9 research outputs found
Extraplanar Dust in Spiral Galaxies: Tracing Outflows in the Disk-Halo Interface
There is now ample evidence that the interstellar thick disks of spiral
galaxies are dusty. Although the majority of extraplanar gas in the first few
kiloparsecs above the plane of a spiral galaxy is matter that has been expelled
from the thin disk, the feedback-driven expulsion does not destroy dust grains
altogether (and there is not yet any good measure suggesting it changes the
dust-to-gas mass ratio). Direct optical imaging of a majority of edge-on spiral
galaxies shows large numbers of dusty clouds populating the thick disk to
heights z~2 kpc. These observations are likely revealing a cold, dense phase of
the thick disk interstellar medium. New observations in the mid-infrared show
emission from traditional grains and polycyclic aromatic hydrocarbons (PAHs) in
the thick disks of spiral galaxies. PAHs are found to have large scale heights
and to arise both in the dense dusty clouds traced through direct optical
imaging and in the diffuse ionized gas. In this contribution, we briefly
summarize these probes of dust in the thick disks of spiral galaxies. We also
argue that not only can dust can be used to trace extraplanar material that has
come from within the thick disk, but that its absence can be a marker for newly
accreted matter from the circumgalactic or intergalactic medium. Thus,
observations of dust can perhaps provide a quantitative measure of the
importance of "outflow versus infall" in spiral galaxies.Comment: 8 pages; Invited review for the proceedings of "The Role of Disk-Halo
Interaction in Galaxy Evolution: Outflow vs. Infall?" (Ed. M. de Avillez), in
Espinho, Portugal, 18-22 August 2008 ; high resolution version at
http://www.nd.edu/~jhowk/Papers/papers.html#conferenc
The Recurrent Nature of Central Starbursts
New hydrodynamic models with feedback show that feedback driven turbulence
and subsequent relaxation can drive recurrent starbursts, though most of these
bursts fizzle due to premature, asymmetric ignition. Strong bursts are
terminated when the turbulence inflates the multiphase central disk. The period
between bursts is about twice a free-fall time onto the central disk. Transient
spirals and bars are common through the burst cycle.Comment: 7 pages + 3 figs. Conf. paper for "Starbursts: from 30 Doradus to
Lyman Break Galaxies," held at Inst. of Astronomy, Cambridge Univ., Sept.
6-10, 2004. Kluwer Academic Publishers, eds. R. de Grijs and R. M. Gonzalez
Delgado + additional materia
Chemical abundances in the Leading Arm of the Magellanic Stream
The Leading Arm (LA) of the Magellanic Stream is a vast debris field of H i clouds connecting the Milky Way and the Magellanic Clouds. It represents an example of active gas accretion onto the Galaxy. Previously, only one chemical abundance measurement had been made in the LA. Here we present chemical abundance measurements using Hubble Space Telescope/Cosmic Origins Spectrograph and Green Bank Telescope spectra of four AGN sightlines passing through the LA and three nearby sightlines that may trace outer fragments of the LA. We find low oxygen abundances, ranging from solar to solar, in the confirmed LA directions, with the lowest values found in the region known as LA III, farthest from the LMC. These abundances are substantially lower than the single previous measurement, S/H = 35 ± 7% solar, but are in agreement with those reported in the SMC filament of the trailing Stream, supporting a common origin in the SMC (not the LMC) for the majority of the LA and trailing Stream. This provides important constraints for models of the formation of the Magellanic System. Finally, two of the three nearby sightlines show high-velocity clouds with H i columns, kinematics, and oxygen abundances consistent with LA membership. This suggests that the LA is larger than traditionally thought, extending at least 20° further to the Galactic northwest
The bimodal absorption system imaging campaign (BASIC). I. A dual population of low-metallicity absorbers at z < 1
Instrumentatio
The cosmic evolution of the metallicity distribution of ionized gas traced by Lyman limit systems
We present the first results from our KODIAQ Z survey aimed to determine the metallicity distribution and physical properties of the z>2 partial and full Lyman limit systems (pLLSs and LLSs; 16.
ESA Voyage 2050 white paper: A complete census of the gas phases in and around galaxies, far-UV spectropolarimetry as a prime tool for understanding galaxy evolution and star formation
(abridged) The far-UV wavelength range (912-2000A) provides access to atomic and molecular transitions of many species the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium, within phases spanning a wide range of ionization, density, temperature, and molecular gas fraction. Far-UV space telescopes have enabled detailed studies of the ISM in the Milky Way thanks to absorption features appearing in the UV spectra of hot stars and yielding fundamental insights into the composition and physical characteristics of all phases of the ISM along with the processes that influence them. However, we have yet to design a spectrometer able to observe the full UV domain at resolving power R>10^5 with a signal-to-noise ratio SNR>500. Such a resolution is necessary to resolve lines from both the cold molecular hydrogen and the warm metal ions with a turbulent velocity of about 1 km s-1, and to differentiate distinct velocity components. Future UV spectroscopic studies of the Milky Way ISM must revolutionize our understanding of the ISM as a dynamical, unstable, and magnetized medium, and rise to the challenge brought forward by current theories. Another interesting prospect is to transpose the same level of details that has been reached for the Milky Way to the ISM in external galaxies, in particular in metal-poor galaxies, where the ISM chemical composition, physical conditions, and topology change dramatically, with significant consequences on the star-formation properties. Finally, we need to be able to perform statistical analyses of background quasar lines of sight intersecting the CGM of galaxies at various redshifts and to comprehend the role of gas exchanges and flows for galaxy evolution