Monday posting. My computer from Berkeley has not arrived yet, so I'm going to read more abstracts today. Start: 9:30 am.
http://arxiv.org/abs/1103.1641
Properties of dark matter haloes and their correlations: the lesson from principal component analysis
Skibba, Maccio
* What does PCA have anything to do with halo correlations?
They study the correlation between structural parameters. [so it's not talking about correlation functions?] Mass, concentration, spin [how?], shape, overdensity, angle between major axis and angular momentum vector, with two more which describes the relaxedness of the halo. Variance in mass and concentration, and also halo relaxedness, where 3 principal components are required to account for most of the variance. Halo mass is not as dominant as expected (i.e., mass does not determine other halo properties). Angular momentum vector angle appears to be irrelevant (i.e., galaxy spin cannot be predicted from halo properties). Halo environment (large-scale overdensity) is relatively unimportant at fixed mass.
* That's interesting, how did they do this? I guess I'll have to read the paper.
http://arxiv.org/abs/1103.4103
Cosmic microwave background bispectrum of tensor passive modes induced from primordial magnetic fields
Shiraishi, Nitta, Yokohama, Ichiki, Takahashi
* Yeech. What is a tensor massive mode?
A surviving tensor mode from anisotropic stresses that were not compensated prior to neutrino decoupling, or magnetic field seeds existing in the early universe. Sachs-Wolfe effect in CMB is boosted due to the magnetic field perturbation decay after recombination. Such CMB anisotropy is called "tensor passive mode." Signature for this can be probed in the bispectrum. Can constrain this magnetic field strength.
http://arxiv.org/abs/1103.6031
Multi-scale initial conditions for cosmological simulations
Hahn, Abel
* Oh, it's Oliver Hahn! What do they mean by multi-scale initial conditions?
For simulations that "zoom-in", there is a need to generate multi-scale initial conditions. This paper discusses a new algorithm to do so. To generate displacements and velocities, start with a Gaussian white noise, take adaptive convolution of this with a real space transfer function kernel, and solve with an adaptive multi-grid Poisson solver. This new method improves errors by two orders of magnitude over previous approaches. Errors are localized at coarse-fine boundaries, and do not induce ringing in Fourier transforms. Can also optionally do the traditional Fourier space approach (the new technique is real-space based). This new method achieves per cent level accuarcy in correlation functions, density profiles, key halo properties and subhalo abundances [compared to non-zooming simulations, I guess].
Then they try the two-component simulation (CM and baryon), and show that the power spectrum evolution is in excellent agreement with linear perturbation theory [I guess it wasn't before]. For initial baryon density fields, local Lagrangian perturbation theory is better than the current practice of Eulerian linearly scaled densities.
* I didn't know the multi-scale simulations that Tom Abel does had precision problems until now.
http://arxiv.org/abs/1106.1180
A systematic search for massive black hole binaries in SDSS spectroscopic sample
Tsalmantza, Decarli, Dotti, Hogg
* I wonder if it's the same as the DEEP2 survey search, what ... ooh, I forget her name ... did? Seeing the slanted shift or a split in the emission line?
Assuming one of the bound BH is active, run a systematic search in SDSS for a massive BH binary (i.e., galaxy cores). The broad line associated with the BH should show a systematic shift relative to the narrow lines which trace the rest frame of the galaxy. Out of 54k quasars and almost 4k galaxies, they find 32 objects by brute-force modeling each spectrum as a mixture of two quasars at two different redshifts, out of which 9 can be interpreted as BH binaries, doubling the number of candidates available.
Also discovered: new class of extreme double-peaked emitters with exceptionally broad and faint Balmer lines.
* It's different, if I remember correctly.
http://arxiv.org/abs/1106.1205
Discover of cold, pristine gas possibly accreting onto an overdensity of star-forming galaxies at redshift z~1.6
Giavalisco et al.
* I think I've read this before. Yes, I have. Skip to next one.
http://arxive.org/abs/1106.1214
Galaxy formation in heavily overdense regions at z~10: the prevalence of disks in massive halos
Romano-Diaz, Choi, Shlosman, Trenti
* It would seem to make sense that, at that high of z, your galaxies in the most massive halos would be spirals and not ellipticals.
