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 850$\mu$m. 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 450$\mu$m 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

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

SCUBA Observations of MAMBO Sources

We have observed 23 sources from the MAMBO 1200 micron survey with SCUBA at 850 microns, detecting 19 of the sources. The sources generally have low values for the ratio of 850 micron to 1200 micron flux. Two possible explanations for the low values are either that the sources are at very high redshift or that the global properties of the dust in the MAMBO sources are different from the global properties of dust in low-redshift galaxies. If the former explanation is correct, we estimate that 15 of the MAMBO sources lie at z > 3.Comment: MNRAS, in pres