Cosmology

Abstract:

Abstract:

Understanding the origin and evolution of supermassive black holes (SMBHs) stands as one of the most important challenges in astrophysics and cosmology, with little current theoretical consensus. Improved observational constraints on the cosmological evolution of SMBH demographics are needed. Here we report results of a search via photometric variability for SMBHs appearing as active galactic nuclei (AGN) in the cosmological volume defined by the Hubble Ultra Deep Field. This work includes particular focus on a new observation carried out in 2023 with the Hubble Space Telescope using the WFC3/IR/F140W, which is compared directly to equivalent data taken 11 yr earlier in 2012. Two earlier pairs of observations from 2009 to 2012 with WFC3/IR/F105W and WFC3/IR/F160W are also analyzed. We identify 521, 188, and 109 AGN candidates as nuclear sources that exhibit photometric variability at a level of 2σ, 2.5σ, and 3σ, respectively, in at least one filter. This sample includes 13, 3, and 2 AGN candidates at redshifts z > 6, when the Universe was ≲900 Myr old. After variability and luminosity function (down to MUV = −17 mag) completeness corrections, we estimate the comoving number density of SMBHs, nSMBH(z). At z ≳ 6, nSMBH ≳ 6 × 10−3 cMpc−3. At low z our observations are sensitive to AGN fainter than MUV = −17 mag, and we estimate nSMBH ≳ 10−2 cMpc−3. We discuss how these results place strong constraints on a variety of SMBH seeding theories.

Abstract:

Observations over the past decade have shown that galaxy clusters undergo the most transformative changes during the z = 1.5–2 epoch. However, challenges such as low lensing efficiency, high shape measurement uncertainty, and a scarcity of background galaxies have prevented us from characterizing their masses with weak gravitational lensing (WL) beyond redshift z ∼ 1.75. In this paper, we report the successful WL detection of JKCS 041 and XLSSC 122 at z = 1.80 and z = 1.98, respectively, utilizing deep infrared imaging data from the Hubble Space Telescope with careful removal of instrumental effects. These are the most distant clusters ever measured through WL. The mass peaks of JKCS 041 and XLSSC 122, which coincide with the X-ray peak positions of the respective clusters, are detected at the ∼3.7σ and ∼3.2σ levels, respectively. Assuming a single spherical Navarro–Frenk–White profile, we estimate that JKCS 041 has a virial mass of M200c = (5.4 ± 1.6) × 1014 M⊙, while the mass of XLSSC 122 is determined to be M200c = (3.3 ± 1.8) × 1014 M⊙. These WL masses are consistent with the estimates inferred from their X-ray observations. We conclude that although the probability of finding such massive clusters at their redshifts is certainly low, their masses can still be accommodated within the current ΛCDM paradigm.

Abstract:

Using the Dark Energy Survey 5-yr sample, we determine the properties of type Ia supernova (SN Ia) host galaxies across a wide multiwavelength range – from the optical to far-infrared – including data from the Herschel and Spitzer space telescopes. We categorize the SNe Ia into three distinct groups according to the distribution of their host galaxies on the star formation rate (SFR) – stellar mass () plane. Each region comprises host galaxies at distinct stages in their evolutionary pathways: Region 1 – low-mass hosts; Region 2 – high-mass, star-forming hosts and Region 3 – high-mass, passive hosts. We find SNe Ia in host galaxies located in Region 1 have the steepest slope (quantified by ) between their colours and luminosities, with . This differs at the significance level to SNe Ia in Region 3, which have the shallowest colour–luminosity slope with . After correcting SNe Ia in each subsample by their respective , events in Region 3 (high-mass, passive hosts) are mag () brighter, post-standardization. We conclude that future cosmological analyses should apply standardization relations to SNe Ia based upon the region in which the SN host galaxy lies in the SFR– plane. Alternatively, cosmological analyses should restrict the SN Ia sample to events whose host galaxies occupy a single region of this plane.

Abstract:

Supermassive black holes are prevalent at the centers of massive galaxies, and their masses scale with galaxy properties, increasing evidence suggesting that these trends continue to low stellar masses. Seeds are needed for supermassive black holes, especially at the highest redshifts explored by the James Webb Space Telescope. We study the hierarchical merging of galaxies via cosmological merger trees and argue that the seeds of supermassive black holes formed in nuclear star clusters via stellar black hole mergers at early epochs. Observable tracers include intermediate-mass black holes, nuclear star clusters, and early gas accretion in host dwarf galaxies, along with a potentially detectable stochastic gravitational-wave background, ejection of intermediate and supermassive black holes, and consequences of a significant population of early tidal disruption events and extreme mass ratio inspirals.