Rob J. Ivison

The SCUBA 8-mJy survey — I. Submillimetre maps, sources and number counts

We present maps, source lists and derived number counts from the largest, unbiased, extragalactic submillimetre (submm) survey so far undertaken with the SCUBA camera on the James Clerk Maxwell Telescope (JCMT). Our maps are located in two regions of sky (ELAIS N2 and Lockman-Hole E) and cover 260arcmin2 , to a typical rms noise level of sigma 850 ~=2.5mJybeam-1 . We have reduced the data using both the standard JCMT surf procedures, and our own IDL -based pipeline which produces zero-footprint maps and noise images. The uncorrelated noise maps produced by the latter approach have enabled us to apply a maximum likelihood method to measure the statistical significance of each peak in our maps, leading to properly quantified errors on the flux density of all potential sources. We detect 19 sources with signal-to-noise ratios (S/N)>4, and 38 with S/N>3.5. To assess both the completeness of this survey and the impact of source confusion as a function of flux density, we have applied our source-extraction algorithm to a series of simulated images. The result is a new estimate of the submm source counts over the flux-density range S 850 ~=5-15mJy, which we compare with estimates derived by other workers, and with the predictions of a number of models. Our best estimate of the cumulative source count at S 850 >8mJy is per square degree. Assuming that the majority of sources lie at z >1.5, this result implies that the comoving number density of high-redshift galaxies forming stars at a rate in excess of 1000Msolar yr-1 is ~=10-5 Mpc-3 , with only a weak dependence on the precise redshift distribution. This number density corresponds to the number density of massive ellipticals with L >3-4L * in the present-day Universe , and is also the same as the comoving number density of comparably massive, passively evolving objects in the redshift band 1<z <2 inferred from recent surveys of extremely red objects. Thus the bright submm sources uncovered by this survey can plausibly account for the formation of all present-day massive ellipticals. Improved redshift constraints, and ultimately an improved measure of submm source clustering can refine or refute this picture.

HiZELS: a high‐redshift survey of Hα emitters – II. The nature of star‐forming galaxies at z= 0.84★

New results from a large survey of Hα emission-line galaxies at z = 0.84 using the Wide Field Camera on the United Kingdom Infrared Telescope and a custom narrow-band filter in the J band are presented as part of the High-z Emission Line Survey (HiZELS). The deep narrow-band images reach an effective flux limit of F Hα ∼ 10 -16 erg s -1 cm -2 in a comoving volume of 1.8 × 10 5 Mpc 3, resulting in the largest and deepest survey of its kind ever done at z ∼ 1. There are 1517 potential line emitters detected across ∼1.4 deg 2, of which 743 are selected as Hα emitters, based on their photometric and spectroscopic redshifts. These are then used to calculate the Hα luminosity function, which is well fitted by a Schechter function with L* = 10 42.26±0.05 erg s -1, φ* = 10 -1.92±0.10 Mpc -3 and α = -1.65 ± 0.15, and are used to estimate the volume average star formation rate (SFR) at z = 0.845, ρ SFR: 0.15 ± 0.01 M ⊙ yr -1 Mpc -3 (corrected for 15 per cent active galactic nucleus contamination and integrated down to 2.5 M ⊙ yr -1). These results robustly confirm a strong evolution of ρ SFR from the present day out to z ∼ 1 and then flattening to z ∼ 2 using a single star formation indicator: Hα luminosity. Out to z ∼ 1, both the characteristic luminosity and space density of the Hα emitters increase significantly; at higher redshifts, L* continues to increase, but φ* decreases. The z = 0.84 Hα emitters are mostly disc galaxies (82 ± 3 per cent), while 28 ± 4 per cent of the sample shows signs of merger activity; mergers account for ∼20 per cent of the total integrated ρ SFR at this redshift. Irregulars and mergers dominate the Hα luminosity function above L*, while discs are dominant at fainter luminosities. These results demonstrate that it is the evolution of normal disc galaxies that drives the strong increase in the SFR density from the current epoch to z ∼ 1, although the continued strong evolution of L* beyond z = 1 suggests an increasing importance of merger activity at higher redshifts.

