254 research outputs found
Diffuse interstellar bands {\lambda}5780 and {\lambda}5797 in the Antennae Galaxy as seen by MUSE
ABRIDGED: Diffuse interstellar bands (DIBs) are faint spectral absorption
features of unknown origin. Research on DIBs beyond the Local Group (LG) will
surely blossom in the era of the ELTs. A possibility that needs to be explored
is the use of integral field spectrographs. We do so by using MUSE data for the
Antennae Galaxy, the closest major galaxy merger. High S-to-N spectra were
created by co-adding the signal of many spatial elements. The emission of the
underlying stellar population was modeled using STARLIGHT. To our knowledge, we
have derived the first maps for the DIBs at l5780 and l5797 in galaxies outside
the LG. The l5780 DIB was detected in an area of ~0.6 arcmin2, corresponding to
a linear scale of ~25 kpc2. This region was sampled using >200 independent
lines of sight. The DIB l5797 was detected in >100 independent lines of sight.
Both DIBs are associated with a region with high emission in the HI 21 cm line,
implying a connection between atomic gas and DIBs, as the correlations for the
Milky Way also suggest. Conversely, there is mild spatial association between
the two DIBs and the molecular gas, in agreement with results for our Galaxy
that indicate a lack of correlation between DIBs and molecular gas. The overall
structure for the DIB strength distribution and extinction are comparable.
Within the system, the l5780 DIB clearly correlates with the extinction. Both
DIBs follow the relationship between equivalent width and reddening when data
for several galaxies are considered. Unidentified Infrared emission Bands
(UIBs, likely caused by PAHs) and the l5780 and l5797 DIBs show similar but not
identical spatial distributions. We attribute the differences to extinction
effects without necessarily implying a radically different nature of the
respective carriers. The results illustrate the enormous potential of integral
field spectrographs for extragalactic DIB research.Comment: 12 pages, 13 figures, accepted by Astronomy & Astrophysics; version
corrected by English edito
A catalog of 1.5273 micron diffuse interstellar bands based on APOGEE hot telluric calibrators
High resolution stellar spectroscopic surveys provide massive amounts of
diffuse interstellar bands (DIBs) measurements. Data can be used to study the
distribution of the DIB carriers and those environmental conditions that favor
their formation. In parallel, recent studies have also proved that DIBs
extracted from stellar spectra constitute new tools for building the 3D
structure of the Galactic Interstellar Medium (ISM). The amount of details on
the structure depends directly on the quantity of available lines of sight
(LOS). Therefore there is a need to construct databases of high-quality DIB
measurements as large as possible. We aim at providing the community with a
catalog of high-quality measurements of the 1.5273 micron DIB towards a large
fraction of the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
hot stars observed to correct for the telluric absorption and not used for ISM
studies so far. This catalog would complement the extensive database recently
extracted from the APOGEE observations and used for 3D ISM mapping. We devised
a method to fit the stellar continuum of the hot calibration stars and
extracted the DIB from the normalized spectrum. Severe selection criteria based
on the absorption characteristics are applied to the results. In particular
limiting constraints on the DIB widths and Doppler shifts are deduced from the
HI 21 cm measurements, following a new technique of decomposition of the
emission spectra. From ~16 000 available hot telluric spectra we have extracted
~ 6700 DIB measurements and their associated uncertainties. The statistical
properties of the extracted absorptions are examined and our selection criteria
are shown to provide a robust dataset. The resulting catalog contains the DIB
total equivalent widths, central wavelengths and widths. We briefly illustrate
its potential use for the stellar and interstellar communities.Comment: The Astrophysical Journal Supplement, in press, 35 pages, 14 figure
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios.Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in
the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been include
p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
The reduction of integral-field spectrograph (IFS) data is demanding work.
Many repetitive operations are required in order to convert raw data into,
typically a large number of, spectra. This effort can be markedly simplified
through the use of a tool or pipeline, which is designed to complete many of
the repetitive operations without human interaction. Here we present our
semi-automatic data-reduction tool p3d that is designed to be used with
fiber-fed IFSs. Important components of p3d include a novel algorithm for
automatic finding and tracing of spectra on the detector, and two methods of
optimal spectrum extraction in addition to standard aperture extraction. p3d
also provides tools to combine several images, perform wavelength calibration
and flat field data. p3d is at the moment configured for four IFSs. In order to
evaluate its performance we have tested the different components of the tool.
