2,402 research outputs found
ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
(abbreviated) We aim to study the inner wind of the well-known AGB star CW
Leo. Different diagnostics probing different geometrical scales have pointed
toward a non-homogeneous mass-loss process: dust clumps are observed at
milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and
multi-concentric shells are detected beyond 1". We present the first ALMA Cycle
0 band 9 data around 650 GHz. The full-resolution data have a spatial
resolution of 0".42x0".24, allowing us to study the morpho-kinematical
structure within ~6". Results: We have detected 25 molecular lines. The
emission of all but one line is spatially resolved. The dust and molecular
lines are centered around the continuum peak position. The dust emission has an
asymmetric distribution with a central peak flux density of ~2 Jy. The
molecular emission lines trace different regions in the wind acceleration
region and suggest that the wind velocity increases rapidly from about 5 R*
almost reaching the terminal velocity at ~11 R*. The channel maps for the
brighter lines show a complex structure; specifically for the 13CO J=6-5 line
different arcs are detected within the first few arcseconds. The curved
structure present in the PV map of the 13CO J=6-5 line can be explained by a
spiral structure in the inner wind, probably induced by a binary companion.
From modeling the ALMA data, we deduce that the potential orbital axis for the
binary system lies at a position angle of ~10-20 deg to the North-East and that
the spiral structure is seen almost edge-on. We infer an orbital period of 55
yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that
the companion is an unevolved low-mass main-sequence star. The ALMA data hence
provide us for the first time with the crucial kinematical link between the
dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen
at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic
The Dark Energy Equation of State using Alternative High-z Cosmic Tracers
We propose to use alternative cosmic tracers to measure the dark energy
equation of state and the matter content of the Universe [w(z) & Omega_m]. Our
proposed method consists of two components: (a) tracing the Hubble relation
using HII galaxies which can be detected up to very large redshifts, z~4, as an
alternative to supernovae type Ia, and (b) measuring the clustering pattern of
X-ray selected AGN at a median redshift of z~1. Each component of the method
can in itself provide interesting constraints on the cosmological parameters,
especially under our anticipation that we will reduce the corresponding random
and systematic errors significantly. However, by joining their likelihood
functions we will be able to put stringent cosmological constraints and break
the known degeneracies between the dark energy equation of state (whether it is
constant or variable) and the matter content of the universe and provide a
powerful and alternative route to measure the contribution to the global
dynamics and the equation of state of dark energy. A preliminary joint analysis
of X-ray selected AGN (based on the largest to-date XMM survey; the 2XMM) and
the currently largest SNIa sample (Hicken et al.), using as priors a flat
universe and the WMAP5 normalization of the power-spectrum, provides:
Omega_m=0.27+-0.02 and w=-0.96+-0.07. Equivalent and consistent results are
provided by the joint analysis of X-ray selected AGN clustering and the latest
Baryonic Acoustic Oscillation measures, providing: Omega_m=0.27+-0.02 and
w=-0.97+-0.04.Comment: Different versions of this paper appear in the "Dark Universe"
conference (Paris, July 2009) and in the "1st Mediterranean Conference in
Classical & Quantum Gravity" (invited
UV Interstellar Absorption Lines towards the Starburst Dwarf Galaxy NGC 1705
Archival Goddard High Resolution Spectrograph low-resolution spectra of NGC
1705, with wavelength ranges 1170.3 to 1461.7 A and 1453.5 to 1740.1 A and a
velocity resolution of about 100 km\s, have been used to derive the velocity
structure and equivalent widths of the absorption lines of Si II 1190.42,
1260.42, 1304.37 and 1526.71 A, S II 1253 , Al II 1670.79 Aand Fe II 1608.45 A
in this sightline. Three relatively narrow absorption components are seen at
LSR velocities --20 km/s, 260 km/sand 540 km/s. Arguments are presented to show
these absorption features are interstellar rather than stellar in origin based
on a comparison with the C III 1175.7 A absorption feature. We identify the
--20 km/s component with Milky Way disk/halo gas and the 260 km/s component
with an isolated high-velocity cloud HVC 487. This small HVC is located about
10 degrees from the H I gas which envelops the Magellanic Clouds and the
Magellanic Stream (MS). The (Si/H) ratio for this HVC is > 0.6 (Si/H)solar
which together with velocity agreement, suggests association with the
Magellanic Cloud and MS gas. H-alpha emission line kinematics of NGC 1705 show
the presence of a kpc-scale expanding supershell of ionized gas centered on the
central nucleus with a blue-shifted emission component at 540 km/s (Meurer et
al. 1992). We identify the 540 km/s absorption component seen in the GHRS
spectra with the front side of this expanding, ionized supershell. The most
striking feature of this component is strong Si II and Al II absorption but
weak Fe II 1608 A absorption. The low Fe II column density derived is most
likely intrinsic since it cannot be accounted for by ionization corrections or
dust depletion. Due to their shallow gravitational potential wells, dwarf
galaxies have small gravitational binding energies and are vulnerable to largeComment: 15 pages, LaTEX, 1 figure. Accepted for publication in Astrophysical
Journal Letter
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies
We present CO observations of a large sample of ultraluminous IR galaxies out
to z = 0.3. Most of the galaxies are interacting, but not completed mergers.
