487 research outputs found
Tracing star formation in galaxies with molecular line and continuum observations
We report our recent progress on extragalactic spectroscopic and continuum
observations, including HCN(J=1-0), HCO(J=1-0), and CN(N=1-0) imaging
surveys of local Seyfert and starburst galaxies using the Nobeyama Millimeter
Array, high-J CO observations (J=3-2 observations using the Atacama
Submillimeter Telescope Experiment (ASTE) and J=2-1 observations with the
Submillimeter Array) of galaxies, and 1.1 mm continuum observations
of high-z violent starburst galaxies using the bolometer camera AzTEC mounted
on ASTE.Comment: 6 pages, 5 figures, To appear in proceedings of "Far-Infrared and
Submillimeter Emission of the Interstellar Medium", EAS Publication Series,
Bad Honnef, November 2007, Eds. C. Kramer, S. Aalto, R. Simon. See
http://www.nro.nao.ac.jp/~f0212kk/FIR07/kk-ver20.pdf for a version with high
resolution figure
ALMA Observations of Warm Molecular Gas and Cold Dust in NGC 34
We present ALMA Cycle-0 observations of the CO (6-5) line emission
(rest-frame frequency = 691.473 GHz) and of the 435 dust continuum
emission in the nuclear region of NGC 34, a local luminous infrared galaxy
(LIRG) at a distance of 84 Mpc (1" = 407 pc) which contains a Seyfert 2 active
galactic nucleus (AGN) and a nuclear starburst. The CO emission is well
resolved by the ALMA beam (), with an integrated flux of
. Both the morphology
and kinematics of the CO (6-5) emission are rather regular, consistent with a
compact rotating disk with a size of 200 pc. A significant emission feature is
detected on the red-shifted wing of the line profile at the frequency of the
line, with an integrated flux of . However, it cannot be ruled out
that the feature is due to an outflow of warm dense gas with a mean velocity of
. The continuum is resolved into an elongated
configuration, and the observed flux corresponds to a dust mass of . An unresolved central core () contributes of the continuum flux and of
the CO (6-5) flux, consistent with insignificant contributions of the AGN to
both emissions. Both the CO (6-5) and continuum spatial distributions suggest a
very high gas column density () in the nuclear
region at .Comment: 10 pages, 13 figures, accepted for publication in Astrophysical
Journa
Extended [CII] Emission in Local Luminous Infrared Galaxies
We present Herschel/PACS observations of extended [CII]157.7{\mu}m line
emission detected on ~ 1 - 10 kpc scales in 60 local luminous infrared galaxies
(LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS). We find that
most of the extra-nuclear emission show [CII]/FIR ratios >~ 4 x 10^-3, larger
than the mean ratio seen in the nuclei, and similar to those found in the
extended disks of normal star-forming galaxies and the diffuse inter-stellar
medium (ISM) of our Galaxy. The [CII] "deficits" found in the most luminous
local LIRGs are therefore restricted to their nuclei. There is a trend for
LIRGs with warmer nuclei to show larger differences between their nuclear and
extra-nuclear [CII]/FIR ratios. We find an anti-correlation between [CII]/FIR
and the luminosity surface density, {\Sigma}_IR, for the extended emission in
the spatially-resolved galaxies. However, there is an offset between this trend
and that found for the LIRG nuclei. We use this offset to derive a beam
filling-factor for the star-forming regions within the LIRG disks of ~ 6 %
relative to their nuclei. We confront the observed trend to photo-dissociation
region (PDR) models and find that the slope of the correlation is much
shallower than the model predictions. Finally, we compare the correlation found
between [CII]/FIR and {\Sigma}_IR with measurements of high-redshift
starbursting IR-luminous galaxies.Comment: Accepted for publication in ApJ Letters. 5 pages, 2 figure
ALMA Observations of Warm Dense Gas in NGC 1614 --- Breaking of Star Formation Law in the Central kpc
We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the
435um dust continuum emission in the central kpc of NGC 1614, a local luminous
infrared galaxy (LIRG) at a distance of 67.8 Mpc (1 arcsec = 329 pc). The CO
emission is well resolved by the ALMA beam (0".26 x 0".20) into a
circum-nuclear ring, with an integrated flux of f_{CO(6-5)} = 898 (+-153) Jy
km/s, which is 63(+-12)% of the total CO(6-5) flux measured by Herschel. The
molecular ring, located between 100pc < r < 350pc from the nucleus, looks
clumpy and includes seven unresolved (or marginally resolved) knots with median
velocity dispersion of 40 km/s. These knots are associated with strong star
formation regions with \Sigma_{SFR} 100 M_\sun/yr/kpc^{2} and \Sigma_{Gas}
1.0E4 M_\sun/pc^{2}. The non-detections of the nucleus in both the CO (6-5)
line emission and the 435um continuum rule out, with relatively high
confidence, a Compton-thick AGN in NGC 1614. Comparisons with radio continuum
emission show a strong deviation from an expected local correlation between
\Sigma_{Gas} and \Sigma_{SFR}, indicating a breakdown of the Kennicutt-Schmidt
law on the linear scale of 100 pc.Comment: 13 pages, 10 figures; accepted by Ap
Rotationally Warm Molecular Hydrogen in the Orion Bar
