Day 4 of Nice vacation and astroph abstract blog. Today I made breakfast for my family (parents & sister) and took a day off from vacation to work on a paper I need to referee.
http://arxiv.org/abs/1105.5642
The evolution of early-type galaxies selected by their spatial clustering
Padilla, Christlein, Gawiser, Marchesini
* I wonder how clustering can probe evolution of red galaxies?
To follow a progenitor-to-descendant relationship, combine clustering with luminosity or stellar mass functions at different redshifts [ah, this is similar to Eric G's research]. This then can be used to infer merger rates. The clustering is used to infer the halo mass of a galaxy at a given redshift; then combine with LCDM prediction and follow the haloes down to their descendant. This shows that MUSYC early type galaxies evolve into brighter galaxies, indicating increase in stellar mass over time [by merger?]; and also indicates that stellar mass selection at different redshifts does not provide samples of progenitor-descendant relationship. They find that the progenitor number density is factor of 5 (with error of +/-4) higher, so infer that there must have been mergers. The luminosity densities of progenitors and descendants are consistent, showing no significant star formation in the early type galaxies since z=1.
* Answer: use galaxy-halo mass relation. This would be a good paper to compare with gg lensing results.
http://arxiv.org/abs/1105.5649
Defrosting in an emergent Galileon cosmology
Levasseur, Brandenberger, Davis
* Why am I doing this to myself? What is Galileon cosmology anyway? I know I looked it up before, and I've already forgotten.
They are talking about before-the-reheating phase of the universe, after inflation but before today's known particles have emerged. This is the "defrosting" or "preheating" phase they're talking about. They mention a "Galileon condensate." Preheating occurs when matter couples to the coherent inflaton [is this the Galileon?] condensate. This coupling has been shown to generate a scale-invariant spectrum of matter fluctuations. Expansion of the universe affects the coupling of the matter to the Galileon condensate. They talk about the defrosting mechanism.
* I guess a Galileon is a type of inflaton? Or something that is responsible for dark energy?
http://arxiv.org/abs/1105.5885
Connecting synchrotron, cosmic rays, and magnetic field in the plane of the galaxy
Jaffe, Banday, Leahy, Leach, Strong
* Ooh, what's the origin of CR's and magnetic fields?
Use synchrotron emission in total and polarized to infer and model the galactic magnetic field in the plane. Extend previous work by including realistic CR e- to match the high-energy data available. This reduces degeneracy, and allows low-energy end of CR e- spectrum to be studied. Assuming pure diffusion propagation, some numbers on the CR e- spectra and synchrotron brightness are predicted, showing CR re-acceleration process to be incompatible with synchrotron data.
* Oh, it's just some extension on the CR modeling they've done. I guess the origin of these things are still not well understood.
http://arxiv.org/abs/1105.5916
Reconstruction of the primordial power spectrum from CMB data
Guo, Schwarz, Zhang
* How did they do the reconstruction?
Use WMAP7 plus ACT data, and a binning method of cubic spline interpolation in log-log space [???]. They find a power-law spectrum [what in the world did they do with the transfer function???]. They find Harrison-Zel'dovich spectrum to be inconsistent with data at 95% confidence.
* The abstract is unclear about how the reconstruction was done.
* The Harrison-Zel'dovich spectrum is the scale-free matter perturbation, P_primordial(k) = Ak (i.e., n=1).
* The transfer function T(k) conveys information about the pre-recombination evolution and the nature of the matter content: P(k) = T^2(k) P_primordial(k).
http://arxiv.org/abs/1105.5644
Direct detection and CMB constraints on light DM scenario of top quark asymmetry and dijet excess at Tevatron
Hektor, Hütsi, Kadastik, Kannike, Raidal, Straub
* Crossover between HEP and cosmology. What do they mean by "light DM"? They all have to be pretty massive, I thought.
Tevatron experiment show Top quark fwd-bkwd asymmetry [mass of top quark is 172 GeV] that can be explained by GeV scale DM [wiki says sub-GeV particles are considered light-DM, I thought it had to be more massive than a GeV], which also improve agreement of the W+jj theory and data. Assuming this particle to be real, they calculate the predicted DM thermal relic density, the nutralino-nucleon cross section, and the CMB constraints on Dirac and Majorana neutralino DM direct detection experiments. They find that DM direct detection experiments and CMB constraints exclude the possibility of stable neutralino, unless local DM density is several times smaller than expected, in which case ~3GeV Dirac DM may be stable. This particle can be tested by the Planck mission, but predicts too broad excess in dijet distribution and strong modification of the missing E distribution in the W+jj events.
* It sounds like real science with both HEP and cosmology, but unfortunately it doesn't sound like a neutralino detection.
Tuesday, May 31, 2011
Monday, May 30, 2011
Day 3
Day 3 of blog and Nice vacation (went to Italy, then Monaco, one day after the Grand Prix).
http://arxiv.org/abs/1105.3980
Cosmic-shear covariance: The log-normal approximation
Hilbert, Hartlap, Schneider
* Is this the same idea about power law "gaussianization", but applied to WL shear power?
