Submm Galaxies Research Articles

Spectroscopic Confirmation of an Extreme Starburst at Redshift 4.547

We report the spectroscopic confirmation of a sub-mm galaxy (SMG) at z=4.547 with an estimated L_IR=0.5-2.0x10^13 L_sun. The spectra, mid-IR, and X-ray properties indicate the bolometric luminosity is dominated by star formation at a rate of >1000M_sun per yr. Multiple, spatially separated components are visible in the Ly-Alpha line with an observed velocity difference of up to 380 km/sec and the object morphology indicates a merger. The best fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10^10 M_sun of stellar mass. This object is a likely progenitor for the massive early type systems seen at z~2.

The SCUBA Half Degree Extragalactic Survey (SHADES) – IX. The environment, mass and redshift dependence of star formation

We present a comparison between the SCUBA (Submillimetre Common User Bolometer Array) Half Degree Extragalactic Survey (SHADES) at 450 and 850 ?m in the Lockman Hole East with a deep Spitzer Space Telescope survey at 3.6–24 ?m conducted in guaranteed time. Using stacking analyses we demonstrate a striking correspondence between the galaxies contributing the submm extragalactic background light, with those likely to dominate the backgrounds at Spitzer wavelengths. Using a combination BRIzK plus Spitzer photometric redshifts, we show that at least a third of the Spitzer-identified submm galaxies at 1 < z < 1.5 appear to reside in overdensities when the density field is smoothed at 0.5–2 Mpc comoving diameters, supporting the high-redshift reversal of the local star formation–galaxy density relation. We derive the dust-shrouded cosmic star formation history of galaxies as a function of assembled stellar masses. For model stellar masses <1011 M?, this peaks at lower redshifts than the ostensible z~ 2.2 maximum for submm point sources, adding to the growing consensus for 'downsizing' in star formation. Our surveys are also consistent with 'downsizing' in mass assembly. Both the mean star formation rates ?dM*/dt? and specific star formation rates ?(1/M*) d M*/d t? are in striking disagreement with some semi-analytic predictions from the Millenium Simulation. The discrepancy could either be resolved with a top-heavy initial mass function, or a significant component of the submm flux heated by the interstellar radiation field.

Clarifying the nature of the brightest submillimetre sources: interferometric imaging of LH 850.02

We present high-resolution interferometric imaging of LH 850.02, the brightest 850- and 1200-μm submillimetre (submm) galaxy in the Lockman Hole. Our observations were made at 890 μm with the Submillimetre Array (SMA). Our high-resolution submm imaging detects LH 850.02 at ≳6σ as a single compact (size ≲1 arcsec or ≲8 kpc) point source and yields its absolute position to ∼0.2-arcsec accuracy. LH 850.02 has two alternative radio counterparts within the Submillimetre Common User Bolometer Array (SCUBA) beam (LH 850.02N and LH 850.02S), both of which are statistically very unlikely to be so close to the SCUBA source position by chance. However, the precise astrometry from the SMA shows that the submm emission arises entirely from LH 850.02N, and is not associated with LH 850.02S (by far the brighter of the two alternative identifications at 24 μm). Fits to the optical–infrared (IR) multicolour photometry of LH 850.02N and LH 850.02S indicate that both lie at z≈ 3.3, and are therefore likely to be physically associated. At these redshifts, the 24-μm-to-submm flux density ratios suggest that LH 850.02N has an Arp 220-type starburst-dominated far-IR spectral energy distribution (SED), while LH 850.02S is more similar to Mrk 231, with less dust enshrouded star formation activity, but a significant contribution at 24 μm (rest frame 5–6 μm) from an active nucleus. This complex mix of star formation and active galactic nucleus (AGN) activity in multicomponent sources may be common in the high-redshift ultraluminous galaxy population, and highlights the need for precise astrometry from high-resolution interferometric imaging for a more complete understanding.