The Orion Bar is one of the nearest and best-studied photodissociation or
photon-dominated regions (PDRs). Observations reveal the presence of H2 lines
from vibrationally or rotationally excited upper levels that suggest warm gas
temperatures (400 to 700 K). However, standard models of PDRs are unable to
reproduce such warm rotational temperatures. In this paper we attempt to
explain these observations with new comprehensive models which extend from the
H+ region through the Bar and include the magnetic field in the equation of
state. We adopt the model parameters from our previous paper which successfully
reproduced a wide variety of spectral observations across the Bar. In this
model the local cosmic-ray density is enhanced above the galactic background,
as is the magnetic field, and which increases the cosmic-ray heating elevating
the temperature in the molecular region. The pressure is further enhanced above
the gas pressure in the H+ region by the momentum transferred from the absorbed
starlight. Here we investigate whether the observed H2 lines can be reproduced
with standard assumptions concerning the grain photoelectric emission. We also
explore the effects due to the inclusion of recently computed H2 + H2, H2 + H
and H2 + He collisional rate coefficients.Comment: Accepted for publication in ApJ (34 pages, including 16 figures
c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines
A survey of mid-IR gas-phase emission lines of H2, H2O and various atoms
toward a sample of 43 embedded low-mass young stars in nearby star-forming
regions is presented. The sources are selected from the Spitzer "Cores to
Disks" (c2d) legacy program. The environment of embedded protostars is complex
both in its physical structure (envelopes, outflows, jets, protostellar disks)
and the physical processes (accretion, irradiation by UV and/or X-rays,
excitation through slow and fast shocks) which take place. A key point is to
spatially resolve the emission in the Spitzer-IRS spectra. An optimal
extraction method is used to separate both spatially unresolved (compact, up to
a few 100 AU) and spatially resolved (extended, 1000 AU or more) emission from
the IRS spectra. The results are compared with the c2d disk sample and
literature PDR and shock models to address the physical nature of the sources.
Both compact and extended emission features are observed. Warm (Tex few 100 K)
H2, observed through the pure rotational H2 S(0), S(1) and S(2) lines, and [S
I] 25 mu emission is observed primarily in the extended component. [S I] is
observed uniquely toward truly embedded sources and not toward disks. On the
other hand hot (Tex>700 K) H2, observed primarily through the S(4) line, and
[Ne II] emission is seen mostly in the compact component. [Fe II] and [Si II]
lines are observed in both spatial components. Hot H2O emission is found in the
compact component of some sources. The observed emission on >=1000 AU scales is
characteristic of PDR emission and likely originates in the outflow cavities in
the remnant envelope created by the stellar wind and jets from the embedded
young stars. Weak shocks along the outflow wall can also contribute. The
compact emission is likely of mixed origin, comprised of optically thick
circumstellar disk and/or jet/outflow emission from the protostellar object.Comment: 22 pages, 11 figures, accepted for publication in A&
HIFI spectroscopy of low-level water transitions in M82
We present observations of the rotational ortho-water ground transition, the
two lowest para-water transitions, and the ground transition of ionised
ortho-water in the archetypal starburst galaxy M82, performed with the HIFI
instrument on the Herschel Space Observatory. These observations are the first
detections of the para-H2O(111-000) (1113\,GHz) and ortho-H2O+(111-000)
(1115\,GHz) lines in an extragalactic source. All three water lines show
different spectral line profiles, underlining the need for high spectral
resolution in interpreting line formation processes. Using the line shape of
the para-H2O(111-000) and ortho-H2O+(111-000) absorption profile in conjunction
with high spatial resolution CO observations, we show that the (ionised) water
absorption arises from a ~2000 pc^2 region within the HIFI beam located about
~50 pc east of the dynamical centre of the galaxy. This region does not
coincide with any of the known line emission peaks that have been identified in
other molecular tracers, with the exception of HCO. Our data suggest that water
and ionised water within this region have high (up to 75%) area-covering
factors of the underlying continuum. This indicates that water is not
associated with small, dense cores within the ISM of M82 but arises from a more
widespread diffuse gas component.Comment: 5 pages, 4 figures. Accepted for publication in A&
Distinct Olfactory Signaling Mechanisms in the Malaria Vector Mosquito Anopheles gambiae
A combination of gene silencing and behavioral studies in the malaria vector mosquito Anopheles gambiae sheds light on the olfactory basis of DEET repulsion as well as reveals the role of another family of chemosensory receptors that facilitate olfaction in An. gambiae
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