High Sensitivity Radio Surveys

radio_surverys.jpg

Murphy et al. present initial results on a flux-limited sample of galaxies from pilot observations aimed at mapping the entire Great Observatories Origins Deep Survey-North (GOODS-N) field at 10 GHz. The GOODS-N field covers 160 arcmin2 centered on the Hubble Deep Field–North and in unrivaled in terms of its ancillary data, including extremely deep Chandra, HST, Spitzer and Herschel observations, deep ground-based imaging from U through K-band, ~3500 spectroscopic redshifts acquired with 8-10m class telescopes, and deep 1.4 GHz observations.

The new VLA X-band data (8-12 GHz) presented by Murphy and his colleagues feature an r.m.s. sensitivity of 0.5 micro-Jansky and a resolution of 0.2 arcsec. This resolution is well-matched to the HST optical and infrared data from GOODS, and delivers a physical resolution of 1.9 kiloparsecs or less at any redshift. These new 10 GHz radio data provide an extinction-free view of the morphologies of dusty starburst galaxies that dominate the cosmic star formation activity between z = 1 and 3. In this redshift range, 10 GHz observations sample ~20 – 40 GHz in the source frame and provide accurate star formation rates for comparison with other diagnostics in the GOODS ancillary data, such as the far ultraviolet continuum, Ha, and [O III] 5007 Å.

These 10 GHz data provide accurate measurements of the radio sizes of high redshift star-forming galaxies. The observed median size is ~ 1.2 kiloparsecs, which corresponds to the dense, star-forming regions as also seen in dust continuum emission. The measured spectral indices of the detected galaxies are flatter than expected, implying a ~50% contribution to the rest from 20 GHz luminosity by free-free thermal emission. This important result opens a new, powerful means to obtain star formation rates for high redshift galaxies that are unbiased by dust.

Image: [Left] A source detected in the 10 GHz Jansky VLA pilot observations. [Center, Right] HST Advanced Camera System z-band and Wide Field Camera 3 F160W images, respectively, with 10 GHz VLA contours overlaid. Each panel is 5 x 5 arcsec. These data illustrate the survey’s ability to resolve the two cores in this merging galaxy pair at z = 1.2234.

Publication: Eric J. Murphy (NRAO, IPAC) et al., The GOODS-N Jansky VLA 10 GHz Pilot Survey: Sizes of Star-forming μJY Radio Sources, 2017, Astrophysical Journal, 839, 35.

Connect with NRAO

The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.