII]9068Å) is observed, the gas velocity field differs from the stellar velocity field. The latter is usually consistent with the classical “spider diagram” characteristic of disk galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Local HII galaxies present a Fundamental Plane of [L–σ] where either the equivalent width of Hβ or the oxygen abundance O/H act as a second parameter. These relations are powerful cosmological distance indicators since emission line galaxies may be found to high redshifts, though some caution must be taken till systematic effects are better understood.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Measuring stellar velocity dispersion (σ) in Narrow-Line Seyfert 1 (NLS1) with optical spectra, can be very difficult because of the large and bright Fe II multiplets, which completely suppress the typically used stellar absorption lines. Indeed, σ values are to date available only for 2 NLS1s. Here we present new σ measurements of three NLS1s observed in the spectral range centered around the Ca II triplet (λ∼8600Å). Moreover, we compare σ with the gaseous velocity dispersion finding that the σ = FWHM([O III]5007Å)/2.35 relation (Nelson & Whittle 1995) is not satisfied by our galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the status of our study of the central region of M 83. Recently a binary mass concentration at the nucleus was suggested by Thatte et al. (2000), and we determined the possible position of the optically hidden mass concentration with 2D Hα kinematics. We continue our study of this region trough IR 3D spectroscopy performed with CIRPASS, attached to the Gemini South telescope. Almost 1500 spectra were obtained, centered in the wavelength 1.3 μm. The velocity field in a region of 13″ × 9″ around the optical nucleus is resolved, with 0.36″ (6.4 pc) sampling. We confirm that the optical nucleus of M 83 is not located at the most important center of symmetry of the velocity field. The largest black hole that could fit to the circular motion in this kinematic center should have a mass less than $2\times10^7M_{\odot}$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

NGC 1241 is a Sy 2 galaxy with a 1.4 kpc circumnuclear ring (CNR) of star formation revealed in Paα. A 0.3 kpc long Paα emitting bar centered on the nucleus is present, apparently without associated absorption features. GEMINI (+QUIRC+Hokupa) IR pixel-photometry reveals instead an azimuthally symmetric (J−Ks) color which is redder at the nucleus than at the CNR. This property may well be due to the increasing importance of dust when going from the ring inward into the nucleus. Nevertheless the (V−H) color does not indicate special absorption conditions in the nucleus with respect to the CNR, and no absorption features are evident, as normally expected near emitting bars. Then, we propose as an alternative explanation an excess of C-stars in the nuclear region which decreases outwards until reaching the CNR and its colors. We have compared the pixel color-magnitude diagram with the 2-MASS (J−Ks) vs. Ks diagram for the Large Magellanic Cloud: about 5×102 C-stars and 2.5×104 AGB Oxygen-rich stars inside r∼50 pc, are enough to reproduce the observed nuclear tip in the diagram. This stars would release gas that, gravitationally bounded, pollutes the nuclear environment and could amount 10−2 to 10−1 M$_{\odot}$ yr−1 of fuel for the central engine during the lifetime of stars with masses 2 M$_{\odot}\lt M_{CStars} \lt 6{\rm M}_{\odot}$. This scenario may also explain the observed increased strength of the CN-bands in the stellar populations of Sy 2 nuclei, and the recent claim of a significant contribution of intermediate age stars to the optical continuum of low luminosity AGNs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present an X-ray binary population synthesis model, and use it to simulate the evolution of X-ray binaries formed in a burst of star formation of duration 20 Myr and star-formation rate 10 M$_{\odot}$ yr−1. We find that the X-ray luminous phase persists long after the star-formation episode has ended. The 2-10 keV X-ray luminosity can reach values of 1040−1041 erg s−1, comparable to those of some Seyfert galaxies. These models are directly applicable to starburst galaxies as well as LINERs powered by vigorous star formation.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have established under which conditions core collapse of a spherical cluster occurs before massive stars have time to evolve off the main sequence (MS). We consider cluster central velocity dispersions of 100 km s−1 and higher, appropriate for galactic nuclei. At such high velocities, binary stars play little dynamical role and are therefore neglected. On the other hand whether collisions allow the growth of very massive stars (VMS, with $\ensuremath{M_{\ast}} \gg 100\,\ensuremath{M_{\odot}}$) or, on the contrary, grind them down is a central unknown addressed in this work. We find that, in spite of the high relative velocities, run-away growth of a VMS, a likely progenitor for an intermediate-mass BH (IMBH), occurs in all clusters with short enough a core collapse time.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a numerical code to synthesize the stellar population of galaxies, using the observed flux as observable, for the visible and IR range This code is an evolution of a previous one, which used the equivalent widths.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present simulation results about the interplay between super star clusters (SSCs) and the host dark-matter (DM) halo, with emphasis on the formation of bulges in very late-type galaxies. Simulations show that the NFW halo close to a stable state has no significant response to sinking of circumnuclear SSCs. Generally speaking, while the halo becomes hotter, its central cusp survives. The structures of the formed bulges are similar to what we obtained with fixed NFW halos, but the bulge formation fraction at various stages are smaller.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a new method to decompose the stellar population mixtures in galaxies. The method combines the spectra of simple stellar populations (SSP) of different ages and metallicities, computed with the recently published high spectral resolution evolutionary synthesis models of Bruzual & Charlot (2003). Statistical mechanics techniques, based on Markov Chain Monte Carlo methods, are used in the search for the combination of SSPs which best matches an observed spectrum. The spectral base covers 10 ages and 3 metallicities. The method provides the Star Formation History (SFH) expressed in a population vector $\vec{x}$, whose components represent the fractional contribution of each SSP to the total flux (or mass). The code also estimates the velocity dispersion σ[sstarf ]. A series of simulations were performed to evaluate the code's ability to recover the input parameters (SFH, extinction and velocity dispersion), to investigate the effects of noise in the data and map intrinsic degeneracies of stellar populations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

It was suggested by Terlevich & Melnick (1985) that many nuclei classified as Seyfert 2s could be associated with WR stars recently formed in a powerful starburst. Since then, the signature of WR stars has been claimed to be observed in several Seyfert 2s and LINERs. Gonçalves et al. (1999) have shown that a small number of Seyfert 2s have very weak [N II] 6548,6584 lines, suggesting that these objects could be partly ionized by WR stars. We have obtained high S/N spectra of such “Weak-[N II] Seyferts” to investigate if WR stars can be observed in galaxies without any other evidence for a starburst nebulosity. Amongst other findings, we have detected the presence of emission features such as Si II 5056,6347 and Ni II 7380. Other lines, such as [Ar VI] 4711,4740 and [Fe III]4658 are possibly present, mimicking the Bowen blend.

The detection of WR stars in AGN poses interesting questions concerning the link between nuclear activity and star formation, providing another angle to the study of the Starburst–AGN connection. However, one must be very careful in interpreting the available data; for the time being, the role played by WR stars in these AGN remains an open debate.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present spectroscopic observations of the peculiar system AM1003-435, which is composed of two strong interacting galaxies, and numerical simulations of the encounter between the galaxies, following the dynamical evolution of the stellar and gaseous components.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from dynamical Monte Carlo simulations of dense star clusters near the Galactic center (GC). While these clusters spiral in toward the GC by dynamical friction, they could undergo core collapse and form an intermediate mass black hole (IMBH) by runaway collisions. Clusters can reach within a parsec of the GC where, following tidal disruption, they would inject many young stars still bound to the IMBH into the GC region. This scenario (Gerhard 2001; Hansen & Milosavljević 2003) provides a possible explanation for the youth paradox raised by recent IR observations (Ghez et al. 2003).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html