[Astronomy seminar] Astronomy seminar on Thursday 2nd of November

[Astronomy seminar announcements]

Dear all,
this week our weekly seminar will take place on *Thursday* at 10:30 
instead of Friday.

Title: A revised picture of properties of clumps observed in distant 
star-forming galaxies.
Speaker: Miroslava Dessauges-Zavadsky (Geneva Observatory).

*Thursday* 2nd of November from 10:30 to 11:30 at *FB54*.

Abstract:
Clumpy rest-frame UV morphologies have been revealed among z=1-3 
star-forming galaxies, with the majority of galaxies shown to be 
dominated by ordered disk rotation. It has been suggested that the 
observed clumps are formed during the disk fragmentation resulting from 
gravitational instabilities maintained by the gas inflow onto galaxies. 
The physical properties (masses and radii) of these clumps and their 
possible role in the galactic bulge formation are, however, largely 
debated both on the observational point of view and in numerical 
simulations. Comparing clumps selected in different ways, and in lensed 
or blank field galaxies, we examine the effects of spatial resolution 
and sensitivity on the inferred stellar masses and radii. Large 
differences are found, with median stellar masses ranging from ~109 M☉ 
for clumps in the often-referenced field galaxies to ~107 M☉ for fainter 
clumps selected in deep-field or lensed galaxies. We argue that the 
clump masses, observed in non-lensed galaxies with a limited spatial 
resolution of ∼1 kpc, are artificially increased due to the clustering 
of clumps of smaller mass. Furthermore, we show that the sensitivity 
threshold used for the clump selection affects the inferred masses even 
more strongly than resolution, biasing clumps at the low-mass end. Both 
improved spatial resolution and sensitivity appear to shift the clump 
stellar mass distribution to lower masses by almost two orders of 
magnitude, in agreement with clump masses found in recent 
high-resolution simulations of disk fragmentation. We discuss: (1) the 
nature of the most massive clumps and the connection with the mass of 
their host galaxies; and (2) the existence of a characteristic clump 
mass scale against the hierarchical structure of clumps. Finally, we 
provide a direct proof of the resolution and sensitivity effects on 
clump properties thanks to a unique case-study supplied by an 
exceptional lensing configuration in the field of the galaxy cluster 
MACSJ1206, allowing to reach in one counter-image 30 pc physical scales 
in a z=1 galaxy. A coherent view of the formation and evolution of 
clumps in distant galaxies emerges fully in agreement with state-of-the 
art numerical and mock simulations.


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