Cosmic voids detection without density measurements Elyiv, Andrii; Marulli, Federico; Pollina, Giorgia ...
Monthly Notices of the Royal Astronomical Society,
03/2015, Volume:
448, Issue:
1
Journal Article
Peer reviewed
Open access
Cosmic voids are effective cosmological probes to discriminate among competing world models. Their identification is generally based on density or geometry criteria that, because of their very ...nature, are prone to shot noise. We propose two void finders that are based on dynamical criterion to select voids in Lagrangian coordinates and minimize the impact of sparse sampling. The first approach exploits the Zel'dovich approximation to trace back in time the orbits of galaxies located in voids and their surroundings; the second uses the observed galaxy–galaxy correlation function to relax the objects’ spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence, which can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance of our methods we used a dark matter halo mock catalogue codecs, and compared the results with those obtained with the zobov void finder. We find that the void divergence profiles are less scattered than the density ones and, therefore, their stacking constitutes a more accurate cosmological probe. The significance of the divergence signal in the central part of voids obtained from both our finders is 60 per cent higher than for overdensity profiles in the zobov case. The ellipticity of the stacked void measured in the divergence field is closer to unity, as expected, than what is found when using halo positions. Therefore, our void finders are complementary to the existing methods, which should contribute to improve the accuracy of void-based cosmological tests.
The stability properties of a low-density ultrarelativistic pair beam produced in the intergalactic medium (IGM) by multi-TeV gamma-ray photons from blazars are analyzed. The problem is relevant for ...probes of magnetic field in cosmic voids through gamma-ray observations. In addition, dissipation of such beams could considerably affect the thermal history of the IGM and structure formation. We use a Monte Carlo method to quantify the properties of the blazar-induced electromagnetic shower, in particular the bulk Lorentz factor and the angular spread of the pair beam generated by the shower, as a function of distance from the blazar itself. We then use linear and nonlinear kinetic theory to study the stability of the pair beam against the growth of electrostatic plasma waves, employing the Monte Carlo results for our quantitative estimates. We find that the fastest growing mode, like any perturbation mode with even a very modest component perpendicular to the beam direction, cannot be described in the reactive regime. Due to the effect of nonlinear Landau damping, which suppresses the growth of plasma oscillations, the beam relaxation timescale is found to be significantly longer than the inverse Compton loss time. Finally, density inhomogeneities associated with cosmic structure induce loss of resonance between the beam particles and plasma oscillations, strongly inhibiting their growth. We conclude that relativistic pair beams produced by blazars in the IGM are stable on timescales that are long compared with the electromagnetic cascades. There appears to be little or no effect of pair beams on the IGM.
The XXL Survey Farahi, Arya; Guglielmo, Valentina; Evrard, August E. ...
Astronomy & astrophysics,
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context. An X-ray survey with the XMM-Newton telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg2 fields. Combining spectroscopic and X-ray observations in one ...field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature. Aims. Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature, T300 kpc, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨lnM200 | T300 kpc, z⟩. Methods. We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts z < 0.6 to model, ⟨lnσgal | T300 kpc, z⟩, where σgal is the velocity dispersion of XXL cluster member galaxies and T300 kpc is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by N-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter. Results. For the XXL-N cluster sample, we find σgal ∝ T300 kpc0.63±0.05 $\sigma_{\textrm{gal}} \propto {{T_{\textrm{300~kpc}}}^{0.63\pm0.05}$ σgal∝T300 kpc0.63±0.05, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift, 〈ln(E(z)M200/1014 M⊙)|T300 kpc, z〉 = πT + αT ln (T300 kpc/Tp) + βT ln (E(z)/E(zp)) $\langle \ln (E(z) M_{200}/10^{14} {{\, M_{\odot}}})|{{T_{\textrm{300~kpc}}},z\rangle=\pi_{T}+\alpha_{T}\ln\left({{T_{\textrm{300~kpc}}}/T_{\textrm{p}}\right)+\beta_{T}\ln\left(E(z)/E(z_{\textrm{p}})\right)$ 〈ln(E(z)M200/1014 M⊙)|T300 kpc,z〉=πT+αTln(T300 kpc/Tp)+βTln(E(z)/E(zp)) using pivot values kTp = 2.2 keV and zp = 0.25, with normalization πT = 0.45 ± 0.24 and slope αT = 1.89 ± 0.15. We obtain only weak constraints on redshift evolution, βT = −1.29 ± 1.14. Conclusions. The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.
