Search

Identifying very high-redshift galaxies is crucial for understanding the formation and evolution of galaxies. However, many questions still remain, and the uncertainty on the epoch of reionization is large. In this approach, some models allow a double-reionization scenario, although the number of confirmed detections at very high $z$ is still too low to serve as observational proof. The main goal of this project is studying whether we can search for Lyman-$\alpha$ emitters (LAEs) at $z \sim 9$ using a narrow-band (NB) filter that was specifically designed by our team and was built for this experiment. We used the NB technique to select candidates by measuring the flux excess due to the Ly$\alpha$ emission. The observations were taken with an NB filter (full width at half minimum of 11 nm and central wavelength $\lambda_{c} = 1.257 \mu$m) and the CIRCE near-infrared camera for the GTC. We describe a data reduction procedure that was especially optimized to minimize instrumental effects. With a total exposure time of 18.3 hours, the final NB image covers an area of $\sim 6.7$ arcmin$^{2}$, which corresponds to a comoving volume of $1.1 \times 10^{3}$ Mpc$^{3}$ at $z = 9.3$. We pushed the source detection to its limit, which allows us to analyze an initial sample of 97 objects. We detail the different criteria we applied to select the candidates. The criteria included visual verifications in different photometric bands. None of the objects resembled a reliable LAE, however, and we found no robust candidate down to an emission-line flux of $2.9 \times 10^{-16}$ erg s$^{-1} $cm$^{-2}$, which corresponds to a Ly$\alpha$ luminosity limit of $3 \times 10^{44}$ erg s$^{-1}$. We derive an upper limit on the Ly$\alpha$ luminosity function at $z \sim 9$ that agrees well with previous constraints. We conclude that deeper and wider surveys are needed to study the LAE population at the cosmic dawn., Comment: 17 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2021, Tutor: Josep Maria Solanes Majúa, We present a study of double-peaked (DP) emission-line galaxies at z < 0:1 based on a subset of 84; 492 spectra extracted from the SDSS catalog. We have performed an automated selection procedure of DP spectra by adapting a previously existing routine developed for stars. A total of 5; 682 galaxies of the parent database have been found to exhibit a significant double peak in at least one of the four emission lines traditionally used in the Baldwin, Phillips and Terlevich (BPT) diagrams to discriminate among different ionization mechanisms. A preliminary investigation on the possible existence of an anti-correlation between the ratios of fluxes from the [OIII] λ 5007 line and velocity shifts of the red and blue components of the DP lines has produced results independent of the BPT classification of the galaxies. For most of the outliers of this relationship we find that the position of the strong [OIII] peak is significantly closer to the stellar velocity than for the weak [OIII] peak. These off-centered outliers could be linked to minor mergers in which central star formation has been enhanced or to objects with asymmetric gas out ows.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2021, Tutor: Alberto Manrique Oliva, Galaxies have been the main protagonist in Cosmology and the study of the Universe for almost a century. Currently, they have become an independent and major field itself. Through the use of AMIGA, an analytic model that examines galaxy formation and evolution since the dark ages, we will study the roles of accretion and mergers as two different ways for galaxies to grow. The model will provide the ratio of mass coming from mergers for several ages. This ratio will be shown according to two different variables: the stellar mass of galaxies and the age of the Universe. We see that the role of mergers increased from z ∼ 10 to z ∼ 4, and had its peak at z ≈ 5, with a value of 30%. This tendency is supported by recent studies on luminosity functions. Finally, even though mergers were the most significant process in the formation of the most massive galaxies, accretion has had the major role in galaxy growth

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2020, Tutors: Friedrich Anders, Mercè Romero-Gómez, We review some of the traits of the Galactic disc and elaborate on the Milky Way's Warp, the recent studies investigating it, and its importance. We focus on the effect of this distortion on different age populations using a broad sample of young objects made up by Cepheids, masers, and HII regions. We attempt a fit on this sample and compare it to other populations models available in the literature. We find less agreement with the similar age population OB model than expected, although some general trends are shared among all the models plotted. We also compare the positions of objects in our sample with respect to a HI Model, but find no evidence regarding a warping trend with age.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2019, Tutor: José María Solanes Majúa, We investigate the process of dynamical friction from the point of view of the dynamics of galaxy mergers. We are particularly interested in providing an accurate formula for the merger time between galactic halos of similar mass, also known as major mergers. We have reviewed the theoretical foundations of this mechanism, as well as used 605 isolated simulations of binary collisions of galaxies to test a new non-separable expression for the merger timescale. Our study reveals some plausible reasons why merger time formulas existing in the literature may not perform successfully for major mergers, related to both the theory and the methodology applied in the analysis of numerical results.

