Are violent events responsible of a galaxy morphological loop?

We use cosmological SPH simulations to investigate the effects of mergers and interactions on the formation of the bulge and disc components of galactic systems. We find that secular evolution during mergers seems to be a key process in the formation of stable disc-bulge systems with observational counterparts and contributes to establish the fundamental relations observed in galaxies. Our findings suggest that the secular evolution phase couples the formation mechanisms of the bulge and disc components. According to our results, depending on the particular stability properties and merger parameters, violents events could drive a morphological loop in which the outcome could be a disc or a spheroid.Facultad de Ciencias Astronómicas y Geofísica

Stellar systems in the direction of the Hickson Compact Group 44 : I. Low surface brightness galaxies

Context. In spite of the numerous studies of low-luminosity galaxies in different environments, there is still no consensus about their formation scenario. In particular, a large number of galaxies displaying extremely low-surface brightnesses have been detected in the last year, and the nature of these objects is under discussion. Aims. In this paper we report the detection of two extended low-surface brightness (LSB) objects (μeffg′ ≃ 27 mag) found, in projection, next to NGC 3193 and in the zone of the Hickson Compact Group (HCG) 44, respectively. Methods. We analyzed deep, high-quality, GEMINI-GMOS images with ELLIPSE within IRAF in order to obtain their brightness profiles and structural parameters. We also searched for the presence of globular clusters (GC) in these fields. Results. We have found that, if these LSB galaxies were at the distances of NGC 3193 and HCG 44, they would show sizes and luminosities similar to those of the ultra-diffuse galaxies (UDGs) found in the Coma cluster and other associations. In that case, their sizes would be rather larger than those displayed by the Local Group dwarf spheroidal (dSph) galaxies. We have detected a few unresolved sources in the sky zone occupied by these galaxies showing colors and brightnesses typical of blue globular clusters. Conclusions. From the comparison of the properties of the galaxies presented in this work with those of similar objects reported in the literature, we have found that LSB galaxies display sizes covering a quite extended continous range (reff ∼ 0.3-4.5 kpc), in contrast to "normal" early-type galaxies, which show reff ∼ 1.0 kpc with a low dispersion. This fact might point to different formation processes for both types of galaxies.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Sistemas estelares en la dirección de Pegasus I - I : Galaxias de bajo brillo superficial

El grupo de galaxias Pegasus I, localizado a una distancia de 50 Mpc, está dominado por dos galaxias elípticas masivas: NGC7626 y NGC7619. Este grupo representa un ambiente de especial interés porque a través de estudios de rayos-X se concluye que existen evidencias de ser un sistema que actualmente se encuentra experimentando una gran fusión de dos subgrupos asociados a sus galaxias dominantes. A pesar de este aspecto interesante, la población de galaxias débiles de Pagasus I ha sido poco estudiada. En el marco de la tesis doctoral de la Lic. Nélida M. González, se ha iniciado un estudio de la región central de Pegasus I, con el fin de identificar galaxias tempranas de baja luminosidad a través de imágenes obtenidas con el telescopio de 8 m de diámetro del Observatorio Gemini Norte. En este momento, se ha podido identificar veinte candidatas a galaxias enanas elípticas, así como ocho galaxias de bajo brillo superficial (μeff,g′≃ 25 mag/arcsec2). En particular, con estos ocho objetos se pretende ampliar la muestra de galaxias conocidas de bajo brillo superficial. El interés en la identificación de nuevos ejemplos de galaxias extremadamente débiles reside en el hecho que pueden brindar importantes condiciones de contorno a los modelos actuales sobre la formación y evolución de las galaxias. El resultado obtenido del análisis fotométrico de las galaxias de bajo brillo superficial en el grupo de Pegasus I fue publicado en la revista Astronomy & Astrophysics (González et al. 2018).Universidad Nacional de La Plat

Sistemas estelares en la dirección de Pegasus I - I : Galaxias de bajo brillo superficial

El grupo de galaxias Pegasus I, localizado a una distancia de 50 Mpc, está dominado por dos galaxias elípticas masivas: NGC7626 y NGC7619. Este grupo representa un ambiente de especial interés porque a través de estudios de rayos-X se concluye que existen evidencias de ser un sistema que actualmente se encuentra experimentando una gran fusión de dos subgrupos asociados a sus galaxias dominantes. A pesar de este aspecto interesante, la población de galaxias débiles de Pagasus I ha sido poco estudiada. En el marco de la tesis doctoral de la Lic. Nélida M. González, se ha iniciado un estudio de la región central de Pegasus I, con el fin de identificar galaxias tempranas de baja luminosidad a través de imágenes obtenidas con el telescopio de 8 m de diámetro del Observatorio Gemini Norte. En este momento, se ha podido identificar veinte candidatas a galaxias enanas elípticas, así como ocho galaxias de bajo brillo superficial (μeff,g′≃ 25 mag/arcsec2). En particular, con estos ocho objetos se pretende ampliar la muestra de galaxias conocidas de bajo brillo superficial. El interés en la identificación de nuevos ejemplos de galaxias extremadamente débiles reside en el hecho que pueden brindar importantes condiciones de contorno a los modelos actuales sobre la formación y evolución de las galaxias. El resultado obtenido del análisis fotométrico de las galaxias de bajo brillo superficial en el grupo de Pegasus I fue publicado en la revista Astronomy & Astrophysics (González et al. 2018).Universidad Nacional de La Plat

