297 research outputs found
On the dust abundance gradients in late-type galaxies: I. Effects of destruction and growth of dust in the interstellar medium
We present basic theoretical constraints on the effects of destruction by
supernovae (SNe) and growth of dust grains in the interstellar medium (ISM) on
the radial distribution of dust in late-type galaxies. The radial gradient of
the dust-to-metals ratio is shown to be essentially flat (zero) if interstellar
dust is not destroyed by SN shock waves and all dust is produced in stars. If
there is net dust destruction by SN shock waves, the dust-to-metals gradient is
flatter than or equal to the metallicity gradient (assuming the gradients have
the same sign). Similarly, if there is net dust growth in the ISM, then the
dust-to-metals gradient is steeper than or equal to the metallicity gradient.
The latter result implies that if dust gradients are steeper than metallicity
gradients, i.e., the dust-to-metals gradients are not flat, then it is unlikely
dust destruction by SN shock waves is an efficient process, while dust growth
must be a significant mechanism for dust production. Moreover, we conclude that
dust-to-metals gradients can be used as a diagnostic for interstellar dust
growth in galaxy discs, where a negative slope indicates dust growth.Comment: 12 pages, 4 figures. Accepted for publication in MNRA
The Canada-UK Deep Submillimetre Survey: First Submillimetre Images, the Source Counts, and Resolution of the Background
We present the first results of a deep unbiased submillimetre survey carried
out at 450 and 850 microns. We detected 12 sources at 850 microns, giving a
surface density of sources with 850-micron flux densities > 2.8mJy of of
0.49+-0.16 per square arcmin. The sources constitute 20-30% of the background
radiation at 850 microns and thus a significant fraction of the entire
background radiation produced by stars. This implies, through the connection
between metallicity and background radiation, that a significant fraction of
all the stars that have ever been formed were formed in objects like those
detected here. The combination of their large contribution to the background
radiation and their extreme bolometric luminosities make these objects
excellent candidates for being proto-ellipticals. Optical astronomers have
recently shown that the UV-luminosity density of the universe increases by a
factor of about 10 between z=0 and z=1 and then decreases again at higher
redshifts. Using the results of a parallel submillimetre survey of the local
universe, we show that both the submillimetre source density and background can
be explained if the submillimetre luminosity density evolves in a similar way
to the UV-luminosity density. Thus, if these sources are ellipticals in the
process of formation, they may be forming at relatively modest redshifts.Comment: 8 pages (LATEX), 6 postscript figures, submitted to ApJ Letter
The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field
We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November
issue of the Astronomical Journa
Dust in the early Universe: Evidence for non-stellar dust production or observational errors?
Observations have revealed unexpectedly large amounts of dust in
high-redshift galaxies and its origin is still much debated. Valiante et al.
(2009, MNRAS, 397, 1661) suggested the net stellar dust production of the
quasar host galaxy SDSS J1148+5251 may be sufficient to explain the large dust
mass detected in this galaxy, albeit under some very special assumptions (e.g.,
'closed box' evolution and a rather high gas mass). Here it is shown that since
accretion of essentially pristine material may lower the efficiency of dust
formation significantly, and the observationally derived dust-to-gas ratios for
these high-redshift galaxies are remarkably high, stellar dust production is
likely insufficient. A model including metallicity-dependent, non-stellar dust
formation ('secondary dust') is presented. The required contribution from this
non-stellar dust component appears too large, however. If all observational
constraints are to be met, the resultant dust-to-metals ratio is close to
unity, which means that almost all interstellar metals exist in the form dust.
This is a very unlikely situation and suggests the large dust-to-gas ratios at
high-redshifts may be due to observational uncertainties and/or or incorrect
calibration of conversion factors for gas and dust tracers.Comment: 16 pages, 11 figures. Accepted for publication in MNRA
New insight into the relation between star formation activity and dust content in galaxies
(Abridged) We assemble a sample of 3258 low-redshift galaxies from the SDSS
DR6 with complementary photometric observations by GALEX, 2MASS and IRAS at
far-ultraviolet and infrared wavelengths. We use a recent, simple but
physically motivated model to interpret the observed spectral energy
distributions of the galaxies in this sample in terms of statistical
constraints on physical parameters describing the star formation history and
dust content. The focus on a subsample of 1658 galaxies with highest S/N
observations enables us to investigate most clearly several strong correlations
between various derived physical properties of galaxies. We find that the
typical dust mass of a star-forming correlates remarkably well with the star
formation rate (SFR). We also find that the dust-to-stellar mass ratio, the
ratio of dust mass to star formation rate and the fraction of dust luminosity
contributed by the diffuse interstellar medium all correlate strongly with
specific SFR. A comparison with recent models of chemical and dust evolution of
galaxies suggests that these correlations could arise, at least in part, from
an evolutionary sequence. As galaxies form stars, their ISM becomes enriched in
dust, while the drop in gas supply makes the specific SFR decrease.
Interestingly, as a result, a young, actively star-forming galaxy with low
dust-to-gas ratio may still be highly dusty because it contains large amounts
of interstellar gas. This may be important for the interpretation of the
infrared emission from young, gas-rich star-forming galaxies at high redshift.
