Unveiling the unseen with the Dark Energy Survey: gravitational waves and dark matter

In this thesis I show how large galaxy surveys, in particular the study of the properties of galaxies, can shed light on gravitational wave sources and dark matter. This is achieved using the latest data from the Dark Energy Survey, an on-going 5000 deg2 optical survey. Galaxy properties such as photometric redshifts and stellar masses are derived through spectral energy distribution fitting methods. The results are used to study host galaxies of gravitational wave events and how light traces dark matter in galaxy clusters. Gravita- tional wave (GW) science, and particularly the electromagnetic follow up of these events, is transforming what had never been seen into a new astronomical field able to unveil the nature of cataclysmic events. Identifying the galaxies that host these events, and es- timating their redshift, stellar mass, and star–formation rate, is crucial for cosmological analysis with gravitational waves, for follow up studies and to understand the formation of the binary systems that are thought to produce observable gravitational wave signals. This thesis describes how the host matching is implemented within the DES–GW pipeline and how observations of NGC 4993, the galaxy host of the event GW170817, provide important information about possible formation scenarios for binary neutron stars. In particular, we find that NGC 4993 presents shell structures and we relate their formation to the binary formation. The same galaxy properties are used to derive an observable mass proxy for galaxy clusters. I show that this mass observable correlates well with the total mass of clusters, which is mainly composed of dark matter. It can therefore be used for cosmological studies with galaxy clusters. The measurement of stellar–to–halo mass relations in clusters provides insights on the connection between the star content and the total matter content in clusters, and how this evolves over cosmic time

Standard Siren Cosmology with Gravitational Waves from Binary Black Hole Mergers in Active Galaxy Nuclei

The detection of gravitational waves (GW) with an electromagnetic counterpart enabled the first Hubble Constant $H_0$ measurement through the standard siren method. Current constraints suggest that $\sim 20-80\%$ of LIGO/Virgo/KAGRA (LVK) Binary Black Hole (BBH) mergers occur in Active Galactic Nuclei (AGN) disks. The claim for a possible association of several BBH mergers with flaring AGNs suggests that cosmological analyses using BBH and AGNs might be promising. We explore standard siren analyses through a method that takes into account the presence of background flaring AGNs, without requiring a unique host galaxy identification, and apply it to realistic GW simulations. Depending on the fraction of LVK BBHs that induce flares, we expect to constrain $H_0$ at the $\sim 3.5-7\%$ ($\sim 2.5-5\%$) precision with $\sim 2$ years or $\sim 160$ events ($\sim 1$ year or $500$ events) of LVK at design (A+) sensitivity, assuming that systematic BBH follow-up searches are performed. Assuming a more restrictive $\Omega_{\rm m}$ prior and that at least $20\%$ of BBHs produces detectable flares, we may reach a $3\%$ ($2\%$) precision in $H_0$ after 2 (1) year of LVK at design (A+) sensitivity. We also show that a $\sim 5-10\%$ precision is possible with complete AGN catalogs and 1 year of LVK run, without the need of time-critical follow-up observations.Comment: 14 pages, 5 figure

Challenges for Fast Radio Bursts as Multi-Messenger Sources from Binary Neutron Star Mergers

Fast radio bursts (FRBs) are a newly discovered class of radio transients that emerge from cosmological sources and last for $\sim$ a few milliseconds. However, their origin remains a highly debated topic in astronomy. Among the plethora of cataclysmic events proposed as potential progenitors, binary neutron star (BNS) mergers have risen as compelling candidates for at least some subset of apparently non-repeating FRBs. However, this connection should not be drawn solely on the basis of chance coincidence probability. In this study, we delineate necessary criteria that must be met when considering an association between FRBs and BNS mergers, focusing on the post-merger ejecta environment. To underscore the significance of these criteria, we scrutinize the proposed association between GW190425 and FRB20190425A. Our investigation meticulously accounts for the challenging condition that the FRB signal must traverse the dense merger ejecta without significant attenuation to remain detectable at 400 MHz. Furthermore, we find that if the FRB is indeed linked to the gravitational wave event, the GW data strongly support a highly off-axis configuration, with a probability of the BNS merger viewing angle $p(\theta_v$ $>$ 30$^{\circ}$) to be $\approx$ 99.99%. Our findings therefore strongly exclude an on-axis system, which we find, on the other hand, to be required in order for this FRB to be detectable. Hence, we conclude that GW190425 is not related to FRB20190425A. We also discuss implications of our results for future detections of coincident multi-messenger observations of FRBs from BNS remnants and GW events and argue that BNS merger remnants cannot account for the formation of > 1% of FRB sources. This observation suggests that short gamma-ray bursts should not be used to explain global attributes of the FRB host population.Comment: 9 pages, 4 figures. Submitte

Weak-lensing calibration of a stellar mass-based mass proxy for redMaPPer and Voronoi Tessellation clusters in SDSS Stripe 82

We present the first weak lensing calibration of $\mu_{\star}$, a new galaxy cluster mass proxy corresponding to the total stellar mass of red and blue members, in two cluster samples selected from the SDSS Stripe 82 data: 230 redMaPPer clusters at redshift $0.1\leq z<0.33$ and 136 Voronoi Tessellation (VT) clusters at $0.1 \leq z < 0.6$. We use the CS82 shear catalog and stack the clusters in $\mu_{\star}$ bins to measure a mass-observable power law relation. For redMaPPer clusters we obtain $M_0 = (1.77 \pm 0.36) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 1.74 \pm 0.62$. For VT clusters, we find $M_0 = (4.31 \pm 0.89) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 0.59 \pm 0.54$ and $M_0 = (3.67 \pm 0.56) \times 10^{14}h^{-1} M_{\odot}$, $\alpha = 0.68 \pm 0.49$ for a low and a high redshift bin, respectively. Our results are consistent, internally and with the literature, indicating that our method can be applied to any cluster finding algorithm. In particular, we recommend that $\mu_{\star}$ be used as the mass proxy for VT clusters. Catalogs including $\mu_{\star}$ measurements will enable its use in studies of galaxy evolution in clusters and cluster cosmology.Comment: Updated to be consistent with the published versio

On the association of GW190425 with its potential electromagnetic counterpart FRB 20190425A

Recent work by Moroianu et al. has suggested that the binary neutron star (BNS) merger GW190425 might have a potential fast radio burst (FRB) counterpart association, FRB20190425A, at the 2.8σ level of confidence with a likely host galaxy association, namely UGC10667. The authors argue that the observations are consistent with a long-lived hypermassive neutron star (HMNS) that formed promptly after the BNS merger and was stable for approximately 2.5 hr before promptly collapsing into a black hole. Recently, Bhardwaj et al. conclusively associated FRB20190425A with UGC10667, potentially providing a direct host galaxy candidate for GW190425. In this work, we examine the multimessenger association based on the spacetime localization overlaps between GW190425 and the FRB host galaxy UGC10667 and find that the odds for a coincident association are O(5) . We validate this estimate by using a Gaussian process density estimator. Assuming that the association is indeed real, we then perform Bayesian parameter estimation on GW190425 assuming that the BNS event took place in UGC10667. We find that the viewing angle of GW190425 excludes an on-axis system at p(θ v > 30°) ≈ 99.99%, highly favoring an off-axis system similar to GRB 170817A. We also find a slightly higher source frame total mass for the binary, namely, mtotal=3.42−0.11+0.34M⊙ , leading to an increase in the probability of prompt collapse into a black hole and therefore disfavors the long-lived HMNS formation scenario. Given our findings, we conclude that the association between GW190425 and FRB20190425A is disfavoured by current state-of-the-art gravitational-wave analyses