The clustering, number counts and morphology of extremely red (R − K > 5) galaxies to K 21

Using K- and R-band imaging of the ELAIS N2 field, we investigate the number counts, clustering, morphology and radio/X-ray emission of extremely red objects (EROs), defined as galaxies with R − K > 5.0. This criterion will select old, passive ellipticals at z > 0.9. To K = 21 we identify a total of 158 EROs in 81.5 arcmin 2 . The ERO number counts are lower than predicted by pure luminosity evolution models, but higher than predicted by current cold dark matter-based hierarchical models. The ERO counts are consistent with a non-evolving model and also with a luminosity evolution model incorporating moderate merging and a decrease with redshift in the comoving number density of passive galaxies (‘M-DE’). We investigate the clustering of the EROs by calculating their angular correlation function, ω(θ ), and obtain a >2σ detection of clustering at K =19‐20 limits. The ω(θ ) amplitude of these EROs is much higher than that of full K-limited samples of galaxies, and is best-fitted by models with a comoving correlation radius r 0 � 10‐13 h −1 Mpc. These results, which are in agreement with Daddi et al., suggest that the intrinsic clustering of at least the brighter EROs is even stronger than that of present-day giant ellipticals. We estimate seeing-corrected angular sizes and morphological types for a K 19.5 subsample of EROs (31 galaxies) and find a ∼3:2 mixture of bulge and disc profiles. Of these EROs ∼ 1 appear to be interacting, disturbed or otherwise irregular, and two are visible mergers. We find the angular sizes of the bulge-profile EROs are consistent with passively evolving ellipticals in the M-DE model, at the expected z ∼ 0.9‐2. The ERO mean radii are smaller than the non-evolving prediction, implying surface brightness evolution. Seven of the 31 bright EROs are detected as F(1.4GHz) 30 µJy radio sources in a VLA survey. The strongest, at 5 mJy, is also a Chandra X-ray detection, and lies at the centre of a significant overdensity of EROs ‐ it is probably an FRI radio galaxy in a z ∼ 1 cluster. Of the other, much fainter, sources, five are point-like and may be weak active galactic nuclei, while the sixth is elongated and aligned with the optical axis of an extended, low-surface brightness ERO, suggesting a powerful but dust-reddened starburst. A possible interpretation is discussed in which the EROs are a mixture of (i) ‘pEROs’, strongly clustered passively evolving giant ellipticals, formed at high redshifts, the oldest EROs and (ii) ‘dsfEROs’, dusty post-interaction galaxies, with a few active starbursts (ULIRGs), and less strongly clustered. With time, the younger dsfEROs are continually assimilated into the ERO class, diluting the clustering and increasing the comoving number density. Both types ultimately evolve into present-day early-type galaxies.

Detection of CO J = 1-0 in the z = 3.79 radio galaxy 4C 60.07

We report on the detection of the lowest CO J = 1−0 transition in the powerful high-redshift radio galaxy 4C 60.07 at z = 3.79. The CO emission is distributed in two spatially and kinematically distinct components as was previously known from the observations of the higher excitation CO J = 4−3 line. The total molecular gas mass in 4C 60.07 inferred from the CO J = 1−0 emission is M(H2) � 1.3 × 10 11 M� ,s ufficient to fuel the inferred star-formation rate of ∼1600 Myr −1 for 10 8 yrs. From our high-resolution CO J = 1−0 VLA maps we find the dynamical mass of 4C 60.07 to be comparable to that of a giant elliptical at the present time. A significant fraction of the mass is in the form of molecular gas suggesting that 4C 60.07 is in an early state of its evolution. The merging nature of 4C 60.07 along with its large dynamical mass imply that this system is a giant elliptical caught in its formative stages.

Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt

Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets. Collisions between such bodies produce small dust particles, the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals (Mg2−2xFe2xSiO4) has been done for the protoplanetary disk HDu2009100546 (refs 3, 4) and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids (xu2009≈u20090.29). In the cold outskirts of the βu2009Pictoris system, an analogue to the young Solar System, olivine crystals were detected but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets. Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of βu2009Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15–45 astronomical units from the star (one astronomical unit is the Sun–Earth distance), determine their magnesium-rich composition (x = 0.01u2009±u20090.001) and show that they make up 3.6u2009±u20091.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System, even though βu2009Pictoris is more massive and more luminous and has a different planetary system architecture.

