Seminario en Cerro Calan, 25 abril 2012, 12:00 hrs.

We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses.

Seminario en Cerro Calan, 18 abril 2012, 12:00 hrs.

Nitrogen is among the six most abundant element in our Galaxy and it is a fundamental component of molecules associated with life. Nitrogen-bearing molecules are routinely observed towards a wide variety of physical and dynamical conditions in the Cold Neutral Medium. The list of interstellar N-bearing species detected since the discovery of the CN radical includes simple (2 atoms) to complex molecules with more than 10 atoms. The interstellar chemistry of nitrogen may be considered a simple one since it can be reduced to a relatively small number of reactions. However, observational constraints have emphasized several caveats of pure gas-phase model predictions. One is the long-lasting problem of the abundance of ammonia. But more recent Herschel observations with the HIFI instruments have revealed that the problem extends to the lighter hydrides NH and NH2. Indeed, other weaknesses of our understanding of the nitrogen chemistry have accumulated in the last decade. In addition, models of nitrogen fractionation under typical dark cloud conditions do not predict strong fractionation levels. This is consistent with some observations, but at odds with others. Nitrogen isotopic ratio 14N/15N is shown to vary strongly in the local interstellar medium, whether it is measured in the diffuse molecular gas or in denser objects including comets. In this talk, we will review general aspects of the nitrogen chemistry. In doing so, we will give particular emphasis to the rates of some key reactions for the production of nitrogen hydrides. We will discuss observations of the nitrogen isotopic fractionation, and recent observational results towards dark clouds will be presented.

Seminario en Cerro Calan, 17 abril 2012, 11:00 hrs.

Every massive galaxy is believed to harbour a supermassive black hole in its centre. These can grow by accretion or by mergers, and these processes will leave different imprints in the spin history of the supermassive black holes. I will discuss several different approaches to estimating the cosmic spin of supermassive black holes, using the mean radiative efficiency of quasars, but more informatively by using radio observations. These radio observations trace the jets produced by supermassive black holes, and using recent theoretical models we have shown that black hole spin can explain the varying jet powers observed amongst active galactic nuclei, as well as the radio luminosity function. We can therefore use the radio observations to infer the cosmic spin history of the most massive black holes, and I will discuss the implications for the processes by which they grow.

Seminario en Cerro Calan, 16 abril 2012, 16:00 hrs.

Polynesians, had a ritual cycle calendar, that divided the year into different periods related with the heliacal rising or setting of different stars, constellations or asterisms, and which served to indicate the periods of the year upon which different crops were planted and harvested, as well as be a sign that foretold the arrival of different species of migrational birds, pelagic fish and turtles to the different islands. During such events, the chiefs were obliged to perform important ritual ceremonies to insure and enhance the fertility of nature, and assure such resources. One of the most important seasons of this ritual calendar was related with the heliacal rising or setting of the Pleiades, which marked the harvest of different fruit crops, and the opening of the offshore fishing season in many places in Eastern Polynesia. Upon such occasions first fruit offerings were presented to the chiefs, and festivals were held in their honor. Such ceremonies apparently have their origin in the ancestral Lapita Culture in Western Polynesia, and herewith we will analyze different variations of such ceremonies and of the archaeological structures that were utilized as astronomical markers in Eastern Polynesia to sight the Pleiades during such times of the year.

Seminario en Cerro Calan, 11 abril 2012, 12:00 hrs.

Because our universe is apparently homogeneous, isotropic and spatially at, it is described in general relativity by an expanding at Robertson-Walker metric. We will describe how its expansion history has been observed by cosmic luminosity or angular aperture distances measured for the matter-radiation epoch in the CBR, for the acoustic horizon in the baryon oscillations, and for supernova Ia at red-shift z < 2. Parametrization of this expansion history leads to the Concor- dance Model CDM for the recently accelerating cosmic expansion, which hopefully will emerge from four-dimensional general relativity models for dark energy or from higher-dimensional models extending general relativity. In any case, revolutionary phenomenological and epistemological conclusions emerge from the recent discovery of the accelerating cosmic expansion.

Seminario en Cerro Calan, 04 abril 2012, 12:00 hrs.

We present Very Large Array 1.3 cm radio continuum and water maser observations as well as Submillimeter Array SO2 (226.300 GHz) and 1.3 mm dust continuum observations toward the massive star formation region IRAS 16547–4247. We find evidence of multiple sources in the central part of the region. There is evidence of a rotating structure associated with the most massive of these sources, traced at small scales (~50 AU) by the water masers. At large scales (~1000 AU), we find a velocity gradient in the SO2 molecular emission with a barely resolved structure that can be modeled as a rotating ring or two separate objects. The velocity gradients of the masers and of the molecular emission have the same sense and may trace the same structure at different size scales. The position angles of the structures associated with the velocity gradients are roughly perpendicular to the outflow axis observed in radio continuum and several molecular tracers. We estimate the mass of the most massive central source to be around 30 solar masses from the velocity gradient in the water maser emission. The main source of error in this estimate is the radius of the rotating structure. We also find water masers that are associated with the large-scale molecular outflow of the system, as well as water masers that are associated with other sources in the region. Our results suggest that the formation of this source, one of the most luminous protostars or protostellar clusters known, is taking place with the presence of ionized jets and disk-like structures.