For these tests we used both simulated and observational data. We demonstrate
that for three of the IFSs a correction for so-called cross-talk due to
overlapping spectra on the detector is required. Without such a correction
spectra will be inaccurate, in particular if there is a significant intensity
gradient across the object. Our tests showed that p3d is able to produce
accurate results. p3d is a highly general and freely available tool. It is
easily extended to include improved algorithms, new visualization tools and
support for additional instruments. The program code can be downloaded from the
p3d-project web site http://p3d.sourceforge.netComment: 18 pages, 15 figures, 3 tables, accepted for publication in A&
The extinction and dust-to-gas structure of the planetary nebula NGC 7009 observed with MUSE
The large field and wavelength range of MUSE is well suited to mapping
Galactic planetary nebulae (PN). The bright PN NGC 7009 was observed with MUSE
on the VLT during the Science Verification of the instrument in seeing of 0.6".
Emission line maps in hydrogen Balmer and Paschen lines were formed from
analysis of the MUSE cubes. The measured electron temperature and density from
the MUSE cube were employed to predict the theoretical hydrogen line ratios and
map the extinction distribution across the nebula. After correction for the
interstellar extinction to NGC 7009, the internal dust-to-gas ratio (A_V/N_H)
has been mapped for the first time in a PN. The extinction map of NGC 7009 has
considerable structure, broadly corresponding to the morphological features of
the nebula. A large-scale feature in the extinction map, consisting of a crest
and trough, occurs at the rim of the inner shell. The nature of this feature
was investigated and instrumental and physical causes considered; no convincing
mechanisms were identified to produce this feature, other than mass loss
variations in the earlier asymptotic giant branch phase. The dust-to-gas ratio
A_V/N_H increases from 0.7 times the interstellar value to >5 times from the
centre towards the periphery of the ionized nebula. The integrated A_V/N_H is
about 2 times the mean ISM value. It is demonstrated that extinction mapping
with MUSE provides a powerful tool for studying the distribution of PN internal
dust and the dust-to-gas ratio. (Abridged.)Comment: 10 pages, 7 figures. Accepted by A&
The MUSE view of the planetary nebula NGC 3132
ABRIDGED: 2D spectroscopic MUSE data for the whole extent of NGC3132 have
been reduced and analised. The dust extinction, electron densities and
temperatures of the ionised gas and abundances were determined. The nebula
presents a complex reddening structure with high values (c(Hb)~0.4) at the rim.
Density maps are compatible with an inner high-ionisation plasma at moderate
high density (~1000cm^-3) while the low-ionisation plasma presents a structure
in density peaking at the rim with values ~700 cm^-3. Median Te using different
diagnostics decreases according to the sequence
[NII],[SII]->[SIII]->[OI]->HeI->PJ. Likewise the range of Te covered by
recombination lines is much larger than those obtained from CELs, with large
spatial variations within the nebula. If these differences were due to the
existence of high density clumps, these spatial variations suggest changes in
the properties and/or distribution of the clumps within the nebula. We
determined a median He/H=0.124. The range of measured ionic abundances for
light elements are compatible with literature values. Our kinematic analysis
nicely illustrates the power of 2D kinematic information in many emission lines
to shed light on the intrinsic structure of the nebula. Our derived velocity
maps support a geometry for the nebula similar to the previously propose
diabolo model, but oriented with its major axis at P.A.~-22^o. We identified
two low-surface brightness arc-like structures towards the northern and
southern tips of the nebula, with high extinction, high helium abundance, and
strong low-ionisation emission lines. They are spatially coincident with some
extended low-surface brightness mid-IR emission. The characteristics of the
features are compatible with being the consequence of precessing jets caused by
the binary star system. This study illustrates the enormous potential of IFS
for the study of Galactic PNe.Comment: 21 pages, 15 figures, 6 tables; accepted by A&
LINER-like Extended Nebulae in ULIRGs: Shocks Generated by Merger Induced Flows
In this work we studied the two-dimensional ionization structure of the
circumnuclear and extranuclear regions in a sample of six low-z Ultraluminous
Infrared Galaxies using Integral Field Spectroscopy. The ionization conditions
in the extranuclear regions of these galaxies (~5-15 kpc) are typical of LINERs
as obtained from the Veilleux-Osterbrock line ratio diagnostic diagrams. The
range of observed line ratios is best explained by the presence of fast shocks
with velocities of 150 to 500 km s^{-1}, while the ionization by an AGN or
nuclear starburst is in general less likely. The comparison of the
two-dimensional ionization level and velocity dispersion in the extranuclear
regions of these galaxies shows a positive correlation, further supporting the
idea that shocks are indeed the main cause of ionization.
The origin of these shocks is also investigated. Despite the likely presence
of superwinds in the circumnuclear regions of these systems, no evidence for
signatures of superwinds such as double velocity components are found in the
extended extranuclear regions. We consider a more likely explanation for the
presence of shocks, the existence of tidally induced large scale gas flows
caused by the merging process itself, as evidenced by the observed velocity
fields characterized by peak-to-peak velocities of 400 km s^{-1}, and velocity
dispersions of up to 200 km s^{-1}.Comment: 21 pages, 5 figures, accepted for publication in The Astrophysical
Journa
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