The redshifts of bright sub-mm sources

One of the key goals in observational cosmology over the next few years will be to establish the redshift distribution of the recently-discovered sub-mm source population. In this brief review I discuss and summarize the redshift information which has been gleaned to date for the ~ 50 bright sub-mm sources which have been uncovered via the six main classes of survey performed with SCUBA on the JCMT over the last 2-3 years. Despite the biases inherent in some of these surveys, and the crudeness of the redshift information available in others, I conclude that all current information suggests that only 10-15 % of luminous sub-mm sources lie at z < 2, and that the median redshift of this population is z ~ 3. I suggest that such a high median redshift is arguably not unexpected given current theories designed to explain the correlation between black-hole mass and spheroid mass found at low redshift. In such scenarios, peak AGN emission is expected to correspond to, or even to cause termination of major star-formation activity in the host spheroid. In contrast, maximum dust emission is expected to occur roughly half-way through the star-formation process. Given that optical emission from bright quasars peaks at z = 2.5, dust-emission from massive ellipticals might be reasonably expected to peak at some point in the preceding ~ 1 Gyr, at z ~ 3. Confirmation or refutation of this picture requires significantly-improved redshift information on bright samples of SCUBA sources.Comment: 11 pages, 5 figures, FIRSED2000 conference proceedings, eds. I.M. van Bemmel, B. Wilkes, & P. Barthel Elsevier New Astronomy Review

A search for symbiotic behaviour amongst OH/IR colour mimics

Recent maser surveys have shown that many potential OH/IR stars have no OH masers in their circumstellar envelopes, despite the modest requirements which should be implicitly met by IRAS colour-selected candidates. It has been suggested that these OH/IR colour mimics must have a degenerate companion which dissociates OH molecules and disrupts the masing action, ie. that they are related to symbiotic Miras. Coincidentally, there is a paucity of long-period symbiotic Miras and symbiotic OH/IR stars. Phenomonologically, those that are known seem to cluster in the zone where field Miras transform into OH/IR stars. If it could be proven that OH/IR colour mimics contain a degenerate star, that observable evidence of this star is hidden from view by CS dust whilst it slowly accretes from the wind of its Mira companion, then we have an excellent explanation for not only the existence of OH/IR colour mimics, but also for the low observed frequency of symbiotic OH/IR stars and the common occurrence of very slow novae in long-period symbiotic Miras. Here, we employ radio continuum radiation (which should escape unhindered from within the dust shells) as a simple probe of the postulated hot degenerate companions which would inevitably ionize a region of their surrounding gas. We compare the radio and infrared properties of the colour mimics with those of normal symbiotic Miras, using the strong correlation between radio and mid-IR emission in symbiotic stars. We show that if a hot companion exists then, unlike their symbiotic counterparts, they must produce radiation-bounded nebulae. Our observations provide no support for the above scenario for the lack of observed masers, but neither do they permit a rejection of this scenario.Comment: 6 pages; no figures attached; LaTeX (MN style); postscript figures via anonymous ftp in users/ers/mimic-figs on astro.caltech.edu; University of Toronto pre-print; ERSRJI

Mm/submm observations of symbiotic binary stars: implications for the mass loss and mass exchange

We discuss mm/submm spectra of a sample of symbiotic binary systems, and compare them with popular models proposed to account for their radio emission. We find that radio emission from quiescent S-type systems originates from a conical region of the red giant wind ionized by the hot companion (the STB model), whereas more complicated models involving winds from both components and their interaction are required to account for radio emission of active systems. We also find that the giant mass-loss rates derived from our observations are systematically higher than those for single cool giants. This result is in agreement with conclusions derived from IRAS observations and with requirements of models for the hot component.Comment: 7 pages, 8 figures. Paper presented at COSPAR 2000 "New results in FIR and Submm Astronomy", to be published in Advances in Space Researc

Variability of sub-mJy radio sources

We present 1.4 GHz VLA observations of the variability of radio sources in the Lockman Hole region at the level of > 100 uJy on timescales of 17 months and 19 days. These data indicate that the areal density of highly variable sources at this level is < 0.005 arcmin^{-2}. We set an upper limit of 2% to the fraction of 50 to 100uJy sources that are highly variable (> 50%). These results imply a lower limit to the beaming angle for GRBs of 1deg, and give a lower limit of 200 arcmin^2 to the area that can be safely searched for GRB radio afterglows before confusion might become an issue.Comment: aastex 2 postscript figures. to appear in the Astrophysical Journa

Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3

We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMM J2135-0102 (hereafter SMM J2135), using new observations with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-μm luminosity, L_(bol), of (2.3±0.2) × 10^(12) L_☉ and a likely star-formation rate (SFR) of ~400 yr-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At ≳70 μm, the SED can be described adequately by dust components with dust temperatures, T_d ~ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the [C ii] 158 μm cooling line. If the [C ii], CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ~ 10^3 cm^(-3), and a far-ultraviolet (-UV) radiation field, G_0, 10^(3)× stronger than the Milky Way. L_[CII]/L_(bol) is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found

The evolutionary sequence of active galactic nuclei and galaxy formation revealed

Today, almost every galaxy spheroid contains a massive black hole: a remnant of, and testament to, a period in its evolution when it contained an active galactic nucleus (AGN). However, the sequence and timescales of the formation of the black hole and surrounding spheroid of stars are completely unknown, leaving a large gap in our knowledge of how the universe attained its present appearance. Here we present submillimeter observations of matched samples of X-ray absorbed and unabsorbed AGNs that have luminosities and redshifts characteristic of the sources responsible for most of the mass in present-day black holes. Strong submillimeter emission, an isotropic signature of copious star formation, is found only in the X-ray–absorbed sample, ruling out orientation effects as the cause of the absorption. The space density and luminosity range of the X-ray–absorbed AGNs indicate that they are undergoing the transition between a hidden growth phase and an unabsorbed AGN phase and imply that the X-ray–absorbed period in the AGN's evolution coincides with the formation of the galaxy spheroid