Long gamma-ray bursts and their host galaxies at high redshift

Motivated by the recent observational and theoretical evidence that long gamma-ray bursts (GRBs) are likely associated with low metallicity, rapidly rotating massive stars, we examine the cosmological star formation rate (SFR) below a critical metallicity Z crit ∼ 1/10-1/5 Z ⊙ , to estimate the event rate of high redshift long GRB progenitors. To this purpose, we exploit a galaxy formation scenario already successfully tested on a wealth of observational data on (proto)spheroids, Lyman break galaxies, Lyman a emitters, submm galaxies, quasars and local early-type galaxies. We find that the predicted rate of long GRBs amounts to about 300 events yr -1 sr -1 , of which about 30 per cent occur at 2 ≥ 6. Correspondingly, the GRB number counts well agree with the bright SWIFT data, without the need for an intrinsic luminosity evolution. Moreover, the above framework enables us to predict the properties of the GRB host galaxies. Most GRBs are associated with low-mass galaxy haloes M H ≤ 10 11 M ⊙ , and effectively trace the formation of small galaxies in such haloes. The hosts are young, with age smaller than 5 x 10 7 yr, gas rich, but poorly extincted (A v ≤ 0.1) because of their chemical immaturity; this also implies high specific SFR and quite extreme α-enhancement. Only the minority of hosts residing in large haloes with M H ≥ 10 12 M ⊙ has larger extinction (A v ∼ 0.7-1), SFRs exceeding 100 M ⊙ yr -1 and can be detected at submm wavelengths. Most of the hosts have ultraviolet magnitudes in the range -20 ≤ M 1350 ≤ -16, and Lyman a luminosity in the range 2 x 10 40 ≤ Layman α ≤ 2 x 10 42 erg s -1 . GRB hosts are thus tracing the faint end of the luminosity function of Lyman break galaxies and Lyman a emitters. Finally, our results imply that the population of 'dark' GRBs occur mostly in faint hosts at high redshift, rather than in dusty hosts at low redshift.

Galaxy evolution in the infrared: comparison of a hierarchical galaxy formation model with Spitzer data

We present predictions for the evolution of the galaxy luminosity function, number counts and redshift distributions in the IR based on the Lambda-CDM cosmological model. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy SEDs including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al (2005), assumes two different IMFs: a normal solar neighbourhood IMF for quiescent star formation in disks, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF seems to be necessary to explain the number counts of faint sub-mm galaxies. We compare the model with observational data from the SPITZER Space Telescope, with the model parameters fixed at values chosen before SPITZER data became available. We find that the model matches the observed evolution in the IR remarkably well over the whole range of wavelengths probed by SPITZER. In particular, the SPITZER data show that there is strong evolution in the mid-IR galaxy luminosity function over the redshift range z ~ 0-2, and this is reproduced by our model without requiring any adjustment of parameters. On the other hand, a model with a normal IMF in starbursts predicts far too little evolution in the mid-IR luminosity function, and is therefore excluded.

Environments of z &gt; 5 quasars: searching for protoclusters at submillimetre wavelengths

The most massive haloes at high redshift are expected, according to hierarchical cosmologies, to reside in the most biased density fields. If powerful active galactic nuclei (AGN) are expected to exist anywhere in the early Universe (z > 5), it is within these massive haloes. The most luminous of these AGN, powered by supermassive black holes (SMBHs)�10 9 M⊙, thereby present an opportunity to test models of galaxy formation. Here, we present submillimetre (submm) continuum images of the fields of three lumin ous quasars at z > 5, obtained at 850 and 450µm using the Submm Common-User Bolometer Array (SCUBA) on theJames Clerk Maxwell Telescope (JCMT). N-body simulations predict that such quasars evolve to become the central dominant galaxies of massive clusters at z = 0, but at z = 5 6 they are actively forming stars and surrounded by a rich proto-filame ntary structure of young galaxies. Our purpose in taking these images was to search for other luminous, star-forming galaxies in the vicinity of the signpost AGN and thus associated with such a protocluster. Two of the quasar host galaxies are luminous SMGs in their own right, implying star-formation rates (SFRs) �10 3 M⊙ yr −1 . Despite the coarse 850-µm beam of the JCMT, our images show evidence of extended emission on a scale of �100-kpc from at least one quasar ‐ indicative of a partially resolved merger or a colossal host galaxy. In addi tion, at >3� significance we detect 12 (5) submm galaxies (SMGs) at 850µm (450µm) in the surrounding fields. Number counts of these SMGs are comparable with those detected in the fields of z � 4 radio galaxies, and both samples are systematically overabundant relative to blank-field submm surveys. Whilst the redshift-sensitive 850 µm/450µm and 850µm/1.4 GHz flux density ratios indicate that some of these SMGs are likely foreground objects, the counts suggest that many probably lie in the same large-scale structures as the quasars.

