107 research outputs found
Altered mafic lower continental crust as a source for low ÎŽ18O-granodiorites (Damara orogen, Namibia)?
Petrogenesis of Tertiary Alkaline Magmas in the Siebengebirge, Germany
Basanites from the Tertiary Siebengebirge area of Germany (part of the Central European Volcanic Province; CEVP) have high Mg# (>0·60), moderate to high Cr (>300 ppm) and Ni (>200 ppm) contents and strong light rare earth element enrichment, but systematic depletion in Rb and K relative to trace elements of similar compatibility in anhydrous mantle. Rare earth element melting models can explain the petrogenesis of these basanites in terms of partial melting of a spinel peridotite source containing residual amphibole. It is inferred that amphibole, indicated by the relative K and Rb depletion and the melting model, was precipitated in the spinel peridotite lithospheric mantle beneath the Siebengebirge, by metasomatic fluids or melts from a rising mantle diapir or plume. Alkali basalts and more differentiated rocks have lower Mg# and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe-Ti oxides, amphibole and plagioclase. Most of the basanites and alkali basalts approach the Sr-Nd-Pb isotope compositions inferred for the European Asthenospheric Reservoir component. Trace element constraints (i.e. low Nb/U and Ce/Pb ratios) and the Sr-Nd-Pb isotope composition of the differentiated rocks indicate that assimilation of lower crustal material has modified the composition of the primary mantle-derived magmas. High 207Pb/204Pb ratios in the differentiated lavas point to assimilation of ancient lower crustal components having high U/Pb and Th/Pb ratios. Relatively shallow melting of inferred amphibole-bearing spinel peridotite sources may suggest an origin from the metasomatized part of the thermal boundary layer. Application of new thermobarometric equations for the basaltic magmas indicates relatively normal mantle potential temperatures (1300-1400°C); thus the inferred mantle âbaby plume' or âhot finger' is not thermally anomalou
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
A multi-scale study of infrared and radio emission from Scd galaxy M33
We investigate the energy sources of the infrared (IR) emission and their
relation to the radio continuum emission at various spatial scales within the
Scd galaxy M33. We use the wavelet transform to analyze IR data at the Spitzer
wavelengths of 24, 70, and 160m, as well as recent radio continuum data at
3.6cm and 20cm. An H map serves as a tracer of the star forming regions
and as an indicator of the thermal radio emission. We find that the dominant
scale of the 70m emission is larger than that of the 24m emission,
while the 160m emission shows a smooth wavelet spectrum. The radio and
H maps are well correlated with all 3 MIPS maps, although their
correlations with the 160m map are weaker. After subtracting the bright
HII regions, the 24 and 70m maps show weaker correlations with the 20cm
map than with the 3.6cm map at most scales. We also find a strong correlation
between the 3.6cm and H emission at all scales. Comparing the results
with and without the bright HII regions, we conclude that the IR emission is
influenced by young, massive stars increasingly with decreasing wavelength from
160 to 24m. The radio-IR correlations indicate that the warm dust-thermal
radio correlation is stronger than the cold dust-nonthermal radio correlation
at scales smaller than 4kpc. A perfect 3.6cm-H correlation implies that
extinction has no significant effect on H emitting structures.Comment: 15 pages, 10 figures, accepted for publication in the Astronomy and
Astrophysics Journa
Molecular gas in the Andromeda galaxy
We present a new 12CO(J=1-0)-line survey of the Andromeda galaxy, M31,
covering the bright disk with the highest resolution to date (85 pc along the
major axis), observed On-the-Fly (in italics) with the IRAM 30-m telescope. We
discuss the distribution of the CO emission and compare it with the
distributions of HI and emission from cold dust traced at 175mum. Our main
results are: 1. Most of the CO emission comes from the radial range R=3-16 kpc,
but peaks near R=10 kpc. The emission is con- centrated in narrow, arm-like
filaments defining two spiral arms with pitch angles of 7d-8d. The average
arm-interarm brightness ratio along the western arms reaches 20 compared to 4
for HI. 2. For a constant conversion factor Xco, the molecular fraction of the
neutral gas is enhanced in the arms and decreases radially. The apparent
gas-to-dust ratios N(HI)/I175 and (N(HI)+2N(H2))/I175 increase by a factor of
20 between the centre and R=14 kpc, whereas the ratio 2N(H2)/I175 only
increases by a factor of 4. Implications of these gradients are discussed. In
