Past Pizza Lunches

Number of entries: 155

08
February 2019

Cosmic acceleration and type Ia supernovae luminosity-redshift dependence


Start: 12:15h
Speaker: Isaac Tutusaus Lleixa (Institute of Space Sciences (ICE, CSIC and IEEC))
Place: Alberto Lobo Seminar Room (ICE, UAB Campus)

The ΛCDM model is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has recently been…
Start: 12:15h
Speaker: Isaac Tutusaus Lleixa (Institute of Space Sciences (ICE, CSIC and IEEC))
Place: Alberto Lobo Seminar Room (ICE, UAB Campus)


The ΛCDM model is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has recently been some debate in the literature concerning the statistical treatment of SNIa, and their ability to prove the cosmic acceleration. In this talk I will focus on the standard assumption that SNIa intrinsic luminosity is independent of the redshift. After briefly motivating the relaxation of this assumption, I will first present the conclusions that we can draw on the accelerated nature of the expansion of the Universe if we only consider low-redshift cosmological probes and an expanding universe with constant velocity: the Rh=ct model. In the second part of the talk, I will further test this exotic model by including high-redshift information coming from the cosmic microwave background. Finally, I will generalize the previous two parts and present the role of SNIa on the accelerated nature of the expansion of the Universe when we account for the main background cosmological probes in a model-independent way.
01
February 2019

The cosmological constant and the size of our Universe


Start: 12:15h
Speaker: Enrique Gaztañaga (Institut de Ciències de l'Espai)
Place: Sala Alberto Lobo (ICE building, Campus UAB)

We consider the cosmological constant 𝚲 to be a free parameter of the symmetries of gravity that can fixed by a boundary condition: the particles should be free when outside causal contact (traditionally at infinity). Under this conditions we show that constant vacuum does not contribute to gravity.…
Start: 12:15h
Speaker: Enrique Gaztañaga (Institut de Ciències de l'Espai)
Place: Sala Alberto Lobo (ICE building, Campus UAB)


We consider the cosmological constant 𝚲 to be a free parameter of the symmetries of gravity that can fixed by a boundary condition: the particles should be free when outside causal contact (traditionally at infinity). Under this conditions we show that constant vacuum does not contribute to gravity. Moreover we find that there is no cosmic acceleration for an infinitely large and uniform Universe, no matter what the values are for the cosmological constant 𝚲 or vacuum energy rho_{vac}. Cosmic acceleration at present time requires either a finite Physical Universe (causal boundary) or significant evolution in the late time vacuum energy (i.e. equation of state w>-1). If we assume that vacuum has not evolved strongly in recent times (or that w = -1 as favored by observations), then the measured cosmic acceleration \rho_ 𝚲 = (2.23 ± 0.03) rho_m just tell us that the Physical Universe (or causal boundary) has a co-moving radius of chi= (3.137 ± 0.004) c/H_0, where H_0 is the present expansion rate. This result predicts the lack of structure seem in our CMB sky on scales larger than 60 degrees and gives new constraints for inflation. We conclude that there is no need for a mysterious Dark Energy to explain the observed cosmic acceleration.
 
25
January 2019

Feeding and feedback from little monsters: black holes in dwarf galaxies


Start: 12:15h
Speaker: Mar Mezcua Pallerola
Place: Sala Alberto Lobo

Supermassive black holes of 10^10 solar masses already existed when the Universe was ~1 Gyr old and are also found in local brightest cluster galaxies. To reach this mass, they should have started as seed intermediate-mass black holes (IMBHs) of 100-10^6 solar masses at z~10 and grow very fast via accretion…
Start: 12:15h
Speaker: Mar Mezcua Pallerola
Place: Sala Alberto Lobo

Supermassive black holes of 10^10 solar masses already existed when the Universe was ~1 Gyr old and are also found in local brightest cluster galaxies. To reach this mass, they should have started as seed intermediate-mass black holes (IMBHs) of 100-10^6 solar masses at z~10 and grow very fast via accretion and mergers. Detecting such IMBHs in the early Universe is extremely challenging; however, those seed black holes that did not become supermassive should be found in local dwarf galaxies resembling the first galaxies formed at early epochs. 
I will show that a population of actively accreting IMBHs exists in local dwarf galaxies and that they can be detected out to z~3 with the use of deep multiwavelength surveys like COSMOS. The black hole occupation fraction of these dwarf galaxies suggests that the early Universe seed black holes formed from direct collapse of pre-galactic gas disk, which is reinforced by the finding that the scaling relations between supermassive black hole mass and host galaxy properties flatten at the low-mass end. This scenario is however challenged by the recent suggestion that dwarf galaxy mergers and black hole feedback can yield significant growth of the primordial seeds. In this case, IMBHs in local dwarf galaxies should not be treated as the fossils of the early Universe seed black holes. 
18
January 2019

Multi-probe Cosmological Analysis with the Dark Energy Survey


Start: 12:15h
Speaker: Anna Maria Porredon Díez de Tejada
Place: Sala Alberto Lobo

