The primary and secondary masses of the binary black holes (BBH) reported by LIGO/Virgo are correlated with a narrow dispersion that appears to increase in proportion to mass. The mean binary mass ratio $1.45pm0.07$ we show is consistent with pairs d
rawn randomly from the mass distribution of black holes in our Galaxy. However, BBH masses are concentrated around $simeq 30M_odot$, whereas black holes in our Galaxy peak at $simeq 10M_odot$. This mass difference can be reconciled by gravitational lensing magnification which allows distant events to be detected with typically $zsimeq 2$, so the waveform is reduced in frequency by $1+z$, and hence the measured chirp masses appear 3 times larger than their intrinsic values. This redshift enhancement also accounts for the dispersion of primary and secondary masses, both of which should increase as $1+z$, thereby appearing to scale with mass, in agreement with the data. Thus the BBH component masses provide independent support for lensing, implying most high chirp mass events have intrinsic masses like the stellar mass black holes in our Galaxy, coalescing at $z>1$, with only two low mass BBH detections, of $simeq 10M_odot$ as expected for unlensed events in the local Universe, $zsimeq 0.1$. This lensing solution requires a rapidly declining BBH event rate below $z<1$, which together with the observed absence of BBH spin suggests most events originate within young globular clusters at $z>1$, via efficient binary capture of stellar mass black holes with randomly oriented spins.
We examine the massive colliding cluster El Gordo, one of the most massive clusters at high redshift. We use a free-form lensing reconstruction method that avoids making assumptions about the mass distribution. We use data from the RELICS program and
identify new multiply lensed system candidates. The new set of constraints and free-form method provides a new independent mass estimate of this intriguing colliding cluster. Our results are found to be consistent with earlier parametric models, indirectly confirming the assumptions made in earlier work. By fitting a double gNFW profile to the lens model, and extrapolating to the virial radius, we infer a total mass for the cluster of $M_{200c}=(1.08^{+0.65}_{-0.12})times10^{15}$M$_{odot}$. We estimate the uncertainty in the mass due to errors in the photometric redshifts, and discuss the uncertainty in the inferred virial mass due to the extrapolation from the lens model. We also find in our lens map a mass overdensity corresponding to the large cometary tail of hot gas, reinforcing its interpretation as a large tidal feature predicted by hydrodynamical simulations that mimic El Gordo. Finally, we discuss the observed relation between the plasma and the mass map, finding that the peak in the projected mass map may be associated with a large concentration of colder gas, exhibiting possible star formation. El Gordo is one of the first clusters that will be observed with JWST, which is expected to unveil new high redshift lensed galaxies around this interesting cluster, and provide a more accurate estimation of its mass.
Microlenses with typical stellar masses (a few ${rm M}_{odot}$) have traditionally been disregarded as potential sources of gravitational lensing effects at LIGO/Virgo frequencies, since the time delays are often much smaller than the inverse of the
frequencies probed by LIGO/Virgo, resulting in negligible interference effects at LIGO/Virgo frequencies. While this is true for isolated microlenses in this mass regime, we show how, under certain circumstances and for realistic scenarios, a population of microlenses (for instance stars and remnants from a galaxy halo or from the intracluster medium) embedded in a macromodel potential (galaxy or cluster) can conspire together to produce time delays of order one millisecond which would produce significant interference distortions in the observed strains. At sufficiently large magnification factors (of several hundred), microlensing effects should be common in gravitationally lensed gravitational waves. We explore the regime where the predicted signal falls in the frequency range probed by LIGO/Virgo. We find that stellar mass microlenses, permeating the lens plane, and near critical curves, can introduce interference distortions in strongly lensed gravitational waves. For those lensed events with negative parity, (or saddle points, never studied before in the context of gravitational waves), and that take place near caustics of macromodels, they are more likely to produce measurable interference effects at LIGO/Virgo frequencies. This is the first study that explores the effect of a realistic population of microlenses, plus a macromodel, on strongly lensed gravitational waves.
Using analytical models and cosmological N-body simulations, we study the free-free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the ma
ss function and scaling relations. Earlier works based on analytical models have shown that the average free-free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the CMB spectrum at low frequencies ($ u <$ 5 GHz). We focus on the period after the reionization time (from redshift $z=0$ up to $z=7$) and on haloes that are more massive than in previous works (groups and clusters). We show how the average signal from haloes with $M > 10^{13} h^{-1} M_{odot}$ is less than 10% the signal from the more abundant and colder smaller mass haloes. However, the individual signal from the massive haloes could be detected with future experiments opening the door for a new window to study the intracluster medium.
WMAP observations at mm wavelengths are sensitive to the Sunyaev-Zeldovich effect in galaxy clusters. Among all the objects in the sky, the Virgo cluster is expected to provide the largest integrated signal. Based on models compatible with the X-ray
emission observed in the ROSAT All Sky Survey, we predict a two-sigma detection of the SZ effect from Virgo in the WMAP 3-year data. Our analysis reveals a 3-sigma signal on scales of 5 degrees, although the frequency dependence deviates from the theoretical expectation for the SZ effect. The main sources of uncertainty are instrumental noise, and most importantly, possible contamination from point sources and diffuse back/foregrounds. In particular, a population of unresolved extragalactic sources in Virgo would explain the observed intensity and frequency dependence. In order to resolve this question one needs to wait for experiments like Planck to achieve the required accuracy.
