4,447 research outputs found
Further multiwavelength observations of the SSA22 Ly_alpha emitting `blob'
We present new follow-up observations of the sub-mm luminous
Ly_alpha-emitting object in the SSA22 z=3.09 galaxy overdensity, referred to as
`Blob 1' by Steidel et al.(2000). In particular we discuss high resolution
Hubble Space Telescope optical imaging, Owens Valley Radio Observatory spectral
imaging, Keck spectroscopy, VLA 20cm radio continuum imaging, and Chandra X-ray
observations. We also present a more complete analysis of the existing James
Clerk Maxwell Telescope sub-mm data. We detect several optical continuum
components which may be associated with the core of the submillimeter emitting
region. A radio source at the position of one of the HST components
(22:17:25.94, +00:12:38.9) identifies it as the likely counterpart to the
submillimeter source. We also tentatively detect the CO(4-3) molecular line,
centered on the radio position. We use the CO(4-3) intensity to estimate a
limit on the gas mass for the system. The optical morphology of sources within
the Ly_alpha cloud appears to be filamentary, while the optical source
identified with the radio source has a dense knot which may be an AGN or
compact starburst. We obtain a Keck-LRIS spectrum of this object, despite its
faintness (R=26.8). The spectrum reveals weak Ly_alpha emission, but no other
obvious features, suggesting that the source is not an energetic AGN (or that
it is extremely obscured). We use non-detections in deep Chandra X-ray images
to constrain the nature of the `Blob'. Although conclusive evidence regarding
the nature of the object remains hard to obtain at this redshift, the evidence
presented here is at least consistent with a dust-obscured AGN surrounded by a
starburst situated at the heart of this giant Ly_alpha cloud.Comment: 8 pages, 9figs (low res), to appear in ApJ, for higher res figures,
http://www.submm.caltech.edu/~schapman/sa22_sept4.ps.g
AzTEC Millimetre Survey of the COSMOS Field - II. Source Count Overdensity and Correlations with Large-Scale Structure
We report an over-density of bright sub-millimetre galaxies (SMGs) in the
0.15 sq. deg. AzTEC/COSMOS survey and a spatial correlation between the SMGs
and the optical-IR galaxy density at z <~ 1.1. This portion of the COSMOS field
shows a ~ 3-sigma over-density of robust SMG detections when compared to a
background, or "blankfield", population model that is consistent with SMG
surveys of fields with no extragalactic bias. The SMG over-density is most
significant in the number of very bright detections (14 sources with measured
fluxes S(1.1mm) > 6 mJy), which is entirely incompatible with sample variance
within our adopted blank-field number densities and infers an over-density
significance of >> 4. We find that the over-density and spatial correlation to
optical-IR galaxy density are most consistent with lensing of a background SMG
population by foreground mass structures along the line of sight, rather than
physical association of the SMGs with the z <~ 1.1 galaxies/clusters. The SMG
positions are only weakly correlated with weak-lensing maps, suggesting that
the dominant sources of correlation are individual galaxies and the more
tenuous structures in the region and not the massive and compact clusters.
These results highlight the important roles cosmic variance and large-scale
structure can play in the study of SMGs.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in MNRA
Presentations of Finitely Generated Cancellative Commutative Monoids and Nonnegative Solutions of Systems of Linear Equations
Varying methods exist for computing a presentation of a finitely generated commutative cancellative monoid. We use an algorithm of Contejean and Devie [An efficient incremental algorithm for solving systems of linear diophantine equations, Inform. and Comput. 113 (1994) 143â172] to show how these presentations can be obtained from the nonnegative integer solutions to a linear system of equations. We later introduce an alternate algorithm to show how such a presentation can be efficiently computed from an integer basis
Spitzer and near-infrared observations of a new bi-polar protostellar outflow in the Rosette Molecular Cloud
We present and discuss \emph{Spitzer} and near-infrared H observations
of a new bi-polar protostellar outflow in the Rosette Molecular Cloud. The
outflow is seen in all four IRAC bands and partially as diffuse emission in the
MIPS 24 m band. An embedded MIPS 24 m source bisects the outflow and
appears to be the driving source. This source is coincident with a dark patch
seen in absorption in the 8 m IRAC image. \emph{Spitzer} IRAC color
analysis of the shocked emission was performed from which thermal and column
density maps of the outflow were constructed. Narrow-band near-infrared (NIR)
images of the flow reveal H emission features coincident with the high
temperature regions of the outflow. This outflow has now been given the
designation MHO 1321 due to the detection of NIR H features. We use these
data and maps to probe the physical conditions and structure of the flow.Comment: Accepted for publication in The Astrophysical Journa
On the Number of Factorizations of an Element in an Atomic Monoid
Let S be a reduced commutative cancellative atomic monoid. If s is a nonzero element of S, then we explore problems related to the computation of η(s), which represents the number of distinct irreducible factorizations of sâS. In particular, if S is a saturated submonoid of Nd, then we provide an algorithm for computing the positive integer r(s) for which
0 \u3c limnââη(sn)nr(s)-1â.