We use Gaia DR2 magnitudes, colours and parallaxes for stars with G1.53 Msun and $��_2 \approx 1.3$ for the mass range between 0,5 and 1,53 Msun. This is the first time that we consider a non-parametric SFH for the thin disc in the Besancon Galaxy Model. This new step, together with the capabilities of the Gaia DR2 parallaxes to break degeneracies between different stellar populations, allow us to better constrain the SFH and the IMF., 6 pages, 3 figures. Accepted for publication to A&A letters

[Context]: Cosmic reionization put an end to the dark ages that came after the recombination era. Observations seem to favor the scenario of massive-star photons generated in low-mass galaxies being responsible for the bulk of reionization and, whereas a possible contribution from AGN accretion disks has been widely considered, they are currently thought to have had a minor role in reionization. [Aims]: We aim to study the possibility of AGN having contributed to reionization not only through their accretion disks, but also through ionizing photons coming from the AGN jets interacting with the intergalactic medium. Methods. We adopt an empirically derived AGN luminosity function at z ≃ 6, use X-ray observations to correct it for the presence of obscured sources, and estimate the density of jetted AGN. We then use analytical calculations to derive the fraction of jet energy that goes into ionizing photons. Finally, we compute the contribution of AGN jets to the H II volume filling factor at redshifts z ≃ 15-5. [Results]: We show that the contribution of the AGN jet lobes to the reionization of the Universe at z ∼ 6 might have been as high as ? 10% of that of star-forming galaxies, under the most favorable conditions of jetted and obscuration fraction. [Conclusions]: The contribution of AGN to the reionization, while most likely not dominant, could have been higher than previously assumed, thanks to the radiation originated in the jet lobes., We acknowledge support by the Spanish Ministerio de Economía y Competitividad (MINECO/FEDER, UE) under grant AYA2016-76012-C3-1-P, with partial support by the European Regional Development Fund (ERDF/FEDER), MDM-2014-0369 of ICCUB (Unidad de Excelencia “María de Maeztu”), and the Catalan DEC Grant 2017 SGR 643. N. T.-A. acknowledges support from MINECO through FPU14/04887 Grant.

The reionization of the Universe ends the dark ages that started after the recombination era. In the case of H, reionization finishes around $z\sim 6$. Faint star-forming galaxies are the best candidate sources of the H-ionizing radiation, although active galactic nuclei may have also contributed. We have explored whether the termination regions of the jets from active galactic nuclei may have contributed significantly to the ionization of H in the late reionization epoch, around $z\sim 6-7$. We assumed that, as it has been proposed, active galactic nuclei at $z\sim 6$ may have presented a high jet fraction, accretion rate, and duty cycle, and that non-thermal electrons contribute significantly to the pressure of jet termination regions. Empirical black-hole mass functions were adopted to characterize the population of active galactic nuclei. From all this, estimates were derived for the isotropic H-ionizing radiation produced in the jet termination regions, at $z\sim 6$, through inverse Compton scattering off CMB photons. We find that the termination regions of the jets of active galactic nuclei may have radiated most of their energy in the form of H-ionizing radiation at $z\sim 6$. For typical black-hole mass functions at that redshift, under the considered conditions (long-lasting, common, and very active galactic nuclei with jets), the contribution of these jets to maintain (and possibly enhance) the ionization of H may have been non-negligible. We conclude that the termination regions of jets from active galactic nuclei could have had a significant role in the reionization of the Universe at $z\gtrsim 6$., Comment: Letter to the Editor accepted for publication in Astronomy & Astrophysics, very minor changes introduced

Context: The Initial Mass Function (IMF) plays a crucial role on galaxy evolution and its implications on star formation theory make it a milestone for the next decade. It is in the intermediate and high mass ranges where the uncertainties of the IMF are larger. This is a major subject of debate and analysis both for Galactic and extragalactic science. Aims: Our goal is to constrain the IMF of the Galactic thin disc population using both Galactic Classical Cepheids and Tycho-2 data. Methods: For the first time the Besan\c{c}on Galaxy Model (BGM) has been used to characterise the Galactic population of the Classical Cepheids. We have modified the age configuration in the youngest populations of the BGM thin disc model to avoid artificial discontinuities in the age distribution of the simulated Cepheids. Three statistical methods, optimized for different mass ranges, have been developed and applied to search for the best IMF that fits the observations. This strategy allows us to quantify variations in the Star Formation History (SFH), the stellar density at Sun position and the thin disc radial scale length. A rigorous treatment of unresolved multiple stellar systems has been undertaken adopting a spatial resolution according to the catalogues used. Results: For intermediate masses, our study favours a composite field-star IMF slope of $\alpha=3.2$ for the local thin disc, excluding flatter values such as the Salpeter IMF ($\alpha=2.35$). Moreover, a constant Star Formation History is definitively excluded, the three statistical methods considered here show that it is inconsistent with the observational data. Conclusions: Using field stars and Galactic Classical Cepheids, we have found, above $1M_\odot$, an IMF steeper than the canonical stellar IMF of associations and young clusters. This result is consistent with the predictions of the Integrated Galactic IMF., Comment: 12 pages, 11 figures, accepted for publication at A&A

[eng] The work presented in this Ph.D. thesis is mostly related to the measurement and interpretation of the cross-correlation of different species. This is achieved using spectroscopic data from the BOSS survey of which I am a member. Along the thesis I will be visiting the cross-correlation of different tracers. This tracers include the Mg II absorbers, the Damped Lyα Systems (DLA), the Lyα forest, the quasars and the galaxies. Save the last mentioned, all tracers are measured from quasar spectra from BOSS. The galaxies are taken from the BOSS CMASS catalogue. The first cross-correlation I address is that of Mg II absorbers with CMASS galaxies. I present a new method for measuring the equivalent width of metal absorbers, developed in collaboration with Britt Lundgren and Jordi Miralda- Escud´e, and I apply it to the absorption doublet. Then I shift my attention to the DLAs and the Ly forest. Since the Lyα forest autocorrelation has already been studied (see e.g. Delubac et al. 2015; Blomqvist et al. 2015), the Lyα parameters are well constrained. I use those constraints to provide more accurate measurements of the DLA bias when analysing the cross-correlation of DLAs with the Lyα forest. The study has been made in collaboration with Andreu Font-Ribera, Nicol´as Busca, and Jordi Miralda-Escud´e. In particular, the estimator for the cross-correlation was orig- inally developed by Nicol´as Busca for the analysis of the Lyα autocorrelation and later adapted to the measurement of the cross-correlation. The first two cross-correlations studied and more importantly their interpre- tation, are mostly focused on large scales, where the linear theory is valid. At smaller scales, non-linear effects start to kick in and the linear approximation is no longer valid. I measure the cross-correlation of quasars with the Lyα forest, and focus on the small scales effects. I show that a contamination from metals is clearly present in the cross-correlation. Also, I discuss some of the possible non-linear effects and give a simple theoretical model to explain the effect that quasar radiation can have in the surrounding hydrogen clouds., [cat] El treball fet en aquesta tesi doctoral es basa principalment en la mesura i interpretació de la correlació creuada entre diferents traçadors. Els traçadors emprats en aquesta tesi són les galàxies del catàleg CMASS, els quàsars del catàleg de Baryon Oscillations Spectroscopic Survey (BOSS), els sistemes absorbidors de MgII, el bosc de Lya i els sistemes Lya esmorteïts o DLAs (els tres darrers són sistemes absorbidors detectats als espectres dels quàsars). El projecte BOSS és un dels quatre projectes que han composat la tercera fase de la col·laboració de l’Sloan Digital Sky Survey (SDSS) el principal objectiu del qual ha estat la detecció del senyal de les oscil·lacions acústiques dels barions (BAO, de l’anglès Baryon Acoustic Oscillations) i que ha estat recollint espectres electromagnètics de quàsars i galàxies des de la tardor de 2013 fins a la tardor de 2014. L’estructura d’aquesta tesi es divideix en tres capítols que fan referència a l’estudi de diferents traçadors. En el capítol ì els traçadors emprats són les galàxies de CMASS i els sistemes absorbidors de MgII; en el capítol 3, els DLA i el bosc de Lya, i en el capítol 5, els quàsars i el bosc de Lya. A més la tesi compta amb una introducció en català, una altra en anglès i un compendi de les conclusions obtingudes.

