321 research outputs found
SIGAME simulations of the [CII], [OI] and [OIII] line emission from star forming galaxies at z ~ 6
Of the almost 40 star forming galaxies at z>~5 (not counting QSOs) observed
in [CII] to date, nearly half are either very faint in [CII], or not detected
at all, and fall well below expectations based on locally derived relations
between star formation rate (SFR) and [CII] luminosity. Combining cosmological
zoom simulations of galaxies with SIGAME (SImulator of GAlaxy
Millimeter/submillimeter Emission) we have modeled the multi-phased
interstellar medium (ISM) and its emission in [CII], [OI] and [OIII], from 30
main sequence galaxies at z~6 with star formation rates ~3-23Msun/yr, stellar
masses ~(0.7-8)x10^9Msun, and metallicities ~(0.1-0.4)xZsun. The simulations
are able to reproduce the aforementioned [CII]-faintness at z>5, match two of
the three existing z>~5 detections of [OIII], and are furthermore roughly
consistent with the [OI] and [OIII] luminosity relations with SFR observed for
local starburst galaxies. We find that the [CII] emission is dominated by the
diffuse ionized gas phase and molecular clouds, which on average contribute
~66% and ~27%, respectively. The molecular gas, which constitutes only ~10% of
the total gas mass is thus a more efficient emitter of [CII] than the ionized
gas making up ~85% of the total gas mass. A principal component analysis shows
that the [CII] luminosity correlates with the star formation activity as well
as average metallicity. The low metallicities of our simulations together with
their low molecular gas mass fractions can account for their [CII]-faintness,
and we suggest these factors may also be responsible for the [CII]-faint normal
galaxies observed at these early epochs.Comment: 24 pages, 14 figures. Accepted for publication in the Astrophysical
Journa
The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. II. Modelling Anisotropies with Cosmological Hydrodynamic Simulations
The isotropy of the Lyman-alpha forest in real-space uniquely provides a
measurement of cosmic geometry at z > 2. The angular diameter distance for
which the correlation function along the line of sight and in the transverse
direction agree corresponds to the correct cosmological model. However, the
Lyman-alpha forest is observed in redshift-space where distortions due to
Hubble expansion, bulk flows, and thermal broadening introduce anisotropy.
Similarly, a spectrograph's line spread function affects the autocorrelation
and cross-correlation differently. In this the second paper of a series on
using the Lyman-alpha forest observed in pairs of QSOs for a new application of
the Alcock-Paczynski (AP) test, these anisotropies and related sources of
potential systematic error are investigated with cosmological hydrodynamic
simulations. Three prescriptions for galactic outflow were compared and found
to have only a marginal effect on the Lyman-alpha flux correlation (which
changed by at most 7% with use of the currently favored variable-momentum wind
model vs. no winds at all). An approximate solution for obtaining the zero-lag
cross-correlation corresponding to arbitrary spectral resolution directly from
the zero-lag cross-correlation computed at full-resolution (good to within 2%
at the scales of interest) is presented. Uncertainty in the observationally
determined mean flux decrement of the Lyman-alpha forest was found to be the
dominant source of systematic error; however, this is reduced significantly
when considering correlation ratios. We describe a simple scheme for
implementing our results, while mitigating systematic errors, in the context of
a future application of the AP test.Comment: 20 page
ASymba: HI global profile asymmetries in the Simba simulation
Asymmetry in the spatially integrated, 1D HI global profiles of galaxies can
inform us on both internal (e.g. outflows) and external (e.g. mergers, tidal
interactions, ram pressure stripping) processes that shape galaxy evolution.
Understanding which of these primarily drive HI profile asymmetry is of
particular interest. In the lead-up to SKA pathfinder and SKA HI emission
surveys, hydrodynamical simulations have proved to be a useful resource for
such studies. Here we present the methodology behind, as well as first results,
of ASymba: Asymmetries in HI of Simba galaxies, the first time this simulation
suite has been used for this type of study. We generate mock observations of
the HI content of these galaxies and calculate the profile asymmetries using
three different methods. We find that has the strongest
correlation with all asymmetry measures, with weaker correlations also found
with the number of mergers a galaxy has undergone, and gas and galaxy rotation.
We also find good agreement with the xGASS sample, in that galaxies with highly
asymmetric profiles tend to have lower HI gas fractions than galaxies with
symmetric profiles, and additionally find the same holds in sSFR parameter
space. For low HI mass galaxies, it is difficult to distinguish between
asymmetric and symmetric galaxies, but this becomes achievable in the high HI
mass population. These results showcase the potential of ASymba and provide the
groundwork for further studies, including comparison to upcoming large HI
emission surveys.Comment: 17 pages, 10 figures, 2 tables. Accepted in MNRA
Cosmological Limits on the Neutrino Mass from the Lya Forest
The Lya forest in quasar spectra probes scales where massive neutrinos can
strongly suppress the growth of mass fluctuations. Using hydrodynamic
simulations with massive neutrinos, we successfully test techniques developed
to measure the mass power spectrum from the forest. A recent observational
measurement in conjunction with a conservative implementation of other
cosmological constraints places upper limits on the neutrino mass: m_nu < 5.5
eV for all values of Omega_m, and m_nu < 2.4 (Omega_m/0.17 -1) eV, if 0.2 <
Omega_m <0.5 as currently observationally favored (both 95 % C.L.).Comment: 4 pages, 2 ps figures, REVTex, submitted to Phys. Rev. Let
Lyman-alpha Forest Constraints on the Mass of Warm Dark Matter and the Shape of the Linear Power Spectrum
High resolution N-body simulations of cold dark matter (CDM) models predict
that galaxies and clusters have cuspy halos with excessive substructure.
