107 research outputs found
W poszukiwaniu porządku. Przyrodniczo-filozoficzne rozważania nad ewolucją obrazów świata
Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 dofinansowane zostało ze środków MNiSW w ramach działalności upowszechniającej naukę
Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438
Ram pressure stripping of the multiphase ISM is studied in the perturbed
Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction
~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA
radio continuum observations at 6 and 20 cm are presented. We detect prominent
extraplanar emission to the west of the galactic center, which extends twice as
far as the other tracers of extraplanar material. The spectral index of the
extraplanar emission does not steepen with increasing distance from the galaxy.
This implies in situ re-acceleration of relativistic electrons. The comparison
with multiwavelength observations shows that the magnetic field and the warm
ionized interstellar medium traced by Halpha emission are closely linked. The
kinematics of the northern extraplanar Halpha emission, which is ascribed to
star formation, follow those of the extraplanar CO emission. In the western and
southern extraplanar regions, the Halpha measured velocities are greater than
those of the CO lines. We suggest that the ionized gas of this region is
excited by ram pressure. The spatial and velocity offsets are consistent with a
scenario where the diffuse ionized gas is more efficiently pushed by ram
pressure stripping than the neutral gas. We suggest that the recently found
radio-deficient regions compared to 24 mum emission are due to this difference
in stripping efficiency.Comment: 8 pages, 6 figures, A&A, accepted for publicatio
Atomic gas far away from the Virgo cluster core galaxy NGC 4388. A possible link to isolated star formation in the Virgo cluster?
We have discovered 6 10^7 M_{\odot} of atomic gas at a projected distance
greater than 4' (20 kpc) from the highly inclined Virgo spiral galaxy NGC 4388.
This gas is most probably connected to the very extended H\alpha plume detected
by Yoshida et al. (2002). Its mass makes a nuclear outflow and its radial
velocity a minor merger as the origin of the atomic and ionized gas very
unlikely. A numerical ram pressure simulation can account for the observed HI
spectrum and the morphology of the H\alpha plume. An additional outflow
mechanism is still needed to reproduce the velocity field of the inner H\alpha
plume. The extraplanar compact HII region recently found by Gerhard et al.
(2002) can be explained as a stripped gas cloud that collapsed and decoupled
from the ram pressure wind due to its increased surface density. The
star-forming cloud is now falling back onto the galaxy.Comment: 8 pages with 7 figures. Accepted for publication in A&
An extragalactic HII region in the Virgo cluster
We present spectroscopic observations for six emission-line objects projected
onto the Virgo cluster. These sources have been selected from narrow band
(H\alpha+[NII]) images showing faint detectable continuum emission and EW>100
Angstrom. Five of these sources result [OIII]\lambda 5007 emitters at z ~ 0.31,
while one 122603+130724 is confirmed to be an HII region belonging to the Virgo
cluster. This point-like source has a recessional velocity of ~ 200 km/s, and
is associated with the giant galaxy VCC873 (NGC 4402). It has a higher
luminosity, star formation rate and metallicity than the extragalactic HII
region recently discovered near the Virgo galaxy VCC836 by Gerhard et al.
(2002).Comment: 7 pages, 2 figures, 4 tables. Accepted for publication on A&A. High
resolution figures and FITS images available at
http://goldmine.mib.infn.it/papers/vcc873.htm
A large HI cloud near the centre of the Virgo cluster
We report the discovery of a large HI cloud in the central regions of the
Virgo cluster. It is 110 x 25 kpc in size and contains 3.4 x 10^8 Msol of HI.
The morphology and kinematics of this cloud strongly suggest that it consists
of HI removed from the galaxy NGC 4388 by ram-pressure stripping. It is more
likely the result of an interaction of the ISM of NGC 4388 with the hot halo of
the M86 group and not with the ICM centred on M87. The large extent of the
plume suggests that gas stripped from cluster galaxies can remain neutral for
at least 10^8 yr. Locally, the column density is well above 10^20 cm^-2,
suggesting that the intra-cluster HII regions known to exist in Virgo may have
formed from gas stripped from cluster galaxies. The existence of the HI plume
suggests that stripping of infalling spirals contributes to the enrichment of
the ICM. The HI object in the Virgo cluster recently reported by Minchin et al.
