arXiv subjects

I. Csabai

Publications and source records attributed to I. Csabai.

At least 19 recordsLinked to original sources

arXiv2026

Probing dark energy evolution with Quaia quasars through the integrated Sachs-Wolfe effect

The Integrated Sachs--Wolfe (ISW) effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. We investigate whether the redshift evolution of the ISW effect can provide new constraints on the time evolution of dark energy. We consider theoretical predictions for the standard $\Lambda$CDM cosmology and alternative $w_0w_a$CDM models favoured by recent DESI BAO and DES Y6 constraints. We perform a tomographic cross-correlation analysis of the {\it Quaia} quasar catalogue and \textit{Planck} CMB temperature maps to measure the ISW signal over a broad redshift range, spanning about $(10h^{-1}~\mathrm{Gpc})^3$ comoving volume. We assess the robustness of the inferred ISW amplitude against variations in sky coverage, multipole range, and tomographic binning. We detect the ISW effect at a significance of $2.8 \, \sigma$, corresponding to an amplitude of $A_{\rm ISW}\simeq1.69\pm0.61$ relative to the \textit{Planck} $\Lambda$CDM prediction. The inferred signal remains stable against various analysis choices, including various CMB maps (SMICA, NILC, SEVEM), different choices of $\ell_{\rm max}$ and the number of multipole bins, and an alternative quasar bias model. The measured ISW amplitude is moderately stronger than predicted by the fiducial $\Lambda$CDM cosmology, and the alternative $w_0w_a$CDM models do not account for this discrepancy. Future tomographic ISW measurements with improved quasar catalogues from {\it Gaia} and forthcoming wide-area galaxy surveys such as {\it Euclid} and DESI will help clarify the origin of this difference.

astro-ph.CO↗

arXiv2024

Classification of colorectal primer carcinoma from normal colon with mid-infrared spectra

In this project, we used formalin-fixed paraffin-embedded (FFPE) tissue samples to measure thousands of spectra per tissue core with Fourier transform mid-infrared spectroscopy using an FT-IR imaging system. These cores varied between normal colon (NC) and colorectal primer carcinoma (CRC) tissues. We created a database to manage all the multivariate data obtained from the measurements. Then, we applied classifier algorithms to identify the tissue based on its yielded spectra. For classification, we used the random forest, a support vector machine, XGBoost, and linear discriminant analysis methods, as well as three deep neural networks. We compared two data manipulation techniques using these models and then applied filtering. In the end, we compared model performances via the sum of ranking differences (SRD).

eess.IV↗

arXiv2023

The CMB lensing imprint of cosmic voids detected in the WISE-Pan-STARRS luminous red galaxy catalog

The cross-correlation of cosmic voids with the lensing convergence ($\kappa$) map of the CMB fluctuations offers a powerful tool to refine our understanding of the dark sector in the consensus cosmological model. Our principal aim is to compare the lensing signature of our galaxy data set with simulations based on the concordance model and characterize the results with an $A_{\kappa}$ consistency parameter. In particular, our measurements contribute to the understanding of the "lensing-is-low" tension of the $\Lambda$CDM model. We selected luminous red galaxies from the WISE-Pan-STARSS data set, allowing an extended 14,200 deg$^2$ sky area, that offers a more precise measurement compared to previous studies. We created 2D and 3D void catalogs to cross-correlate their locations with the Planck lensing map and studied their average imprint signal using a stacking methodology. Applying the same procedure, we also generated a mock catalog from the WebSky simulation for comparison. The 2D void analysis revealed good agreement with the standard cosmological model with $A_{\kappa}\approx1.06 \pm 0.08$, i.e. $S/N=13.3$, showing a higher $S/N$ than previous studies using voids detected in the Dark Energy Survey data set. The 3D void analysis exhibited a lower $S/N$ and demonstrated worse agreement with our mock catalog than the 2D voids. These deviations might be attributed to limitations in the mock catalog, such as imperfections in the LRG selection, as well as a potential asymmetry between the North and South patches of the WISE-Pan-STARSS data set in terms of data quality. Overall, we present a significant detection of a CMB lensing signal associated with cosmic voids, largely consistent with the concordance model. Future analyses using even larger data sets also hold great promise of further sharpening these results, given their complementary nature to large-scale structure analyses.

astro-ph.CO↗

arXiv2022

Evidence for a high-z ISW signal from supervoids in the distribution of eBOSS quasars

