Is J 133658.3-295105 a Radio Source at z >= 1.0 or at the Distance of M 83?

We present Gemini optical imaging and spectroscopy of the radio source J 133658.3-295105. This source has been suggested to be the core of an FR II radio source with two detected lobes. J 133658.3-295105 and its lobes are aligned with the optical nucleus of M 83 and with three other radio sources at the M 83 bulge outer region. These radio sources are neither supernova remnants nor H II regions. This curious configuration prompted us to try to determine the distance to J 133658.3-295105. We detected H_alpha emission redshifted by ~ 130 km s^-1 with respect to an M 83 H II region 2.5" east-southeast of the radio source. We do not detect other redshifted emission lines of an optical counterpart down to m_i = 22.2 +/- 0.8. Two different scenarios are proposed: the radio source is at z >= 2.5, a much larger distance than the previously proposed lower limit z >= 1.0, or the object was ejected by a gravitational recoil event from the M 83 nucleus. This nucleus is undergoing a strong dynamical evolution, judging from previous three-dimensional spectroscopy.Comment: 6 pages, 4 figure

The Relationship Between the Sersic Law Profiles Measured Along the Major and Minor Axes of Elliptical Galaxies

In this paper we discuss the reason why the parameters of the Sersic model best-fitting the major axis light profile of elliptical galaxies can differ significantly from those derived for the minor axis profile. We show that this discrepancy is a natural consequence of the fact that the isophote eccentricity varies with the radius of the isophote and present a mathematical transformation that allows the minor axis Sersic model to be calculated from the major axis model, provided that the elliptical isophotes are aligned and concentric and that their eccentricity can be represented by a well behaved, though quite general, function of the radius. When there is no variation in eccentricity only the effective radius changes in the Sersic model, while for radial-dependent eccentricity the transformation which allows the minor axis Sersic model to be calculated from the major axis model is given by the Lerch Phi transcendental function. The proposed transformation was tested using photometric data for 28 early-type galaxies.Comment: 16 pages, 14 figures, LaTex with mn2e.cls. Accepted to MNRA

A Morphological Method to Determine Co-Rotation Radii in Spiral Galaxies

Shock induced star formation in a stellar density wave scenario produces an azimuthal gradient of ages across the spiral arms which has opposite signs on either side of the corotation resonance (CR). We present a method based on the Fourier analysis of azimuthal profiles, to locate the CR and determine the arm character (trailing or leading) in spiral galaxies. Basically, we compare the behavior of the phase angle of the two-armed spiral in blue and infrared colors which pick out respectively young and older disk stellar population. We illustrate the method using theoretical leading and trailing, spirals. We have also applied the method to the spiral galaxies NGC 7479, for which we confirm the reported leading arms, and NGC 1832. In these galaxies we find two and three CRs respectively.Comment: 9 pages, accepted for publication in ApJL, figures 4 and 6 avaliables at ftp://ftp.inaoep.mx/pub/salida/puerari, full paper also avaliable at http://www.inaoep.mx/~puerar

Modeling the Black Hole Recoil from the Nucleus

GEMINI + GMOS and Chandra emission-line spectroscopy reveal that the Fanaroff-Riley II radio-source J133658.3- 295105 is a local object behind the barred-spiral galaxy M83 that is projected onto the galaxy?s disk at about 60" from the galaxy?s optical nucleus. J133658.3-295105 and its radiolobes are aligned with the optical nucleus of M83 and two other radio-sources neither of which are supernova remnants or HII regions. The optical nucleus of M83 is off-centered by 2.7" (~60 pc) with regard to the kinematic center. Its mass is within the range (1 - 4) × 106 Msun and the velocity dispersion at its center points to a non-resolved mass concentration of <~106 Msun. In this paper we study the circumstances in which the radio source would have been ejected from the central region of M83. We analyze different types of collisions of binary and triple systems of super-massive black holes (SMBHs) by numerical simulations using a Post-New- tonian approximation of order 7/2 (~1/c7). We developed an N-body code specially built to numerically integrate the Post-Newtonian equations of motion with a symplectic method. Numerical experiments show that the code is robust enough to handle virtually any mass ratio between particles and to follow the interaction up to a SMBH separation of three Schwarzschild radii. We show that within the current Post-Newtonian approximation, a scenario in which one of the three SMBHs suffers a slingshot-like kick is best suited to explain the ejection of J133658.3-295105, which simultaneously produces the recoil of the remaining BH pair, which drags together a subset of stars from the original cluster forming a structure that mimics the offcenter optical nucleus of M83. The simulation parameters are tuned to reproduce the velocities and positions of J133658.3-295105 as well as the optical nucleus and the putative SMBH at its center.Fil: Ferrari, Guilherme. Instituto de Física. Universidade Federal do Rio Grande do Sul; Brazil;Fil: Dottori, Horacio Alberto. Instituto de Física. Universidade Federal do Rio Grande do Sul; Brazil;Fil: Diaz, Ruben Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Cientifico Tecnológico - Conicet - San Juan. Instituto de Ciencias Astronómicas de la Tierra y del Espacio; Argentina