Sistemas estelares en la dirección de Pegasus I - I : Galaxias de bajo brillo superficial

El grupo de galaxias Pegasus I, localizado a una distancia de 50 Mpc, está dominado por dos galaxias elípticas masivas: NGC7626 y NGC7619. Este grupo representa un ambiente de especial interés porque a través de estudios de rayos-X se concluye que existen evidencias de ser un sistema que actualmente se encuentra experimentando una gran fusión de dos subgrupos asociados a sus galaxias dominantes. A pesar de este aspecto interesante, la población de galaxias débiles de Pagasus I ha sido poco estudiada. En el marco de la tesis doctoral de la Lic. Nélida M. González, se ha iniciado un estudio de la región central de Pegasus I, con el fin de identificar galaxias tempranas de baja luminosidad a través de imágenes obtenidas con el telescopio de 8 m de diámetro del Observatorio Gemini Norte. En este momento, se ha podido identificar veinte candidatas a galaxias enanas elípticas, así como ocho galaxias de bajo brillo superficial (μeff,g′≃ 25 mag/arcsec2). En particular, con estos ocho objetos se pretende ampliar la muestra de galaxias conocidas de bajo brillo superficial. El interés en la identificación de nuevos ejemplos de galaxias extremadamente débiles reside en el hecho que pueden brindar importantes condiciones de contorno a los modelos actuales sobre la formación y evolución de las galaxias. El resultado obtenido del análisis fotométrico de las galaxias de bajo brillo superficial en el grupo de Pegasus I fue publicado en la revista Astronomy & Astrophysics (González et al. 2018).Universidad Nacional de La Plat

Development of the red sequence in galaxy clusters

We investigate the origin of the color-magnitude relation (CMR) observed in cluster galaxies by using a combination of a cosmological N-body simulation of a cluster of galaxies and a semi-analytic model of galaxy formation. The departure of galaxies in the bright end of the CMR with respect to the trend defined by less luminous galaxies could be explained by the influence of minor mergers.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

Interactions, mergers and the fundamental mass relations of galaxies

We present a study of the effects of mergers and interactions on the mass distribution of galactic systems in hierarchical clustering scenarios using the disc-bulge structural parameters and their dynamical properties to quantify them. We focus on the analysis of the Fundamental Mass Plane relation, finding that secular evolution phases contribute significantly to the determination of a plane with a slope in agreement to that of the observed luminosity relation. In these simulations, secular phases are responsible for the formation of compact stellar bulges with the correct structural parameter combination. We also test that the relations among these parameters agree with observations. The Kormendy mass relation is also reproduced after secular evolution phases. From our findings, we predict that the departure of systems from the z = 0 Fundamental Mass Plane, involving a change in the slope, could indicate a lack of secular evolution in their formation histories. Taking into account these results, the hierarchical growth of the structure predicts a bulge formation scenario for typical field spiral galaxies where secular evolution during dissipate mergers plays a fundamental role. Conversely, subsequent mergers can help to enlarge the bulges but do not seem to strongly modify their fundamental mass relations. Systems get to the local mass relations at different stages of evolution (i.e. different redshifts) so that their formation histories introduce a natural scatter in the relations. We also found that the parameters of the Tully-Fisher Mass relation for the disc components are correlated with those of the Fundamental mass one for the bulge components at least during mergers events, so that as the systems increase their circular velocity, the bulges get more concentrated. Our results suggest that the formation mechanisms of the bulge and disc components, satisfying their corresponding fundamental mass relations, might be coupled and that secular evolution could be the possible connecting process.Facultad de Ciencias Astronómicas y Geofísica

Are violent events responsible of a galaxy morphological loop?

We use cosmological SPH simulations to investigate the effects of mergers and interactions on the formation of the bulge and disc components of galactic systems. We find that secular evolution during mergers seems to be a key process in the formation of stable disc-bulge systems with observational counterparts and contributes to establish the fundamental relations observed in galaxies. Our findings suggest that the secular evolution phase couples the formation mechanisms of the bulge and disc components. According to our results, depending on the particular stability properties and merger parameters, violents events could drive a morphological loop in which the outcome could be a disc or a spheroid.Facultad de Ciencias Astronómicas y Geofísica

Deep MOS Spectroscopy of NGC1316 Globular Clusters

The giant elliptical galaxy NGC1316 is the brightest galaxy in the Fornax cluster, and displays a number of morphological features that might be interpreted as an intermediate age merger remanent ( 3 Gyr). Based on the idea that globular clusters systems (GCS) constitute genuine tracers of the formation and evolution of their host galaxies, we conducted a spectroscopic study of approximately 40 globular clusters (GCs) candidates associated with this interesting galaxy. We determined ages, metallicities, and a-element abundances for each GC present in the sample, through the measurement of different Lick indices and their subsequent comparison with simple stellar populations models (SSPs).Facultad de Ciencias Astronómicas y Geofísica

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

We revisit the color-magnitude relation of Virgo Cluster early-type galaxies in order to explore its alleged nonlinearity. 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 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 〈μeff〉-luminosity diagram define a trend different from that followed by normal early-type dwarf galaxies, setting an upper limit in effective surface brightness and a lower limit in the effective radius for their luminosities. Based on the distribution of different galaxy sub-samples in the color-magnitude and 〈μeff〉-luminosity diagrams, we draw some conclusions on their formation and the history of their evolution.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica