479 research outputs found
Variation of Molecular Cloud Properties across the Spiral Arm in M 51
We present the results of high-resolution 13CO(1-0) mapping observations with
the NRO 45m telescope of the area toward the southern bright arm region of M51,
including the galactic center. The obtained map shows the central depression of
the the circumnuclear ring and the spiral arm structure.The arm-to-interarm
ratio of the 13CO(1-0) integrated intensity is 2-4. We also have found a
feature different from that found in the 12CO results. The 12CO/13CO ratio
spatially varies, and shows high values (~20) for the interarm and the central
region, but low values(~10) for the arm. These indicate that there is a denser
gas in the spiral arm than in the interarm. The distribution of the 13CO shows
a better correspondence with that of the H\alpha emission than with the 12CO in
the disk region, except for the central region. We found that the 13CO emission
is located on the downstream side of the 12CO arm, namely there is an offset
between the 12CO and the 13CO as well as the H\alpha emission. This suggests
that there is a time delay between the accumulation of gas caused by the
density wave and dense gas formation, accordingly star formation. This time
delay is estimated to be ~10^7 yr based on the assumption of galactic rotation
derived by the rotation curve and the pattern speed of M51. It is similar to
the growth timescale of a gravitational instability in the spiral arm of M51,
suggesting that the gravitational instability plays an important role for dense
gas formation.Comment: 23 pages, 10 figures, PASJ Vol.54, No.2 (2002), in pres
Observations of Stripped Edge-on Virgo Cluster Galaxies
We present observations of highly inclined, HI deficient, Virgo cluster
spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies
allow us to distinguish extraplanar gas from disk gas. All of our galaxies have
truncated H-alpha disks, with little or no disk gas beyond a truncation radius.
While all the gas disks are truncated, the observations show evidence for a
continuum of stripping states: symmetric, undisturbed truncated gas disks
indicate galaxies that were stripped long ago, while more asymmetric disks
suggest ongoing or more recent stripping. We compare these timescale estimates
with results obtained from two-dimensional stellar spectroscopy of the outer
disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is
a clear example of active ram-pressure stripping, with 40% of its detected HI
being extraplanar. As expected, the outer disk stellar populations of this
galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat
less expected, however, is the fact that the spectrum of the outer disk of this
galaxy, with very strong Balmer absorption and no observable emission, would be
classified as ``k+a'' if observed at higher redshift. Our observations of NGC
4522 and other galaxies at a range of cluster radii allow us to better
understand the role that clusters play in the structure and evolution of disk
galaxies.Comment: 4 pages, 2 figures, to appear in the proceedings of the Island
Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de
Jong, version with high resolution figures can be downloaded from
ftp://ftp.astro.yale.edu/pub/hugh/papers/iu_crowl_h.ps.g
Ionization Source of a Minor-axis Cloud in the Outer Halo of M82
The M82 `cap' is a gas cloud at a projected radius of 11.6 kpc along the
minor axis of this well known superwind source. The cap has been detected in
optical line emission and X-ray emission and therefore provides an important
probe of the wind energetics. In order to investigate the ionization source of
the cap, we observed it with the Kyoto3DII Fabry-Perot instrument mounted on
the Subaru Telescope. Deep continuum, Ha, [NII]6583/Ha, and [SII]6716,6731/Ha
maps were obtained with sub-arcsecond resolution. The superior spatial
resolution compared to earlier studies reveals a number of bright Ha emitting
clouds within the cap. The emission line widths (< 100 km s^-1 FWHM) and line
ratios in the newly identified knots are most reasonably explained by slow to
moderate shocks velocities (v_shock = 40--80 km s^-1) driven by a fast wind
into dense clouds. The momentum input from the M82 nuclear starburst region is
enough to produce the observed shock. Consequently, earlier claims of
photoionization by the central starburst are ruled out because they cannot
explain the observed fluxes of the densest knots unless the UV escape fraction
is very high (f_esc > 60%), i.e., an order of magnitude higher than observed in
