We present an alternative formation scenario for the gravitational wave event GW190521 that can be explained as the merger of central black holes (BHs) from two ultradwarf galaxies of stellar mass ...∼10^{5}-10^{6} M_{⊙}, which had themselves previously undergone a merger. The GW190521 components' masses of 85_{-14}^{+21} M_{⊙} and 66_{-18}^{+17} M_{⊙} challenge standard stellar evolution models, as they fall in the so-called mass gap. We demonstrate that the merger history of ultradwarf galaxies at high redshifts (1≲z≲2) matches well the LIGO-Virgo inferred merger rate for BHs within the mass range of the GW190521 components, resulting in a likely time delay of ≲4 Gyr considering the redshift of this event. We further demonstrate that the predicted timescales are consistent with expectations for central BH mergers, although with large uncertainties due to the lack of high-resolution simulations in low-mass dwarf galaxies. Our findings show that this BH production and merging channel is viable and extremely interesting as a new way to explore galaxies' BH seeds and galaxy formation. We recommend this scenario be investigated in detail with simulations and observations.
Abstract
We present the complete set of Hubble Space Telescope imaging of the binary neutron star merger GW170817 and its optical counterpart AT 2017gfo. Including deep template imaging in F814W, ...F110W, F140W, and F160W at 3.4 yr post-merger, we reanalyze the full light curve of AT 2017gfo across 12 bands from 5 to 1273 rest-frame days after merger. We obtain four new detections of the short
γ
-ray burst 170817A afterglow from 109 to 170 rest-frame days post-merger. These detections are consistent with the previously observed
β
= −0.6 spectral index in the afterglow light curve with no evidence for spectral evolution. We also analyze our limits in the context of kilonova afterglow or IR dust echo emission but find that our limits are not constraining for these models. We use the new data to construct deep optical and IR stacks, reaching limits of
M
= −6.3 to −4.6 mag, to analyze the local environment around AT 2017gfo and low surface brightness features in its host galaxy NGC 4993. We rule out the presence of any globular cluster at the position of AT 2017gfo to 2.3 × 10
4
L
⊙
, including those with the reddest
V
−
H
colors. Finally, we analyze the substructure of NGC 4993 in deep residual imaging and find shell features that extend up to 71.″8 (14.2 kpc) from NGC 4993. The shells have a cumulative stellar mass of 6.3 × 10
8
M
⊙
, roughly 2% of NGC 4993, and mass-weighted ages of >3 Gyr. We conclude that it was unlikely that the GW170817 progenitor system formed in the galaxy merger.
Abstract FRB 20220610A is a high-redshift fast radio burst (FRB) that has not been observed to repeat. Here, we present rest-frame UV and optical Hubble Space Telescope observations of the field of ...FRB 20220610A. The imaging reveals seven extended sources, one of which we identify as the most likely host galaxy with a spectroscopic redshift of z = 1.017. We spectroscopically confirm three additional sources to be at the same redshift and identify the system as a compact galaxy group with possible signs of interaction among group members. We determine the host of FRB 20220610A to be a star-forming galaxy with a stellar mass of ≈10 9.7 M ⊙ , mass-weighted age of ≈2.6 Gyr, and star formation rate (integrated over the last 100 Myr) of ≈1.7 M ⊙ yr −1 . These host properties are commensurate with the star-forming field galaxy population at z ∼ 1 and trace their properties analogously to the population of low- z FRB hosts. Based on estimates of the total stellar mass of the galaxy group, we calculate a fiducial contribution to the observed dispersion measure from the intragroup medium of ≈90–182 pc cm −3 (rest frame). This leaves a significant excess of 515 − 272 + 122 pc cm −3 (in the observer frame); further observation will be required to determine the origin of this excess. Given the low occurrence rates of galaxies in compact groups, the discovery of an FRB in one demonstrates a rare, novel environment in which FRBs can occur. As such groups may represent ongoing or future mergers that can trigger star formation, this supports a young stellar progenitor relative to star formation.
The DESGW group seeks to identify electromagnetic counterparts of gravitational wave events seen by the LIGO-VIRGO network, such as those expected from binary neutron star mergers or neutron ...star-black hole mergers. DESGW was active throughout the first two LIGO observing seasons, following up several binary black hole mergers and the first binary neutron star merger, GW170817. This work describes the modifications to the observing strategy generation and image processing pipeline between the second (ending in August 2017) and third (beginning in April 2019) LIGO observing seasons. The modifications include a more robust observing strategy generator, further parallelization of the image reduction software and difference imaging processing pipeline, data transfer streamlining, and a web page listing identified counterpart candidates that updates in real time. Taken together, the additional parallelization steps enable the identification of potential electromagnetic counterparts within fully calibrated search images in less than one hour, compared to the 3-5 hours it would typically take during the first two seasons. These performance improvements are critical to the entire EM follow-up community, as rapid identification (or rejection) of candidates enables detailed and rapid spectroscopic follow-up by multiple instruments, leading to more information about the environment immediately following such gravitational wave events.
