28 research outputs found
Spatially Resolved Spitzer-IRS Spectroscopy of the Central Region of M82
We present high spatial resolution (~ 35 parsec) 5-38 um spectra of the
central region of M82, taken with the Spitzer Infrared Spectrograph. From these
spectra we determined the fluxes and equivalent widths of key diagnostic
features, such as the [NeII]12.8um, [NeIII]15.5um, and H_2 S(1)17.03um lines,
and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in
six representative regions and analysed the spatial distribution of these lines
and their ratios across the central region. We find a good correlation of the
dust extinction with the CO 1-0 emission. The PAH emission follows closely the
ionization structure along the galactic disk. The observed variations of the
diagnostic PAH ratios across M82 can be explained by extinction effects, within
systematic uncertainties. The 16-18um PAH complex is very prominent, and its
equivalent width is enhanced outwards from the galactic plane. We interpret
this as a consequence of the variation of the UV radiation field. The EWs of
the 11.3um PAH feature and the H_2 S(1) line correlate closely, and we conclude
that shocks in the outflow regions have no measurable influence on the H_2
emission. The [NeIII]/[NeII] ratio is on average low at ~0.18, and shows little
variations across the plane, indicating that the dominant stellar population is
evolved (5 - 6 Myr) and well distributed. There is a slight increase of the
ratio with distance from the galactic plane of M82 which we attribute to a
decrease in gas density. Our observations indicate that the star formation rate
has decreased significantly in the last 5 Myr. The quantities of dust and
molecular gas in the central area of the galaxy argue against starvation and
for negative feedback processes, observable through the strong extra-planar
outflows.Comment: 15 pages, 12 figures, 3 tables, ApJ, emulateap
A Spitzer high resolution mid-infrared spectral atlas of starburst galaxies
We present an atlas of Spitzer/IRS high resolution (R~600) 10-37um spectra
for 24 well known starburst galaxies. The spectra are dominated by
fine-structure lines, molecular hydrogen lines, and emission bands of
polycyclic aromatic hydrocarbons. Six out of the eight objects with a known AGN
component show emission of the high excitation [NeV] line. This line is also
seen in one other object (NGC4194) with, a priori, no known AGN component. In
addition to strong polycyclic aromatic hydrocarbon emission features in this
wavelength range (11.3, 12.7, 16.4um), the spectra reveal other weak
hydrocarbon features at 10.6, 13.5, 14.2um, and a previously unreported
emission feature at 10.75um. An unidentified absorption feature at 13.7um is
detected in many of the starbursts. We use the fine-structure lines to derive
the abundance of neon and sulfur for 14 objects where the HI 7-6 line is
detected. We further use the molecular hydrogen lines to sample the properties
of the warm molecular gas. Several basic diagrams characterizing the properties
of the sample are also shown. We have combined the spectra of all the pure
starburst objects to create a high S/N template, which is available to the
community.Comment: 25 pages (emulate apj), 6 tables, 14 figures, Accepted for
publication in ApJ
Lack of PAH emission toward low-mass embedded young stellar objects
PAHs have been detected toward molecular clouds and some young stars with
disks, but have not yet been associated with embedded young stars. We present a
sensitive mid-IR spectroscopic survey of PAH features toward a sample of
low-mass embedded YSOs. The aim is to put constraints on the PAH abundance in
the embedded phase of star formation using radiative transfer modeling.
VLT-ISAAC L-band spectra for 39 sources and Spitzer IRS spectra for 53
sources are presented. Line intensities are compared to recent surveys of
Herbig Ae/Be and T Tauri stars. The radiative transfer codes RADMC and RADICAL
are used to model the PAH emission from embedded YSOs consisting of a PMS star
with a circumstellar disk embedded in an envelope. The dependence of the PAH
feature on PAH abundance, stellar radiation field, inclination and the
extinction by the surrounding envelope is studied.
The 3.3 micron PAH feature is undetected for the majority of the sample
(97%), with typical upper limits of 5E-16 W/m^2. Compact 11.2 micron PAH
emission is seen directly towards 1 out of the 53 Spitzer Short-High spectra,
for a source that is borderline embedded. For all 12 sources with both VLT and
Spitzer spectra, no PAH features are detected in either. In total, PAH features
are detected toward at most 1 out of 63 (candidate) embedded protostars (<~
2%), even lower than observed for class II T Tauri stars with disks (11-14%).
Assuming typical class I stellar and envelope parameters, the absence of PAHs
emission is most likely explained by the absence of emitting carriers through a
PAH abundance at least an order of magnitude lower than in molecular clouds but
similar to that found in disks. Thus, most PAHs likely enter the protoplanetary
disks frozen out in icy layers on dust grains and/or in coagulated form.Comment: 13 pages, 9 figures, accepted for publication in A&
The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy
We present 5-38um mid-infrared spectra at a spectral resolution of R~65-130
of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph
IRS on board the Spitzer Space Telescope. The spectra show a vast range in
starburst SEDs. The silicate absorption ranges from essentially no absorption
to heavily obscured systems with an optical depth of tau(9.8um)~5. The spectral
slopes can be used to discriminate between starburst and AGN powered sources.
