George K. Miley

Distant Radio Galaxies and their Environments

We review the properties and nature of luminous high-redshift radio galaxies (HzRGs, z > 2) and the environments in which they are located. HzRGs have several distinct constituents which interact with each other—relativistic plasma, gas in various forms, dust, stars and an active galactic nucleus (AGN). These building blocks provide unique diagnostics about conditions in the early Universe. We discuss the properties of each constituent. Evidence is presented that HzRGs are massive forming galaxies and the progenitors of brightest cluster galaxies in the local Universe. HzRGs are located in overdense regions in the early Universe and are frequently surrounded by protoclusters. We review the properties and nature of these radio-selected protoclusters. Finally we consider the potential for future progress in the field during the next few decades. A compendium of known HzRGs is given in an appendix.

Jet-Induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C 41.17

The high-redshift radio galaxy 4C 41.17 has been shown in earlier work to consist of a powerful radio source in which there is strong evidence for jet-induced star formation along the radio axis. We argue that nuclear photoionization is not responsible for the excitation of the emission line clouds, and we construct a jet-cloud interaction model to explain the major features revealed by the detailed radio, optical, and spectroscopic data of 4C 41.17. The interaction of a high-powered (~1046 ergs s-1) jet with a dense cloud in the halo of 4C 41.17 produces shock-excited emission-line nebulosity through ~1000 km s-1 shocks and induces star formation. The C IV luminosity emanating from the shock implies that the preshock density in the line-emitting cloud is high enough (hydrogen density ~ 1-10 cm-3) that shock-initiated star formation could proceed on a timescale (~a few × 106 yr) well within the estimated dynamical age (~3 × 107 yr) of the radio source. Broad (FWHM ≈ 1100-1400 km s-1) emission lines are attributed to the disturbance of the gas cloud by a partial bow shock, and narrow emission lines (FWHM ≈ 500-650 km s-1; in particular, C IV λλ1548, 1550) arise in precursor emission in relatively low-metallicity gas or in shocked line emission in the lateral regions of the bow shock. The implied baryonic mass ~8 × 1010 M☉ of the cloud is high and implies that Milky Way size condensations existed in the environments of forming radio galaxies at a redshift of 3.8. Our interpretation of the data provides a physical basis for the alignment of the radio, emission-line, and UV continuum images in some of the highest redshift radio galaxies, and the analysis presented here may form a basis for the calculation of densities and cloud masses in other high-redshift radio galaxies.

HST Snapshot Survey of 3CR Radio Source Counterparts. I. Intermediate Redshifts

We have obtained images of 267 3CR radio galaxies and quasars by conducting a snapshot survey with HSTs WFPC2 through a broadband red (F702W) filter. This is the first in a series of papers resulting from this survey, describing and presenting the basic data. Here we focus on the 77 radio galaxies within the redshift range 0.1 < z < 0.5 (91% of the total number of 3CR radio galaxies within this redshift range). The images show that on the 01 scale of the HST observations there is a wide variety of structure in radio galaxy morphology. At least 30% of the galaxies show dust, either well-defined dust lanes or chaotically distributed throughout the galaxy. We find disturbed morphologies, such as multiple nuclei and tails of emission, that could indicate merging systems. There is an obvious optical synchrotron jet in 3C 346, and another eight jet candidates are present.

Evidence for large-scale winds from starburst galaxies. II - An optical investigation of powerful far-infrared galaxies

The results of long-split spectroscopy of 20 powerful (about 10 to the 12th solar luminosities) far-infrared galaxies (FIRGs) are discussed, and deep narrowband images of the prototypical tepid FIRGs Arp 220 and NGC 6240 are presented. The results show that, as a class, the emission-line spectra of tepid FIRGs are most similar to LINERs, but about half are intermediate between LINERs and low-excitation H II regions. Huge (10,000-100,000-pc) and morphologically spectacular emission-line nebulae resembling the M82 filament system are associated with both NGC 6240 and Arp 220. It is proposed that the model of Chevalier and Clegg (1985) and McCarthy et al. (1987) for M82 be generalized to encompass powerful FIRGs as a class. 43 references.

The European Large Area ISO Survey – II. Mid‐infrared extragalactic source counts

We present preliminary source counts at 6.7um and 15um from the Preliminary Analysis of the European Large Area ISO survey, with limiting flux densities of \~2mJy at 15um&~1mJy at 6.7um. We separate the stellar contribution from the extragalactic using identifications with APM sources made with the likelihood ratio technique. We quantify the completeness&reliability of our source extraction using (a) repeated observations over small areas, (b) cross-IDs with stars of known spectral type, (c) detections of the PSF wings around bright sources, (d) comparison with independent algorithms. Flux calibration at 15um was performed using stellar IDs; the calibration does not agree with the pre-flight estimates, probably due to effects of detector hysteresis and photometric aperture correction. The 6.7um extragalactic counts are broadly reproduced in the Pearson&Rowan-Robinson model, but the Franceschini et al. (1997) model underpredicts the observed source density by ~0.5-1 dex, though the photometry at 6.7um is still preliminary. At 15um the extragalactic counts are in excellent agreement with the predictions of the Pearson&Rowan-Robinson (1996), Franceschini et al. (1994), Guiderdoni et al. (1997) and the evolving models of Xu et al. (1998), over 7 orders of magnitude in 15um flux density. The counts agree with other estimates from the ISOCAM instrument at overlapping flux densities (Elbaz et al. 1999), provided a consistent flux calibration is used. Luminosity evolution at a rate of (1+z)^3, incorporating mid-IR spectral features, provides a better fit to the 15um differential counts than (1+z)^4 density evolution. No-evolution models are excluded, and implying that below around 10mJy at 15um the source counts become dominated by an evolving cosmological population of dust-shrouded starbursts and/or active galaxies.

A deep VLA survey at 20 cm of the ISO ELAIS survey regions

We have used the Very Large Array (VLA) in C configuration to carry out a sensitive 20-cm radio survey of regions of sky that have been surveyed in the far-infrared (FIR) over the wavelength range 5--200 μm with ISO (Infrared Space Observatory) as part of the European Large-Area ISO Survey (ELAIS). As usual in surveys based on a relatively small number of overlapping VLA pointings, the flux limit varies over the area surveyed: from a 5σ limit of 0.135 mJy over an area of 0.12 deg2 to 1.15 mJy or better over the whole region covered of 4.22 deg2. In this paper we present the complete radio catalogue of 867 sources, 428 of which form a complete sample in the flux range 0.2--1.0 mJy. These regions of sky have previously been surveyed to shallower flux limits at 20 cm with the VLA as part of the VLA D configuration NVSS (full width at half-maximum, FWHM=45 arcsec) and VLA B configuration FIRST (FWHM=5 arcsec) surveys. Our whole survey has a nominal 5σ flux limit a factor of 2 below that of the NVSS; 3.4 deg2 of the survey reaches the nominal flux limit of the FIRST survey and 1.5 deg2 reaches 0.25 mJy, a factor of 4 below the nominal FIRST survey limit. In addition, our survey is at a resolution intermediate between the two surveys and thus is well suited for a comparison of the reliability and resolution-dependent surface brightness effects that affect interferometric radio surveys. We have carried out a detailed comparison of our own survey and these two independent surveys in order to assess the reliability and completeness of each. Considering the whole sample, we found that to the 5σ nominal limits of 2.3 and 1.0 mJy, respectively, the NVSS and FIRST surveys have a completeness of 96+2-3 and 89+2-3 per cent and a reliability of 99+1-2 and 94+2-2 per cent.

THE SPIDERWEB GALAXY: A FORMING MASSIVE CLUSTER GALAXY AT z ∼ 2

We present a deep image of the radio galaxy MRC 1138262 taken with the Hubble Space Telescope(HST) at a redshift of . The galaxy is known to have properties of a cD galaxy progenitor and be surrounded z p 2.2 by a 3 Mpc–sized structure, identified with a protocluster. The morphology shown on the new deep HST ACS image is reminiscent of a spider’s web. More than 10 individual clumpy features are observed, apparently starforming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a kpc region 50 # 40 at a rate of more than 100 yr 1 . A striking feature of the newly named “Spiderweb galaxy” is the presence M, of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centers of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies.

Spatially resolved optical images of high-redshift quasi-stellar objects

U and B continuum and Ly-alpha images obtained with the UV-flooded TI2 CCD at the prime focus of the 4-m telescope at KPNO during May and November 1988 are reported for 19 radio-loud high-redshift QSOs. The data are presented in extensive contour maps, radial surface-brightness profiles, and tables and discussed in detail. Ly-alpha emission with typical luminosity about 10 to the 44th erg/sec and spatial extent about 100 kpc is spatially resolved in 15 QSOs, and these nebulae are attributed to the photoionization of the interstellar or intergalactic medium of young or proto galaxies by radiation escaping anisotropically along the radio axis of the QSO. The mechanisms possibly responsible for the Ly-alpha emission and for the UV fuzz seen around some of the QSOs are explored. 84 refs.

The European Large Area ISO Survey – III. 90-μm extragalactic source counts

We present results and source counts at 90micron extracted from the Preliminary Analysis of the European Large Area ISO Survey (ELAIS). The survey covered about 11.6 square degrees of the sky in four main areas and was carried out with the PHOT instrument onboard the Infrared Space Observatory (ISO). The survey is at least an order of magnitude deeper than the IRAS 100micron survey and is expected to provide constraints on the formation and evolution of galaxies. The majority of the detected sources are associated with galaxies on optical images. In some cases the optical associations are interacting pairs or small groups of galaxies suggesting the sample may include a significant fraction of luminous infrared galaxies. The source counts extracted from a reliable subset of the detected sources are in agreement with strongly evolving models of the starburst galaxy population.

Multicolor optical imaging of powerful far-infrared galaxies - more evidence for a link between galaxy mergers and far-infrared emission

Broadband optical (B and R) imaging results are presented for a sample of 39 powerful far-infrared galaxies detected by IRAS. The imaging program has revealed that (1) at least 70 percent of the galaxies have very distorted optical morphologies (much larger than the value 14 percent obtained for a control sample of averarage galaxies); (2) there is an unusually low occurrence of apparently flattened members of the sample compared to either an optical- or infrared-selected sample of spiral galaxies; (3) the galaxies are moderately luminous in the optical; and (4) the galaxy colors most closely resemble Sb or Sbc galaxies seen at the appropriate redshift. These results demonstrate that the optical properties of NGC 6240 and Arp 220 are typical of powerful far-infrared galaxies, and add to the impressive body of evidence linking the collision/merger of disk galaxies to the production of intense infrared emission. 27 references.