Abstract
The recent report of an association of the gravitational-wave (GW) binary black hole (BBH) merger GW190521 with a flare in the active galactic nuclei (AGNs) J124942.3 + 344929 has generated ...tremendous excitement. However, GW190521 has one of the largest localization volumes among all of the GW events detected so far. The 90% localization volume likely contains 7400 unobscured AGNs brighter than
g
≤ 20.5 AB mag, and it results in a ≳70% probability of chance coincidence for an AGN flare consistent with the GW event. We present a Bayesian formalism to estimate the confidence of an AGN association by analyzing a population of BBH events with dedicated follow-up observations. Depending on the fraction of BBHs arising from AGNs, counterpart searches of
(
1
)
−
(
100
)
GW events are needed to establish a confident association, and more than an order of magnitude more for searches without follow-up (i.e., using only the locations of AGN and GW events). Follow-up campaigns of the top ∼5% (based on volume localization and binary mass) of BBH events with total rest-frame mass ≥50
M
⊙
are expected to establish a confident association during the next LIGO/Virgo/KAGRA observing run (O4), as long as the true value of the fraction of BBHs giving rise to AGN flares is >0.1. Our formalism allows us to jointly infer cosmological parameters from a sample of BBH events that include chance coincidence flares. Until the confidence of AGN associations is established, the probability of chance coincidence must be taken into account to avoid biasing astrophysical and cosmological constraints.
The origins of the black hole-black hole mergers discovered through gravitational waves with the LIGO/Virgo Collaboration are a mystery. We investigate the idea that some of these black holes ...originate from the centers of extremely low mass ultradwarf galaxies that have merged together in the distant past at z > 1. Extrapolating the central black hole/stellar mass ratio suggests that the black holes in these mergers could arise from galaxies of masses ∼105-106 M . We investigate whether these galaxies merge at a rate consistent with the observed black hole rate of ∼9.7-101 Gpc−3 yr−1 using the latest LIGO/Virgo results. We show that in the nearby universe the merger rate and number densities of ultradwarf galaxies are too low, by an order or magnitude, to produce these black hole mergers. However, by considering that the merger fraction, merger timescales, and the number densities of low-mass galaxies all conspire at z > 1-1.5 to increase the merger rate for these galaxies at higher redshifts, we argue that it is possible that these observed gravitational wave events could arise from black holes in the centers of low-mass galaxies. The major uncertainty in this calculation is the merger dynamical timescales for black holes in low-mass galaxies. Our results suggest that a very long black hole merger timescale of 4-7 Gyr is needed, consistent with an extended merger history. Further simulations of black hole merger timescales are needed to test this possibility; however, our theory can be tested by searching for host galaxies of gravitational wave events. Results from these searches will put limits on dwarf galaxy mergers and/or the presence and formation mechanisms of black holes through Population III stars in the lowest-mass galaxies.
Cosmology intertwined III: fσ8 and S8 Di Valentino, Eleonora; Anchordoqui, Luis A.; Akarsu, Özgür ...
Astroparticle physics,
September 2021, Letnik:
131
Journal Article
Recenzirano
The standard Λ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few statistically significant tensions and anomalies were found in the latest data ...analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension between Planck data and weak lensing measurements and redshift surveys, in the value of the matter energy density Ωm and the amplitude σ8 (or the growth rate fσ8) of cosmic structure. We list a few promising models for solving this tension, and discuss the importance of trying to fit multiple cosmological datasets with complete physical models, rather than fitting individual datasets with a few handpicked theoretical parameters.
We investigate the possibility of the gravitational-wave event GW170817 being a light, solar-mass black hole (BH) — neutron star (NS) merger. We explore two exotic scenarios involving primordial ...black holes (PBH) that could produce such an event, taking into account available observational information on NGC 4993. First, we entertain the possibility of dynamical NS-PBH binary formation where a solar-mass PBH and a NS form a binary through gravitational interaction. We find that while dynamical NS-PBH formation could account for the GW170817 event, the rate is highly dependent on unknown density contrast factors and could potentially be affected by galaxy mergers. We also find that PBH-PBH binaries would likely have a larger merger rate, assuming the density contrast boost factor of an order similar to the NS-PBH case. These exotic merger formations could provide new channels to account for the volumetric rate of compact-object mergers reported by LIGO/Virgo. Secondly, we consider the case where one of the NS's in a binary NS system is imploded by a microscopic PBH. We find that the predicted rate for NS implosion into a BH is very small, at least for the specific environment of NGC 4993. We discuss how our analysis can be applied to similar existing (GW190425 and GW190814) and future observations.
ABSTRACT
We present a simulated cosmology analysis using the second and third moments of the weak lensing mass (convergence) maps. The second moment, or variances, of the convergence as a function of ...smoothing scale contains information similar to standard shear two-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The analysis is geared towards the third year (Y3) data from the Dark Energy Survey (DES), but the methodology can be applied to other weak lensing data sets. We present the formalism for obtaining the convergence maps from the measured shear and for obtaining the second and third moments of these maps given partial sky coverage. We estimate the covariance matrix from a large suite of numerical simulations. We test our pipeline through a simulated likelihood analyses varying 5 cosmological parameters and 10 nuisance parameters and identify the scales where systematic or modelling uncertainties are not expected to affect the cosmological analysis. Our simulated likelihood analysis shows that the combination of second and third moments provides a 1.5 per cent constraint on S8 ≡ σ8(Ωm/0.3)0.5 for DES Year 3 data. This is 20 per cent better than an analysis using a simulated DES Y3 shear two-point statistics, owing to the non-Gaussian information captured by the inclusion of higher order statistics. This paper validates our methodology for constraining cosmology with DES Year 3 data, which will be presented in a subsequent paper.
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