170 research outputs found
Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/10
I present two-band HST STIS imaging, and WIYN spectral mapping, of ongoing
mass transfer in the interacting galaxy pair NGC 1409/10 (where NGC 1410 is the
Seyfert galaxy also catalogued as III Zw 55). Archival snapshot WFPC2 imaging
from the survey by Malkan et al. showed a dust feature stretching between the
galaxies, apparently being captured by NGC 1409. The new images allow estimates
of the mass being transferred and rate of transfer. An absorption lane
typically 0.25" (100 pc) wide with a representative optical depth tau_B = 0.2
cuts across the spiral structure of NGC 1410, crosses the 7-kpc projected space
between the nuclei, wraps in front of and, at the limits of detection, behind
NGC 1409, and becomes a denser (tau_B = 0.4) polar feature around the core of
NGC 1409. Combination of extinction data in two passbands allows a crude
three-dimensional recovery of the dust structure, supporting the front/back
geometry derived from colors and extinction estimates. The whole feature
contains of order solar masses in dust, implying about 2x10^7 solar
masses of gas, requiring a mass transfer rate averaging ~1 solar mass per year
unless we are particularly unlucky in viewing angle. Curiously, this
demonstrable case of mass transfer seems to be independent of the occurrence of
a Seyfert nucleus, since the Seyfert galaxy in this pair is the donor of the
material. Likewise, the recipient shows no signs of recent star formation from
incoming gas, although NGC 1410 has numerous luminous young star clusters and
widespread H-alpha emission.Comment: 27 pages, 9 figures. Accepted for the Astronomical Journal, March
200
Revealing electronic state-switching at conical intersections in alkyl iodides by ultrafast XUV transient absorption spectroscopy
Conical intersections between electronic states often dictate the chemistry
of photoexcited molecules. Recently developed sources of ultrashort extreme
ultraviolet (XUV) pulses tuned to element-specific transitions in molecules
allow for the unambiguous detection of electronic state-switching at a conical
intersection. Here, the fragmentation of photoexcited iso-propyl iodide and
tert-butyl iodide molecules (i-CHI and t-CHI) through a
conical intersection between Q/Q spin-orbit states is
revealed by ultrafast XUV transient absorption measuring iodine 4d
core-to-valence transitions. The electronic state-sensitivity of the technique
allows for a complete mapping of molecular dissociation from photoexcitation to
photoproducts. In both molecules, the sub-100 fs transfer of a photoexcited
wave packet from the Q state into the Q state at the
conical intersection is captured. The results show how differences in the
electronic state-switching of the wave packet in i-CHI and
t-CHI directly lead to differences in the photoproduct branching
ratio of the two systems
Small scale systems of galaxies I. Photometric and spectroscopic properties of members
This paper is the first of a series addressed to the investigation of galaxy
formation/evolution in small scale systems of galaxies (SSSGs) which are
located in low density cosmic environments. Our algorithm for SSSG selection
includes galaxy systems of 2 or more galaxies lying within 1000 km/s and a 200
h_{100}^{-1} kpc radius volume. We present the analysis of the photometric and
spectroscopic properties of 19 member galaxies belonging to a sample of 11
SSSGs.
In the plane, early-type members may be considered "ordinary",
not "bright" galaxies in the definition given by Capaccioli et al.(1992) with a
significant fraction of galaxies having a disk or disky isophotes. We do not
detect fine structure and signatures of recent interaction events in the
early-type galaxy population, a picture also confirmed by the spectroscopy.
At odd, there are several spiral members with open arm configurations as
expected in interacting systems. At the same time, emission lines in the
spectra of spiral members fall in the HII regions regime defined with
diagnostic diagrams (Veilleux & Osterbrock 1987). None of the objects displays
unambiguous indication of nuclear activity, although fourspiral nuclei could be
ascribed to the class of Seyferts. The star formation rate seems enhanced over
the average expected in spiral galaxies only for poorer SSSGs in particular
pairs (<50 solar masses per year) but without being in the range of starburst
systems.Comment: 24 pages, including 6 figures and 6 tables. Accepted for publication
in A
Attosecond electronic recollision as field detector
We demonstrate the complete reconstruction of the electric field of
visible-infrared pulses with energy as low as a few tens of nanojoules. The
technique allows for the reconstruction of the instantaneous electric field
vector direction and magnitude, thus giving access to the characterisation of
pulses with an arbitrary time-dependent polarisation state. The technique
combines extreme ultraviolet interferometry with the generation of isolated
attosecond pulses.Comment: 5 figure
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
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