233 research outputs found
L'CO/LFIR Relations with CO Rotational Ladders of Galaxies Across the Herschel SPIRE Archive
We present a catalog of all CO (J=4-3 through J=13-12)), [CI], [NII] lines
available from extragalactic spectra from the Herschel SPIRE Fourier Transform
Spectrometer (FTS) archive combined with observations of the low-J CO lines
from the literature and from the Arizona Radio Observatory. This work examines
the relationships between LFIR, L'CO, and LCO/LCO(1-0). We also present a new
method for estimating probability distribution functions (PDFs) from marginal
signal-to-noise ratio Herschel} FTS spectra, which takes into account the
instrumental "ringing" and the resulting highly correlated nature of the
spectra. The slopes of log(LFIR) vs. log(L'CO) are linear for all mid- to
high-J CO lines and slightly sublinear if restricted to (U)LIRGs. The mid- to
high-J CO luminosity relative to CO J=1-0 increases with increasing LFIR,
indicating higher excitement of the molecular gas, though these ratios do not
exceed ~ 180. For a given bin in LFIR, the luminosities relative to CO J=1-0
remain relatively flat from J=6-5 through J=13-12, across three orders of
magnitude of LFIR. A single component theoretical photon-dominated region (PDR)
model cannot match these flat SLED shapes, though combinations of PDR models
with mechanical heating added qualitatively match the shapes, indicating the
need for further comprehensive modeling of the excitation processes of warm
molecular gas in nearby galaxies.Comment: 17 pages, 4 figures (including appendix), accepted by ApJ. Full
tables will be in VizieR upon publication, email first author for tables in
the meantim
Recovering the Physical Properties of Molecular Gas in Galaxies from CO SLED Modeling
Modeling of the spectral line energy distribution (SLED) of the CO molecule
can reveal the physical conditions (temperature, density) of molecular gas in
Galactic clouds and other galaxies. Recently, the Herschel Space Observatory
and ALMA have offered, for the first time, a comprehensive view of the
rotational J = 4-3 through J = 13-12 lines, which arise from a complex, diverse
range of physical conditions that must be simplified to one, two, or three
components when modeled. Here we investigate the recoverability of physical
conditions from SLEDs produced by galaxy evolution simulations containing a
large dynamical range in physical properties. These simulated SLEDs were
generally fit well by one component of gas whose properties largely resemble or
slightly underestimate the luminosity-weighted properties of the simulations
when clumping due to non-thermal velocity dispersion is taken into account. If
only modeling the first three rotational lines, the median values of the
marginalized parameter distributions better represent the luminosity-weighted
properties of the simulations, but the uncertainties in the fitted parameters
are nearly an order of magnitude, compared to approximately 0.2 dex in the
"best-case" scenario of a fully sampled SLED through J = 10-9. This study
demonstrates that while common CO SLED modeling techniques cannot reveal the
underlying complexities of the molecular gas, they can distinguish bulk
luminosity-weighted properties that vary with star formation surface densities
and galaxy evolution, if a sufficient number of lines are detected and modeled.Comment: 13 pages, accepted by The Astrophysical Journa
Submillimetre line spectrum of the Seyfert galaxy NGC1068 from the Herschel-SPIRE Fourier Transform Spectrometer
The first complete submillimetre spectrum (190-670um) of the Seyfert 2 galaxy
NGC1068 has been observed with the SPIRE Fourier Transform Spectrometer onboard
the {\it Herschel} Space Observatory. The sequence of CO lines (Jup=4-13),
lines from water, the fundamental rotational transition of HF, two o-H_2O+
lines and one line each from CH+ and OH+ have been detected, together with the
two [CI] lines and the [NII]205um line. The observations in both single
pointing mode with sparse image sampling and in mapping mode with full image
sampling allow us to disentangle two molecular emission components, one due to
the compact circum-nuclear disk (CND) and one from the extended region
encompassing the star forming ring (SF-ring). Radiative transfer models show
