arXiv subjects

Jukka Nevalainen

Publications and source records attributed to Jukka Nevalainen.

16 recordsLinked to original sources

arXiv2022

Quasi-spherical superclusters

Generally the dynamical state of superclusters is poorly known. We study properties of superclusters and select a sample of quasi-spherical superclusters, the dynamics of which can be studied using the $Λ$ significance diagram. We extracted our supercluster sample with an adaptive local threshold density method from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) data and estimated their masses using the dynamical masses for member galaxies and groups. We used topological analysis based on Minkowski functionals and the positions of galaxies and galaxy groups in superclusters. Finally, we highlight the dynamical state of a few exceptional types of superclusters found in this study using the $Λ$ significance diagram. Our final sample contains 65 superclusters in the distance range of 130 to 450 Mpc. Supercluster masses range between $1.1 \times 10^{15} M_{\sun}$ and $1.4 \times 10^{16} M_{\sun}$ and sizes between 25 Mpc and 87 Mpc. We find that pancake-type superclusters form the low-luminosity, small, poor and low-mass end of superclusters. We find four superclusters of unusual types, exhibiting exceptionally spherical shapes. These so-called quasi-spherical systems contain a high-density core surrounded by a relatively spherical density and galaxy distribution.The mass-to-light ratio of these quasi-sphericals is higher than those of the other superclusters, suggesting a relatively high dark matter content. Using the $Λ$ significance diagram for oblate and prolate spheroids, we find that three quasi-spherical superclusters are gravitationally bound at the present epoch. Quasi-spherical superclusters are among the largest gravitationally bound systems found to date, and form a special class of giant systems that, dynamically, are in between large gravitationally unbound superclusters and clusters of galaxies in an equilibrium configuration.

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arXiv2022

The Scaling Relation between Galaxy Luminosity and WHIM Density from EAGLE Simulations with application to SDSS data

This paper presents an updated scaling relation between the optical luminosity density (LD) of galaxies in the $r$ band and the density of the warm-hot intergalactic medium (WHIM) in cosmic filaments, using the high-resolution EAGLE simulations. We find a strong degree of correlation between the WHIM density and the galaxy luminosity density, resulting in a scaling relation between the two quantities that permits to predict the WHIM density of filaments with a scatter of less than $\frac{1}{2}$ dex in a broad range of smoothed filament luminosity densities. In order to estimate the performance of the simulation-based calibration of the LD-WHIM density relation, we applied it to a sample of low-redshift filaments detected with the \emph{Bisous} method in the Legacy Survey SDSS~DR12 data. In the volume covered by the SDSS data, our relation predicts a WHIM density amounting to $31\pm7\pm12$ % (statistical errors followed by systematic) of cosmic baryon density. This agrees, albeit within the large uncertainties, with the current estimates of the cosmological missing baryon fraction, implying that our LD-WHIM density relation may be a useful tool in the search for the missing baryons. This method of analysis provides a new promising avenue to study the physical properties of the missing baryons, using an observable that is available for large volumes of the sky, complementary and independent from WHIM searches with absorption-line systems in the FUV or X-rays.

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arXiv2020

An EAGLE view of the missing baryons

Context. A significant fraction of the predicted baryons remains undetected in the local universe. We adopted the common assumption that a large fraction of the missing baryons corresponds to the hot (log T(K) = 5.5-7) phase of the Warm Hot Intergalactic Medium (WHIM). We base our missing baryons search on the scenario whereby the WHIM has been heated up via accretion shocks and galactic outflows, and is concentrated towards the filaments of the Cosmic Web. Aims. Our aim is to improve the observational search of the poorly detected hot WHIM. Methods. We detect the filamentary structure within the EAGLE simulation by applying the Bisous formalism to the galaxy distribution. In addition, we use the MMF/NEXUS+ classification of the large scale environment of the dark matter component in EAGLE. We then study the spatio-thermal distribution of the hot baryons within the extracted filaments. Results. While the filaments occupy only 5% of the full simulation volume, the diffuse hot intergalactic medium in filaments amounts to 23% $-$ 25% of the total baryon budget, or 79% $-$ 87% of all the hot WHIM. The most optimal filament sample, with a missing baryon mass fraction of 82%, is obtained by selecting Bisous filaments with a high galaxy luminosity density. For these filaments we derived analytic formulae for the radial gas density and temperature profiles, consistent with recent Planck SZ and CMB lensing observations within the central $r$~ 1 Mpc. Conclusions. Results from EAGLE suggest that the missing baryons are strongly concentrated towards the filament axes. Since the filament finding methods used here are applicable to galaxy surveys, a large fraction of the missing baryons can be localised by focusing the observational efforts on the central 1 Mpc regions of the filaments. Moreover, focusing on high galaxy luminosity density regions will optimise the observational signal.

