Further Discoveries of 12CO in Low Surface Brightness Galaxies

Using the IRAM 30m telescope we have obtained seven new, deep CO J(1-0) and J(2-1) observations of low surface brightness (LSB) galaxies. Five of the galaxies have no CO detected to extremely low limits (0.1-0.4 K km/s at J(1-0)), while two of the galaxies, UGC 01922 and UGC 12289, have clear detections in both line transitions. When these observations are combined with all previous CO observations taken of LSB systems, we compile a total of 34 observations, in which only 3 galaxies have had detections of their molecular gas. Comparing the LSB galaxies with and without CO detections to a sample of high surface brightness (HSB) galaxies with CO observations indicates that it is primarily the low density of baryonic matter within LSB galaxies which is causing their low CO fluxes. Finally, we note that one of the massive LSB galaxies studied in this project, UGC 06968 (a Malin-1 `cousin'), has upper limits placed on both M_H2 and M_H2/M_HI which are 10-20 times lower than the lowest values found for any galaxy (LSB or HSB) with similar global properties. This may be due to an extremely low temperature and metallicity within UGC 06968, or simply due to the CO distribution within the galaxy being too diffuse to be detected by the IRAM beam.Comment: 18 pages, 8 figures, 4 tables. Accepted by Ap

On the relation between low-energy constants and resonance saturation

Although there are phenomenological indications that the low-energy constants in the chiral lagrangian may be understood in terms of a finite number of hadronic resonances, it remains unclear how this follows from QCD. One of the arguments usually given is that low-energy constants are associated with chiral symmetry breaking, while QCD perturbation theory suggests that at high energy chiral symmetry is unbroken, so that only low-lying resonances contribute to the low-energy constants. We revisit this argument in the limit of large Nc, discussing its validity in particular for the low-energy constant L8, and conclude that QCD may be more subtle that what this argument suggests. We illustrate our considerations in a simple Regge-like model which also applies at finite Nc.Comment: 15 pages, one figur

Star Formation and Tidal Encounters with the Low Surface Brightness Galaxy UGC 12695 and Companions

We present VLA H I observations of the low surface brightness galaxy UGC 12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy 2333+1234. UGC 12695 shows solid body rotation but has a very lopsided morphology of the H I disk, with the majority of the H I lying in the southern arm of the galaxy. The H I column density distribution of this very blue, LSB galaxy coincides in detail with its light distribution. Comparing the H I column density of UGC 12695 with the empirical (but not well understood) value of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the star formation to be a local affair, occurring only in those regions where the column density is above this star formation threshold. The low surface brightness nature of this galaxy could thus be attributed to an insufficient gas surface density, inhibiting star formation on a more global scale. Significantly, though, the Toomre criterion places a much lower critical density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low SFR to not be applicable. Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and 2333+1234, a dwarf galaxy discovered during this investigation. The close proximity of the three galaxies, combined with UGC 12695's extremely blue color and regions of localized starburst and UGC 12687's UV excess bring to mind mutually induced star formation through tidal activity.Comment: 14 pages, 8 figures (2 color), To be published in A.J., May 2000

On the Determination of ∣Vub∣|V_{ub}| from Inclusive Semileptonic Decay Spectra

We propose a model independent method to determine $|V_{ub}|$ from the energy spectrum of the charged lepton in inclusive semileptonic $B$ decays. The method includes perturbative QCD corrections as well as nonperturbative ones.Comment: LaTeX, 19 pages, 8 figures appended after \end{document} as uu-encoded and compressed .eps files, uses epsf, Technion-PH-94/9, CERN-TH.7308/9

Towards understanding Regge trajectories in holographic QCD

We reassess a work done by Migdal on the spectrum of low-energy vector mesons in QCD in the light of the AdS-QCD correspondence. Recently, a tantalizing parallelism was suggested between Migdal's work and a family of holographic duals of QCD. Despite the intriguing similarities, both approaches face a major drawback: the spectrum is in conflict with well-tested Regge scaling. However, it has recently been shown that holographic duals can be modified to accomodate Regge behavior. Therefore, it is interesting to understand whether Regge behavior can also be achieved in Migdal's approach. In this paper we investigate this issue. We find that Migdal's approach, which is based on a modified Pade approximant, is closely related to the issue of quark-hadron duality breakdown in QCD.Comment: 17 pages, 1 figure. Typos fixed, references added, improved discussion. Minor changes to match the journal versio

