CMB Likelihood Functions for Beginners and Experts

Although the broad outlines of the appropriate pipeline for cosmological likelihood analysis with CMB data has been known for several years, only recently have we had to contend with the full, large-scale, computationally challenging problem involving both highly-correlated noise and extremely large datasets ($N > 1000$). In this talk we concentrate on the beginning and end of this process. First, we discuss estimating the noise covariance from the data itself in a rigorous and unbiased way; this is essentially an iterated minimum-variance mapmaking approach. We also discuss the unbiased determination of cosmological parameters from estimates of the power spectrum or experimental bandpowers.Comment: Long-delayed submission. In AIP Conference Proceedings "3K Cosmology" held in Rome, Oct 5-10, 1998, edited by Luciano Maiani, Francesco Melchiorri and Nicola Vittorio, 343-347, New York, American Institute of Physics 199

Shock heating in the nearby radio galaxy NGC 3801

Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright American Astronomical SocietyPeer reviewe

R=100,000 Spectroscopy of Photodissociation Regions: H2 Rotational Lines in the Orion Bar

Ground state rotational lines of H2 are good temperature probes of moderately hot (200-1000 K) gas. The low A-values of these lines result in low critical densities while ensuring that the lines are optically thin. ISO observations of H2 rotational lines in PDRs reveal large quantities of warm gas that are difficult to explain via current models, but the spatial resolution of ISO does not resolve the temperature structure of the warm gas. We present and discuss high spatial resolution observations of H2 rotational line emission from the Orion Bar.Comment: 4 pages, 1 figure, Proceedings of the ESO Workshop on High Resolution Infrared Spectroscop

A Thin HI Circumnuclear Disk in NGC4261

We report on high sensitivity, spectral line VLBI observations of the HI absorption feature in the radio galaxy NGC4261. Although absorption is only detectable on the most sensitive baseline, it can be unambiguously associated with the counterjet and is interpreted to originate in a thin atomic circumnuclear disk. This structure is probably a continuation of the dusty accretion disk inferred from HST imaging, which could be feeding the massive black hole. HI column densities in front of the counterjet of the order of 10^{21}(T_sp/100 K) cm^{-2} are derived, consistent with X-ray data and VLBI scale free-free absorption. The data presented here are the result of the first scientific project processed on the new EVN MkIV data processor.Comment: 4 pages, 3 postscript figures, Astronomy and Astrophysics Letters, in pres

Cluster abundance and large scale structure

We use the presently observed number density of large X-ray clusters and the linear mass power spectra to constrain $\sigma_8$ and the redshift distortion parameter $\beta$, in both OCDM and $\Lambda$CDM models. The best fit to the observed mass power spectra gives $n=0.84\pm 0.67$ and $\Gamma=0.27^{+0.42}_{-0.16}$, with the theoretically expected degeneracy $\Gamma'=0.247\Gamma\exp(1.4n)=0.220^{+0.036}_{-0.031}$ (all at 95% confidence level). Based on this, we then calculate the cluster-abundance-normalized $\sigma_8$, using different models of mass function: Press & Schechter (1974), Sheth & Tormen (1999), and Lee & Shandarin (1999). The $\sigma_8$ based on the non-spherical-collapse models (ST & LS) are significantly lower, mainly due to the larger mass function within the scale range of our interest. In particular, we found $\sigma_{8{\rm (ST+LS)}}=0.477\Omega_{\rm m0}^\alpha$, where $\alpha=-0.3-0.17\Omega_{\rm m0}^{0.34}-0.13\Omega_{\Lambda 0}$. We also derive the probability distribution function of cluster formation redshift using the Lacey-Cole formalism (1993), but with modifications to incorporate non-spherical collapse. The uncertainties in our $\sigma_8$ are mainly contributed from the normalization in the virial mass-temperature relation. We also obtain for the IRAS galaxies $\sigma_{8\rm (I)}=0.78\pm 0.06$ (at 95% confidence level), and found $\beta_{\rm I(ST+LS)}=0.613\Omega_{\rm m0}^{0.24-0.16(\Omega_{\rm m0}+\Omega_{\Lambda 0})}$. This is more consistent with the recent observations than the result based on the PS formalism.Comment: 11 pages, 8 figures MNRAS, in press (2001