Aims.We present the low frequency (610 MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. Methods: .We use new deep (rms≃ 50~μJy/beam) observations of the VVDS-VLA field obtained at 610 MHz with the GMRT and matched in resolution (6 arcsec) with already available VLA data at 1.4 GHz on the same field. Results: .We find evidence of a change of the dominant population of radio sources below 0.5 mJy (at 1.4 GHz): between 0.15 and 0.5 mJy the median spectral index is significantly flatter (α=-0.46± 0.03) than that of brighter sources (α=-0.67± 0.05). A relevant contribution below 0.5 mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15 mJy at 1.4 GHz, the median spectral index steepens again (α=-0.61± 0.04) suggesting that the contribution of starburst galaxies becomes important below ˜ 0.2 mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/519
Bondi M., Ciliegi P., Venturi T., Dallacasa D., Bardelli S., Zucca E., et al. (2007). The VVDS-VLA deep field. III. GMRT observations at 610 MHz and the radio spectral index properties of the sub-mJy population. ASTRONOMY & ASTROPHYSICS, 463, 519-527 [10.1051/0004-6361:20066428].
The VVDS-VLA deep field. III. GMRT observations at 610 MHz and the radio spectral index properties of the sub-mJy population
DALLACASA, DANIELE;GREGORINI, LORETTA;
2007
Abstract
Aims.We present the low frequency (610 MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. Methods: .We use new deep (rms≃ 50~μJy/beam) observations of the VVDS-VLA field obtained at 610 MHz with the GMRT and matched in resolution (6 arcsec) with already available VLA data at 1.4 GHz on the same field. Results: .We find evidence of a change of the dominant population of radio sources below 0.5 mJy (at 1.4 GHz): between 0.15 and 0.5 mJy the median spectral index is significantly flatter (α=-0.46± 0.03) than that of brighter sources (α=-0.67± 0.05). A relevant contribution below 0.5 mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15 mJy at 1.4 GHz, the median spectral index steepens again (α=-0.61± 0.04) suggesting that the contribution of starburst galaxies becomes important below ˜ 0.2 mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/519I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
