267 research outputs found
The Herschel exploitation of local galaxy Andromeda (HELGA) V: Strengthening the case for substantial interstellar grain growth
In this paper we consider the implications of the distributions of dust and
metals in the disc of M31. We derive mean radial dust distributions using a
dust map created from Herschel images of M31 sampling the entire far-infrared
(FIR) peak. Modified blackbodies are fit to approximately 4000 pixels with a
varying, as well as a fixed, dust emissivity index (beta). An overall metal
distribution is also derived using data collected from the literature. We use a
simple analytical model of the evolution of the dust in a galaxy with dust
contributed by stellar sources and interstellar grain growth, and fit this
model to the radial dust-to-metals distribution across the galaxy. Our analysis
shows that the dust-to-gas gradient in M31 is steeper than the metallicity
gradient, suggesting interstellar dust growth is (or has been) important in
M31. We argue that M31 helps build a case for cosmic dust in galaxies being the
result of substantial interstellar grain growth, while the net dust production
from stars may be limited. We note, however, that the efficiency of dust
production in stars, e.g., in supernovae (SNe) ejecta and/or stellar
atmospheres, and grain destruction in the interstellar medium (ISM) may be
degenerate in our simple model. We can conclude that interstellar grain growth
by accretion is likely at least as important as stellar dust production
channels in building the cosmic dust component in M31.Comment: 12 pages, 7 figures. Published in MNRAS 444, 797. This version is
updated to match the published versio
HERschel Observations of Edge-on Spirals (HEROES). II: Tilted-ring modelling of the atomic gas disks
Context. Edge-on galaxies can offer important insights in galaxy evolution as
they are the only systems where the distribution of the different components
can be studied both radially and vertically. The HEROES project was designed to
investigate the interplay between the gas, dust, stars and dark matter (DM) in
a sample of 7 massive edge-on spiral galaxies.
Aims. In this second HEROES paper we present an analysis of the atomic gas
content of 6 out of 7 galaxies in our sample. The remaining galaxy was recently
analysed according to the same strategy. The primary aim of this work is to
constrain the surface density distribution, the rotation curve and the geometry
of the gas disks in a homogeneous way. In addition we identify peculiar
features and signs of recent interactions.
Methods. We construct detailed tilted-ring models of the atomic gas disks
based on new GMRT 21-cm observations of NGC 973 and UGC 4277 and re-reduced
archival HI data of NGC 5907, NGC 5529, IC 2531 and NGC 4217. Potential
degeneracies between different models are resolved by requiring a good
agreement with the data in various representations of the data cubes.
Results. From our modelling we find that all but one galaxy are warped along
the major axis. In addition, we identify warps along the line of sight in three
galaxies. A flaring gas layer is required to reproduce the data only for one
galaxy, but (moderate) flares cannot be ruled for the other galaxies either. A
coplanar ring-like structure is detected outside the main disk of NGC 4217,
which we suggest could be the remnant of a recent minor merger event. We also
find evidence for a radial inflow of 15 +- 5 km/s in the disk of NGC 5529,
which might be related to the ongoing interaction with two nearby companions.
(Abridged)Comment: 39 pages, 38 figures, Accepted for publication in Astronomy &
Astrophysic
HERschel Observations of Edge-on Spirals (HEROES). I: Far-infrared morphology and dust mass determination
Context. Edge-on spiral galaxies with prominent dust lanes provide us with an
excellent opportunity to study the distribution and properties of the dust
within them. The HEROES project was set up to observe a sample of seven large
edge-on galaxies across various wavelengths for this investigation.
Aims. Within this first paper, we present the Herschel observations and
perform a qualitative and quantitative analysis on them, and we derive some
global properties of the far infrared and submillimetre emission.
Methods. We determine horizontal and vertical profiles from the Herschel
observations of the galaxies in the sample and describe the morphology.
Modified black-body fits to the global fluxes, measured using aperture
photometry, result in dust temperatures and dust masses. The latter values are
compared to those that are derived from radiative transfer models taken from
the literature.