The late-time integrated Sachs-Wolfe (ISW) imprint of $R\gtrsim 100~h^{-1}{\rm Mpc}$ super-structures is sourced by evolving large-scale potentials due to a dominant dark energy component in the $Λ$CDM model. The aspect that makes the ISW effect distinctly interesting is the repeated observation of stronger-than-expected imprints from supervoids at $z\lesssim0.9$. Here we analyze the un-probed key redshift range $0.8<z<2.2$ where the ISW signal is expected to fade in $Λ$CDM, due to a weakening dark energy component, and eventually become consistent with zero in the matter dominated epoch. On the contrary, alternative cosmological models, proposed to explain the excess low-$z$ ISW signals, predicted a sign-change in the ISW effect at $z\approx1.5$ due to the possible growth of large-scale potentials that is absent in the standard model. To discriminate, we estimated the high-$z$ $Λ$CDM ISW signal using the Millennium XXL mock catalogue, and compared it to our measurements from about 800 supervoids identified in the eBOSS DR16 quasar catalogue. At $0.8<z<1.2$, we found an excess ISW signal with $A_\mathrm{ ISW}\approx3.6\pm2.1$ amplitude. The signal is then consistent with the $Λ$CDM expectation ($A_\mathrm{ ISW}=1$) at $1.2<z<1.5$ where the standard and alternative models predict similar amplitudes. Most interestingly, we also detected an opposite-sign ISW signal at $1.5<z<2.2$ that is in $2.7σ$ tension with the $Λ$CDM prediction. Taken at face value, these moderately significant detections of ISW anomalies suggest an alternative growth rate of structure in low-density environments at $\sim100~h^{-1}{\rm Mpc}$ scales.

astro-ph.CO↗

arXiv2016

Searching for electromagnetic counterpart of LIGO gravitational waves in the Fermi GBM data with ADWO

The Fermi collaboration identified a possible electromagnetic counterpart of the gravitational wave event of September 14, 2015. Our goal is to provide an unsupervised data analysis algorithm to identify similar events in Fermi's Gamma-ray Burst Monitor CTTE data stream. We are looking for signals that are typically weak. Therefore, they can only be found by a careful analysis of count rates of all detectors and energy channels simultaneously. Our Automatized Detector Weight Optimization (ADWO) method consists of a search for the signal, and a test of its significance. We developed ADWO, a virtual detector analysis tool for multi-channel multi-detector signals, and performed successful searches for short transients in the data-streams. We have identified GRB150522B, as well as possible electromagnetic candidates of the transients GW150914 and LVT151012. ADWO is an independently developed, unsupervised data analysis tool that only relies on the raw data of the Fermi satellite. It can therefore provide a strong, independent test to any electromagnetic signal accompanying future gravitational wave observations.

astro-ph.HE↗

arXiv2009

Wide-Field Astronomical Surveys in the Next Decade

Wide-angle surveys have been an engine for new discoveries throughout the modern history of astronomy, and have been among the most highly cited and scientifically productive observing facilities in recent years. This trend is likely to continue over the next decade, as many of the most important questions in astrophysics are best tackled with massive surveys, often in synergy with each other and in tandem with the more traditional observatories. We argue that these surveys are most productive and have the greatest impact when the data from the surveys are made public in a timely manner. The rise of the "survey astronomer" is a substantial change in the demographics of our field; one of the most important challenges of the next decade is to find ways to recognize the intellectual contributions of those who work on the infrastructure of surveys (hardware, software, survey planning and operations, and databases/data distribution), and to make career paths to allow them to thrive.

astro-ph.IM↗

arXiv2007

Redshifts of the Long Gamma-Ray Bursts

The low energy spectra of some gamma-ray bursts' show excess components beside the power-law dependence. The consequences of such a feature allows to estimate the gamma photometric redshift of the long gamma-ray bursts in the BATSE Catalog. There is good correlation between the measured optical and the estimated gamma photometric redshifts. The estimated redshift values for the long bright gamma-ray bursts are up to z=4, while for the the faint long bursts - which should be up to z=20 - the redshifts cannot be determined unambiguously with this method. The redshift distribution of all the gamma-ray bursts with known optical redshift agrees quite well with the BATSE based gamma photometric redshift distribution.

astro-ph↗

arXiv2006

The Rest-frame Optical Colors of 99,000 SDSS Galaxies

We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088 galaxies selected from Data Release 1. This narrow-band ~200 AA photometric system (uz, vz, bz, yz), first designed for the determination of effective temperature, metallicity and gravity of stars, measures the continuum spectral slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies form a remarkably narrow locus (~0.03 mag) in the resulting color-color diagram. The Bruzual & Charlot population synthesis models suggest that the position of a galaxy along this locus is controlled by a degenerate combination of metallicity and age of the dominant stellar population. Galaxy distribution along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr old single stellar population. The position perpendicular to the locus is independent of metallicity and age, and reflects the galaxy's dust content, as implied by both the models and the statistics of IRAS detections. A comparison of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight correlation, although the two analyzed spectral ranges barely overlap. Overall, the galaxy spectral energy distribution in the entire UV to near-IR range can be described as a single-parameter family with an accuracy of 0.1 mag, or better. This nearly one-dimensional distribution of galaxies in the multi-dimensional space of measured parameters strongly supports the conclusion of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy spectra can be described by a small number of eigenspectra. Apparently, the contributions of stellar populations that dominate the optical emission from galaxies are combined in a simple and well-defined way.

