TUNA Lunch Talk:

Jim Condon


Starbursts and Feedback in QSOs

March 20

12:10PM, Note unusual location: CV Auditorium


We used the 1.4 GHz NVSS and the EVLA at 6 GHz to investigate the radio emission from large color-selected samples of bright SDSS QSOs in the redshift ranges 0.2 < z < 0.45 and 1.8 < z < 2.5. About 10% of these QSOs contain radio-loud AGN stronger than 2.4 mJy at 1.4 GHz. Although the radio-loud QSOs have exceptionally flat flux-density distributions (approximately equal numbers in each decade of flux density), they are similar to radio galaxies: we reject claims that there is something "wrong" with the radio emission from QSOs. Our surprising new result is that nearly all QSOs contain faint radio sources detectable either statistically (by the NVSS) or individually (by the EVLA) at typical 1.4 GHz flux densities ranging from ~ 0.3 mJy (0.2 < z < 0.3) to 0.06 mJy (1.8 < z < 2.5). We propose that these unexpected faint radio sources are powered by starbursts in QSO host galaxies. If so, the typical star-formation rate for a luminous high-redshift QSO is about 500 solar masses per year. Such high star-formation rates are consistent with "feedback" models in which cold gas fuels both the final starburst and a fatally luminous AGN that turns the host galaxy into a "red and dead" elliptical. Straightforward ALMA observations should be able to confirm or reject our starburst hypothesis.