Michiel Reuland

Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. I. The Role of ISM Pressure and the Molecular Cloud Dissipation Timescale

In this paper, we combine the stellar spectral synthesis code STARBURST99, the nebular modeling code MAPPINGS IIIq, a one-dimensional dynamical evolution model of H ii 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 � 10 8 yr. 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. In particular, theshapeofthefar-infrared(dustre-emission)bumpisstronglydependentonthemeanpressureinthestar-forming or starburst galaxy. This can explain the range offar-infrared (FIR) colors seen in starburst galaxies. In the case of objects of composite excitation, such diagrams potentially provide a means of estimating the fraction of the FIR emission that is contributed by an active nucleus. 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 Telescope MIPS and IRAC instruments. Our models reproduce the spread in observed colors of starburst galaxies. From both the SED fits and the color :color diagrams, we infer the presence of a population of compact and ultracompact H ii regions around single OB stars or small OB clusters. Finally, we present absolute calibrations to convert observed fluxes into star formation rates in the UV (GALEX ), at optical wavelengths (H� ), and in the IR (IRAS or Spitzer). We show that 25 � m fluxes are particularly valuable as star formation indicators, since they largely eliminate one of the parameters controlling the IR SED. Subject headingg dust, extinction — galaxies: general — galaxies: starburst — H ii regions — infrared: galaxies — radio continuum: galaxies — ultraviolet: galaxies

Giant Lyα Nebulae Associated with High-Redshift Radio Galaxies*

We report deep, Keck narrowband Ly? 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, that 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 Ly? absorption. We discuss these features within a general scenario in which the nebular gas cools gravitationally in large cold dark matter 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 supermassive black holes, which produce the powerful radio jets and lobes. The radio sources, starburst superwinds, and radiation pressure from active galactic nucleus then disrupt the accretion process, limiting galaxy and black hole growth, and imprint the observed filamentary and cone-shaped structures of the Ly? nebulae.

Dust and star formation in distant radio galaxies

In this thesis I discuss recent observations of distant (z > 2) radio galaxies. There is strong evidence that radio galaxies are the progenitors of the brightest cluster ellipticals and are among the most luminous and massive galaxies at any epoch, allowing relatively detailed studies of their formation process out to large distances. Submillimeter emission has been detected in many, implying star formation rates of order 1000 Msun/yr over scales of tens of kpc, consistent with a scenario in which these galaxies are currently forming the bulk of their eventual stellar population. Many radio galaxies also host giant (~ 150 kpc) emission line nebulae. We obtaind very deep narrow-band Ly-a images for a select few of these. The observations show spectacular detail with a wealth of morphological structure, such as extended (~ 80 kpc) filamentary structures, giving insight in feedback processes during their formation. I discuss the possible origin and the ionization source of these halos in connection with the sub-mm results, and discuss possible implications for theories of galaxy formation.

A multi-wavelength study of the proto-cluster surrounding the z = 4.1 radio galaxy TN J1338–1942

We present a 1.2 mm (250 GHz) map obtained with MAMBO on the IRAM 30 m telescope of the central 25 arcmin 2 of the proto-cluster surrounding the z = 4.1 radio galaxy TN J1338−1942. The map reaches a 1σ sensitivity of 0.6 mJy in the central area, increasing to 1.2 mJy at the edges. We detect 10 candidate mm sources, of which 8 are also detected in a deep VLA 1.4 GHz map and/or a VLT R-band image. Three sources have a flux density S 1. 2m m > 4. 0m Jy, representing a 7σ overdensity compared to random field surveys, which predict only 1 such source in our map area. We obtained SCUBA/JCMT 850 µm and 450 µm photometry of six radio/optically identified MAMBO sources, confirming 5 of them with S/N > 4. Radio-to-mm and mm-to-submm redshift estimators cannot put strong constraints on the redshifts of these MAMBO sources, but 9 of them are consistent within the uncertainties (mean ∆z =+ 2.6) with z = 4.1. One faint MAMBO source is possibly identified with an extremely red object (R − K = 6.1) at a likely spectroscopic redshift z = 1.18. The four brightest MAMBO sources are all located north of the radio galaxy, while the densest area of companion Lyα excess and Lyman break galaxies is to the southeast. None of the 14 spectroscopically confirmed Lyα emitters in the MAMBO field are detected at 1.2 mm; their average 1.2 mm flux density isS 1. 2m m� = 0.25 ± 0.24 mJy. If the mm sources lie at z = 4.1, none of them show excess Lyα emission in our narrow-band images. Both populations thus show no apparent overlap, possibly due to dust quenching the Lyα emission. If the mm sources are part of the proto-cluster, our results suggest that galaxies with star formation rates of a few 1000 Myr −1 could be spread throughout the proto-cluster over projected scales of at least 2 Mpc.

SCUBA Observations of High Redshift Radio Galaxies

High redshift radio galaxies (HzRGs) are key targets for studies of the formation and evolution of massive galaxies.The role of dust in these processes is uncertain. We have therefore observed the dust continuum emission from a sample of z > 3 radio galaxies with the SCUBA bolometer array. We confirm and strengthen the result found by Archibald et al. (1), that HzRGs are massive starforming systems and that submillimeter detection rate appears to be primarily a strong function of redshift. We also observed HzRG-candidates that have so far eluded spectroscopic redshift determination. Four of these have been detected, and provide evidence that they may be extremely obscured radio galaxies, possibly in an early stage of their evolution.