Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.

VLA H I Observations of Gas Stripping in the Virgo Cluster Spiral NGC 4522

Abstract: We present VLA H I observations at ~20'' 1.5 kpc resolution of the highly inclined, H I–deficient Virgo Cluster spiral galaxy NGC 4522, which is one of the clearest and nearest cases of ongoing intracluster medium–interstellar medium (ICM-ISM) stripping. H I is abundant and spatially coincident with the stellar disk in the center, but beyond R = 3 kpc the H I distribution in the disk is sharply truncated, and the only H I is extraplanar and all on the northwest side. Forty percent of the total H I, corresponding to 1.5 × 108 M⊙, is extraplanar and has likely been removed from the galaxy disk by an ICM-ISM interaction. The kinematics and the morphology of the H I appear more consistent with ongoing stripping and less consistent with gas fall-back, which may occur long after peak pressure. Some of the extraplanar gas has line widths (FWZI) of 150 km s-1, including a blueshifted tail of weaker emission, and much of the extraplanar gas exhibits a modest net blueshift with respect to the galaxy's disk rotational velocities, consistent with gas accelerated toward the mean cluster velocity. The southwest side of the galaxy has less H I in the disk but more H I in the halo, suggesting more effective gas removal on the side of the galaxy that is rotating into the ICM wind. In recent simulations of ICM-ISM interactions large surface densities of extraplanar gas like that in NGC 4522 are seen at relatively early stages of active stripping and not during later gas fall-back stages. The galaxy is 33 800 kpc from M87, somewhat outside the region of strongest cluster X-ray emission. The ram pressure at this location, assuming a static smooth ICM and standard values for ICM density and galaxy velocity, appears inadequate to cause the observed stripping. We consider the possibility that the ram pressure is significantly stronger than standard values, because of large bulk motions and local density enhancements of the ICM gas, which may occur in a dynamic, shock-filled ICM experiencing subcluster merging. The H I and Hα distributions are similar, with both truncated in the disk at the same radius and H II regions located throughout much of the extraplanar H I. This implies that the star-forming molecular ISM has been effectively stripped from the outer disk of the galaxy along with the H I. The inferred peak stripping rate of ~10 M⊙ yr-1 is much larger than the galaxy's total star formation rate of ~0.1 M⊙ yr-1, implying that the rate of triggered star formation due to ICM pressure is presently minor compared with the rate of gas lost as a result of stripping.

Integral Field Spectroscopy of Massive, Kiloparsec-scale Outflows in the Infrared-luminous QSO Mrk 231

Abstract: The quasi-stellar object (QSO)/merger Mrk 231 is arguably the nearest and best laboratory for studying QSO feedback. It hosts several outflows, including broad-line winds, radio jets, and a poorly understood kpc-scale outflow. In this Letter, we present integral field spectroscopy from the Gemini telescope that represents the first unambiguous detection of a wide-angle, kiloparsec-scale outflow from a powerful QSO. Using neutral gas absorption, we show that the nuclear region hosts an outflow with blueshifted velocities reaching 1100 km s{sup -1}, extending 2-3 kpc from the nucleus in all directions in the plane of the sky. A radio jet impacts the outflow north of the nucleus, accelerating it to even higher velocities (up to 1400 km s{sup -1}). Finally, 3.5 kpc south of the nucleus, star formation is simultaneously powering an outflow that reaches more modest velocities of only 570 km s{sup -1}. Blueshifted ionized gas is also detected around the nucleus at lower velocities and smaller scales. The mass and energy flux from the outflow are {approx}>2.5 times the star formation rate and {approx}>0.7% of the active galactic nucleus luminosity, consistent with negative feedback models of QSOs.

