85 research outputs found
Physical Conditions and Star Formation Activity in the Intragroup Medium of Stephan's Quintet
New multi-band observations of the famous compact group of galaxies Stephan's
Quintet (SQ) are presented and analyzed. These include far infrared (FIR)
images at 60 and 100 (ISOPHOT C-100 camera), radio continuum
images at 1.4 GHz (VLA B-array) and 4.86 GHz (VLA C-array), and long-slit
optical spectrographs (Palomar telescope). With these new data, we aim
to learn more about the X-ray/radio ridge in the middle of the intragroup
medium (IGM) and the IGM starburst SQ-A, both are likely to be caused by the
high speed collision ( km s) between the intruder galaxy NGC
7318b ( km s) and the IGM ( km s).Comment: 31 pages text, 17 figures. Accepted by ApJ. A PS file including all
figures can be found in
http://spider.ipac.caltech.edu/staff/cxu/preprints/sq/apj_sq.ps.g
Environmental Effects in Clusters: Modified Far-Infrared--Radio Relations within Virgo Cluster Galaxies
(abridged) We present a study on the effects of the intracluster medium (ICM)
on the interstellar medium (ISM) of 10 Virgo cluster spiral galaxies using {\it
Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the
FIR-radio correlation within normal galaxies, we use our infrared data to
create model radio maps which we compare to the observed radio images. For 6 of
our sample galaxies we find regions along their outer edges that are highly
deficient in the radio compared with our models. We believe these observations
are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit
region to lie just exterior to a region of high radio polarization and flat
radio spectral index, although the total 20 cm radio continuum in this region
does not appear strongly enhanced. These characteristics seem consistent for
other galaxies with radio polarization data in the literature. The strength of
the radio deficit is inversely correlated with the time since peak pressure as
inferred from stellar population studies and gas stripping simulations,
suggesting the strength of the radio deficit is good indicator of the strength
of the current ram pressure. We also find that galaxies having {\it local}
radio {\it deficits} appear to have {\it enhanced global} radio fluxes. Our
preferred physical picture is that the observed radio deficit regions arise
from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated
magnetic field, thereby creating synchrotron tails as observed for some of our
galaxies. We propose that CR particles are also re-accelerated by ICM-driven
shocklets behind the observed radio deficit regions which in turn enhances the
remaining radio disk brightness.Comment: 19 pages, 10 figures; Astrophysical Journa
An analysis of the FIR/RADIO Continuum Correlation in the Small Magellanic Cloud
The local correlation between far-infrared (FIR) emission and radio-continuum
(RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales
from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ~15 pc.
The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is
shown to be greatest in the most active star forming regions with a power law
slope of ~1.14 indicating that the RC emission increases faster than the FIR
emission. The slope of the other regions and the SMC are much flatter and in
the range of 0.63-0.85. The slopes tend to follow the thermal fractions of the
regions which range from 0.5 to 0.95. The thermal fraction of the RC emission
alone can provide the expected FIR/RC correlation. The results are consistent
with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray
electrons (CRe-s) diffusing away from the star forming regions. Since the CRe-s
appear to escape the SMC so readily, the results here may not provide support
for coupling between the local gas density and the magnetic field intensity.Comment: 19 pages, 7 Figure
An Initial Look at the Far Infrared-Radio Correlation within Nearby Star-forming Galaxies using the Spitzer Space Telescope
(Abridged) We present an initial look at the far infrared-radio correlation
within the star-forming disks of four nearby, nearly face-on galaxies (NGC
2403, NGC 3031, NGC 5194, and NGC 6946). Using Spitzer MIPS imaging and WSRT
radio continuum data, observed as part of the Spitzer Infrared Nearby Galaxies
Survey (SINGS), we are able to probe variations in the logarithmic 24mu/22cm
(q_24) and 70mu/22cm (q_70) surface brightness ratios across each disk at
sub-kpc scales. We find general trends of decreasing q_24 and q_70 with
declining surface brightness and with increasing radius. The residual
dispersion around the trend of q_24 and q_70 versus surface brightness is
smaller than the residual dispersion around the trend of q_24 and q_70 versus
radius, on average by ~0.1 dex, indicating that the distribution of star
formation sites is more important in determining the infrared/radio disk
appearance than the exponential profiles of disks. We have also performed
preliminary phenomenological modeling of cosmic ray electron (CRe^-) diffusion
using an image-smearing technique, and find that smoothing the infrared maps
improves their correlation with the radio maps. Exponential kernels tend to
work better than Gaussian kernels which suggests that additional processes
besides simple random-walk diffusion in three dimensions must affect the
evolution of CRe^-s. The best fit smoothing kernels for the two less active
star-forming galaxies (NGC 2403 and NGC 3031) have much larger scale-lengths
than those of the more active star-forming galaxies (NGC 5194 and NGC 6946).