From high-res simulation, studied galaxy evolution at z~10. Possible precursors of qso at z~6. Use Constrained Realizations method to overcome sampling and resolution parameters. At z~10, all massive galaxies are disks, disks are gas-rich and DM halos baryon-rich by a factor of 2.
http://arxiv.org/abs/1106.1418
The origin of dust in high redshift qso's: The case of SDSS J1148+5251
Valiante, Schneider, Salvadori, Bianchi
* I've read this one before, too. They model with SAM with all the gas & astrophysics, for the purpose of analysing SDSS J1148+5251, but don't tell us exactly what the origin of dust is for the nigh z qso's.
http://arxiv.org/abs/1106.1182
Condensate cosmology in O'Raifeartaigh models
Barnard
* Yeech. What is an O'Raifeartaigh model?
* O'Raifeartaigh "no-go" Theorem is an important result in unification theory: it is impossible to combine internal and relativisitic symmetries other than in a trivial fashion. Later generalized to the Coleman-Mandula theorem.
* O'Raifeartaigh Model of supersymmetry breaking: he showed that new supersymmetries could provide a mechanism for circumventing his no-go theorem (which assumed only classical Lie group symmetries).
R-balls (non-topological solitons associated with R-symmetry) decay into gravitinos in gravity- mediated SUSY breaking, which reheats the universe. For gauge mediation R-balls can provide a good dark matter candidate; alternatively they can decay, either reheating or cooling the universe. Conserved R-symmetry permits decay to gravitions or gauginos, whereas spontaneous broken R-symmetry results in decay to visible sector gauge bosons.
* Sorta understood the abstract.
http://arxiv.org/abs/1106.1416
Evolution of curvture and anisotropy near a nonsingular bounce
Xue, Steinhardt
* What is a nonsingular bounce?
* Ekpyrotic phase preceeds bouncing phase, but what are these phases exactly?
* Ekpyrotic model is a precursor to, and part of, the cyclic model. Thanks Wikipedia.
Ekpyrotic contraction phase with w>>1 is followed by a bouncing phase with w<-1 that violates the null energy condition [what is the null energy condition?]. Bouncing phase induced by ghost condensation [what's that?]. Initial curvature and anisotropy, diluted in the ekpyrotic phase, grow back exponentially during the bouncing phase. Curvature perturbations and anisotropy are generated by quantum fluctuations during the ekpyrotic phase. But in the bouncing phase, an adiabatic curvature perturbation grows to dominate which spoils the scale-invariance [which spoils ekpyrotic theory]. A scalar shear perturbation grows nonlinear and creates and overwhelming anisotropy that disrupts the nonsingular bounce altogether.
* I guess this paper lists the problems ekpyrotic theory if certain assumptions are made.
http://arxiv.org/abs/1005.0148
CMB constraints on a stochastic background of primordial magnetic fields
Paoletti, Finelli
* Is this article similar to 1103.4103? That one used bispectrum on CMB.
Consider primordial magnetic field (PMF) contribution to C_l of CMB as a stochastic background or power-law spectrum with index n_B and gaussian amplitude B_lambda at comoving length lambda. Placed upper limit on non-helical PMF; scalar and vector contirubtion to CMB anisotropies discussed to obtain this constraint; also forecast Planck capabilities in constraining B_lambda.
* I wonder why it's a power law? The constraint is B_{1 Mpc} < 5.0 nG at 2 sigma--I don't know if that's big or small (probably small).
http://arxiv.org/abs/1104.3494
Observational signatures of a non-singular bouncing cosmology
Lilley, Lorenz, Clesse
* Okay, what is a non-singular bouncing cosmology? Is it Ekpyrotic?
