4,016 research outputs found
Completing HI observations of galaxies II. The Coma Supercluster
High sensitivity 21-cm HI line observations, with an rms noise level of \sim
0.5 mJy, were made of 35 spiral galaxies in the Coma Supercluster, using the
refurbished Arecibo telescope, which resulted in the detection of 25 objects.
These data, combined with the measurements available from the literature,
provide the set of HI data for 94% of all late-type galaxies in the Coma
Supercluster with an apparent photographic magnitude m_p <15.7 mag. We confirm
that the typical scale of HI deficiency around the Coma cluster is 2 Mpc, i.e.
one virial radius. Comparing the HI mass function (HIMF) of cluster with
non-cluster members of the Coma Supercluster we detect a shortage of high HI
mass galaxies among cluster members that can be ascribed to the pattern of HI
deficiency found in rich clusters.Comment: 16 pages, 8 figures, 4 tables. Accepted for publication on A&
Toward the total synthesis of spirastrellolide A. Part 3: Intelligence gathering and preparation of a ring-expanded analogue
Different methods for the formation of the C.25–C.26 bond of spirastrellolide A (1) are evaluated that might qualify for the end game of the projected total synthesis, with emphasis on metathetic ways to forge the macrocyclic frame
The dependence of HII region properties on global and local surface brightness within galaxy discs
Using B, R, and H-alpha images of roughly equal-sized samples of low surface
brightness (LSB) and high surface brightness (HSB) galaxies (~40 galaxies
apiece), we have explored the dependence of HII region properties on local and
global disc surface brightness. We have done this by constructing co-added HII
region luminosity functions (LFs) according to local and central disc surface
brightness and fitting Schechter functions to these LFs. The results show that
the shape of the HII region LF within LSB galaxies does not change noticeably
as different limiting (i.e., mu>mu_lim) local surface brightness values are
used. However, the LFs for HSB galaxies have larger values of L_* and are less
steep at the faint-end than those of LSB galaxies for limiting B-band local
surface brightness values as faint as mu_B,lim~23-24. Both the LFs and the data
for individual HII regions show that luminous (log L>39 ergs/s) HII regions are
much more common within HSB discs than within LSB discs, implying that the
newly formed star clusters are also larger. Taking this into account along with
the results of Monte Carlo simulations, the shapes of the LFs imply that the
regions within LSB discs and those within the LSB areas of HSB discs are
relatively old (~5 Myr) while the regions within HSB discs for mu_B<24 are
significantly younger (<1 Myr). Since the majority of the LSB galaxies do not
have noticeable spiral arms and the majority of the HSB galaxies do, this may
indicate a transition within HSB discs from spiral arm-driven star formation to
a more locally driven, possibly sporadic form of star formation at mu_B~24, a
transition that does not appear to occur within LSB discs.Comment: Accepted to MNRA
B-Alkyl Suzuki couplings for the stereoselective synthesis of substituted pyrans
Unprotected homoallylic alcohols can be directly converted to cis-2,6-disubstituted pyrans by palladium catalyzed B-alkyl Suzuki coupling and subsequent Michael addition
The First CO Map of a Low Surface Brightness Galaxy
Using the Owens Valley Radio Observatory Millimeter-Wavelength Array (OVRO)
we have obtained the first CO map of a low surface brightness (LSB) galaxy. The
studied galaxy, UGC 01922, was chosen for these observations because both of
its previous CO detection with the IRAM 30m telescope and its classification as
a Malin 1 `cousin' - an LSB galaxy with M_HI > 10^10 Msol. The OVRO map
detected approximately 65% of the CO(1-0) flux found earlier with the single
dish measurements, giving a detected gas mass equivalent to M_H2 = 1.1X10^9
Msol. The integrated gas peak lies at the center of the galaxy and coincides
with both the optical and 1.4 GHz continuum emission peaks. The molecular gas
extends well beyond the OVRO beam size (~4'' or 3 kpc), covering ~25% of the
optical bulge. In all, perhaps the most remarkable aspect of this map is its
unexceptional appearance. Given that it took over ten years to successfully
detect molecular gas in any low surface brightness system, it is surprising
that the appearance and distribution of UGC 01922's CO is similar to what would
be expected for a high surface brightness galaxy in the same morphological
class.Comment: 5 pages, including 3 figures and 3 tables. also available online at
http://www.gb.nrao.edu/~koneil. Accepted by ApJ
Observations on Regularization and the Labor Market Performance of Unauthorized and Regularized Immigrants
Task Force Policy Brief No. 4. This author argues that legalization (or "regularization" in Europe) of unauthorized migrants can not only prevent the illegally resident population from building to unacceptable levels, but can also make the management of migration more effective when used in concert with other policy initiatives
- …