1,235 research outputs found
Constraining the Thermal Dust Content of Lyman-Break Galaxies in an Overdense Field at z~5
We have carried out 870 micron observations in the J1040.7-1155 field, known
to host an overdensity of Lyman break galaxies at z=5.16 +/- 0.05. We do not
detect any individual source at the S(870)=3.0 mJy/beam (2 sigma) level. A
stack of nine spectroscopically confirmed z>5 galaxies also yields a
non-detection, constraining the submillimeter flux from a typical galaxy at
this redshift to S(870)<0.85 mJy, which corresponds to a mass limit
M(dust)<1.2x10^8 M_sun (2 sigma). This constrains the mass of thermal dust in
distant Lyman break galaxies to less than one tenth of their typical stellar
mass. We see no evidence for strong submillimeter galaxies associated with the
ultraviolet-selected galaxy overdensity, but cannot rule out the presence of
fainter, less massive sources.Comment: 5 pages, 2 figures. MNRAS in pres
The contribution of AGN to the sub-mm population
We find that X-ray sources in the Extended Chandra Deep Field South are
strongly spatially correlated with LABOCA 870 micron sources. We investigate
the dependence of this correlation on X-ray flux, hardness ratio and column
density, finding that specifically faint and absorbed X-ray sources are
significant sub-mm emitters. In the X-ray source redshift subsample we confirm
the previous result that higher luminosity sources (L_X>10^44 ergs/s) have
greater 870um fluxes but we also find that this subsample selects against
absorbed sources, faint in X-ray flux. Overall, we find that X-ray sources
contribute 1.5 \pm 0.1 Jy/deg^2 to the sub-mm background, ~3% of the total, in
agreement with the prediction of an obscured AGN model which also gives a
reasonable fit to the bright sub-mm source counts. This non-unified model also
suggests that when Compton-thick, X-ray-undetected sources are included, then
the fractional AGN contribution to the sub-mm background would rise from ~3% to
a total of 25-40%, although in a unified model the AGN contribution would only
reach ~13%, because the sub-mm flux of the X-ray sources is then more
representative of the whole AGN population. Measurements of the dependence of
sub-mm flux on X-ray flux, luminosity and column density all agree well with
the predictions of the non-unified AGN model. Heavily absorbed,
X-ray-undetected AGN could explain the further cross-correlation we find
between sub-mm sources and z > 0.5 red galaxies. We conclude that sub-mm
galaxies may contain the long-sought absorbed AGN population needed to explain
the X-ray background.Comment: 15 pages, 13 figures; submitted to MNRA
Limits on dust emission from z~5 LBGs and their local environments
We present 1.2mm MAMBO-2 observations of a field which is over-dense in Lyman
Break Galaxies (LBGs) at z~5. The field includes seven
spectroscopically-confirmed LBGs contained within a narrow (z=4.95+/-0.08)
redshift range and an eighth at z=5.2. We do not detect any individual source
to a limit of 1.6 mJy/beam (2*rms). When stacking the flux from the positions
of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these
sources of 0.6mJy/beam. This limit is consistent with FIR imaging in other
fields which are over-dense in UV-bright galaxies at z~5. Independently and
combined, these limits constrain the FIR luminosity (8-1000 micron) to a
typical z~5 LBG of LFIR<~3x10^11 Lsun, implying a dust mass of Mdust<~10^8 Msun
(both assuming a grey body at 30K). This LFIR limit is an order of magnitude
fainter than the LFIR of lower redshift sub-mm sources (z~1-3). We see no
emission from any other sources within the field at the above level. While this
is not unexpected given millimetre source counts, the clustered LBGs trace
significantly over-dense large scale structure in the field at z = 4.95. The
lack of any such detection in either this or the previous work, implies that
massive, obscured star-forming galaxies may not always trace the same
structures as over-densities of LBGs, at least on the length scale probed here.
We briefly discuss the implications of these results for future observations
with ALMA.Comment: 10 pages, 6 figures, MNRAS Accepte
The local FIR Galaxy Colour-Luminosity distribution: A reference for BLAST, and Herschel/SPIRE sub-mm surveys
We measure the local galaxy far-infrared (FIR) 60-to-100 um colour-luminosity
distribution using an all-sky IRAS survey. This distribution is an important
reference for the next generation of FIR--submillimetre surveys that have and
will conduct deep extra-galactic surveys at 250--500 um. With the peak in
dust-obscured star-forming activity leading to present-day giant ellipticals
now believed to occur in sub-mm galaxies near z~2.5, these new
FIR--submillimetre surveys will directly sample the SEDs of these distant
objects at rest-frame FIR wavelengths similar to those at which local galaxies
were observed by IRAS. We have taken care to correct for temperature bias and
evolution effects in our IRAS 60 um-selected sample. We verify that our
colour-luminosity distribution is consistent with measurements of the local FIR
luminosity function, before applying it to the higher-redshift Universe. We
compare our colour-luminosity correlation with recent dust-temperature
measurements of sub-mm galaxies and find evidence for pure luminosity evolution
of the form (1+z)^3. This distribution will be useful for the development of
evolutionary models for BLAST and SPIRE surveys as it provides a statistical
distribution of rest-frame dust temperatures for galaxies as a function of
luminosity.Comment: 12 pages, 7 figures. MNRAS in press. This revision matches final
published version. Fixes typos in footnote 1 and equation 8. Minor
modifications to text and references. Final results unchange
Deep, ultra-high-resolution radio imaging of submillimetre galaxies using Very Long Baseline Interferometry
We present continent-scale VLBI - obtained with the European VLBI Network
(EVN) at a wavelength of 18cm - of six distant, luminous submm-selected
galaxies (SMGs). Our images have a synthesized beam width of ~30 milliarcsec
FWHM - three orders of magnitude smaller in area than the highest resolution
VLA imaging at this wavelength - and are capable of separating radio emission
from ultra-compact radio cores (associated with active super-massive black
holes - SMBHs) from that due to starburst activity. Despite targeting compact
sources - as judged by earlier observations with the VLA and MERLIN - we
identify ultra-compact cores in only two of our targets. This suggests that the
radio emission from SMGs is produced primarily on larger scales than those
probed by the EVN, and therefore is generated by star formation rather than an
AGN - a result consistent with other methods used to identify the presence of
SMBHs in these systems.Comment: MNRAS, in pres
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