We present an Analytic Model of Intergalactic-medium and GAlaxy evolution since the dark ages. AMIGA is in the spirit of the popular semi-analytic models of galaxy formation, although it does not use halo merger trees but interpolates halo properties in grids that are progressively built. This strategy is less memory-demanding and allows one to start the modeling at redshifts high enough and halo masses low enough to have trivial boundary conditions. The number of free parameters is minimized by making the causal connection between physical processes usually treated as independent from each other, which leads to more reliable predictions. But the strongest points of AMIGA are: i) the inclusion of molecular cooling and metal-poor, population III (Pop III) stars, with the most dramatic feedback, and ii) the accurate follow-up of the temperature and volume filling factor of neutral, singly, and doubly ionized regions, taking into account the distinct halo mass functions in those environments. We find the following general results. Massive Pop III stars determine the IGM metallicity and temperature, and the growth of spheroids and disks is self-regulated by that of massive black holes developed from the remnants of those stars. Yet, the properties of normal galaxies and active galactic nuclei appear to be quite insensitive to Pop III star properties owing to the much higher yield of ordinary stars compared to Pop III stars and the dramatic growth of MBHs when normal galaxies begin to develop, which cause the memory loss of the initial conditions., Comment: 18 pages, 7 figures, accepted for publication in ApJS

We present an analysis of [OI]63, [OIII]88, [NII]122 and [CII]158 far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ~240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS). We find pronounced declines -deficits- of line-to-FIR-continuum emission for [NII]122, [OI]63 and [CII]158 as a function of FIR color and infrared luminosity surface density, $\Sigma_{\rm IR}$. The median electron density of the ionized gas in LIRGs, based on the [NII]122/[NII]205 ratio, is $n_{\rm e}$ = 41 cm$^{-3}$. We find that the dispersion in the [CII]158 deficit of LIRGs is attributed to a varying fractional contribution of photo-dissociation-regions (PDRs) to the observed [CII]158 emission, f([CII]PDR) = [CII]PDR/[CII], which increases from ~60% to ~95% in the warmest LIRGs. The [OI]63/[CII]158PDR ratio is tightly correlated with the PDR gas kinetic temperature in sources where [OI]63 is not optically-thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, $n_{\rm H}$, and intensity of the interstellar radiation field, in units of G$_0$, and find G$_0$/$n_{\rm H}$ ratios ~0.1-50 cm$^3$, with ULIRGs populating the upper end of the distribution. There is a relation between G$_0$/$n_{\rm H}$ and $\Sigma_{\rm IR}$, showing a critical break at $\Sigma_{\rm IR}^{\star}$ ~ 5 x 10$^{10}$ Lsun/kpc$^2$. Below $\Sigma_{\rm IR}^{\star}$, G$_0$/$n_{\rm H}$ remains constant, ~0.32 cm$^3$, and variations in $\Sigma_{\rm IR}$ are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above $\Sigma_{\rm IR}^{\star}$, G$_0$/$n_{\rm H}$ increases rapidly with $\Sigma_{\rm IR}$, signaling a departure from the typical PDR conditions found in normal star-forming galaxies towards more intense/harder radiation fields and compact geometries typical of starbursting sources., Comment: 23 pages, 12 figures. Submitted to ApJ, including 2nd round of referee comments. Data tables can be found at: http://goals.ipac.caltech.edu/ and will also appear on the electronic version of the journal

Context. The understanding of Galaxy evolution can be facilitated by the use of population synthesis models, which allow to test hypotheses on the star formation history, star evolution, as well as chemical and dynamical evolution of the Galaxy. Aims. The new version of the Besanc¸on Galaxy Model (hereafter BGM) aims to provide a more flexible and powerful tool to investigate the Initial Mass Function (IMF) and Star Formation Rate (SFR) of the Galactic disc. Methods. We present a new strategy for the generation of thin disc stars which assumes the IMF, SFR and evolutionary tracks as free parameters. We have updated most of the ingredients for the star count production and, for the first time, binary stars are generated in a consistent way. We keep in this new scheme the local dynamical self-consistency as in Bienayme et al (1987). We then compare simulations from the new model with Tycho-2 data and the local luminosity function, as a first test to verify and constrain the new ingredients. The effects of changing thirteen different ingredients of the model are systematically studied. Results. For the first time, a full sky comparison is performed between BGM and data. This strategy allows to constrain the IMF slope at high masses which is found to be close to 3.0, excluding a shallower slope such as Salpeter"s one. The SFR is found decreasing whatever IMF is assumed. The model is compatible with a local dark matter density of 0.011 M pc−3 implying that there is no compelling evidence for significant amount of dark matter in the disc. While the model is fitted to Tycho2 data, a magnitude limited sample with V

