2,106 research outputs found
The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy
We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214
observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O
I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to
the full telescope spatial resolution and reveal unprecedented detail on ~ 150
pc size scales. We detect [C II] emission over the whole mapped area, [O III]
being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2
toward the sites of massive star formation, higher than ratios seen in dusty
starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2
massive clusters, which are at least an order of magnitude larger than spiral
or dusty starbursts, and cannot be reconciled with single-slab PDR models.
Toward the 2 massive star-forming regions, we find that L[CII] is 0.5 to 0.8%
of the LTIR . All of the lines together contribute up to 2% of LTIR . These
extreme findings are a consequence of the lower metallicity and young,
massive-star formation commonly found in dwarf galaxies. These conditions
promote large-scale photodissociation into the molecular reservoir, which is
evident in the FIR line ratios. This illustrates the necessity to move to
multiphase models applicable to star-forming clusters or galaxies as a whole.Comment: Accepted for publication in the A&A Herschel Special Issu
Acute Phase Proteinâs Levels as Potential Biomarkers for Early Diagnosis of Neurodegenerative Diseases
Extinction law variations and dust excitation in the spiral galaxy NGC 300
We investigate the origin of the strong radial gradient in the
ultraviolet-to-infrared ratio in the spiral galaxy NGC 300, and emphasize the
importance of local variations in the interstellar medium geometry, concluding
that they cannot be neglected with respect to metallicity effects. This
analysis is based upon a combination of maps from GALEX and Spitzer, and from
the ground (UBVRI, Halpha and Hbeta). We select ionizing stellar clusters
associated with HII regions of widely varying morphologies, and derive their
fundamental parameters from population synthesis fitting of their spectral
energy distributions, measured to eliminate local backgrounds accurately. From
these fits, we conclude that the stellar extinction law is highly variable in
the line of sight of young clusters of similar ages. In the particular model
geometry that we consider most appropriate to the sampled regions, we checked
that our findings are not significantly altered by the correct treatment of
radiative transfer effects. The variations are systematic in nature: extinction
laws of the Milky Way or LMC type are associated with compact HII regions (the
compacity being quantified in two different ways), while clusters surrounded by
diffuse HII regions follow extinction laws of the 30 Doradus or SMC type. The
Calzetti starburst attenuation law, although most often degenerate with the 30
Doradus extinction law, overpredicts ionizing photon fluxes by large amounts.
We also find that the extinction law variations are correlated with the column
density of dust species emitting in the near- and mid-infrared. Finally, we
briefly discuss the nebular to stellar extinction ratios, and the excitation of
aromatic band carriers, invalidating their claimed association with cold dust.Comment: accepted for publication in ApJ -- figure 6 abridged her
The dust energy balance in the edge-on spiral galaxy NGC 4565
We combine new dust continuum observations of the edge-on spiral galaxy NGC
4565 in all Herschel/SPIRE (250, 350, 500 micron) wavebands, obtained as part
of the Herschel Reference Survey, and a large set of ancillary data (Spitzer,
SDSS, GALEX) to analyze its dust energy balance. We fit a radiative transfer
model for the stars and dust to the optical maps with the fitting algorithm
FitSKIRT. To account for the observed UV and mid-infrared emission, this
initial model was supplemented with both obscured and unobscured star-forming
regions. Even though these star-forming complexes provide an additional heating
source for the dust, the far-infrared/submillimeter emission long wards of 100
micron is underestimated by a factor of 3-4. This inconsistency in the dust
energy budget of NGC 4565 suggests that a sizable fraction (two-thirds) of the
total dust reservoir (Mdust ~ 2.9e+8 Msun) consists of a clumpy distribution
with no associated young stellar sources. The distribution of those dense dust
clouds would be in such a way that they remain unresolved in current
far-infrared/submillimeter observations and hardly comtribute to the
attenuation at optical wavelengths. More than two-thirds of the dust heating in
NGC 4565 is powered by the old stellar population, with localized embedded
sources supplying the remaining dust heating in NGC 4565. The results from this
detailed dust energy balance study in NGC 4565 is consistent with that of
similar analyses of other edge-on spirals.Comment: 16 pages, 7 figures, accepted for publication in MNRA
Herschel and JCMT observations of the early-type dwarf galaxy NGC 205
We present Herschel dust continuum, James Clerk Maxwell Telescope CO(3-2)
observations and a search for [CII] 158 micron and [OI] 63 micron spectral line
emission for the brightest early-type dwarf satellite of Andromeda, NGC 205.
While direct gas measurements (Mgas ~ 1.5e+6 Msun, HI + CO(1-0)) have proven to
be inconsistent with theoretical predictions of the current gas reservoir in
NGC 205 (> 1e+7 Msun), we revise the missing interstellar medium mass problem
based on new gas mass estimates (CO(3-2), [CII], [OI]) and indirect
measurements of the interstellar medium content through dust continuum
emission. Based on Herschel observations, covering a wide wavelength range from
70 to 500 micron, we are able to probe the entire dust content in NGC 205
(Mdust ~ 1.1-1.8e+4 Msun at Tdust ~ 18-22 K) and rule out the presence of a
massive cold dust component (Mdust ~ 5e+5 Msun, Tdust ~ 12 K), which was
suggested based on millimeter observations from the inner 18.4 arcsec. Assuming
a reasonable gas-to-dust ratio of ~ 400, the dust mass in NGC 205 translates
into a gas mass Mgas ~ 4-7e+6 Msun. The non-detection of [OI] and the low
L_[CII]-to-L_CO(1-0) line intensity ratio (~ 1850) imply that the molecular gas
phase is well traced by CO molecules in NGC 205. We estimate an atomic gas mass
of 1.5e+4 Msun associated with the [CII] emitting PDR regions in NGC 205. From
the partial CO(3-2) map of the northern region in NGC 205, we derive a
molecular gas mass of M_H2 ~ 1.3e+5 Msun. [abridged]Comment: 16 pages, 7 figures, accepted for publication in MNRA
Exploring dust around HD142527 down to 0.025" / 4au using SPHERE/ZIMPOL
We have observed the protoplanetary disk of the well-known young Herbig star
HD 142527 using ZIMPOL Polarimetric Differential Imaging with the VBB (Very
Broad Band, ~600-900nm) filter. We obtained two datasets in May 2015 and March
2016. Our data allow us to explore dust scattering around the star down to a
radius of ~0.025" (~4au). The well-known outer disk is clearly detected, at
higher resolution than before, and shows previously unknown sub-structures,
including spirals going inwards into the cavity. Close to the star, dust
scattering is detected at high signal-to-noise ratio, but it is unclear whether
the signal represents the inner disk, which has been linked to the two
prominent local minima in the scattering of the outer disk, interpreted as
shadows. An interpretation of an inclined inner disk combined with a dust halo
is compatible with both our and previous observations, but other arrangements
of the dust cannot be ruled out. Dust scattering is also present within the
large gap between ~30 and ~140au. The comparison of the two datasets suggests
rapid evolution of the inner regions of the disk, potentially driven by the
interaction with the close-in M-dwarf companion, around which no polarimetric
signal is detected.Comment: 11 pages, 7 figures, accepted for publication in A
Dust heating sources in galaxies: the case of M33 (HERM33ES)
Dust emission is one of the main windows to the physics of galaxies and to
star formation as the radiation from young, hot stars is absorbed by the dust
and reemitted at longer wavelengths. The recently launched Herschel satellite
now provides a view of dust emission in the far-infrared at an unequaled
resolution and quality up to 500 \mu m. In the context of the Herschel HERM33ES
open time key project, we are studying the moderately inclined Scd local group
galaxy M33 which is located only 840 kpc away. In this article, using Spitzer
and Herschel data ranging from 3.6 \mu m to 500 \mu m, along with HI, H\alpha\
maps, and GALEX ultraviolet data we have studied the emission of the dust at
the high spatial resolution of 150 pc. Combining Spitzer and Herschel bands, we
have provided new, inclination corrected, resolved estimators of the total
infrared brightness and of the star formation rate from any combination of
these bands. The study of the colors of the warm and cold dust populations
shows that the temperature of the former is, at high brightness, dictated by
young massive stars but, at lower brightness, heating is taken over by the
evolved populations. Conversely, the temperature of the cold dust is tightly
driven by the evolved stellar populations.Comment: 29 pages, 12 figures, accepted for publication in A
VLT/SPHERE deep insight of NGC 3603's core: Segregation or confusion?
We present new near-infrared photometric measurements of the core of the
young massive cluster NGC 3603 obtained with extreme adaptive optics. The data
were obtained with the SPHERE instrument mounted on ESO Very Large Telescope,
and cover three fields in the core of this cluster. We applied a correction for
the effect of extinction to our data obtained in the J and K broadband filters
and estimated the mass of detected sources inside the field of view of
SPHERE/IRDIS, which is 13.5"x13.5". We derived the mass function (MF) slope for
each spectral band and field. The MF slope in the core is unusual compared to
previous results based on Hubble space telescope (HST) and very large telescope
(VLT) observations. The average slope in the core is estimated as
-1.06^{+0.26}_{-0.26} for the main sequence stars with 3.5 Msun < M < 120
Msun.Thanks to the SPHERE extreme adaptive optics, 814 low-mass stars were
detected to estimate the MF slope for the pre-main sequence stars with 0.6
Msun< M < 3.5 Msun , Gamma = -0.54^{+0.11}_{-0.11} in the K-band images in two
fields in the core of the cluster. For the first time, we derive the mass
function of the very core of the NGC 3603 young cluster for masses in the range
0.6 - 120 Msun. Previous studies were either limited by crowding, lack of
dynamic range, or a combination of both
A multi-scale study of infrared and radio emission from Scd galaxy M33
We investigate the energy sources of the infrared (IR) emission and their
relation to the radio continuum emission at various spatial scales within the
Scd galaxy M33. We use the wavelet transform to analyze IR data at the Spitzer
wavelengths of 24, 70, and 160m, as well as recent radio continuum data at
3.6cm and 20cm. An H map serves as a tracer of the star forming regions
and as an indicator of the thermal radio emission. We find that the dominant
scale of the 70m emission is larger than that of the 24m emission,
while the 160m emission shows a smooth wavelet spectrum. The radio and
H maps are well correlated with all 3 MIPS maps, although their
correlations with the 160m map are weaker. After subtracting the bright
HII regions, the 24 and 70m maps show weaker correlations with the 20cm
map than with the 3.6cm map at most scales. We also find a strong correlation
between the 3.6cm and H emission at all scales. Comparing the results
with and without the bright HII regions, we conclude that the IR emission is
influenced by young, massive stars increasingly with decreasing wavelength from
160 to 24m. The radio-IR correlations indicate that the warm dust-thermal
radio correlation is stronger than the cold dust-nonthermal radio correlation
at scales smaller than 4kpc. A perfect 3.6cm-H correlation implies that
extinction has no significant effect on H emitting structures.Comment: 15 pages, 10 figures, accepted for publication in the Astronomy and
Astrophysics Journa
ISM properties in low-metallicity environments I. mid-infrared spectra of dwarf galaxies
We present new ISOCAM mid-infrared spectra of three starbursting nearby dwarf
galaxies, NGC1569, IIZw40, NGC1140 and the 30Dor region of the LMC and explore
the properties of the ISM in low-metallicity environments, also using
additional sources from the literature. We analyse the various components of
the ISM probed by the mid-infrared observations and compare them with other
Galactic and extragalactic objects. The MIR spectra of the low-metallicity
starburst sources are dominated by the [NeIII] and [SIV] lines, as well as a
steeply rising dust continuum. PAH bands are generaly faint, both locally and
averaged over the full galaxy, in stark contrast to dustier starburst galaxies,
where the PAH features are very prominant and even dominate on global scales.
The hardness of the modeled interstellar radiation fields for the dwarf
galaxies increases as the presence of PAH band emission becomes less
pronounced. The [NeIII]/[NeII] ratios averaged over the full galaxy are
strikingly high, often >10. Thus, the hard radiation fields are pronounced and
pervasive. We find a prominent correlation between the PAHs/VSGs and the
[NeIII]/[NeII] ratios for a wide range of objects, including the low
metallicity galaxies as well as Galactic HII regions and other metal-rich
galaxies. This effect is consistent with the hardness of the interstellar
radiation field playing a major role in the destruction of PAHs in the low
metallicity ISM. We see a PAHs/VSGs and metallicity correlation, also found by
Engelbracht et al. (2005) for a larger survey. Combined effects of metallicity
and radiation field seem to be playing important roles in the observed behavior
of PAHs in the low metallicity systems.Comment: accepted by A&
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