The discovery of a galaxy-wide superwind from a young massive galaxy at redshift z ≈ 3

Abstract

High-velocity galactic outflows, driven by intense bursts of star formation and black hole accretion, are invoked by current theories of galaxy formation 1 to terminate star formation in the most massive galaxies and to deposit heavy elements in the intergalactic medium. From existing observational evidence 2,3 on high-redshift galaxies, it is unclear whether such outflows are localized to regions of intense star formation just a few kiloparsecs in extent, or whether they instead have a significant impact on the entire galaxy and its surroundings. Here we present two-dimensional spectroscopy of a star-forming galaxy 4 at redshift z=3.09 (seen 11.5 gigayears ago, when the Universe was 20 per cent of its current age): its spatially extended Lyα line emission appears to be absorbed by HI in a foreground screen covering the entire galaxy, with a lateral extent of at least 100kpc and remarkable velocity coherence. It was plausibly ejected from the galaxy during a starburst several 10 8 years earlier and has subsequently swept up gas from the surrounding intergalactic medium and cooled. This demonstrates the galaxy-wide impact of high-redshift superwinds.The formation of galaxies requires gas to cool in haloes of dark matter that collapse under gravity from the expansion of the Universe. However, cooling alone overproduces bright galaxies at the present day, so models incorporate thermal conduction, photoionization and galaxy merging, together with additional 'feedback' 1 in the form of galactic-scale outflows. The latter are powered by supernovae and massive stellar winds, or by relativistic winds and jets resulting from gas accretion onto supermassive black holes. Although starburst superwinds have been studied 5 in local dwarf galaxies (such as M82), observational evidence for their counterparts in young massive galaxies at high redshift has been less direct.In Lyman-break galaxies (LBGs) -high-redshift galaxies with moderate masses and star-formation rates -spectroscopic evidence points to powerful outflows 2,3 of interstellar gas, with absorption lines being blueshifted by several hundred kilometres per second from the galaxy's systemic velocity. The gravitationally lensed LBG MS1512-cB58 at redshift z=2.73 is a clear example 3 : absorbing gas is outflowing at ∼ 255 km s −1 at a rate exceeding the star-formation rate, and although it covers the entire starforming region, this shows only that the radius of any shell exceeds ∼ 1 kpc; it is not known whether the outflows are collimated and localized to star-forming regions, or whether they are galaxy-wide. The latter is suggested by the observed decrease in the intergalactic medium (IGM) HI opacity in background quasar sightlines that are close in projection to LBGs 6 (within 0.7 Mpc co-moving). This may indicate that LBGs drive superwinds at ∼ 600 km s −1 for several 10 8 yr, or it might be a statistical fluctuation since there are few LBG-quasar pairs at the smallest separations.To characterize such outflows better via absorption studies, a background light source...

ALMA observations of az≈ 3.1 protocluster: star formation from active galactic nuclei and Lyman-alpha blobs in an overdense environment

“…Previous studies of the LABs in the SSA 22 protocluster have suggested that the extended Lyα emission is predominantly due to the heating of the gas rather than cooling (e.g. Bower et al 2004;Geach et al 2005Geach et al , 2009Geach et al , 2014Wilman et al 2005;Smith et al 2008;Webb et al 2009;Colbert et al 2011;Hayes, Scarlata & Siana 2011). By selection, all of our ALMAobserved LABs host X-ray AGNs which, as shown by Geach et al (2009), already provides a potential source of heating for the Lyα emission through photoionization.…”

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

“…Line widths in the extended gas of NVSS J210626-314003 and TXS 2353-003 are FWHM = 300−400 km s −1 (Figs. 1 and 2), more akin to those observed in a quasar illumination cone at z ∼ 2 (Lehnert et al 2009) and Lyα blobs without a powerful central radio source (e.g., Wilman et al 2005;Overzier et al 2013), than to powerful radio galaxies, including the central regions of our two sources here.…”

The environments of Ly α blobs – I. Wide-field Ly α imaging of TN J1338−1942, a powerful radio galaxy at z ≃ 4.1 associated with a giant Ly α nebula★

“…those in the SA 22 protocluster at z = 3.1) have been extensively observed, and are thought to be driven by starburst events in massive galaxies forming galactic winds (e.g. Ohyama et al 2003;Geach et al 2005Geach et al , 2009Wilman et al 2005;Matsuda et al 2006;Uchimoto et al 2008Uchimoto et al , 2012. Moreover, recent surveys targeting Ly α 'blobs' have also suggested a possible connection between their properties (specifically morphologies) and the environments they reside in (Erb, Bogosavljević & Steidel 2011;Matsuda et al 2011Matsuda et al , 2012.…”

“…For example, the large velocity widths exceeding ∼1000 km s −1 (van Ojik et al 1997) or absorption across the full extent of the Ly α nebulae (Röttgering et al 1995;van Ojik et al 1996) are also seen in the Ly α nebulae in protoclusters (e.g. Wilman et al 2005;Matsuda et al 2006). Furthermore, observational studies suggest that large fraction of very luminous Ly α blobs ( 10 44 erg s −1 ) are likely to be driven by obscured AGNs (e.g.…”