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arXiv2019

Hot WHIM counterparts of FUV OVI absorbers: Evidence in the line-of-sight towards quasar 3C 273

We explore the high spectral resolution X-ray data towards the quasar 3C273 to search for signals of hot ($\sim10^{6-7}$ K) X-ray-absorbing gas co-located with two established intergalactic FUV OVI absorbers. We analyze the soft X-ray band grating data of all XMM-Newton and Chandra instruments to search for the hot phase absorption lines at the FUV predicted redshifts. The viability of potential line detections is examined by adopting the constraints of a physically justified absorption model. The WHIM hypothesis is investigated with a complementary 3D galaxy distribution analysis, and by comparison of the measurement results to the WHIM properties in the EAGLE cosmological, hydrodynamical simulation. At FUV redshift z=0.09017, we measured signals of two hot ion species, OVIII and NeIX, with a $3.9σ$ combined significance level. Considering the line features in all instruments collectively and assuming collisional equilibrium for absorbing gas, we were able to constrain the temperature ($kT=0.26\pm0.03$ keV) and the column density ($N_H\times{Z_\odot/Z}=1.3_{-0.5}^{+0.6}\times10^{19}$ cm$^{-2}$) of the absorber. Thermal analysis indicates that FUV and X-ray absorption relate to different phases, with estimated temperatures $T_{FUV}\approx3\times10^5$ and $T_{X-ray}\approx3\times10^6$ K, which match the EAGLE predictions for WHIM at the FUV/X-ray measured $N_{ion}$-ranges. We detected a large scale galactic filament crossing the sightline at the redshift of the absorption, linking the absorption to this structure. This study provides insights into co-existing warm and hot gas within a WHIM filament and estimates the ratio of the hot and warm phases. Because the hot phase is thermally distinct from the OVI gas, the estimated baryon content of the absorber is increased, conveying the promise of X-ray follow-up studies of FUV detected WHIM in refining the picture of the missing baryons.

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arXiv2019

New Chandra observations of PG 1116+215 to investigate an extragalactic OVIII WHIM absorption line

This is a short AAS Research Note on the analysis of new Chandra observations of PG 1116+215, for which an extragalactic OVIII WHIM line was reported by Bonamente et al. (2016). The new observations occurred at a time when the source flux was three times lower, and the background was three times higher, than in the earlier observations. The analysis described in this research note show that the new observations are consistent with the old one at the wavelengths of the OVIII WHIM line, and the lower signal-to-noise of the new data did not permit a significant detection of the line in the new data.

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arXiv2015

Summary of the 2015 IACHEC meeting

We summarize the outcome of the 10th meeting of the International Astronomical Consortium for High Energy Calibration (IACHEC), held in Beijing (People's Republic of China) in April 2015. Over 80 scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the status of the X-ray payload inter-calibration, as well as possible ways to improve it. A recent study on a large sample of galaxy clusters confirmed that the calibration of the effective area shape above 2 keV between XMM-Newton/EPIC and Chandra/ACIS is consistent, but showed a significant discrepancy at lower energies. Temperatures measured by EPIC are therefore smaller, the difference being largest for the highest temperatures, up to ~20% at kT=10 keV (Schellenberger et al. 2015). The latest multi-mission study of the Crab Nebula above 10 keV shows a +/-13% agreement in the relative normalization of the INTEGRAL, NuSTAR, RXTE, and {\it Suzaku} hard X-ray instruments.

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arXiv2015

Unusual A2142 supercluster with a collapsing core: distribution of light and mass

We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. We analyse the global luminosity density distribution in the supercluster and divide the supercluster into the high-density core and the low-density outskirts regions. We find galaxy groups and filaments in the regions of different global density, calculate their masses and mass-to-light ratios and analyse their dynamical state with several 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. We show that in A2142 supercluster groups and clusters with at least ten member galaxies lie along an almost straight line forming a 50 Mpc/h long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirt regions. The total estimated mass of the supercluster is M_est = 6.2 10^{15}M_sun. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centered at the rich X-ray cluster A2142. Most of the galaxy groups in the core region are multimodal. In the outskirts of the supercluster, the number of groups is larger than in the core, and groups are poorer. The orientation of the cluster A2142 axis follows the orientations of its X-ray substructures and radio halo, and is aligned along the supercluster axis. The high-density core of the supercluster with the global density D8 > 17 and perhaps with D8 > 13 may have reached the turnaround radius and started to collapse. A2142 supercluster with luminous, collapsing core and straight body is an unusual object among galaxy superclusters. In the course of the future evolution the supercluster may be split into several separate systems.

