81 research outputs found
Using SCUBA to place upper limits on arcsecond scale CMB anisotropies at 850 microns
The SCUBA instrument on the James Clerk Maxwell Telescope has already had an
impact on cosmology by detecting relatively large numbers of dusty galaxies at
high redshift. Apart from identifying well-detected sources, such data can also
be mined for information about fainter sources and their correlations, as
revealed through low level fluctuations in SCUBA maps. As a first step in this
direction we analyse a small SCUBA data-set as if it were obtained from a
Cosmic Microwave Background (CMB) differencing experiment. This enables us to
place limits on CMB anisotropy at 850 microns. Expressed as Q_{flat}, the
quadrupole expectation value for a flat power spectrum, the limit is 152
microKelvin at 95 per cent confidence, corresponding to C_0^{1/2} < 355
microKelvin for a Gaussian autocorrelation function, with a coherence angle of
about 20--25 arcsec; These results could easily be reinterpretted in terms of
any other fluctuating sky signal. This is currently the best limit for these
scales at high frequency, and comparable to limits at similar angular scales in
the radio. Even with such a modest data-set, it is possible to put a constraint
on the slope of the SCUBA counts at the faint end, since even randomly
distributed sources would lead to fluctuations. Future analysis of sky
correlations in more extensive data-sets ought to yield detections, and hence
additional information on source counts and clustering.Comment: 12 pages, 9 postscript figures, uses mn.st
An upper limit to [C II] emission in a z ~= 5 galaxy
Low-ionization-state far-infrared (FIR) emission lines may be useful
diagnostics of star-formation activity in young galaxies, and at high redshift
may be detectable from the ground. In practice, however, very little is known
concerning how strong such line emission might be in the early Universe. We
attempted to detect the 158 micron [C II] line from a lensed galaxy at z =
4.926 using the Caltech Submillimeter Observatory. This source is an ordinary
galaxy, in the sense that it shows high but not extreme star formation, but
lensing makes it visible. Our analysis includes a careful consideration of the
calibrations and weighting of the individual scans. We find only modest
improvement over the simpler reduction methods, however, and the final spectrum
remains dominated by systematic baseline ripple effects. We obtain a 95 per
cent confidence upper limit of 33 mJy for a 200 km/s full width at half maximum
line, corresponding to an unlensed luminosity of 1x10^9 L_sun for a standard
cosmology. Combining this with a marginal detection of the continuum emission
using the James Clerk Maxwell Telescope, we derive an upper limit of 0.4 per
cent for the ratio of L_CII/L_FIR in this object.Comment: 5 pages, 2 figures, accepted for publication in MNRA
An upper limit to polarized submillimetre emission in Arp 220
We report the results of pointed observations of the prototypical ultraluminous infrared galaxy (ULIRG) Arp 220 at 850 ÎĽm using the polarimeter on the Submillimetre Common User Bolometer Array instrument on the James Clerk Maxwell Telescope. We find a Bayesian 99 per cent confidence upper limit on the polarized emission for Arp 220 of 1.54 per cent, averaged over the 15-arcsec beam-size. Arp 220 can serve as a proxy for other, more distant such galaxies. This upper limit constrains the magnetic field geometry in Arp 220 and also provides evidence that polarized ULIRGs will not be a major contaminant for next-generation cosmic microwave background polarization measurements
The brighter side of sub-mm source counts: a SCUBA scan-map of the Hubble Deep Field
We present an 11 X 11 arcminute map centred on the Hubble Deep Field taken at
850 microns with the SCUBA camera on the JCMT. The map has an average one-sigma
sensitivity to point sources of about 2.3 mJy and thus probes the brighter end
of the sub-mm source counts. We find 7 sources with a flux greater than 9 mJy
(roughly 4 sigma), and therefore estimate N(>9 mJy)= 208 (+90/-72) per degree.
This result is consistent with work from other groups, but improves the
statistics at the bright end, and is suggestive of a steepening of the counts.Comment: 4 pages, 2 figures. UMass/INAOE conference proceedings on Deep
Millimeter Survey
An 850-micron SCUBA map of the Groth Strip and reliable source extraction
We present an 850-micron map and list of candidate sources in a 70 arcmin^2
sub-area of the Groth Strip observed using SCUBA. We initially detect 7
candidate sources with signal-to-noise ratios (SNRs) between 3.0 and 3.5 and 4
candidate sources with SNR > 3.5. Simulations suggest that on average in a map
this size one expects 1.6 false positive sources for SNR > 3.5 and 4.5 for 3 <
SNR < 3.5. Flux boosting in maps is a well known effect and we have developed a
simple Bayesian prescription for estimating the unboosted flux distribution and
used this method to determine the best flux estimates of our sources. This
method is easily adapted for any other modest signal-to-noise survey in which
there is prior knowledge of the source counts. We performed follow-up
photometry in an attempt to confirm or reject 5 of our source candidates. We
confirm the reality of 2 of the SCUBA sources, although at lower levels than
suggested in the map and we find that the photometry results are consistent
with and confirm the de-boosted map fluxes. Our final candidate source list
contains 3 sources, including the 2 confirmed detections and 1 further
candidate source with SNR > 3.5 which has a reasonable chance of being real.Comment: 8 pages, 4 figures, accepted for publication in MNRAS December 9,
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Known and unknown SCUBA sources
Summary and discussion of some projects to use SCUBA to target sources
selected at other wavebands, as well as to find new sub-mm galaxies in `blank
fields': FIRBACK galaxies; Lyman break galaxies and `the Blob'; HDF flanking
fields and the Groth Strip; survey of lensing cluster fields.Comment: 8 pages, 4 figures, UMass/INAOE conference proceedings on Deep
Millimeter Surveys, eds. J. Lowenthal and D. Hughes, references included for
extragalactic backgrounds figur
The spatial clustering of ultraluminous infrared galaxies over 1.5 < z < 3
We present measurements of the spatial clustering of galaxies with stellar masses 1011 M, infrared luminosities 1012 L, and star formation rates 200 M yr-1 in two redshift intervals: 1.5 < z < 2.0 and 2 < z < 3. Both samples cluster moderately strongly, with spatial correlation lengths of r0 = 6.14 B1 0.84 h-1 Mpc for the 2 < z < 3 sample and r0 = 5.36 B1 1.28 h-1 Mpc for the 1.5 < z < 2.0 sample. These clustering amplitudes are consistent with both populations residing in dark matter halos with masses of 7 C 1012 M, which is comparable to that seen for optical QSOs at the same epochs. We infer that a minimum dark matter halo mass is an important factor for all forms of luminous, obscured activity in galaxies at z > 1, both starbursts and active galactic nuclei. Adopting plausible models for the growth of dark matter halos with redshift, the halos hosting the 2 < z < 3 sample will likely host poor to rich clusters of galaxies at z = 0, whereas the halos hosting the 1.5 < z < 2.0 sample will likely host L* elliptical galaxies or poor clusters at z = 0. We conclude that ultraluminous infrared galaxies (ULIRGs) at z 2.5 likely signpost stellar buildup in galaxies that will reside in clusters at z = 0 and that ULIRGs at z 1.7 signpost stellar buildup in sources that will either become L* elliptical galaxies or reside in poor clusters at z = 0
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