Highly beamed relativistic e super(+ or -)-pair energy distributions result in double photon collisions of the beamed gamma rays from TeV blazars at cosmological distances with the isotropically ...distributed extragalactic background light (EBL) in the intergalactic medium. The typical energies k sub(0) Asymptotically = to 10 super(-7) in units of m sub(e)c super(2) of the EBL are more than 10 orders of magnitude smaller than the observed gamma-ray energies k sub(1) > or =, slanted 10 super(7). Using the limit k sub(0) << k sub(1), we demonstrate that the angular distribution of the generated pairs in the lab frame is highly beamed in the direction of the initial gamma-ray photons. For the astrophysically important case of power-law distributions of the emitted gamma-ray beam up to the maximum energy M interacting with Wien-type N(k sub(0)) is proportional to (ProQuest: Formulae and/or non-USASCII text omitted) exp(-k sub(0)/Theta) soft photon distributions with total number density N sub(0), we calculate analytical approximations for the electron production spectrum. For distant objects with luminosity distances d sub(L) >>y r sub(0) = (sigmaTN sub(0)) super(-1) = (ProQuest: Formulae and/or non-USASCII text omitted) Mpc (with Thomson cross section sigmaT), the implied large values of the optical depth tau sub(0) = d sub(L)/r sub(0) indicate that the electron production spectra differ at energies inside and outside the interval (Thetaln tau sub(0)) super(-1), tau sub(0)/Theta, given the maximum gamma-ray energy M >> Theta super(-1). In the case M >> Theta super(-1) the production spectrum is strongly peaked near E Asymptotically = to Theta super(-1), being exponentially reduced at small energies and decreasing with the steep power law is proportional to E super(-1-)p up to the maximum energy E =M - (1/2).
The XXL Survey Farahi, Arya; Guglielmo, Valentina; Evrard, August E. ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
Context.
An X-ray survey with the
XMM-Newton
telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg
2
fields. Combining spectroscopic and X-ray observations in one ...field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature.
Aims.
Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature,
T
300 kpc
, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨ln
M
200
|
T
300 kpc
,
z
⟩.
Methods.
We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts
z
< 0.6 to model, ⟨ln
σ
gal
|
T
300 kpc
,
z
⟩, where
σ
gal
is the velocity dispersion of XXL cluster member galaxies and
T
300 kpc
is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by
N
-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter.
Results.
For the XXL-N cluster sample, we find σ
gal
∝ T
300 kpc
0.63±0.05
, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift,
〈ln(
E
(
z
)
M
200
/10
14
M
⊙
)|T
300
kpc,
z
〉 = π
T
+ α
T
ln (
T
300
kpc/
T
p
) +
β
T
ln (
E
(
z
)/
E
(
z
p
)) using pivot values
kT
p
= 2.2 keV and
z
p
= 0.25, with normalization
π
T
= 0.45 ± 0.24 and slope
α
T
= 1.89 ± 0.15. We obtain only weak constraints on redshift evolution,
β
T
= −1.29 ± 1.14.
Conclusions.
The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.
We show that images of TeV blazars in the GeV energy band should contain, along with point-like sources, degree-scale jet-like extensions. These GeV extensions are the result of electromagnetic ...cascades initiated by TeV γ-rays interacting with extragalactic background light and the deflection of the cascade electrons/positrons in extragalactic magnetic fields (EGMFs). Using Monte Carlo simulations, we study the spectral and timing properties of the degree-scale extensions in simulated GeV band images of TeV blazars. We show that the brightness profile of such degree-scale extensions can be used to infer the light curve of the primary TeV γ-ray source over the past 107 yr, i.e., over a time scale comparable to the lifetime of the parent active galactic nucleus. This implies that the degree-scale jet-like GeV emission could be detected not only near known active TeV blazars, but also from "TeV blazar remnants," whose central engines were switched off up to 10 million years ago. Since the brightness profile of the GeV "jets" depends on the strength and the structure of the EGMF, their observation provides additional information about the EGMF.
