arXiv subjects

Steve Eales

Publications and source records attributed to Steve Eales.

34 records · Page 2Linked to original sources

arXiv2003

The Subillimeter Properties of Extremely Red Objects in the CUDSS Fields

We discuss the submillimeter properties of Extremely Red Objects (EROs) in the two Canada-UK Deep Submillimeter Survey (CUDSS) Fields. We measure the mean submillimeter flux of the ERO population (to K < 20.7) and find 0.4 +/- 0.07 mJy for EROs selected by (I-K) > 4.0 and 0.56 +/- 0.09 mJy for EROs selected by (R-K) > 5.3 but, these measurements are dominated by discrete, bright submillimeter sources. We estimate that EROs produce 7-11% of the far-infrared background at 850um. This is substantially less than a previous measurement by Wehner, Barger & Kneib (2002) and we discuss possible reasons for this discrepancy. We show that ERO counterparts to bright submillimeter sources lie within the starburst region of the near-infrared color-color plot of Pozzetti & Mannucci (2000). Finally, we claim that pairs or small groups of EROs with separations of < 10 arcseconds often mark regions of strong submillimeter flux.

astro-ph↗

arXiv2003

The Canada-UK Deep Submillimeter Survey VII: Optical and near-infrared identifications for the 14h field

We present the multi-wavelength identifications for 23 sources in the Canada-UK Deep Submillimeter Survey (CUDSS) 14h field. The identifications have been selected on the basis of radio and near-infrared data and we argue that, to our observational limits, both are effective at selecting the correct counterparts of the SCUBA sources. We discuss the properties of these identifications and find that they are very red in near-infrared color, with many classified as Extremely Red Objects, and show disturbed morphologies. Using the entire CUDSS catalogue of 50 sources we use a combination of spectroscopic redshifts (4 objects), 1.4GHz-to-850um flux ratio redshift estimates (10 objects), and redshift lower-limits based on non-detections at 1.4GHz (the rest of the sample) to estimate a lower-limit on the median redshift of the population of z_med > 1.4. Working from simple models and using the properties of the secure identifications, we discuss general and tentative constraints on the redshift distribution and the expected colors and magnitudes of the entire population.

astro-ph↗

arXiv2003

SCUBA Observations of MAMBO Sources

We have observed 23 sources from the MAMBO 1200 micron survey with SCUBA at 850 microns, detecting 19 of the sources. The sources generally have low values for the ratio of 850 micron to 1200 micron flux. Two possible explanations for the low values are either that the sources are at very high redshift or that the global properties of the dust in the MAMBO sources are different from the global properties of dust in low-redshift galaxies. If the former explanation is correct, we estimate that 15 of the MAMBO sources lie at z > 3.

astro-ph↗

arXiv2001

The mass of radio galaxies from low to high redshift

Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along with the complete 3CRR and 6CE sample we extend the radio galaxy K-z relation to z~4.5. The 6C* K-z data significantly improve delineation of the K-z relation for radio galaxies at high redshift (z >2). In a spatially flat universe with a cosmological constant (Omega_M=0.3 and Omega_Lambda=0.7), the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (~5L*), and a low dispersion (~0.5 mag) which formed their stars at epochs corresponding to z >~ 2.5.

astro-ph↗

arXiv2001

On the redshift cut-off for steep-spectrum radio sources

We use three samples (3CRR, 6CE and 6C*) selected at low radio frequency to constrain the cosmic evolution in the radio luminosity function (RLF) for the `most luminous' steep-spectrum radio sources. Although intrinsically rare, such sources give the largest possible baseline in redshift for the complete flux-density-limited samples currently available. Using parametric models to describe the RLF which incorporate distributions in radio spectral shape and linear size as well as the usual luminosity and redshift, we find that the data are consistent with a constant comoving space density between z~2.5 and z~4.5. We find this model is favoured over a model with similar evolutionary behaviour to that of optically-selected quasars (i.e. a roughly Gaussian distribution in redshift) with a probability ratio of ~25:1 and ~100:1 for spatially-flat cosmologies with Omega_Lambda = 0 and Omega_Lambda = 0.7 respectively. Within the uncertainties, this evolutionary behaviour may be reconciled with the shallow decline preferred for the comoving space density of flat-spectrum sources by Dunlop & Peacock (1990) and Jarvis & Rawlings (2000), in line with the expectations of Unified Schemes.