Results. On the whole, our Herschel flux measurements agree well with
archival values. We find that the exponential horizontal dust distribution
model often used in the literature generally provides a good description of the
observed horizontal profiles. Three out of the seven galaxies show signatures
of extended vertical emission at 100 and 160 {\mu}m at the 5{\sigma} level, but
in two of these it is probably due to deviations from an exactly edge-on
orientation. Only for NGC 4013, a galaxy in which vertically extended dust has
already been detected in optical images, we can detect vertically extended
dust, and the derived scaleheight agrees with the value estimated through
radiative transfer modelling. Our analysis hints at a correlation between the
dust scaleheight and its degree of clumpiness, which we infer from the
difference between the dust masses as calculated from modelling of optical data
and from fitting the spectral energy distribution of Herschel datapoints.Comment: 21 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
The selective effect of environment on the atomic and molecular gas-to-dust ratio of nearby galaxies in the Herschel Reference Survey
We combine dust, atomic (HI) and molecular (H) hydrogen mass
measurements for 176 galaxies in the Herschel Reference Survey to investigate
the effect of environment on the gas-to-dust mass ()
ratio of nearby galaxies. We find that, at fixed stellar mass, the average
ratio varies by no more than a factor of 2
when moving from field to cluster galaxies, with Virgo galaxies being slightly
more dust rich (per unit of gas) than isolated systems. Remarkably, once the
molecular and atomic hydrogen phases are investigated separately, we find that
\hi-deficient galaxies have at the same time lower
ratio but higher ratio than \hi-normal systems. In
other words, they are poorer in atomic but richer in molecular hydrogen if
normalized to their dust content. By comparing our findings with the
predictions of theoretical models, we show that the opposite behavior observed
in the and ratios is
fully consistent with outside-in stripping of the interstellar medium (ISM),
and is simply a consequence of the different distribution of dust, \hi\ and
H across the disk. Our results demonstrate that the small environmental
variations in the total ratio, as well as in the
gas-phase metallicity, do not automatically imply that environmental mechanisms
are not able to affect the dust and metal content of the ISM in galaxies.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA
The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey
The dust in nearby galaxies absorbs a fraction of the
UV-optical-near-infrared radiation produced by stars. This energy is
consequently re-emitted in the infrared. We investigate the portion of the
stellar radiation absorbed by spiral galaxies from the HRS by modelling their
UV-to-submillimetre spectral energy distributions. Our models provide an
attenuated and intrinsic SED from which we find that on average 32 % of all
starlight is absorbed by dust. We define the UV heating fraction as the
percentage of dust luminosity that comes from absorbed UV photons and find that
this is 56 %, on average. This percentage varies with morphological type, with
later types having significantly higher UV heating fractions. We find a strong
correlation between the UV heating fraction and specific star formation rate
and provide a power-law fit. Our models allow us to revisit the IRX-AFUV
relations, and derive these quantities directly within a self-consistent
framework. We calibrate this relation for different bins of NUV-r colour and
provide simple relations to relate these parameters. We investigated the
robustness of our method and we conclude that the derived parameters are
reliable within the uncertainties which are inherent to the adopted SED model.
This calls for a deeper investigation on how well extinction and attenuation
can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy &
Astrophysic
High-resolution radiative transfer modelling of M33
The authors thank the anonymous reviewer, whose comments
have certainly improved the manuscript. The authors also thank
Peter Camps for valuable technical advice, along with all of
the participants at the recent SKIRT meeting for comments and
discussions. I.D.L. gratefully acknowledges the supports of the
Research Foundation â Flanders (FWO). M.W.L.S acknowledges
funding from the UK Science and Technology Facilities Council
consolidated grant ST/K000926/1. M.R. acknowledges support by
the research projects AYA2014-53506-P and AYA2017-84897P
from the Spanish Ministerio de EconomŽıa y Competitividad. This
research made use of MONTAGE (http://montage.ipac.caltech.edu/),
which is funded by the National Science Foundation under Grant
Number ACI-1440620, and was previously funded by the National
Aeronautics and Space Administrationâs Earth Science Technology
Office, Computation Technologies Project, under Cooperative
Agreement Number NCC5-626 between NASA and the California
Institute of Technology. This research has made use of Astropy, a community-developed core PYTHON package for Astronomy (http:
//www.astropy.org/; Astropy Collaboration et al. 2013, 2018). This
research has made use of NumPy (http://www.numpy.org/; van der
Walt, Colbert & Varoquaux 2011), SciPy (http://www.scipy.org/),
andMatPlotLib (http://matplotlib.org/; Hunter 2007). This research
made use of APLpy, an open-source plotting package for PYTHON
(https://aplpy.github.io/; Robitaille & Bressert 2012).In this work, we characterize the contributions from both ongoing star formation and the
ambient radiation field in Local Group galaxy M33, as well as estimate the scale of the local
dust-energy balance (i.e. the scale at which the dust is re-emitting starlight generated in that
same region) in this galaxy through high-resolution radiative transfer (RT) modelling, with
defined stellar and dust geometries. We have characterized the spectral energy distribution
(SED) of M33 from UV to sub-mm wavelengths, at a spatial scale of 100 pc. We constructed
