Found 183 talks archived in Galaxies

simon_diaz_garcia_140212s
Wednesday February 12, 2014
Mr. Simon Diaz Garcia
University of Oulu (Finland)

Abstract

The ΛCDM model predicts that galaxies originate in dark matter haloes, undergoing in their early age a process of continuous merges with other galaxies that determines the first part of their evolution. The frequency of these events decreases with time and their gradual change turns to be internally driven, becoming much slower. Bars, elongated stellar structures in the central regions of galaxies, are known to play an active role in this phase of their evolution, so-called secular.

Bars are fundamentally responsible for the redistribution of matter and the angular momentum of the baryonic and dark matter components of disc galaxies. Different simulations predict that bars get stronger and longer in time, slowing down their rotation speed.

Based on the Spitzer Survey of Stellar Structure in Galaxies (S4G) 3.6 μm imaging, we aim to study the secular evolution of disc galaxies by focusing on their stellar bar parameters. We take a large well-defined sample of about 650 nearby barred galaxies and we infer the gravitational potential from 3.6 μm images. We calculate gravitational torques, the ratio of the maximal tangential force to the mean axisymmetric radial force, in order to obtain a quantitative measure of the bar-induced perturbation strengths. In addition, we estimate the bar strength from the m=2 normalized Fourier density amplitudes and determine bar lengths both visually and by using an ellipse fitting method. Bar morphology and the interplay with spiral arms are studied via image-stacking methods as well.

In this talk I will present the statistical results derived from our measurements, providing observational evidence for the evolution of bars in accordance with the current theoretical predictions. We study bar parameters as a function of the Hubble type, addressing how the different measurements of the bar strength correlate with each other and with the galactic mass. The quality of our data allows us to probe the properties of bars in the Local Universe and connect them to the evolution of other galactic structures.


divakara_mayya_140129s
Wednesday January 29, 2014
Dr. Divakara Mayya
INAOE

Abstract

The nearby spiral galaxy M81 contains a population of 3 kinds of stellar clusters - super star clusters, globular clusters and fuzzy clusters. Over the past few years, we have taken GTC longslit spectra of around 20 of these clusters, with the intention of obtaining their spectroscopic ages. These spectra have allowed us to understand the nature of the brightest globular cluster in this galaxy. In addition, we were able to address the problem of the origin of the fuzzy clusters. In the talk, I will summarize the results we have obtained so far.


francisco_prada_140121s
Tuesday January 21, 2014
Prof. Francisco Prada
Instituto de Física Teórica UAM/CSIC, Madrid

Abstract

DESI is a massively multiplexed fiber-fed spectrograph that will make the next
major advance in dark energy in the timeframe 2018-2022. On the Mayall
telescope, DESI will obtain spectra and redshifts for tens of millions of
galaxies and cuasars with 5,000 fiber postioner robots, constructing a
3-dimensional map spanning the nearby universe to 10 billion light years. DESI
is supported by the US Department of Energy Office of Science to perform this
Stage IV dark energy measurement using baryon acoustic oscillations and other
techniques that rely on spectroscopic measurements. Spain has a major role in
DESI with the construction of the Focal Plate and the development of the fiber
positioners. I will give an overview of the DESI science, instrument, and Spain
participation in the project.


anna_ferre_mateu_140114s
Tuesday January 14, 2014
Dr. Anna Ferré-Mateu
National Astronomical Observatory of Japan

Abstract

Galaxy clusters are the perfect places to study both the always controversial nature vs nurture problem and the still not well understood evolution that galaxies follow. By studying the properties of the galaxies at different locations of the cluster we can assess the first problem, while studying the same properties over cosmic time, helps constraining the different proposed evolutionary theories. In this work we have focused in an intermediately-redshift rich cluster, RX J0152.7-1357 (z=0.83), by fully characterizing its stellar population properties with new state-of-the-art tools . By this means, we have derived for the first time in such a high-z cluster the ages, metallicities, abundance patterns and Star Formation Histories of the cluster ETGs on an individual galaxy-basis . The relations that these properties follow with galaxy velocity dispersion allow us to discuss a passive evolution scenario with respect to a cluster at z~0. Our results favor a downsizing picture where the relation between the position within the cluster, the velocity dispersion and the type of star formation history of the galaxies allow us to better understand the cluster evolution. We find that the most massive galaxies evolve passively while the lower-mass ones, generally located at the outskirts of the cluster, experience a more extended star formation history related to their later incorporation in the cluster.