Ongoing and future galaxy surveys will enable detailed measurements of the late-time Universe and powerful tests of the nature of dark energy and General Relativity. These surveys are able to obtain cosmological constraints from multiple probes, and the combination of these probes can improve the robustness…
Start: 12:15h
Speaker: Anna Maria Porredon Díez de Tejada
Place: Sala Alberto Lobo

Ongoing and future galaxy surveys will enable detailed measurements of the late-time Universe and powerful tests of the nature of dark energy and General Relativity. These surveys are able to obtain cosmological constraints from multiple probes, and the combination of these probes can improve the robustness and the constraining power of their cosmological constraints. In this talk I am going to present some of the efforts in obtaining cosmological constraints from the combination of multiple probes with the Dark Energy Survey.
14
December 2018

Especial Christmas Seminar: A Systems and Computational approach in Neuroscience. Or why we need more physicists to study the brain.


Start: 12:00h
Speaker: Dr. Jaime de la Rocha (Institut d'Investigacions Biomèdiques August Pi i Sunyer)
Place: Alberto Lobo room

Modern neuroscience requires in one hand, of the use of novel techniques to measure animal behavior, record and manipulate neuronal activity and in the other hand of sophisticated methods to analyse these complex data sets and the expertise to develop computational models that can bear some mechanistic…
Start: 12:00h
Speaker: Dr. Jaime de la Rocha (Institut d'Investigacions Biomèdiques August Pi i Sunyer)
Place: Alberto Lobo room

Modern neuroscience requires in one hand, of the use of novel techniques to measure animal behavior, record and manipulate neuronal activity and in the other hand of sophisticated methods to analyse these complex data sets and the expertise to develop computational models that can bear some mechanistic understanding of the observed neural circuit dynamics. In this talk, I will present an  (incomplete) overview of the state-of-the-art methods in Systems and Computational Neuroscience aim to understand how brain circuits guide our behaviour. This approach stresses the necessity of a new generation of neuroscientists with  a quantitative mindset, which can be trained (to a large extent) in a modern physics degree.
30
November 2018

First measurements of heavy precipitation in the ROHP-PAZ mission


Start: 12:15h
Speaker: Sergio Tomás Martínez (ICE, CSIC & IEEC)
Place: ICE, Bellaterra

The ROHP-PAZ mission has been successfully launched on this February 2018. It carries a payload to detect GNSS radio occultations which for the first time measures polarimetric signals. This allows the detection and a possible quantification of heavy precipitation events together with the thermodynamic…
Start: 12:15h
Speaker: Sergio Tomás Martínez (ICE, CSIC & IEEC)
Place: ICE, Bellaterra


The ROHP-PAZ mission has been successfully launched on this February 2018. It carries a payload to detect GNSS radio occultations which for the first time measures polarimetric signals. This allows the detection and a possible quantification of heavy precipitation events together with the thermodynamic measurements of a conventional radio occultation. This set of simultaneous observations obtained by a single instrument is regarded as a valuable tool to improve the knowledge about cloud formation and precipitations worldwide. In this dissertation I will explain the first results obtained with this novel technique using the collected data up to October as well as its main challenges and future work for the next years at ICE.
23
November 2018

Meeting a neighbour: the discovery of Barnard b


Start: 12:15h
Speaker: Ignasi Ribas (ICE - IEEC)
Place: Alberto Lobo room

Last week we announced the discovery of a candidate super-Earth planet around Barnard’s Star. The planet was found using nearly 800 radial velocities from seven different spectrographs in a large observational effort spanning over 20 years. Because of its proximity, at only 6 light years, Barnard…
Start: 12:15h
Speaker: Ignasi Ribas (ICE - IEEC)
Place: Alberto Lobo room


Last week we announced the discovery of a candidate super-Earth planet around Barnard’s Star. The planet was found using nearly 800 radial velocities from seven different spectrographs in a large observational effort spanning over 20 years. Because of its proximity, at only 6 light years, Barnard b has potential for further characterisation, including direct imaging. In this talk we will present the details of the search and the analysis of the data, and we will put this new planet in a broad context.
(E. Herrero, M. Perger., A Rosich, I. Ribas)
 
16
November 2018

SEAGLE: Disentangling galaxy formation with strong gravitational lensing


Start: 12:15h
Speaker: Sampath Mukherjee
Place: Sala Alberto Lobo

The structure and formation of early-type galaxies (ETGs) can be studied in details using the technique of strong gravitational lensing. In particular, analyzing ETGs in hydrodynamical simulations. I will introduce the SEAGLE (i.e. Simulating EAGLE LEnses) pipeline, that approaches the study of galaxy…
Start: 12:15h
Speaker: Sampath Mukherjee
Place: Sala Alberto Lobo

