• A Library of Synthetic X-Ray Spectra for Fitting Tidal Disruption Events

      Wen, S.; Jonker, P.G.; Stone, N.C.; Zabludoff, A.I.; Cao, Z.; University of Arizona (Institute of Physics, 2022)
      We present a tabulated version of our slim-disk model for fitting tidal disruption events (TDEs). We create a synthetic X-ray spectral library by ray-tracing stationary general relativistic slim disks and including gravitational redshift, Doppler, and lensing effects self-consistently. We introduce the library to reduce computational expense and increase access for fitting future events. Fitting requires interpolation between the library spectra; the interpolation error in the synthetic flux is generally <10% (it can rise to 40% when the disk is nearly edge-on). We fit the X-ray spectra of the TDEs ASASSN-14li and ASASSN-15oi, successfully reproducing our earlier constraints on black hole mass M • and spin a • from full on-the-fly ray-tracing. We use the library to fit mock observational data to explore the degeneracies among parameters, finding that (1) spectra from a hotter thermal disk and edge-on inclination angle offer tighter constraints on M • and a •; (2) the constraining power of spectra on M • and a • increases as a power law with the number of X-ray counts, and the index of the power law is higher for hotter thermal disk spectra; (3) multiepoch X-ray spectra partially break the degeneracy between M • and a •; (4) the time-dependent level of X-ray absorption can be constrained from spectral fitting. The tabulated model and slim-disk model are available at https://doi.org/10.25739/hfhz-xn60. © 2022. The Author(s). Published by the American Astronomical Society.
    • After the Fall: Resolving the Molecular Gas in Post-starburst Galaxies

      Smercina, A.; Smith, J.-D.T.; French, K.D.; Bell, E.F.; Dale, D.A.; Medling, A.M.; Nyland, K.; Privon, G.C.; Rowlands, K.; Walter, F.; et al. (Institute of Physics, 2022)
      Post-starburst (PSB), or "E + A,"galaxies represent a rapid transitional phase between major, gas-rich mergers and gas-poor, quiescent, early-type galaxies. Surprisingly, many PSBs have been shown to host a significant interstellar medium (ISM), despite theoretical predictions that the majority of the star-forming gas should be expelled in active galactic nuclei- or starburst-driven outflows. To date, the resolved properties of this surviving ISM have remained unknown. We present high-resolution ALMA continuum and CO(2-1) observations in six gas- and dust-rich PSBs, revealing for the first time the spatial and kinematic structure of their ISM on sub-kpc scales. We find extremely compact molecular reservoirs, with dust and gas surface densities rivaling those found in (ultra)luminous infrared galaxies. We observe spatial and kinematic disturbances in all sources, with some also displaying disk-like kinematics. Estimates of the internal turbulent pressure in the gas exceed those of normal star-forming disks by at least 2 orders of magnitude, and rival the turbulent gas found in local interacting galaxies, such as the Antennae. Though the source of this high turbulent pressure remains uncertain, we suggest that the high incidence of tidal disruption events in PSBs could play a role. The star formation in these PSBs' turbulent central molecular reservoirs is suppressed, forming stars only 10% as efficiently as starburst galaxies with similar gas surface densities. "The fall"of star formation in these galaxies was not precipitated by complete gas expulsion or redistribution. Rather, this high-resolution view of PSBs' ISM indicates that star formation in their remaining compact gas reservoirs is suppressed by significant turbulent heating. © 2022. The Author(s). Published by the American Astronomical Society.
    • Discovery of a possible splashback feature in the intracluster light of MACS J1149.5+2223

      Gonzalez, A.H.; George, T.; Connor, T.; Deason, A.; Donahue, M.; Montes, M.; Zabludoff, A.I.; Zaritsky, D.; Department of Astronomy, University of Arizona; Steward Observatory, University of Arizona (Oxford University Press, 2021)
      We present an analysis of the intracluster light (ICL) in the Frontier Field Cluster MACS J1149.5+2223 (z = 0.544), which combines new and archival Hubble WFC3/IR imaging to provide continuous radial coverage out to 2.8 Mpc from the brightest cluster galaxy (BCG). Employing careful treatment of potential systematic biases and using data at the largest radii to determine the background sky level, we reconstruct the surface brightness profile out to a radius of 2 Mpc. This radius is the largest to which the ICL has been measured for an individual cluster. Within this radius, we measure a total luminosity of 1.5 × 1013 L⊙ for the BCG plus ICL. From the profile and its logarithmic slope, we identify the transition from the BCG to ICL at r ∼70 kpc. Remarkably, we also detect an apparent inflection in the profile centred in the 1.2-1.7 Mpc (0.37-0.52 r200m) radial bin, a signature of an infall caustic in the stellar distribution. Based upon the shape and strength of the feature, we interpret it as potentially being at the splashback radius, although the radius is smaller than theoretical predictions. If this is the splashback radius, then it is the first such detection in the ICL and the first detection of the splashback radius for an individual cluster. Similar analyses should be possible with the other Frontier Field clusters, and eventually with clusters observed by the Euclid and Roman missions. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
    • Mass, spin, and ultralight boson constraints from the intermediate-mass black hole in the tidal disruption event 3XMM J215022.4–055108

      Wen, S.; Jonker, P.G.; Stone, N.C.; Zabludoff, A.I.; University of Arizona (IOP Publishing Ltd, 2021)
      We simultaneously and successfully fit the multiepoch X-ray spectra of the tidal disruption event (TDE) 3XMM J215022.4-055108 using a modified version of our relativistic slim disk model that now accounts for angular momentum losses from radiation. We explore the effects of different disk properties and of uncertainties in the spectral hardening factor fc and redshift z on the estimation of the black hole mass M• and spin a•. Across all choices of theoretical priors, we constrain M• to less than 2.2 × 104 Me at 1σ confidence. Assuming that the TDE host is a star cluster associated with the adjacent, brighter, barred lenticular galaxy at z = 0.055, we constrain M• and a• to be 1.75-+0.050.45 ´ 104 Me and 0.8-+0.020.12, respectively, at 1σ confidence. The high, but sub-extremal, spin suggests that, if this intermediate-mass black hole (IMBH) has grown significantly since formation, it has acquired its last e-fold in mass in a way incompatible with both the “standard” and “chaotic” limits of gas accretion. Ours is the first clear IMBH with a spin measurement. As such, this object represents a novel laboratory for astroparticle physics; its M• and a• place tight limits on the existence of ultralight bosons, ruling out those with masses from ∼10-15 to 10-16 eV. © 2021. The American Astronomical Society. All rights reserved.