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Red galaxies in the Lockman Hole: gas properties from an HI stacking experiment

Submitter: Katinka Gereb, Raffaella Morganti, Tom Oosterloo
Description: Red galaxies are an intriguing population when it comes to gas content and star formation properties. This group displays a large diversity in neutral hydrogen (HI) content, from being very HI rich to being completely depleted of gas.

In this work, we perform an HI spectral stacking analysis of galaxies located in the Lockman Hole area in the redshift range 0.06 < z < 0.09 to study the HI content in relation with star-forming/AGN properties. Previous studies of the Lockman Hole provided radio continuum observations for our sample. Galaxies with radio continuum counterparts mostly belong to the faint sub-mJy population. At this low level of radio emission, the presence of a strong AGN is not obvious, and it becomes difficult to disentangle whether the origin of radio emission is star formation or AGN.

We identify a gas poor group without any HI and ionized gas. This group seems to be the prototype of inactive, non-star-forming galaxies (Fig.1). The stacked profile of red galaxies with Low Ionization Nuclear Emission Region (LINER) reveals an HI detection (Fig.1). The presence of 24 micron emission is a good indicator of star formation activity, and we use this diagnostic to identify galaxies with star formation. LINERs with a 24 m detection show relatively large amounts of HI (Fig.2) and are also often detected in radio continuum, probably as a result of ongoing star formation. LINERs which are not detected at 24 micron are also depleted of HI gas (Fig.2). Radio LINERs in the latter group are the best candidates for hosting low-luminosity radio AGN.

This result shows that in faint radio sources at low redshift the radio emission may be originated/dominated by star formation, however low luminosity AGN are also present.

The results are published in Geréb, K.; Morganti, R.; Oosterloo, T. A.; Guglielmino, G.; Prandoni, I. 2013 A&A 558,54 http://arxiv.org/abs/1309.1036) "The Lockman Hole project: gas and galaxy properties from a stacking experiment"
Copyright: ASTRON
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