2,929 research outputs found
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
The bimodal spiral galaxy surface brightness distribution
We have assessed the significance of Tully and Verheijen's (1997) bimodal
Ursa Major Cluster spiral galaxy near-infrared surface brightness distribution,
focussing on whether this bimodality is simply an artifact of small number
statistics. A Kolmogorov-Smirnov style of significance test shows that the
total distribution is fairly represented by a single-peaked distribution, but
that their isolated galaxy subsample (with no significant neighbours within a
projected distance of around 80 kpc) is bimodal at the 96 per cent level. We
have also investigated the assumptions underlying the isolated galaxy surface
brightness distribution, finding that the (often large) inclination corrections
used in the construction of this distribution reduce the significance of the
bimodality. We conclude that the Ursa Major Cluster dataset is insufficient to
establish the presence of a bimodal near-infrared surface brightness
distribution: an independent sample of around 100 isolated, low inclination
galaxies is required to establish bimodality at the 99 per cent level.Comment: 5 pages LaTeX; 2 embedded figures; re-submitted to MNRAS after
replying to referee's comment
First Detection of CO in a Low Surface Brightness Galaxy
We report on the first attempts at searching for CO in red low surface
brightness galaxies, and the first detection of molecular gas in a low surface
brightness (mu_B(0)_{obs} > 23 mag arcsec^{-2}) galaxy. Using the IRAM 30m
telescope, CO(1-0) and CO(2-1) lines were searched for in four galaxies --
P06-1, P05-5, C05-3, & C04-2. In three of the galaxies no CO was detected, to
T_{MB} ~ 1.8mK (at the 3 sigma level). In the fourth galaxy, P06-1, both lines
were detected. Comparing our findings with previous studies shows P06-1 to have
a molecular-to-atomic mass ratio considerably lower than is predicted using
theoretical models based on high surface brightness galaxy studies. This
indicates the N(H_2)/(int{T(CO)dv}) conversion factor for low surface
brightness galaxies may currently be consistently underestimated by a factor of
3 - 20.Comment: 8 pages, 2 figures, accepted by the ApJ
Saving energy: bringing down Europe's enery prices
In June 2011 the European Commission proposed a new Directive on Energy Efficiency. Its purpose is to put forward a framework
to deliver the EU’s target of reducing its energy consumption by 20% by 2020. Currently, the EU is only on track to achieve half
of those savings.
Apart from the environmental benefits -notably, reducing greenhouse gas emissions- energy savings have significant economic
benefits for European economies: (1) they reduce the amount of money businesses and consumers need to spend on energy, (2)
they have positive effects on employment and (3) they decrease dependency on fossil fuel imports.
But the actual scale of the benefits is often underestimated. In this paper, we show that energy savings do not only bring direct
cost savings; they also indirectly reduce energy prices. Real cost savings resulting from meeting the 20% savings target are likely
to be considerably higher than figures commonly cited. In other words, consumers would use fewer units of energy, and the price
of the units they do use would be lower than they would otherwise be.
Energy savings can reduce energy prices in the following ways:
1. Decreasing fossil fuel prices: international fossil fuel markets are under pressure because there is little reserve production
capacity. This means prices are very sensitive to changes in energy demand. Because energy savings in Europe and the
spillover effects of this action in other world regions will reduce global demand, we expect significant reductions in future
energy prices.
2. Decreasing electricity prices: cheaper fossil fuel prices will reduce electricity prices (because roughly 50% of the EU’s electricity
is produced from fossil fuels). In addition, a lower demand will impact the fuel mix in electricity production: it will occur more
often that lower-priced fuels determine the marginal costs.This will have an additional reduction effect on electricity prices.
3. Decreasing energy prices in the longer term: meeting the EU’s 20% by 2020 energy saving target is expected to save tens
of billions of Euros per year due to avoided investments in energy infrastructure (power generation and transmission, fuel
import and storage facilities). Since it is usual practice to pass on investment costs to energy consumers, a reduction in these
investments will lead to an additional cost saving.
On the basis of the evidence examined in this report, we estimate that the indirect impact on energy prices will be of the same
order as the direct impact of the energy savings. Put simply, for every €1 of energy cost saving, an additional €1 could be saved
due to lower energy prices
Two distance-regular graphs
We construct two families of distance-regular graphs, namely the subgraph of
the dual polar graph of type B_3(q) induced on the vertices far from a fixed
point, and the subgraph of the dual polar graph of type D_4(q) induced on the
vertices far from a fixed edge. The latter is the extended bipartite double of
the former
A Structural and Dynamical Study of Late-Type, Edge-On Galaxies: I. Sample Selection and Imaging Data
We present optical (B & R) and infrared (K_s) images and photometry for a
sample of 49 extremely late-type, edge-on disk galaxies selected from the Flat
Galaxy Catalog of Karenchentsev et al. (1993). Our sample was selected to
include galaxies with particularly large axial ratios, increading the
likelihood that the galaxies in the sample are truly edge-on. We have also
concentrated the sample on galaxies with low apparent surface brightness, in
order to increase the representation of intrinisically low surface brightness
galaxies. Finally, the sample was chosen to have no apprarent bulges or optical
warps so that the galaxies represent undisturbed, ``pure disk'' systems. The
resulting sample forms the basis for a much larger spectroscopic study designed
to place constraints on the physical quantities and processes which shape disk
galaxies. The imaging data presented in this paper has been painstakingly
reduced and calibrated to allow accurate surface photometry of features as
faint as 30 mag/sqr-arcsec in B and 29 mag/sqr-arcsec in R on scales larger
than 10 arcsec. Due to limitations in sky subtraction and flat fielding, the
infrared data can reach only to 22.5 mag/sqr-arcsec in K_s on comparable
scales. As part of this work, we have developed a new method for quantifying
the reliability of surface photometry, which provides useful diagnostics for
the presence of scattered light, optical emission from infrared cirrus, and
other sources of non-uniform sky backgrounds.Comment: scheduled to appear in the Astronomical Journal, LaTeX, 36 pages
including 7 pages of figures (fig 1-2,4). A low resolution version of Figure
3 is included in JPEG format; contours are seriously degraded. A full
resolution Postscript version of Figure 3 (10.6Mb,gzipped) is available
through anonymous ftp at
ftp://ftp.astro.washington.edu/pub/users/jd/FGC/dalcanton.f3.ps.g
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