Day 89

Sunday.  Reading Friday's astro-ph.


1109.4633
Secular evolution and a non-evoloving black hole to galaxy mass ratio in the last 7 Gyr
Cisternas, Jahnke, Bongiorno, Inskip, Impey, Koekemoer, Merloni, Salvato, Trump


New constraints on the ratio of BH mass to total galaxy stellar mass at 0.3<z<0.9.  Sample size of type-1 AGNs in XMM-COSMOS: 32.  BH mass range: M_BH/M_sun~1e7.2 to 1e8.7, estimated from H_beta in the spectra.  Estimate stellar mass from HST images of host galaxies to remove the AGN component, and using specially-built mass-to-light ratio.  Find no evolution in the mass ratio M_BH/M* = (1+z)^{0.02pm0.34} up to z~0.9.  There is an offset in relation to mass ratio at z=0.  This can be explained by a redistribution of stellar mass to the bulge, likely driven by secular processes (i.e., internal instabilities and minor merging).


1109.4635
Hydrodynamical simulations and semi-analytic models of galaxy formation: two sides of the same coin
Neistein, Khochfar, Vecchia, Schaye


New method to turn Hydro sim into a simply SAM (semi-analytic model), by summarizing the efficiencies of accretion, cooling, star formation, and feedback from Hydro sims, as a function of halo mass and redshift.  (Surprisingly) the mass of individual galaxies is conserved, with deviation at the level of 0.1 dex, with no significant systematics; true for all redshifts, and mass of stars and gas components; although the agreement reaches 0.2 dex [scatter] for stellite galaxies at low redshift.  Show same level of accuracy even in case where SAM uses only one phase of gas within each galaxy [what?].  Moreover, the formation history of one massive galaxy provides sufficient information for the SAM to reproduce population of galaxies within the entire cosmological box.  The reason for the small scatter between the hydro syms and SAM galaxies are: a) efficiencies are matched as functions of the halo mass and redshift, meaning that the evolution within merger-trees agrees on average.  b) For a given galaxy, efficiencies fluctuate around the mean value on time scales of 0.2-2Gyr.  c) The various mass components of galaxies are obtained by integrating the efficiencies over time, averaging out these fluctuations.  Compare efficiencies found here to standard SAM recipes and find that they often deviate significantly.  E.g., smooth accretion is less effective for low mass haloes, and is always composed of hot or dilute gas; cooling is less effective at high redshift; star formation changes only mildly with cosmic time.  Recipe to convert hydro sim to SAM can be applied to any hydro sim, can thus serve as a common language between the two.


1109.4638
Moving mesh cosmology: characteristics of galaxies and halos
Kares, Vogelsberger, Sijacki, Springel, Hernquist


Moving-mesh hydro sims AREPO:  investigate influence on the baryonic properties of simulated galaxies and their surrounding haloes, compared to well-tested SPH code GADGET.  AREPO leads to significantly higher star formation rages for galaxies in massive haloes and more extended gaseous disks in galaxies, which also feature a thinner and smoother morphology than GADGET; AREPO have galaxies with larger sizes and higher specific angular momentum.  These differences persist as a function of numerical resolution.  Galaxy formation simulations greatly benefit from the use of more accurate hydro techniques such as AREPO.


1109.4640
Bayesian power spectrum analysis of interferometric data
Sutter, Wandelt, Malu


* Gibbs sampling: in statistics and statistical physics, Gibbs sampling is an algorithm to generate a sequence of samples from the joint probability distribution of two or more random variables.  The purpose of such a sequence is to approximate the joint distribution; to approximate the marginal distribution of one of the variables, or some subset of the variables (e.g., the unknown parameters or latent variables); or to compute an integral (i.e., expected value of one of the variables).  Typically, some of the variables correspond to observations whose values are known, and hence do not need to be sampled.  Gibbs sampling is an example of MCMC algorithm.


Bayesian power spectrum and signal map inference engine which can be adapted to interferometric observations of anisotropies in CMB, 21cm emission line mapping of galactic brightness fluctuations, or 21cm absorption line mapping of neutral hydrogen in the dark ages.  Method uses Gibbs sampling to generate a sampled representation of the power spectrum posterior and the posterior of signal maps given a set of measured visibilities in the uv-plane.  Use mock interferometric CMB observations to demonstrate the validity of this method in the flat-sky approximation when adapted to take into account arbitrary coverage of the uv-plane, mode correlations due to observations on a finite patch, and heteroschedastic visibility errors.  Computational requirements scale as O(n_p log n_p) where n_p measures the ratio of the size of the detector array to the inter-detector spacing, meaning that Gibbs sampling is a viable technique for meeting the data analysis requirements of future cosmology missions.  


