118 research outputs found
The SCUBA Local Universe Galaxy Survey Optically-Selected Sample
We discuss the progress of the SCUBA Local Universe Galaxy Survey (SLUGS),
the first large, statistical sub-mm survey of the local universe. Since our
original survey of a sample of 104 IRAS-selected galaxies we have recently
completed a sample of 78 Optically-Selected galaxies. Since SCUBA is sensitive
to the large proportion of dust too cold to be detected by IRAS the addition of
this optically-selected sample allows us for the first time to determine the
amount of cold dust in galaxies of different Hubble types. We detect 6
ellipticals in the sample and find them to have dust masses in excess of 10^7
solar masses. We derive local sub-mm luminosity functions, both directly for
the two samples, and by extrapolation from the IRAS PSCz, and find excellent
agreement.Comment: 2 pages, 2 figures. In the proceedings of the conference:
"Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork
Strikes a New Note", South Africa, June 2004 (Kluwer
The SCUBA Local Universe Galaxy Survey: Results from the Optically-Selected Sample
We present new results from the SCUBA Local Universe Galaxy Survey, the first
large statistical submillimetre survey of the local Universe. Following our
initial survey of a sample of 104 IRAS-selected galaxies we now present the
results of a sample of 80 Optically-selected galaxies. Since SCUBA is sensitive
to the large proportion of dust too cold to be detected by IRAS the addition of
this Optically-selected sample allows us for the first time to determine the
amount of cold dust in galaxies of different Hubble types. We detect 6
ellipticals in the sample and find them to have dust masses in excess of 10^7
solar masses. We derive local submillimetre Luminosity Functions and Dust Mass
functions, both directly for the Optically-Selected SLUGS sample and by
extrapolation from the IRAS PSCz survey, and find them to be well-fitted by
Schechter functions. We find excellent agreement between the two LFs and DMFs
and show that, whereas the slope of the IRAS-selected LF at lower luminosities
was steeper than -2 (a submm "Olbers' Paradox"), as expected the
PSCz-extrapolated LF flattens out at the low luminosity end.Comment: 2 pages, 4 figures. To be published in proceedings of the conference:
"The Dusty and Molecular Universe - A Prelude to HERSCHEL and ALMA", Paris,
October 2004 (ESA Publications
The SCUBA Local Universe Galaxy Survey II. 450 micron data - evidence for cold dust in bright IRAS Galaxies
This is the second in a series of papers presenting results from the SCUBA
Local Universe Galaxy Survey. In our first paper we provided 850 micron flux
densities for 104 galaxies selected from the IRAS Bright Galaxy Sample and we
found that the 60, 100 micron (IRAS) and 850 micron (SCUBA) fluxes could be
adequately fitted by emission from dust at a single temperature. In this paper
we present 450 micron data for the galaxies. With the new data, the spectral
energy distributions of the galaxies can no longer be fitted with an isothermal
dust model - two temperature components are now required. Using our 450 micron
data and fluxes from the literature, we find that the 450/850 micron flux ratio
for the galaxies is remarkably constant and this holds from objects in which
the star formation rate is similar to our own Galaxy, to ultraluminous infrared
galaxies (ULIRGS) such as Arp 220. The only possible explanation for this is if
the dust emissivity index for all of the galaxies is ~2 and the cold dust
component has a similar temperature in all galaxies (20-21 K). The dust masses
estimated using the new temperatures are higher by a factor ~2 than those
determined previously using a single temperature. This brings the gas-to-dust
ratios of the IRAS galaxies into agreement with those of the Milky Way and
other spiral galaxies which have been intensively studied in the submm.Comment: 20 pages, 14 figures, accepted for publication in MNRA
The FIR-Radio Relationship at High and Low Redshift
We use the results of the SCUBA Local Universe Galaxy Survey, a submillimetre
survey of galaxies in the nearby Universe, to investigate the relationship
between the far-infrared--submillimetre and radio emission of galaxies at both
low and high redshift. At low redshift we show that the correlation between
radio and far-infrared emission is much stronger than the correlation between
radio and submillimetre emission, which is evidence that massive stars are the
source of both the far-infrared and radio emission. At high redshift we show
that the submillimetre sources detected by SCUBA are brighter sources of radio
emission than are predicted from the properties of galaxies in the local