This difference may be due to the relative deficit of recent CRe^- injection
into the interstellar medium (ISM) for the galaxies having largely quiescent
disks.Comment: 41 pages including 6 tables and 12 figures; accepted for publication
in the Astrophysical Journal. A full-resolution color version can be found at
http://www.astro.yale.edu/murphy/a-ph/murphy_FIR-radio.pdf ; Corrected typo
Contact metamorphism associated to the Penamacor - Monsanto granitic intrusion (Central Portugal): geochemical, isotopic and mineralogical features
Contact metamorphism related to Variscan and late-Variscan granitic plutons in the Iberian Peninsula is superimposed on medium-grade regional metamorphism, making it often difficult to evaluate per se the thermal effects due to those intrusions and explaining the paucity of scientific literature on the subject. An exhaustive set of geochemical, isotopic and mineralogical data on the contact-zone metasediments hosting the Penamacor-Monsanto granite (Central Iberian Zone, Portugal) provides a significant contribution to the characterization of low- to intermediate-grade contact metamorphism in geological contexts formerly affected by regional metamorphism.
The metasediments hosting the Penamacor-Monsanto pluton belong to the extensive detrital sequence of the ante-Ordovician Schist-Greywacke Complex. Bulk geochemistry, oxygen isotope data and crystal-chemistry of key minerals from those contact-zone and neighbouring metasediments have made it possible to infer metamorphic conditions on the contact zone of this granitic intrusion, and to distinguish them from late boron-metasomatism at the exocontact.
Mineral paragenesis (muscovite + biotite + chlorite quartz plagioclase cordierite, in spotted-schists; biotite + chlorite quartz plagioclase ( cordierite), in hornfelses) and the composition of these coexisting mineral phases indicate that most of the contact rocks reached the biotite zone (or even the cordierite zone, in some cases), equivalent to upper greenschist – lower amphibolite metamorphic grade. The relatively narrow range of O-isotope temperatures estimated for the crystallization of the marginal granites (550-625ºC) explains the absence of significant effects of thermal flow anisotropy on the contact-zone rocks. Besides, textural, paragenetic, mineralogical, isotopic and geochemical nuances observed in hornfelses and spotted-schists seem mainly related to the local host-rock heterogeneities, rather than to thermal effects.
The relatively low temperatures estimated for granitoid emplacement and their restricted isotopic and mineralogical impacts on the metasedimentary host-rocks account for the narrow metamorphic aureole associated with the Penamacor-Monsanto pluton, and suggest this massif may correspond to the outcropping tip of a larger granitic intrusion at depth.Las intrusions graníticas Varíscicas y tardivaríscicas de la Península Ibérica dieron lugar a un metamorfsmo de contacto
que afecta a un encajante previamente sometido a un metamorfsmo regional de grado medio, lo que difculta separar los
efectos térmicos de aquellos regionales, y explica la escasez de estudios sobre el mismo. El estudio detallado de la zona
de contacto entre el Granito de Penamacor-Monsanto (Zona Centro-Ibérica; Portugal) y su encajante metasedimentario
mediante técnicas geoquímicas, mineralógicas e isotópicas supone una notable contribución al conocimiento y caracterización del metamorfsmo de contacto de grados bajos a intermedios en contextos geológicos previamente afectados por
metamorfsmo regional. El encajante metasedimentario del Plutón de Penamacor-Monsanto es parte de la amplia secuencia detrítica ante-Ordovícia conocida como Complejo Esquisto-Grawackico. Datos geoquímicos de roca total y cristaloquímicos
de los minerales más característicos, y relaciones isotópicas de oxígeno en la zona de contacto y metasedimentos aledaños
permiten inferir las condiciones metamórfcas en la zona de contacto de dicha intrusión, y diferenciarla de aquella afectada
por metasomatismo tardío por B. La paragénesis mineral (muscovita + biotita + clorita ± cuarzo ± plagioclasa ± cordierita
en los esquistos moteados; biotita + clorita ± cuarzo ± plagiclasa (± cordierita) en corneanas) y la composición de las fases
minerales coexistentes indican que la mayoría de rocas del contacto alcanzaron la zona de la biotita (e incluso, en algunos
casos, aquella de la cordierita), equivalente a la parte alta del grado metamórfco de los esquistos verdes, o a la parte baja de
las anfbolitas. El rango relativamente pequeño de temperaturas de cristalización de los granitos marginales (550-625°C),
calculado mediante isótopos de oxígeno, explica la carencia de anisotropías térmicas signifcativas en las rocas del contacto.
