5 research outputs found
Thick disks in the Hubble Space Telescope Frontier Fields
Thick disk evolution is studied using edge-on galaxies in two Hubble Space
Telescope Frontier Field Parallels. The galaxies were separated into 72 clumpy
types and 35 spiral types with bulges. Perpendicular light profiles in F435W,
F606W and F814W (B, V and I) passbands were measured at 1 pixel intervals along
the major axes and fitted to sech^2 functions convolved with the instrument
line spread function (LSF). The LSF was determined from the average point
spread function (PSF) of ~20 stars in each passband and field, convolved with a
line of uniform brightness to simulate disk blurring. A spread function for a
clumpy disk was also used for comparison. The resulting scale heights were
found to be proportional to galactic mass, with the average height for a
10^9.5-10^10.5 Msun galaxy at z=1.5-2.5 equal to 0.63+-0.24 kpc. This value is
probably the result of a blend between thin and thick disk components that
cannot be resolved. Evidence for such two-component structure is present in an
inverse correlation between height and midplane surface brightness. Models
suggest that the thick disk is observed best between the clumps, and there the
average scale height is 1.06+-0.43 kpc for the same mass and redshift. A
0.63+-0.68 mag V-I color differential with height is also evidence for a
mixture of thin and thick components.Comment: 11 pages, 19 figures, accepted by Ap
The June 2016 Optical and Gamma-Ray Outburst and Optical Micro-Variability of the Blazar 3C454.3
The quasar 3C454.3 underwent a uniquely-structured multi-frequency outburst
in June 2016. The blazar was observed in the optical band by several
ground-based telescopes in photometric and polarimetric modes, at -ray
frequencies by the \emph{Fermi}\ Large Area Telescope, and at 43 GHz with the
Very Long Baseline Array. The maximum flux density was observed on 2016 June 24
at both optical and -ray frequencies, reaching
mJy and ph cm s, respectively. The June 2016
outburst possessed a precipitous decay at both -ray and optical
frequencies, with the source decreasing in flux density by a factor of 4 over a
24-hour period in band. Intraday variability was observed throughout the
outburst, with flux density changes between 1 and 5 mJy over the course of a
night. The precipitous decay featured statistically significant quasi-periodic
micro-variability oscillations with an amplitude of - about the
mean trend and a characteristic period of 36 minutes. The optical degree of
polarization jumped from to nearly 20\% during the outburst, while
the position angle varied by \sim120\degr. A knot was ejected from the 43 GHz
core on 2016 Feb 25, moving at an apparent speed .
From the observed minimum timescale of variability
hr and derived Doppler factor
, we find a size of the emission region
cm. If the quasi-periodic micro-variability
oscillations are caused by periodic variations of the Doppler factor of
emission from a turbulent vortex, we derive a rotational speed of the vortex
.Comment: 19 pages, 13 figures, 3 tables, accepted to the Astrophysical Journal
2019 March