115 research outputs found
On the ongoing multiple blowout in NGC 604
Several facts regarding the structure of NGC 604 are examined here. The three
main cavities, produced by the mechanical energy from massive stars which in
NGC 604 are spread over a volume of 10 pc, are shown here to be
undergoing blowout into the halo of M33. High resolution long slit spectroscopy
is used to track the impact from massive stars while HST archive data is used
to display the asymmetry of the nebula.
NGC 604 is found to be a collection of photoionized filaments and sections of
shells in direct contact with the thermalized matter ejected by massive stars.
The multiple blowout events presently drain the energy injected by massive
stars and thus the densest photoionized gas is found almost at rest and is
expected to suffer a slow evolution.Comment: 15 pages (11 text), 4 figures. To be published in Ap
Young Super Star Clusters in the Starburst of M82: The Catalogue
Recent results from Hubble Space Telescope (HST) have resolved starbursts as
collections of compact young stellar clusters. Here we present a photometric
catalogue of the young stellar clusters in the nuclear starburst of M82,
observed with the HST WFPC2 in Halpha (F656N) and in four optical broad-band
filters. We identify 197 young super stellar clusters. The compactness and high
density of the sources led us to develop specific techniques to measure their
sizes. Strong extinction lanes divide the starburst into five different zones
and we provide a catalogue of young super star clusters for each of these. In
the catalogue we include relative coordinates, radii, fluxes, luminosities,
masses, equivalent widths, extinctions, and other parameters. Extinction values
have been derived from the broad-band images. The radii range between 3 and 9
pc, with a mean value of 5.7 +/- 1.4pc, and a stellar mass between 10e4 and
10e6 Mo. The inferred masses and mean separation, comparable to the size of
super star clusters, together with their high volume density, provides strong
evidence for the key ingredients postulated by Tenorio et al. (2003) as
required for the development of a supergalactic wind.Comment: 45 pages, 5 figures, 12 tables. Accepted for publication in ApJ.
Added Erratu
FIELD TRIP TO THE YPRESIAN/LUTETIAN BOUNDARY AT THE GORRONDATXE BEACH SECTION (BASQUE COUNTRY, W PYRENEES)
One of the Paleogene Stage boundaries still needing official definition is the Ypresian/Lutetain (Early-
Middle Eocene) boundary. With the aim of contributing to attain this definition, a high-resolution multidisciplinary
study, including physical stratigraphy (lithostratigraphy, sequence stratigraphy and
magnetostratigraphy) and biostratigraphy (calcareous nannofossil, planktic foraminifer and larger
foraminifer), has been carried out over the 700 m thick uppermost Ypresian â lower Lutetian Gorrondatxe
section. The results show that the different events traditionally used to place the Ypresian/Lutetian
boundary, hitherto thought to be simultaneous (i.e., the planktic foraminifer P9 (=E7) / P10 (=E8) Zone
boundary; the calcareous nannofossil CP12a / CP12b Subzone boundary; the larger foraminifer SBZ12 /
SBZ13 Zone boundary; and the boundary between magnetic polarity chrons C22n and C21r), actually
occur at very different levels. Therefore, before considering any section to place the Ypresian/Lutetian
boundary stratotype, the criterion to precisely define this boundary should be selected. To this end, the
succession of events pinpointed in the Ypresian/Lutetian boundary interval of the Gorrondatxe beach
section might prove a useful database.
The Gorrondatxe section fulfils most of the requirements demanded of a prospective stratotype section. In
addition, the great sedimentary thickness, which implies a very high deep-marine sedimentation rate,
provides the Gorrondatxe section an additional value, as it offers the opportunity to chronologically order
successive biomagnetostratigraphic events more precisely than elsewhere. Therefore, we consider that,
once the criterion to define the Ypresian/Lutetian boundary is selected, the Gorrondatxe beach section
should be deemed a firm candidate to place the Global Stratotype Section and Point of the base of the
Lutetian Stage
Cyclostratigraphy of the Early/Middle Eocene transition: a Pyrenean perspective
An integrated bio-, magneto- and cyclostratigraphic study of the Ypresian/Lutetian (Early/Middle Eocene)
transition along the Pyrenean Otsakar section (Payros et al., 2011) resulted in the identification of the
C22n/C21r chron boundary and of the calcareous nannofossil CP12a/b zonal boundary; the latter is the
main correlation criterion of the Lutetian Global Stratotype Section and Point (GSSP) recently defined
at Gorrondatxe (Basque Country). By counting precession-related mudstone-marl couplets of 21 ka,
the time lapse between both events was calculated to be of 819 ka. This suggests that the age of the
CP12a/b boundary, and hence that of the Early/Middle Eocene boundary, is 47.76 Ma, 250 ka younger
than previously thought. This age agrees with, and is supported by, estimates from Gorrondatxe based
on the time lapse between the Lutetian GSSP and the C21r/C21n boundary. The duration of Chron
C21r is estimated at 1.326 Ma. Given that the base of the Eocene is dated at 55.8 Ma, the duration of
the Early Eocene is of 8 Ma, 0.8 Ma longer than in current time scales. The Otsakar results further show
that the bases of planktic foraminiferal zones E8 and P10 are younger than the CP12a/b boundary. The
first occurrence of Turborotalia frontosa, being approximately 550 ka older that the CP12a/b boundary,
is the planktic foraminiferal event that lies closest to the Early/Middle Eocene boundary. The larger
foraminiferal SBZ12/13 boundary is located close to the CP12a/b boundary and correlates with Chron
C21r, not with the C22n/C21r boundary
The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214
We present the first interferometric study of the molecular gas in the
metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission,
obtained at the OVRO millimeter array, reveals an unexpected structural wealth.