Covariance of the cosmic shear correlation functions is needed to get accurate error estimates on the cosmological parameters. Assume that the underlying convergence field follow log-normal statistics, then derive expressions for the cosmic shear covariance. A simplified version: retain only the "most important terms" beyond normal statistics. This has been compared against simulated WL measurements for all 3 cases (normal, log-normal, simplified log-normal). Normal approximation underestimates the confidence region. Log-normal approximation give more realistic confidence regions, but [takes longer--it mentions evaluating complex expressions]? The simplified log-normal approximation has the same confidence region accuracy.
* Answer: yes, it seems to be the case.
http://arxiv.org/abs/1105.4099
On a novel approach using massive clusters at hight redshifts as cosmological probe
Waizmann, Ettori, Moscardini
* Something other than the cluster mass function's dependence (namely the high-mass tail) on the cosmological parameters?
Measure the cumulative distribution of the most massive halos in a sample of sub-volumes tiled in the sky at fixed redshift (just like a set of "test cosmologies")---to validate the fiducial LCDM model. Use the high-mass tail of the mass function, along with general extreme value statistics (GEV) to obtain cumulative distribution function of the massive halos in a given volume. The distribution within the test-cosmology volumes gives a different probe. Need accuracy of 20-30% in cluster mass required, as well as a large area survey over z=1 (1.5) for 10^14.5 M_sun/h (10^14M_sun/h) halos.
* I guess it's more robust to check for the "extreme statistics" over many independent volumes, than just doing so from a single volume. Using the cumulative distribution function helps with reducing the uncertainty.
http://arxiv.org/abs/1105.5421
Towards and observational appraisal of string cosmology
Mulryne, Ward
* Why am I bothering with an abstract that I probably won't understand?
They discuss the observational footprints of several string theory models in the paper. Unfortunately, no details given in the abstract. As you may have noticed, I'm only doing an abstract reading, not a paper reading.
* ...and that's that.
http://arxiv.org/abs/1105.5596
A dynamical model of the local group
Peebles, Tully, Shaya
* What does Peebles have to say?
The dynamics of the Local Group is modeled: 28 galaxies, distances less than 1.5 Mpc. They must have had small peculiar velocities at high redshift, which grew according to standard cosmology. Model mostly consistent (MW rotation speed), with the following notes: 10 of the LG galaxies seem to be remnants from failed galaxy assembly. NGC6822 was closest to MW at z~0.27. Leo I has large angular velocity that may be measurable by the mean stellar motion. 15 galaxies have proper motions greater than 0.05 mas/yr, measurable for with masers.
* Cool.
http://arxiv.org/abs/1105.5599
Long-term transit timing monitoring and refined light curve parameters of HAT-P-13b
Fulton, Shporer, Winn, Holman, Pal, Zachary, Gazak
* Uh oh, is this going to be about cosmology? At least maybe SNe?
It's about a hot Jupiter transit curve
http://arxiv.org/abs/1105.3980
Cosmic-shear covariance: The log-normal approximation
Hilbert, Hartlap, Schneider
* Is this the same idea about power law "gaussianization", but applied to WL shear power?
Covariance of the cosmic shear correlation functions is needed to get accurate error estimates on the cosmological parameters. Assume that the underlying convergence field follow log-normal statistics, then derive expressions for the cosmic shear covariance. A simplified version: retain only the "most important terms" beyond normal statistics. This has been compared against simulated WL measurements for all 3 cases (normal, log-normal, simplified log-normal). Normal approximation underestimates the confidence region. Log-normal approximation give more realistic confidence regions, but [takes longer--it mentions evaluating complex expressions]? The simplified log-normal approximation has the same confidence region accuracy.
* Answer: yes, it seems to be the case.
http://arxiv.org/abs/1105.4099
On a novel approach using massive clusters at hight redshifts as cosmological probe
Waizmann, Ettori, Moscardini
* Something other than the cluster mass function's dependence (namely the high-mass tail) on the cosmological parameters?
Measure the cumulative distribution of the most massive halos in a sample of sub-volumes tiled in the sky at fixed redshift (just like a set of "test cosmologies")---to validate the fiducial LCDM model. Use the high-mass tail of the mass function, along with general extreme value statistics (GEV) to obtain cumulative distribution function of the massive halos in a given volume. The distribution within the test-cosmology volumes gives a different probe. Need accuracy of 20-30% in cluster mass required, as well as a large area survey over z=1 (1.5) for 10^14.5 M_sun/h (10^14M_sun/h) halos.
* I guess it's more robust to check for the "extreme statistics" over many independent volumes, than just doing so from a single volume. Using the cumulative distribution function helps with reducing the uncertainty.
http://arxiv.org/abs/1105.5421
Towards and observational appraisal of string cosmology
Mulryne, Ward
* Why am I bothering with an abstract that I probably won't understand?
They discuss the observational footprints of several string theory models in the paper. Unfortunately, no details given in the abstract. As you may have noticed, I'm only doing an abstract reading, not a paper reading.
* ...and that's that.
http://arxiv.org/abs/1105.5596
A dynamical model of the local group
Peebles, Tully, Shaya
* What does Peebles have to say?
