Discovery of strong Balmer line absorption in two luminous LoBAL quasars at z~1.5

TL;DR

This paper reports the discovery of strong Balmer line absorption in two luminous LoBAL quasars at z~1.5, revealing rare spectral features that suggest complex gas dynamics near supermassive black holes.

Contribution

It presents the first detailed analysis of Balmer absorption in high-redshift LoBAL quasars, including measurements of absorption properties and implications for gas inflow or outflow.

Findings

Detection of Balmer absorption in two quasars at z~1.5

Evidence of saturated absorption indicating partial coverage

Estimates of neutral hydrogen column densities around 10^{18} cm^{-2}

Abstract

We present the discovery of strong Balmer line absorption in H$\alpha$ to H$\gamma$ in two luminous low-ionization broad absorption line quasars (LoBAL QSOs) at z~1.5, with black hole masses around $10^{10}$ $M_\odot$ from near-IR spectroscopy. There are only two previously known quasars at z>1 showing Balmer line absorption. SDSS J1019+0225 shows blueshifted absorption by ~1400 km/s with an H$\alpha$ rest-frame equivalent width of 13 \AA{}. In SDSS J0859+4239 we find redshifted absorption by ~500 km/s with an H$\alpha$ rest-frame equivalent width of 7 \AA{}. The redshifted absorption could indicate an inflow of high density gas onto the black hole, though we cannot rule out alternative interpretations. The Balmer line absorption in both objects appears to be saturated, indicating partial coverage of the background source by the absorber. We estimate the covering fractions and optical depth of the absorber and derive neutral hydrogen column densities, $N_{\rm{H\,I}}\sim1.3\times 10^{18}$ cm$^{-2}$ for SDSS J1019+0225 and $N_{\rm{H\,I}}\sim9\times 10^{17}$ cm$^{-2}$ for SDSS J0859+4239, respectively. In addition, the optical spectra reveal also absorption troughs in HeI* $\lambda3889$ and $\lambda3189$ in both objects.