High-resolution radio observations of submillimetre galaxies

We have produced sensitive, high-resolution radio maps of 12 submillimetre (submm) galaxies (SMGs) in the Lockman Hole using combined Multi-Element Radio Linked Interferometer Network (MERLIN) and Very Large Array (VLA) data at a frequency of 1.4 GHz. Integrating for 350 h yielded an rms noise of 6.0 μJy beam−1 and a resolution of 0.2–0.5 arcsec. For the first time, wide-field data from the two arrays have been combined in the (u, v) plane and the bandwidth smearing response of the VLA data has been removed. All of the SMGs are detected in our maps as well as sources comprising a non-submm luminous control sample. We find evidence that SMGs are more extended than the general μJy radio population and that therefore, unlike in local ultraluminous infrared galaxies (ULIRGs), the starburst component of the radio emission is extended and not confined to the galactic nucleus. For the eight sources with redshifts we measure linear sizes between 1 and 8 kpc with a median of 5 kpc. Therefore, they are in general larger than local ULIRGs which may support an early-stage merger scenario for the starburst trigger. X-rays betray active galactic nuclei (AGN) in six of the 33 sources in the combined sample. All but one of these are in the control sample, suggesting a lower incidence of AGN amongst the submm-luminous galaxies which is, in turn, consistent with increased X-ray absorption in these dust-obscured starbursts. Only one of our sources is resolved into multiple, distinct components with our high-resolution data. Finally, compared to a previous study of faint radio sources in the GOODS-N field we find systematically smaller source sizes and no evidence for a tail extending to ∼4 arcsec. Possible reasons for this are discussed.

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - V. Submillimetre properties of near-infrared-selected galaxies in the Subaru/XMM-Newton deep field

We have studied the submillimetre (submm) properties of the following classes of near‐infrared‐selected (NIR‐selected) massive galaxies at high redshifts: BzK‐selected star‐forming galaxies (BzKs); distant red galaxies (DRGs); and extremely red objects (EROs). We used the SCUBA HAlf Degree Extragalactic Survey (SHADES), the largest uniform submm survey to date. Partial overlap of SIRIUS/NIR images and SHADES in Subaru/XMM–Newton deep field has allowed us to identify four submm‐bright NIR‐selected galaxies, which are detected in the mid‐IR, 24μ m, and the radio, 1.4GHz. We find that all of our submm‐bright NIR‐selected galaxies satisfy the BzK selection criteria, i.e. BzK≡ (z−K)AB− (B−z)AB≥−0.2, except for one galaxy whose B−z and z−K colours are however close to the BzK colour boundary. Two of the submm‐bright NIR‐selected galaxies satisfy all of the selection criteria we considered, i.e. they belong to the BzK–DRG–ERO overlapping population, or ‘extremely red’BzKs. Although these extremely red BzKs are rare (0.25 arcmin−2), up to 20 per cent of this population could be submm galaxies. This fraction is significantly higher than that found for other galaxy populations studied here. Via a stacking analysis, we have detected the 850‐μ m flux of submm‐faint BzKs and EROs in our SCUBA maps. While the contribution of z∼ 2 BzKs to the submm background is about 10–15 per cent and similar to that from EROs typically at z∼ 1, BzKs have a higher fraction (∼30 per cent) of submm flux in resolved sources compared with EROs and submm sources as a whole. From the spectral energy distribution (SED) fitting analysis for both submm‐bright and submm‐faint BzKs, we found no clear signature that submm‐bright BzKs are experiencing a specifically luminous evolutionary phase, compared with submm‐faint BzKs. An alternative explanation might be that submm‐bright BzKs are more massive than submm‐faint ones.

The SCUBA HAlf Degree Extragalactic Survey - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies

Determining an accurate position for a submillimetre (submm) galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample – source counts and 2D clustering – to an assessment of their detailed, multiwavelength properties, their contribution to the history of cosmic star formation and their links with present-day galaxy populations. In this paper, we identify robust radio and/or infrared (IR) counterparts, and hence accurate positions, for over two-thirds of the SCUBA HAlf-Degree Extragalactic Survey (SHADES) Source Catalogue, presenting optical, 24-μm and radio images of each SMG. Observed trends in identification rate have given no strong rationale for pruning the sample. Uncertainties in submm position are found to be consistent with theoretical expectations, with no evidence for significant additional sources of error. Employing the submm/radio redshift indicator, via a parametrization appropriate for radio-identified SMGs with spectroscopic redshifts, yields a median redshift of 2.8 for the radio-identified subset of SHADES, somewhat higher than the median spectroscopic redshift. We present a diagnostic colour–colour plot, exploiting Spitzer photometry, in which we identify regions commensurate with SMGs at very high redshift. Finally, we find that significantly more SMGs have multiple robust counterparts than would be expected by chance, indicative of physical associations. These multiple systems are most common amongst the brightest SMGs and are typically separated by 2–6 arcsec, ~15–50/ sin i kpc at z∼ 2, consistent with early bursts seen in merger simulations.