the range R=8-14 kpc total gas and cold dust are well correlated; molecular gas
is better correlated with cold dust than atomic gas.Comment: 21 pages, 16 figures. Accepted for publication in A&
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
Molecular gas in NGC6946
We present imaging of molecular gas emission in the star-forming spiral
galaxy NGC6946. Our CO(1-0) and CO(3-2) images, made at 22" resolution with the
IRAM 30-m and the Heinrich Hertz 10-m radio telescopes, are the most extensive
CO observations of this galaxy and are among the most extensive observations of
molecular gas in any spiral galaxy. The molecular component in NGC6946 is
unusually massive, with a ratio of molecular to atomic Hydrogen of 0.57. A star
formation efficiency image for NGC6946 ranges by over two orders of magnitude
with highest values found in the northeastern spiral arm, and anticorrelates
with the 6cm polarized emission image, which traces the regular part of the
magnetic field. We analyse the ISM in NGC6946's disk by making 1-D and 2-D
comparisons of images made in several wavebands. A point-by-point correlation
technique finds that the molecular gas is closely associated with the
7micron-emitting dust. The high correlation found between the MIR emission and
the radio continuum at 6cm cannot be due to dust heating and gas ionization in
star-forming regions because the thermal radio emission is less correlated with
the MIR than the nonthermal emission. A coupling of magnetic fields to gas
clouds is proposed as a possible scenario.Comment: A&A accepted, 23 pages, 11 figures. Version with high resolution
figures available at: http://cfa-www.harvard.edu/~wwalsh/sp.htm
Magnetic fields in barred galaxies I. The atlas
The total and polarized radio continuum emission of 20 barred galaxies was
observed with the Very Large Array (VLA) at 3, 6, 18 and 22 cm and with the
Australia Telescope Compact Array (ATCA) at 6 cm and 13 cm. Maps at 30 arcsec
angular resolution are presented here. Polarized emission (and therefore a
large-scale regular magnetic field) was detected in 17 galaxies. Most galaxies
of our sample are similar to non-barred galaxies with respect to the
radio/far-infrared flux correlation and equipartition strength of the total
magnetic field. Galaxies with highly elongated bars are not always
radio-bright. We discuss the correlation of radio properties with the aspect
ratio of the bar and other measures of the bar strength. We introduce a new
measure of the bar strength, \Lambda, related to the quadrupole moment of the
bar's gravitational potential. The radio surface brightness I of the barred
galaxies in our sample is correlated with \Lambda, I \propto \Lambda^0.4+/-0.1,
and thus is highest in galaxies with a long bar where the velocity field is
distorted by the bar over a large fraction of the disc. In these galaxies, the
pattern of the regular field is significantly different from that in non-barred
galaxies. In particular, field enhancements occur upstream of the dust lanes
where the field lines are oriented at large angles to the bar's major axis.
Polarized radio emission seems to be a good indicator of large-scale
non-axisymmetric motions.Comment: 29 pages with 66 PostScript figures. Accepted for publication in A&A.
Figures 5-24 also available at http://www.mpifr-bonn.mpg.d
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
The far-IR/radio correlation in the ISO era
We present the correlation between the far-infrared (FIR) and radio emissions
from a composite sample of 72 nearby normal galaxies observed with the ISOPHOT
instrument on board the Infrared Space Observatory. The galaxies in the sample
have measurements at three FIR wavelengths (60, 100 and 170 micron), which
allowed a direct determination of the warm and cold FIR emission components.
This is the first time that the correlation has been established for the total
FIR luminosity, of which most is carried by the cold dust component
predominantly emitting longwards of the spectral coverage of IRAS. The slope of
this correlation is slightly non-linear (1.10+/-0.03). Separate correlations
between the warm and cold FIR emission components and the radio emission have
also been derived. The slope of the warm FIR/radio correlation was found to be
linear (1.03+/-0.03). For the cold FIR/radio correlation we found a slightly
non-linear (1.13+/-0.04) slope. We qualitatively interpret the correlations in
terms of star formation rate and find that both the FIR and radio emissions may
be consistent with a non-linear dependence on star formation rate for galaxies
not undergoing starburst activity.Comment: 15 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
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