Constraining Star Formation and AGN in z~2 Massive Galaxies using High Resolution MERLIN Radio Observations

Abstract

We present high spatial resolution MERLIN 1.4GHz radio observations of two high redshift (z~2) sources, RGJ123623 (HDF147) and RGJ123617 (HDF130), selected as the brightest radio sources from a sample of submillimetre-faint radio galaxies. They have starburst classifications from their rest-frame UV spectra. However, their radio morphologies are remarkably compact (<80mas and <65mas respectively), demanding that the radio luminosity be dominated by Active Galactic Nuclei (AGN) rather than starbursts. Near-IR imaging (HST NICMOS F160W) shows large scale sizes (R_(1/2)~0.75", diameters ~12kpc) and SED fitting to photometric points (optical through the mid-IR) reveals massive (~5x10^(11) M_sun), old (a few Gyr) stellar populations. Both sources have low flux densities at observed 24um and are undetected in observed 70um and 850um, suggesting a low mass of interstellar dust. They are also formally undetected in the ultra-deep 2Ms Chandra data, suggesting that any AGN activity is likely intrinsically weak. We suggest both galaxies have evolved stellar populations, low star formation rates, and low accretion rates onto massive black holes (10^(8.6) M_sun) whose radio luminosity is weakly beamed (by factors of a few). A cluster-like environment has been identified near HDF130 by an over-density of galaxies at z=1.99, reinforcing the claim that clusters lead to more rapid evolution in galaxy populations. These observations suggest that high-resolution radio (MERLIN) can be a superb diagnostic tool of AGN in the diverse galaxy populations at z~2.

8 pages, 4 figures; accepted for publication in MNRAS

References in corpus (55)

• The Global Schmidt Law in Star Forming Galaxies
• The Demography of Massive Dark Objects in Galaxy Centres
• A Relationship Between Nuclear Black Hole Mass and Galaxy Velocity Dispersion
• Energy input from quasars regulates the growth and activity of black holes and their host galaxies
• Detailed Structural Decomposition of Galaxy Images
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• NYU-VAGC: a galaxy catalog based on new public surveys
• A fundamental plane of black hole activity
• A Redshift Survey of the Submillimeter Galaxy Population
• An Observational Determination of the Bolometric Quasar Luminosity Function
• The SDSS Quasar Survey: Quasar Luminosity Function from Data Release Three
• Passively Evolving Early-type Galaxies at 1.4<z<2.5 in the Hubble Ultra Deep Field
• Submillimeter Galaxies
• SCUBA: A common-user submillimetre camera operating on the James Clerk Maxwell Telescope
• The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs
• Confirmation of the remarkable compactness of massive quiescent galaxies at z~2.3: early-type galaxies did not form in a simple monolithic collapse
• A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5
• A Survey of Star-Forming Galaxies in the z=1.4-2.5 `Redshift Desert': Overview
• High-resolution Millimeter Imaging of Submillimeter Galaxies
• Strong size evolution of the most massive galaxies since z~2
• Deep Extragalactic X-ray Surveys
• A New Approach to Galaxy Morphology: I. Analysis of the Sloan Digital Sky Survey Early Data Release
• Old Galaxies in the Young Universe
• Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts
• The X-ray Spectral Properties of SCUBA Galaxies
• A 20cm VLA Survey of Abell Clusters of Galaxies VI. Radio/Optical Luminosity Functions
• High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data IV: Luminosity Function from the Fall Equatorial Stripe Sampl
• Multiwavelength study of massive galaxies at z~2. II. Widespread Compton thick AGN and the concurrent growth of black holes and bulges
• Clustering of Submillimeter-Selected Galaxies
• Selection Bias in Observing the Cosmological Evolution of the Mbh-sigma and Mbh-L Relationships
• The Nature of Radio Emission from Distant Galaxies: The 1.4 GHz Observations
• The Gemini Deep Deep Survey: I. Introduction to the Survey, Catalogs and Composite Spectra
• The Luminosity, Stellar Mass, and Number Density Evolution of Field Galaxies of Known Morphology from z = 0.5 - 3
• The Structures of Distant Galaxies I: Galaxy Structures and the Merger Rate to z~3 in the Hubble Ultra-Deep Field
• The Relationship Between Stellar and Black-Hole Mass in Submillimeter Galaxies
• Weighing the Black Holes in z~2 Submillimeter-Emitting Galaxies Hosting Active Galactic Nuclei
• On the evolution of the black hole:spheroid mass ratio
• A large sample of spectroscopic redshifts in the ACS-GOODS region of the HDF-N
• Compton Thick AGN: the dark side of the X-ray background
• A population of hot, dusty ultra-luminous galaxies at z~2
• Reliable Identification of Compton-thick Quasars at z~2: Spitzer Mid-IR spectroscopy of HDF-oMD49
• High Resolution Studies of Radio Sources in the Hubble Deep and Flanking Fields
• Do submillimeter galaxies really trace the most massive dark matter halos? Discovery of a high-z cluster in a highly active phase of evolution
• Spitzer 70-micron Source Counts in GOODS-North
• The Properties and Evolution of a K-band Selected Sample of Massive Galaxies at z~0.4 - 2 in the Palomar/DEEP2 Survey
• The Chandra Deep Field North Survey. XII. The Link Between Faint X-ray and Radio Source Populations
• High-resolution radio observations of submillimetre galaxies
• A catalogue of micro-Jy radio sources in northern legacy fields
• Galactic bulge formation as a maximum intensity starburst
• Tracing the Mass-Dependent Star Formation History of Late-Type Galaxies using X-ray Emission: Results from the Chandra Deep Fields
• Optically Faint Microjansky Radio Sources
• The Properties of Microjansky Radio Sources in the HDF-N, SSA13, and SSA22 Fields
• The X-ray Properties of Early-Type Galaxies in the Extended Chandra Deep Field-South
• Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies
• Optical Selection of Faint AGN in the COSMOS Field

Cited by in corpus (17)

• Dusty Star-Forming Galaxies at High Redshift
• Characterisation of SCUBA-2 450um and 850um-selected Galaxies in the COSMOS Field
• A Redshift Survey of Herschel Far-Infrared Selected Starbursts and Implications for Obscured Star Formation
• The Ubiquity of Coeval Starbursts in Massive Galaxy Cluster Progenitors
• High-resolution CO and radio imaging of z~2 ULIRGs: extended CO structures, and implications for the universal star formation law
• The AzTEC/SMA Interferometric Imaging Survey of Submillimeter-Selected High-Redshift Galaxies
• The Hubble Space Telescope GOODS NICMOS Survey: Overview and the Evolution of Massive Galaxies at 1.5 < z < 3
• Confirming a Population of Hot-Dust Dominated, Star Forming Ultraluminous Galaxies at High-Redshift
• Molecular Gas in Submillimetre-Faint, Star-Forming Ultraluminous Galaxies at z>1
• Comprehensive Gas Characterization of a $z=2.5$ Protocluster: A Cluster Core Caught in the Beginning of Virialization?
• Deep, wide-field, global VLBI observations of the Hubble Deep Field North and Flanking Fields
• Spectroscopic Characterisation of 250um-Selected Hyper-Luminous Star Forming Galaxies
• An ALMA survey of submillimetre galaxies in the COSMOS field: The extent of the radio-emitting region revealed by 3 GHz imaging with the Very Large Array
• Nowhere to Hide: Radio-faint AGN in the GOODS-N field. II. Multi-wavelength AGN selection techniques and host galaxy properties
• The Nature of the Faint Low-Frequency Radio Source Population
• SuperCLASS -- I. The Super CLuster Assisted Shear Survey: Project overview and Data Release 1
• The inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolution