[seminar] Astro Journal Club on 28 September

[Oskari Miettinen]

Dear all,

Our Astro Journal Club will start again on Wednesday at 3:00 pm (sharp) in
the seminar room F-201 of the Physics Department. This time we will
discuss about ultra-high-resolution ALMA observations of an intriguing
pair of dusty starbursts at z=3.442.

Presenter: Oskari Miettinen
Paper title: ALMACAL II: Extreme star-formation-rate densities in a pair
of dusty starbursts at z=3.442 revealed by ALMA 20-milliarcsec resolution
imaging
Authors: Oteo, I., Zwaan, M. A., Ivison, R. J., et al.
Paper status: submitted to ApJ

Summary:
We present ALMA ultra-high-spatial resolution (20 mas) observations of
dust continuum at 920 micron and 1.2 mm in a pair of submm galaxies (SMGs)
at z = 3.442, ALMACAL-1 (A-1: S870=6.5+/-0.2 mJy) and ALMACAL-2 (A-2:
S870=4.4+/-0.2 mJy). The spectroscopic redshifts of A-1 and A-2 have been
confirmed via serendipitous detection of up to nine emission lines. Our
ultra-high-spatial resolution data reveal that about half of the star
formation in each of these starbursts is dominated by a single compact
clump (FWHM size of 350 pc). This structure is confirmed by independent
datasets at 920 micron and 1.2 mm. The star-formation rate (SFR) surface
densities of all these clumps are extremely high, Sigma_SFR=1200 to 3000
Msun/yr/kpc2, the highest found in high-redshift galaxies. There is a
small probability that A-1 and A-2 are the lensed components of a
background source gravitationally amplified by the blazar host. If this
was the case, the effective radius of the source would be Reff= 40 pc, and
the de-magnified SFR surface density would be Sigma_SFR=10000
Msun/yr/kpc2, comparable with the eastern nucleus of Arp 220. Despite
being unable to rule out an AGN contribution, our results suggest that a
significant percentage of the enormous far-IR luminosity in some dusty
starbursts is concentrated in very small star-forming regions. The high
Sigma_SFR in our pair of SMGs could only be measured thanks to the
ultra-high-resolution ALMA observations used in this work, demonstrating
that long-baseline observations are essential to study and interpret the
properties of dusty starbursts in the early Universe.

Link to the paper: http://adsabs.harvard.edu/abs/2016arXiv160706464O

See you all on Wednesday!

If you are willing to present a paper in our journal club, please contact
one or both of the following persons:
Lana Ceraj; lceraj at phy.hr
Oskari Miettinen; oskari at phy.hr

Cheers,
Oskari