804 research outputs found
The Asymmetric Rotor. IX. The Heavy Water Bands at 2787 cm^–1 and 5373 cm^–1
The combination band (110) of the two stretching fundamentals of D2O is reported and analyzed to yield nu0=5373.2 cm^–1 and the excited state moments of inertia 1.910, 3.931, and 5.929×10^–40 g cm^2. The same method of analysis applied to the unsymmetrical fundamental band (100) envelope gives nu0=2787.5 cm^–1 and the excited state moments 1.881, 3.876, and 5.843×10^–40 g cm^2
Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies
Advances in instrumentation have recently extended detailed measurements of gas kinematics to large samples of high-redshift galaxies. Relative to most nearby, thin disc galaxies, in which gas rotation accurately traces the gravitational potential, the interstellar medium (ISM) of z ≳ 1 galaxies is typically more dynamic and exhibits elevated turbulence. If not properly modelled, these effects can strongly bias dynamical mass measurements. We use high-resolution FIRE-2 cosmological zoom-in simulations to analyse the physical effects that must be considered to correctly infer dynamical masses from gas kinematics. Our analysis covers a range of galaxy properties from low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (M⋆ > 10¹¹ M⊙ at z = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile v_ϕ(r) of the cool (10^(3.5) < T <10^(4.5) K) gas and compare it to the circular velocity v_c = √GM_(enc)/r. In the simulated galaxies, the gas rotation traces the circular velocity at intermediate radii, but the two quantities diverge significantly in the centre and in the outer disc. Our simulations appear to over-predict observed rotational velocities in the centres of massive galaxies (likely from a lack of black hole feedback), so we focus on larger radii. Gradients in the turbulent pressure at these radii can provide additional radial support and bias dynamical mass measurements low by up to 40 per cent. In both the interior and exterior, the gas’ motion can be significantly non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the accuracy of commonly used analytic models for pressure gradients (or ‘asymmetric drift’) in the ISM of high-redshift galaxies
The origin of ultra diffuse galaxies: stellar feedback and quenching
We test if the cosmological zoom-in simulations of isolated galaxies from the
FIRE project reproduce the properties of ultra diffuse galaxies. We show that
stellar feedback-generated outflows that dynamically heat galactic stars,
together with a passively aging stellar population after imposed quenching
(from e.g. infall into a galaxy cluster), naturally reproduce the observed
population of red UDGs, without the need for high spin halos or dynamical
influence from their host cluster. We reproduce the range of surface
brightness, radius and absolute magnitude of the observed z=0 red UDGs by
quenching simulated galaxies at a range of different times. They represent a
mostly uniform population of dark matter-dominated galaxies with M_star ~1e8
Msun, low metallicity and a broad range of ages. The most massive simulated
UDGs require earliest quenching and are therefore the oldest. Our simulations
provide a good match to the central enclosed masses and the velocity
dispersions of the observed UDGs (20-50 km/s). The enclosed masses of the
simulated UDGs remain largely fixed across a broad range of quenching times
because the central regions of their dark matter halos complete their growth
early. A typical UDG forms in a dwarf halo mass range of Mh~4e10-1e11 Msun. The
most massive red UDG in our sample requires quenching at z~3 when its halo
reached Mh ~ 1e11 Msun. If it, instead, continues growing in the field, by z=0
its halo mass reaches > 5e11 Msun, comparable to the halo of an L* galaxy. If
our simulated dwarfs are not quenched, they evolve into bluer low-surface
brightness galaxies with mass-to-light ratios similar to observed field dwarfs.
While our simulation sample covers a limited range of formation histories and
halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy
type around Ms~1e8 Msun, both in the field and in clusters.Comment: 20 pages, 13 figures; match the MNRAS accepted versio
On the dust temperatures of high redshift galaxies
Dust temperature is an important property of the interstellar medium (ISM) of
galaxies. It is required when converting (sub)millimeter broadband flux to
total infrared luminosity (L_IR), and hence star formation rate, in high-z
galaxies. However, different definitions of dust temperatures have been used in
the literature, leading to different physical interpretations of how ISM
conditions change with, e.g., redshift and star formation rate. In this paper,
we analyse the dust temperatures of massive (M* > 10^10 Msun) z=2-6 galaxies
with the help of high-resolution cosmological simulations from the Feedback in
Realistic Environments (FIRE) project. At z~2, our simulations successfully
predict dust temperatures in good agreement with observations. We find that
dust temperatures based on the peak emission wavelength increase with redshift,
in line with the higher star formation activity at higher redshift, and are
strongly correlated with the specific star formation rate. In contrast, the
mass-weighted dust temperature does not strongly evolve with redshift over
z=2-6 at fixed IR luminosity but is tightly correlated with L_IR at fixed z.
