3,140 research outputs found
Spectrophotometric investigations of Blue Compact Dwarf Galaxies: Markarian 35
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy Mrk 35 (Haro 3), based on deep optical (B,V,R,I) and
near-IR (J,H,K) imaging, Halpha narrow-band observations and long-slit
spectroscopy. The optical emission of the galaxy is dominated by a central
young starburst, with a bar-like shape, while an underlying component of stars,
with elliptical isophotes and red colors, extends more than 4 kpc from the
galaxy center. High resolution Halpha and color maps allow us to identify the
star-forming regions, to spatially discriminate them from the older stars, and
to recognize several dust patches. We derive colors and Halpha parameters for
all the identified star-forming knots. Observables derived for each knot are
corrected for the contribution of the underlying older stellar population, the
contribution by emission lines, and from interstellar extinction, and compared
with evolutionary synthesis models. We find that the contributions of these
three factors are by no means negligible and that they significantly vary
across the galaxy. Therefore, careful quantification and subtraction of
emission lines, galaxy host contribution, and interstellar reddening at every
galaxy position, are essential to derive the properties of the young stars in
BCDs. We find that we can reproduce the colors of all the knots with an
instantaneous burst of star formation and the Salpeter initial mass function
with an upper mass limit of 100 M_solar. In all cases the knots are just a few
Myr old. The underlying population of stars has colors consistent with being
several Gyr old.Comment: 21 pages, 13 figures. Accepted for publication in ApJ, tentatively
scheduled for the ApJ November 1, 2007 v669n1 issu
Spectrophotometric Observations of Blue Compact Dwarf Galaxies: Mrk 370
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy (BCD) Mrk 370, based on deep UBVRI broad-band and Halpha
narrow-band observations, and long-slit and two-dimensional spectroscopy of its
brightest knots. The spectroscopic data are used to derive the internal
extinction, and to compute metallicities, electronic density and temperature in
the knots. By subtracting the contribution of the underlying older stellar
population, modeled by an exponential function, removing the contribution from
emission lines, and correcting for extinction, we can measure the true colors
of the young star-forming knots. We show that the colors obtained this way
differ significantly from those derived without the above corrections, and lead
to different estimates of the ages and star-forming history of the knots. Using
predictions of evolutionary synthesis models, we estimate the ages of both the
starburst regions and the underlying stellar component. We found that we can
reproduce the colors of all the knots with an instantaneous burst of star
formation and the Salpeter initial mass function with an upper mass limit of
100 solar masses. The resulting ages range between 3 and 6 Myrs. The colors of
the low surface brightness component are consistent with ages larger than 5
Gyr. The kinematic results suggest ordered motion around the major axis of the
galaxy.Comment: 26 pages with 14 figures; accepted for publication in Ap
The Crust beneath Morocco: From the surface topography to the upper mantle a 700 km long seismic section across Morocco.
The most characteristic topographic features of Morocco are the Atlas Mountains and the Rif Coordillera. These two orogenic belts are the response of different geodynamic processes acting at lithospheric scale caused by a complex plate interaction. Both are located within the diffuse plate boundary zone separating Africa and Europe. The boundary zone is characterized by a relatively broad zone of deformation that includes mountain chains in southern Iberia, the Betics and in Morocco, the Rif Cordillera, separated by the Alboran basin. The zone delineates an arcuate arc system known as the Gibraltar arc. The area is characterized by a relatively large amount of earthquake activity at various depths and with a broad spectra of focal mechanisms. Within the last decade a large international effort have been devoted to the area. The topic has fostered a strong collaborations between Spanish and international research teams form Europe and USA. Key multi-seismic projects have been developed that aim to constrain the structure, composition and tectonic scenario from south of the Atlas to the Betics, across the Rif cordillera and the Alboran basin. The multidisciplinary research program included: natural source (earthquakes) recording with temporal deployments of broad band (BB) instrumentation and, controlled source seismic acquisition experiments where, spatially dense recording of wide-angle seismic reflection shot gathers were acquired. The natural source experiments consisted on a transect from Merzouga across the Gibraltar Arc and into the Iberian Peninsula (until south of Toledo) and, a nearly regular grid of BB. The controlled source data-sets were able to constrain the crustal structure and provide seismic P-wave propagation velocity models from the coast across the Rif and the Atlas. From south to north the crust features a relatively moderate crustal root beneath the Middle Atlas which can reach 40 km clearly differing from the 35 km thickness value observed at both sides of this root. Travel time inversion results position the crustal root just south of the High Atlas defining a thrusted mantle wedge and, also a limited crustal imbrication is suggested in the Middle Atlas. The most surprising feature is a prominent and unexpected crustal root (over 50 km) located beneath the external Rif and identified by both the wide-angle data and receiver function studies. To