Seminario en Cerro Calan, 20 Marzo 2012, 16:00 hrs.

Clusters and their outskirts encompass a wide range of environmental conditions and their galaxies experience a variety of interactions. Virgo is the nearest cluster, so processes in its member galaxies can be observed at high resolution with a wealth of available data. Most of the spiral galaxies with the largest star formation rates in Virgo are HI-rich galaxies with very extended HI distributions, located in the cluster outskirts. We propose that the disks of these galaxies are actively accreting gas, which enhances their star formation rates. Most cluster galaxies (located closer to the cluster center) are gas-deficient and have reduced star formation rates. Many galaxies show clear evidence for ongoing ram pressure stripping, including "radio deficit regions" and ridges of polarized radio continuum emission on the leading sides, and HI tails on the trailing sides. From stellar population studies and comparisons of observations with simulations, we can identify galaxies in different stages of stripping. Many galaxies which were stripped in the past have truncated and symmetric gas disks but normal stellar disks, and have properties intermediate between spiral and S0 galaxies. While ram pressure stripping is undoubtedly responsible for producing the many cluster galaxies with truncated gas disks, the origin of anemic galaxies, with extended but low surface brightness disks of gas and star formation, has been less clear. We propose that these disks are starved, with their gas reservoirs at large radii (perhaps like those seen in the gas-rich galaxies, although on average less extreme) removed by either tidal forces or ram pressure stripping, which stops accretion onto the disks.

Seminario en Cerro Calan, 14 Marzo 2012, 16:00 hrs.

The Exoplanetary& Planetary Science groups at the University of New South Wales in Sydney, Australia is a quite young one, as we've only been in existence for the last 5 years. However, it has grown in that time into a research group engaged in exoplanetary searches ranging from Dopler searches of nearby stars, to searches for planetary mass objects in young clusters and the Solar neighbourhood, to direct imaging searches for gas giant planets. I'll give an overview of the research programs currently in progress and those planned for the future.

Seminario en Cerro Calan, 05 Marzo 2012, 16:00 hrs.

The novae are runaway thermonuclear reactions on the surfaces of white dwarf stars, generally in binary systems. These highly dynamic phenomena exhibit a wide range of properties. For over 7 years I have taken advantage of access to the SMARTS facilities at Cerro Tololo to pursue a high cadence spectroscopic and photometric study of a large sample of mostly southern novae, in concert with monitoring of the X-ray emission of some of these novae with the Swift satellite. The sample consists of over 70 novae, some followed for up to 7 years, with a cadence that exceeds that of the William's CTIO nova survey of 2 decades ago. After briefly describing the data, I will concentrate on some recent recurrent and recurrent-like He-N novae. I shall discuss the relation of the super-soft X-ray emission to the optically-visible lines. I will interpret the tripartite emission line profiles as arising not in an ejected expanding torus, but rather as diagnostic of an accretion disk that either survives the explosion or reconstitutes itself within days.

Seminario en Cerro Calan, 25 Enero 2012, 16:00 hrs.

Substellar objects populate the ultracool Teff regime, and encompass brown dwarfs and giant planets. Large-scale surveys like UKIDSS, VISTA, and WISE are providing powerful tools to probe for the coolest sub-stellar objects, as well as rare examples that can be used as benchmarks to test our understanding of ultracool physics. I will introduce the subject and present new results from my team.

Seminario en Cerro Calan, 16 Enero 2012, 16:00 hrs.

Proto Planetary (PP) disks have received much attention in the last 15 years, and for good reasons. As cradle of terrestrial planets especially the inner PP disk holds my interest, some of which I hope to "infect" you with. In my talk I shortly introduce these PP disks and the toolkit we use to study them. As my PhD was on warm gas in PP disks, I use its (NIR and optical) data to illustrate what using different gas diagnostics can teach us about the inner disks and how they can betray tell-tale signs of planet formation. I will also introduce ProDiMo, a thermo-chemical disk code that self consistenly calculates the vertical hydrodynamic disk structure, the chemical composition, and the gas and dust temperatures in model disks. Such models are essential to interpret the multi-wavelength data sets that are (luckily) becoming more and more common.

Seminario en Cerro Calan, 05 Enero 2012, 16:00 hrs.

Nuestro entendimiento actual del Cosmos está fuertemente basado en el estudio del fondo de radiación cósmica. Este fondo consiste en un gas de fotones primitivos -producidos apenas después del Big-Bang- que contiene información exquisita sobre el pasado y presente de nuestro Universo. En esta charla describiré de qué manera el estudio del fondo ha revolucionado el desarrollo de la Cosmología contemporánea. También contaré cómo observaciones próximas a realizarse podrían ayudarnos a comprender aspectos claves (y posiblemente revolucionarios) sobre el origen del Universo.