Micro-Jy radio sources in the z=0.83 cluster MS1054-03

An extremely deep 5 GHz radio observation is presented of the rich cluster MS1054-03 at redshift z=0.83. 34 radio sources are detected down to a 32 micro-Jy (6 sigma), compared to about 25 expected from previous blank field radio source count determinations; the sources giving rise to these excess counts lie within 2 arcmins (700 kpc) of the cluster centre. Existing imaging and spectroscopy has provided optical identifications for 21 of the radio sources and redshifts for 11, of which 8 are confirmed cluster members. 4 of these 8 confirmed cluster sources are associated with close galaxy pairs (10-25 kpc projected offset) of similar magnitude, implying that the radio source may be triggered by an interaction. However, although MS1054-03 has a very high fraction (17%) of on-going mergers (separations <~ 10 kpc), no radio emission is detected towards any of these merger events, setting a mean upper limit of 10 Msun/yr for any star formation associated with these mergers. This supports a hypothesis that low luminosity radio sources may be onset by initial weak interactions rather than direct mergers. The host galaxies of the other four confirmed cluster radio sources are all isolated, and show a range of morphologies from early-type to Sc. A comparison between the emission line and radio luminosities suggests that two of these four radio sources are low-luminosity AGN, whilst for at least one of the other two the radio emission is associated with on-going star formation. All of the radio sources associated with the galaxy pairs appear more likely AGN than starburst origin. The overall proportion of radio sources associated with AGN in this cluster (>75%) is higher than at these flux density levels in the field (40-50%).

The micro-Jy Radio Source Population: the VLA-CDFS View

We analyse the 267 radio sources from our deep (flux limit of 42 microJy at the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey. The radio population is studied by using a wealth of multi-wavelength information, including morphology and spectral types, in the radio, optical, and X-ray bands. The availability of redshifts for ~ 70% of our sources allows us to derive reliable luminosity estimates for the majority of the objects. Contrary to some previous results, we find that star-forming galaxies make up only a minority (~ 1/3) of sub-mJy sources, the bulk of which are faint radio galaxies, mostly of the Fanaroff-Riley I type.

VLA/JVLA Monitoring of Bright Northern Radio Sources

We report multiple epoch VLA/JVLA observations of 89 northern hemisphere sources, most with 37,GHz flux density > 1 Jy, observed at 4.8, 8.5, 33.5, and 43.3 GHz. The high frequency selection leads to a predominantly flat spectrum sample, with 85% of our sources being in the Planck Early Release Compact Source Catalog (ERCSC). These observations allow us to: 1) validate Plancks 30 and 44 GHz flux density scale, 2) extend the radio SEDs of Planck sources to lower frequencies allowing for the full 5-857GHz regime to be studied, and 3) characterize the variability of these sources. At 30 GHz and 44 GHz, the JVLA and Planck flux densities agree to within 3%. On timescales of less than two months the median variability of our sources is 2%. On timescales of about a year the median variability increases to 14%. Using the WMAP 7-year data, the 30 GHz median variability on a 1-6 years timescale is 16%.

The IPHAS Catalogue of Halpha Emission Line Sources in the Northern Galactic Plane

We present a catalogue of point-source Halpha emission line objects selected from the INT/WFC Photometric H$alpha$ Survey of the Northern Galactic Plane (IPHAS). The catalogue covers the magnitude range 13 < r < 19.5 and includes northern hemisphere sources in the Galactic latitude range -5 < b < 5 degress. It is derived from ~1500 square degress worth of imaging data, which represents 80 percent of the final IPHAS survey area. The electronic version of the catalogue will be updated once the full survey data becomes available. In total, the present catalogue contains 4853 point sources that exhibit strong photometric evidence for Halpha emission. We have so far analyzed spectra for ~300 of these sources, confirming more than 95 percent of them as genuine emission-line stars. A wide range of stellar populations are represented in the catalogue, including early-type emission line stars, active late-type stars, interacting binaries, young stellar objects and compact nebulae. The spatial distribution of catalogue objects shows overdensities near sites of recent or current star formation, as well as possible evidence for the warp of the Galactic plane. Photometrically, the incidence of Halpha emission is bimodally distributed in r-i. The blue peak is made up mostly of early-type emission line stars, whereas the red peak may signal an increasing contribution from other objects, such as young/active low-mass stars. We have cross-matched our Halpha-excess catalogue against the emission-line star catalogue of Kohoutek & Wehmeyer, as well as against sources in SIMBAD. We find that fewer than 10 per cent of our sources can be matched to known objects of any type. Thus IPHAS is uncovering an order of magnitude more faint (r > 13) emission line objects than were previously known in the Milky Way.

Planck intermediate results. XLV. Radio spectra of northern extragalactic radio sources

Continuum spectra covering centimetre to submillimetre wavelengths are presented for a northern sample of 104 extragalactic radio sources, mainly active galactic nuclei, based on four-epoch Planck data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous ground-based radio observations between 1.1 and 37 GHz. The single-survey Planck data confirm that the flattest high-frequency radio spectral indices are close to zero, indicating that the original accelerated electron energy spectrum is much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The radio spectra peak at high frequencies and exhibit a variety of shapes. For a small set of low-z sources, we find a spectral upturn at high frequencies, indicating the presence of intrinsic cold dust. Variability can generally be approximated by achromatic variations, while sources with clear signatures of evolving shocks appear to be limited to the strongest outbursts.