902 research outputs found
Unstable 06.5f?p star HD 148937 and its interstellar environment
The massive, early-type star HD 148937 (spectral type 06.5?p) is surrounded by a unique set of nebulosities. A spherically symmetric Stromgren sphere (Radius approx. - 25 pc), an ellipsoidal filamentary nebulosity (semimajor axis approx. - 5 pc) interpreted as a stellar-wind-blown shell, and a bipolar nebular complex (semimajor axis approx. - 1 pc) with HD 148937 located in the apparent center of symmetry. Observations of these nebulosities are reported (narrow-band charge coupled devices imaging, image dissector scanner (IDS) spectrophotometry, high resolution spectroscopy) in an attempt to establish a consistent model of HD 148937 and its nebulosities
A Far-Ultraviolet View of Starburst Galaxies
Recent observational and theoretical results on starburst galaxies related to
the wavelength regime below 1200 A are discussed. The review covers stars,
dust, as well as hot and cold gas. This wavelength region follows trends
similar to those seen at longer wavelengths, with several notable exceptions.
Even the youngest stellar populations show a turn-over in their spectral energy
distributions, and line-blanketing is much more pronounced. Furthermore, the O
VI line allows one to probe gas at higher temperatures than possible with lines
at longer wavelengths. Molecular hydrogen lines (if detected) provide a glimpse
of the cold phase. I cover the crucial wavelength regime below 912 A and the
implications of recent attempts to detect the escaping ionizing radiation.Comment: 8 pages, 3 figures, Invited Talk, Starbursts--From 30 Doradus to
Lyman-Break Galaxies, ed. R. de Grijs & R. M. Gonzalez Delgado (Dordrecht:
Kluwer
Starbursts and Star Clusters in the Ultraviolet
Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies
reveal them to be highly irregular, even after excluding compact sources
(clusters and resolved stars). Most (7/9) are found to have a similar intrinsic
effective surface brightnesses, suggesting that a negative feedback mechanism
is setting an upper limit to the star formation rate per unit area. All
starbursts in our sample contain UV bright star clusters indicating that
cluster formation is an important mode of star formation in starbursts. On
average about 20% of the UV luminosity comes from these clusters. The brightest
clusters, or super star clusters (SSC), are preferentially found at the very
heart of starbursts. The size of the nearest SSCs are consistent with those of
Galactic globular clusters. The luminosity function of SSCs is well represented
by a power law with a slope alpha ~ -2. There is a strong correlation between
the far infrared excess and the UV spectral slope. The correlation is well
modeled by a geometry where much of their dust is in a foreground screen near
to the starburst, but not by a geometry of well mixed stars and dust.Comment: 47 pages, text only, LaTeX with aaspp.sty (version 3.0), compressed
postscript figures available at
ftp://eta.pha.jhu.edu/RecentPublications/meurer
Metal-enriched galactic outflows shape the mass-metallicity relationship
The gas-phase metallicity of low-mass galaxies increases with increasing
stellar mass () and is nearly constant for high-mass galaxies. Theory
suggests that this tight mass-metallicity relationship is shaped by galactic
outflows removing metal-enriched gas from galaxies. Here, we observationally
model the outflow metallicities of the warm outflowing phase from a sample of
seven local star-forming galaxies with stellar masses between
10-10 M. We estimate the outflow metallicities using four
weak rest-frame ultraviolet absorption lines, the observed stellar continua,
and photoionization models. The outflow metallicity is flat with , with
a median metallicity of Z. The observed outflows are
metal-enriched: low and high-mass galaxies have outflow metallicities 10-50 and
2.6 times larger than their ISM metallicities, respectively. The observed
outflows are mainly composed of entrained ISM gas with at most 22% of the
metals directly coming from recent supernovae enrichment. The metal outflow
rate shallowly increases with , as , because the
mass outflow rate shallow increases with . Finally, we normalize the
metal outflow rate by the rate at which star formation retains metals to
calculate the metal-loading factor. The metal-loading factor inversely scales
with . The normalization and scaling of the metal-loading factor agree
with analytic expressions that reproduce observed mass-metallicity relations.
Galactic outflows fundamentally shape the observed mass-metallicity
relationship.Comment: 15 pages, 7 figures, Accepted for publication in MNRA
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