1109.4678
Search for Gamma-ray emission from X-ray selected Seyfert galaxies with Fermi-LAT
Fermi-LAT Collarboration


We did not find a statistically significant gamma-ray excess (TS>25) positionally coincident with any target Seyferts ('radio-quiet' objects), with 2 possible exceptions, out of 120 X-ray bright Seyfert galaxies looked into.


1109.4685
The evolution of Ly-alpha emitting galaxies between z=2.1 and z=3.1
Ciardullo, Gronwall, Wolf, McCathran, Bond, Gawiser, et al


* Heteroscedasticity: in statistics, a collection of random variables is heteroscedastic if there are sub-populations that have different variables than others.  (lack of homoscedasticity, or same finite variance)


Complete sample of 141 objects in ECDF-S, remove x-ray sources and foreground objects, left with 130 LAE candidates (39 spectroscopically confirmed).  Apparent anti-correlation between equivalent width and continuum brightness is likely due to the effect of correlated errors in the heteroskedastic dataset.  Between z=3.1 and z=2.1 (~1Gyr), the LAE luminosity function evolved significantly, with L* fading by 0.4 mag; the number density of sources with L>1.5e43 ergs/s declining by 50%, and the equivalent width scale-length contracting from 70 to 50 Angstroms.  When combined with literature results, observations demonstrate that over the redshift range z=0 to 4, LAEs contain less than 10% of the SF rate density of the universe.


1109.4690
One fewer solution to the cosmological lithium problem
Kirsebom, Davids


As the title says.


1109.4717
Supernovae without host galaxy?  Hypervelocity stars in foreign galaxies
Zinn, Grunden, Bomans


Distinguish between two possible causes for SNe that apparently do not occur within a distinct host galaxy: (i) a host galaxy which is too fait to be detected, or (ii) a hypervelocity star (HVS) as progenitor of the SN.  Use deep imaging to 27mag/arcsec^2 to test case (i).  Out of 4 hostless SNe, find one (SN2006bx) to be put in the hypervelocity progenitor category with high probability, exhibiting a projected velocity of >800 km/s.  SN is due to in situ star formation [how do they know?]


1109.4740
A highly magnified SNe at z=1.703 behind the massive galaxy cluster A1689
Ramanullah et al.


The magnification due to the cluster is 4.3 pm 0.3, allowing high z SNe lightcurves to be observed.  [I guess this is the upper z limit of SNe].


1109.4820
An application of extreme value statistics to the most massive galaxy clusters at low and high redshifts
Waizmann, Ettori, Moscardini


ACT-CL J0102-4915, M200m=2e15, z=0.87
SPT-CL J2106-5844, M200m=1e15, z=1.132
XMMU J2235.32557, M200c=7e14, z=1.4
XMMU J0044.0-2033, M200c=4e14, z=1.579
None of the systems alone is in extreme tension with LCDM (ACT-CL most extreme).  The high-z systems are no more extreme that the low-z systems (A2163, A370, RXJ1347-1145, 1E0657-558)


* Q: what kind of extreme value statistic did they use?  A: GEV (general extreme-value statistics) in extreme value theory, concerning the stochastic behaviour of the maxima or minima of i.i.d. random variables.  Gumbel 1958, Kotz&Nadarajah 2000, Coles 2001.  It's not straightforward (at least, not to me).


1109.4934
Cross-correlating the thermal SZ errect and the distribution of galaxy clusters
Fang, Kadota, Takada


Stacked SZ signal: bin clusters according to their redshift and mass, then cross-correlate the tSZ effect and the galaxy clusters.  This reveals the average SZ profile around the clusters.  Derive error covariance matrix for measuring the stacked SZ signal, then study forecasts for its detection from combined CMB-optical surveys.  Find: stacked SZ signal can be detected with a significant S/N over a wide z range; value peaks for clusters with intermediate mass and redshift.  Stacking allows one to probe the clusters' SZ profiles over a wide range of scales, even out to projected radii as large as around the virial radius, hence provides a promising way to study gas physics at the outskirts of galaxy clusters.


* Done with today's astro-ph (2 hours).