Observations reveal smooth halos with central density cores. One possible
resolution of this conflict is that the dark matter is warm (WDM); this will
suppress the power spectrum on small scales. The Lyman-alpha forest is a
powerful probe of the linear power spectrum on these scales. We use
collisionless N-body simulations to follow the evolution of structure in WDM
models, and analyze artificial Lyman-alpha forest spectra extracted from them.
By requiring that there is enough small-scale power in the linear power
spectrum to reproduce the observed properties of the Lyman-alpha forest in
quasar spectra, we derive a lower limit to the mass of the WDM particle of 750
eV. This limit is robust to reasonable uncertainties in our assumption about
the temperature of the mean density gas (T0) at z=3. We argue that any model
that suppresses the CDM linear theory power spectrum more severely than a 750
eV WDM particle cannot produce the Lyman-alpha forest.Comment: 13 pages including 4 color Figures and 1 Table, submitted to ApJ
Letter
The halo mass function conditioned on density from the Millennium Simulation: insights into missing baryons and galaxy mass functions
The baryon content of high-density regions in the universe is relevant to two
critical unanswered questions: the workings of nurture effects on galaxies and
the whereabouts of the missing baryons. In this paper, we analyze the
distribution of dark matter and semianalytical galaxies in the Millennium
Simulation to investigate these problems. Applying the same density field
reconstruction schemes as used for the overall matter distribution to the
matter locked in halos we study the mass contribution of halos to the total
mass budget at various background field densities, i.e., the conditional halo
mass function. In this context, we present a simple fitting formula for the
cumulative mass function accurate to ~ 5% for halo masses between 10^{10} and
10^{15}Msol/h. We find that in dense environments the halo mass function
becomes top heavy and present corresponding fitting formulae for different
redshifts. We demonstrate that the major fraction of matter in high-density
fields is associated with galaxy groups. Since current X-ray surveys are able
to nearly recover the universal baryon fraction within groups, our results
indicate that the major part of the so-far undetected warm-hot intergalactic
medium resides in low-density regions at low temperatures. Similarly, we show
that the differences in galaxy mass functions with environment seen in observed
and simulated data stem predominantly from differences in the mass distribution
of halos. In particular, the hump in the galaxy mass function is associated
with the central group galaxies, and the bimodality observed in the galaxy mass
function is therefore interpreted as that of central galaxies versus
satellites.Comment: aligned with version published in Ap
Do Hot Haloes Around Galaxies Contain the Missing Baryons?
Galaxies are missing most of their baryons, and many models predict these
baryons lie in a hot halo around galaxies. We establish observationally
motivated constraints on the mass and radii of these haloes using a variety of
independent arguments. First, the observed dispersion measure of pulsars in the
Large Magellanic Cloud allows us to constrain the hot halo around the Milky
Way: if it obeys the standard NFW profile, it must contain less than 4-5% of
the missing baryons from the Galaxy. This is similar to other upper limits on
the Galactic hot halo, such as the soft X-ray background and the pressure
around high velocity clouds. Second, we note that the X-ray surface brightness
of hot haloes with NFW profiles around large isolated galaxies is high enough
that such emission should be observed, unless their haloes contain less than
10-25% of their missing baryons. Third, we place constraints on the column
density of hot haloes using nondetections of OVII absorption along AGN
sightlines: in general they must contain less than 70% of the missing baryons
or extend to no more than 40 kpc. Flattening the density profile of galactic
hot haloes weakens the surface brightness constraint so that a typical L
galaxy may hold half its missing baryons in its halo, but the OVII constraint
remains unchanged, and around the Milky Way a flattened profile may only hold
of the missing baryons from the Galaxy (). We also show that AGN and supernovae at low to moderate redshift -
the theoretical sources of winds responsible for driving out the missing
baryons - do not produce the expected correlations with the baryonic
Tully-Fisher relationship and so are insufficient to explain the missing
baryons from galaxies. We conclude that most of missing baryons from galaxies
do not lie in hot haloes around the galaxies, and that the missing baryons
never fell into the potential wells of protogalaxies in the first place. They
may have been expelled from the galaxies as part of the process of galaxy
formation.Comment: accepted for publication in the Astrophysical Journa
The COS-Dwarfs Survey: The Carbon Reservoir Around sub-L* Galaxies
We report new observations of circumgalactic gas from the COS-Dwarfs survey,
a systematic investigation of the gaseous halos around 43 low-mass z 0.1
galaxies using background QSOs observed with the Cosmic Origins Spectrograph.
From the projected 1D and 2D distribution of C IV absorption, we find that C IV
absorption is detected out to ~ 0.5 R of the host galaxies. The C IV
absorption strength falls off radially as a power law and beyond 0.5 R,
no C IV absorption is detected above our sensitivity limit of ~ 50-100 m.
We find a tentative correlation between detected C IV absorption strength and
star formation, paralleling the strong correlation seen in highly ionized
oxygen for L~L* galaxies by the COS-Halos survey. The data imply a large carbon
reservoir in the CGM of these galaxies, corresponding to a minimum carbon mass
of 1.2 out to ~ 110 kpc. This mass is
comparable to the carbon mass in the ISM and more than the carbon mass
currently in stars of these galaxies. The C IV absorption seen around these
sub-L* galaxies can account for almost two-thirds of all > 100 m C IV
absorption detected at low z. Comparing the C IV covering fraction with
hydrodynamical simulations, we find that an energy-driven wind model is
consistent with the observations whereas a wind model of constant velocity
fails to reproduce the CGM or the galaxy properties.Comment: 18 Pages, 11 Figures, ApJ 796 13
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