dwarf galaxies to date. Using these results, we discuss the evolutionary
history of the M82 superwind. Future UV/X-ray surveys are expected to confirm
that the temperature of the gas is consistent with our moderate shock model.Comment: 7 pages, 5 figures, 2 tables; Accepted for publication in Ap
A simple proof of Perelman's collapsing theorem for 3-manifolds
We will simplify earlier proofs of Perelman's collapsing theorem for
3-manifolds given by Shioya-Yamaguchi and Morgan-Tian. Among other things, we
use Perelman's critical point theory (e.g., multiple conic singularity theory
and his fibration theory) for Alexandrov spaces to construct the desired local
Seifert fibration structure on collapsed 3-manifolds. The verification of
Perelman's collapsing theorem is the last step of Perelman's proof of
Thurston's Geometrization Conjecture on the classification of 3-manifolds. Our
proof of Perelman's collapsing theorem is almost self-contained, accessible to
non-experts and advanced graduate students. Perelman's collapsing theorem for
3-manifolds can be viewed as an extension of implicit function theoremComment: v1: 9 Figures. In this version, we improve the exposition of our
arguments in the earlier arXiv version. v2: added one more grap
On the Hidden Nuclear Starburst in Arp 220
We construct a starburst model for the hidden starbursts in Arp 220 based on
the new Starburst99 models of Leitherer et al. Comparing these stellar
population synthesis models with observations, we show that the hidden power
source must be due to star formation (as opposed to an AGN) at the 50% level or
more in order to avoid an ionizing photon excess problem, and this starburst
must be young ( yr). We derive a current star formation rate
of yr, and an extinction mag for our line of
sight to this hidden starburst.Comment: 4 pages, 1 figure, Accepted for publication in ApJ
Effects of a burst of formation of first-generation stars on the evolution of galaxies
First-generation (Population III) stars in the universe play an important
role inearly enrichment of heavy elements in galaxies and intergalactic medium
and thus affect the history of galaxies. The physical and chemical properties
of primordial gas clouds are significantly different from those of present-day
gas clouds observed in the nearby universe because the primordial gas clouds do
not contain any heavy elements which are important coolants in the gas.
Previous theoretical considerations have suggested that typical masses of the
first-generation stars are between several and
although it has been argued that the formation of very massive stars (e.g., ) is also likely. If stars with several are most popular
ones at the epoch of galaxy formation, most stars will evolve to hot (e.g.,
K), luminous () stars with gaseous and dusty
envelope prior to going to die as white dwarf stars. Although the duration of
this phase is short (e.g., yr), such evolved stars could contribute
both to the ionization of gas in galaxies and to the production of a lot of
dust grains if the formation of intermediate-mass stars is highly enhanced. We
compare gaseous emission-line properties of such nebulae with some interesting
high-redshift galaxies such asIRAS F10214+4724 and powerful radio galaxies.Comment: 25 pages, 7 figures, ApJ, in pres
A Multi-band Photometric Study of Tidal Debris in A Compact Group of Galaxies: Seyfert's Sextet
In order to investigate the properties of the prominent tidal debris feature
extending to the northeast of the compact group of galaxies Seyfert's Sextet,
we analyzed multi-band (U, B, V, VR, R, I, J, H and K') photometric imaging
data and obtained the following results: 1) The radial surface brightness
distribution of this tidal debris in Seyfert's Sextet (TDSS) in each band
appears to be well approximated by an exponential profile. 2) The observed B-V
color of TDSS is similar to those of dwarf elliptical galaxies in nearby
clusters. 3) Comparing the spectral energy distribution (SED) of TDSS with
theoretical photometric evolution models and with the SED of the stars in the
outer part of HCG 79b, we find that its SED is comparable to that of a
10 Gyr-old stellar population with solar metallicity, similar to the stellar
population in the outer part of HCG 79b. This suggests that TDSS consists of
stars that may have been liberated from HCG 79b by strong galaxy interactions,
not a pre-existing dwarf galaxy previously thought.Comment: 9 pages, included 6 figures (5 PS files and 6 EPS files), emulateapj
LaTeX, Publications of the Astronomical Society of Japan, 2002, 54, No.1, in
pres
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