601 research outputs found
A new observational and numerical study of tidal interactions in M81-M82-NGC3077 system
A nearby system of interacting galaxies M81-M82-NGC3077 triplet (D = 3.3 Mpc; Freeman & Madore 1988) has been studied using multi-wavelength observations and numerical simulations to obtain a comprehensive understanding on the dynamics and the consequences of tidal interactions in a group environment. The VLA 12-field Mosaic H I observations of 2 x 1.5 deg. region have revealed a vast array of H I filaments which suggests that the severity and extent of tidal disruptions far exceed the previous estimates. A tidal remnant of the former H I disk of M82 extending up to 30 kpc (in projection) is identified for the first time, and the pervasive effects of the tidal disruption are traced into the inner disk by optical and CO observations, including a kinematic trace of a large scale bar potential (Yun, Ho, & Lo 1992). The H I disk of M81 is traced out to 40 kpc in radius, and a large scale (l approx. 20 kpc) velocity anomaly ('High Velocity Trough'), which may be a remnant of a gaseous collision, is found within the disk of M81. The large H I bridge between M81 and NGC 3077 (van der Hulst 1979) is also found to extend approx. greater than 50 kpc further, bending around NGC 3077, toward M82. The total H I detected in this experiment, 5.6 x 10(exp 9) solar mass, represents the majority of the single-dish flux (Appleton, Davies, & Stephenson 1981) and suggests that the bulk of H I found in the region belongs to the three galaxies and the tidal filaments. The impact and details of the tidal interactions have been further examined through the use of numerical techniques. The 'restricted 3-body' approach was used to simulate the observed distribution of tidal H I streamers connecting the three galaxies, and the success of the simulation is further strengthened by the accurate predictions on the gas kinematics
HCOOCH3 as a probe of temperature and structure of Orion-KL
We studied the O-bearing molecule HCOOCH3 to characterize the physical
conditions of the different molecular source components in Orion-KL. We
identify 28 methyl formate emission peaks throughout the 50" field of
observations. The two strongest peaks are in the Compact Ridge (MF1) and in the
SouthWest of the Hot Core (MF2). Spectral confusion is still prevailing as half
of the expected transitions are blended over the region. Assuming that the
transitions are thermalized, we derive the temperature at the five main
emission peaks. At the MF1 position we find a temperature of 80K in a 1.8"x0.8"
beam size and 120K on a larger scale (3.6" x2.2"), suggesting an external
source of heating, whereas the temperature is about 130K at the MF2 position on
both scales. Transitions of HCOOCH3 in vt=1 are detected as well and the good
agreement of the positions on the rotational diagrams between the vt=0 and the
vt=1 transitions suggests a similar temperature. The velocity of the gas is
between 7.5 and 8.0km/s depending on the positions and column density peaks
vary from 1.6x10^16 to 1.6x10^17cm^-2. A second velocity component is observed
around 9-10 km/s in a North-South structure stretching from the Compact Ridge
up to the BN object; this component is warmer at the MF1 peak. The two other
C2H4O2 isomers are not detected and the derived upper limit for the column
density is <3x10^14cm^-2 for glycolaldehyde and <2x10^15cm^-2 for acetic acid.