Universe. We discuss possible reasons for the cosmic evolution of the
relationship between radio and far-infrared emission.Comment: 8 pages including 4 figures. Version accepted for publication in
MNRA
The SCUBA Local Universe Galaxy Survey - III. Dust along the Hubble sequence
We present new results from the SCUBA Local Universe Galaxy Survey (SLUGS),
the first large systematic submillimetre survey of the local Universe. Since
our initial survey of a sample of 104 IRAS-selected galaxies we have now
completed a survey of a sample of 81 optically-selected galaxies, observed with
the SCUBA camera on the James Clerk Maxwell Telescope. Since SCUBA is sensitive
to the 90% of dust too cold to radiate significantly in the IRAS bands our new
sample represents the first unbiased survey of dust in galaxies along the whole
length of the Hubble sequence. We find little change in the properties of dust
in galaxies along the Hubble sequence and detected 6 out of 11 elliptical
galaxies. As in our earlier work on IRAS galaxies we find that the IRAS and
submm fluxes are well-fitted by a two-component dust model with dust emissivity
index beta=2. The major difference from our earlier work is that we find the
ratio of the mass of cold dust to the mass of warm dust is much higher for our
optically-selected galaxies and can reach values of ~1000. Comparison of the
results for the IRAS- and optically-selected samples shows that there is a
population of galaxies containing a large proportion of cold dust that is
unrepresented in the IRAS sample. We derive local submm luminosity and dust
mass functions, both directly from our optically-selected SLUGS sample, and by
extrapolation from the IRAS PSCz survey using the method of Serjeant &
Harrison, and find excellent agreement between the two. We find them to be
well-fitted by Schechter functions except at the highest luminosities. We find
that as a consequence of the omission of cold galaxies from the IRAS sample the
luminosity function presented in our earlier work is too low by a factor of 2.Comment: 36 pages including 16 figures and 8 tables. Accepted for publication
in MNRA
Revised masses of dust and gas of SLUGS FIR bright galaxies based on a recent CO survey
Recent CO measurements of an essentially complete sub-sample of galaxies from
the SCUBA Local Universe Survey (SLUGS) are used to examine their implications
for dust and gas masses in this sample. Estimates of dust masses are affected
by a contribution to the SCUBA brightness measurements by CO(3-2) emission, and
molecular gas masses by the use of a modified value of the CO-to-H_2 conversion
factor X. The average dust mass is reduced by 25-38 per cent, which has no
bearing on earlier conclusions concering the shapes of the dust mass luminosity
function derived from the SLUGS. The value of X found from the CO survey, when
applied together with the reduction in dust masses, leads to lower estimates
for the mean gas-to-dust mass ratios, where the gas includes both H_2 and HI.
For the CO sample, the mean global ratio is reduced from approximately 430 to
about 320-360, but is further reduced to values near 50 when applied to the
nuclear regions relevant to the CO observations. We discuss these results and
suggest that the differences between the nuclear and outer regions may simply
reflect differences in metallicity or the existence of considerable amounts of
unobserved cold dust in the outer regions of these galaxiies.Comment: 18 pages, 2 tables, 4 figures, accepted for publication in MNRA
The Canada-UK Deep Sub-Millimeter Survey II: First identifications, redshifts and implications for galaxy evolution
Identifications are sought for 12 sub-mm sources detected by Eales et al
(1998). Six are securely identified, two have probable identifications and four
remain unidentified with I_AB > 25. Spectroscopic and estimated photometric
redshifts indicate that four of the sources have z < 1, and four have 1 < z <
3, with the remaining four empty field sources probably lying at z > 3. The
spectral energy distributions of the identifications are consistent with those
of high extinction starbursts such as Arp 220. The far-IR luminosities of the
sources at z > 0.5 are of order 3 x 10^12 h_50^-2 L_sun, i.e. slightly larger
than that of Arp 220. Based on this small sample, the cumulative bolometric
luminosity function shows strong evolution to z ~ 1, but weaker or possibly
even negative evolution beyond. The redshift dependence of the far-IR
luminosity density does not appear, at this early stage, to be inconsistent
with that seen in the ultraviolet luminosity density. Assuming that the energy
source in the far-IR is massive stars, the total luminous output from
star-formation in the Universe is probably dominated by the far-IR emission.