Context. The XMM-Large Scale Structure survey, covering an area of 11.1 sq. deg., contains more than 6000 X-ray point-like sources detected with the XMM-Newton to a flux of 3 × 10-15 erg s-1 cm-2 in ...the 0.5−2 keV band. The vast majority of these sources have optical (CFHTLS), infrared (SWIRE IRAC and MIPS), near-infrared (UKIDSS), and/or ultraviolet (GALEX) counterparts. Aims. We wish to investigate the environmental properties of the different types of the XMM-LSS X-ray sources by defining their environment using the i′-band CFHTLS W1 catalog of optical galaxies to a magnitude limit of 23.5 mag. Methods. We have classified 4435 X-ray selected sources on the basis of their spectra, SEDs, and X-ray luminosity, and estimated their photometric redshifts, which have a 4−11 band photometry with an accuracy of σ△z/(1+zsp) = 0.076 with 22.6% outliers for i′ < 26 mag. We estimated the local overdensities of 777 X-ray sources that have spectro-z or photo-z calculated by using more than seven bands (accuracy of σ△z/(1+zsp) = 0.061 with 13.8% outliers) within the volume-limited region defined by 0.1 ≤ z ≤ 0.85 and −23.5 < Mi′ < −20. Results. Although X-ray sources may be found in variety of environments, a high fraction (≳55−60%), as verified by comparing with the random expectations, reside in overdense regions. The galaxy overdensities within which X-ray sources reside show a positive recent redshift evolution (at least for the range studied; z ≲ 0.85). We also find that X-ray selected galaxies, when compared to AGN, inhabit significantly higher galaxy overdensities, although their spatial extent appear to be smaller than that of AGN. Hard AGN (HR ≥ −0.2) are located in more overdense regions than soft AGN (HR < −0.2), which is clearly seen in both redshift ranges, although it appears to be stronger in the higher redshift range (0.55 < z < 0.85). Furthermore, the galaxy overdensities (with δ ≳ 1.5) within which soft AGN are embedded appear to evolve more rapidly compared to the corresponding overdensities around hard AGN.
A geometric method based on the high-order 3D Voronoi tessellation is proposed for identifying single galaxies, pairs and triplets. This approach allows us to select small galaxy groups and isolated ...galaxies in different environments and to find the isolated systems. The volume-limited sample of galaxies from the Sloan Digital Sky Survey Data Release 5 spectroscopic survey was used. We conclude that in such small groups as pairs and triplets, segregation by luminosity is clearly observed: galaxies in isolated pairs and triplets are on average two times more luminous than isolated galaxies. We consider the dark matter content in different systems. The median values of mass-to-luminosity ratio are 12 M⊙/L⊙ for the isolated pairs and 44 M⊙/L⊙ for the isolated triplets, and 7 (8) M⊙/L⊙ for the most compact pairs (triplets). We also found that systems in denser environments have greater rms velocity and mass-to-luminosity ratio.
Aims. Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. Methods. We measure the two-point angular correlation function of ~5700 and 2500 ...X-ray point-like sources over the ~11 sq. deg. XMM-LSS field in the soft (0.5–2 keV) and hard (2–10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function. Results. We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ0 = 1.3′′ ± 0.2′′ for the soft, and γ = 2.00 ± 0.04, θ0 = 7.3′′ ± 1.0′′ for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for fx ≲ 10-14 erg s-1 cm-2 and lower above this flux limit. We confirm that the clustering strength θ0 grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r0 ≃ 10h-1 Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of ~2.5 for the soft band sources (at a median \bar{z}$z̅ ≃ 1.1 ≃ 1.1) and ~3.3 for the hard band sources (at a median $\bar{z}$z̅ ≃ 1 ≃ 1), which translates into a host dark matter halo mass of ~1013h-1M⊙ and ~1013.7h-1M⊙ for the soft and hard bands, respectively.
Aims. We present V and R photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756. The data were taken by the MiNDSTEp collaboration with the 1.54 m Danish telescope at the ESO ...La Silla observatory from 2008 to 2012. Methods. Differential photometry has been carried out using the image subtraction method as implemented in the HOTPAnTS package, additionally using GALFIT for quasar photometry. Results. The quasar WFI 2033-4723 showed brightness variations of order 0.5 mag in V and R during the campaign. The two lensed components of quasar HE 0047-1756 varied by 0.2–0.3 mag within five years. We provide, for the first time, an estimate of the time delay of component B with respect to A of Δt = (7.6 ± 1.8) days for this object. We also find evidence for a secular evolution of the magnitude difference between components A and B in both filters, which we explain as due to a long-duration microlensing event. Finally we find that both quasars WFI 2033-4723 and HE 0047-1756 become bluer when brighter, which is consistent with previous studies.
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