From the 223GHz continuum map, we identify several dust clumps with associated
gas masses in the range 0.8 to 5.8Msun. Assuming that the HCOOCH3 is spatially
distributed as the dust, we find relative abundances of HCOOCH3 in the range
<0.1x10^-8 to 5.2x10^-8. We suggest a relation between the methyl formate
distribution and shocks as traced by 2.12 mum H2 emission.Comment: Accepted for publication in A&
Exploiting cation aggregation in new magnesium amidohaloaluminate electrolytes for magnesium batteries
Mg batteries present an attractive and sustainable alternative to Li-ion batteries, wherein magnesium metal as an anode displays a superior theoretical volumetric energy density of 3833 A h L−1versus 2062 A h L−1 for lithium. An outstanding crucial bottleneck in realising their more widespread uptake is the development of suitable electrolytes, where electrode passivation, a limited electrochemical window, conditioning requirements, low ion mobility and low coulombic efficiencies all contribute to current limitations in Mg batteries. In an area thus far dominated by the thermodynamically stable [Mg2Cl3]+ dinuclear cation, we present here a novel family of magnesium amidohaloaluminate electrolytes [(Dipp)(SiMe3)2NAlCl3]− [MgxCl2x−1]+ where the magnesium chloride cation aggregation has been tailored (x = 1, 2, 3) by substitution of the coordinating ligand to the Mg2+ centre, and show how directly altering this cation affects battery performance (Dipp = 2,6-diisopropylphenyl, Me = methyl). The electrochemical activity of these new electrolytes has been evaluated by cyclic voltammetry, galvanostatic cycling and impedance spectroscopy in Mg–metal symmetrical cells as well as in battery cells with the Mo6S8 Chevrel phase cathode material against magnesium metal. The mononuclear and dinuclear magnesium amidohaloaluminate electrolytes facilitate reversible Mg plating and stripping from the Mg–metal anode with excellent stability, withstanding over 70 hours of continuous cycling. We demonstrate the compatibility of these novel electrolytes with the Mo6S8 Chevrel intercalation cathode material, allowing cycling of a Mg–metal cell up to 100 cycles with coulombic efficiencies above 95%
Extended Star Formation and Molecular Gas in the Tidal Arms near NGC3077
We report the detection of ongoing star formation in the prominent tidal arms
near NGC 3077 (member of the M 81 triplet). In total, 36 faint compact HII
regions were identified, covering an area of ~4x6 kpc^2. Most of the HII
regions are found at HI column densities above 1x10^21 cm^-2 (on scales of 200
pc), well within the range of threshold columns measured in normal galaxies.
The HII luminosity function resembles the ones derived for other low-mass dwarf
galaxies in the same group; we derive a total star formation rate of 2.6x10^-3
M_sun/yr in the tidal feature. We also present new high-resolution imaging of
the molecular gas distribution in the tidal arm using CO observations obtained
with the OVRO interferometer. We recover about one sixth of the CO flux (or
M_H2~2x10^6 M_sun, assuming a Galactic conversion factor) originally detected
in the IRAM 30m single dish observations, indicating the presence of a diffuse
molecular gas component in the tidal arm. The brightest CO peak in the
interferometer map (comprising half of the detected CO flux) is coincident with
one of the brightest HII regions in the feature. Assuming a constant star
formation rate since the creation of the tidal feature (presumably ~3x10^8
years ago), a total mass of ~7x10^5 M_sun has been transformed from gas into
stars. Over this period, the star formation in the tidal arm has resulted in an
additional enrichment of Delta(Z)>0.002. The reservoir of atomic and molecular
gas in the tidal arm is ~3x10^8 M_sun, allowing star formation to continue at
its present rate for a Hubble time. Such wide-spread, low-level star formation
would be difficult to image around more distant galaxies but may be detectable
through intervening absorption in quasar spectra.Comment: Accepted for publication in the Astronomical Journa
Role of EG-VEGF in Human Placentation: Physiological and Pathological Implications
International audienc
Gemini Spectroscopy and HST Imaging of the Stellar Cluster Population in Region B of M82
We present new spectroscopic observations of the stellar cluster population
of region B in the prototype starburst galaxy M82 obtained with the Gillett
Gemini-North 8.1-metre telescope. By coupling the spectroscopy with UBVI
photometry acquired with the Advanced Camera for Surveys (ACS) on the Hubble
Space Telescope (HST), we derive ages, extinctions and radial velocities for
seven young massive clusters (YMCs) in region B. We find the clusters to have
ages between 70 and 200 Myr and velocities in the range 230 to 350 km/s, while
extinctions Av vary between ~1-2.5 mag. We also find evidence of differential
extinction across the faces of some clusters which hinders the photometric
determination of ages and extinctions in these cases. The cluster radial
velocities indicate that the clusters are located at different depths within
