912 research outputs found
PAH Strength and the Interstellar Radiation Field around the Massive Young Cluster NGC3603
We present spatial distribution of polycyclic aromatic hydrocarbons and
ionized gas within the Galactic giant HII region NGC3603. Using the IRS
instrument on board the Spitzer Space Telescope, we study in particular the PAH
emission features at ~5.7, 6.2, 7.7, 8.6, and 11.3um, and the [ArII] 6.99um,
[NeII] 12.81um, [ArIII] 8.99um, and [SIV] 10.51um forbidden emission lines. The
observations probe both ionized regions and photodissociation regions. Silicate
emission is detected close to the central cluster while silicate absorption is
seen further away. We find no significant variation of the PAH ionization
fraction across the whole region. The emission of very small grains lies closer
to the central stellar cluster than emission of PAHs. The PAH/VSG ratio
anticorrelates with the hardness of the interstellar radiation field suggesting
a destruction mechanism of the molecules within the ionized gas, as shown for
low-metallicity galaxies by Madden et al. (2006).Comment: Accepted for publication in ApJ. Corrected typo
Empirical comparison of a fixed-base and a moving-base simulation of a helicopter engaged in visually conducted slalom runs
Combined visual, motion, and aural cues for a helicopter engaged in visually conducted slalom runs at low altitude were studied. The evaluation of the visual and aural cues was subjective, whereas the motion cues were evaluated both subjectively and objectively. Subjective and objective results coincided in the area of control activity. Generally, less control activity is present under motion conditions than under fixed-base conditions, a fact attributed subjectively to the feeling of realistic limitations of a machine (helicopter) given by the addition of motion cues. The objective data also revealed that the slalom runs were conducted at significantly higher altitudes under motion conditions than under fixed-base conditions
Interacting Qubit-Photon Bound States with Superconducting Circuits
Qubits strongly coupled to a photonic crystal give rise to many exotic
physical scenarios, beginning with single and multi-excitation qubit-photon
dressed bound states comprising induced spatially localized photonic modes,
centered around the qubits, and the qubits themselves. The localization of
these states changes with qubit detuning from the band-edge, offering an avenue
of in situ control of bound state interaction. Here, we present experimental
results from a device with two qubits coupled to a superconducting microwave
photonic crystal and realize tunable on-site and inter-bound state
interactions. We observe a fourth-order two photon virtual process between
bound states indicating strong coupling between the photonic crystal and
qubits. Due to their localization-dependent interaction, these states offer the
ability to create one-dimensional chains of bound states with tunable and
potentially long-range interactions that preserve the qubits' spatial
organization, a key criterion for realization of certain quantum many-body
models. The widely tunable, strong and robust interactions demonstrated with
this system are promising benchmarks towards realizing larger, more complex
systems of bound states
Elemental Abundances of Blue Compact Dwarfs from mid-IR Spectroscopy with Spitzer
We present a study of elemental abundances in a sample of thirteen Blue
Compact Dwarf (BCD) galaxies, using the 10--37m high resolution
spectra obtained with Spitzer/IRS. We derive the abundances of neon and sulfur
for our sample using the infrared fine-structure lines probing regions which
may be obscured by dust in the optical and compare our results with similar
infrared studies of starburst galaxies from ISO. We find a good correlation
between the neon and sulfur abundances, though sulfur is under-abundant
relative to neon with respect to the solar value. A comparison of the elemental
abundances (neon, sulfur) measured from the infrared data with those derived
from the optical (neon, sulfur, oxygen) studies reveals a good overall
agreement for sulfur, while the infrared derived neon abundances are slightly
higher than the optical values. This indicates that either the metallicities of
dust enshrouded regions in BCDs are similar to the optically accessible
regions, or that if they are different they do not contribute substantially to
the total infrared emission of the host galaxy.Comment: 11 pages, 6 figures, accepted by Ap
Chemical composition and mixing in giant HII regions: NGC3603, 30Doradus, and N66
We investigate the chemical abundances of NGC3603 in the Milky Way, of
30Doradus in the Large Magellanic Cloud, and of N66 in the Small Magellanic
Cloud. Mid-infrared observations with the Infrared Spectrograph onboard the
Spitzer Space Telescope allow us to probe the properties of distinct physical
regions within each object: the central ionizing cluster, the surrounding
ionized gas, photodissociation regions, and buried stellar clusters. We detect
[SIII], [SIV], [ArIII], [NeII], [NeIII], [FeII], and [FeIII] lines and derive
the ionic abundances. Based on the ionic abundance ratio (NeIII/H)/(SIII/H), we
find that the gas observed in the MIR is characterized by a higher degree of
ionization than the gas observed in the optical spectra. We compute the
elemental abundances of Ne, S, Ar, and Fe. We find that the alpha-elements Ne,
S, and Ar scale with each other. Our determinations agree well with the
abundances derived from the optical. The Ne/S ratio is higher than the solar
value in the three giant HII regions and points toward a moderate depletion of
sulfur on dust grains. We find that the neon and sulfur abundances display a
remarkably small dispersion (0.11dex in 15 positions in 30Doradus), suggesting
a relatively homogeneous ISM, even though small-scale mixing cannot be ruled
out.Comment: Accepted for submission to ApJ. The present version replaces the
submitted one. Changes: new title, new figure, the text was modified in the
discussio
Confinement of supernova explosions in a collapsing cloud
We analyze the confining effect of cloud collapse on an expanding supernova
shockfront. We solve the differential equation for the forces on the shockfront
due to ram pressure, supernova energy, and gravity. We find that the expansion
of the shockfront is slowed and in fact reversed by the collapsing cloud.