may have a similar origin and may therefore not be a ``dark galaxy''.Comment: Accepted for publication in A&A. 5 pages, 2 figures. Version with
high-resolution figures at http://www.astron.nl/~oosterlo/n438
The Stellar Winds of Galactic Centre and the Low Accretion Rate of Sgr A*
An attempt is made to reconcile the large wind-loss rates of stars in the
Galactic Centre (GC) with the predicted low accretion rate for Sgr A*, the
putative blackhole at the heart of the Milky Way. It is found that, independent
of the details of the accretion, the bound but unaccreted gas has been
accumulating in the potential well of Sgr A* for <1000 yrs and thus is not in
equilibrium. Otherwise, the gas flows of the region would be visible in both
the IR and X-ray. It appears that the blackhole was more active in the recent
past due to the passing of a supernova blast shock but is presently in a
short-lived dormant phase. The extended low frequency radio emission from the
central parsec should visibily increase over the next few decades, as the shock
passes completely in front of the absorbing gas and dust near Sgr A*. The GC
may become more active in < 100,000 yrs due to either another supernova or
sufficient accumulation of stellar winds in the central arcsecond.Comment: accepted by A&A Letter
Spectacular X-ray tails, intracluster star formation and ULXs in A3627
We present the discovery of spectacular double X-ray tails associated with
ESO137-001 and a possibly heated X-ray tail associated with ESO137-002, both
late-type galaxies in the closest rich cluster Abell 3627. A deep Chandra
observation of ESO137-001 allows us for the first time to examine the spatial
and spectral properties of such X-ray tails in detail. Besides the known bright
tail that extends to ~ 80 kpc from ESO137-001, a fainter and narrower secondary
tail with a similar length was surprisingly revealed. There is little
temperature variation along both tails. We also identified six X-ray point
sources as candidates of intracluster ULXs with L(0.3-10 keV) of up to
2.5x10^40 erg s^-1. Gemini spectra of intracluster HII regions downstream of
ESO137-001 are also presented, as well as the velocity map of these HII regions
that shows the imprint of ESO137-001's disk rotation. For the first time, we
unambiguously know that active star formation can happen in the cold ISM
stripped by ICM ram pressure and it may contribute a significant amount of the
intracluster light. We also report the discovery of a 40 kpc X-ray tail of
another late-type galaxy in A3627, ESO137-002. Its X-ray tail seems hot, ~ 2
keV (compared to ~ 0.8 keV for ESO137-001's tails). We conclude that the high
pressure environment around these two galaxies is important for their bright
X-ray tails and the intracluster star formation.Comment: ApJ in press, January 2010, v708, only several minor word changes,
emulateapj5.sty, 24 pages, 11 color + 5 B/W figures (figure quality degraded)
and 4 tables. The abstract has been abbreviated. A high-resolution PDF is
available at: http://www.astro.virginia.edu/~ms4ar/eso137_p3.pd
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Kinematics and excitation of the ram pressure stripped ionized gas filaments in the Coma cluster of galaxies
We present the results of deep imaging and spectroscopic observations of very
extended ionized gas (EIG) around four member galaxies of the Coma cluster of
galaxies: RB199, IC4040, GMP2923 and GMP3071. The EIGs were serendipitously
found in an H-alpha narrow band imaging survey of the central region of the
Coma cluster. The relative radial velocities of the EIGs with respect to the
systemic velocities of the parent galaxies from which they emanate increase
almost monotonically with the distance from the nucleus of the respective
galaxies, reaching -400 - -800 km/s at around 40 - 80 kpc from the galaxies.
The one-sided morphologies and the velocity fields of the EIGs are consistent
with the predictions of numerical simulations of ram pressure stripping. We
found a very low-velocity filament (v_rel = -1300 km/s) at the southeastern
edge of the disk of IC4040. Some bright compact knots in the EIGs of RB199 and
IC4040 exhibit blue continuum and strong H-alpha emission. The equivalent
widths of the H-alpha emission exceed 200 A, and are greater than 1000 A for
some knots. The emission line intensity ratios of the knots are basically
consistent with those of sub-solar abundance HII regions. These facts indicate
that intensive star formation occurs in the knots. Some filaments, including
the low velocity filament of the IC4040 EIG, exhibit shock-like emission line
spectra, suggesting that shock heating plays an important role in ionization
and excitation of the EIGs.Comment: Accepted for publication in The Astrophysical Journal. 14 pages, 23
figures, emulateapj forma
Star Formation in Ram Pressure Stripped Tails
We investigate the impact of star formation and feedback on ram pressure
stripping using high-resolution adaptive mesh simulations, building on a
previous series of papers that systematically investigated stripping using a
realistic model for the interstellar medium, but without star formation. We
find that star formation does not significantly affect the rate at which
stripping occurs, and only has a slight impact on the density and temperature
distribution of the stripped gas, indicating that our previous (gas-only)
results are unaffected. For our chosen (moderate) ram pressure strength,
stripping acts to truncate star formation in the disk over a few hundred
million years, and does not lead to a burst of star formation. Star formation
in the bulge is slightly enhanced, but the resulting change in the
bulge-to-disk ratio is insignificant. We find that stars do form in the tail,
primarily from gas that is ablated from the disk and the cools and condenses in
the turbulent wake. The star formation rate in the tail is low, and any
contribution to the intracluster light is likely to be very small. We argue
that star formation in the tail depends primarily on the pressure in the
intracluster medium, rather than the ram pressure strength. Finally, we compare
to observations of star formation in stripped tails, finding that many of the
discrepancies between our simulation and observed wakes can be accounted for by
different intracluster medium pressures.Comment: 18 pages, 14 figures, accepted to MNRA
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