that the two CO components are characterized by density of n(H_2)=10^4.5 and
10^2.9 cm^-3 and temperature of T=100K and 127K, respectively. The comparison
of the CO line intensities with photodissociation region (PDR) and X-ray
dominated region (XDR) models, together with other observational constraints,
such as the observed CO surface brightness and the radiation field, indicate
that the best explanation for the CO excitation of the CND is an XDR with
density of n(H_2) 10^4 cm^-3 and X-ray flux of 9 erg s^-1 cm^-2, consistent
with illumination by the active galactic nucleus, while the CO lines in the
SF-ring are better modeled by a PDR. The detected water transitions, together
with those observed with the \her \sim PACS Spectrometer, can be modeled by an
LVG model with low temperature (T_kin \sim 40K) and high density (n(H_2) in the
range 10^6.7-10^7.9 cm^-3).Comment: Accepted for publication on the Astrophysical Journal, 30 August 201
Mid-J CO Emission in Nearby Seyfert Galaxies
We study for the first time the complete sub-millimeter spectra (450 GHz to
1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier
Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup =
4 to 12) is the most prominent spectral feature in this range. These CO lines
probe warm molecular gas that can be heated by ultraviolet photons, shocks, or
X-rays originated in the active galactic nucleus or in young star-forming
regions. In these proceedings we investigate the physical origin of the CO
emission using the averaged CO spectral line energy distribution (SLED) of six
Seyfert galaxies. We use a radiative transfer model assuming an isothermal
homogeneous medium to estimate the molecular gas conditions. We also compare
this CO SLED with the predictions of photon and X-ray dominated region (PDR and
XDR) models.Comment: Proceedings of the Torus Workshop 2012 held at the University of
Texas at San Antonio, 5-7 December 2012. C. Packham, R. Mason, and A.
Alonso-Herrero (eds.); 6 pages, 3 figure
ALMA Observations of Supernova 1987A
Supernova (SN) 1987A has provided a unique opportunity to study how SN ejecta evolve in 30 years time scale. We report our ALMA spectral observations of SN 1987A, taken in 2014, 2015 and 2016, with detections of CO, 28SiO, HCO+ and SO, with weaker lines of 29SiO.
We find a dip in the SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that Rayleigh-Taylor instabilities causes mixing of gas, with heavier elements much more disturbed, making more elongated structure.
Using 28SiO and its isotopologues, Si isotope ratios were estimated for the first time in SN 1987A. The estimated ratios appear to be consistent with theoretical predictions of inefficient formation of neutron rich atoms at lower metallicity, such as observed in the Large Magellanic Cloud (about half a solar metallicity).
The deduced large HCO+ mass and small SiS mass, which are inconsistent to the predictions of chemical model, might be explained by some mixing of elements immediately after the explosion. The mixing might have made some hydrogen from the envelope to sink into carbon and oxygen-rich zone during early days after the explosion, enabling the formation of a substantial mass of HCO+. Oxygen atoms may penetrate into silicon and sulphur zone, suppressing formation of SiS.
Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive-nucleosynthesis in supernovae
Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation
Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer
The influence of cosmic rays in the circumnuclear molecular gas of NGC1068
We surveyed the circumnuclear disk of the Seyfert galaxy NGC1068 between the
frequencies 86.2 GHz and 115.6 GHz, and identified 17 different molecules.
Using a time and depth dependent chemical model we reproduced the observational
results, and show that the column densities of most of the species are better
reproduced if the molecular gas is heavily pervaded by a high cosmic ray
ionization rate of about 1000 times that of the Milky Way. We discuss how
molecules in the NGC1068 nucleus may be influenced by this external radiation,
as well as by UV radiation fields.Comment: 6 pages. Conference proceeding for the workshop on "Cosmic-ray
induced phenomenology in star-forming environments" held in Sant Cugat,
Spain, on April 16-19, 201
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