We further show that r(s) is constant on the Archimedean components of S. We apply the algorithm to show how to compute
limnââη(sn)nr(s)-1
and also consider various stability conditions studied earlier for Krull monoids with finite divisor class group
Density Variations in the NW Star Stream of M31
The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the
M31-M33 system has found a star stream which extends about 120 kpc NW from the
center of M31. The great length of the stream, and the likelihood that it does
not significantly intersect the disk of M31, means that it is unusually well
suited for a measurement of stream gaps and clumps along its length as a test
for the predicted thousands of dark matter sub-halos. The main result of this
paper is that the density of the stream varies between zero and about three
times the mean along its length on scales of 2 to 20 kpc. The probability that
the variations are random fluctuations in the star density is less than 10^-5.
As a control sample we search for density variations at precisely the same
location in stars with metallicity higher than the stream, [Fe/H]=[0, -0.5] and
find no variations above the expected shot noise. The lumpiness of the stream
is not compatible with a low mass star stream in a smooth galactic potential,
nor is it readily compatible with the disturbance caused by the visible M31
satellite galaxies. The stream's density variations appear to be consistent
with the effects of a large population of steep mass function dark matter
sub-halos, such as found in LCDM simulations, acting on an approximately 10Gyr
old star stream. The effects of a single set of halo substructure realizations
are shown for illustration, reserving a statistical comparison for another
study.Comment: ApJ revised version submitte
Submillimeter Observations of the Ultraluminous BAL Quasar APM 08279+5255
With an inferred bolometric luminosity of 5\times10^{15}{\rm \lsun}, the
recently identified z=3.87, broad absorption line quasar APM 08279+5255 is
apparently the most luminous object currently known. As half of its prodigious
emission occurs in the infrared, APM 08279+5255 also represents the most
extreme example of an Ultraluminous Infrared Galaxy. Here, we present new
submillimeter observations of this phenomenal object; while indicating that a
vast quantity of dust is present, these data prove to be incompatible with
current models of emission mechanisms and reprocessing in ultraluminous
systems. The influence of gravitational lensing upon these models is considered
and we find that while the emission from the central continuum emitting region
may be significantly enhanced, lensing induced magnification cannot easily
reconcile the models with observations. We conclude that further modeling,
including the effects of any differential magnification is required to explain
the observed emission from APM 08279+5255.Comment: 12 Pages with Two figures. Accepted for publication in the
Astrophysical Journal Letter
Genesis of the dusty Universe: modeling submillimetre source counts
We model the evolution of IR galaxies using a phenomenological approach to
match the observed source counts at different IR wavelengths. We introduce a
new algorithm for reproducing source counts based on direct integration of
probability distributions rather than Monte-Carlo sampling. We construct a
simple model for the evolution of the luminosity function and the colour
distribution of IR galaxies which utilizes a minimum number of free parameters.
Moreover we analyze how each of these parameters is constrained by
observational data. The model is based on pure luminosity evolution and adopts
the Dale & Helou SED templates. We find that the 850um source counts and their
redshift distribution depend strongly on the shape of the luminosity evolution
function, but only weakly on the details of the SEDs. We derive the best-fit
evolutionary model using the 850um counts and redshift distribution as
constraints. Moreover our best-fit shows a flattening of the faint end of the
luminosity function towards high redshifts and requires a colour evolution
which implies the typical dust temperatures of objects with the same
luminosities to decrease with redshift. We compare our best-fit model to
observed source counts at shorter and longer wavelengths which indicates our
model reproduces the 70um and 1100um source counts remarkably well, but
under-produces the counts at intermediate wavelengths. Analysis reveals that
the discrepancy arises at low redshifts, indicating that revision of the
adopted SED library towards lower dust temperatures (at a fixed infrared
luminosity) is required. This modification is equivalent to a population of
cold galaxies existing at low redshifts, as also indicated by recent Herschel
results, which are underrepresented in IRAS sample. We show that the modified
model successfully reproduces the source counts in a wide range of IR and submm
wavelengths.Comment: 21 pages, 11 figures, 2 tables. Accepted for publication in MNRAS.
Supplementary information could be found at
http://www.strw.leidenuniv.nl/genesis
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