[OIII] Emission and Gas Kinematics in a Lyman-alpha Blob at z ~ 3.1

TL;DR

This study measures [OIII] emission in a high-redshift Lyman-alpha blob to investigate gas kinematics and outflows, revealing modest velocity offsets that suggest outflows may not dominate Lyman-alpha escape.

Contribution

First spectroscopic measurements of [OIII] in a z~3.1 Lyman-alpha blob, providing insights into gas motions and the role of outflows in Lyman-alpha emission.

Findings

Velocity offsets between [OIII] and Lyman-alpha are near zero or negative.

Outflows are unlikely to be the main mechanism for Lyman-alpha escape.

[OIII] flux from galaxy-unassociated regions is significantly fainter.

Abstract

We present spectroscopic measurements of the [OIII] emission line from two subregions of strong Lyman-alpha emission in a radio-quiet Lyman-alpha blob (LAB). The blob under study is LAB1 (Steidel et al. 2000) at z ~ 3.1, and the [OIII] detections are from the two Lyman break galaxies embedded in the blob halo. The [OIII] measurements were made with LUCIFER on the 8.4m Large Binocular Telescope and NIRSPEC on 10m Keck Telescope. Comparing the redshift of the [OIII] measurements to Lyman-alpha redshifts from SAURON (Weijmans et al. 2010) allows us to take a step towards understanding the kinematics of the gas in the blob. Using both LUCIFER and NIRSPEC we find velocity offsets between the [OIII] and Lyman-alpha redshifts that are modestly negative or consistent with 0 km/s in both subregions studied (ranging from -72 +/- 42 -- +6 +/- 33 km/s). A negative offset means Lyman-alpha is blueshifted with respect to [OIII], a positive offset then implies Lyman-alpha is redshifted with respect to [OIII]. These results may imply that outflows are not primarily responsible for Lyman alpha escape in this LAB, since outflows are generally expected to produce a positive velocity offset (McLinden et al. 2011). In addition, we present an [OIII] line flux upper limit on a third region of LAB1, a region that is unassociated with any underlying galaxy. We find that the [OIII] upper limit from the galaxy-unassociated region of the blob is at least 1.4 -- 2.5 times fainter than the [OIII] flux from one of the LBG-associated regions and has an [OIII] to Lyman-alpha ratio measured at least 1.9 -- 3.4 times smaller than the same ratio measured from one of the LBGs.