Found 188 talks archived in Galaxies

Tuesday February 19, 2013
Dr. Helena Domínguez Sánchez


In this talk we will show the evolution of high-redshift (z≥ 1.4) quiescent galaxies in the COSMOS field. We have studied an IRAC (mag 3.6 μm < 22.0) selected sample of ~ 18 000 galaxies at z≥ 1.4 in the COSMOS field with multiwavelength coverage extending from the U band to the Spitzer 24 μm one. We have derived accurate photometric redshifts and other important physical parameters [masses, ages and star formation rates (SFR)] through a SED-fitting procedure. Galaxies have been divided according to their star formation activity into actively star-forming, intermediate and quiescent galaxies depending on their specific star formation rate (sSFR = SFR/M). The evolution of the Galaxy Stellar Mass Funtion (GSMF) of the different populations, in particular of the quiescent galaxies, has been investigated in detail. There is a significant evolution of the quiescent stellar mass function from 2.5 < z < 3.0 to 1.4 < z < 1.6, increasing by ~1 dex in this redshift interval. We find that z ~1.5 is an epoch of transition of the GSMF: while the GSMF at z≳ 1.5 is dominated by the star-forming galaxies at all stellar masses, at z≲ 1.5 the contribution to the total GSMF of the quiescent galaxies is significant and becomes higher than that of the star-forming population for M≥ 1010.75 Msun. We derive the fraction of quiescent/star-forming galaxies with redshift, as well as the stellar mass density. We also compare our results with the predictions of theoretical models. Finally, I will introduce my current project: studying in deeper detail the IRAC drop-outs of the sample with new nIR (ULTRA-VISTA) and fIR (Herschel) data to elucidate between very dust-obscured objects or high-z star forming galaxies, which could help us to put some constrains to the high-mass end of the GSMF at high-z.

Tuesday January 29, 2013
Dr. Jairo Méndez Abreu


The effects that environment produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To shed light on this issue, we derive the bar fraction in three different environments ranging from the field to Virgo and Coma Clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma Cluster is statistically significant, with Virgo being an intermediate case. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies, the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges probed by the galaxy samples studied so far.

Thursday January 24, 2013
Dr. Emily Wisnioski
Max Planck Institute for Extraterrestrial Physics


Morphologies of star-forming galaxies at z>1 are typically irregular containing a handful of dominant bright regions. Recent observational evidence suggest that many of these galaxies are governed by disc-like rotation. Using Halpha galaxy kinematics from OSIRIS+LGSAO we find that within z~1 turbulent discs star-forming regions have average sizes of 1.5 kpc and average Jeans masses of 4.2x10^9 \Msun, in total accounting for 20-30% of the stellar mass of the discs. These findings lend observational support to models that predict larger star-forming regions will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion.  As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, high-z star-forming regions and HII regions are found to follow tight scaling relations over the range z=0-2 for Halpha size, velocity dispersion, luminosity and mass when comparing >2000 HII regions locally and 30 regions at z>1.  While the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes likely govern their formation from high redshift to the current epoch. We are now able to test this conclusion with first results from a new sample of z=0.1-0.2 highly star-forming turbulent galaxies from the Sloan Digital Sky Survey.

Thursday December 20, 2012
Prof. Clive Tadhunter
University of Sheffield


In the 50 years since their discovery, it has become increasingly recognised that quasars are not merely signposts to the distant Universe, but also play a key role in the overall galaxy evolution process. However, if we are to incorporate quasars into models of galaxy evolution, it's important to understand how, when and where they are triggered. In this talk I will review the latest observational results on the triggering of quasars, based on the morphologies of their host galaxies and star formation properties; I will also discuss the future prospects for understanding quasar triggering using Herschel and ALMA data.

Thursday December 13, 2012
Dr. Eduardo Bataner
Universidad de Granada


Hablaré de tres caprichos. El primero pretende responder a la pregunta: ¿Existen lentes magnéticas en el Cosmos? El segundo trata de un problema de Milagro, viendo cómo el campo magnético de nuestra galaxia puede resolver la anisotropía en la distribución de rayos cósmicos de unos 10 TeV. El tercero considera las curvas de rotación de algunas galaxias espirales que tras haber alcanzado la velocidad asintótica, vuelve a tener pendiente positiva.