The first appearance of the red sequence of galaxies in proto-clusters at 2 lsimzlsim 3

We explore the evolved galaxy population in the proto-clusters around four high-z radio galaxies at 2 ≤ z ≤ 3 based on wide-field near-infrared (NIR) imaging. Three of the four fields are known proto-clusters as demonstrated by overdensities of line-emitting galaxies at the same redshifts as the radio galaxies found by narrow-band surveys and spectroscopic follow-up observations. We imaged the fields of three targets (PKS 1138-262, USS 0943-242 and MRC 0316-257) to a depth of K s ∼ 22 (Vega magnitude, 5σ) over a 4 x 7 arcmin 2 area centred on the radio galaxies with a new wide-field NIR camera, Multi-Object Infra-Red Camera and Spectrograph (MOIRCS), on the Subaru Telescope. Another target (USS 1558-003) was observed with Son of ISAAC on the New technology Telescope (NTT) to a depth of K s = 20.5 (5σ) over a 5 x 5 arcmin 2 area. We apply colour cuts in J-K s and/or JHK s in order to exclusively search for galaxies located at high redshifts: z > 2. To the 5σ limiting magnitudes, we see a significant excess of NIR-selected galaxies by a factor of 2 to 3 compared to those found in the field of GOODS-South. The spatial distribution of these NIR-selected galaxies is not uniform and traces structures similar to those of emission-line galaxies, although the samples of NIR-selected galaxies and emitters show little overlap, from which we conclude that the former tend to be an evolved population with much higher stellar mass than the latter, young and active emitters. We focus on the NIR colour-magnitude sequence of the evolved population and find that the bright-end (M stars > 10 11 M ⊙ ) of the red sequence is well populated by z ∼ 2 but much less so in the z ∼ 3 proto-clusters. This may imply that the bright-end of the colour-magnitude sequence first appeared between z = 3 and 2, an era coinciding with the appearance of sub-mm galaxies and the peak of the cosmic star formation rate. Our observations show that during the same epoch, massive galaxies are forming in high-density environments by vigorous star formation and assembly.

The SCUBA Half Degree Extragalactic Survey - IV. Radio-mm-FIR photometric redshifts

We present the redshift distribution of the Submillimetre Common-User Bolometer Array (SCUBA) Half Degree Survey (SHADES) galaxy population based on the rest-frame radio–mm–far-infrared (FIR) colours of 120 robustly detected 850 μm sources in the Lockman Hole East (LH) and Subaru XMM–Newton Deep Field (SXDF). The redshift distribution derived from the full spectral energy distribution (SED) information is shown to be narrower than that determined from the radio–sub-mm spectral index, as more photometric bands contribute to a higher redshift accuracy. The redshift distribution of sources derived from at least two photometric bands peaks at z≈ 2.4 and has a near-Gaussian distribution, with 50 per cent (interquartile range) of sources at z= 1.8–3.1 . We find a statistically significant difference between the measured redshift distributions in the two fields; the SXDF peaking at a slightly lower redshift (median z ≈ 2.2 ) than the LH (median z ≈ 2.7 ), which we attribute to the noise properties of the radio observations. We demonstrate, however, that there could also be field-to-field variations that are consistent with the measured differences in the redshift distributions and, hence, that the incomplete area observed by SHADES with SCUBA, despite being the largest sub-mm survey to date, may still be too small to fully characterize the bright sub-mm galaxy population. Finally, we present a brief comparison with the predicted, or assumed, redshift distributions of sub-mm galaxy formation and evolution models, and we derive the contribution of these SHADES sources and the general sub-mm galaxy population to the star formation rate density at different epochs.