Las sutiles diferencias texturales, paragenéticas, mineralógicas, isotópicas y geoquímicas en esquistos moteados y corneanas
parecen relacionadas con heterogeneidades locales de los encajantes, y no con efectos térmicos diferenciados. Las temperaturas relativamente bajas estimadas durante la intrusión del granito de Penamacor-Monsanto, y el limitado efecto mineralógico
e isotópico sobre el encajante metasedimentario, dan lugar a una aureola de contacto estrecha, y sugieren que este macizo
puede corresponder al techo de una intrusión mayor en profundidad.Funding was provided by FCT—Fundação para a Ciên cia e Tecnologia, through project METMOB (PTDC/CTE-GIX/116204/2009
Superdeformation in Gd und Entwicklung eines Softwarepakets zur Datensortierung
An experiment to search for superdeformation in Gd was performed using the Mo(Ti,4n)Gd reaction at 221 MeV. The beam was delivered by the tandem accelerator at the INFN/LNL at Legnaro, -radiation was measured with the GASP array consisting of 40 compton supressed germanium detectors. A new superdeformed band was found and clearly assigned to Gd. This band shows a strong backbending in the J moment of inertia at a rotation energy of 0.4 MeV. In good correlation with theoretical predictions this effect was interpreted as a crossing of proton quasiparticle levels. A search for linking transitions out of the superdeformed band in Gd was performed by summing each two -energies in coincidence with the band. Several candidates for two-step decay transitions were found and a absolute energy assignment for the band was made. Also possibilities for the absolute spins could be set up. A software package for sorting data delivered by second generation spectrometers was developed and documented
The polarized disk in M 31 at
We present a radio continuum survey of M 31 at λ6.2 cm
with high sensitivity in total power and polarization, observed with
the 100-m Effelsberg dish with an angular resolution of 2\farcm 4.
(1) Combination with the VLA + Effelsberg map at λ20.5 cm in
total power yielded a spectral index map at 3\arcmin resolution. Both
the spectrum of the integrated emission and the spectral index
distribution across M 31 indicate a nonthermal spectral index
. We derived maps of thermal and
nonthermal emission at λ6.2 cm. Radial profiles of the various
emission components north and south of the minor axis revealed that the
stronger total emission in the northern part of M 31 is entirely due
to stronger thermal emission, whereas the profiles of nonthermal and
polarized emission are nearly identical on either side of the minor
axis. This suggests that recent star formation does not lead to a local
increase of the number of relativistic electrons and/or magnetic field
strength.
(2) We discuss several properties of the polarized emission from
M 31 and their implications for the magnetic field. At λ6.2 cm
the polarized intensity systematically varies along the bright “ring” of
emission which shows that the regular magnetic field, ,
is nearly aligned with the spiral arms forming this “ring”. The
variation of the rotation measures between λ11.1 cm and
λ6.2 cm, RM(11, 6), across the galaxy confirms this
alignment. The nonthermal degree of polarization reaches values
>
near the polarization maxima, implying that the magnetic
field in M 31 is exceptionally regular.
(3) We derived the distribution of the nonthermal depolarization
between λ11.1 cm and λ6.2 cm, , which is a
measure of Faraday depolarization. Gradients in RM(11, 6) may be an
important cause of Faraday depolarization in M 31. The lack of
anticorrelation between the thermal emission, which comes mainly from
dense \ion{H}{ii} regions with small filling factors, and RM(11, 6) and
indicates that rotation measures and Faraday
depolarization originate in the extended diffuse ionized gas
A deep
We present a survey of the total and linearly polarized
radio continuum emission of the Andromeda galaxy at 20 cm
wavelength with the VLA-D array. 7 fields were observed with
45 angular resolution. The missing large-scale total
emission observed with the Effelsberg telescope was inserted.
This survey is the most sensitive radio continuum survey of M 31 so
far and the first one in linear polarization with the VLA.
The total emission of M 31 comes from extended regions and point
sources. Both components are concentrated in the bright "ring”
of maximum star formation at about 10 kpc radius. Nearly half of the
extended emission emerges from numerous filamentary features which are
typically a few arcminutes long ( pc). In the field of
M 31, 36 linearly polarized background sources were detected.
The smallest degrees of polarization occur on the centre of the
"ring” where the total emission is highest, hence on the spiral arms
as delineated by Hα emission and OB associations. The
distribution of polarization angles reveals coherent features of
typically 1 kpc in extent, some of which show a relation to an OB
association
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