The detected systems have individual star-formation rates (exceeding 300
h_50^-2 M_O yr^-1) that are much higher than seen in the ultraviolet selected
samples, and which are sufficient to form substantial stellar populations on
dynamical timescales of 10^8 yr. The association with merger-like morphologies
and the obvious presence of dust makes it attractive to identify these systems
as forming the metal-rich spheroid population, in which case we would infer
that much of this activity has occurred relatively recently, at z ~ 2.Comment: 17 pages text + 14 figures. Accepted for publication in the
Astrophysical Journal. Gzipped tar file contains one text.ps file for text
and tables, one Fig2.jpg file for Fig 2, and 13 Fig*.ps files for the
remaining figure
Gas and Dust in the Taffy Galaxies: Ugc12914/15
We present a comprehensive study of the dust and gas properties in the
after-head-on-collision UGC12914/15 galaxy system using multi-transition CO
data and SCUBA sub-mm continuum images at both 450 and 850m. CO(3-2) line
emission was detected in the disks of UGC 12914 and UGC 12915 as well as in a
bridge connecting the two galaxies. Dust emission at 450m was detected for
the first time in the two galactic disks and in the connecting bridge. Using an
LVG excitation analysis model we have obtained good estimates of the physical
parameters in different regions of this system and the amount of molecular gas
was found to be 3-4 times lower than that estimated by other investigators
using the standard Galactic CO-to-H2 conversion factor. Comparing with the dust
mass derived from the SCUBA data, we found that the gas-to-dust ratio was
comparable to the Galactic value in the two galaxy disks but a factor of ~3
higher in the bridge. The physical condition of the molecular gas in the bridge
is comparable to that in the diffuse clouds in our Galaxy. Our result is
consistent with the scenario that the bridge molecular gas originated from the
disk molecular clouds and has been drawn out of the galactic disks due to
direct cloud-cloud collision.
Our data indicate that the global star formation efficiency (SFE) in UGC
12915 is comparable to that of normal spiral galaxies, and the SFE is 40% lower
in UGC 12914 than in UGC 12915. Little star formation activity was found in the
bridge except in an HII region adjacent to the disk of UGC 12915.Comment: Accepted by AJ. 45 pages, 10 figures (Fig 1-5 and Fig 7 in gif
format
Metal factories in the early universe
We have estimated the mass of metals in the molecular gas in 13 dusty star-forming galaxies at z ⌠4 in which the gas, based on previous observations, lies in a cold rotating disk. We estimated the metal masses using either the submillimetre line or continuum emission from three tracers of the overall metal content - carbon atoms, carbon monoxide molecules and dust grains - using the first simultaneous calibration of all three tracers. We obtain very similar mass estimates from the different tracers, which are similar to the entire metal content of a present-day massive early-type galaxy. We used the dynamical masses of these galaxies to estimate an upper limit on the mass of the molecular gas in each galaxy, allowing us to estimate a lower limit on the metal abundance of the gas, finding values for many of the galaxies well above the solar value. We show that the high metal masses and metal abundances are what is expected shortly after the formation of a galaxy for a top-heavy IMF. We suggest a scenario for galaxy evolution in which massive galaxies reach a high metal abundance during their formation phase, which is then gradually reduced by dry mergers with lower mass galaxies. We show that the metals in the outflows from high-redshift dusty star-forming galaxies can quantitatively explain the long-standing puzzle that such a large fraction of the metals in galaxy clusters (â0.75) is in the intracluster gas rather than in the galaxies themselves
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
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