EROs found behind lensing clusters

Context. On the nature, redshift, stellar populations and dust properties of optically faint or non-detected extremely red objects. Aims. Determining the nature, redshift, stellar populations and dust properties of optically faint or non-detected, extremely red objects (ERO) found from our survey of the lensing clusters A1835 and AC114 (Richard et al. 2006, A&A, 456, 861). Comparison with properties of related galaxies, such as IRAC selected EROs and a z ~ 6.5 post-starburst galaxy candidate from the Hubble Ultra Deep Field. Methods. Using an updated version of Hyperz (Bolzonella et al. 2000, A&A, 363, 476) and a large number of spectral templates we perform broad-band SED fitting. The photometric observations, taken from Hempel et al. (2007, A&A, submitted), include deep optical, ACS/HST, ISAAC/VLT, IRAC/Spitzer data, and for some objects 24 m MIPS/Spitzer and sub-mm data as well. Results. For most of the lensed EROs we find photometric redshifts showing a strong degeneracy between low-z (z ~ 1-3) and high-z (z ~ 6-7). Although formally best fits are often found at high-z, their resulting bright absolute magnitudes, the number density of these objects, and in some cases Spitzer photometry or longer wavelength observations, suggest strongly that all of these objects are at low-z. The majority of these objects are best fitted with relatively young (≲0.5-0.7 Gyr) and dusty starbursts. Three of our objects show indications for strong extinction, with A_V ~ 2.4-4. The typical stellar masses of our objects are M_* ~ (0.5-5) × 10^(10) M_☉ after correction for lensing; for the most extreme ERO in our sample, the sub-mm galaxy SMMJ14009+0252 most likely at z_(fit) ~ 3, we estimate M_* ~ 6. × 10^(11) M_☉. For dusty objects star formation rates (SFR) have been estimated from the bolometric luminosity determined after fitting of semi-empirical starburst, ERO, and ULIRG templates.Typically we find SFR ~ (1-18) M_☉ yr^(-1). Again, SMMJ14009+0252 stands out as a LIRG with SFR ~ 1000 M_☉ yr^(-1). Finally, we predict the mid-IR to sub-mm SED of the dusty objects for comparison with future observations with APEX, Herschel, and ALMA. Concerning the comparison objects, we argue that the massive post-starburst z ~ 6.5 galaxy candidate HUDF-J2 showing observed properties very similar to our EROs, is more likely a dusty starburst at z ~ 2.3-2.6. This interpretation also naturally explains the observed 24 m emission from this object and we predict its IR to sub-mm SED. Both empirically and from our SED fits we find that the IRAC selectec EROs from Yan et al. (2004, ApJ, 616, 63) show very similar properties to our lensed EROs. Reasonable fits are found for most of them with relatively young and dusty stellar populations.

Sub-millimetre properties of massive star-forming galaxies at z ~ 2 in SHADES/SXDF

AbstractWe study the submillimetre (submm) properties of the following near-infrared (NIR)-selected massive galaxies at high redshifts: BzK-selected star-forming galaxies (BzKs), distant red galaxies (DRGs) and extremely red objects (EROs). We used the SCUBA HAlf Degree Extragalactic Survey (SHADES), the largest uniform submm survey to date. Since BzKs are expected to include obscured star-forming galaxies at 1.4 &lt; z &lt; 2.5, it is possible that the submm galaxies are a sub-group of BzKs. We identified 4 BzKs as submm galaxies within 93 arcmin2 by using high resolution radio images. This indicates that only ~20% of submm galaxies are BzKs. However, this fraction is consistent with the assumption that the most of submm galaxies at 1.4 &lt; z &lt; 2.5 are BzKs, considering the redshift distribution, radio-detection rate and observed K-band magnitudes of submm galaxies. We found no submm detections for EROs which are clearly non-BzKs. We identify two submm-bright NIR-selected galaxies, which satisfy all the selection criteria we adopt; i.e. they belong to the BzK-DRG-ERO overlapping population, or ‘extremely red’ BzKs. Although these extremely red BzKs are rare (0.25 arcmin−2), about 10% of this population could be submm galaxies. With a stacking analysis, we detected the 850-μm flux of submm-faint BzKs and EROs in our SCUBA maps. While the contribution from BzKs at z ~ 2 to submm background is about 10–15% and similar to that from EROs typically at z ~ 1, BzKs have a higher fraction (~30%) of submm flux in resolved sources than EROs and submm sources as a whole do. Therefore, submm flux of BzKs seems to be biased high. From the SED fitting using an evolutionary model of starbursts with radiative transfer, submm-bright BzKs are found to have the stellar mass of &gt;5 × 1010M⊙ with the luminosity of &gt;3 × 1012L⊙. From an average SED of submm-faint BzKs having similar B − z and z − K colours to submm-bright ones, we suggest that submm-bright BzKs are more massive than submm-faint ones.

