[seminar] Astro Journal Club on 28 October

[Oskari Miettinen]

Dear all,

Our Astro Journal Club will be held today at 3:00 pm (sharp) in the
seminar room F-201 of the Physics Department. This time we will discuss
about atomic hydrogen gas in a young radio galaxy.

Presenter: Jacinta Delhaize
Paper title: Discovery of HI gas in a young radio galaxy at z=0.44 using
the Australian Square Kilometre Array Pathfinder
Authors: J. R. Allison, E. M. Sadler, V. A. Moss, et al.

Summary:

We report the discovery of a new 21-cm HI absorption system using
commissioning data from the Boolardy Engineering Test Array of the
Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5 -
1015.5 MHz band of ASKAP we were able to conduct a blind search for the
21-cm line in a continuous redshift range between z=0.4 and 1.0, which
has, until now, remained largely unexplored. The absorption line is
detected at z=0.44 towards the GHz-peaked spectrum radio source PKS
B1740-B517 and demonstrates ASKAP's excellent capability for performing a
future wide-field survey for HI absorption at these redshifts. Optical
spectroscopy and imaging using the Gemini-South telescope indicates that
the HI gas is intrinsic to the host galaxy of the radio source. The narrow
OIII emission lines show clear double-peaked structure, indicating either
large-scale outflow or rotation of the ionized gas. Archival data from the
XMM-Newton satellite exhibit an absorbed X-ray spectrum that is consistent
with a high column density obscuring medium around the active galactic
nucleus. The HI absorption profile is complex, with four distinct
components ranging in width from 5 to 300 km/s  and fractional depths from
0.2 to 20 per cent. In addition to systemic HI gas, in a circumnuclear
disc or ring structure aligned with the radio jet, we find evidence for a
possible broad outflow of neutral gas moving at a radial velocity of v~300
km/s . We infer that the expanding young radio source (tage~2500 yr) is
cocooned within a dense medium and may be driving circumnuclear neutral
gas in an outflow of ~1 Msun/yr

Link to the paper: http://arxiv.org/abs/1503.01265

Cheers,
Oskari