A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60: wide-field photometry and kinematics of the globular cluster system

We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster. Imaging of NGC 4649 was assembled from a recently obtained Hubble Space Telescope/Advanced Camera for Surveys mosaic, and new Subaru/Suprime-Cam and archival Canada-France- Hawaii Telescope/MegaCam data. About 1200 sources were followed up spectroscopically using combined observations from three multi-object spectrographs: Keck/Deep Imaging Multi-Object Spectrograph, Gemini/Gemini Multi-Object Spectrograph and Multiple Mirror Telescope/Hectospec. We confirm 431 unique GCs belonging to NGC 4649, a factor of 3.5 larger than previous data sets and with a factor of 3 improvement in velocity precision. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended. We infer negative GC colour gradients in the innermost 20 kpc and flat gradients out to large radii. Rotation is detected along the galaxy major axis for all tracers: blue GCs, red GCs, galaxy stars and planetary nebulae. We compare the observed properties of NGC 4649 with galaxy formation models. We find that formation via amajor merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii. We find no strong evidence to support an interaction between NGC 4649 and the neighbouring spiral galaxy NGC 4647. We identify interesting GC kinematic features in our data, such as counter-rotating subgroups and bumpy kinematic profiles, which encode more clues about the formation history of NGC 4649.La lista completa de autores que integran el documento puede consultarse en el archivo.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Clasificación espectral y función de luminosidad en el campo de NGC 3372

Se presentan los resultados de la clasificación espectral de unas 50 estrellas realizada en base a espectrogramas obtenidos con tubo de imágenes. Esta muestra posee "LS" un elevado porcentaje de estrellas de secuencia principal cuyo módulo promedio es 11.9 ± 0.56 y que parecen vinculadas con la asociación Carina OBI. Se discuten los resultados finales acerca de las funciones de luminosidad y de masa de dicho sistema estelar.Asociación Argentina de Astronomí

Un sistema W Cephei lejano en Puppis

Se presentan las características de un sistema VV Cephei descubiero sobre placas de prisma objetivo en la constelación Puppis (l = 249° b = -1°.5). Las componentes del sistema fueron clasificadas sobre espectrogramas de tubo de imágenes como B1 V + M2 lab. No se observaron líneas de emisión excepto Fe II 4244. La fotometría UBV (V = 10.67, B-V = 1.67 , U-V = 0.40) es consistente con los colores teóricos correspondientes a los tipos espectrales y un exceso de color E(B-V)=0.30. Este valor también aparece como apropiado en el plano polarización vs exceso de color. El módulo de distancia Vₒ-Mᵥ=15.2 ubica a estrella a unos 11 Kpc del Sol e indica una probable vinculación con el llamado "brazo espiral de 15 Kpc".Asociación Argentina de Astronomí

About the linearity of the color-magnitude relation of early-type galaxies in the Virgo cluster

We revisit the color-magnitude relation (CMR) of the Virgo cluster early-type galaxies in order to explore its alleged non-linearity. To this aim, we reanalyze the relation already published from data obtained within the ACS Virgo Cluster Survey of the Hubble Space Telescope, and perform our own photometry and analysis of the images of the 100 early-type galaxies observed as part of this survey. In addition, we compare our results with those reported in the literature from data of the Sloan Digital Sky Survey. We have found that when the brightest galaxies and untypical systems are excluded from the sample, a linear relation arises in agreement with what is observed in other groups and clusters. The central regions of the brightest galaxies also follow this relation. In addition, we notice that Virgo contains at least four compact elliptical galaxies besides the well known object VCC 1297 (NGC 4486B). Their locations in the -luminosity diagram define a different trend to that followed by normal early-type dwarf galaxies, setting an upper limit in effective surface brightness and a lower limit in effective radius for their luminosities. Based on the distribution of different galaxy sub-samples in the color-magnitude and -luminosity diagrams we draw some conclusions on their formation and the history of their evolution.Comment: 21 pages, 4 figures, 2 tables. Accepted for publication in Ap

Globular clusters as tracers of stellar bimodality in elliptical galaxies: The case of NGC 1399

Globular cluster systems (GCSs) frequently show a bimodal distribution of cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. The particular case of NGC 1399, one of the dominant central galaxies in the Fornax cluster, for which a new B surface brightness profile and (B ‒ RKC) colours are presented, is discussed taking advantage of a recently published wide-field study of its GCS. The results show that the galaxy brightness profile and colour gradient, as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so-called 'blue' and 'red' globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn = 3.3 ± 0.3 in the case of the red globulars and Sn = 14.3 ± 2.5 for the blue ones. We stress that this result does not necessarily conflict with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The region within 0.5 arcmin of the centre shows a deviation from the model profile (in both surface brightness and colour) that may be explained in terms of the presence of a bulge-like high-metallicity component. Otherwise, the model gives an excellent fit up to 12 arcmin (or 66.5 Kpc) from the centre, the galactocentric limit of our blue brightness profile. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about six times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X-ray-emitting hot gas associated with NGC 1399, is emphasized. The impact of a relatively inconspicuous low-metallicity population, that shares the properties of the blue globulars, as a possible source of chemical enrichment early in the formation history of the galaxy is also briefly discussed.Facultad de Ciencias Astronómicas y Geofísica

A quantitative link between globular clusters and the stellar haloes in elliptical galaxies