Including radiative losses and a potential time lag between supernova explosion
and cloud collapse shows that the expansion is reversed at smaller distances as
compared to the non-radiative case. We also consider the case of multiple
supernova explosions at the center of a collapsing cloud. For instance, if we
scale our self-similar solution to a single supernova of energy 10^51 ergs
occurring when a cloud of initial density 10^2 H/cm^3 has collapsed by 50%, we
find that the shockfront is confined to ~15 pc in ~1 Myrs. Our calculations are
pertinent to the observed unusually compact non-thermal radio emission in blue
compact dwarf galaxies (BCDs). More generally, we demonstrate the potential of
a collapsing cloud to confine supernovae, thereby explaining how dwarf galaxies
would exist beyond their first generation of star formation.Comment: 3 pages, 4 figure
[CII] 158 micron Luminosities and Star Formation Rate in Dusty Starbursts and AGN
Results are presented for [CII] 158 micron line fluxes observed with the
Herschel PACS instrument in 112 sources with both starburst and AGN
classifications, of which 102 sources have confident detections. Results are
compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and
with L(IR) from IRAS fluxes; AGN/starburst classifications are determined from
equivalent width of the 6.2 micron PAH feature. It is found that the [CII] line
flux correlates closely with the flux of the 11.3 micron PAH feature
independent of AGN/starburst classification, log [f([CII] 158 micron)/f(11.3
micron PAH)] = -0.22 +- 0.25. It is concluded that [CII] line flux measures the
photodissociation region associated with starbursts in the same fashion as the
PAH feature. A calibration of star formation rate for the starburst component
in any source having [CII] is derived comparing [CII] luminosity L([CII]) to
L(IR) with the result that log SFR = log L([CII)]) - 7.08 +- 0.3, for SFR in
solar masses per year and L([CII]) in solar luminosities. The decreasing ratio
of L([CII]) to L(IR) in more luminous sources (the "[CII] deficit") is shown to
be a consequence of the dominant contribution to L(IR) arising from a luminous
AGN component because the sources with largest L(IR) and smallest
L([CII])/L(IR) are AGN.Comment: Accepted for publication in The Astrophysical Journa
The extraordinary mid-infrared spectral properties of FeLoBAL Quasars
We present mid-infrared spectra of six FeLoBAL QSOs at 1<z<1.8, taken with
the Spitzer space telescope. The spectra span a range of shapes, from hot dust
dominated AGN with silicate emission at 9.7 microns, to moderately obscured
starbursts with strong Polycyclic Aromatic Hydrocarbon (PAH) emission. The
spectrum of one object, SDSS 1214-0001, shows the most prominent PAHs yet seen
in any QSO at any redshift, implying that the starburst dominates the mid-IR
emission with an associated star formation rate of order 2700 solar masses per
year. With the caveats that our sample is small and not robustly selected, we
combine our mid-IR spectral diagnostics with previous observations to propose
that FeLoBAL QSOs are at least largely comprised of systems in which (a) a
merger driven starburst is ending, (b) a luminous AGN is in the last stages of
burning through its surrounding dust, and (c) which we may be viewing over a
restricted line of sight range.Comment: ApJ, accepte
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