449 research outputs found
An Interacting Galaxy System Along a Filament in a Void
Cosmological voids provide a unique environment for the study of galaxy
formation and evolution. The galaxy population in their interior have
significantly different properties than average field galaxies. As part of our
Void Galaxy Survey (VGS), we have found a system of three interacting galaxies
(VGS_31) inside a large void. VGS_31 is a small elongated group whose members
are embedded in a common HI envelope. The HI picture suggests a filamentary
structure with accretion of intergalactic cold gas from the filament onto the
galaxies. We present deep optical and narrow band H_alpha data, optical
spectroscopy, near-UV and far-UV GALEX and CO(1-0) data. We find that one of
the galaxies, a Markarian object, has a ring-like structure and a tail evident
both in optical and HI. While all three galaxies form stars in their central
parts, the tail and the ring of the Markarian object are devoid of star
formation. We discuss these findings in terms of a gravitational interaction
and ongoing growth of galaxies out of a filament. VGS_31 is one of the first
observed examples of a filamentary structure in a void. It is an important
prototype for understanding the formation of substructure in a void. This
system also shows that the galaxy evolution in voids can be as dynamic as in
high density environments.Comment: 17 pages, 8 figures, accepted for publication in A
KK246, a dwarf galaxy with extended H I disk in the Local Void
We have found that KK 246, the only confirmed galaxy located within the
nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and
signs of an H I cloud with anomalous velocity. It also exhibits clear
misalignment between the kinematical major and minor axes, indicative of an
oval distortion, and a general misalignment between the H I and optical major
axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5
times that of the stellar disk, one of the most extended H I disks known. We
estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the
darkest galaxies known, with a mass-to-light ratio of 89. The relative
isolation and extreme underdense environment make this an interesting case for
examining the role of gas accretion in galaxy evolution.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in A
A dynamical model for the heavily ram pressure stripped Virgo spiral galaxy NGC 4522
A dynamical model including ram pressure stripping is applied to the strongly
HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is
compared with existing VLA HI observations. The model successfully reproduces
the large-scale gas distribution and the velocity field. However it fails to
reproduce the large observed HI linewidths in the extraplanar component, for
which we give possible explanations. In a second step, we solve the induction
equation on the velocity fields of the dynamical model and calculate the large
scale magnetic field. Assuming a Gaussian distribution of relativistic
electrons we obtain the distribution of polarized radio continuum emission
which is also compared with our VLA observations at 6 cm. The observed maximum
of the polarized radio continuum emission is successfully reproduced. Our model
suggests that the ram pressure maximum occurred only ~50 Myr ago. Since NGC
4522 is located far away from the cluster center (~1 Mpc) where the
intracluster medium density is too low to cause the observed stripping if the
intracluster medium is static and smooth, two scenarios are envisaged: (i) the
galaxy moves very rapidly within the intracluster medium and is not even bound
to the cluster; in this case the galaxy has just passed the region of highest
intracluster medium density; (ii) the intracluster medium is not static but
moving due to the infall of the M49 group of galaxies. In this case the galaxy
has just passed the region of highest intracluster medium velocity. This study
shows the strength of combining high resolution HI and polarized radio
continuum emission with detailed numerical modeling of the evolution of the gas
and the large-scale magnetic field.Comment: 15 pages, 11 figures, accepted for publication in A&
A circumnuclear disk of atomic hydrogen in Centaurus A
We present new observations, performed with the Australia Telescope Compact
Array, of the HI absorption in the central regions of Centaurus A. For the
first time, absorption is detected against the radio core at velocities
blueshifted with respect to the systemic velocity. Moreover, the data show that
the nuclear redshifted absorption component is broader than reported before.
With these new results, the kinematics of the HI in the inner regions of Cen A
appears very similar to that observed in emission for the molecular
circumnuclear disk. This suggests that the central HI absorption is not, as was
previously claimed, evidence of gas infall into the AGN, but instead is due to
a cold, circumnuclear disk.Comment: Accepted for publication in A&A Letter, 4 pages, 2 figure
How Dry Are Red Mergers?
The focus of current research in galaxy evolution has increasingly turned to
understanding the effect that mergers have on the evolution of systems on the
red sequence. For those interactions purported to occur dissipationlessly (so
called "dry mergers"), it would appear that the role of gas is minimal.
However, if these mergers are not completely dry, then even low levels of gas
may be detectable. The purpose of our study is to test whether early type
galaxies with HI in or around them, or "wet" ellipticals, would have been
selected as dry mergers by the criteria in van Dokkum (2005, AJ, 130, 2647). To
that end, we examine a sample of 20 early types from the HI Rogues Gallery with
neutral hydrogen in their immediate environs. Of these, the 15 brightest and
reddest galaxies match the optical dry merger criteria, but in each case, the
presence of HI means that they are not truly dry.Comment: 8 pages plus 1 table and 5 figures; accepted for publication in A
Optical and mechanical design of the extreme AO coronagraphic instrument MagAO-X
Here we review the current optical mechanical design of MagAO-X. The project
is post-PDR and has finished the design phase. The design presented here is the
baseline to which all the optics and mechanics have been fabricated. The
optical/mechanical performance of this novel extreme AO design will be
presented here for the first time. Some highlights of the design are: 1) a
floating, but height stabilized, optical table; 2) a Woofer tweeter (2040
actuator BMC MEMS DM) design where the Woofer can be the current f/16 MagAO ASM
or, more likely, fed by the facility f/11 static secondary to an ALPAO DM97
woofer; 3) 22 very compact optical mounts that have a novel locking clamp for
additional thermal and vibrational stability; 4) A series of four pairs of
super-polished off-axis parabolic (OAP) mirrors with a relatively wide FOV by
matched OAP clocking; 5) an advanced very broadband (0.5-1.7micron) ADC design;
6) A Pyramid (PWFS), and post-coronagraphic LOWFS NCP wavefront sensor; 7) a
vAPP coronagraph for starlight suppression. Currently all the OAPs have just
been delivered, and all the rest of the optics are in the lab. Most of the
major mechanical parts are in the lab or instrument, and alignment of the
optics has occurred for some of the optics (like the PWFS) and most of the
mounts. First light should be in 2019A.Comment: 10 pages, proc. SPIE 10703, Adaptive Optics IV, Austin TX, June 201
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