201 research outputs found
Herschel-SPIRE-Fourier Transform Spectroscopy of the nearby spiral galaxy IC342
We present observations of the nearby spiral galaxy IC342 with the Herschel
Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform
Spectrometer. The spectral range afforded by SPIRE, 196-671 microns, allows us
to access a number of 12CO lines from J=4--3 to J=13--12 with the highest J
transitions observed for the first time. In addition we present measurements of
13CO, [CI] and [NII]. We use a radiative transfer code coupled with Bayesian
likelihood analysis to model and constrain the temperature, density and column
density of the gas. We find two 12CO components, one at 35 K and one at 400 K
with CO column densities of 6.3x10^{17} cm^{-2} and 0.4x10^{17} cm^{-2} and CO
gas masses of 1.26x10^{7} Msolar and 0.15x10^{7} Msolar, for the cold and warm
components, respectively. The inclusion of the high-J 12CO line observations,
indicate the existence of a much warmer gas component (~400 K) confirming
earlier findings from H_{2} rotational line analysis from ISO and Spitzer. The
mass of the warm gas is 10% of the cold gas, but it likely dominates the CO
luminosity. In addition, we detect strong emission from [NII] 205microns and
the {3}P_{1}->{3}P_{0} and {3}P_{2} ->{3}P_{1} [CI] lines at 370 and 608
microns, respectively. The measured 12CO line ratios can be explained by
Photon-dominated region (PDR) models although additional heating by e.g. cosmic
rays cannot be excluded. The measured [CI] line ratio together with the derived
[C] column density of 2.1x10^{17} cm^{-2} and the fact that [CI] is weaker than
CO emission in IC342 suggests that [CI] likely arises in a thin layer on the
outside of the CO emitting molecular clouds consistent with PDRs playing an
important role.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
Comparing [CII], HI, and CO dynamics of nearby galaxies
The HI and CO components of the interstellar medium (ISM) are usually used to
derive the dynamical mass M_dyn of nearby galaxies. Both components become too
faint to be used as a tracer in observations of high-redshift galaxies. In
those cases, the 158 m line of atomic carbon [CII] may be the only way to
derive M_dyn. As the distribution and kinematics of the ISM tracer affects the
determination of M_dyn, it is important to quantify the relative distributions
of HI, CO and [CII]. HI and CO are well-characterised observationally, however,
for [CII] only very few measurements exist. Here we compare observations of CO,
HI, and [CII] emission of a sample of nearby galaxies, drawn from the HERACLES,
THINGS and KINGFISH surveys. We find that within R_25, the average [CII]
exponential radial profile is slightly shallower than that of the CO, but much
steeper than the HI distribution. This is also reflected in the integrated
spectrum ("global profile"), where the [CII] spectrum looks more like that of
the CO than that of the HI. For one galaxy, a spectrally resolved comparison of
integrated spectra was possible; other comparisons were limited by the
intrinsic line-widths of the galaxies and the coarse velocity resolution of the
[CII] data. Using high-spectral-resolution SOFIA [CII] data of a number of star
forming regions in two nearby galaxies, we find that their [CII] linewidths
agree better with those of the CO than the HI. As the radial extent of a given
ISM tracer is a key input in deriving M_dyn from spatially unresolved data, we
conclude that the relevant length-scale to use in determining M_dyn based on
[CII] data, is that of the well-characterised CO distribution. This length
scale is similar to that of the optical disk.Comment: Accepted for publication in the Astronomical Journa
A far-IR view of the starburst driven superwind in NGC 2146
NGC 2146, a nearby luminous infrared galaxy (LIRG), presents evidence for
outflows along the disk minor axis in all gas phases (ionized, neutral atomic
and molecular). We present an analysis of the multi-phase starburst driven
superwind in the central 5 kpc as traced in spatially resolved spectral line
observations, using far-IR Herschel PACS spectroscopy, to probe the effects on
the atomic and ionized gas, and optical integral field spectroscopy to examine
the ionized gas through diagnostic line ratios. We observe an increased ~250
km/s velocity dispersion in the [OI] 63 micron, [OIII] 88 micron, [NII] 122
micron and [CII] 158 micron fine-structure lines that is spatially coincident
with high excitation gas above and below the disk. We model this with a slow
~200 km/s shock and trace the superwind to the edge of our field of view 2.5
kpc above the disk. We present new SOFIA 37 micron observations to explore the
warm dust distribution, and detect no clear dust entrainment in the outflow.