Spectroscopic follow-up of a cluster candidate at z = 1.45

We have obtained deep optical spectroscopic data of the highest-redshift cluster candidate (z ∼ 1.4, CVB13) selected by Van Breukelen et al. in a photometric optical/infrared catalogue of the Subaru XMM‐Newton Deep Field. The data, which comprise 104 targeted galaxies, were taken with the DEep Imaging Multi-Object Spectrograph on the Keck 2 telescope and yielded 31 secure redshifts in the range 1.25 < z < 1.54 within a 7 × 4-arcmin 2 field centred on CVB13. Instead of one massive cluster at z = 1.4, we find evidence for three projected structures at z = 1.40, 1.45 and 1.48. The most statistically robust of these structures, at z = 1.454, has

Far-Infrared Characterization of an Ultraluminous Starburst Associated with a Massively Accreting Black Hole at z = 1.15

As part of the All-Wavelength Extended Groth Strip International Survey (AEGIS), we describe the panchromatic characterization of an X-ray–luminous active galactic nucleus (AGN) in a merging galaxy at z = 1.15. This object is detected at infrared (8, 24, 70, and 160 μm), submillimeter (850 μm), and radio wavelengths, from which we derive a bolometric luminosity Lbol ∼ 9 x 10^12 L☉. We find that the AGN clearly dominates the hot dust emission below 40 μm but its total energetic power inferred from the hard X-rays is substantially less than the bolometric output of the system. About 50% of the infrared luminosity is indeed produced by a cold dust component that probably originates from enshrouded star formation in the host galaxy. In the context of a coeval growth of stellar bulges and massive black holes, this source might represent a “transition” object, sharing properties with both quasars and luminous starbursts. Study of such composite galaxies will help address how the star formation and disk-accretion phenomena may have regulated each other at high redshift and how this coordination may have participated in the buildup of the relationship observed locally between the masses of black holes and stellar spheroids.

An unbiased survey of 500 nearby stars for debris disks: A JCMT legacy program

We present the scientific motivation and observing plan for an upcoming detection survey for debris disks using the James Clerk Maxwell Telescope. The SCUBA‐2 Unbiased Nearby Stars (SUNS) survey will observe 500 nearby main‐sequence and subgiant stars (100 of each of the A, F, G, K, and M spectral classes) to the 850 μm extragalactic confusion limit to search for evidence of submillimeter excess, an indication of circumstellar material. The survey distance boundaries are 8.6, 16.5, 22, 25, and 45 pc for M, K, G, F, and A stars, respectively, and all targets lie between the declinations of −40° to 80°. In this survey, no star will be rejected based on its inherent properties: binarity, presence of planetary companions, spectral type, or age. The survey will commence in late 2007 and will be executed over 390 hr, reaching 90% completion within 2 years. This will be the first unbiased survey for debris disks since the Infrared Astronomical Satellite. We expect to detect ~125 debris disks, including ~50 cold disks not detectable in current shorter wavelength surveys. To fully exploit the order of magnitude increase in debris disks detected in the submillimeter, a substantial amount of complementary data will be required, especially at shorter wavelengths, to constrain the temperatures and masses of discovered disks. High‐resolution studies will likely be required to resolve many of the disks. Therefore, these systems will be the focus of future observational studies using a variety of observatories, including Herschel, ALMA, and JWST, to characterize their physical properties. For nondetected systems, this survey will set constraints (upper limits) on the amount of circumstellar dust, of typically 200 times the Kuiper Belt mass, but as low as 10 times the Kuiper Belt mass for the nearest stars in the sample (≈2 pc).

AEGIS: A PANCHROMATIC STUDY OF IRAC-SELECTED EXTREMELY RED OBJECTS WITH CONFIRMED SPECTROSCOPIC REDSHIFTS

We study 87 extremely red objects (EROs), selected both to have color redder than R - [3.6] = 4.0 and to have confirmed spectroscopic redshifts. Together, these two constraints result in this sample populating a fairly narrow redshift range at 0.76 < z < 1.42. The key new ingredient included here is deep Spitzer Space Telescope Infrared Array Camera (IRAC) data. Based on [3.6] - [8.0] color, we demonstrate that it is possible to classify EROs as early-type galaxies, dusty starburst galaxies, or active galactic nuclei (AGNs; power-law types). We present ultraviolet-to-mid-infrared spectral energy distributions (SEDs) and Advanced Camera for Surveys (ACS) images, both of which support our simple IRAC color classification.

Bright Lyα emitters at z∼ 9: constraints on the LF from HizELS★

New results are presented, as part of the Hi-z Emission Line Survey (HiZELS), from the largest area survey to date (1.4 sq.deg) for Lyman-alpha emitters (LAEs) at z~9. The survey, which is primarily targeting H-alpha emitters at z 7 by Galactic brown dwarf stars is also examined, leading to the conclusion that such contamination may well be significant for searches at 7.7