Tuesday December 4, 2012
Dr. Sharon Meidt
Max Planck Institute for Astronomy, Germany


Gas kinematics on the scales of Giant Molecular Clouds (GMCs) are essential for probing the framework that links the large-scale organization of interstellar gas to cloud formation and subsequent star formation. I will present an overview of results from the PdBI Arcsecond Whirlpool Survey (PAWS, PI: E. Schinnerer), which has mapped CO(1-0) emission over 9 kpc in the nearby grand-design spiral galaxy M51 at 40 pc resolution, and is sensitive to giant molecular clouds (GMCs) with masses above 10^5 Msun. This unprecedented view challenges the conventional picture of how molecular gas is structured and organized in galaxies: clouds are not ‘universal’, but respond to their environment, resulting in a diversity of cloud properties that not only depend on (dynamical) environment but also vary from galaxy to galaxy. I will discuss how this sensitivity to environment emerges, in consideration of the stability of M51’s GMCs (including the effects of pressure, shear, turbulence) and our view of non-circular motions in the gas disk. As a result of the strong streaming motions that arise due to departures from axisymmetry in the gravitational potential (i.e. the nuclear bar and spiral arms), embedded clouds feel a reduced surface pressure, which can prevent collapse. This dynamical pressure naturally leads to changes in the efficiency of star formation and hence gas depletion time along the spiral arms. I will show that local reductions to cloud surface pressure in M51 dominate over shear and star formation feedback-driven turbulence in determining the observed radial variation the depletion time. I will also describe how incorporating a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies, across cosmic time.

Thursday November 8, 2012
Prof. Piet van der Kruit
University Groningen


Disks in spiral galaxies consist of stars and gas. The stellar disks show radially an exponential surface brightness distribution (and vertically one resembling an isothermal sheet), with relatively sharp truncations at of order 4 scalelengths. These truncations are most easily seen in edge-on galaxies. The evidence for these truncations and their statistics will be reviewed. Truncations appear to be not only truncations in the distribution of stars, but also in the total density. The origin of these truncations seem related to the maximum specific angular momentum in the material that formed the disks. Disks are extremely flat. The HI-gas often extends beyond the eructations in the stellar disks, but when they do they also show a warp. Again edge-on galaxies show this mostly readily. Analysis shows that the warps start abruptly, just beyond the truncation radius and some other properties also show abrupt changes at the radius of the onset of the warp. This suggests that warps are the result of infall of gas at later times, when the formation of the stellar disks has been completed. The open issue is still that we have not conclusively shown that we can discover the face-on analogs of the truncations we see in edge-on disk. I will outline some recent research I have been involved in and some ideas for further work and collaborations.

Thursday September 20, 2012
Dr. Gavin Dalton
University of Oxford


I will describe the major scientific motivation and outline design concept for a new 2 degree field, 1000 fibre multi-object spectroscopy facility for the WHT. WEAVE is expected to be completed by early 2017 and will be capable of addressing a wide range of Galactic and extra-Galactic goals, covering the redial velocity follow-up to the full depth of the Gaia astrometric catalogue, stellar abundances and chemical labelling in the Galactic halo, galaxy evolution from integral field studies and from the identification of the LOFAR source population, and Cosmology. The instrument is complex, but not necessarily challenging, and will provide a major resource for the whole ING community for the next decade.

Thursday July 12, 2012
Dr. Sébastien Comerón
Korea Astronomy and Space Science Institute


Thick discs are disc-like components with a scale height larger than that of the classical discs. They are  most easily detected in close to edge-on galaxies in which they appear as a roughly exponential excess of light which appears a few thin disc scale heights above the midplane. Their origin has been considered mysterious until recently and several formation theories have been proposed. Unveiling the origin of thick discs is important for understanding galaxy evolutionary processes.
I will review the results we obtained on thick discs using data from the S4G:
1) Thick discs are ubiquitous.
2) Thick discs are much more massive than previously thought. This advocates for an in situ origin of thick discs at high redshift and for them being a reservoir of missing baryons.
3) The superposition of thin and thick discs with different scale lengths is the reason of at least half of disc antitruncations.

Thursday July 5, 2012
Dr. Ignacio Ferreras
University College of London


Massive early-type galaxies constitute an ideal test bed to probe our understanding of galaxy formation and evolution. Their high mass, spheroidal morphology and overly old stellar populations, along with their presence over a wide range of redshifts put to the test our current paradigm of formation via hierarchical growth. In this talk I will review recent work focused on the dark and bright sides of this problem. The former is tackled via gravitational lensing, comparing the dark matter and luminous components out to several effective radii, probing the efficiency of baryon collapse and ejection, and its feedback on the dark matter distribution (adiabatic compression). The bright side of early-type galaxies is approached via photo-spectroscopic analyses of the stellar populations, revealing a complex formation and assembly history with two well-defined phases of growth, and an intriguing connection with the "microphysics" of star formation.

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