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arXiv2015

Reconciling Planck cluster counts and cosmology? Chandra/XMM instrumental calibration and hydrostatic mass bias

The mass of galaxy clusters can be inferred from the temperature of their X-ray emitting gas, $T_{\mathrm{X}}$. Their masses may be underestimated if it is assumed that the gas is in hydrostatic equilibrium, by an amount $b^{\mathrm{hyd}}\sim(20\pm10)$ % suggested by simulations. We have previously found consistency between a sample of observed \textit{Chandra} X-ray masses and independent weak lensing measurements. Unfortunately, uncertainties in the instrumental calibration of {\em Chandra} and {\em XMM-Newton} observatories mean that they measure different temperatures for the same gas. In this paper, we translate that relative instrumental bias into mass bias, and infer that \textit{XMM-Newton} masses of $\sim 10^{14}\,\mbox{M}_{\odot}$ ($> 5\cdot 10^{14} \mbox{M}_{\odot}$) clusters are unbiased ($\sim 35$ % lower) compared to WL masses. For massive clusters, \textit{Chandra}'s calibration may thus be more accurate. The opposite appears to be true at the low mass end. We observe the mass bias to increase with cluster mass, but presence of Eddington bias precludes firm conclusions at this stage. Nevertheless, the systematic \textit{Chandra} -- \textit{XMM-Newton} difference is important because {\em Planck}'s detections of massive clusters via the Sunyaev-Zeldovich (SZ) effect are calibrated via {\em XMM-Newton} observations. The number of detected SZ clusters are inconsistent with {\em Planck}'s cosmological measurements of the primary Cosmic Microwave Background (CMB). Given the \textit{Planck} cluster masses, if an (unlikely) uncorrected $\sim 20$ % calibration bias existed, this tension would be eased, but not resolved.

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arXiv2014

Summary of the 2014 IACHEC Meeting

We present the main results of the 9th meeting of the International Astronomical Consortium for High Energy Calibration (IACHEC), held in Warrenton (Virginia) in May 2014. Over 50 scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the status of the X-ray payloads inter-calibration, as well as possible ways to improve it. Sect.2 of this Report summarises our current understanding of the energy-dependent inter-calibration status.

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arXiv2013

The Hot and Energetic Universe: The missing baryons and the warm-hot intergalactic medium

The backbone of the large-scale structure of the Universe is determined by processes on a cosmological scale and by the gravitational interaction of the dominant dark matter. However, the mobile baryon population shapes the appearance of these structures. Theory predicts that most of the baryons reside in vast unvirialized filamentary structures that connect galaxy groups and clusters, but the observational evidence is currently lacking. Because the majority of the baryons are supposed to exist in a large-scale, hot and dilute gaseous phase, X-rays provide the ideal tool to progress our understanding. Observations with the Athena+ X-ray Integral Field Unit will reveal the location, chemical composition, physical state and dynamics of the active population of baryons.

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arXiv2013

Summary of the 2013 IACHEC Meeting

We present the main results of the 8th International Astronomical Consortium for High Energy Calibration (IACHEC) meeting, held in Theddingworth, Leicestershire, between March 25 and 28, 2013. Over 50 scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the status of the X-ray payload inter-calibration, as well as possible ways to improve it. Sect. 4 of this Report summarises our current understanding of the energy-dependent inter-calibration status.