The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the northern GLIMPSE region (10 deg < l < 65 deg), observed by the Spitzer satellite in the mid-infrared. Observations with the Very Large Array in B and BnA configurations have yielded a 1.5" resolution Stokes I map with a root-mean-squared noise level better than 0.4 mJy/beam. Here we describe the data-processing methods and data characteristics, and present a new, uniform catalogue of compact radio-emission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimised to detect emission on size scales up to 14" and for unresolved sources the catalogue is more than 90 percent complete at a flux density of 3.9 mJy. We have detected 3,062 sources above a 7-sigma detection limit and present their ensemble properties. The catalogue is highly reliable away from regions containing poorly-sampled extended emission, which comprise less than two percent of the survey area. Imaging problems have been mitigated by down-weighting the shortest spacings and potential artefacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: regions, planetary nebulae and radio-galaxies. The CORNISH data and catalogue are available online at http://cornish.leeds.ac.uk, 25 pages, 22 figures. To appear in ApJ. Sup

The understanding of the origin and evolution of the Milky Way is one of the primary goals of the Gaia mission (ESA, launch autumn 2013). In order to study and analyse fully the Gaia data it will be useful to have a Galaxy model able to test various hypothesis and scenarios of galaxy formation and evolution. Kinematic and star count data, together with the physical parameters of the stars - ages and metallicities-, will allow to characterize our galaxy's populations and, from that, the overall Galactic gravitational potential. One of the promising procedures to reach such goal is to optimize the present Population Synthesis models (Robin et al. (2003)) by fitting, through robust statistical techniques, the large and small scale structure and kinematics parameters that best will reproduce Gaia data. This PhD thesis was focused on the optimization of the structure parameters of the Milky Way Galactic disc. We improved the Besançon Galaxy Model and then by comparing the simulations to real data studied the process of Galaxy evolution. The Besançon Galaxy Model is a stellar population synthesis model, built over the last two decades in Besançon (Robin and Crézé(1986); Robin et al. (2003)). Until now the star production process in that model was based on the drawing from the so called Hess diagrams. Each Galaxy population had one such a diagram, which was calculated once given a particular Initial Mass Function (IMF), Star Formation Rate (SFR), evolutionary tracks and age-metallicity relation and since then remained fixed in the model. As that feature was not enabling to test any other scenario of Galaxy evolution, because none of the evolutionary parameters could be modified, it was one of the biggest weaknesses of the model. It has served us as a motivation to dedicate this PhD project to the construction of a new version of the model, which would be able to handle variations of the SFR, IMF, evolutionary tracks, atmosphere models among others. When the evolutionary parameters are changed one must repeat the process of accomplishing the dynamical self-consistency of the model as described in Bienayme et al. (1987). For that we have recalculated the Galactic gravitational potential for all new evolutionary scenarios, which have been tested. The second very important improvement of the model, which is delivered in this thesis, is the implementation of the stellar binarity. That is, the new version of Besançon Galaxy Model presented here is not any more a single star generator, but it considers binary systems maintaining constraints on the local mass density. This is an important change since binaries can account for about 50 % of the total stellar content of the Milky Way. Once the tool was developed we tested several possible combinations of IMF and SFR in the Solar Neighborhood and identified those which best reproduce the Local Luminosity Function and Tycho-2 data. We have accomplished an unprecedented task using the new version of the model, namely we have performed the whole sky comparisons for a magnitude limited sample in order to study the bright stars. The Tycho-2 catalogue turned out to be an ideal sample for that task due to its two important advantages, the homogeneity and completeness until VT ~ 11 mag. Different techniques and strategies were designed and applied when comparing the simulated and the real data. We have looked at small and specific Galactic directions and also performed general comparisons with a global sky coverage. In order to increase the efficiency of numerous simulations and comparisons, a processing pipeline based on C, Java and scripting programming languages has been developed and applied. It is a fully automated, portable and robust tool, allowing to split the work across several computational units., La misión Gaia (ESA, 2013) revolucionará el conocimiento sobre el origen y la evolución de nuestra Galaxia. Una óptima explotación científica de sus datos requiere disponer de modelos que permitan contrastar hipótesis y escenarios sobre estos procesos de formación. En esta tesis hemos optimizado el modelo de síntesis de poblaciones estelares de Besançon, ampliamente utilizado por la comunidad internacional, centrándonos en la componente del disco delgado. Hemos diseñado, desarrollado, implementado y testeado una nueva estructura de generación de las estrellas que permite encontrar la mejor combinación de función inicial de masa (IMF) y ritmo de formación estelar (SFR) que ajusta a las observaciones. El código permite imponer la autoconsistencia dinámica, recalculando el potencial galáctico para cada nuevo escenario de evolución. También, por primera vez, se generan sistemas binarios bajo esta consistencia dinámica, marcada por la función de luminosidad observada en el entorno solar. Esta, junto con el catálogo Tycho, han sido los dos ingredientes observacionales clave para el ajuste entre modelo y observación. También, por primera vez, hemos conseguido un ajuste aceptable a los recuentos estelares de todo el cielo hasta V=11. Se han evaluado con rigor los efectos en los recuentos estelares derivados del uso de los modelos de atmosfera, de evolución estelar y de extinción interestelar así como de parámetros tan críticos como la masa dinámica del sistema galáctico. El ajuste de estos ingredientes usando el catálogo Tycho nos ha permitido confirmar, de una vez por todas, que la SFR en el disco galáctico no ha sido constante sino decreciente desde los inicios de la formación de esta estructura. En conclusión, esta tesis proporciona un nuevo código, optimizado y flexible en el uso de los ingredientes básicos, en el que se ha realizado una rigurosa evaluación y actualización de los ingredientes que lo componen.