astro-ph↗

arXiv2006

The Effect of Large-Scale Structure on the SDSS Galaxy Three-Point Correlation Function

We present measurements of the normalised redshift-space three-point correlation function (Q_z) of galaxies from the Sloan Digital Sky Survey (SDSS) main galaxy sample. We have applied our "npt" algorithm to both a volume-limited (36738 galaxies) and magnitude-limited sample (134741 galaxies) of SDSS galaxies, and find consistent results between the two samples, thus confirming the weak luminosity dependence of Q_z recently seen by other authors. We compare our results to other Q_z measurements in the literature and find it to be consistent within the full jack-knife error estimates. However, we find these errors are significantly increased by the presence of the ``Sloan Great Wall'' (at z ~ 0.08) within these two SDSS datasets, which changes the 3-point correlation function (3PCF) by 70% on large scales (s>=10h^-1 Mpc). If we exclude this supercluster, our observed Q_z is in better agreement with that obtained from the 2dFGRS by other authors, thus demonstrating the sensitivity of these higher-order correlation functions to large-scale structures in the Universe. This analysis highlights that the SDSS datasets used here are not ``fair samples'' of the Universe for the estimation of higher-order clustering statistics and larger volumes are required. We study the shape-dependence of Q_z(s,q,theta) as one expects this measurement to depend on scale if the large scale structure in the Universe has grown via gravitational instability from Gaussian initial conditions. On small scales (s <= 6h^-1 Mpc), we see some evidence for shape-dependence in Q_z, but at present our measurements are consistent with a constant within the errors (Q_z ~ 0.75 +/- 0.05). On scales >10h^-1 Mpc, we see considerable shape-dependence in Q_z.

astro-ph↗

arXiv2005

Measuring the halo mass of MgII absorbers from their cross-correlation with Luminous Red Galaxies

We study the cross-correlation between 716 MgII quasar absorption systems and about 100,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 3 in the redshift range 0.4<z<0.8. The MgII systems were selected to have 2796 & 2803 rest-frame equivalent widths greater than 1.0 Åand identifications confirmed by the FeII 2600 or MgI 2852 lines. Over co-moving scales 0.2--13/h Mpc, the MgII--LRG cross-correlation has an amplitude 0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have halo-masses of 10^{13} \msun, this strong cross-correlation implies that the absorber host-galaxies have halo-masses 1--2 times 10^{12} \msun.

astro-ph↗

arXiv2005

The Sloan Digital Sky Survey Quasar Catalog III. Third Data Release

We present the third edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than M_i = -22 (in a cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7), have at least one emission line with FWHM larger than 1000 km/s or are unambiguously broad absorption line quasars, are fainter than i = 15.0, and have highly reliable redshifts. The area covered by the catalog is 4188 sq. deg. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than four, of which 17 are at redshifts greater than five. For each object the catalog presents positions accurate to better than 0.2 arcsec. rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800--9200A at a spectral resolution about 2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.

astro-ph↗

arXiv2005

Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies

We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16<z<0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute distance to z=0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density Omega_mh^2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273 +- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties.

astro-ph↗

arXiv2005

The SDSS u-band Galaxy Survey: Luminosity functions and evolution

We construct and analyze a u-band selected galaxy sample from the SDSS Southern Survey, which covers 275 sq. deg. The sample includes 43223 galaxies with spectroscopic redshifts in the range 0.005<z<0.3 and with 14.5<u<20.5. The S/N in the u-band Petrosian aperture is improved by coadding multiple epochs of imaging data and by including sky-subtraction corrections. Luminosity functions for the near-UV ^{0.1}u band (322+-26 nm) are determined in redshift slices of width 0.02, which show a highly significant evolution in M^{star} of -0.8+-0.1 mag between z=0 and 0.3; with M^{star} = -18.84+-0.05 (AB mag), log phi^{star} = -2.06+-0.03 (Mpc^{-3}) and log rho_L = 19.11+-0.02 (W Hz^{-1} Mpc^{-3}) at z=0.1. The faint-end slope determined for z<0.06 is given by alpha=-1.05+-0.08. This is in agreement with recent determinations from GALEX at shorter wavelengths. Comparing our z<0.3 luminosity density measurements with 0.2<z<1.2 from COMBO-17, we find that the 280-nm density evolves as rho_L proportional to (1+z)^{beta} with beta=2.1+-0.2; and find no evidence for any change in slope over this redshift range. By comparing with other measurements of cosmic star formation history, we estimate that the effective dust attenuation at 280 nm has increased by 0.8+-0.3 mag between z=0 and 1.