A Search for Old Star Clusters in the Large Magellanic Cloud

We report the first results of a color-magnitude diagram survey of 25 candidate old LMC clusters. For almost all of the sample, it was possible to reach the turnoff region, and in many clusters we have several magnitudes of the main sequence. Age estimates based on the magnitude difference $\delta T_1$ between the giant branch clump and the turnoff revealed that no new old clusters were found. The candidates turned out to be of intermediate age (1-3 Gyr) We show that the apparently old ages as inferred from integrated UBV colors can be explained by a combination of stochastic effects produced by bright stars and by photometric errors for faint clusters lying in crowded fields. The relatively metal poor candidates from the CaII triplet spectroscopy also turned out to be of intermediate age. This, combined with the fact that they lie far out in the disk, yields interesting constraints regarding the formation and evolution of the LMC disk. We also study the age distribution of intermediate age and old clusters This homogeneous set of accurate relative ages allows us to make an improved study of the history of cluster formation/destruction for ages $>1$Gyr. We confirm previous indications that there was apparently no cluster formation in the LMC during the period from 3-8 Gyr ago, and that there was a pronounced epoch of cluster formation beginning 3 Gyrs ago that peaked at about 1.5 Gyrs ago. Our results suggest that there are few, if any, genuine old clusters in the LMC left to be found.Comment: LaTeX, to be published in Nov. 1997 Astronomical Journa

Analysis of resonances in grand design spiral galaxies

We have searched for corotations (CR) in three Southern grand design spiral galaxies: NGC 1365, NGC 1566 and NGC 2997. We have also introduced a method of quantifying errors in the phase diagram used to detect CR. We established the m=2 pattern CR at 12.1 kpc, 9.4 kpc and 7 kpc, for NGC 1365, NGC 1566 and NGC 2997, respectively. By using published rotation curves, we could determine spiral pattern angular speeds of 25.0 km/sec/kpc, 12.2 km/sec/kpc and 17.6 km/sec/kpc, respectively. A three armed component has been detected in NGC 2997, with the CR placed at 8.7 kpc with a pattern angular speed Omega_{CR_3}=12.7 km/sec/kpc. An m=1 component was detected in NGC 1566. We warily locate the CR at 7.1 kpc, with a pattern angular speed Omega_{CR} approx. 16.6 km/sec/kpc. This pattern does not present ILR. Ages have been determined by studying the radial density profile of the m=2 Fourier components in g (newly formed stars) and i (perturbing SDW supported by the disk of old stars), aided by the global aspect of the real spiral pattern in comparison with numerical simulations. The pattern is approx. 1200 Myr old in NGC 1365, approx. 800 Myr old in NGC 1566 and younger than 80 Myr in NGC 2997.Comment: 49 pages, 24 figures, 2 tables. Accepted for publication in ApJ Large figures can be find at http://www.inaoep.mx/~puerari/resonance

Separating C-stars from Dust in the Central Region of the Seyfert 2 Galaxy NGC 1241

The Sy 2 galaxy NGC 1241 presents a 1.5 kpc large circumnuclear ring of star formation (CNR) embracing a small bar plus leading arms. Those structures are P alpha emitters, but barely seen in H alpha. It presents also stellar trailing arms inside the CNR. GEMINI and HST imagery allow the construction of high resolution (V-H) and (J-K_s) color maps as well as a (J-K_s) vs. K color-magnitude diagram (CMD) of this complex region. The CNR is heavily obscured in V, but a fairly transparent window appears in the direction of the nucleus. Nonetheless, the nucleus presents a (J-K_s) color that is redder than the CNR. The CNR is composed of extremely young HII regions still enshrouded in their dust cocoons. However, the nuclear (J-K_s) color can not be explained in this manner. Therefore, we propose the contribution of C-Stars as the most feasible mechanism for explaining the colors. If the nuclear stellar population is comparable to that of the LMC bar, 500 C-stars and 25000 AGB O-rich stars inside 50 pc may reproduce the observed colors. C-Stars release enriched material to the nuclear environment, probably fueling the central engine of this Sy 2 galaxy during the lifetime of stars with masses between 2 M_sun < M_C-star < 6 M_sun (C-star phase). The ejected material that remains trapped in the central potential might also explain the systematically observed increased strength of the optical CN-bands in Sy 2 galaxies and is consistent with the significant contribution of intermediate age stars to the optical continuum of low luminosity AGNs.Comment: The Astrophysical Journal Letters, accepted. 5 figure

