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Star Formation in Disks: Spiral Arms, Turbulence, and Triggering Mechanisms
Bruce G. Elmegreen
Star formation is enhanced in spiral arms because of a combination of orbit crowding, cloud collisions, and gravitational instabilities. The characteristic mass for the instability…
Bulge and Clump Evolution in Hubble Ultra Deep Field Clump Clusters, Chains and Spiral Galaxies
Bruce G. Elmegreen, Debra Meloy Elmegreen, Maria Ximena Fernandez +1
Clump clusters and chain galaxies in the Hubble Ultra Deep Field are examined for bulges in the NICMOS images. Approximately 50% of the clump clusters and 30% of the chains have re…
Bulge Formation by the Coalescence of Giant Clumps in Primordial Disk Galaxies
Bruce G. Elmegreen, Frederic Bournaud, Debra Meloy Elmegreen
Gas-rich disks in the early universe are highly turbulent and have giant star-forming clumps. Models suggest the clumps form by gravitational instabilities, and if they resist disr…
Nuclear Black Hole Formation in Clumpy Galaxies at High Redshift
Bruce G. Elmegreen, Frederic Bournaud, Debra Meloy Elmegreen
Massive stellar clumps in high redshift galaxies interact and migrate to the center to form a bulge and exponential disk in <1 Gyr. Here we consider the fate of intermediate mass b…
Observations and modelling of a clumpy galaxy at z=1.6: Spectroscopic clues to the origin and evolution of chain galaxies
F. Bournaud, E. Daddi, B. G. Elmegreen +7
We investigate the properties of a clump-cluster galaxy at redshift 1.57. The morphology of this galaxy is dominated by eight star-forming clumps in optical observations, and has p…
On the Constancy of the Characteristic Mass of Young Stars
Bruce G. Elmegreen, Ralf S. Klessen, Christine D. Wilson
The characteristic mass M_c in the stellar initial mass function (IMF) is about constant for most star-forming regions. Numerical simulations consistently show a proportionality be…
The Stellar Initial Mass Function in 2007: A Year for Discovering Variations
Bruce G. Elmegreen
The characteristic mass M_c and slope Gamma of the IMF are reviewed for clusters, field regions, galaxies, and regions formed during cosmological times. Local star formation has a…
Variation of Galactic Bar Length with Amplitude and Density as Evidence for Bar Growth over a Hubble Time
Bruce G. Elmegreen, Debra Meloy Elmegreen, Johan H. Knapen +3
K_s-band images of 20 barred galaxies show an increase in the peak amplitude of the normalized m=2 Fourier component with the R_25-normalized radius at this peak. This implies that…
Variations in Stellar Clustering with Environment: Dispersed Star Formation and the Origin of Faint Fuzzies
Bruce G. Elmegreen
The observed increase in star formation efficiency with average cloud density, from several percent in whole giant molecular clouds to ~30 or more in cluster-forming cores, can be…
Rapid formation of exponential disks and bulges at high redshift from the dynamical evolution of clump cluster and chain galaxies
F. Bournaud, B. G. Elmegreen, D. M. Elmegreen
Many galaxies at high redshift have peculiar morphologies dominated by 10^8-10^9 Mo kpc-sized clumps. Using numerical simulations, we show that these "clump clusters" can result fr…
On the Rapid Collapse and Evolution of Molecular Clouds
Bruce G. Elmegreen
Stars generally form faster than the ambipolar diffusion time, suggesting that several processes short circuit the delay and promote a rapid collapse. These processes are considere…
A Catalog of HI Clouds in the Large Magellanic Cloud
S. Kim, E. Rosolowsky, Y. Lee +9
A 21 cm neutral hydrogen interferometric survey of the Large Magellanic Cloud (LMC) combined with the Parkes multi-beam HI single-dish survey clearly shows that the HI gas is distr…
Smooth and Starburst Tidal Tails in the GEMS and GOODS Fields
Debra Meloy Elmegreen, Bruce G. Elmegreen, Thomas Ferguson +1
GEMS and GOODS fields were examined to z~1.4 for galaxy interactions and mergers. The basic morphologies are familiar: antennae with long tidal tails, tidal dwarfs, and merged core…
Resolved Galaxies in the Hubble Ultra Deep Field: Star Formation in Disks at High Redshift
Debra Meloy Elmegreen, Bruce G. Elmegreen, Swara Ravindranath +1
The photometric redshift distributions, spectral types, Sersic indices, and sizes of all resolved galaxies in the Hubble Space Telescope Ultra Deep Field (UDF) are studied in order…
The Initial Mass Function in Clusters
Bruce G. Elmegreen
The stellar initial mass function (IMF) in star clusters is reviewed. Uncertainties in the observations are emphasized. We suggest there is a distinct possibility that cluster IMFs…
Formation and Evolution of Young Massive Clusters
Bruce G. Elmegreen
Clusters are the dense inner regions of a wide-spread hierarchy of young stellar structures. They often reveal a continuation of this hierarchy inside of them, to smaller scales, w…
Rings and Bent Chain Galaxies in the GEMS and GOOD Fields
Debra Meloy Elmegreen, Bruce G. Elmegreen
Twenty-four galaxies with rings or partial rings were studied in the GEMS and GOODS fields out to z~1.4. Most resemble local collisional ring galaxies in morphology, size, and clum…
Observations of Thick Disks in the Hubble Space Telescope Ultra Deep Field
Bruce G. Elmegreen, Debra Meloy Elmegreen
The vertical profiles of chain and spiral galaxies in the Hubble Space Telescope Ultra Deep Field (UDF) are fit to sech^2(z/z_0) functions convolved with stellar profiles in order…
IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission
Debra Meloy Elmegreen, Bruce G. Elmegreen, Michele Kaufman +4
IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics an…
Hierarchical Star Formation in the Spiral Galaxy NGC 628
Bruce G. Elmegreen, Debra Meloy Elmegreen, Rupali Chandar +2
The distributions of size and luminosity for star-forming regions in the nearby spiral galaxy NGC 628 are studied over a wide range of scales using progressively blurred versions o…
On the Similarity between Cluster and Galactic Stellar Initial Mass Functions
Bruce G. Elmegreen
The stellar initial mass functions (IMFs) for the Galactic bulge, the Milky Way, other galaxies, clusters of galaxies, and the integrated stars in the Universe are composites from…
Hierarchical Formation of Galactic Clusters
Bruce G. Elmegreen
Young stellar groupings and clusters have hierarchical patterns ranging from flocculent spiral arms and star complexes on the largest scale to OB associations, OB subgroups, small…
The Initial Mass Function of Stars
Bruce G. Elmegreen
Observations and theory of the IMF are briefly reviewed. Slight variations have been observed, although they are difficult to prove unambiguously. Most detailed theoretical models…
Mid-Infrared Images of Stars and Dust in Irregular Galaxies
Deidre A. Hunter, Bruce G. Elmegreen, Emily Martin
We present mid-infrared to optical properties of 22 representative irregular galaxies: 18 Im, 3 BCDs, and one Sm. The mid-IR is based on images from the Spitzer Space Telescope arc…