[seminar] Astro Journal Club on 13 April

[Oskari Miettinen]

Dear all,

Our Astro Journal Club will be held on Wednesday at 3:00 pm (sharp) in the
seminar room F-201 of the Physics Department. This time we will discuss
about galaxy overdensities that are hosting the so-called submillimetre
galaxies.

Presenter: Vernesa Smolcic
Paper title: (Sub)millimetre interferometric imaging of a sample of
COSMOS/AzTEC submillimetre galaxies III. Environments
Authors: Smolcic, V., Miettinen, O., Tomicic, N., et al.
Paper status: Accepted by Astronomy & Astrophysics

Summary:
We study the environment of 23 submillimetre galaxies (SMGs) drawn from
the JCMT/AzTEC 1.1 mm S/N-limited sample in the COSMOS field, as well as 4
COSMOS SMGs at z(spec)>4.5, and 1 at z(spec)=2.49, yielding a sample of 28
SMGs. We search for overdensities using the COSMOS photometric redshifts
based on over 30 UV-NIR photometric bands, reaching an accuracy of
sigma(Delta z/(1+z))=0.0067 (0.0155) at z<3.5 (>3.5). To identify
overdensities we apply the Voronoi tessellation analysis, and estimate the
overdensity estimator delta(g_ as a function of distance from the SMG
and/or overdensity center. We test and validate our approach via
simulations, X-ray detected groups, and spectroscopic verifications using
VUDS and zCOSMOS catalogues showing that even with photometric redshifts
in COSMOS we can efficiently retrieve overdensities out to z=5. Our
results yield that 11/23 (48%) JCMT/AzTEC 1.1mm SMGs occupy overdense
environments. Considering the entire JCMT/AzTEC 1.1mm S/N>4 sample, and
accounting for the expected fraction of spurious detections, yields that
35-61% of the SMGs in the S/N-limited sample occupy overdense
environments. We perform an X-ray stacking analysis in the 0.5-2keV band
using a 32 arcsec aperture and our SMG positions, and find statistically
significant detections. For our z<2 [z>2] subsample we find an average
flux of (4.0+/-0.8)x1e-16 [(1.3+/-0.5)x1e-16] erg/s/cm2 and a
corresponding total mass of M(200) = 2.8x1e13 [2x1e13] MSol. Our results
suggest a higher occurrence of SMGs occupying overdense environments at
z>3, than at z<3. This may be understood if highly star forming galaxies
can only be formed in the highest peaks of the density field tracing the
most massive dark matter haloes at early cosmic epochs, while at later
times cosmic structure may have matured sufficiently that more modest
overdensities correspond to sufficiently massive haloes to form SMGs.

Link to the paper: http://adsabs.harvard.edu/abs/2016arXiv160401775S

Hope to see you all on Wednesday!

Cheers,
Oskari