19,705 research outputs found
Arp 65 interaction debris: massive HI displacement and star formation
Context: Pre-merger interactions between galaxies can induce significant
changes in the morphologies and kinematics of the stellar and ISM components.
Large amounts of gas and stars are often found to be disturbed or displaced as
tidal debris. This debris then evolves, sometimes forming stars and
occasionally tidal dwarf galaxies. Here we present results from our HI study of
Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an
effort to understand the evolution of tidal debris produced by interacting
pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we
are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is one
of them. Methods: Our resolved HI 21 cm line survey is being carried out using
the Giant Metrewave Radio Telescope (GMRT). We used our HI survey data as well
as available SDSS optical, Spitzer infra-red and GALEX UV data to study the
evolution of the tidal debris and the correlation of HI with the star-forming
regions within it. Results: In Arp 65 we see a high impact pre-merger
interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have
a stellar mass ratio of ~ 1:3. The interaction, which probably occurred ~ 1.0
-- 2.5 10 yr ago, appears to have displaced a large fraction of
the HI in NGC 90 (including the highest column density HI) beyond its optical
disk. We also find extended ongoing star formation in the outer disk of NGC 90.
In the major star-forming regions, we find the HI column densities to be ~ 4.7
10 cm or lower. But no signature of star formation was
found in the highest column density HI debris, SE of NGC 90. This indicates
conditions within the highest column density HI debris remain hostile to star
formation and it reaffirms that high HI column densities may be a necessary but
not sufficient criterion for star formation.Comment: Accepted in A&
Observation of quantum depletion in a nonequilibrium exciton-polariton condensate
The property of superfluidity, first discovered in liquid 4He, is closely
related to Bose-Einstein condensation (BEC) of interacting bosons. However,
even at zero temperature, when one would expect the whole bosonic quantum
liquid to become condensed, a fraction of it is excited into higher momentum
states via interparticle interactions and quantum fluctuations -- the
phenomenon of quantum depletion. Quantum depletion of weakly interacting atomic
BECs in thermal equilibrium is well understood theoretically but is difficult
to measure. This is even more challenging in driven-dissipative systems such as
exciton-polariton condensates(photons coupled to electron-hole pairs in a
semiconductor), since their nonequilibrium nature is predicted to suppress
quantum depletion. Here, we observe quantum depletion of an optically trapped
high-density exciton-polariton condensate by directly detecting the spectral
branch of elementary excitations populated by this process. Analysis of the
population of this branch in momentum space shows that quantum depletion of an
exciton-polariton condensate can closely follow or strongly deviate from the
equilibrium Bogoliubov theory, depending on the fraction of matter (exciton) in
an exciton-polariton. Our results reveal the effects of exciton-polariton
interactions beyond the mean-field description and call for a deeper
understanding of the relationship between equilibrium and nonequilibrium BECs.Comment: 18 pages, 5 figures, with supplementary informatio
Hubble Space Telescope Wide Field Planetary Camera 2 observations of hyperluminous infrared galaxies
We present Hubble Space Telescope Wide Field Planetary Camera 2 I-band imaging for a sample of nine hyperluminous infrared galaxies (HLIRGs) spanning a redshift range 0.45 < z < 1.34. Three of the sample have morphologies showing evidence for interactions and six are quasi-stellar objects (QSOs). Host galaxies in the QSOs are detected reliably out to z ∼ 0.8. The detected QSO host galaxies have an elliptical morphology with scalelengths spanning 6.5 < re (kpc) < 88 and absolute k-corrected magnitudes spanning −24.5 < MI < −25.2. There is no clear correlation between the infrared (IR) power source and the optical morphology. None of the sources in the sample, including F15307+3252, shows any evidence for gravitational lensing. We infer that the IR luminosities are thus real. Based on these results, and previous studies of HLIRGs, we conclude that this class of object is broadly consistent with being a simple extrapolation of the ULIRG population to higher luminosities; ULIRGs being mainly violently interacting systems powered by starbursts and/or active galactic nuclei. Only a small number of sources, the infrared luminosities of which exceed 1013 L⊙, are intrinsically less luminous objects that have been boosted by gravitational lensing
HST imaging of hyperluminous infrared galaxies
We present HST WFPC2 I band imaging for a sample of 9 Hyperluminous Infrared
Galaxies spanning a redshift range 0.45 < z < 1.34. Three of the sample have
morphologies showing evidence for interactions, six are QSOs. Host galaxies in
the QSOs are reliably detected out to z ~ 0.8. The detected QSO host galaxies
have an elliptical morphology with scalelengths spanning 6.5 < r_{e}(Kpc) < 88
and absolute k corrected magnitudes spanning -24.5 < M_{I} < -25.2. There is no
clear correlation between the IR power source and the optical morphology. None
of the sources in the sample, including F15307+3252, show any evidence for
gravitational lensing. We infer that the IR luminosities are thus real. Based
on these results, and previous studies of HLIRGs, we conclude that this class
of object is broadly consistent with being a simple extrapolation of the ULIRG
population to higher luminosities; ULIRGs being mainly violently interacting
systems powered by starbursts and/or AGN. Only a small number of sources whose
infrared luminosities exceed 10^{13}Lsun are intrinsically less luminous
objects which have been boosted by gravitational lensing.Comment: 16 Pages. Accepted for publication in MNRA
Optical Properties of 4248 IRAS Galaxies
We have investigated optical properties of 4248 infrared galaxies (IRGs) by
positionally matching data from the IRAS and the SDSS DR3. Our sample includes
3 hyper luminous infrared galaxies (L >10^13Lsun) and 178 ultra luminous
infrared galaxies (10^12Lsun < L < 10^13Lsun). Our findings are as follows: (i)
more IR luminous galaxies tend to have smaller local galaxy density, being
consistent with the picture where luminous IRGs are created by the
merger-interaction of galaxies that happens more often in lower density
regions; (ii) the fractions of AGNs increase as a function of Lir; (iii) there
is a good correlation between Lir and L[OIII] for AGNs, suggesting both of the
parameters can be a good estimator of the total power of AGNs; (iv) a good
correlation is found between Lir and optically estimated star formation rate
(SFR) for star-forming galaxies, suggesting Lir is a good indicator of galaxy
SFR. However, caution is needed when SFR is estimated using Lir, i.e., high SFR
galaxies selected by Lir is frequently merger/interaction, whereas high SFR
galaxies selected by optical emission is often normal spiral or
Magellanic-cloud like irregular galaxies. (v) more IR luminous galaxies have
slightly larger Halpha/Hbeta ratio; (vi) more IR luminous galaxies have more
centrally-concentrated morphology, being consistent with the morphological
appearance of galaxy-galaxy merger remnants. Optical image of ultra/very
luminous infrared galaxies also show frequent signs of merger/interaction.
(vii) comparison with the SED synthesis models indicate that majority of
luminous infrared galaxies (L > 10^11Lsun) may be in a post-starburst phase,
sharing a similar (but not the same) merger/interaction origin with E+A
galaxies. (abridged)Comment: MNRAS in pres
Evolution of secondary cellular circulation flow above submarine bedforms imaged by remote sensing techniques
Normalized radar cross section (NRCS) modulation and acoustic Doppler current profiler (ADCP) measurements above submarine sand ribbons and sand waves are presented. The two study areas are located in the Southern Bight of the North Sea at the Birkenfels wreck and in the sand wave field of the Lister Tief in the German Bight of the North Sea. These measurements reveal the developments of secondary cellular circulations in tidally induced coastal sea areas. Secondary circulation cells can develop perpendicular as well as parallel to the direction of the dominant tidal current flow. Circulation cells developed perpendicular to the direction of the dominant tidal current flow are associated with marine sand ribbons manifested near an underwater wreck. Secondary circulation cells within the water column observed parallel to the direction of the dominant tidal current flow have been initiated during flood and ebb tidal current phases associated with submarine sand waves. These two types of cellular circulations must obey the Hamiltonian principle of classical mechanics. The current–short surface wave interaction is described by the action balance or radiation balance-equation based on weak hydrodynamic interaction theory. The calculated current gradient or strain rate of the applied imaging theory has the same order of magnitude for both bedforms such as marine sand ribbons and sand waves, respectively
Galaxy evolution in nearby groups. II. Galaxy evolution in nearby loose groups. II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud
We present the photometric and kinematic characterization of two groups, USGC
U268 and USGC U376 located in different regions of the Leo cloud. U268,
composed of 10 catalogued members and 11 new added members, has a small
fraction (~24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added
members, with ~38% of ETGs. We find the presence of significant substructures
in both groups suggesting that they are likely accreting galaxies. U268 is
located in a more loose environment than U376. For each member galaxy, broad
band integrated and surface photometry have been obtained in far-UV and near-UV
with GALEX, and in u,g, r, i, z (SDSS) bands. H_alpha imaging and 2D high
resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot
interferometer at the 2.12 m telescope in San Pedro M\'artir, (Baja California,
M\'exico). We improved the galaxy classification and we detected morphological
and kinematical distortions that may be connected to either on-going and/or
past interaction/accretion events or environmental induced secular evolution.
U268 appears more active than U376, with a large fraction of galaxies showing
interaction signatures (60% vs. 13%). The presence of bars among late-type
galaxies is ~10% in U268 and ~$29% in U376. The cumulative distribution of (FUV
- NUV) colours of galaxies in U268 is significantly different than that in U376
with galaxies in U268 bluer than those in U376. In the (FUV-r vs. M_r) and
(NUV-r vs. M_r) planes no members of U268 are found in the `red sequence', even
early-type galaxies lie in the `blue sequence' or in the `green valley'. Most
(80%) of the early-type members in U376 inhabits the `red sequence, a large
fraction of galaxies, of different morphological types, are located in the
`green valley', while the `blue sequence' is under-populated with respect to
U268.Comment: 27 pages, 11 figures, 8 tables, accepted for publication in MNRAS
(abridged abstract
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