Scenario: inflation preceded by a bounce. The bounce is non-singular. Study the transfer of cosmological perturbation through the bounce, and any possible observational effects of bouncing cosmologies. Focus on symmetric bounce; compute the evolution of perturbations during contracting, bouncing and inflationary phases. The universe is not in a Bunch-Davies vacuum, but in an excited states that depends on the time scale of the bounce, inducing oscillations superimposed on the nearly scale-invariant primordial spectra for scalar and tensor perturbations. Discuss effects of these oscillations in the CMB and P(k).
* Bunch-Davies vacuum?
* A unique, quantum, thermal state (at T=H/2 pi) that is invariant under all isometries. Explains the origin of cosmological perturbation fluctuations in inflationary models.
http://arxiv.org/abs1106.1429
Tidal disruptions of separated binaries in galactic nuclei
Amaro-Seoane, Miller, Kennedy
* Binaries of what? Galactic nuclei? Tidally disrupting what?
Some galaxies show X-ray flares that can be tidal disruption of stars by a central supermassive black hole [ah.]. Calculations assume nearly parabolic orbit into the BH, and show t^{-5/3} [what is this number?] decay of the bolometric luminosity, which is consistent with measurements. But if a close binary pair of stars fall in, the decay can be slower, ~t^{-1.2}. These scenarios checked with 3-body simulations.
* Title was confusing, but the abstract explained it.
http://arxiv.org/abs/1106.1435
From asymptotic safety to dark energy
Ahn, Kim, Linder
* what is a renormalization group flow?
* I can't tell from the wikipedia abstract, but I'm guessing it's about the rescaling procedure.
Apply renormalization group flow to the cosmological dynamical equations. Flow parameters are linked to cosmological evolution due to a consistency condition from energy-momentum conservation. [what are we renormalizing anyways?] Found: 3 classes of cosmological fixed points for DE, and a barotropic (isotropic pressure) fluid. (1) DE dominated universe which can either be accelerating or decelerating; (2) barotropic dominated universe where DE fades away, and (3) solutions where the gravitational and potential coupling cease to flow. Some details about IR fixed point and UV fixed point coinciding (in which case DE pressure vanishes), and also about only in the deSitter limit does the 3rd class of RG cutoff scale become the Hubble scale. [is it important that the cutoff be Hubble scale?]
http://arxiv.org/as/1106.1438
Primordial magnetism in the CMB: exact treatment of Farday rotation and WMAP7 bounds
Pogosian, Yadav, Ng, Vachaspati
* Another one of the primordial magnetic field detection in CMB papers.
* Faraday rotations: a magneto-optical phenomenon in a medium, causing a rotation of the plan of polarization.
B-modes induced by Faraday rotation can provide signature of primordial magnetic fields because of the frequency dependence, and are only weakly damped o small scales. Measure it in CMB, and found it to be stronger than BBN range of parameters [but presumably very small, though]. Would like CMB polarization at small angular scales.
* Yet another detection method! Signatures in power spectra, angular power, bispectra, and now in B-modes too. Seems like somehow all these should be combined.
http://arxiv.org/abs/1106.1444
The intergalactic medium over the last 10 billion years II: Metal-line absorption and physical conditions
Oppenheimer, Dave, Katz, Kollmeier, Weinberg
* Since z~2.
From cosmolgical hydro simulations: detectability of UV resonance metal-line absorbers observable from Hubble COS spectrograph. Galactic superwind outflow is required to enrich IGM. OIV, CIV, SiIV, and NeVIII absorbers primarily arive from t<10e5 K. OVI probe delta<100 to Zsol~1/50 at z=0; CIV and SiIV absorbers trace primarily T~10e4K gas inside halos. Predict: NeVIII absorbers trace t<10e5K, delta~10 gas. MgX and SiXII are rarely detected, although they trace T=10e6-7K halo gas. [where do the temperature, location and density relation come from with these elements? I guess high temperature can strip electrons off. Maybe density cannot be too high for certain ions to exist. what does the halo potential have anything to do with this--I guess that's also related to the density.]
IGM is enriched in an outsid-in manner, where wind-blown metals released at higher redshift reach lower overdensities. This results in higher ionization species tracing lower-density, older metals.