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arXiv2011

X-ray spectroscopy of Abell S1101 with Chandra, XMM-Newton and ROSAT: band-pass dependence of he temperature profile and soft excess emission

We present spatially-resolved spectroscopy of the galaxy cluster Abell S1101, also known as Sersic 159-03, with Chandra, XMM-Newton and ROSAT, and investigate the presence of soft X-ray excess emission above the contribution from the hot intra-cluster medium. In earlier papers we reported an extremely bright soft excess component that reached 100% of the thermal radiation in the R2 ROSAT band (0.2-0.4 keV), using the HI column density measurement by Dickey and Lockman. In this paper we use the newer Leiden-Argentine-Bonn survey measurements of the HI column density towards Abell S1101, significantly lower than the previous value, and show that the soft excess emission in Abell S1101 is now at the level of 10-20% of the hot gas emission, in line with those of a large sample of clusters analyzed by Bonamente et al. in 2002. The ROSAT soft excess emission is detected regardless of calibration uncertainties between Chandra and XMM-Newoton. This new analysis of Abell S1101 indicate that the 1/4keV band emission is compatible with the presence of WHIM filaments connected to the cluster and extending outward into the intergalactic medium; the temperatures we find in this study are typically lower than the WHIM probed in other X-ray studies. We also show that the soft excess emission is compatible with a non-thermal origin as the inverse Compton scattering of relativistic electrons off the cosmic microwave background, with pressure less than 1% of the thermal electrons.

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arXiv2007

Constraints on the parameters of radiatively decaying dark matter from the dark matter halo of the Milky Way and Ursa Minor

We improve the earlier restrictions on parameters of the dark matter (DM) in the form of a sterile neutrino. The results were obtained from non-observing the DM decay line in the X-ray spectrum of the Milky Way (using the recent XMM-Newton PN blank sky data). We also present a similar constraint coming from the recent XMM-Newton observation of Ursa Minor -- dark, X-ray quiet dwarf spheroidal galaxy. The new Milky way data improve on (by as much as the order of magnitude at masses ~3.5 keV) existing constraints. Although the observation of Ursa Minor has relatively poor statistics, the constraints are comparable to those recently obtained using observations of the Large Magellanic Cloud or M31. This confirms a recent proposal that dwarf satellites of the MW are very interesting candidates for the DM search and dedicated studies should be made to this purpose.

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arXiv2005

$XMM-Newton$ $Ω$ project: III. Gas mass fraction shape in high redshift clusters

We study the gas mass fraction, $f\_{\rm gas},$ behavior in $XMM-Newton$ $Ω$ project. The typical $f\_{\rm gas}$ shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean $f\_{\rm gas} in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our $XMM$ clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.

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arXiv2001

Thermal Comptonization in GRS 1915+105

The Rossi X-ray Timing Explorer data of GRS 1915+105 from several observing periods are modeled with a thermal Comptonization model. Best-fit models indicate that there is a strong correlation between the inner disk temperature and the disk luminosity. The hard Comptonized luminosity does not depend significantly on the total luminosity. The spectral hardness of the Comptonized radiation, the fraction of seed soft photons scattered by the Comptonizing cloud, its Thomson optical depth, and the fraction of the total power dissipated in the optically thin hot plasma, all strongly anticorrelate with the luminosity. We find that the inner disk radius is almost constant and that the hot Comptonizing corona shrinks at high luminosities. We note that the fits using xspec diskbb + power law model underestimate the amplitude of the blackbody component (and therefore the corresponding size of the emitting region) and overestimate the absorption column density and the total, corrected for absorption, luminosity.

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arXiv1998

Two-phase modelling of the rings in the RXTE two-color diagram of GRS 1915+105

The Galactic superluminal source GRS 1915+105 was found to experience a peculiar X-ray variability in a narrow count rate range of the PCA detector onboard RXTE. This can be seen as a ring-shaped pattern in the two-color diagram of count rates, where the hard hardness F(13-40keV)/F(2-13keV) is plotted against the soft hardness F(5-13keV)/F(2-5keV). The system runs one cycle with periods ranging between 50 - 100 s for different observations, one rotation in the 2-color diagram corresponding to the time between two contiguous maxima in the light curve. We model this behaviour successfully with the help of a self-consistent 2-phase thermal model where seed photons from an optically thick classical disk are Comptonized in a hot spherical corona surrounding the inner disk. In the model, changes of two parameters regulate the paths in the 2-color diagram: the black body temperature (Tin) of the inner disk and the Thomson optical depth multiplied by the electron temperature of the hot phase (tau*Te). These parameters oscillate with time but with a phase-shift between each other, causing the ring-shaped pattern. During the observation studied in more detail (20402-01-30-00), the inner disk radius varied with 97 s period between 20 - 35 km with an anticorrelation between the coronal and the mass accretion rate through the disk, possibly indicating a coupling between the disk and coronal accretion. During a typical cycle, the inner disk radius rapidly shrinked and returned more slowly back to the original larger value. In the rings we may see phenomena close to the black hole horizon under near Eddington accretion rates.

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