Ruben_Sanchez_Janssen_140108s
Wednesday January 8, 2014
Dr. Ruben Sanchez-Janssen
NRC Herzberg Institute of Astrophysics

Abstract

Two competing effects appear to govern galaxy multiplicity (pairs orgroups) at low masses: while associations of low-mass haloes are naturally expected in a LCDM cosmology, galaxy formation within these haloes is thought to be rendered inefficient due to the action of several ionizing agents. Yet associations of dwarf galaxies are known to exist in the Local Volume, and their frequency appears to be unexpectedly high for LCDM expectations even in our own Local Group. Unfortunately, it is not yet well understood what role do interactions between low-mass galaxies play in determining their star formation histories, structural properties, and neutral gas content. Here I will present an investigation of the impact of dwarf-dwarf galaxy tidal interactions on their morphological and star formation properties. The UGC5205 close pair consists of two low-mass (M* ~ 5E7 Msun), late-type galaxies with a relative projected distance of only 10 kpc, and no nearby massive companions. I will show that these equal-mass interactions can be an important 'pre-processing' mechanism that acts before dwarfs are affected by a more massive central galaxy, profoundly impacting their star formation histories and morphologies.


aurelio_carnero_crosell_140101s
Tuesday January 7, 2014
Dr. Aurelio Carnero Crosell
Observatorio Nacional de Rio de Janeiro

Abstract

In this talk I will show how we can study cosmolgy in a photometric redshift galaxy survey, by means of the angular clustering of galaxies. Previously to fit your data to a cosmological model, the need for a representative, clean and reliable galaxy catalog imposes many constrains in the selection of your data, from the day the data was taken, up to the final galaxy catalog used in the cosmological Analysis. I will try to introduce those issues that are most important for the analysis of galaxy clustering: data reduction and detection limit, catalog pruning, sample selection, photometric redshifts, star/galaxy separation and the need for a detailed angular and depth mask. Once a neat catalog is build upon the raw data of the survey, the cosmological analysis can start confidently. In this context, I will show as an example, the last cosmological results obtained from the DR8 SDSS-III photometric sample, conveniently corrected from systematic errors.


daniel_rosa_131219s
Thursday December 19, 2013
Dr. Daniel Rosa
Instituto Nacional de Astrofisica, Optica y Electronica, Mexico

Abstract

I will present the first Large Millimiter Telescope spectra of 4 nearby galaxies with known high star formation rates. The individual spectra were acquired with the Redshift Search Receiver, a 3 mm spectrograph that covers simultaneously the 3 mm band from 75 to 110 GHz. The spectra show rms temperatures of around 4 mK that allow us to detect not only common molecular species such as CO, HCN, HCO+, HCN, 13CO reported widely in the literature but also other more rare molecular transitions (HC3N, CN, CH3OH, CH3C2H) and even Hydrogen recombination lines (from H39alpha to H42alpha). We are making use of theoretical radiative transfer models to analize these spectra in order to understand the variations of the observed line ratios of different lines in galaxies classified as ultraluminous infrared galaxies where the star formation rate may be as high as 100 solar masses per year. These data will help to understand the physical conditions of the gas in regions that are forming stars very efficiently. The observed line ratios in star forming galaxies are also compared to those galaxies that is known to contain an AGN.


leticia_carigi_131212s
Thursday December 12, 2013
Prof. Leticia Carigi
UNAM

Abstract

Based on the double exponential behaviour of the gas mass profile and on the O/H gradient, Robles-Valdez, Carigi & Peimbert (2013) built a sucessful chemical evolution model for M33. The model predicts that in the inner parts of M33 the star formation history follows an inside-out scenario, like M31 or the MW, but in the outer parts of M33 the star formation history follows an outside-in scenario, as dwarf galaxies of the Local Group.


sandesh_kulkarni_131205s
Thursday December 5, 2013
Dr. Sandesh Kulkarni
MPIE, Garching, Germany

Abstract

 How does the group environment hamper star-formation in star-forming galaxies?

Abstract: We present the first results from the H-alpha Galaxy Groups Imaging Survey (HAGGIS), a narrow-band imaging survey of SDSS groups at z < 0.05 conducted using the Wide Field Imager (WFI) on the ESO/MPG 2.2 meter telescope and the Wide Field Camera (WFC) on the Issac Newton Telescope (INT). In total, we observed 100 galaxy groups with wide range of halo mass 10^12 - 10^14 M_sun in pairs of narrow-band filters selected to get continuum subtracted rest-frame H-alpha images for each galaxy in these groups. The excellent data allows us to detect H-alpha down to the 10^(-18) ergs/s/cm^2/arcsec^2 level. Here, we examine the role played by halo mass and galaxy stellar mass in deciding the overall star formation activity in star forming disks by comparing stacked H-alpha profiles of galaxies in different halo mass and stellar mass bins. With this preliminary study, we have found that the star-formation activity in star-forming galaxies decreases in larger halos compared to the field galaxies. Using median equivalent width profiles, we can infer how environmental processes affect star-forming galaxies differently at different radii.


ignacio_trujillo_1311203s
Tuesday December 3, 2013
Dr. Ignacio Trujillo
IAC

Abstract

As early as 10 Gyr ago, galaxies with more than 10^11 M* in stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (<0.1%) may have survived untouched till today. Searches for such relic galaxies, useful windows to explore the early Universe, have been inconclusive to date. In this talk, we will present the first case of a nearby galaxy, NGC1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfils many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H]=0.20+-0.04 with a smooth decline towards the outer regions) and alpha enriched ([alpha/Fe]=0.4+-0.1). This suggests a very short formation time scale for the bulk of stars of this galaxy. This object also rotates very fast (V_{rot}~300 km/s) and has a large central velocity dispersion (sigma>300 km/s). NGC1277 allows the explorations in full detail of properties such as the structure, internal dynamics, metallicity and initial mass function at ~10-12 Gyr back in time when the first massive galaxies were built.



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