input maps of the various stellar and dust geometries for use in the RTmodelling. By modifying
our dust mix (fewer very small carbon grains and a lower silicate-to-carbon ratio as compared
to the Milky Way), we can much better fit the sub-mm dust continuum. Using this new dust
composition, we find that we are able to well reproduce the observed SED of M33 using our
adopted model. In terms of stellar attenuation by dust, we find a reasonably strong, broad
UV bump, as well as significant systematic differences in the amount of dust attenuation
when compared to standard SED modelling.We also find discrepancies in the residuals of the
spiral arms versus the diffuse interstellar medium (ISM), indicating a difference in properties
between these two regimes. The dust emission is dominated by heating due to the young stellar
populations at all wavelengths (âŒ80 per cent at 10 ÎŒm to âŒ50 per cent at 1 mm). We find that
the local dust-energy balance is restored at spatial scales greater than around 1.5 kpc.Funding from the UK Science and Technology Facilities Council consolidated grant ST/K000926/1. M.R. acknowledges support by the research projects AYA2014-53506-P and AYA2017-84897P from the Spanish Ministerio de EconomĂa y Competitividad. This research made use of MONTAGE (http://montage.ipac.caltech.edu/), which is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administrationâs Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technolog
Taxonomic study of entomopathogenic nematodes (Nematoda : Steinernematidae, Heterorhabditidae) from Benin
A study on the biodiversity of entomopathogenic nematodes was conducted during 2010 and 2011 in South Benin. Soil samples from eight sites production of annual and perennial crops were analysed. We obtained 13.21 % of positive soil samples out of 280. We here report on the identification of six of these isolates. Molecular, morphometrical and morphological observations classified the isolates within the genus Heterorhabditis ; one isolate was conspecific with H. indica and two other isolates with H. sonorensis. More information is needed for effective identification of the remaining three isolates. Phylogenic analysis based on sequences of ITS regions of rDNA grouped our isolates with H. sonorensis and H. taysearae with bootstrap support values of 94 and 99 % in Maximum Parsimony and Neighbour Joining trees, respectively. Morphological characters of the infective juveniles and males did not correspond to those of H. taysearae, but were close to H. sonorensis. In contrast, the female of the H. sonorensis populations did show some minor differences with the originally described one. No progeny was obtained from the crossbreeding of Beninese isolates and H. taysearae. Crossing with an isolate of H. sonorensis would have been more conclusive, but no isolates were available even for specimenâs morphological comparison.Keywords : Survey, identification, Molecular, cross-hybridization, Heterorhabditis.Etude taxonomique desnematodes entomopathogenes (Nematoda : Steinernematidae, Heterorhabditidae) du BeninUne Ă©tude diagnostique rĂ©alisĂ©e sur les nĂ©matodes entomopathogĂšnes (NEP) en 2010 et 2011 dans le Sud- BĂ©nin sur huit sites de production de cultures annuelles et pĂ©rennes a conduit Ă 13,21 % dâĂ©chantillons de sols positifs sur 280. Le prĂ©sent travail a portĂ© sur lâidentification de six des isolats de NEP extraits. Les Ă©tudes molĂ©culaires, morphologiques, morphomĂ©triques et dâhybridation effectuĂ©es utilisant les stades dĂ©veloppementaux des nĂ©matodes ont rĂ©vĂ©lĂ© un isolat dâH. indica, deux dâH. sonorensis. Pour les autres isolats, des informations complĂ©mentaires sont nĂ©cessaires pour une identification complĂšte. Le sĂ©quençage et lâanalyse phylogĂ©nĂ©tique de la rĂ©gion interspĂ©cifique de lâADN ribosomal ont groupĂ© nos isolats avec H. sonorensis et H. Taysearae dans les arbres de parcimonie maximale et de Neighbour Joining avec les supports respectifs 94 et 99 %. Les caractĂšres morphologiques des juvĂ©niles infectieux et des mĂąles ne correspondent pas Ă ceux de la premiĂšre description dâH. taysearae, mais sont proches dâH. sonorensis. Cependant, certaines femelles avec bouchon copulatoire ne correspondent pas Ă H. sonorensis. Nos isolats nâont pas Ă©tĂ© fĂ©conds avec H. taysearae. Un croisement avec H. sonorensis population type serait plus concluant, mais il nây avait aucun isolat disponible dans la base de gĂšnes.Mots-clĂ©s : Etude, identification, molĂ©culaire, hybridation-croisĂ©e, Heterorhabditis
The identification of dust heating mechanisms in nearby galaxies using Herschel 160/250 and 250/350 micron surface brightness ratios
We examined variations in the 160/250 and 250/350 micron surface brightness
ratios within 24 nearby (<30 Mpc) face-on spiral galaxies observed with the
Herschel Space Observatory to identify the heating mechanisms for dust emitting
at these wavelengths. The analysis consisted of both qualitative and
quantitative comparisons of the 160/250 and 250/350 micron ratios to H alpha
and 24 micron surface brightnesses, which trace the light from star forming
regions, and 3.6 micron emission, which traces the light from the older stellar
populations of the galaxies. We find broad variations in the heating mechanisms
for the dust. In one subset of galaxies, we found evidence that emission at
<=160 microns (and in rare cases potentially at <=350 microns) originates from
dust heated by star forming regions. In another subset, we found that the
emission at >=250 microns (and sometimes at >=160 microns) originates from dust
heated by the older stellar population. In the rest of the sample, either the
results are indeterminate or both of these stellar populations may contribute
equally to the global dust heating. The observed variations in dust heating
mechanisms does not necessarily match what has been predicted by dust emission
and radiative transfer models, which could lead to overestimated dust
temperatures, underestimated dust masses, false detections of variability in
dust emissivity, and inaccurate star formation rate measurements.Comment: Accepted for publication in MNRA
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