Deep sub-mm surveys with SCUBA

We review published deep surveys in the submillimeter (sub-mm) regime from the new Sub-millimetre Common User Bolometer Array (SCUBA) on the 15-m James Clerk Maxwell Telescope (JCMT), Mauna Kea, Hawaii. Summarising the number counts of faint sub-mm sources determined from the different surveys we show that the deepest counts from our completed SCUBA Lens Survey, down to 0.5mJy at 850um fully account for the far-infrared background (FIRB) detected by COBE. We conclude that a population of distant, dust-enshrouded ultraluminous infrared galaxies dominate the FIRB emission around 1mm. We go on to discuss the nature of this population, starting with the identification of their optical counterparts, where we highlight the important role of deep VLA radio observations in this process. Taking advantage of the extensive archival Hubble Space Telescope (HST) observations of our fields, we then investigate the morphological nature of the sub-mm galaxy population and show that a large fraction exhibit disturbed or interacting morphologies. By employing existing broadband photometry, we derive crude redshift limits for a complete sample of faint sub-mm galaxies indicating that the majority lie at z<5, with at most 20% at higher redshifts. We compare these limits to the initial spectroscopic results from various sub-mm samples. Finally we discuss the nature of the sub-mm population, its relationship to other classes of high-redshift galaxies and its future role in our understanding of the formation of massive galaxies.Comment: 10 pages LaTeX, 4 figures, uses AIP style (included). Invited review at Maryland Astrophysics Conference ``After the dark ages: when galaxies were young (the Universe at 2<z<5)'

Dust in high-z radio-loud AGN

We present continuum observations of a small sample of high-redshift, radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal emission from dust. Seven AGN were observed with IRAM and SEST at 1.25mm; two of them, the radio galaxies 1243+036 ($z \sim 3.6$) and MG1019+0535 ($z \sim 2.8$) were also observed at 0.8mm with the JCMT submillimetre telescope. Additional VLA observations were obtained in order to derive the spectral shape of the synchrotron radiation of MG1019+0535 at high radio frequencies. MG1019+0535 and TX0211$-$122 were expected to contain a large amount of dust based on their depleted Ly$\alpha$ emission. The observations suggest a clear 1.25-mm flux density excess over the synchrotron radiation spectrum of MG1019+0535, suggesting the presence of thermal emission from dust in this radio galaxy, whereas the observations of TX0211$-$122 were not sensitive enough to meaningfully constrain its dust content. On the other hand, our observations of 1243+036 provide a stringent upper limit on the total dust mass of $<10^8$ M$_{\odot}$. Finally, we find that the spectra of the radio-loud quasars in our sample ($2 < z < 4.5$) steepen between rest-frame radio and the far-infrared. We discuss the main implications of our results, concentrating on the dusty radio galaxy, MG1019+0535.Comment: 11 pages, A&A LaTeX, 4 figure

The prevalence of AGN feedback in massive galaxies at z~1

We use the optical--infrared imaging in the UKIDSS Ultra Deep Survey field, in combination with the new deep radio map of Arumugam et al., to calculate the distribution of radio luminosities among galaxies as a function of stellar mass in two redshift bins across the interval 0.4<z<1.2. This is done with the use of a new Bayesian method to classify stars and galaxies in surveys with multi-band photometry, and to derive photometric redshifts and stellar masses for those galaxies. We compare the distribution to that observed locally and find agreement if we consider only objects believed to be weak-lined radio-loud galaxies. Since the local distribution is believed to be the result of an energy balance between radiative cooling of the gaseous halo and mechanical AGN heating, we infer that this balance was also present as long ago as z~1. This supports the existence of a direct link between the presence of a low-luminosity ('hot-mode') radio-loud active galactic nucleus and the absence of ongoing star formation.Comment: 10 pages, MNRAS, in pres

Beneath the Baselines: Detecting Molecular Emission from Submillimeter Galaxies with the GBT

We report the first detection of a submillimeter galaxy (SMG) in CO(1 →0) emission using the GBT. We identify a line with Δv_(FWHM) ~1000 kms^(−1) in the 1 cm spectrum of SMM J13120+4242 at z = 3.408, which is significantly greater than the width of the previously detected CO(4→3) line. If the observed CO(1→0) line profile arises from a single object and not several merging objects, the CO(4 →3)/CO(1→0) brightness temperature ratio of ~0.26 suggests n(H_2) > 10^3 cm^(−3) and the presence of sub-thermally excited gas. The 10σ integrated line flux implies a cold molecular gas mass M(H2) ~10^(11)M_⊙, comparable to the dynamical mass estimate and four times larger than the H_2 mass found from the CO(4 →3) line. While our observations confirm that this SMG is massive and highly gas-rich, they also suggest that J_(upper) > 3 transitions of CO may not accurately trace cold, diffuse molecular gas in SMGs