* does this mean that ions produced at high-z are more highly ionized?
http://arxiv.org/abs/1106.1528
Updated CMB constraints on dark matter annihilation cross-sections
Galli, Iocco, Bertone, Melchiorri
* DM annihilation cross section--how does CMB constrain it?
Injection of secondary particles produced by DM annihilation at redshift 100<z<1000 affects the process of recombination, leaving an imprint on CMB anisotropies. Reassessment with WMAP7 and ACT data, as well as improved treatment of the time-dependent coupling between DM annihilation energy with the thermal gas. Findings rule out "thermal" WIMPS with M<10GeV.
* question answered in abstract.
http://arxiv.org/abs/1105.5916
Reconstruction of the primordial power spectrum from CMB data
Guo, Schwarz, Zhang
* how will they reconstruct the primordial power spectrum?
Reconstruct the shape of the primordial power spectrum from CMB, including WMAP7 and ACT 148GHz data.
* just the normal way, I guess.
At this point: 3:15pm. Restart: 5:30pm.
http://arxiv.org/abs/1106.2023
Non Axi-symmetric anisotropy of solar wind turbulence
Turner, Gogoberidze, Chapman, Hnat, Mueller
* I read this abstract, and I don't understand it, and I"m going to leave it at that.
http://arxiv.org/abs/1106.2041
A hierarchy of voids: More ado about nothing
Paranjape, Lam, Sheth
* Hey, it's Yan! What's so important about voids?
Estimate the void-volume function, the abundance and evolution of large voids, in two ways. (1) remove ambiguity about how void-in-cloud (erases small voids) should be incorporated into the excursion set approach. (2) account for correlations between different scales. Both changes modify the predicted abundances substantially.
* I guess this is a methods paper.
http://arxiv.org/abs/1106.2158
SPIDER: a balloon-borne CMB polarimeter for large angular scales
Filippini, Dore, Halpern, Kuo, Netterfield, Ruhl, Turner etal
* I only listed the names I know on the truncated author list above.
Polarization of the millimeter-wave sky with degree angular resolution. Consists of six monochromatic refracting telescopes. 3 bands: 90, 150, 280 GHz. 20-30 day Antarctic balloon campaign in December 2011; map ~8% of the sky.
* This must be an improvement over WMAP, in terms of resolution (because it can't be in terms of area coverage).
1006.0301
Metallicity-dependent quenching of star formation at high z in small galaxies
Krumholz, Dekel
Metallicity affects SFR because it allows efficient cooling to molecular gas. At z>2, there is a suppression of SFR in dark halos with >~10e11 M_sun; below that, the suppression is near total. At high z, the SFR cannot catch up with the inflow rate (IR), and the accreted gas acts as a reservoir for higher mass halos at later times (z~1-3). At z<1, the IR drops and SFR drops as well.
1106.0496
Ly alpha emitting galaxies as early stages in galaxy formation
Cowie, Barger, Hu
Two samples of GALEX grism selected Ly alpha emitters (LAE): (1) z=[0.195-0.44] and (2) z=[0.65-1.25]. Compare with normal galaxies in the same redshift range with same UV mag distributions, but no Ly alpha. Eliminate AGNs with optical spectroscopy.
There is dramatic evolution in the maximum Ly alpha luminosity over z of 0 to 1. The higher Halpha EW has lower metallicities, bluer color, smaller sizes, and less extinction--consistent with being in the early stages of galaxy formation process. EW>100A is a ~30% indicator that it is a LAE, and 75% of LAE's have EW>100A. LAE's are young (1e8 yr) compared to others (1e9 yr), and the median metallicity of LAE's is 12+log(O/H)8.24, about 0.4 dex lower than UV continuum sample.
1006.0498
Dust-obscured star formation and the contirubtion of galaxies excaping UV/optical color selections at z~2
Riguccini, LeFloc'h, Ilbert, Aussel, Salvato, Capak, McCracken, Kartaltepe, Sanders, Scoville
Stellar mass growth occurs in dust-enshrouded environments. Use Spitzer observation of COSMOS to see how much fraction of SF we're missing.