astro-ph↗

arXiv2004

Self-generated Self-similar Traffic

Self-similarity in the network traffic has been studied from several aspects: both at the user side and at the network side there are many sources of the long range dependence. Recently some dynamical origins are also identified: the TCP adaptive congestion avoidance algorithm itself can produce chaotic and long range dependent throughput behavior, if the loss rate is very high. In this paper we show that there is a close connection between the static and dynamic origins of self-similarity: parallel TCPs can generate the self-similarity themselves, they can introduce heavily fluctuations into the background traffic and produce high effective loss rate causing a long range dependent TCP flow, however, the dropped packet ratio is low.

physics.data-an↗

arXiv2003

Physical Evidence for Dark Energy

We present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. We find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. We do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although we do see evidence for some SZ effect for our highest redshift samples. Assuming a flat universe, our preliminary detection of the ISW effect provides independent physical evidence for the existence of dark energy.

astro-ph↗

arXiv2003

Observing the dark matter density profile of isolated galaxies

Using the Sloan Digital Sky Survey (SDSS), we probe the halo mass distribution by studying the velocities of satellites orbiting isolated galaxies. In a subsample that covers 2500 sq. degrees on the sky, we detect about 3000 satellites with absolute blue magnitudes going down to M_B = -14; most of the satellites have M_B=-16 to -18, comparable to the magnitudes of M32 and the Magellanic Clouds. After a careful, model-independent removal of interlopers, we find that the line-of-sight velocity dispersion of satellites declines with distance to the primary. For an L* galaxy the r.m.s. line-of-sight velocity changes from ~120 km/s at 20 kpc to ~60 km/s at 350 kpc. This decline agrees remarkably well with theoretical expectations, as all modern cosmological models predict that the density of dark matter in the peripheral parts of galaxies declines as rho_DM propto r^{-3}. Thus, for the first time we find direct observational evidence of the density decline predicted by cosmological models; we also note that this result contradicts alternative theories of gravity such as MOND. We also find that the velocity dispersion of satellites within 100 kpc scales with the absolute magnitude of the central galaxy as sigma propto L^{0.3}; this is very close to the Tully-Fisher relation for normal spiral galaxies.

astro-ph↗

arXiv2002

Gamma photometric redshifts for long gamma-ray bursts

It is known that the soft tail of the gamma-ray bursts' spectra show excesses from the exact power-law dependence. In this article we show that this departure can be detected in the peak flux ratios of different BATSE DISCSC energy channels. This effect allows to estimate the redshift of the bright long gamma-ray bursts in the BATSE Catalog. A verification of these redshifts is obtained for the 8 GRB which have both BATSE DISCSC data and measured optical spectroscopic redshifts. There is good correlation between the measured and esti redshifts, and the average error is $Δz \approx 0.33$. The method is similar to the photometric redshift estimation of galaxies in the optical range, hence it can be called as "gamma photometric redshift estimation". The estimated redshifts for the long bright gamma-ray bursts are up to $z \simeq 4$. For the the faint long bursts - which should be up to $z \simeq 20$ - the redshifts cannot be determined unambiguously with this method.

astro-ph↗

arXiv2002

The Broad-band Optical Properties of Galaxies with Redshifts 0.0 < z < 0.2

Using photometry and spectroscopy of 144,609 galaxies from the Sloan Digital Sky Survey, we present bivariate distributions of pairs of seven galaxy properties: four optical colors, surface brightness, radial profile shape as measured by the Sersic index, and absolute magnitude. In addition, we present the dependence of local galaxy density (smoothed on 8 h^{-1} Mpc scales) on all of these properties. Several classic, well-known relations among galaxy properties are evident at extremely high signal-to-noise ratio: the color-color relations of galaxies, the color-magnitude relations, the magnitude-surface brightness relation, and the dependence of density on color and absolute magnitude. We show that most of the i-band luminosity density in the universe is in the absolute magnitude and surface brightness ranges used. Some of the relationships between parameters, in particular the color--magnitude relations, show stronger correlations for exponential galaxies and concentrated galaxies taken separately than for all galaxies taken together. We provide a simple set of fits of the dependence of galaxy properties on luminosity for these two sets of galaxies.

astro-ph↗