astro-ph↗

arXiv2001

A sample of 6C radio sources designed to find objects at redshift > 4: II --- spectrophotometry and emission line properties

(Abridged) This is the second in a series of three papers which present and interpret basic observational data on the 6C* 151-MHz radio sample: a low-frequency selected sample which exploits filtering criteria based on radio properties (steep spectral index and small angular size) to find radio sources at redshift z > 4 within a 0.133sr patch of sky. We present results of a programme of optical spectroscopy which has yielded redshifts in the range 0.5 < z < 4.4 for the 29 sources in the sample, all but six of which are secure. We find that the fil tering criteria used for 6C* are very effective in excluding the low-redshift, low-luminosity radio sources: the median redshift of 6C* is z~1.9 compared to z~1.1 for a complete sample matched in 151-MHz flux density. By combining the emission-line dataset for the 6C* radio sources with those for the 3CRR, 6CE and 7CRS samples we establish that z > 1.75 radio galaxies follow a rough proportionality between Lyalpha- and 151 MHz-luminosity which, like similar correlations seen in samples of lower-redshift radio sources, are indicative of a primary link between the power in the source of the photoionising photons (most likely a hidden quasar nucleus) and the power carried by the radio jets. We argue that radio sources modify their environments and that the range of emission-line properties seen is determined more by the range of source age than by the range in ambient environment. This is in accord with the idea that all high-redshift, high-luminosity radio sources are triggered in similar environments, presumably recently collapsed massive structures.

astro-ph↗

arXiv2001

A sample of 6C radio sources designed to find objects at redshift > 4: III --- imaging and the radio galaxy K-z relation

In this paper, the third and final of a series, we present complete K-band imaging and some complementary I-band imaging of the filtered 6C* sample. We find no systematic differences between the K-z relation of 6C* radio galaxies and those from complete samples, so the near-infrared properties of luminous radio galaxies are not obviously biased by the additional 6C* radio selection criteria (steep spectral index and small angular size). The 6C* K-z data significantly improve delineation of the K-z relation for radio galaxies at high-redshift (z >2). Accounting for non-stellar contamination, and for correlations between radio luminosity and stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z >2. In a particular spatially-flat universe with a cosmological constant, the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (~5 Lstar), and a low dispersion (sigma ~ 0.5 mag) which formed their stars at epochs corresponding to z >~2.5. This result is in line with recent sub-mm studies of high-redshift radio galaxies and the inferred ages of extremely red objects from faint radio samples.

astro-ph↗

arXiv2001

The radio galaxy K-z relation to z ~ 4.5

Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along with the complete 3CRR and 6CE sample we extend the radio galaxy K-z relation to z~4.5. The 6C* K-z data significantly improve delineation of the K-z relation for radio galaxies at high redshift (z > 2). Accounting for non-stellar contamination, and for correlations between radio luminosity and estimates of stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z > 2. This indicates that we are not probing into the formation epoch until at least z > 3.

astro-ph↗

arXiv2000

A sample of 6C radio sources with virtually complete redshifts. II - optical spectroscopy

This is the second of two papers presenting basic observational data on the 6CE sample of extragalactic radio sources. It presents the results of optical spectroscopy which has yielded virtually complete redshift information for the 6CE sample: 56 of the 59 sample members have spectroscopic redshifts which, with the exception of seven cases, are secure. The redshift distribution N(z) is fairly flat over the redshift range 0 < z < 2, with a median redshift of 1.1 and a high-redshift tail reaching to z = 3.4. The highest-redshift (z > 1.75) members of the 6CE sample have similar optical spectra and a tight (less than one dex) spread in narrow-Lyalpha emission line luminosity.

astro-ph↗

arXiv1999

No evidence for a `redshift cut-off' for the most powerful classical double radio sources

We use three samples (3CRR, 6CE and 6C*) to investigate the radio luminosity function (RLF) for the `most powerful' low-frequency selected radio sources. We find that the data are well fitted by a model with a constant co-moving space density at high redshift as well as by one with a declining co-moving space density above some particular redshift. This behaviour is very similar to that inferred for steep-spectrum radio quasars by Willott et al (1998) in line with the expectations of Unified Schemes. We conclude that there is as yet no evidence for a `redshift cut-off' in the co-moving space densities of powerful classical double radio sources, and rule out a cut-off at z < 2.5.

astro-ph↗

arXiv1998

The Angular Correlation Function and Hierarchical Moments of 70000 Faint Galaxies to R=23.5

We investigate the angular correlation function, omega(theta), and third and fourth-order hierarchical moments of a survey with approx. 70000 faint galaxies detected on a total area 1.74 sq. deg. to a limit of R=23.5. The omega(theta) amplitudes and scaling with magnitude limit are most consistent with approximately stable clustering (epsilon=0). On the larger of our fields, the amplitude of omega(theta) is significantly higher at 2-5 arcsec separations than at >5 arcsec, indicating an excess of physically close galaxy pairs above the number expected from omega(theta) seen at larger scales. This is consistent with the number of interacting galaxy pairs seen locally combined with a merger/interaction rate evolving as (1+z)^m with m=2.01_{-0.69}^{+0.52}. We also estimate the hierarchical moments s_3 and s_4 from the galaxy counts-in-cells. For 18.5<R<23.5 galaxies, these have relatively steep slopes (approximately -0.4 for s_3 and -0.6 for s_4), similar to the hierarchical moments of 17<B<20 galaxies in the EDSGCS at the same physical scales, and show only a small reduction in normalization relative to the shallower survey. This implies that there is little change in the mean linear or non-linear biasing of the galaxy distribution out to z=1.

astro-ph↗

arXiv1998

Modelling ISO Galaxy Counts with Luminosity and Merger Rate Evolution

We model galaxy evolution in the 6.75 and 15 micron passbands of the ISO satellite, by combining models of galaxy evolution at optical wavelengths (which are consistent with the optical galaxy counts) with observed spectral energy distributions in the infra-red. Our model is consistent with the local 12 micron galaxy luminosity, if 3.5 per cent of spirals at z=0 are in interacting pairs with mid-infra-red luminosities enhanced by major starbursts. Source counts from deep ISO surveys exceed non-evolving predictions but are more consistent with our evolving model. The steep number count of 6.75 micron sources appears to be explained primarily by evolving early-type galaxies, whereas at 15 microns the main contributors are star-forming spirals and starbursting interacting/merging galaxies. The 31 per cent of 15 micron sources which are visibly interacting galaxies have high mid-infra-red/optical flux ratios indicating major starbursts combined with dust extinction. The numbers and high mean redshift of these sources suggest the merger-starbursts are increasing in luminosity with redshift, approximately as (1+z)^2, in addition to undergoing (1+z)^2 number evolution reflecting the optically observed increase with redshift in the fraction of interacting galaxies.

astro-ph↗

arXiv1998

The Angular Correlation Function of K=19.5 Galaxies and the Detection of a Cluster at z=0.775

On five K-band Omega camera images, covering a total of 162.2 sq. arcmin to K=19.5, we investigate (i) the clustering environment of 5 radio galaxies at 0.7 1.5) redshifts. We also find a significant excess of 1.5--5.0 arcsec separation pairs of galaxies compared to the expectation from the inward extrapolation of omega(theta). To K=19.5, we estimate that 11.0\pm 3.4 per cent of galaxies are in close pairs in excess of omega(theta). This can be explained if the local rate of galaxy mergers and interactions increases with redshift as $\sim (1+z)^m$ with $m=1.33_{-0.51}^{+0.36}$.

astro-ph↗

arXiv1998

Deep optical imaging of the field of PC1643+4631A&B, I: Spatial distributions and the counts of faint galaxies