We detected three regions of molecular emission in the north-west (NW),
south-east (SE) and centre of NGC 4214 which are in very different and distinct
evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences
are apparent most dramatically when the CO morphologies are compared to optical
ground based and HST imaging: massive star formation has not started yet in the
NW region; the well-known starburst in the centre is the most evolved and star
formation in the SE complex started more recently. We derive a star formation
efficiency of 8% for the SE complex. Using high--resolution VLA observations of
neutral hydrogen HI and our CO data we generated a total gas column density map
for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI,
CO and the sites of ongoing star formation. This emphasizes the irregular
nature of dwarf galaxies. The HI and CO velocities agree well, so do the
H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our
results from a virial mass analysis are compatible with a Galactic CO-to-H_2
conversion factor for NGC 4214 (lower than what is usually found in metal-poor
dwarf galaxies).Comment: accepted for publication in the AJ (February 2001), full ps file at:
ftp://ftp.astro.caltech.edu/users/fw/ngc4214/walter_prep.p
Metal enrichment in near-IR luminous galaxies at z~2: signatures of proto-ellipticals?
We present the analysis of the coadded rest-frame UV spectrum (1200<z<2000 A)
of five K-luminous galaxies at z~2 from the K20 survey. The composite spectrum
is characterized by strong absorption lines over the UV continuum from C, N, O,
Al, Si, and Fe in various ionization stages. While some of these lines are
interstellar, several among the strongest absorptions are identified with
stellar photospheric lines. Most of the photospheric and interstellar features
are stronger in the K-luminous composite spectrum than in LBGs at z~3. This
suggests higher metallicity and possibly also larger interstellar velocity
dispersion caused by macroscopic motions. The absorption lines and the slope of
the UV continuum is well matched by the spectrum of the nearby luminous
infrared galaxy NGC 6090, which is in the process of merging. A metallicity
higher than solar is suggested by comparing the pure photospheric lines (SiIII,
CIII, FeV) with starburst models. The evidence of high metallicity, together
with the high masses, high star-formation rates, and possibly strong
clustering, well qualify these galaxies as progenitors of local massive
ellipticals.Comment: 4 pages, 3 figures, Accepted ApJ Letter
A Galactic O-Star Catalog
We have produced a catalog of 378 Galactic O stars with accurate spectral
classifications which is complete for V<8 but includes many fainter stars. The
catalog provides cross-identifications with other sources; coordinates
(obtained in most cases from Tycho-2 data); astrometric distances for 24 of the
nearest stars; optical (Tycho-2, Johnson, and Stromgren) and NIR photometry;
group membership, runaway character, and multiplicity information; and a
web-based version with links to online services.Comment: 76 pages, 13 tables, and 3 figures. Accepted for publication in
Astrophysical Journal. Online version of the catalog available at
http://www.stsci.edu/~jmaiz/GOSmain.htm
Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations
We present evidence of the co-existence of either an AGN or an ultraluminous
X-ray source (ULX), together with a young super stellar cluster in the 3
central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts
a number of starburst regions in a circumnuclear spiral, as well as in the
nucleus itself. A high spatial resolution Chandra image of this source reveals
that the soft X-ray emission traces the ultraviolet nuclear spiral down to a
core, which is unresolved both in soft and hard X-rays. The astrometry of the
X-ray core coincides with the UV core within the Chandra positioning accuracy.
The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that
from some LINERs or from the weakest Seyferts detected so far. The soft X-rays
in both the core and the extended structure surrounding it can be well
reproduced by evolutionary synthesis models (which include the emission
expected from single stars, the hot diffuse gas, supernova remnants and binary
systems), consistent with the properties of the young stellar clusters
identified in the UV. The hard X-ray tail detected in the core spectrum,
however, most likely requires the presence of an additional source. This
additional source could either be a weak active nucleus black hole or an
ultraluminous X-ray object. The implications of these results are discussed.Comment: 37 pages, 7 figures, ApJ accepte
New Wolf-Rayet Galaxies with Detection of WC Stars
We report the discovery of two new Wolf-Rayet (WR) galaxies: Mrk~1039, and
F082082816. Two broad WR bumps at 5808\AA~ and 4650\AA~ indicate the
presence of WCE and WNL star population in all two sources. We also confirm the
presenceof WR features in Mrk~35, previously detected in a different position.
The observed equivalent width of the WR bump at 4650\AA~ and the derived number
ratios of WR/(WRO) imply that star formation in these sources takes place
inshort burst duration. Comparisons with the recent models of WR populations in
young starbursts with the observed EW(\HeII)/EW(\CIV)/EW(WRbump) and their
relative intensitie provide an indication that the stellar initial mass
function in some WR galaxies might not be Salpeter-like. It is interesting to
find that the luminous IRAS source, F082082816, has little dust reddening,
probably because of the existence of a powerful superwind. By comparisons with
other starbursts observed with the Hopkins Ultraviolet Telescope, F082082816
as a merging system renders a chance to study the contribution from young
starbursts to the UV background radiation in universe.Comment: 22 pages, 6 figures, 4 tables, accepted by The Astrophysical Journa
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