55 research outputs found
The Asymmetric Wind in M82
We have obtained detailed imaging Fabry-Perot observations of the nearby
galaxy M82, in order to understand the physical association between the
high-velocity outflow and the starburst nucleus. The observed velocities of the
emitting gas in M82 reveal a bipolar outflow of material, originating from the
bright starburst regions in the galaxy's inner disk, but misaligned with
respect to the galaxy spin axis. The deprojected outflow velocity increases
with radius from 525 to 655 km/s. Spectral lines show double components in the
centers of the outflowing lobes, with the H-alpha line split by ~300 km/s over
a region almost a kiloparsec in size. The filaments are not simple surfaces of
revolution, nor is the emission distributed evenly over the surfaces. We model
these lobes as a composite of cylindrical and conical structures, collimated in
the inner ~500 pc but expanding at a larger opening angle of ~25 degrees beyond
that radius. We compare our kinematic model with simulations of
starburst-driven winds in which disk material surrounding the source is
entrained by the wind. The data also reveal a remarkably low [NII]/H-alpha
ratio in the region of the outflow, indicating that photoionization by the
nuclear starburst may play a significant role in the excitation of the optical
filament gas, particularly near the nucleus.Comment: 42 pages AASTeX with 16 figures; accepted for publication in ApJ;
figures reformatted for better printin
The Star Formation History of the Disk of the Starburst galaxy M82
Spectroscopic, photometric and dynamical data of the inner 3 kpc part of the
starburst galaxy M82 are analyzed in order to investigate the star formation
history of the stellar disk. The long-slit spectra along the major axis are
dominated by Balmer absorption lines in the region outside the nuclear
starburst all the way up to ~3.5 scalelengths (mu_B=22 mag/arcsec**2). Single
Stellar Population (SSP) spectra of age 0.4-1.0 Gyr match well the observed
spectra in the 1-3 kpc zone, with a mean age of the stellar population
marginally higher in the outer parts. The mass in these populations, along with
that in the gas component, make up for the inferred dynamical mass in the same
annular zone for a Kroupa initial mass function, with a low mass cut-off
m_l=0.4 Msun. The observed ratio of the abundances of alpha elements with
respect to Fe, is also consistent with the idea that almost all the stars in
M82 disk formed in a burst of short duration (0.3 Gyr) around 0.8 Gyr ago. We
find that the optical/near infrared colors and their gradients in the disk are
determined by the reddening with visual extinction exceeding 1 mag even in the
outer parts of the disk, where there is apparently no current star formation.
The disk-wide starburst activity was most likely triggered by the interaction
of M82 with its massive neighbor M81 around 1~Gyr ago. The properties of the
disk of M82 very much resemble the properties of the disks of luminous compact
blue galaxies seen at 0.2-1.0 redshift.Comment: 7 pages, Accepted for publication in Ap
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
Initialization of the shallow water equations with open boundaries by the bounded derivative method
Narrow and variable lines in the ultraviolet spectrum of the Seyfert galaxy NGC4151
The Seyfert galaxy NGC4151 observed when the nucleus is at a minimum has two emission lines of full width at half maximum less than 7 and 16 A, respectively, and varying in intensity by a factor of three in 10 days. These lines are too narrow to be emitted by the whole broad-line region and must arise instead from two localized regions which have a special excitation mechanism, possibly a two-sided jet
A Detailed Study of the CIV 1550 Line Profile and Adjacent Spectral Features in NGC 4151 from 1978 UP to 1983
Fitting technics are applied to study the variations of the 1550 line profile and adjacent features in the IUE spectrum of the Seyfert galaxy NGC 4151, from 1978 up to 1983. New important results are found concerning the kinematics and physics of the emission line gas at a few light-days from the continuum source
Optical colours and polarization of a model reflection nebula. III. Composite and mixture of grains in the nebula with the star in the rear
Detailed observations of NGC 4151 with IUE. IV. absorption line spectrum and variability
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