All but one have high CO(1-0) luminosities, log(Lco [K-km/s-pc^2]) = 9.92 +/-
0.12. The dispersion in Lco is only 30%, less than that in the FIR luminosity.
The integrated CO intensity correlates Strongly with the 100 micron flux
density, as expected for a black body model in which the mid and far IR
radiation are optically thick. We use this model to derive sizes of the FIR and
CO emitting regions and the enclosed dynamical masses. Both the IR and CO
emission originate in regions a few hundred parsecs in radius. The median value
of Lfir/Lco = 160 Lsun/(K-km/s-pc^2), within a factor of two of the black body
limit for the observed FIR temperatures. The entire ISM is a scaled up version
of a normal galactic disk with densities a factor of 100 higher, making even
the intercloud medium a molecular region. Using three different techniques of
H2 mass estimation, we conclude that the ratio of gas mass to Lco is about a
factor of four lower than for Galactic molecular clouds, but that the gas mass
is a large fraction of the dynamical mass. Our analysis of CO emission reduces
the H2 mass from previous estimates of 2-5e10 Msun to 0.4-1.5e10 Msun, which is
in the range found for molecular gas rich spiral galaxies. A collision
involving a molecular gas rich spiral could lead to an ultraluminous galaxy
powered by central starbursts triggered by the compression of infalling
preexisting GMC's.Comment: 34 pages LaTeX with aasms.sty, 14 Postscript figures, submitted to
ApJ Higher quality versions of Figs 2a-f and 7a-c available by anonymous FTP
from ftp://sbast1.ess.sunysb.edu/solomon/
Polarisation Observations of HO 620.701 GHz Maser Emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some
astronomical masers make them ideal tools for studying star-forming giant
molecular clouds. The water maser transition at
620.701 GHz can only be observed from above Earth's strongly absorbing
atmosphere; its emission has recently been detected from space. Aims. We sought
to further characterize the star-forming environment of Orion KL by
investigating the linear polarisation of a source emitting a narrow 620.701 GHz
maser feature with the heterodyne spectrometer HIFI on board the Herschel Space
Observatory. Methods. High-resolution spectral datasets were collected over a
thirteen month period beginning in 2011 March, to establish not only the linear
polarisation but also the temporal variability of the source. Results. Within a
uncertainty, no polarisation was detected to an upper limit of
approximately 2%. These results are compared with coeval linear polarisation
measurements of the 22.235 GHz maser line from
the Effelsberg 100-m radio telescope, typically a much stronger maser
transition. Although strongly polarised emission is observed for one component
of the 22.235 GHz maser at 7.2 km s, a weaker component at the same
velocity as the 620.701 GHz maser at 11.7 km s is much less polarised.Comment: Accepted for publication in A&
The Low End of the Initial Mass Function in Young LMC Clusters: I. The Case of R136
We report the result of a study in which we have used very deep broadband V
and I WFPC2 images of the R136 cluster in the Large Magellanic Cloud from the
HST archive, to sample the luminosity function below the detection limit of 2.8
Mo previously reached. In these new deeper images, we detect stars down to a
limiting magnitude of m_F555W = 24.7 (~ 1 magnitude deeper than previous
works), and identify a population of red stars evenly distributed in the
surrounding of the R136 cluster. A comparison of our color-magnitude diagram
with recentely computed evolutionary tracks indicates that these red objects
are pre-main sequence stars in the mass range 0.6 - 3 Mo. We construct the
initial mass function (IMF) in the 1.35 - 6.5 Mo range and find that, after
correcting for incompleteness, the IMF shows a definite flattening below ~ 2
Mo. We discuss the implications of this result for the R136 cluster and for our
understanding of starburst galaxies formation and evolution in general.Comment: 29 pages, 6 tables, 11 figures included + 3 external files, accepted
for publication by Ap.
