A Glimpse at Quasar Host Galaxy Far-UV Emission, Using DLAs as Natural Coronagraphs

Abstract

In merger-driven models of massive galaxy evolution, the luminous quasar phase is expected to be accompanied by vigorous star formation in quasar host galaxies. In this paper, we use high column density Damped Lyman Alpha (DLA) systems along quasar sight lines as natural coronagraphs to directly study the far-UV (FUV) radiation from the host galaxies of luminous background quasars. We have stacked the spectra of $\sim$2,000 DLA systems (N_HI>10^{20.6} cm^{-2}) with a median absorption redshift < z > = 2.6 selected from quasars observed in the SDSS-III Baryon Oscillation Spectroscopic Survey. We detect residual flux in the dark troughs of the composite DLA spectra. The level of this residual flux significantly exceeds systematic errors in the SDSS fiber sky subtraction; furthermore, the residual flux is strongly correlated with the continuum luminosity of the background quasar, while uncorrelated with DLA column density or metallicity. We conclude that the flux could be associated with the average FUV radiation from the background quasar host galaxies (with medium redshift < z > = 3.1) that is not blocked by the intervening DLA. Assuming all of the detected flux originates from quasar hosts, for the highest quasar luminosity bin (< L >= 2.5x 10^{13} L_sun), the host galaxy has a FUV intensity of 1.5 +/- 0.2 x 10^{40} erg s^{-1} A^{-1}; this corresponds to an unobscured UV star formation rate of 9 M_sun/yr.

15 pages, 10 figures, Accepted for publication in ApJ

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Cited by in corpus (7)

• Directly imaging damped Ly-alpha galaxies at z>2. III: The star formation rates of neutral gas reservoirs at z~2.7
• The Ly$\alpha$ emission from high-$z$ galaxies hosting strong Damped Ly$\alpha$ systems
• UV-Luminous, Star-Forming Hosts of z~2 Reddened Quasars in the Dark Energy Survey
• Nature of the DLA towards Q0528-250: High pressure and strong UV field revealed by excitation of CI, H2 and SiII
• Constraining the Halo Mass of Damped Ly$\alpha$ Absorption Systems (DLAs) at $z=2-3.5$ using the Quasar-CMB Lensing Cross-correlation
• Deep Hubble Space Telescope Imaging on the Extended Ly$\alpha$ Emission of a QSO at $z=2.19$ with Damped Lyman Alpha System as a Natural Coronagraph
• Star-Formation in Neutral Hydrogen Gas Reservoirs at Cosmic Noon