The monochromatic continuum fluxes at 15um and 30um enable a remarkably
accurate estimate of the total infrared luminosity of the starburst. We find
that the PAH equivalent width is independent of the total starburst luminosity
L_IR as both continuum and PAH feature scale proportionally. However, the
luminosity of the 6.2um feature scales with L_IR and can be used to approximate
the total infrared luminosity of the starburst. Although our starburst sample
covers about a factor of ten difference in the [NeIII]/[NeII] ratio, we found
no systematic correlation between the radiation field hardness and the PAH
equivalent width or the 7.7um/11.3um PAH ratio. These results are based on
spatially integrated diagnostics over an entire starburst region, and local
variations may be ``averaged out''. It is presumably due to this effect that
unresolved starburst nuclei with significantly different global properties
appear spectrally as rather similar members of one class of objects.Comment: 22 pages, accepted for publication in ApJ, a high-resolution version
is available from http://www.strw.leidenuniv.nl/~brandl/IRS_starbursts.pd
Stromal Vascular Fraction Transplantation as an Alternative Therapy for Ischemic Heart Failure: Anti-inflammatory Role
<p>Abstract</p> <p>Background</p> <p>The aims of this study were: (1) to show the feasibility of using adipose-derived stromal vascular fraction (SVF) as an alternative to bone marrow mono nuclear cell (BM-MNC) for cell transplantation into chronic ischemic myocardium; and (2) to explore underlying mechanisms with focus on anti-inflammation role of engrafted SVF and BM-MNC post chronic myocardial infarction (MI) against left ventricular (LV) remodelling and cardiac dysfunction.</p> <p>Methods</p> <p>Four weeks after left anterior descending coronary artery ligation, 32 Male Lewis rats with moderate MI were divided into 3 groups. SVF group (n = 12) had SVF cell transplantation (6 à 10<sup>6 </sup>cells). BM-MNC group (n = 12) received BM-MNCs (6 à 10<sup>6</sup>) and the control (n = 10) had culture medium. At 4 weeks, after the final echocardiography, histological sections were stained with Styrus red and immunohistochemical staining was performed for α-smooth muscle actin, von Willebrand factor, CD3, CD8 and CD20.</p> <p>Results</p> <p>At 4 weeks, in SVF and BM-MNC groups, LV diastolic dimension and LV systolic dimension were smaller and fractional shortening was increased in echocardiography, compared to control group. Histology revealed highest vascular density, CD3+ and CD20+ cells in SVF transplanted group. SVF transplantation decreased myocardial mRNA expression of inflammatory cytokines TNF-α, IL-6, MMP-1, TIMP-1 and inhibited collagen deposition.</p> <p>Conclusions</p> <p>Transplantation of adipose derived SVF cells might be a useful therapeutic option for angiogenesis in chronic ischemic heart disease. Anti-inflammation role for SVF and BM transplantation might partly benefit for the cardioprotective effect for chronic ischemic myocardium.</p
PAH chemistry and IR emission from circumstellar disks
Aims. The chemistry of, and infrared (IR) emission from, polycyclic aromatic
hydrocarbons (PAHs) in disks around Herbig Ae/Be and T Tauri stars are
investigated. The equilibrium distribution of the PAHs over all accessible
charge/hydrogenation states depends on the size and shape of the PAHs and on
the physical properties of the star and surrounding disk.
Methods. A chemistry model is created to calculate this equilibrium
distribution. Destruction of PAHs by ultraviolet (UV) photons, possibly in
multi-photon absorption events, is taken into account. The chemistry model is
coupled to a radiative transfer code to provide the physical parameters and to
combine the PAH emission with the spectral energy distribution (SED) from the
star+disk system.
Results. Normally hydrogenated PAHs in Herbig Ae/Be disks account for most of
the observed PAH emission, with neutral and positively ionized species
contributing in roughly equal amounts. Close to the midplane, the PAHs are more
strongly hydrogenated and negatively ionized, but these species do not
contribute to the overall emission because of the low UV/optical flux deep
inside the disk. PAHs of 50 carbon atoms are destroyed out to 100 AU in the
disk's surface layer, and the resulting spatial extent of the emission does not
agree well with observations. Rather, PAHs of about 100 carbon atoms or more
are predicted to cause most of the observed emission. The emission is extended
on a scale similar to that of the size of the disk. Furthermore, the emission
from T Tauri disks is much weaker and concentrated more towards the central
star than that from Herbig Ae/Be disks. Positively ionized PAHs are predicted
to be largely absent in T Tauri disks because of the weaker radiation field.Comment: 13 pages, 8 figures, accepted for publication in A&
Spitzer-IRS spectra of disks around T Tauri stars II. PAH emission features
Aims: We search for PAH features towards T Tauri stars and compare them with
surveys of Herbig Ae/Be stars. The presence and strength of the PAH features
are interpreted with disk radiative transfer models exploring the PAH feature
dependence on the incident UV radiation, PAH abundance and disk parameters.
Methods: Spitzer Space Telescope 5-35 micron spectra of 54 pre-main sequence
stars with disks were obtained, consisting of 38 T Tauri, 7 Herbig Ae/Be and 9
stars with unknown spectral type.
Results: Compact PAH emission is detected towards at least 8 sources of which
5 are Herbig Ae/Be stars. The 11.2 micron PAH feature is detected in all of
these sources, as is the 6.2 micron PAH feature where short wavelength data are
available. However, the 7.7 and 8.6 micron features appear strongly in only 1
of these 4 sources. PAH emission is observed towards at least 3 T Tauri stars
(8% detection rate). The lowest mass source with PAHs in our sample is T Cha
(G8). All 4 sources in our sample with evidence for dust holes in their inner
disk show PAH emission, increasing the feature/continuum ratio. Typical 11.2
micron line intensities are an order of magnitude lower than those observed for
the more massive Herbig Ae/Be stars. Measured line fluxes indicate PAH
abundances that are factors of 10-100 lower than standard interstellar values.
Conversely, PAH features from disks exposed to stars with Teff<=4200K without
enhanced UV are predicted to be below the current detection limit, even for
high PAH abundances. Disk modeling shows that the 6.2 and 11.2 micron features
are the best PAH tracers for T Tauri stars, whereas the 7.7 and 8.6 micron
bands have low feature over continuum ratios due to the strongly rising
silicate emission.Comment: 20 pages, 15 figures, accepted for publication in A&