the east of this feature the crust thins rapidly by 20 km across the Nekkor fault zone, suggested to be related to the sharp change in crustal thickness. On shore-offshore recording of marine shots reveal further complexities in the transition to the Alboran basin. The low values of the Bouguer gravity anomalies beneath the Rif Cordillera are consistent with the crustal models derived from the new seismic data. The detailed knowledge on the crustal structure achieved by this high resolution imaging geophysical techniques is an asset to evaluate the earthquake and potential tsunami hazard for the coasts of North Africa and western Europe.This work has been primarily funded by the Spanish MEC project CGL2007–63889. Additional funding was provided by projects CGL2010–15416, CSD2006-00041, and CGL2009–09727 (Spain), CGL2008–03474-E, 07- TOPO_EUROPE_FP-006 (ESF Eurocores) and EAR-0808939 (US, NSF).Peer Reviewe
Mapping the properties of blue compact dwarf galaxies: integral field spectroscopy with PMAS
(Abridged) We perform integral field spectroscopy of a sample of Blue compact
dwarf (BCD) galaxies with the aim of analyzing their morphology, the spatial
distribution of some of their physical properties (excitation, extinction, and
electron density) and their relationship with the distribution and evolutionary
state of the stellar populations. Integral field spectroscopy observations of
the sample galaxies were carried out with the Potsdam Multi-Aperture
Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. An
area 16 arcsec x 16 arcsec in size was mapped with a spatial sampling of 1
arcsec x 1 arcsec. We obtained data in the 3590-6996 Angstroms spectral range,
with a linear dispersion of 3.2 Angstroms per pixel. From these data we built
two-dimensional maps of the flux of the most prominent emission lines, of two
continuum bands, of the most relevant line ratios, and of the gas velocity
field. Integrated spectra of the most prominent star-forming regions and of
whole objects within the FOV were used to derive their physical parameters and
the gas metal abundances. Six galaxies display the same morphology both in
emission line and in continuum maps; only in two objects, Mrk 32 and Tololo
1434+032, the distributions of the ionized gas and of the stars differ
considerably. In general the different excitation maps for a same object
display the same pattern and trace the star-forming regions, as expected for
objects ionized by hot stars; only the outer regions of Mrk 32, I Zw 123 and I
Zw 159 display higher [SII]/Halpha values, suggestive of shocks. Six galaxies
display an inhomogeneous dust distribution. Regarding the kinematics, Mrk 750,
Mrk 206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk 475
and I Zw 123 the velocity fields are flat.Comment: 27 pages, 11 figures; Accepted for publication in A&
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Long-term acidification of pH neutral grasslands affects soil biodiversity, fertility and function in a heathland restoration
In the wider context of heathland restoration, we investigated how field scale experimental acidification with sulphur (sulfur)affected soil biodiversity, fertility and function over a period of 17 years. A field experiment was conducted in the Isle of Purbeck, England, using ferrous sulphate and elemental sulphur as acidifying agents. We tested the effects of acidification on soil fertility, plant communities, litter decomposition, microbiology (including fungi bacteria and actinomycetes), arbuscular and ericoid mycorrhizal colonisation, and soil fauna (including earthworms, nematodes, rotifers and tardigrades). We found that elemental sulphur had a considerable and persistent effect on soil pH, lowering it to levels found in the surrounding reference acid grassland and heathland sites. A newly adapted heathland restoration index based on soil chemistry, found that elemental sulphur was by far the most successful treatment leading to soil conditions similar to the heathlands. Overall, acidification caused a loss of base cations and an increase in toxic aluminium compounds. Consequently the more mesotrophic components of soil biology were reduced by acidification during the course of the experiment. This transformed the soil biological system into one typical of acid grasslands and heathlands. Concomitant litter decomposition was similarly inhibited by acidification, with the microbiota more strongly hindered in acidified soil than the macroscopic fauna. Acidification resulted in a reduction in nematode and rotifer abundance and earthworm biomass. The vegetation community was also strongly modified by the elemental sulphur treatments and, where grazing was restricted, soil acidification allowed a restored heathland community to endure. Arbuscular mycorrhizal colonisation of grasses was reduced where heather plants were established, while ericoid mycorrhizas had developed sufficient populations in the acidified pastures to match the colonisation rate in the native heathlands
Coulomb breakup of neutron-rich Na isotopes near the island of inversion
First results are reported on the ground state configurations of the
neutron-rich Na isotopes, obtained via Coulomb dissociation (CD)
measurements as a method of the direct probe. The invariant mass spectra of
those nuclei have been obtained through measurement of the four-momentum of all
decay products after Coulomb excitation on a target at energies of
400-430 MeV/nucleon using FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated
Coulomb-dissociation cross-sections (CD) of 89 mb and 167 mb up to
excitation energy of 10 MeV for one neutron removal from Na and
Na respectively, have been extracted. The major part of one neutron
removal, CD cross-sections of those nuclei populate core, in its' ground state.