the disk, and are on regular disk orbits. Our results overall contradict the
findings of previous studies, where region B was thought to be a bound region
populated by intermediate-age clusters that formed in an independent, offset
starburst episode that commenced 600 Myr-1 Gyr ago. Our findings instead
suggest that region B is optically bright because of low extinction patches,
and this allows us to view the cluster population of the inner M82 disk, which
probably formed as a result of the last encounter with M81. This study forms
part of a series of papers aimed at studying the cluster population of M82
using deep optical spectroscopy and multi-band photometry.Comment: 12 pages, 8 figures; accepted for publication in The Astrophysical
Journa
Observation of the Halo of NGC 3077 Near the "Garland" Region Using the Hubble Space Telescope
We report the detection of upper main sequence stars and red giant branch
stars in the halo of an amorphous galaxy, NGC3077. The observations were made
using Wide Field Planetary Camera~2 on board the Hubble Space Telescope. The
red giant branch luminosity function in I-band shows a sudden discontinuity at
I = 24.0 +- 0.1 mag. Identifying this with the tip of the red giant branch
(TRGB), and adopting the calibration provided by Lee, Freedman, & Madore (1993)
and the foreground extinction of A_B = 0.21 mag, we obtain a distance modulus
of (m-M)_0 = 27.93 +- 0.14(random) +- 0.16(sys). This value agrees well with
the distance estimates of four other galaxies in the M81 Group. In addition to
the RGB stars, we observe a concentration of upper main sequence stars in the
halo of NGC3077, which coincides partially with a feature known as the
``Garland''. Using Padua isochrones, these stars are estimated to be <150 Myrs
old. Assuming that the nearest encounter between NGC3077 and M81 occurred 280
Myrs ago as predicted by the numerical simulations (Yun 1997), the observed
upper main sequence stars are likely the results of the star formation
triggered by the M81-NGC3077 tidal interaction.Comment: 15 pages, 8 figures. Accepted for publication in Astrophysical
Journa
The Eastern Arm of M83 Revisited: High-Resolution Mapping of 12CO 1-0 Emission
We have used the Owens Valley Millimeter Array to map 12CO (J=1-0) along a
3.5 kpc segment of M83's eastern spiral arm at resolutions of 6.5"x3.5", 10",
and 16". The CO emission in most of this segment lies along the sharp dust lane
demarking the inner edge of the spiral arm, but beyond a certain point along
the arm the emission shifts downstream from the dust lane to become better
aligned with the young stars seen in blue and H-beta images. This morphology
resembles that of the western arm of M100. Three possibilities, none of which
is wholly satisfactory, are considered to explain the deviation of the CO arm
from the dust lane: heating of the CO by UV radiation from young stars, heating
by low-energy cosmic rays, and a molecular medium consisting of two (diffuse
and dense) components which react differently to the density wave. Regardless,
the question of what CO emission traces along this spiral arm is a complicated
one. Strong tangential streaming is observed where the arm crosses the
kinematic major axis of the galaxy, implying that the shear becomes locally
prograde in the arms. Inferred from the streaming is a very high gas surface
density of about 230 solar masses/pc**2 and an arm-interarm contrast greater
than 2.3 in the part of the arm near the major axis. Using two different
criteria, we find that the gas at this location is well above the threshold for
gravitational instability -- much more clearly so than in either M51 or M100.Comment: Accepted for publication in ApJ. 25 pages, 5 figures. Manuscript in
LaTeX, figures in pdf. Fig 3 in colo
The Discovery of a Molecular Complex in the Tidal Arms near NGC 3077
We present the discovery of a giant molecular complex (r=350 pc, M_ vir=10^7
M_sun) in the tidal arms south-east of NGC 3077, a member of the M 81 triplet.
The complex is clearly detected in the 12CO (J=1-0) transition at five
independent positions. The position relative to NGC 3077, the systemic velocity
(v_hel=14km/s) and the cloud averaged line width (15km/s) indicate that the
object is not related to Galactic cirrus but is extragalactic. The tidal HI arm
where the molecular complex is located has an total HI mass of M_HI=3x10^8
M_sun. This tidal material was presumably stripped off the outer parts of NGC
3077 during the closest encounter with M 81, about 3x10^8 years ago. After the
complex detected along a torn-out spiral arm of M 81 by Brouillet et al., it is
the second of its kind reported so far. Based on published optical
observations, we have no evidence for on--going star formation in the newly
detected molecular complex. Since the system has all the ingredients to form
stars in the future, we speculate that it might eventually resemble the young
dwarf galaxies in the M 81 group.Comment: 12 pages (including 3 figures), accepted for publication in the ApJ
Letter
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