22 research outputs found
Figuring Out Gas & Galaxies In Enzo (FOGGIE) V: The Virial Temperature Does Not Describe Gas in a Virialized Galaxy Halo
The classical definition of the virial temperature of a galaxy halo excludes
a fundamental contribution to the energy partition of the halo: the kinetic
energy of non-thermal gas motions. Using simulations of low-redshift, galaxies from the FOGGIE project (Figuring Out Gas & Galaxies In Enzo)
that are optimized to resolve low-density gas, we show that the kinetic energy
of non-thermal motions is roughly equal to the energy of thermal motions. The
simulated FOGGIE halos have lower bulk temperatures than
expected from a classical virial equilibrium, owing to significant non-thermal
kinetic energy that is formally excluded from the definition of
. We derive a modified virial temperature explicitly including
non-thermal gas motions that provides a more accurate description of gas
temperatures for simulated halos in virial equilibrium. Strong bursts of
stellar feedback drive the simulated FOGGIE halos out of virial equilibrium,
but the halo gas cannot be accurately described by the standard virial
temperature even when in virial equilibrium. Compared to the standard virial
temperature, the cooler modified virial temperature implies other effects on
halo gas: (i) the thermal gas pressure is lower, (ii) radiative cooling is more
efficient, (iii) O VI absorbing gas that traces the virial temperature may be
prevalent in halos of a higher mass than expected, (iv) gas mass estimates from
X-ray surface brightness profiles may be incorrect, and (v) turbulent motions
make an important contribution to the energy balance of a galaxy halo.Comment: 30 pages, 14 figures, accepted to Ap
Figuring Out Gas & Galaxies in Enzo (FOGGIE). III. The Mocky Way:Investigating Biases in Observing the Milky Way's Circumgalactic Medium
The circumgalactic medium (CGM) of the Milky Way is mostly obscured by nearby
gas in position-velocity space because we reside inside the Galaxy. Substantial
biases exist in most studies on the Milky Way's CGM that focus on
easier-to-detect high-velocity gas. With mock observations on a Milky-Way
analog from the FOGGIE simulation, we investigate four observational biases
related to the Milky Way's CGM. First, QSO absorption-line studies probe a
limited amount of the CGM mass: only 35% of the mass is at high Galactic
latitudes degrees, of which only half is moving at km s. Second, the inflow rate () of the cold
gas observable in HI 21cm is reduced by a factor of as we switch from
the local standard of rest to the galaxy's rest frame; meanwhile of
the cool and warm gas does not change significantly. Third, OVI and NV are
promising ions to probe the Milky Way's outer CGM (15 kpc), but CIV
may be less sensitive. Lastly, the scatter in ion column density is a factor of
2 higher if the CGM is observed from inside-out than from external views
because of the gas radial density profile. Our work highlights that
observations of the Milky Way's CGM, especially those using HI 21cm and QSO
absorption lines, are highly biased. We demonstrate that these biases can be
quantified and calibrated through synthetic observations with simulated
Milky-Way analogs.Comment: ApJ in pres
Figuring Out Gas & Galaxies In Enzo (FOGGIE). IV. The Stochasticity of Ram Pressure Stripping in Galactic Halos
We study ram pressure stripping in simulated Milky Way-like halos at z>=2
from the Figuring Out Gas & Galaxies In Enzo (FOGGIE) project. These
simulations reach exquisite resolution in their circumgalactic medium (CGM) gas
owing to FOGGIE's novel refinement scheme. The CGM of each halo spans a wide
dynamic range in density and velocity over its volume---roughly 6 dex and 1000
km/s, respectively---translating into a 5 dex range in ram pressure imparted to
interacting satellites. The ram pressure profiles of the simulated CGM are
highly stochastic, owing to kpc-scale variations of the density and velocity
fields of the CGM gas. As a result, the efficacy of ram pressure stripping
depends strongly on the specific path a satellite takes through the CGM. The
ram-pressure history of a single satellite is generally unpredictable and not
well correlated with its approach vector with respect to the host galaxy. The
cumulative impact of ram pressure on the simulated satellites is dominated by
only a few short strong impulses---on average, 90% of the total surface
momentum gained through ram pressure is imparted in 20% or less of the total
orbital time. These results reveal an erratic mode of ram pressure stripping in
Milky-Way like halos at high redshift---one that is not captured by a smooth
spherically-averaged model of the circumgalactic medium.Comment: 18 pages, 10 figures. Submitted to Ap
Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy
A new class of extragalactic astronomical sources discovered in 2021, named
Odd Radio Circles (ORCs, Norris et al. 2021), are large rings of faint, diffuse
radio continuum emission spanning ~1 arcminute on the sky. Galaxies at the
centers of several ORCs have photometric redshifts of z~0.3-0.6, implying
physical scales of several 100 kiloparsecs in diameter for the radio emission,
the origin of which is unknown. Here we report spectroscopic data on an ORC
including strong [OII] emission tracing ionized gas in the central galaxy of
ORC4 at z=0.4512. The physical extent of the [OII] emission is ~40 kpc in
diameter, larger than expected for a typical early-type galaxy (Pandya et al,
2017) but an order of magnitude smaller than the large-scale radio continuum
emission. We detect a ~200 km/s velocity gradient across the [OII] nebula, as
well as a high velocity dispersion of ~180 km/s. The [OII] equivalent width
(EW, ~50 Ang) is extremely high for a quiescent galaxy. The morphology,
kinematics, and strength of the [OII] emission are consistent with the infall
of shock ionized gas near the galaxy, following a larger-scale, outward moving
shock driven by a galactic wind. Both the extended optical and radio emission,
while observed on very different scales, may therefore result from the same
dramatic event.Comment: 7 figures, accepted to Natur
Reverberation Mapping of Optical Emission Lines in Five Active Galaxies
We present the first results from an optical reverberation mapping campaign executed in 2014 targeting the active galactic nuclei (AGNs) MCG+08-11-011, NGC 2617, NGC 4051, 3C 382, and Mrk 374. Our targets have diverse and interesting observational properties, including a changing look AGN and a broad-line radio galaxy. Based on continuum-Hβ lags, we measure black hole masses for all five targets. We also obtain Hγ and He ii λ4686 lags for all objects except 3C 382. The He ii λ4686 lags indicate radial stratification of the BLR, and the masses derived from different emission lines are in general agreement. The relative responsivities of these lines are also in qualitative agreement with photoionization models. These spectra have extremely high signal-to-noise ratios (100-300 per pixel) and there are excellent prospects for obtaining velocity-resolved reverberation signatures