We describe the motivation, design, and implementation of the CORNISH survey, an arcsecondresolution radio continuum survey of the inner galactic plane at 5 GHz using the Very Large Array (VLA). It is a blind survey coordinated with the northern SpitzerGLIMPSE I region covering 10°

Using the publicly available VESPA database of SDSS Data Release 7 spectra, we calculate the stellar Mass Weighted Age (hereafter MWA) as a function of local galaxy density and dark matter halo mass. We compare our results with semi-analytic models from the public Millennium Simulation. We find that the stellar MWA has a large scatter which is inherent in the data and consistent with that seen in semi-analytic models. The stellar MWA is consistent with being independent (to first order) with local galaxy density, which is also seen in semi-analytic models. As a function of increasing dark matter halo mass (using the SDSS New York Value Added Group catalogues), we find that the average stellar MWA for member galaxies increases, which is again found in semi-analytic models. Furthermore we use public dark matter Mass Accretion History (MAH) code calibrated on simulations, to calculate the dark matter Mass Weighted Age as a function of dark matter halo mass. In agreement with earlier analyses, we find that the stellar MWA and the dark matter MWA are anti correlated for large mass halos, i.e, dark matter accretion does not seem to be the primary factor in determining when stellar mass was compiled. This effect can be described by down-sizing., Comment: 11 pages, 3 figures, submitted to MNRAS