The structure and formation of early-type galaxies (ETGs) can be studied in details using the technique of strong gravitational lensing. In particular, analyzing ETGs in hydrodynamical simulations. I will introduce the SEAGLE (i.e. Simulating EAGLE LEnses) pipeline, that approaches the study of galaxy formation through strong gravitational lensing, using a suite of high-resolution hydrodynamic simulations, Evolution and Assembly of GaLaxies and their Environments (EAGLE) project, with the aim of inferring their mass density profiles, dark matter (DM) and baryonic content and mass structure on kilo-parsec scales. This involves bridging analytic modeling, hydrodynamic-numerical simulations, and observations in studying the signature of different galaxy formation physics going on. I will present evidence for mass fluctuations in the DM halos of lensing galaxies via power spectrum studies and constrain the contribution of DM and baryons in them. This also includes generating synthetic realistic lenses systems corresponding to ongoing and upcoming surveys e.g. KiDS, DES, JWST, LSST, and Euclid, in order to predict what can be expected from them. I will show that the galaxy evolution models with either too weak or too strong stellar and/or AGN feedback fail to explain the distribution of observed mass-density slopes. On the other hand, models with constant stellar feedback, or weaker AGN feedback produce strong lenses with total mass density slopes close to isothermal. Further, I will disentangle the degeneracies among DM and stellar initial mass function (IMF) with new IMF variation simulations of EAGLE.
09
November 2018

Voyager probing dark matter


Start: 12:15h
Speaker: Mathieu Boudaud (Laboratoire de Physique Théorique et Hautes Energies )
Place: Sala Alberto Lobo (ICE building, Campus UAB)

About 40 years after its launch in 1977, the famous Voyager-1 spacecraft has crossed the heliopause in 2012 and is now exploring the local interstellar medium while sending us unprecedented data. This opens up a new avenue to probe local dark matter via cosmic ray electrons and positrons in the sub-GeV…
Start: 12:15h
Speaker: Mathieu Boudaud (Laboratoire de Physique Théorique et Hautes Energies )
Place: Sala Alberto Lobo (ICE building, Campus UAB)

About 40 years after its launch in 1977, the famous Voyager-1 spacecraft has crossed the heliopause in 2012 and is now exploring the local interstellar medium while sending us unprecedented data. This opens up a new avenue to probe local dark matter via cosmic ray electrons and positrons in the sub-GeV energy range. After describing a novel semi-analytical method (pinching method) which provides us a complete description of the transport of electrons and positrons at low energy, I’ll present predictions for both the secondary astrophysical background and the pair production mechanisms relevant to dark matter particles annihilation or decay down to the MeV mass range. We combined the constraints from the Voyager and AMS-02 data to get novel and robust limits covering a very extended dark matter particle mass range, from MeV to TeV. For velocity dependent annihilation processes (p-wave), we make use of the Eddington method to compute the phase space distribution function of dark matter particles from the most recent constrained mass model of the Galaxy. Primordial black holes are alternative and also well-motivated candidates for dark matter. Black holes with a mass smaller than ~10^17 g are expected to inject electrons and positrons in the Galaxy through Hawking radiation. I’ll show that Voyager is sensitive to signatures from such black holes and I’ll present novel constraints on the contribution of primordial black holes to dark matter in this mass window. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the extragalactic gamma ray background.
26
October 2018

Water in chondritic asteroids: astrobiological implications for the delivery of water to Earth


Start: 12:15h
Speaker: Josep M. Trigo-Rodríguez (ICE)
Place: Sala Alberto Lobo (ICE building, Campus UAB)

The chondritic meteorites are fragments of undifferentiated asteroids, and their rock-forming minerals carry chemical signatures providing information about the early solar system environment. A hot topic of debate is the delivery of volatiles to terrestrial planets, understanding that the…
Start: 12:15h
Speaker: Josep M. Trigo-Rodríguez (ICE)
Place: Sala Alberto Lobo (ICE building, Campus UAB)

The chondritic meteorites are fragments of undifferentiated

asteroids, and their rock-forming minerals carry chemical signatures

providing information about the early solar system environment. A hot

topic of debate is the delivery of volatiles to terrestrial planets,

understanding that the rocks forming our planet were formed under far

more reducing conditions than the carbonaceous chondritic bodies. I'll

present evidence for the accretion of ices and hydrated minerals in

carbonaceous asteroids formed in distant regions of the protoplanetary

disk. At about 5 A.U. highly porous carbon and water-rich materials

consolidated, including stellar grains from nearby stars with

particular isotopic signatures. Some well-preserved carbonaceous

chondrites escaped significant thermal and aqueous alteration so they

present unique features that can be interpreted as evidence of wet

accretion, with direct implications for the delivery of water to Earth

and terrestrial planets. Being the Earth formed 4.5 Ga ago from a more

reducing environment, the last stages of heavy bombardment were

protagonized by transitional asteroids that delivered a significant

part of the terrestrial water.
Institute of Space Sciences (IEEC-CSIC)

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An institute of the Consejo Superior de Investigaciones Científicas

An institute of the Consejo Superior de Investigaciones Científicas
Affiliated with the Institut d'Estudis Espacials de Catalunya

Affiliated with the Institut d'Estudis Espacials de Catalunya