The stellar kinematics appear decoupled from the regular disk rotation seen in
all gas phases, consistent with a recent merger event disrupting the system. We
consider the role of the superwind in the evolution of NGC 2146 and speculate
on the evolutionary future of the system. Our observations of NGC 2146 in the
far-IR allow an unobscured view of the wind, crucial for tracing the superwind
to the launching region at the disk center, and provide a local analog for
future ALMA observations of outflows in high redshift systems.Comment: 16 pages, 13 figures, accepted for publication in Ap
Anomalous Coulomb Drag in Electron-Hole Bilayers
We report Coulomb drag measurements on GaAs-AlGaAs electron-hole bilayers. The two layers are separated by a 10 or 25 nm barrier. Below T approximate to 1 K we find two features that a Fermi-liquid picture cannot explain. First, the drag on the hole layer shows an upturn, which may be followed by a downturn. Second, the effect is either absent or much weaker in the electron layer, even though the measurements are within the linear response regime. Correlated phases have been anticipated in these, but surprisingly, the experimental results appear to contradict Onsager's reciprocity theorem
A Study of Heating and Cooling of the ISM in NGC 1097 with Herschel-PACS and Spitzer-IRS
NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst
ring, a strong large-scale bar and an active nucleus. We present a detailed
study of the spatial variation of the far infrared (FIR) [CII]158um and
[OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling,
and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the
photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral
maps. We focus on the nucleus and the ring, and two star forming regions (Enuc
N and Enuc S). We estimated a photoelectric gas heating efficiency
([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The
average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a
larger fraction of ionized PAHs, but no clear correlation with
[CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a
factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in
the Enuc S. SED modeling indicates that at most 25% of the FIR power in the
ring and Enuc S can come from high intensity photodissociation regions (PDRs),
in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values
of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the
the H2 emission in the starburst ring could come from warm regions in the
diffuse ISM that are heated by turbulent dissipation or shocks.Comment: 17 pages, 14 figures, 5 tables; accepted for publication in Ap
Far-Infrared Line Imaging of the Starburst Ring in NGC 1097 with the Herschel/PACS Spectrometer
NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst
ring. We study the physical properties of the interstellar medium (ISM) in the
ring using spatially resolved far-infrared spectral maps of the circumnuclear
starburst ring of NGC 1097, obtained with the PACS spectrometer on board the
Herschel Space Telescope. In particular, we map the important ISM cooling and
diagnostic emission lines of [OI] 63 m, [OIII] 88 m, [NII] 122
m, [CII] 158 m and [NII] 205 m. We observe that in the [OI] 63
m, [OIII] 88 m, and [NII] 122 m line maps, the emission is
enhanced in clumps along the NE part of the ring. We observe evidence of rapid
rotation in the circumnuclear ring, with a rotation velocity of ~220^{-1}\mu\mu\mu\mu\mu\mu^{-3}$.Comment: Accepted for publication on the A&A Herschel Special Issu
Calibration of the total infrared luminosity of nearby galaxies from Spitzer and Herschel bands
When combined with infrared observations with the Spitzer telescope (3 to 160 μm), the Herschel Space Observatory now fully samples the thermal dust emission up to 500 μm and enables us to better estimate the total infrared-submm energy budget (L_(TIR)) of nearby galaxies. We present new empirical calibrations to estimate resolved and integrated total infrared luminosities from Spitzer and Herschel bands used as monochromatic or combined tracers. We base our calibrations on resolved elements of nearby galaxies (3 to 30 Mpc) observed with Herschel. We perform a resolved spectral energy distribution (SED) modelling of these objects using the Draine & Li dust models and investigate the influence of the addition of Spectral and Photometric Imaging Receiver (SPIRE) measurements in the estimation of L_(TIR). We find that using data up to 250 μm leads to local L_(TIR) values consistent with those obtained with a complete coverage (up to 500 μm) within ±10 per cent for most of our resolved elements. We then study the distribution of energy in the resolved SEDs of our galaxies. The bulk of energy (30–50 per cent) is contained in the [70–160 μm] band. The [24–70 μm] fraction decreases with increasing metallicity. The [160–1100 μm]submillimetre band can account for up to 25 per cent of the L_(TIR) in metal-rich galaxies. We investigate the correlation between the total infrared (TIR) surface brightnesses/luminosities and monochromatic Spitzer and Herschel surface brightnesses/luminosities. The three Photodetector Array Camera and Spectrometer (PACS) bands can be used as reliable monochromatic estimators of the L_(TIR), the 100 μm band being the most reliable monochromatic tracer. There is also a strong correlation between the SPIRE 250 μm and L_(TIR), although with more scatter than for the PACS relations. We also study the ability of our monochromatic relations to reproduce integrated L_(TIR) of nearby galaxies as well as L_(TIR) of z ∼ 1–3 sources. Finally, we provide calibration coefficients that can be used to derive TIR surface brightnesses/luminosities from a combination of Spitzer and Herschel surface brightnesses/fluxes and analyse the associated uncertainties
Herschel Far-Infrared and Sub-millimeter Photometry for the KINGFISH Sample of Nearby Galaxies
New far-infrared and sub-millimeter photometry from the Herschel Space
Observatory is presented for 61 nearby galaxies from the Key Insights on Nearby
Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) sample. The
spatially-integrated fluxes are largely consistent with expectations based on
Spitzer far-infrared photometry and extrapolations to longer wavelengths using
popular dust emission models. Dwarf irregular galaxies are notable exceptions,
as already noted by other authors, as their 500um emission shows evidence for a
sub-millimeter excess. In addition, the fraction of dust heating attributed to
intense radiation fields associated with photo-dissociation regions is found to
be (21+/-4)% larger when Herschel data are included in the analysis. Dust
masses obtained from the dust emission models of Draine & Li are found to be on
average nearly a factor of two higher than those based on single-temperature
modified blackbodies, as single blackbody curves do not capture the full range
of dust temperatures inherent to any galaxy. The discrepancy is largest for
galaxies exhibiting the coolest far-infrared colors.Comment: Accepted for publication in Ap
- …