Our study provides a useful local reference for future statistical studies of
the star formation and dust properties of galaxies at high redshifts.Comment: 15 pages, 10 figures, accepted for publication in MNRAS.
Full-resolution figures available from
http://users.physics.uoc.gr/~dacunha/paper_dacunha.pd
On the dust abundance gradients in late-type galaxies: II. Analytical models as evidence for massive interstellar dust growth in SINGS galaxies
We use simple analytical models of the build up of the dust component and
compare these with radial dust distributions derived from observations of SINGS
galaxies. The observations show that dust gradients are indeed typically
steeper than the corresponding metallicity gradients and our models indicate
very little dust destruction, but significant dust growth in the ISM for most
of these galaxies. Hence, we conclude that there is evidence for significant
non-stellar dust production, and little evidence for dust destruction due to
SNe shock waves. We find that dust is reprocessed rather than destroyed by
shocks from SNe. Finally, we argue that dust abundances derived using standard
methods may be overestimated, since even very 'generous' estimates of the
metallicity results in dust-to-metals ratios above unity in several cases, if
the dust abundances given in the literature are taken at face value.Comment: 12 pages, 3 figures. Accepted for publication in MNRA
Probing the Dust Properties of Galaxies at Submillimetre Wavelengths II. Dust-to-gas mass ratio trends with metallicity and the submm excess in dwarf galaxies
We are studying the effects of submm observations on the total dust mass and
thus dust-to-gas mass ratio measurements. We gather a wide sample of galaxies
that have been observed at submm wavelengths to model their Spectral Energy
Distributions using submm observations and then without submm observational
constraints in order to quantify the error on the dust mass when submm data are
not available. Our model does not make strong assumptions on the dust
temperature distribution to precisely avoid submm biaises in the study. Our
sample includes 52 galaxies observed at submm wavelengths. Out of these, 9
galaxies show an excess in submm which is not accounted for in our fiducial
model, most of these galaxies being low- metallicity dwarfs. We chose to add an
independant very cold dust component (T=10K) to account for this excess. We
find that metal-rich galaxies modelled with submm data often show lower dust
masses than when modelled without submm data. Indeed, these galaxies usually
have dust SEDs that peaks at longer wavelengths and require constraints above
160 um to correctly position the peak and sample the submillimeter slope of
their SEDs and thus correctly cover the dust temperature distribution. On the
other hand, some metal-poor dwarf galaxies modelled with submm data show higher
dust masses than when modelled without submm data. Using submm constraints for
the dust mass estimates, we find a tightened correlation of the dust-to-gas
mass ratio with the metallicity of the galaxies. We also often find that when
there is a submm excess present, it occurs preferentially in low-metallicity
galaxies. We analyse the conditions for the presence of this excess and find a
relation between the 160/850 um ratio and the submm excess.Comment: 19 pages, 10 figures, 1 table, accepted for publication in A&
The Herschel Virgo cluster survey: V. Star-forming dwarf galaxies - dust in metal-poor environments
We present the dust properties of a small sample of Virgo cluster dwarf
galaxies drawn from the science demonstration phase data set of the Herschel
Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 +
log(O/H) < 8.3) and star-formation rates < 10^{-1} M_{sun}/yr. We measure the
spectral energy distribution (SED) from 100 to 500 um and derive dust
temperatures and dust masses. The SEDs are fitted by a cool component of
temperature T < 20 K, implying dust masses around 10^{5} M_{sun} and
dust-to-gas ratios D within the range 10^{-3}-10^{-2}. The completion of the
full survey will yield a larger set of galaxies, which will provide more
stringent constraints on the dust content of star-forming dwarf galaxies.Comment: Letter accepted for publication in A&A (Herschel special issue
A Census of Oxygen in Star-Forming Galaxies: An Empirical Model Linking Metallicities, Star Formation Rates and Outflows
In this contribution we present the first census of oxygen in star-forming
galaxies in the local universe. We examine three samples of galaxies with
metallicities and star formation rates at z = 0.07, 0.8 and 2.26, including the
SDSS and DEEP2 surveys. We infer the total mass of oxygen produced and mass of
oxygen found in the gas-phase from our local SDSS sample. The star formation
history is determined by requiring that galaxies evolve along the relation
between stellar mass and star formation rate observed in our three samples. We
show that the observed relation between stellar mass and star formation rate
for our three samples is consistent with other samples in the literature. The
mass-metallicity relation is well established for our three samples and from
this we empirically determine the chemical evolution of star-forming galaxies.
Thus, we are able to simultaneously constrain the star formation rates and
metallicities of galaxies over cosmic time allowing us to estimate the mass of
oxygen locked up in stars. Combining this work with independent measurements
reported in the literature we conclude that the loss of oxygen from the
interstellar medium of local star-forming galaxies is likely to be a ubiquitous
process with the oxygen mass loss scaling (almost) linearly with stellar mass.
We estimate the total baryonic mass loss and argue that only a small fraction
of the baryons inferred from cosmological observations accrete onto galaxies.Comment: 24 pages, 18 figures. Accepted for publication in Ap
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
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