New submillimeter diagnostics of physical properties of ISM in high redshift galaxies

AbstractWe present a new diagnosis method for determining physical properties of star-forming gas in high-z galaxies. In this method, we employed three key observational quantities, [CI], CO, and FIR luminosities, including our new detections of CO J = 4–3 emission from the pure-starburst (non-AGN) submm galaxy SMM J14011+0252 (z = 2.6) and the type-2 AGN IRAS FSC 10214+4724 (z = 2.3) obtained with the Nobeyama Millimeter Array (NMA) at the Nobeyama Radio Observatory. These two sources have extremely high star formation rate, and exhibit strong emission of CO and [CI] 609 μm lines. We determined ISM physical conditions for the two objects and another three high-z quasars in order to investigate the relationship between their ISM and power sources (i.e., massive star formation or AGN). A new PDR analysis (Wolfire et al. 2005, private communication) using CO, [CI], and FIR on five high-z sources provides new evidence that AGN host galaxies harbor denser (log nH ~ 5–6) ISM exposed to stronger far-UV fluxes of log G0 ~ 3.5–4 than the non-AGN submm galaxy. Volume filling factors of the star-forming dense gas in the AGN hosts are an order of magnitude smaller than that of the pure-starburst submm galaxy. This suggests that, in these AGN hosts, dense molecular clouds are dominating the central kpc around AGN, triggering extensive circumnuclear starbursts, and possibly feeding their central supermassive black hole simultaneously.

Star Formation Through Cosmic Time

AbstractThis paper reviews the star formation history of the Universe, from the first stars to the current day, with emphasis on the critical analysis of the techniques that have been used to determine it, especially considering the role of dust. We consider the first population of stars, the Population III stars, were formed at redshifts ranging as high asz~ 60, the formation of the Globular Clusters, the main epoch of galaxy formation. In the sub-mm galaxies and high-redshift radio galaxies the collapse of massive galaxies was surprisingly rapid, and that the growth of super-massive black holes at their centers provides the energy input to eject the galactic interstellar medium while at the same time precipitating a final burst of star formation and the ejection of their ISM so that the subsequent evolution of these galaxies is passive.

HCN Observations of Submillimeter Galaxies and QSOs at High Redshift

We have conducted sensitive HCN(1-0) line observations of four high redshift submillimeter (sub-mm) galaxies and QSOs with the VLA. Although none is significantly detected in either line or continuum emission, thanks to the gravitational lens, sub-mm galaxy SMM J16359+6612 is marginally (at the 3-4σ level) detected once the three lensed components are stacked up. The HCN source appears to be double with a separation of ~1.5'', consistent with what has been implied from other observations. This first possible HCN detection of a submm galaxy, and three stringent HCN upper limits, combined with previous HCN detections and upper limits strongly constrain the HCN/CO ratios at high-z to be comparable to that of local ULIRGs.

Searching for a gigamaser in APM-08279+5255, and other short stories

Bolometer arrays on large antennas at high, dry sites have unveiled a dusty population of massive, luminous galaxies - submillimetre galaxies, or SMGs - which make a significant contribution to the star formation rate density at z > 1. The most crucial piece of information required to derive the history of obscured star formation is the redshift distribution of this galaxy population, N(z), which breaks degeneracies in the models and allows the mass and dynamics of the galaxies to be explored via high-resolution three-dimensional imaging in CO and by determining their level of clustering. Many SMGs are extremely faint, optically; some have no plausible counterparts, even in the infrared (IR), making the determination of an unbiased N(z) very difficult. The arrival of the Herschel Space Observatory and next-generation ground-based submm cameras will likely exacerbate this so-called redshift deadlock. Here, we report the first test of a new method for determining redshifts, based on the observed dependence of maser and IR luminosities. We have searched the dusty, lensed, hyperluminous quasar, APM 08279+5255, for the 1612-, 1665- and 1667-MHz hydroxyl lines as well as the 22-GHz water line. At z = 3.9, these are shifted to 329, 340 and 4538 MHz. Our relatively shallow test data reveal no convincing maser activity, but we set a meaningful constraint on the OH maser luminosity and we approach the expected thermal noise levels, meaning progress is possible. As an aside, we present deep new submm and radio imaging of this field. Using a simple shift-and-add technique, we uncover a new submm galaxy, conceivably at the redshift of APM 08279+5255.