Gas accretion on spiral galaxies: Bar formation and renewal

Abstract: The eects of gas accretion on spiral disk dynamics and stability are studied through N-body simulations, including star formation and gas/stars mass exchange. The detailed processes of bar formation, bar destruction and bar re-formation are followed, while in the same time the disk to bulge ratio is varying. The accreted gas might be first prevented to flow inwards to the center by the bar gravity torques, which maintains it to the outer Lindblad resonance. While the first bar is weakening, the accreted gas replenishes the disk, increasing the disk-to-bulge ratio, and the disk self-gravity. A second bar is then unstable, with a higher pattern speed, due both to the increased mass, and shorter bar length. Three or four bar episodes have been followed over a Hubble time. Their strength is decreasing with time, while their pattern speed is increasing. Detailed balance of the angular momentum transfer and evolution can account for these processes. The gas recycled through star formation, and rejected through stellar mass loss plays also a role in the disk dynamics. Implications on the spiral galaxy dynamics and evolution along the Hubble sequence, and as a function of redshift are discussed.

The initial mass function 50 years later

Abstract: Preface,List of Participants,Part I The IMF Concept through Time, Introduction to IMF@50, Ed, me, and the Insterstellar Medium,The IMF challenge - 25 questions, Fifty years of IMF variation: the intermediate-mass stars, The Initial Mass Function: from Salpeter 1955 to 2005, Part II The IMF in our Galaxy: Clusters and field stars, The field IMF across the H-burning, The 0.03-10M.mass function of young open clusters, The time spread of star formation in the Pleiades, Age spreads in clusters and associations: the lithium test, The Initial Mass Function of three galactic open clusters, The stellar IMF of galactic clusters and its evolution, Two stages of star formation in globular clusters and the IMF, The stellar Initial Mass Function in the Galactic Center, The Initial Mass Function in the Galactic Bulge, Halo mass function 101, Part III The IMF in our Galaxy: Star forming regions, Embedded clusters and the IMF, The IMF of stars and brown dwarfs in star forming regions, The substellar IMF of the Taurus cloud, The low-mass end of the IMF in Chamaeleon I, Limitations of the IR-excess method for identifying young stars, The IMF of Class II objects in the active Serpens cloud core, Orionis: a 0.02-50M. IMF, Does the "stellar" IMF extend to planetary masses?, Estimating the low-mass IMF in OB associations: Orionis, Young brown dwarfs in Orion, The formation of free-floating brown dwarves & planetary-mass objects by photo-erosion of prestellar cores, IMF in small young embedded star clusters, The Arches cluster - a case for IMF variations?, The IMF and mass segregation in young galactic starburst clusters, A 2.2 micron catalogue of stars in NGC 3603, The IMF of the massive star forming region NGC 3603 from VLT adaptive optics observations, X-rays and young clusters, NGC 2264: a Chandra view, Part IV The Extragalactic IMF, Variations of the IMF, On the form of the IMF: upper-mass cutoff and slope, Evidence for a fundamental stellar upper mass limit from clustered star formation, Monte Carlo experiments on star cluster induced integrated-galaxy IMF variations, The initial conditions to star formation: low-mass stars at low metallicity, Stellar associations in the LMC, The IMF long ago and far away, The massive star IMF at high metallicity, The Initial Mass Function in disc galaxies and in galaxy clusters: the chemo-photometric picture, Steeper, flatter, or just Salpeter? Evidence from galaxy evolution and galaxy clusters, Initial mass function and galactic chemical evolution models, New database of SSPs with different IMFs, The starburst IMF n An impossible measurement?, Gould's Belt to starburst galaxies: the IMF of extreme star formation, Mid-IR observations at high spatial resolution: constraints on the IMF in very young embedded super star clusters, Wolf-Rayet stars as IMF probes, Part V The Origin of the IMF: Atomic and molecular gas tracers, Smidgens of fuel for star formation, The Initial Mass Function in the context of warm ionized gas in disk galaxies, Tracing the star formation cycle through the diffuse Interstellar Medium, Examining the relationship between interstellar turbulence and star formation, The IMF of Giant Molecular Clouds, Multiphase molecular gas and star forming sites in M33, How does star formation build a galactic disk?, Mapping extragalactic molecular clouds: Centaurus A (NGC 5128), Tiny HI clouds in the local ISM, Submm observations of prestellar condensations: probing the initial conditions for the IMF, How well determined is the core mass function of Oph?, From dense cores to protostars in low-mass star forming regions, Fragmentation of a high-mass star forming core, Part VI The Origin of the IMF: Cloud fragmentation and collapse, Understanding the IMF, Flows, filaments and fragmentation, Minimum mass for opacity-limited fragmentation in dynamically triggered star formation, Origin of the core mass function, The connection between the core mass function and the IMF in Taurus, The stellar IMF as a property of turbulence, The stellar mass spectrum from non-isothermal gravoturbulent fragmentation, Turbulent control of the star formation efficiency, Thermal condensation in a turbulent atomic hydrogen flow, The formation of molecular clouds, Turbulence-accelerated star formation in magnetized clouds, Cluster density and the IMF, Part VII The Origin of the IMF: From gas to stars, A theory of the IMF, A class of IMF theories, An effective Initial Mass Function for galactic disks, Competitive accretion and the IMF, The dependence of the IMF on initial conditions, A minimum hypothesis explanation for an IMF with a lognormal body and power law tail, Feedback and the Initial Mass Function, Feedback in star formation simulations: implications for the IMF, Massive star feedback on the IMF, Discussion: Turbulence and magnetic fields in clouds, Part VIII The "Initial" IMF, The primordial IMF, Cosmic relevance of the first stars, Star formation triggered by first supernovae, Detecting primordial stars, Constraints on the IMF in low metallicity and PopIII environments, Thermal evolution of star forming clouds in low metallicity environment, Observational evidence for a different IMF in the early Galaxy, The role of the IMF in the cosmic metal production, From Population III stars to (super)massive black holes, Gamma-ray burst afterglows as probes of high-z star formation, Part IX Chuzpah talks, Electrostatic screening of nuclear reactions 50 years later, The life and death of Planetary Nebulae, Early results from the infrared spectrograph on the Spitzer Space Telescope, Future observational opportunities, Author Index