Arp 302: Non-starburst Luminous Infrared Galaxies
Arp 302, a luminous infrared source (L_{IR} = 4.2x10^{11} Lsun), consisting
of two spiral galaxies (VV340A and VV340B) with nuclear separation of 40'', has
the highest CO luminosity known. Observations with the BIMA array at 5'' X 7''
resolution reveal that the CO emission is extended over 23.0 kpc in the edge-on
spiral galaxy, VV340A, corresponding to 6.7x10^{10} Msun of H_2. In the
companion face-on galaxy, VV340B, the CO emission is extended over ~10.0 kpc,
with 1.1x10^{10} Msun of H_2. The large CO extent is in strong contrast to
starburst systems, such as Arp 220, in which the CO extent is typically 1
kpc. Furthermore, (H_2) is found to be 6.0 Lsun/Msun throughout
both galaxies. Thus the high IR luminosity of Arp 302 is apparently not due to
starbursts in the nuclear regions, but is due to its unusually large amount of
molecular gas forming stars at a rate similar to giant molecular clouds in the
Milky Way disk. Arp 302 consists of a pair of very gas-rich spiral galaxies
that may be interacting and in a phase before a likely onset of starbursts.Comment: AAS Latex plus two postscript figures. ApJ Letters (accepted
GGD 37: An Extreme Protostellar Outflow
We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom
Mapping water in protostellar outflows with Herschel: PACS and HIFI observations of L1448-C
We investigate on the spatial and velocity distribution of H2O along the
L1448 outflow, its relationship with other tracers, and its abundance
variations, using maps of the o-H2O 1_{10}-1_{01} and 2_{12}-1_{01} transitions
taken with the Herschel-HIFI and PACS instruments, respectively. Water emission
appears clumpy, with individual peaks corresponding to shock spots along the
outflow. The bulk of the 557 GHz line is confined to radial velocities in the
range \pm 10-50 km/s but extended emission associated with the L1448-C extreme
high velocity (EHV) jet is also detected. The H2O 1_{10}-1_{01}/CO(3-2) ratio
shows strong variations as a function of velocity that likely reflect different
and changing physical conditions in the gas responsible for the emissions from
the two species. In the EHV jet, a low H2O/SiO abundance ratio is inferred,
that could indicate molecular formation from dust free gas directly ejected
from the proto-stellar wind. We derive averaged Tkin and n(H2) values of about
300-500 K and 5 10^6 cm-3 respectively, while a water abundance with respect to
H2 of the order of 0.5-1 10^{-6} along the outflow is estimated. The fairly
constant conditions found all along the outflow implies that evolutionary
effects on the timescales of outflow propagation do not play a major role in
the H2O chemistry. The results of our analysis show that the bulk of the
observed H2O lines comes from post-shocked regions where the gas, after being
heated to high temperatures, has been already cooled down to a few hundred K.
The relatively low derived abundances, however, call for some mechanism to
diminish the H2O gas in the post-shock region. Among the possible scenarios, we
favor H2O photodissociation, which requires the superposition of a low velocity
non-dissociative shock with a fast dissociative shock able to produce a FUV
field of sufficient strength.Comment: 16 pages, 13 figures, accepted for publication on Astronomy &
Astrophysic
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