The dynamics of the Local Group is modeled: 28 galaxies, distances less than 1.5 Mpc. They must have had small peculiar velocities at high redshift, which grew according to standard cosmology. Model mostly consistent (MW rotation speed), with the following notes: 10 of the LG galaxies seem to be remnants from failed galaxy assembly. NGC6822 was closest to MW at z~0.27. Leo I has large angular velocity that may be measurable by the mean stellar motion. 15 galaxies have proper motions greater than 0.05 mas/yr, measurable for with masers.
* Cool.
http://arxiv.org/abs/1105.5599
Long-term transit timing monitoring and refined light curve parameters of HAT-P-13b
Fulton, Shporer, Winn, Holman, Pal, Zachary, Gazak
* Uh oh, is this going to be about cosmology? At least maybe SNe?
It's about a hot Jupiter transit curve
Sunday, May 29, 2011
Day 2
Nice, France. Day 2 of vacation and astroph blog.
1105.3975
Photometric redshifts and quasar probabilities from a single, data-driven generative model
Bovy, Meyers, Hennawi, Hogg, etal.
* Are they talking about spectra or multi-band photometry classification? I guess normally it would be from spectra, but I'm preoccupied with multi-band photometry and so easily confused.
A new technique: simultaneously classifies and estimate z of quasars; incorporates flux uncertainties, missing data, multi-wavelength photometry (is spectra given assumed??), from models of quasars ("extreme deconvolution technique") in flux-redshift space, to estimate the underlying density. This allows for quasar flux densities to be estimated over a chosen redshift range. Speed obtained by combining using analytical forms for the basis, and using many simple components. This method is competitive with the best photometric techniques and photo-z techniques. Inclusion of UV and NIR data significantly improves quasar-star separation (they were talking about ugriz system!) by a factor of 3. Code publicly available.
* This abstract was hard to decipher to a non-expert like myself, mostly because the basic assumptions are not described.
1105.3975
Photometric redshifts and quasar probabilities from a single, data-driven generative model
Bovy, Meyers, Hennawi, Hogg, etal.
* Are they talking about spectra or multi-band photometry classification? I guess normally it would be from spectra, but I'm preoccupied with multi-band photometry and so easily confused.
A new technique: simultaneously classifies and estimate z of quasars; incorporates flux uncertainties, missing data, multi-wavelength photometry (is spectra given assumed??), from models of quasars ("extreme deconvolution technique") in flux-redshift space, to estimate the underlying density. This allows for quasar flux densities to be estimated over a chosen redshift range. Speed obtained by combining using analytical forms for the basis, and using many simple components. This method is competitive with the best photometric techniques and photo-z techniques. Inclusion of UV and NIR data significantly improves quasar-star separation (they were talking about ugriz system!) by a factor of 3. Code publicly available.
* This abstract was hard to decipher to a non-expert like myself, mostly because the basic assumptions are not described.
Saturday, May 28, 2011
A new blog
I'm going to be posting about my astro-ph reading. It will mostly be abstract summaries (if that's possible) and what I've learned from them.
http://arxiv.org/abs/1105.5139
The Morphology of the Thermal Sunyaev-Zel'dovich Sky
Munshi, Smidt, Joudaki, Coles
tSZ effect (in CMB at high angular frequencies) is the large scale pressure fluctuations in the baryonic distribution, and estimates the properties of the projected 3d pressure fluctuations. It is a sensitive probe of the density fluctuations, and its bias associated with pressure can be separated from bispectrum (or the one-point statistics analogue, the skewness).
The morphological properties (I assume we're talking about the power spectra), in addition to skewness, is probed by the Minkowski Functionals (which at low order is identical to skewness). Generalized skewness parameters can be extended to define a set of 3 associated generalized skew-spectra. Use skew-spectra to probe the morphology of the tSZ sky. The skew-spectra can be recovered from the data when mask and noise present using Pseudo-Cl (PCL) approach.
This will allow mode by mode estimation and will help differentiate various other sources of non-Gaussianity.
* This abstract is not very clear in what they mean by "morphology" (IMO)
* I guess this is about how to sort out tSZ from the primordial non-G effects
http://arxiv.org/abs/1105.5292
The linear power spectrum of observed source number counts
Challinor, Lewis
* What in the world do they mean by linear power spectra of source number counts?
Gives: the exact results on observer number of galaxies per solid angle and redshift to the underlying proper source density and velocity, BG evolution and LOS potentials, based on linear perturbations assuming GR. Correctly incorporates clustering, z-space distortions, magnification, radial displacement, and other linear terms on sub-horizon scales. Gives result for amgnitude-limited survey at low z; discuss angular power spectrum of total count distribution (nb: I think they mean what the powser spectrum is given these selection effects). Also calculates X-corr with the CMB polarization and temperatures (magnification and velocity effects for the sources). Contribution of z-space distortions is generally small. Also relate source counts to line radiation (e.g., 21-cm) from sources.
* Are they going to include NL effects, so that it can model the real Universe?
* What is the significance of this paper?
== this is how far I got in about one hour today. BBC news is on its third cycle. ==
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