1006.0499
How supernova feedback turns dark matter cusps into cores
Pontzen, Governato
* ooh, cool; something about DM central cusps
Propose and test a noval physical model of the origin of cored dark matter density profiles. In simulations, central kpc repeatedly fluctuates on sub-dynamical timescales over 2<z<4 because of concentrated SF at center generating large underdense bubbles, and they are responsible for generating the core. Describe with analytic models, the orbits of objects around rapidly fluctuating potentials. Constant DM cores generated in systems of a wide mass range, if central starbursts or AGN phases are sufficiently frequent and energetic.
1106.0317
Modelling stellar populations at high redshift
Maraston
Stellar population carry information about the formation of galaxies and evolution. Most people use stellar population models to obtain (1) age (2) SF history (3) stellar masses, but there are different SPM's out there. Use these to interpret high-z galaxies at z>5.
1106.0766
Statistical properties of thermal Sunyaev-Zel'dovich maps
Munshi, Joudaki, Smidt, Coles
* What about tSZ maps that is special (besides the fact that it has SZ signal in them)?
Use well-motivated models of DM clustering to investigate statistical properties of the SZ maps, that will allow tje determination of probability distribution function. Introduce cumulant correlations as tools to analyse tSZ and relate them to the underlying density distribution.
* I don't get the significance of modeling this; they probably should have mentioned it in the abstract. Probably useful for comparison with observation, is my guess.
1106.1039
Towards a fast, model-independent CMB bispectrum estimator
Pires, Plaszczynski, Lavabre
* I didn't know that bispectrum were model dependent.
The current approach to measure the degree of non-Gaussianity of the CMB is to estimate a single parameter, which is highly model-dependent. [ah.] The bispectrum is a natural and widely studied tool for measuring the non-Gaussianity in a model-independent way. This paper sets grounds for a full CMB bispectrum estimator based on the decomposition of the sphere onto projected patches; this can be quickly calculated and is model-independent. This approach is very flexible.
* Oh, I guess they meant: bispectrum is model independent way of measuring non-Gaussianity.
1106.1079
Observational selection effects and the M-sigma relation
Gultekin, Tremaine, Loeb, Richstone
* about SMBH?
M-sigma relation can possibly be a observational selection effect [!]. It's hard to detect BH whose sphere of influence is smaller than the telescope resolution. "M-sigma relation only representing upper limit to a broad distribution of BH masses in galaxies for a given velocity dispersion" --this hypothesis rejected at a high confidence level; at least for early type galaxies with high velocity dispersions (sigma~268km/s, median).
Also, they describe general procedure for incorporating selection effects in M-sigma relation estimates, but applying this does not change previous results much--the M-sigma relation is intact, and most ellipticals at z=0 contain SMBH. This result may not apply to late type or small galaxies.
1007.4279
Maximal spin and energy conversion efficiency in a symbiotic system of BH, disk and jet
Kovacs, Gergely, Biermann
* sounds like serious GR/astrophysics.
Dominant effect comes from the closed magnetic field line region [where is that?], which reduces the spin limit to values of ~0.89 (instead of ~0.99 in its absence). Observations of spin can constrain the existence of closed magnetic field line region. Also: suppression of radiation from the innermost part of the accretion disk and a collimated jet both increase the spin limit and energy conversion efficiency.
1007.5256
ACT: Extragalactic sources at 148 GHz in the 2008 survey
Marriage, et al
* The source catalog took a year to get accepted by ApJ.
157 sources spanning two orders of magnitude: 15 to 1500 mJy. 98% of ACT sources correspond to sources detected at lower radio frequencies. These are not dust-reemitting galaxies [so it's just primary synchrotron radiation?].
1010.2636
How to make a clean separation between CMB E and B modes with proper foreground masking
Kim
* if you mask, then separating the two modes become difficult, because the information at the masked regions are missing, and E and B modes are non-local information.
I actually completed this one, and had 3 more abstracts, but I failed to save it before the computer crashed. I learned about Hamiltonian mean field model, Gibbs phenomena (in FFT), delta Scuti, Cepheid (Type I, Type II and dwarf), and RR Lyrae variables.
No comments:
Post a Comment