The availability of the Hipparcos Catalogue has triggered many kinematic and dynamical studies ofthe solar neigh-bourhood. Nevertheless, those studies generally lacked the third component of the space velocities, i.e., the radial velocities.This work presents the kinematic analysis of 5952 K and 739 M giants in the solar neighbourhood which includes for the firsttime radial velocity data from a large survey performed with the CORAVEL spectrovelocimeter. It also uses proper motionsfrom the Tycho-2 catalogue, which are expected to be more accurate than the Hipparcos ones. An important by-product of thisstudy is the observed fraction of only 5.7% of spectroscopic binaries among M giants as compared to 13.7% for K giants. Afterexcluding the binaries for which no center-of-mass velocity could be estimated, 5311 K and 719 M giants remain in the finalsample.TheUV-plane constructed from these data for the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scalestructure, with several clumps corresponding to the Hercules stream, the Sirius moving group, and the Hyades and Pleiadessuperclusters. A maximum-likelihood method, based on a Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes) and to derive the kinematic properties of these subgroups.Isochrones in the Hertzsprung-Russell diagram reveal a very wide range of ages for stars belonging to these groups. Thesegroups are most probably related to the dynamical perturbation by transient spiral waves (as recently modelled by De Simoneet al. 2004) rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same area oftheUV-plane is that they have been put there by the spiral wave associated with their formation, while the kinematics of theolder stars of our sample has also been disturbed by the same wave. The emerging picture is thus one ofdynamical streamspervading the solar neighbourhood and travelling in the Galaxy with similar space velocities. The termdynamical streamismore appropriate than the traditional termsuperclustersince it involves stars of different ages, not born at the same place norat the same time. The position of those streams in theUV-plane is responsible for the vertex deviation of 16.2◦±5.6◦for thewhole sample. Our study suggests that the vertex deviation for younger populations could have the samedynamicalorigin.The underlying velocity ellipsoid, extracted by the maximum-likelihood method after removal of the streams, is not centeredon the value commonly accepted for the radial antisolar motion: it is centered on〈U〉=−2.78±1.07 km s−1.However,thefull data set (including the various streams)doesyield the usual value for the radial solar motion, when properly accountingfor the biases inherent to this kind of analysis (namely,〈U〉=−10.25±0.15 km s−1). This discrepancy clearly raises theessential question of how to derive the solar motion in the presence of dynamical perturbations altering the kinematics of thesolar neighbourhood: does there exist in the solar neighbourhood a subset of stars having no net radial motion which can beused as a reference against which to measure the solar motion?

This thesis is focused on the implication of de dynamics of clusters on the HI content of galaxies. Target of this study has been the Virgo cluster region.We have first inferred the three-dimensional galaxy distribution of the Virgo cluster using Tully-Fisher distance estimates from eight published datasets. The spiral distribution is found to be very elongated along the line of sight. This filamentary structure is also reflected by the HI-deficient objects. We found a central enhancement in the HI distribution, arising from galaxies that belong to the Virgo cluster proper. However, significant gas deficiencies were also detected outside the main body of the cluster in a probable group of galaxies at distances circa 25 to 30 Mpc, as well as in various foreground galaxies. The presence on the Virgo cluster outskirts of spiral galaxies with gas deficiencies as strong as those of the inner galaxies likely stripped by the intracluster medium (ICM) has led us to explore the possibility that some of these peripheral objects were not newcomers. A dynamical model for the collapse and rebound of spherical shells was developed. According to our analysis, it is not unfeasible that galaxies far from the cluster went through its core a few Gyr ago. In order to further investigate this possibility, we have estimated the maximum radius out to which galaxies can bounce out of a virialized system, using both cosmological N-body simulations and analytical arguments. We have shown that material that falls into a cosmological structure cannot bounce out beyond circa2.5 virial radii. This would explain the presence of stripped galaxies up to circa2 virial radii, which is more than twice the extension of the ICM revealed by the X-ray maps. After estimating the virial radius and mass of the Virgo cluster from X-ray observations, the peripheral HI-deficient galaxies appear to lie significantly farther away from the cluster centre. Therefore, it does not seen plausible that these galaxies have crossed the cluster core if their distance estimates are accurate. The velocity field drawn by the Virgo cluster has been further studied by comparing the positions of both spiral and elliptical galaxies in velocity-distance plots with simulated diagrams obtained from cosmological N-body simulations. We have found that circa20% relative Tully-Fisher distance error is consistent with the great majority of the galaxies. We have shown, moreover, that distance errors may lead to an incorrect fitting of infall models that can generate significant errors in the distance and, specially, in the mass estimates of clusters. In addition, we have investigated in detail the feasibility of four possibilities for the origin of the dearth of neutral gas in the outlying HI-deficient Virgo spirals: 1) large relative distance errors so these galaxies have passed through its core and seen their gas removed by ram pressure stripping; 2) tidal interactions with other galaxies; 3) recent mergers with smaller galaxies; and 4) an erroneous determination of their gas content (e.g. S0/a's misclassified as Sa's).Finally, the cosmological N-body simulations of dark matter halos have also been used to study the effects of non-sphericity, substructure and streaming motions on the structure and internal kinematics of clusters recovered from the Jeans analysis. We found that the virial mass, concentration parameter and velocity anisotropy of the halos can be reproduced satisfactory independently of the halo shape, although the viral mass tends to be underestimated, the concentration parameter overestimated, while the recovered anisotropy is typically more tangential that the true one. The mass, concentration and velocity anisotropy of halos are recovered with better precision when their mean velocity profiles are near zero.

