On Macroscopic Complexity and Perceptual Coding

The theoretical limits of 'lossy' data compression algorithms are considered. The complexity of an object as seen by a macroscopic observer is the size of the perceptual code which discards all information that can be lost without altering the perception of the specified observer. The complexity of this macroscopically observed state is the simplest description of any microstate comprising that macrostate. Inference and pattern recognition based on macrostate rather than microstate complexities will take advantage of the complexity of the macroscopic observer to ignore irrelevant noise

Large Scale Structure in Dark Matter and Galaxies

Galaxy evolution and AGN growth in the early universe are believed to be strongly driven by merging (hierarchical growth) and galaxy dynamical interactions. Thus, a fall exploration of the environmental influences is absolutely essential to understanding this early evolution. The Cosmic Evolution Survey (COSMOS, [Scoville et al. 2007a]) is specifically designed to probe the correlated coevolution of galaxies, star formation, active galactic nuclei (AGN) and dark matter (DM) largescale structures (LSS) over the redshift range z > 0.5 to 6. The survey includes midti-wavelength imaging and spectroscopy from X-ray to radio wavelengths covering a 2 square degree equatorial field. Photometric redshifts are derived using 34 photometric UV-IR bands for 800,000 galaxies with accuracy reaching σ_z/(l +z) = 0.7 — 1.6% for bright galaxies (I_(AB) = 22 —24mag). Large scale structures have been traced in COSMOS from z = 0.2 to 2.5 in the baryons (from the galaxy density distribution) and in the dark matter to z = 1.1 (from weak tensing analysis of HST ACS images). These LSS extend over 20 Mpc with total mass up to ~10^(15)_ ⊙. The overall distribution of galaxy overdensities is similar with those predicted from the Millennium simulation. A trend for an increasing high overdensities at low z is clearly apparent in these data. At higher redshifts of z ~ 1, there appears to be a significant discrepancy between the observations and the simulations - with the simidations exhibiting earUer development of high density structores than is seen in the observed galaxy distributions. The observed galaxy spectral energy distributions (SEDs) and star formation rates (SFRs) clearly depend systematically on both redshift and environmental density - early SED types and lower SFRs in denser regions and at lower redshift. This evolution is probably driven by the exhaustion of the ISM and by galaxy interactions, the latter being strongly correlated with regions of highest dark matter density. Strong evolution is seen the frequency of close pairs of galaxies - particidarly for lower mass companions at projected separations 10 - 20 kpc

Fast Autocorrelated Context Models for Data Compression

A method is presented to automatically generate context models of data by calculating the data's autocorrelation function. The largest values of the autocorrelation function occur at the offsets or lags in the bitstream which tend to be the most highly correlated to any particular location. These offsets are ideal for use in predictive coding, such as predictive partial match (PPM) or context-mixing algorithms for data compression, making such algorithms more efficient and more general by reducing or eliminating the need for ad-hoc models based on particular types of data. Instead of using the definition of the autocorrelation function, which considers the pairwise correlations of data requiring O(n^2) time, the Weiner-Khinchin theorem is applied, quickly obtaining the autocorrelation as the inverse Fast Fourier transform of the data's power spectrum in O(n log n) time, making the technique practical for the compression of large data objects. The method is shown to produce the highest levels of performance obtained to date on a lossless image compression benchmark.Comment: v2 includes bibliograph

Massive Accretion Disks

Recent high resolution near infrared (HST-NICMOS) and mm-interferometric imaging have revealed dense gas and dust accretion disks in nearby ultra-luminous galactic nuclei. In the best studied ultraluminous IR galaxy, Arp 220, the 2 micron imaging shows dust disks in both of the merging galactic nuclei and mm-CO line imaging indicates molecular gas masses approx. 10^9 M_sun for each disk. The two gas disks in Arp 220 are counterrotating and their dynamical masses are approx. 2x10^9 M_sun, that is, only slightly larger than the gas masses. These disks have radii approx 100 pc and thickness 10-50 pc. The high brightness temperatures of the CO lines indicate that the gas in the disks has area filling factors of approx. 25-50% and mean densities of >~ 10^4 cm^(-3). Within these nuclear disks, the rate of massive star formation is undoubtedly prodigious and, given the high viscosity of the gas, there will also be high radial accretion rates, perhaps >~ 10 M_sun/yr. If this inflow persists to very small radii, it is enough to feed even the highest luminosity AGNs.Comment: LaTex, 6 pages with 1 postscript and 1 jpg figure, and 1 postscript table, To appear in the proc. of the Ringberg workshop on "Ultraluminous Galaxies: Monsters or Babies" (Ringberg castle, Sept. 1998), Ap&SS, in pres

The Extreme Nuclear Environments of Sgr A* and Arp 220

The dense ISM which is the fuel for both nuclear starbursts is believed to be accreted to the nucleus by stellar bars and galactic interactions. In this contribution, I summarize the observational results for two galactic nuclei at the extreme ends of starburst/AGN activity − our own Galactic nucleus with SgrA* and the ULIRG Arp 220. I discuss theoretical considerations for the properties of the ISM − its density and scale height, whether it is likely to clump into gravitational bound GMCs − and the self-regulation of SB and AGN fueling due to radiation pressure support of the ISM. The latter yields an Eddington-like limit on the activity for both SB and AGN, corresponding to approximately 500 L_ʘ/M_ʘ for optically thick regions in which the radiation has been degraded to the NIR