Kinematics and Modeling of the Inner Region of M83

Two-dimensional kinematics of the central region of M 83 (NGC 5236) were obtained through three-dimensional NIR spectroscopy with Gemini South telescope. The spatial region covered by the integral field unit (~5" x 13" or ~90 x 240 pc), was centered approximately at the center of the bulge isophotes and oriented SE-NW. The Pa_beta emission at half arcsecond resolution clearly reveals spider-like diagrams around three centers, indicating the presence of extended masses, which we describe in terms of Satoh distributions. One of the mass concentrations is identified as the optical nucleus (ON), another as the center of the bulge isophotes, similar to the CO kinematical center (KC), and the third as a condensation hidden at optical wavelengths (HN), coincident with the largest lobe in 10 micron emission. We run numerical simulations that take into account ON, KC and HN and four more clusters, representing the star forming arc at the SW of the optical nucleus. We show that ON, KC and HN suffer strong evaporation and merge in 10-50 Myr. The star-forming arc is scattered in less than one orbital period, also falling into the center. Simulations also show that tidal-striping boosts the external shell of the condensations to their escape velocity. This fact might lead to an overestimation of the mass of the condensations in kinematical observations with spatial resolution smaller than the condensations' apparent sizes. Additionally the existence of two ILR resonances embracing the chain of HII regions, claimed by different authors, might not exist due to the similarity of the masses of the different components and the fast dynamical evolution of M83 central 300 pc

Capture of field stars by globular clusters in dense bulge regions

The recent detection of a double Red Giant Branch in the optical color-magnitude diagram (CMD) of the bulge globular cluster HP1 (Ortolani et al. 1997), a more populated metal-poor steep one corresponding to the cluster itself, and another metal-rich curved, led us to explore in the present Letter the possibility of capture of field stars by a globular cluster orbiting in dense bulge regions over several gigayears. Analytical arguments, as well as N-body calculations for a cluster model of 10^5 solar masses in a bulge-like environment, suggest that a significant fraction of cluster stars may consist of captures. Metal-poor globular clusters in the inner bulge, like HP1, contrasting at least in Delta [Fe/H] = 1.0 dex with respect to the surrounding metal-rich stars, are ideal probes to further test the capture scenario. In turn, if this scenario is confirmed, the double RGB of HP1 could provide direct estimates of blanketing amounts, which is fundamental for the photometric calibration of metal-rich stellar populations.Comment: 6 pages, 2 included figures, aas2pp4,sty Latex style. To be published in Astrophysical Journal Letter

A New Giant Branch Clump Structure In the Large Magellanic Cloud

We present Washington C, T1 CCD photometry of 21 fields located in the northern part of the Large Magellanic Cloud (LMC), and spread over a region of more than 2.52 degrees approximately 6 degrees from the bar. The surveyed areas were chosen on the basis of their proximity to SL 388 and SL 509, whose fields showed the presence of a secondary giant clump, observationally detected by Bica et al. (1998, AJ, 116, 723). From the collected data we found that most of the observed field CMDs do not show a separate secondary clump, but rather a continuous vertical structure (VS), which is clearly seen for the first time. Its position and size are nearly the same throughout the surveyed regions: it lies below the Red Giant Clump (RGC) and extends from the bottom of the RGC to approximately 0.45 mag fainter, spanning the bluest color range of the RGC. The more numerous the VS stars in a field, the larger the number of LMC giants in the same zone. Our analysis demonstrate that VS stars belong to the LMC and are most likely the consequence of some kind of evolutionary process in the LMC, particularly in those LMC regions with a noticeable large giant population. Our results suggest that in order to trigger the formation of VS stars, there should be other conditions besides the appropriate age, metallicity, and the necessary red giant star density. Indeed, stars satisfying the requisites mentioned above are commonly found throughout the LMC, but the VS phenomenon is only clearly seen in some isolated regions. Finally, the fact that clump stars have an intrinsic luminosity dispersion further constrains the use of the clump magnitude as a reliable distance indicator.Comment: 25 pages, 9 figures, 3 tables; to be published in AJ, Dec. issu