5 research outputs found
The cosmic baryon partition between the IGM and CGM in the SIMBA simulations
We use the SIMBA suite of cosmological hydrodynamical simulations to investigate the importance of various stellar and active galactic nuclei (AGN) feedback mechanisms in partitioning the cosmic baryons between the intergalactic (IGM) and circumgalactic (CGM) media in the z ≤ 1 Universe. We identify the AGN jets as the most prominent mechanism for the redistribution of baryons between the IGM and CGM. In contrast to the full feedback models, deactivating AGN jets results in ≈20 per cent drop in fraction of baryons residing in the IGM and a consequent increase of CGM baryon fraction by ≈50 per cent.We find that stellar feedback modifies the partition of baryons on a 10 per cent level. We further examine the physical propertiesof simulated haloes in different mass bins, and their response to various feedback models. On average, a sixfold decrease inthe CGM mass fraction due to the inclusion of feedback from AGN jets is detected in 1012 M ≤ M200 ≤ 1014 M haloes. Examination of the average radial gas density profiles of M200 > 1012 M haloes reveals up to an order of magnitude decrease in gas densities due to the AGN jet feedback. We compare gas density profiles from SIMBA simulations to the predictions of the modified Navarro–Frenk–White model, and show that the latter provides a reasonable approximation within the virial radii of the full range of halo masses, but only when rescaled by the appropriate mass-dependent CGM fraction of the halo. The relative partitioning of cosmic baryons and, subsequently, the feedback models can be constrained observationally with fast radio bursts in upcoming surveys
The FRB20190520B Sightline Intersects Foreground Galaxy Clusters
The repeating fast radio burst FRB20190520B is an anomaly of the FRB
population thanks to its high dispersion measure (DM)
despite its low redshift of . This excess has been
attributed to a host contribution of , far larger than any other known FRB. In this paper,
we describe spectroscopic observations of the FRB20190520B field obtained as
part of the FLIMFLAM survey on the 2dF/AAOmega facility, which yielded 701
galaxies redshifts in a field of . Applying a
friends-of-friends group finder reveals multiple galaxy groups and clusters,
for which we then estimated halo masses by comparing their richness with
forward-modeled mocks from numerical simulations. We discover two separate
galaxy clusters, at and
, respectively, that are directly intersected by the FRB sightline
within their characteristic radius . Subtracting off their estimated
DM contributions as well that of the diffuse intergalactic medium, we estimate
a host contribution of or
(observed frame)
depending on whether we assume the halo gas extends to or . This significantly smaller -- no longer the largest known
value -- is now consistent with H emission measure estimates of the
host galaxy without having to invoke unusually high gas temperatures. We also
re-estimate the turbulent fluctuation and geometric amplification factor of the
scattering layer to be . This
result illustrates the importance of incorporating foreground data for FRB
analyses, both for understanding the nature of FRBs and to realize their
potential as a cosmological probe.Comment: 14 pages, 5 figures, 2 tables. Interactive figure (link in text).
Submitted to ApJ
The first measurement of the quasar lifetime distribution
Understanding the growth of the supermassive black holes powering luminous
quasars, their co-evolution with host galaxies, and impact on the surrounding
intergalactic medium depends sensitively on the duration of quasar accretion
episodes. Unfortunately, this time-scale, known as the quasar lifetime, , is still uncertain by orders of magnitude (). However, the extent of the He II Ly proximity zones
in the absorption spectra of quasars constitutes a unique
probe, providing sensitivity to lifetimes up to Myr. Our recent
analysis of archival He II proximity zone spectra reveals a surprisingly
broad range of emission timescales, indicating that some quasars turned on
Myr ago, whereas others have been shining for Myr.
Determining the underlying quasar lifetime distribution (QLD) from proximity
zone measurements is a challenging task owing to: 1) the limited sensitivity of
individual measurements; 2) random sampling of the quasar light curves; 3)
density fluctuations in the quasar environment; and 4) the inhomogeneous
ionization state of He II in a reionizing IGM. We combine a semi-numerical He
II reionization model, hydrodynamical simulations post-processed with ionizing
radiative transfer, and a novel statistical framework to infer the QLD from an
ensemble of proximity zone measurements. Assuming a log-normal QLD, we infer a
mean and standard deviation . Our results allow us to estimate the
probability of detecting young quasars with Myr from their
proximity zone sizes yielding , which is broadly consistent with recent
determination at .Comment: 14 pages, 10 figures, submitted to MNRA
Searching for the Sources of Excess Extragalactic Dispersion of FRBs
The FLIMFLAM survey is collecting spectroscopic data of field galaxies near fast radio burst (FRB) sight lines to constrain key parameters describing the distribution of matter in the Universe. In this work, we leverage the survey data to determine the source of the excess extragalactic dispersion measure (DM), compared to Macquart relation estimates of four FRBs: FRB20190714A, FRB20200906A, FRB20200430A, and FRB20210117A. By modeling the gas distribution around the foreground galaxy halos and galaxy groups of the sight lines, we estimate DM _halos , their contribution to the FRB DMs. The FRB20190714A sight line shows a clear excess of foreground halos which contribute roughly two-thirds of the observed excess DM, thus implying a sight line that is baryon dense. FRB20200906A shows a smaller but nonnegligible foreground halo contribution, and further analysis of the intergalactic medium is necessary to ascertain the true cosmic contribution to its DM. FRB20200430A and FRB20210117A show negligible foreground contributions, implying a large host galaxy excess and/or progenitor environment excess