The zCOSMOS 10k-sample: the role of galaxy stellar mass in the colour-density relation up to z ~ 1

Aims. With the first ~10 000 spectra of the flux limited zCOSMOS sample (I_(AB) ≤ 22.5) we want to study the evolution of environmental effects on galaxy properties since z ~ 1.0, and to disentangle the dependence among galaxy colour, stellar mass and local density. Methods. We use our previously derived 3D local density contrast δ, computed with the 5th nearest neighbour approach, to study the evolution with z of the environmental effects on galaxy U-B colour, D4000 Å break and [OII]λ3727 equivalent width (EW[OII]). We also analyze the implications due to the use of different galaxy selections, using luminosity or stellar mass, and we disentangle the relations among colour, stellar mass and δ studying the colour-density relation in narrow mass bins. Results. We confirm that within a luminosity-limited sample (M_B ≤ −20.5 − z) the fraction of red (U − B ≥ 1) galaxies depends on δ at least up to z ~ 1, with red galaxies residing mainly in high densities. This trend becomes weaker for increasing redshifts, and it is mirrored by the behaviour of the fraction of galaxies with D4000 Å break ≥1.4. We also find that up to z ~ 1 the fraction of galaxies with log(EW[OII]) ≥ 1.15 is higher for lower δ, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and δ, the colour-δ relation that we find in the luminosity-selected sample can be due to the broad range of stellar masses embedded in the sample. Thus, we study the colour-δ relation in narrow mass bins within mass complete subsamples, defining red galaxies with a colour threshold roughly parallel to the red sequence in the colour-mass plane. We find that once mass is fixed the colour-δ relation is globally flat up to z ~ 1 for galaxies with log(M/M_⊙) ≳ 10.7. This means that for these masses any colour-δ relation found within a luminosity-selected sample is the result of the combined colour-mass and mass-δ relations. On the contrary, even at fixed mass we observe that within 0.1 ≤ z ≤ 0.5 the fraction of red galaxies with log(M/M_⊙) ≲ 10.7 depends on δ. For these mass and redshift ranges, environment affects directly also galaxy colours. Conclusions. We suggest a scenario in which the colour depends primarily on stellar mass, but for an intermediate mass regime (10.2 ≲ log(M/M_⊙) ≲ 10.7) the local density modulates this dependence. These relatively low mass galaxies formed more recently, in an epoch when more evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time

A boost for the EW SUSY hunt: monojet-like search for compressed sleptons at LHC14 with 100 fb^-1

Current Large Hadron Collider (LHC) analyses are blind to compressed supersymmetry (SUSY) models with sleptons near the lightest super partner (LSP) in mass: $m_{\tilde{l}} - m_{\tilde{\chi}_1^0} \equiv \Delta m \lesssim 60$ GeV. We present a search sensitive to the very compressed range $3~\text{GeV} < \Delta m < 24~\text{GeV}$ using the channel $p p \rightarrow \tilde{l}^+ \tilde{l}^- +\rm{jet} \rightarrow$ $l^+ l^- \tilde{\chi}_1^0 \tilde{\chi}_1^0 +\rm{jet}$ with soft same-flavor leptons and one hard jet from initial state radiation ($p_{\rm T}^j >100$ GeV). The sleptons recoil against the jet boosting them and their decay products, making the leptons detectable and providing substantial missing transverse momentum. We use the kinematic variable $m_{\rm T 2}$ along with a different-flavor control region to reduce the large standard model backgrounds and control systematic uncertainty. We find the analysis should allow LHC14 with $100~\text{fb}^{-1}$ to search for degenerate left-handed selectrons and smuons in the compressed region up to $m_{\tilde{l}_L} \lesssim 150$ GeV. In addition, it should be sensitive to $m_{\tilde{l}_L} \lesssim 110$ GeV for the very challenging case of auto-concealed SUSY, in which left-handed sleptons decay to the Kaluza-Klein tower of a modulino LSP which lives in $d=6$ extra dimensions. In both the compressed spectrum and auto-concealed SUSY scenarios this analysis will need more data to improve on LEP2 limits for right-handed sleptons due to their smaller cross sections.Comment: 15 pages, 3 figures, updated citations in v

Comparison Between Simulated and Observational Results of Galaxy Formation for Large Scale Structures

The Millennium simulation is the largest numerical simulation of how minor fluctuations in the density of the universe’s dark matter distribution are amplified by gravity to develop into the large scale structures(LSS) and galaxy clusters seen today(Springel et al. 2005). Although the simulations have been compared with the astronomical observations of the local universe, the simulations have not been widely compared with high redshift, early universe observations. In our study we compare the simulation data(Wang et al. 2008; Guo et al. 2008(in preparation)) for the first time with observations from the COSMOS survey(Scoville et al. 2006). Three quantities are proposed to characterize the structures and the structures distribution, namely the percent area occupied by LSS at each redshift, the average area of LSS and the shapes as characterized by the square root of the area divided by the circumference. We calculate these quantities for both the observations and the simulations, and quantify discrepancies between the existing simulations and observations. In particular, the simulations exhibit earlier development of dense structures than is seen in the observational data