In a first paper, HIPPARCOS astrometric and kinematic data were used to calibrate both infrared K and IRAS luminosities at the same time as kinematic parameters of Long Period Variable stars (LPVs). Individual estimated absolute magnitudes and a probabilistic assignation to galactic populations were deduced from these calibrations for each LPV of our sample. Here we propose a scenario of simultaneous stellar and circumstellar evolution according to the galactic populations. The transitory states of S and Tc stars allow us to confirm the location of the first dredge-up at $M_{bol}=-3.5$. There is also evidence suggesting that a previous enrichment in s-elements from a more evolved companion may accelerate the evolution along the AGB. The possible evolution to OH LPVs is included in this scenario, and any of these stars may have a mass at the limit of the capability for a C enrichment up to C/O > 1. A list of bright massive LPVs with peculiar envelope and luminosity properties is proposed as Hot Bottom Burning candidates. The He-shell flash star, R Cen, is found to be exceptionally bright and could become, before leaving the AGB, a C-rich LPV brighter than the usual luminosity limit of carbon stars., Accepted for publication in Astronomy & Astrophysics

[spa] Un modelo de evolución galáctica permite representar los cambios que ocurren desde la formación de la galaxia hasta su estado actual, atendiendo fundamentalmente a las características evolutivas de las estrellas que la constituyen y a su ritmo de crecimiento. Dado que un modelo global de evolución debe ser necesariamente un compendio de los resultados de numerosas teorías individuales que describen fenómenos particulares de la galaxia, se trata de un instrumento de gran utilidad para buscar y confirmar (o en su caso negar) relaciones entre las teorías que lo componen, o bien para comparar modelos galácticos que representen galaxias de diversas clases. Actualmente no puede hablarse de un modelo evolutivo úinico, ya que el escaso conocimiento que se tiene de algunas cuestiones dan lugar a varios modelos, todos ellos coherentes con los datos de que se dispone. En su ya clásico artículo de 1957, Burbidge et al. conseguían explicar la síntesis del litio a partir del hidrógeno y del helio en las reacciones termonucleares que se dan en el interior de las estrellas. Sin embargo, al ser un elemento muy frágil y hallarse expuesto continuamente al bombardeo por protones, era destruido “in situ”. Su conclusión era que los elementos ligeros se deberían producer en un medio a temperatura y densidad bajas, por un mecanismo entonces no conocido que denominaron “proceso x”. El hecho de que los elementos ligeros sean fácilmente destruidos en los interiors estelares hace especialmente interesante su inclusion y studio en un modelo de evolución química de la galaxia, pues del conocimiento de la variación de sus abundancias en el gas interestelar y en las estrellas se podrá deducir la importancia de los diversos mecanismos que los sintetizan y destruyen, y su incidencia en la evolución de la galaxia. Dejando aparte la possible producción cosmológica del litio, las contribuciones más importantes a la formación de elementos ligeros se dan a partir de la radiación cósmica, al interaccionar ésta con el medio interestelar produciéndose reacciones de astillado a alta energía, y por reacciones del mismo tipo con partículas supratérmicas de baja energía en las inmediaciones de las supernovas y en las atmósferas de estrellas gigantes, material que posteriormente pierde la Estrella por viento estelar. La abundancia final de elementos ligeros en el medio interestelar será el resultado de la mezcla del gas con el material irradiado y enriquecido en estos procesos. En este trabajo se estudiará la evolución de dichos elementos en el marco de diversos modelos galáctivos y a la luz de los últimos resultados sobre su formación por la radiación cósmica galáctica (Reeves y Meyer 1978), y en las supernovas y estrellas gigantes (Canal, Isern y Sanahuja 1975, 1977 a/b).

We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to $M_{*} = 10^{8}M_{\odot}$ with mass ratios of $$4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at $\sim1.3-2\%$ between $10^{9.5}, Comment: Accepted for publication in MNRAS: 14 Pages, 16 Figures, 3 Tables