Obscured star formation in Ly-alpha blobs at z = 3.1

TL;DR

This study uses millimetre-wave observations to show that Ly-alpha blobs at z=3.1 have minimal obscured star formation, challenging previous beliefs of intense dusty star-formation activity.

Contribution

First large millimetre survey of Ly-alpha blobs providing upper limits on their obscured star formation, suggesting they are not as dusty or actively star-forming as previously thought.

Findings

No significant millimetre emission detected in individual LABs.

Stacking analysis constrains average star formation rate to be below 450 Msun/yr.

Results challenge the idea that LABs undergo intense dusty star-formation episodes.

Abstract

We present results from the AzTEC/ASTE 1.1-mm imaging survey of 35 Ly-alpha blobs (LABs) found in the SSA22 protocluster at z = 3.1. These 1.1-mm data reach an r.m.s. noise level of 0.7-1 mJy/beam, making this the largest millimetre-wave survey of LABs to date. No significant (> 3.5-sigma) emission is found in any of individual 35 LABs, and from this, we estimate 3-sigma upper limits on the far-infrared luminosity of L_FIR < 2e+12 Lsun. Stacking analysis reveals that the 1.1-mm flux density averaged over the LABs is S(1.1mm) < 0.40 mJy (3-sigma), which places a constraint of L_FIR < 4.5e+11 Lsun. This indicates that earlier 850-um measurements of the LABs may have overestimated their flux densities. Our results suggest that LABs on average have little ultra-luminous obscured star-formation, in contrast to a long-believed picture that LABs undergo an intense episode of dusty star-formation activities with star-formation rates of ~ 10^3 Msun/yr. Observations with ALMA are needed to directly study the obscured part of star-formation activity in the LABs.