A comparison with the direct breakup model, suggests the predominant occupation
of the valence neutron in the ground state of Na and
Na is the orbital with small contribution in the
-orbital which are coupled with ground state of the core. The ground state
configurations of these nuclei are as Na_{gs (1^+)\otimes\nu_{s,d} and
Na, respectively. The ground state spin
and parity of these nuclei, obtained from this experiment are in agreement with
earlier reported values. The spectroscopic factors for the valence neutron
occupying the and orbitals for these nuclei in the ground state have
been extracted and reported for the first time. A comparison of the
experimental findings with the shell model calculation using MCSM suggests a
lower limit of around 4.3 MeV of the sd-pf shell gap in Na.Comment: Modified version of the manuscript is accepted for publication in
Journal of Physics G, Jan., 201
Mapping the ionized gas of the metal-poor HII galaxy PHL 293B with MEGARA
Here we report the first spatially resolved spectroscopic study for the
galaxy PHL293B using the high-resolution GTC/MEGARA IFU. PHL293B is a local,
extremely metal-poor, high ionization galaxy. This makes PHL 293B an excellent
analogue for galaxies in the early Universe. The MEGARA aperture (~12.5''x
11.3'') covers the entire PHL 293B main body and its far-reaching ionized gas.
We created and discussed maps of all relevant emission lines, line ratios and
physical-chemical properties of the ionized ISM. The narrow emission gas
appears to be ionized mainly by massive stars according to the observed
diganostic line ratios, regardless of the position across the MEGARA aperture.
We detected low intensity broad emission components and blueshifted absorptions
in the Balmer lines (H,H) which are located in the brightest
zone of the galaxy ISM. A chemically homogeneity, across hundreds of parsecs,
is observed in O/H. We take the oxygen abundance 12+log(O/H)=7.64 0.06
derived from the PHL293B integrated spectrum as the representative metallicity
for the galaxy. Our IFU data reveal for the first time that the nebular
HeII4686 emission from PHL 293B is spatially extended and coincident with the
ionizing stellar cluster, and allow us to compute its absolute HeII ionizing
photon flux. Wolf-Rayet bumps are not detected excluding therefore Wolf-Rayet
stars as the main HeII excitation source. The origin of the nebular HeII4686 is
discussed.Comment: 14 pages, 9 Figures, 3 Tables; Accepted for publication in MNRA
An Aromatic Inventory of the Local Volume
Using infrared photometry from the Spitzer Space Telescope, we perform the
first inventory of aromatic feature emission (AFE, but also commonly referred
to as PAH emission) for a statistically complete sample of star-forming
galaxies in the local volume. The photometric methodology involved is
calibrated and demonstrated to recover the aromatic fraction of the IRAC 8
micron flux with a standard deviation of 6% for a training set of 40 SINGS
galaxies (ranging from stellar to dust dominated) with both suitable
mid-infrared Spitzer IRS spectra and equivalent photometry. A potential factor
of two improvement could be realized with suitable 5.5 and 10 micron
photometry, such as what may be provided in the future by JWST. The resulting
technique is then applied to mid-infrared photometry for the 258 galaxies from
the Local Volume Legacy (LVL) survey, a large sample dominated in number by
low-luminosity dwarf galaxies for which obtaining comparable mid-infrared
spectroscopy is not feasible. We find the total LVL luminosity due to five
strong aromatic features in the 8 micron complex to be 2.47E10 solar
luminosities with a mean volume density of 8.8E6 solar luminosities per cubic
Megaparsec. Twenty-four of the LVL galaxies, corresponding to a luminosity cut
at M = -18.22 in the B band, account for 90% of the aromatic luminosity. Using
oxygen abundances compiled from the literature for 129 of the 258 LVL galaxies,
we find a correlation between metallicity and the aromatic to total infrared
emission ratio but not the aromatic to total 8 micron dust emission ratio. A
possible explanation is that metallicity plays a role in the abundance of
aromatic molecules relative to the total dust content, but other factors such
as star formation and/or the local radiation field affect the excitation of
those molecules.Comment: ApJ in press; 29 pages, 14 figures, 3 tables; emulateapj forma
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