The Hubble Deep Field-North SCUBA Super-map - IV. Characterizing submillimetre galaxies using deep Spitzer imaging

We present SEDs, Spitzer colours, and IR luminosities for 850 micron selected galaxies in the GOODS-N field. Using the deep Spitzer Legacy images and new data and reductions of the VLA-HDF radio data, we find statistically secure counterparts for 60 per cent (21/35) of our submm sample, and identify tentative counterparts for another 12 objects. This is the largest sample of submm galaxies with statistically secure counterparts detected in the radio and with Spitzer. We find that in most cases the 850 micron emission is dominated by a single 24 micron source. A composite rest-frame SED shows that the submm sources peak at longer wavelengths than those of local ULIRGs of the same luminosity and therefore appear to be cooler. The SEDs of submm galaxies are also different from those of their high redshift neighbours, the near-IR selected BzK galaxies, whose mid-IR to radio SEDs are more like those of local ULIRGs. Using 24 micron. 850 micron and 1.4 GHz observations, we fit templates that span the mid-IR through radio to derived the integrated IR luminosity of the submm galaxies. By themselves, 24 micron and radio fluxes are able to predict LIR reasonably well because they are relatively insensitive to temperature. However, the submm flux by itself consistently overpredicts LIR when using spectral templates which obey the local ULIRG temperature-luminosity relation. The shorter Spitzer wavelengths sample the stellar bump at the redshifts of the submm sources, and we find that the Spitzer photometry alone provides a model independent estimate of the redshift. Using X-ray and mid-IR data, only 5 per cent of our secure counterparts show strong evidence for an active galactic nucleus dominating the IR luminosity.

Millimetric properties of gamma-ray burst host galaxies

We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of gamma-ray bursts (GRBs), obtained using the Max Planck Millimetre Bolometer (MAMBO2) array and Submillimetre Common-User Bolometer Array (SCUBA). These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as likely candidate submm galaxies: the extremely red (R−K≈ 5) host of GRB 030115, and the extremely faint (R > 29.5) host of GRB 020124. Neither of these galaxies is detected, but the deep upper limits for GRB 030115 impose constraints on its spectral energy distribution, requiring a warmer dust temperature than is commonly adopted for submillimetre galaxies (SMGs). As a framework for interpreting these data, and for predicting the results of forthcoming submm surveys of Swift-derived host samples, we model the expected flux and redshift distributions based on luminosity functions of both submm galaxies and GRBs, assuming a direct proportionality between the GRB rate density and the global star formation rate density. We derive the effects of possible sources of uncertainty in these assumptions, including (1) introducing an anticorrelation between GRB rate and the global average metallicity, and (2) varying the dust temperature.

On the cross-correlation of sub-mm sources and optically selected galaxies

Bright submillimetre (sub-mm) galaxies are expected to arise in massive highly biased haloes, and hence exhibit strong clustering. We argue that a valuable tool for measuring these clustering properties is the cross-correlation of sub-mm galaxies with faint optically selected sources. We analyse populations of sub-mm detected and optical galaxies in the Great Observatories Origins Deep Survey-North (GOODS-N) survey area. Using optical/infrared photometric-redshift information, we search for correlations induced by two separate effects: (i) cosmic magnification of background sub-mm sources by foreground dark matter haloes traced by optical galaxies at lower redshifts and (ii) galaxy clustering due to sub-mm and optical sources tracing the same population of haloes where their redshift distributions overlap. Regarding cosmic magnification, we find no detectable correlation. Our null result is consistent with a theoretical model for the cosmic magnification, and we show that a dramatic increase in the number of sub-mm sources will be required to measure the effect reliably. Regarding clustering, we find evidence at the 3.5σ level for a cross-correlation between sub-mm and optical galaxies analysed in identical photometric redshift slices. The data hint that the sub-mm sources have an enhanced bias parameter compared to the optically selected population (with a significance of 2σ). The next generation of deep sub-mm surveys can potentially perform an accurate measurement of each of these cross-correlations, adding a new set of diagnostics for understanding the development of massive structure in the Universe.