Found 37 talks width keyword star formation

How do the first galaxies form and evolve? Optical and near-infrared deep surveys are now finding galaxies at very high redshifts. However, they are typically small, not massive and present some but not very high star formation. But now the Herschel Multi-tiered Extragalactic Survey (HerMES), the largest project that has being carried out with the Herschel Space Observatory, in collaboration with other groups, has discovered a massive, maximum-starburst galaxy at a redshift of 6.34. The presence of galaxies like HFLS3 in the early Universe challenges current theories of galaxy fomation and evolution. I will describe the method we have developed to find these galaxies, the follow-up observations with different facilities and the main physical properties of this extreme object.

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.

I will review some recent results about the molecular content of galaxies and its dynamics, obtained from CO lines, dense tracers (HCN,HCO+), or the dust continuum emission. New data to constrain the conversion factor XCO will be discussed. The molecular surface density is essential to determine the star formation efficiency in galaxies, and the resolved Kennicutt-Schmidt law will be presented as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

Luminous Infrared Galaxies (LIR=10^11-10^12Lsun) have star formation rates in the range of ~20-200Msun/yr. In the local Universe ~50% LIRGs show AGN or AGN/SB composite nuclear activity from optical spectroscopy. We decompose Spitzer/IRS 5-35micron spectra of a complete sample of 50 local (d<75Mpc) LIRGs using SB and AGN clumpy torus model templates. We derive a mid-IR AGN detection rate in our sample of local LIRGs of 50%. We also compare the continuum mid-IR AGN detection with other indicators in the mid-IR, optical and X-rays. We estimate for the first time the AGN bolometric contribution to the IR luminosity of the galaxies in local LIRGs. We find that one-third of local LIRGs have LAGN(bol)/LIR>0.05, with only ~10% having a significant contribution LAGN(bol)/LIR>0.25. This is in line with results of Nardini et al. (2010) that only at LIR>3x10^12Lsun the AGN starts dominating bolometrically the IR luminosity in the majority of the systems.

We present the detailed Star Formation History of the nearby Sculptor and Fornax dwarf spheroidal galaxies, from wide-field photometry of resolved stars, going down to the oldest Main Sequence Turn-Off. The accurately flux calibrated, wide-field Colour-Magnitude Diagrams are used directly in combination with spectroscopic metallicities of individual RGB stars to constrain the ages of different stellar populations, and derive the Star Formation History with particular accuracy.
The detailed Star Formation History shows the star formation at different ages and metallicities, at different positions in the galaxy, and shows that the known metallicity gradients are well matched to an age gradient. The obtained SFH is used to determine accurate age estimates for individual RGB stars, for which spectroscopic abundances (alpha-elements, r- and s-process elements) are known. In this way, we obtain the accurate age-metallicity relation of each galaxy, as well as the temporal evolution of alpha-element abundances.
This allows us to study, for the first time, the timescale of chemical evolution in these two dwarf galaxies, and determine an accurate age of the "knee" in the alpha-element distribution. Finally, we compare the timescale of chemical evolution in both dwarf galaxies, and determine whether the chemical abundance patterns seen in galaxies with recent episodes of star formation are a direct continuation of those with only old populations.

To understand the formation and evolution of galaxies, it is important to have a full comprehension of the role played by Metallicity, Star Formation Rate (SFR), and stellar mass of galaxies. The interplay of these parameters at different redshifts will substantially affect the evolution of galaxies and, as a consequence, the evolution of these parameters provides important constraints for the galaxy evolution models. We studied the relationships and dependencies between the SFR, stellar mass, and gas metallicity of star forming galaxies from the Sloan Digital Sky Survey-Data Release 7 (SDSS DR7) and Galaxy and Mass Assembly (GAMA) surveys. We have combined both surveys finding evidence of SFR and metallicity evolution for galaxies down to redshift ~0.2. Also, we have proved the existence of a Fundamental Plane in the 3D space formed by the SFR, mass and metallicity for the SDSS and GAMA samples.

With the discovery of several massive, young clusters in the last five years, the area around the base of the Scutum-Crux arm (around l=28) has become one of the more intense stellar formation areas in the whole Galaxy. This is not totally unexpected, as it is just there where it was predicted that the long bar of the Milky Way would come into contact with the disk, triggering stellar formation. With this talk we review all these evidences and we bring others into light, as we try to obtain a clearer picture of what is happening in these areas and what does it tell us about the inner structure of the Galaxy, particularly of the bulge+bar complex.

In this talk I consider two questions. First, I investigate the formation of molecular clouds from diffuse interstellar gas. It has been argued that the midplane pressure controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of the disk controls both. I present numerical results demonstrating that the observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation. Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.

The proper characterization of the least massive population of the young Sigma Orionis star cluster is required to understand the form of the cluster mass function and its impact on our comprehension of the substellar formation processes. SOri70 (T5.5±1) and SOri73, two T-type cluster member candidates, would have likely masses between 3 and 7 MJup if their age is 3 Myr. SOri73 awaits confirmation of its methane atmosphere. Here I present the results of a search of T-type objects in an area of ~120 arcmin^2 in the Sigma Orionis cluster, the confirmation of the presence of methane absorption in SOri73 and the study of SOri70 and 73 cluster membership via photometric colors and accurate proper motion analysis. This results would have a dramatic impact in the cluster mass function, in one of the scenarios explored, they suggest a decrease in cluster members with planetary masses in the interval 3.5-6 Mjup.

This lecture will address recent progress in modeling the emergence of cosmic structure at high redshifts. Also new insights gained from numerical simulations into the processes relevant for star formation are presented. Rapid magnetic field growth in galaxies and the important role of proto-stellar outflows regulating star formation up to pc scales are particularly highlighted.