This paper explores the quantitative connection between globular clusters and the 'diffuse' stellar population of the galaxies they are associated with. Both NGC 1399 and NGC 4486 (M87) are well suited for this kind of analysis due to their large globular cluster populations. The main assumption of our Monte Carlo based models is that each globular cluster is formed along with a given diffuse stellar mass that shares the same spatial distribution, chemical composition and age. The main globular cluster subpopulations, that determine the observed bimodal colour distribution, are decomposed avoiding a priori parametric (e.g. Gaussian) fits and using a new colour (C - T 1)-metallicity relation. The eventual detectability of a 'blue' tilt in the colour-magnitude diagrams of the blue globular cluster subpopulation is also addressed. A successful link between globular clusters and the stellar galaxy halo is established by assuming that the number of globular clusters per associated diffuse stellar mass t is a function of total abundance [Z/H] and behaves as t = γ exp(-δ[Z/H]) (i.e. increases when abundance decreases). The simulations allow the prediction of a surface brightness profile for each galaxy through these two free parameters' approximation. The γ, δ parameters that provide the best fit to the observed profiles in the B band, in turn, determine several features, namely, large-scale halo colour gradients, globular cluster-halo colour offset, clusters' cumulative specific frequencies, and stellar metallicity distributions, that compare well with observations. The results suggest the co-existence of two distinct stellar populations characterized by widely different metallicities and spatial distributions. One of these populations (connected with the blue globular clusters) is metal poor, highly homogeneous, exhibits an extended spatial distribution and becomes more evident at large galactocentric radius contributing with some 20 per cent of the total stellar mass. In turn, the stellar population associated with the red globular clusters is extremely heterogeneous and dominates the inner region of both galaxies. Remarkably, and although the cluster populations of these galaxies exhibit detectable differences in colour distribution, the δ parameter that determines the shape of the brightness profiles of both galaxies has the same value, δ ≈ 1.1 to 1.2 ± 0.1.Facultad de Ciencias Astronómicas y Geofísica

Globular clusters as tracers of stellar bimodality in elliptical galaxies: The case of NGC 1399

Globular cluster systems (GCSs) frequently show a bimodal distribution of cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. The particular case of NGC 1399, one of the dominant central galaxies in the Fornax cluster, for which a new B surface brightness profile and (B ‒ RKC) colours are presented, is discussed taking advantage of a recently published wide-field study of its GCS. The results show that the galaxy brightness profile and colour gradient, as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so-called 'blue' and 'red' globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn = 3.3 ± 0.3 in the case of the red globulars and Sn = 14.3 ± 2.5 for the blue ones. We stress that this result does not necessarily conflict with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The region within 0.5 arcmin of the centre shows a deviation from the model profile (in both surface brightness and colour) that may be explained in terms of the presence of a bulge-like high-metallicity component. Otherwise, the model gives an excellent fit up to 12 arcmin (or 66.5 Kpc) from the centre, the galactocentric limit of our blue brightness profile. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about six times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X-ray-emitting hot gas associated with NGC 1399, is emphasized. The impact of a relatively inconspicuous low-metallicity population, that shares the properties of the blue globulars, as a possible source of chemical enrichment early in the formation history of the galaxy is also briefly discussed.Facultad de Ciencias Astronómicas y Geofísica

Significado de la función de luminosidad Hα en galaxias australes

By means of CCD frames and image processing techniques we measured the luminosity function of H-alpha of HII regions of nearby galaxies with a high S/N. Several studies were done recently assuming that the shape of the observed luminosity function can be use to determine physical parameters (e.g. mass distribution, stellar evolution, stellar mass distribution, etc) of the hidden stellar population. Some of the models only consider the distribution of the integrated stellar mass of the HII regions and others only the evolution of the stellar ionizating population of H11 region. In this work we consider the two effects simultaneously plus the effect of taking in account different stellar formation rate for the host galaxy. This a summary of the results: - The turnover point discover by Kennicutt et al. (1989) appears to have an explanation as the convolution of the stellar formation rate and the stellar mass distribution. - From comparison with observational data (from Feinstein et al. - 1992, this issue and Thesis) some galaxies NGC 2997, NGC 6070, NGC 6384, NGC 7552 seem to have luminosity functions compatible with a constant SFR. NGC 1672 exhibits to have a more complex situation, not compatible with a constant SFR. - In the case of constant SFR, the slope of-2 (Kennicutt et al., 1989, Apj 337,761) can only fit the luminosity function in the bright side of the distribution.Asociación Argentina de Astronomí

Función de luminosidad Hα en galaxias australes

Hα images of 20 nearby Southern galaxies were obtained using narrow interferometric filters. Positions, fluxes and diameters of the objects were obtained from these frames. A study of the completeness of the sample is made and after a proper calibration, the absolute fluxes and the Hα luminosity function were obtained for each galaxy. Two galaxies in the sample (NGC 1672, NGC 5861) show profiles of type II luminosity function while NGC 6221 shows extended Hα emission.Asociación Argentina de Astronomí

The complex star cluster system of NGC 1316 (Fornax A)

This paper presents Gemini-gri' high-quality photometry for cluster candidates in the field of NGC 1316 (Fornax A) as part of a study that also includes GMOS spectroscopy. A preliminary discussion of the photometric data indicates the presence of four stellar cluster populations with distinctive features in terms of age, chemical abundance and spatial distribution. Two of them seem to be the usually old (metal poor and metal rich) populations typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr) globular cluster population is the dominant component of the sample (as reported by previous papers). We also find a younger cluster population with a tentative age of ≈ 1 Gyr.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat