Science > Highlights

Recent Science Highlights

by Davis Murphy last modified Sep 08, 2015

Browse NRAO Science Highlights Archives: FY2014 | FY2013Full Archive
Click on each figure to see a larger version.

The Riddle of Infrared Faint Radio Sources

by Davis Murphy last modified Sep 08, 2015

faint_sources.jpgInfrared-faint radio sources (IFRS) form a new class of galaxies characterized by radio flux densities ~ milli-Janskys, with faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs), at high redshift, although very young starburst galaxies at lower redshift cannot be ruled out. Herzog et al report the results of a 1.4 GHz VLBA survey of 57 IFRS at 10mas resolution and a sensitivity of ~ 60 micro-Jansky/beam rms. They detect compact cores in 35 of the 57 galaxies they surveyed. These results answer conclusively that IFRS are indeed radio AGN at substantial redshifts, and provide a sample of lower luminosity radio AGN to study in the distant Universe, possibly the youngest radio jet sources.

View Paper: Active galactic nuclei cores in infrared-faint radio sources: Very long baseline interferometry observations using the Very Long Baseline Array, A. Herzog (Bochum, Macquarie, CSIRO), E. Middelberg (Bochum), R.P. Norris (CSIRO), L.R. Spitler (Macquarie, AAO), A.T. Deller (ASTRON), J.D. Collier (Western Sydney, CSIRO), and Q.A. Parker (Macquarie, AAO), 2015 A&A, 578, A67 (published online 5 June 2015).

VLBA Images HI Clouds at z = 0.123

by Davis Murphy last modified Sep 08, 2015

vlba_HI_clouds.jpgUsing long-slit optical spectra obtained with the 2-m telescope at IUCAA Girawali Observatory, the authors show that the radio source J094221.98+062335.2 (z = 0.123) is associated with a galaxy pair undergoing a major merger. Its companion is a normal star-forming galaxy infalling with a velocity of 185 km s1at a projected separation of 4.8 kpc. Using the Westerbork Synthesis Radio Telescope (WSRT) and Giant Metrewave Radio Telescope (GMRT), Srianand et al detect a strong H I 21 cm absorption at the systemic redshift of the radio galaxy with N(HI) ∼ 9 × 1021 cm2. Such a strong HI 21 cm absorption is rare and has been seen only in a few compact radio sources associated with similar merging galaxy pairs.

Milliarcsecond resolution VLBA observations resolve the radio source into a compact symmetric object with the hotspot separation of 89 pc. The 21 cm absorption is detected in the VLBA spectra towards both the radio lobes, albeit with a strong optical depth gradient. The strong 21 cm absorption is consistent with it being arising from a clumpy circum-nuclear disc/torus. Two weaker absorption lines were also detected redshifted with respect to the radio source in the WSRT/GMRT spectrum. They probably represent cold (i.e. T ≤ 104 K) H I gas falling into the radio source. The presence of high concentration of H I gas in the circum-nuclear regions and signature of infalling cold gas suggests that the young radio source may have been triggered by the gas infall due to the ongoing merger.

View Paper: Circumnuclear and infalling H I gas in a merging galaxy pair at z = 0.123, R. Srianand (IUCAA), N. Gupta (IUCAA), E. Momjian (NRAO), and M. Vivek (Utah), 2015 MNRAS, 451, 917 (1 June 2015).