A Galactic Wind at z = 5.190

We report the serendipitous detection in high-resolution optical spectroscopy of a strong, asymmetric Ly-alpha emission line at z = 5.190. The detection was made in a 2.25 hour exposure with the Echelle Spectrograph and Imager on the Keck II telescope through a spectroscopic slit of dimensions 1" x 20". The progenitor of the emission line, J123649.2+621539 (hereafter ES1), lies in the Hubble Deep Field North West Flanking Field where it appears faint and compact, subtending just 0.3" (FWHM) with I(AB) = 25.4. The ES1 Ly-alpha line flux of 3.0 x 10^(-17) ergs/cm^2/s corresponds to a luminosity of 9.0 x 10^(42) ergs/s, and the line profile shows the sharp blue cut-off and broad red wing commonly observed in star-forming systems and expected for radiative transfer in an expanding envelope. We find that the Ly-alpha profile is consistent with a galaxy-scale outflow with a velocity of v > 300 km/s. This value is consistent with wind speeds observed in powerful local starbursts (typically 10^2 to 10^3 km/s), and compares favorably to simulations of the late-stage evolution of Ly-alpha emission in star-forming systems. We discuss the implications of this high-redshift galactic wind for the early history of the evolution of galaxies and the intergalactic medium, and for the origin of the UV background at z > 3.Comment: 12 pages, 7 figures, accepted for publication in the Astrophysical Journa

An Obscured Radio Galaxy at High Redshift

Perhaps as many as 10% of high redshift radio galaxy (HzRG; z > 2) candidates that are selected using an Ultra Steep radio Spectrum (USS) criterion fail to show optical emission (continuum, lines) in deep Keck exposures. Their parent objects are only detected in the near-IR and are probably heavily obscured and/or at very high redshift. To search for signatures of dust and help constrain the nature and redshifts of these ``no-z'' radio galaxies, we have conducted a program of submillimeter and millimeter observations. Here we report the first results of a detailed study of one of these objects, WN J0305+3525. WN J0305+3525 appears associated with a small group of K ~ 21 - 22 objects and is strongly detected at both 850 micron and 1.25 mm. On the basis of its faint K-band magnitude, spectral energy distribution (SED) and other evidence we estimate that the radio galaxy is probably at a redshift z = 3 +/- 1. This would make WN J0305+3525 a radio-loud Hyper Luminous Infrared Galaxy (LFIR ~ 10^13 Lsun) similar to, but more obscured than, other dusty radio galaxies in this redshift range. This, together with the absence of Lya emission and compact (theta < 1.9") radio structure, suggests that WN J0305+3525 is embedded in a very dense, dusty medium and is probably at an early stage of its formation.Comment: 13 Pages LaTeX, including 3 Postscript figure

Giant Lya nebulae associated with high redshift radio galaxies

We report deep Keck narrow-band Lya images of the luminous z > 3 radio galaxies 4C 41.17, 4C 60.07, and B2 0902+34. The images show giant, 100-200 kpc scale emission line nebulae, centered on these galaxies, which exhibit a wealth of morphological structure, including extended low surface brightness emission in the outer regions, radially directed filaments, cone-shaped structures and (indirect) evidence for extended Lya absorption. We discuss these features within a general scenario where the nebular gas cools gravitationally in large Cold Dark Matter (CDM) halos, forming stars and multiple stellar systems. Merging of these ``building'' blocks triggers large scale starbursts, forming the stellar bulges of massive radio galaxy hosts, and feeds super-massive black holes which produce the powerful radio jets and lobes. The radio sources, starburst superwinds and AGN radiation then disrupt the accretion process limiting galaxy and black hole growth, and imprint the observed filamentary and cone-shaped structures of the Lya nebulae.Comment: 36 Pages, including 8 Postscript figures. Accepted for publication in the Astrophysical Journa

Metal-Enriched Gaseous Halos around Distant Radio Galaxies: Clues to Feedback in Galaxy Formation

We present the results of an optical and near-IR spectroscopic study of giant nebular emission-line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07, and B2 0902+34. Previous deep narrowband Lyα imaging revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s^(-1) and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions >1000 km s^(-1). The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of ≈60 kpc along the radio axis. The dynamical structures traced in the Lyα line are, in most cases, closely echoed in the carbon and oxygen lines. This shows that the Lyα line is produced in a highly clumped medium of small filling factor and can therefore be used as a tracer of the dynamics of high-redshift radio galaxies (HzRGs). We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming "red and dead" elliptical galaxies

Dust and star formation in distant radio galaxies

We present the results of an observing program with the SCUBA bolometer array to measure the submillimetre (submm) dust continuum emission of 24 distant (z > 1) radio galaxies. We detected submm emission in 12 galaxies with S/N > 3, including 9 detections at z > 3. When added to previous published results these data almost triple the number of radio galaxies with z > 3 detected in the submm and yield a sample of 69 observed radio galaxies over the redshift range z = 1-5. We find that the range in rest-frame far-infrared luminosities is about a factor of 10. We have investigated the origin of this dispersion, correlating the luminosities with radio source power, size, spectral index, K-band magnitude and Lya luminosity. No strong correlations are apparent in the combined data set. We confirm and strengthen the result from previous submm observations of radio galaxies that the detection rate is a strong function of redshift. We compare the redshift dependence of the submm properties of radio galaxies with those of quasars and find that for both classes of objects the observed submm flux density increases with redshift to z ~ 4, beyond which, for the galaxies, we find tentative evidence for a decline. We find evidence for an anti-correlation between submm luminosity and UV polarisation fraction, for a subsample of 13 radio galaxies, indicating that starbursts are the dominant source of heating for dust in radio galaxies.Comment: 15 pages, 11 PS figures, accepted for publication in MNRAS; corrected sample analysis, minor changes in tables and figure

Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: I. The role of ISM pressure & the Molecular Cloud Dissipation Timescale

In this paper, we combine the stellar spectral synthesis code STARBURST 99, the nebular modelling code MAPPINGS IIIq, a 1-D dynamical evolution model of \HII regions around massive clusters of young stars and a simplified model of synchrotron emissivity to produce purely theoretical self-consistent synthetic spectral energy distributions (SEDs) for (solar metallicity) starbursts lasting some $10^8$ years. These SEDs extend from the Lyman Limit to beyond 21 cm. We find that two ISM parameters control the form of the SED; the pressure in the diffuse phase of the ISM (or, equivalently, its density), and the molecular cloud dissipation timescale. We present detailed SED fits to Arp 220 and NGC 6240, and we give the predicted colors for starburst galaxies derived from our models for the IRAS and the Spitzer Space Observatory MIPS and IRAC instruments. Our models reproduce the spread in observed colors of starburst galaxies. Finally, we present absolute calibrations to convert observed fluxes into star formation rates in the UV (GALEX), at optical wavelengths (H$\alpha$), and in the IR (IRAS or the Spitzer Space Observatory). (Abstract Truncated)Comment: 56 pages, 16 figures, accepted by The Apstrophysical Journal For version with full, colour figures go to http://www.mso.anu.edu.au/~bgroves/starburst

Dust and star formation in distant radio galaxies

International audienceWe present the results of an observing programme with the Submillimetre Common User Bolometer Array (SCUBA) to measure the submillimetre (submm) dust continuum emission of 24 distant (z > 1) radio galaxies. We detected submm emission in 12 galaxies with signal-to-noise > 3, including nine detections at z > 3. When added to previous published results these data almost triple the number of radio galaxies with z > 3 detected in the submm and yield a sample of 69 observed radio galaxies over the redshift range z= 1-5. We find that the range in rest-frame far-infrared luminosities is about a factor of 10. We have investigated the origin of this dispersion, correlating the luminosities with radio source power, size, spectral index, K-band magnitude and Lyα luminosity. No strong correlations are apparent in the combined data set. We confirm and strengthen the result from previous submm observations of radio galaxies that the detection rate is a strong function of redshift. We compare the redshift dependence of the submm properties of radio galaxies with those of quasars and find that for both classes of objects the observed submm flux density increases with redshift to z~ 4, beyond which, for the galaxies, we find tentative evidence for a decline. We find evidence for an anticorrelation between submm luminosity and ultraviolet polarization fraction, for a subsample of 13 radio galaxies, indicating that starbursts are the dominant source of heating for dust in radio galaxies

AGN or starburst powered? Untangling the pan-spectral SEDs of the high-redshift radio galaxies and sub-mm galaxies

Here we show how theoretical pan-spectral modelling is beginning to decode the physical parameters of the interstellar medium of starburst and high-redshift galaxies, is revealing the star formation rate, identifying the bolometric contribution due to a