The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies

Abstract: We present a stellar population analysis of the absorption line strength maps for 48 early-type galaxies from the SAURON sample. Using the line strength index maps of H beta, Fe5015 and Mgb, measured in the Lick/IDS system and spatially binned to a constant signal-to-noise ratio, together with predictions from up-to-date stellar population models, we estimate the simple stellar population-equivalent (SSP-equivalent) age, metallicity and abundance ratio [alpha/Fe] over a two-dimensional field extending up to approximately one effective radius. A discussion of calibrations and differences between model predictions is given. Maps of SSP-equivalent age, metallicity and abundance ratio [alpha/Fe] are presented for each galaxy. We find a large range of SSP-equivalent ages in our sample, of which similar to 40 per cent of the galaxies show signs of a contribution from a young stellar population. The most extreme cases of post-starburst galaxies, with SSP-equivalent ages of The flattened components with disc-like kinematics previously identified in all fast rotators are shown to be connected to regions of distinct stellar populations. These range from the young, still star-forming circumnuclear discs and rings with increased metallicity preferentially found in intermediate-mass fast rotators, to apparently old structures with extended disc-like kinematics, which are observed to have an increased metallicity and mildly depressed [alpha/Fe] ratio compared to the main body of the galaxy. The slow rotators, often harbouring kinematically decoupled components (KDC) in their central regions, generally show no stellar population signatures over and above the well-known metallicity gradients in early-type galaxies and are largely consistent with old (>= 10 Gyr) stellar populations. Using radially averaged stellar population gradients we find in agreement with Spolaor et al. a mass-metallicity gradient relation where low-mass fast rotators form a sequence of increasing metallicity gradient with increasing mass. For more massive systems (above similar to 3.5 x 10(10) M-circle dot) there is an overall downturn such that metallicity gradients become shallower with increased scatter at a given mass leading to the most massive systems being slow rotators with relatively shallow metallicity gradients. The observed shallower metallicity gradients and increased scatter could be a consequence of the competition between different star formation and assembly scenarios following a general trend of diminishing gas fractions and more equal-mass mergers with increasing mass, leading to the most massive systems being devoid of ordered motion and signs of recent star formation.