Luminous starbursts in the redshift desert at z∼ 1-2: Star formation rates, masses and evidence for outflows

We present a spectroscopic catalogue of 40 luminous starburst galaxies at z= 0.7–1.7 (median z= 1.3). 19 of these are submillimetre galaxies (SMGs) and 21 are submillimetre-faint radio galaxies (SFRGs). This sample helps us to fill in the redshift desert at z= 1.2–1.7 in previous studies as well as to probe a lower luminosity population of galaxies. Radio fluxes are used to determine star formation rates for our sample which range from around 50–500 M⊙ yr−1 and are generally lower than those in z∼ 2 SMGs. We identify nebular [O ii] 3727 emission in the rest-UV spectra and use the linewidths to show that SMGs and SFRGs in our sample have larger linewidths and therefore dynamical masses than optically selected star-forming galaxies at similar redshifts. The linewidths are indistinguishable from those measured in the z∼ 2 SMG populations suggesting little evolution in the dynamical masses of the galaxies between redshift 1 and 2. [Ne v] and [Ne iii] emission lines are identified in a subset of the spectra indicating the presence of an active galactic nucleus (AGN). In addition, a host of interstellar absorption lines corresponding to transitions of Mg ii and Fe ii ions are also detected. These features show up prominently in composite spectra and we use these composites to demonstrate that the absorption lines are present at an average blueshift of −240 ± 50 km s−1 relative to the systemic velocities of the galaxies derived from [O ii]. This indicates the presence of large-scale outflowing interstellar gas in these systems. We do not find any evidence for differences in outflow velocities between SMGs and SFRGs of similar infrared luminosities. We find that the outflow velocities of z∼ 1.3 SMGs and SFRGs are consistent with the V∝ SFR0.3 local envelope seen in lower redshift ultraluminous infrared galaxies (ULIRGs). These observations are well explained by a momentum-driven wind model

A Hubble Space Telescope NICMOS and ACS morphological study of z similar to 2 submillimetre galaxies

We present a quantitative morphological analysis using Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer H160-band imaging and Advanced Camera for Surveys I775-band imaging of 25 spectroscopically confirmed submillimetre galaxies (SMGs) which have redshifts between Graphic (Graphic). Our analysis also employs a comparison sample of more typical star-forming galaxies at similar redshifts (such as Lyman-break Galaxies) which have lower far-infrared luminosities. This is the first large-scale study of the morphologies of SMGs in the near-infrared at ∼ 0.1 arcsec resolution (≲1 kpc). We find that the half-light radii of the SMGs (rh= 2.3 ± 0.3 and 2.8 ± 0.4 kpc in the observed I and H bands, respectively) and asymmetries are not statistically distinct from the comparison sample of star-forming galaxies. However, we demonstrate that the SMG morphologies differ more between the rest-frame UV and optical bands than typical star-forming galaxies and interpret this as evidence for structured dust obscuration. We show that the composite observed H-band light profile of SMGs is better fitted with a high Sersic index (n∼ 2) than with an exponential disc suggesting the stellar structure of SMGs is best described by a spheroid/elliptical galaxy light distribution. We also compare the sizes and stellar masses of SMGs to local and high-redshift populations and find that the SMGs have stellar densities which are comparable to (or slightly larger than) local early-type galaxies and comparable to luminous, red and dense galaxies at z∼ 1.5 which have been proposed as direct SMG descendants, although the SMG stellar masses and sizes are systematically larger. Overall, our results suggest that the physical processes occurring within the galaxies are too complex to be simply characterized by the rest-frame UV/optical morphologies which appear to be essentially decoupled from all other observables, such as bolometric luminosity, stellar or dynamical mass

Extremely red objects in the UKIDSS Uultra Deep Survey Early Data Release

We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM–Newton Deep Field. We find a total of 3715 objects over 2013 arcmin2 with R−K > 5.3 and K≤ 20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that active galactic nuclei are more prevalent among the passive ERO population

The evolution of the near-infrared galaxy luminosity function and colour bimodality up to z similar or equal to 2 rom the UKIDSS Ultra Deep Survey Early Data Release

We present new results on the cosmological evolution of the near-infrared (near-IR) galaxy luminosity function (LF), derived from the analysis of a new sample of similar to 22000K(AB) <= 22.5 galaxies selected over an area of 0.6 deg(2) from the Early Data Release of the UKIDSS Ultra Deep Survey (UDS). Our study has exploited the multiwavelength coverage of the UDS field provided by the new UKIDSS WFCAM K- and J- band imaging, the Subaru/XMM-Newton Deep Survey and the SpitzerWide-Area Infrared Extragalactic survey. The unique combination of large area and depth provided by this newsurvey minimizes the complicating effect of cosmic variance and has allowed us, for the first time, to trace the evolution of the brightest sources out to z similar or equal to 2 with good statistical accuracy.In agreement with previous studies, we find that the characteristic luminosity of the near-IR LF brightens by similar or equal to 1 mag between z = 0 and z similar or equal to 2, while the total density decreases by a factor of similar or equal to 2. Using the rest-frame (U - B) colour to split the sample into red and blue galaxies, we confirm the classic luminosity-dependent colour bimodality at z less than or similar to 1. However, the strength of the colour bimodality is found to be a decreasing function of redshift, and seems to disappear by z greater than or similar to 1.5. Due to the large size of our sample, we are able to investigate the differing cosmological evolution of the red and blue galaxy populations. It is found that the space density of the brightest red galaxies (MK <= - 23) stays approximately constant with redshift, and that these sources dominate the bright end of the LF at redshifts z less than or similar to 1. In contrast, the brightening of the characteristic luminosity and mild decrease in space density displayed by the blue galaxy population leads them to dominate the bright end of the LF at redshifts z greater than or similar to 1

High-resolution CO and radio imaging of z similar to 2 ULIRGs: extended CO structures and implications for the universal star formation law

We present high spatial resolution (0.4 arcsec, Graphic kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at Graphic: two submillimetre galaxies (SMGs) and one submillimetre faint star-forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either 12CO (J= 4Graphic3) or 12CO (J= 3Graphic2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of Graphic2) for intermediate-excitation CO emission in Graphic ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3 arcsec) combined Multi-Element Radio-Linked Interferometer Network-Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This ‘matched beam’ approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt–Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high-z star-forming galaxies

The SCUBA-2 Cosmology Legacy Survey: The clustering of submillimetre galaxies in the UKIDSS UDS field

Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850 μm) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes (Mhalo > 1013 M⊙) at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift

The SCUBA-2 Cosmology Legacy Survey: the clustering of submillimetre galaxies in the UKIDSS UDS field

Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850 μm) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes (Mhalo > 1013 M⊙) at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift.ISSN:0035-8711ISSN:1365-296

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, Graphic at z∼ 2, consistent with early bursts seen in merger simulations