The Kinematics in the Core of the Low Surface Brightness Galaxy DDO 39

We present a high resolution, SparsePak two-dimensional velocity field for the center of the low surface brightness (LSB) galaxy DDO 39. These data are a significant improvement on previous HI or Halpha long slit data, yet the inner rotation curve is still uncertain due to significant noncircular and random motions. These intrinsic uncertainties, probably present in other LSB galaxies too, result in a wide range of inner slopes being consistent with the data, including those expected in cold dark matter (CDM) simulations. The halo concentration parameter provides a more useful test of cosmological models than the inner slope as it is more tightly constrained by observations. DDO 39's concentration parameter is consistent with, but on the low end of the distribution predicted by CDM.Comment: 4 pages, accepted for publication in ApJ Letter

Constraints on Warm Dark Matter from Cosmological Reionization

We study the constraints that high-redshift structure formation in the universe places on warm dark matter (WDM) dominated cosmological models. We modify the extended Press-Schechter formalism to derive the halo mass function in WDM models. We show that our predictions agree with recent numerical simulations at low redshift over the halo masses of interest. Applying our model to galaxy formation at high redshift, we find that the loss of power on small scales, together with the delayed collapse of low-mass objects, results in strong limits on the root-mean-square velocity dispersion v_rms of the WDM particles at z=0. For fermions decoupling while relativistic, these limits are equivalent to constraints on the mass m_X of the particles. The presence of a 4 billion solar mass black hole at z=5.8, believed to power the quasar SDSS 1044-1215, implies m_X > 0.5 keV (or v_rms < 0.10 km/s), assuming that the quasar is unlensed and radiating at or below the Eddington limit. Reionization by z=5.8 also implies a limit on m_X. If high-redshift galaxies produce ionizing photons with an efficiency similar to their z=3 counterparts, we find m_X > 1.2 keV (or v_rms < 0.03 km/s). However, given the uncertainties in current measurements from the proximity effect of the ionizing background at redshift 3, values of m_X as low as 0.75 keV (v_rms = 0.06 km/s) are not ruled out. The limit weakens further if, instead, the ionizing-photon production efficiency is greater at high z, but this limit will tighten considerably if reionization is shown in the future to have occurred at higher redshifts. WDM models with m_X 0.04 km/s) produce a low-luminosity cutoff in the high-redshift galaxy luminosity function which is directly detectable with the Next Generation Space Telescope (abridged).Comment: 38 pages, 10 figures, to appear in ApJ. One figure added, some discussion revise

Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence

The rotation curves of low surface brightness galaxies provide a unique data set with which to test alternative theories of gravitation over a large dynamic range in size, mass, surface density, and acceleration. Many clearly fail, including any in which the mass discrepancy appears at a particular length-scale. One hypothesis, MOND [Milgrom 1983, ApJ, 270, 371], is consistent with the data. Indeed, it accurately predicts the observed behavior. We find no evidence on any scale which clearly contradicts MOND, and a good deal which supports it.Comment: Accepted for publication in the Astrophysical Journal. 35 pages AAStex + 9 figures. This result surprised the bejeepers out of us, to

A Morphological-type dependence in the mu_0-log(h) plane of Spiral galaxy disks

We present observational evidence for a galaxy `Type' dependence to the location of a spiral galaxy's disk parameters in the mu_0-log(h) (central disk surface-brightness - disk scale-length) plane. With a sample of ~40 Low Surface Brightness galaxies (both bulge- and disk-dominated) and ~80 High Surface Brightness galaxies, the early-type disk galaxies (<=Sc) tend to define a bright envelope in the mu_0-log(h) plane, while the late-type (>=Scd) spiral galaxies have, in general, smaller and fainter disks. Below the defining surface brightness threshold for a Low Surface Brightness galaxy (i.e. more than 1 mag fainter than the 21.65 B-mag arcsec^(-2) Freeman value), the early-type spiral galaxies have scale-lengths greater than 8-9 kpc, while the late-type spiral galaxies have smaller scale-lengths. All galaxies have been modelled with a seeing-convolved Sersic r^(1/n) bulge and exponential disk model. We show that the trend of decreasing bulge shape parameter (n) with increasing Hubble type and decreasing bulge-to-disk luminosity ratio, which has been observed amongst the High Surface Brightness galaxies, extends to the Low Surface Brightness galaxies, revealing a continuous range of structural parameters.Comment: To be published in ApJ. Inc. three two-part figure