The mass-weighted temperature is important for accurately estimating the total
dust mass. We also analyse an 'equivalent' dust temperature for converting
(sub)millimeter flux density to total IR luminosity, and provide a fitting
formula as a function of redshift and dust-to-metal ratio. We find that
galaxies of higher equivalent (or higher peak) dust temperature ('warmer dust')
do not necessarily have higher mass-weighted temperatures. A 'two-phase'
picture for interstellar dust can explain the different scaling relations of
the various dust temperatures.Comment: 26 pages, 15 figures, accepted for publication in MNRA
Seen and unseen: bursty star formation and its implications for observations of high-redshift galaxies with JWST
Both observations and simulations have shown strong evidence for highly
time-variable star formation in low-mass and/or high-redshift galaxies, which
has important observational implications because high-redshift galaxy samples
are rest-UV selected and therefore particularly sensitive to the recent star
formation. Using a suite of cosmological "zoom-in" simulations at from
the Feedback in Realistic Environments (FIRE) project, we examine the
implications of bursty star formation histories for observations of
high-redshift galaxies with JWST. We characterize how the galaxy observability
depends on the star formation history. We also investigate selection effects
due to bursty star formation on the physical properties measured, such as the
gas fraction, specific star formation rate, and metallicity. We find the
observability to be highly time-dependent for galaxies near the survey's
limiting flux due to the SFR variability: as the star formation rate
fluctuates, the same galaxy oscillates in and out of the observable sample. The
observable fraction at and to for a JWST/NIRCam survey reaching a limiting
magnitude of -, representative of
surveys such as JADES and CEERS. JWST-detectable galaxies near the survey limit
tend to have properties characteristic of galaxies in the bursty phase: on
average, they show approximately 2.5 times higher cold, dense gas fractions and
20 times higher specific star formation rates at a given stellar mass than
galaxies below the rest-UV detection threshold. Our study represents a first
step in quantifying selection effects and the associated biases due to bursty
star formation in studying high-redshift galaxy properties.Comment: 8 pages, 4 figures, resubmitted after incorporating referee's
comments; analysis expanded to include more galaxies and some quantitative
results correcte
The failure of stellar feedback, magnetic fields, conduction, and morphological quenching in maintaining red galaxies
The quenching "maintenance'" and related "cooling flow" problems are
important in galaxies from Milky Way mass through clusters. We investigate this
in halos with masses , using
non-cosmological high-resolution hydrodynamic simulations with the FIRE-2
(Feedback In Realistic Environments) stellar feedback model. We specifically
focus on physics present without AGN, and show that various proposed "non-AGN"
solution mechanisms in the literature, including Type Ia supernovae, shocked
AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fields,
Spitzer-Braginskii conduction, or "morphological quenching" do not halt or
substantially reduce cooling flows nor maintain "quenched" galaxies in this
mass range. We show that stellar feedback (including cosmic rays from SNe)
alters the balance of cold/warm gas and the rate at which the cooled gas within
the galaxy turns into stars, but not the net baryonic inflow. If anything,
outflowing metals and dense gas promote additional cooling. Conduction is
important only in the most massive halos, as expected, but even at reduces inflow only by a factor (owing to
saturation effects and anisotropic suppression). Changing the morphology of the
galaxies only slightly alters their Toomre- parameter, and has no effect on
cooling (as expected), so has essentially no effect on cooling flows or
maintaining quenching. This all supports the idea that additional physics,
e.g., AGN feedback, must be important in massive galaxies.Comment: 16 pages, 12 figure
Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes
We study the morphologies and sizes of galaxies at z>5 using high-resolution
cosmological zoom-in simulations from the Feedback In Realistic Environments
project. The galaxies show a variety of morphologies, from compact to clumpy to
irregular. The simulated galaxies have more extended morphologies and larger
sizes when measured using rest-frame optical B-band light than rest-frame UV
light; sizes measured from stellar mass surface density are even larger. The UV
morphologies are usually dominated by several small, bright young stellar
clumps that are not always associated with significant stellar mass. The B-band
light traces stellar mass better than the UV, but it can also be biased by the
bright clumps. At all redshifts, galaxy size correlates with stellar
mass/luminosity with large scatter. The half-light radii range from 0.01 to 0.2
arcsec (0.05-1 kpc physical) at fixed magnitude. At z>5, the size of galaxies
at fixed stellar mass/luminosity evolves as (1+z)^{-m}, with m~1-2. For
galaxies less massive than M_star~10^8 M_sun, the ratio of the half-mass radius
to the halo virial radius is ~10% and does not evolve significantly at z=5-10;
this ratio is typically 1-5% for more massive galaxies. A galaxy's "observed"
size decreases dramatically at shallower surface brightness limits. This effect
may account for the extremely small sizes of z>5 galaxies measured in the
Hubble Frontier Fields. We provide predictions for the cumulative light
distribution as a function of surface brightness for typical galaxies at z=6.Comment: 11 pages, 11 figures, resubmitted to MNRAS after revision for
referee's comment
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