We present deep optical images of the PC1643+4631 field obtained at the WHT. This field contains two quasars at redshifts z=3.79 & 3.83 and a cosmic microwave background (CMB) decrement detected with the Ryle Telescope. The images are in U,G,V,R and I filters, and are complete to 25th magnitude in R and G and to 25.5 in U. The isophotal galaxy counts are consistent with the results of Metcalde et al. (1996), Hogg et al. (1997), and others. We find an excess of robust high-redshift Ly-break galaxy candidates with 25.0<R<25.5 compared with the mean number found in the fields studied by Steidel et al. -we expect 7 but find 16 - but we do not find that the galaxies are concentrated in the direction of the CMB decrement. However, we are still not sure of the distance to the system causing the CMB decrement. We have also used our images to compare the commonly used object-finding algorithms of FOCAS and SExtractor: we find FOCAS the more efficient at detecting faint objects and the better at dealing with composite objects, whereas SExtractor's morphological classification is more reliable, especially for faint objects near the resolution limit. More generally, we have also compared the flux lost using isophotal apertures on a real image with that on a noise-only image: recovery of artificial galaxies from the noise-only image significantly overestimates the flux lost from the galaxies, and we find that the corrections made using this technique suffer a systematic error of some 0.4 magnitudes.

astro-ph↗

arXiv1997

Dust, gas and the evolutionary status of the radio galaxy, 8C1435+635, at z = 4.25

We present the results of new rest-frame far-IR observations of the z = 4.25 radio galaxy, 8C1435+635, which not only confirm that it contains an enormous quantity of dust (as first inferred from its mm-wave detection by Ivison 1995) but also allow the first meaningful constraints to be placed on the mass of this dust and associated gas. The new measurements consist of: (i) clear detections of sub-mm continuum emission at 450 and 850um obtained with the new sub-mm bolometer array, SCUBA, on the JCMT, (ii) continuum upper limits at 350, 750 and 175um obtained with SCUBA and the PHT far-IR camera aboard ISO, and (iii) a sensitive upper limit on the CO(4-3) line flux obtained with the IRAM 30-m MRT. The resulting rest-frame 33- to 238-um continuum coverage allows us to deduce that 2E8 Msun of dust at a temperature of 40 +/- 5 K is responsible for the observed mm/sub-mm emission. Using our CO upper limit, which constrains M(H2)/M(dust) to <950, we go on to calculate robust limits on the total gas reserves (H2 + HI) which are thereby constrained to between 4E10 and 1.2E12 Msun. The sub-mm properties of 8C1435+635 are thus strikingly similar to those of the z = 3.80 radio galaxy, 4C41.17, the only other high-redshift galaxy detected to date at sub-mm wavelengths whose properties appear not to be exaggerated by gravitational lensing (Dunlop et al. 1994; Hughes, Dunlop & Rawlings 1997). The inferred gas masses of both objects are sufficiently large to suggest that the formative starbursts of massive elliptical galaxies are still in progress at around z = 4. Observations of complete samples of radio galaxies spanning a range of redshifts and radio luminosities will be required to determine if the spectacular far-IR properties of 8C1435+635 and 4C41.17 are primarily due to their extreme redshifts or their extreme radio luminosities.

astro-ph↗

arXiv1996

Optical and infrared investigation towards the z=3.8 quasar pair PC1643+4631A&B

In a companion paper (Paper I: Jones et al. 1996) we report the discovery of a cosmic microwave background decrement, indicative of a distant cluster with mass ~10^{15} solar masses, towards the quasar pair PC1643+4631A&B (z=3.79,3.83, separation 198''). To search for the cluster responsible, we have obtained R-, J- and K-band images of the field and have also carried out optical spectroscopy of selected objects in it. No such cluster is evident in these images. Assuming the cluster causing the decrement is similar to massive clusters already known, our magnitude limits imply that it must lie about or beyond z=1. This provides independent support for the X-ray-based distance argument of Paper I. The cluster must gravitationally lens objects behind it; for a cluster z around 1-2, the Einstein-ring radius for sources at z ~= 3.8 is ~ 100''. Simple modelling, producing simultaneously the S-Z effect and the lensing, shows that the source positions of quasars A and B lie within ~10'' of each other and may indeed be coincident. The two quasar spectra are found to be remarkably similar apart from their one-percent redshift difference. Assuming A and B are images of a single quasar, we present a possible explanation of this difference.

astro-ph↗