4,505 research outputs found
New Reference Galaxy Standards for HI Emission Observations
We have taken advantage of the improved baselines and higher sensitivity
available with the upgraded Arecibo 305m telescope to create a new HI spectral
line catalog of disk galaxies which can be used as a reference catalog for
anyone interested in 21-cm spectral line work. In all 108 galaxies were
observed, covering 24h of the sky at declinations between 0 < delta < 36
degrees and velocities between 0 - 25,000 km s-1. The majority of the galaxies
were observed at least two times on different nights to avoid problems with
RFI, baselines fluctuations, etc. Comparing our measured values with all those
available in the literature show that while large individual variations may
exist, the average differences between the measurements to be zero. In all we
have considerable confidence in our measurements, and the resultant catalog
should be extremely useful as a well defined reference catalog for anyone
interested in 21-cm spectral line work.Comment: Accepted for publication by AJ. 23 pages, with 10 figures and 3
tables. Data tables, paper, etc. available online at
http://www.gb.nrao.edu/~koneil/HIsurvey Replacement paper corrects one error
in Table 1 and two errors in Table
Star Formation in Massive Low Surface Brightness Galaxies
Massive low surface brightness galaxies have disk central surface
brightnesses at least one magnitude fainter than the night sky, but total
magnitudes and masses that show they are among the largest galaxies known. Like
all low surface brightness (LSB) galaxies, massive LSB galaxies are often in
the midst of star formation yet their stellar light has remained diffuse,
raising the question of how star formation is proceeding within these galaxies.
We have undertaken a multi-wavelength study to clarify the structural
parameters and stellar and gas content of these enigmatic systems. The results
of these studies, which include HI, CO, optical, near UV, and far UV images of
the galaxies will provide the most in depth study done to date of how, when,
and where star formation proceeds within this unique subset of the galaxy
population.Comment: to be published in proceeding of IAU 244 - Dark Galaxies and Lost
Baryons IAU Symposiu
The z<=0.1 Surface Brightness Distribution
The surface brightness distribution (SBD) function describes the number
density of galaxies as measured against their central surface brightness.
Because detecting galaxies with low central surface brightnesses is both
time-consuming and complicated, determining the shape of this distribution
function can be difficult. In a recent paper Cross, et al. suggested a
bell-shaped SBD disk-galaxy function which peaks near the canonical Freeman
value of 21.7 and then falls off significantly by 23.5 B mag arcsec-2. This is
in contradiction to previous studies which have typically found flat (slope=0)
SBD functions out to 24 - 25 B mag arcsec^-2 (the survey limits). Here we take
advantage of a recent surface-brightness limited survey by Andreon & Cuillandre
which reaches considerably fainter magnitudes than the Cross, et.al sample (M_B
reaches fainter than -12 for Andreon & Cuillandre while the Cross, et.al sample
is limited to M_B < -16) to re-evaluate both the SBD function as found by their
data and the SBD for a wide variety of galaxy surveys, including the Cross, et
al. data. The result is a SBD function with a flat slope out through the survey
limits of 24.5 B mag arcsec^-2, with high confidence limits.Comment: 5 pages including 5 figures. accepted by A&A
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&
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
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