330 research outputs found
Evolution of the atomic and molecular gas content of galaxies in dark matter haloes
We present a semi-empirical model to infer the atomic and molecular hydrogen
content of galaxies as a function of halo mass and time. Our model combines the
SFR-halo mass-redshift relation (constrained by galaxy abundances) with
inverted SFR-surface density relations to infer galaxy H I and H2 masses. We
present gas scaling relations, gas fractions, and mass functions from z = 0 to
z = 3 and the gas properties of galaxies as a function of their host halo
masses. Predictions of our work include: 1) there is a ~ 0.2 dex decrease in
the H I mass of galaxies as a function of their stellar mass since z = 1.5,
whereas the H2 mass of galaxies decreases by > 1 dex over the same period. 2)
galaxy cold gas fractions and H2 fractions decrease with increasing stellar
mass and time. Galaxies with M* > 10^10 Msun are dominated by their stellar
content at z < 1, whereas less-massive galaxies only reach these gas fractions
at z = 0. We find the strongest evolution in relative gas content at z < 1.5.
3) the SFR to gas mass ratio decreases by an order of magnitude from z = 3 to z
= 0. This is consistent with lower H2 fractions; these lower fractions in
combination with smaller gas reservoirs correspond to decreased present-day
galaxy SFRs. 4) an H2-based star- formation relation can simultaneously fuel
the evolution of the cosmic star-formation and reproduce the observed weak
evolution in the cosmic HI density. 5) galaxies residing in haloes with masses
near 10^12 Msun are most efficient at obtaining large gas reservoirs and
forming H2 at all redshifts. These two effects lie at the origin of the high
star-formation efficiencies in haloes with the same mass.Comment: accepted for publication in MNRAS, 20 pages, 16 figures (+ 1 figure
in appendix), data files are accessible through
http://www.eso.org/~gpopping/Gergo_Poppings_Homepage/Data.htm
The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of
intergalactic gas, but its mass, heavy element enrichment, and relation to
galaxy properties are poorly constrained by observations. In a survey of the
outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the
Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of
ionized oxygen surrounding star-forming galaxies, but we find much less ionized
oxygen around galaxies with little or no star formation. This ionized CGM
contains a substantial mass of heavy elements and gas, perhaps far exceeding
the reservoirs of gas in the galaxies themselves. It is a basic component of
nearly all star-forming galaxies that is removed or transformed during the
quenching of star formation and the transition to passive evolution.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with the Cosmic Origins Spectrograph on HST, to be published in
Science, together with related papers by Tripp et al. and Lehner & Howk, in
the November 18, 2011 edition. This version has not undergone final
copyediting. Please see Science online for the final printed versio
The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution
We investigate the thermal history of the intergalactic medium (IGM) in the
redshift interval z=1.7--3.2 by studying the small-scale fluctuations in the
Lyman alpha forest transmitted flux. We apply a wavelet filtering technique to
eighteen high resolution quasar spectra obtained with the Ultraviolet and
Visual Echelle Spectrograph (UVES), and compare these data to synthetic spectra
drawn from a suite of hydrodynamical simulations in which the IGM thermal state
and cosmological parameters are varied. From the wavelet analysis we obtain
estimates of the IGM thermal state that are in good agreement with other
recent, independent wavelet-based measurements. We also perform a reanalysis of
the same data set using the Lyman alpha forest flux probability distribution
function (PDF), which has previously been used to measure the IGM
temperature-density relation. This provides an important consistency test for
measurements of the IGM thermal state, as it enables a direct comparison of the
constraints obtained using these two different methodologies. We find the
constraints obtained from wavelets and the flux PDF are formally consistent
with each other, although in agreement with previous studies, the flux PDF
constraints favour an isothermal or inverted IGM temperature-density relation.
We also perform a joint analysis by combining our wavelet and flux PDF
measurements, constraining the IGM thermal state at z=2.1 to have a temperature
at mean density of T0/[10^3 K]=17.3 +/- 1.9 and a power-law temperature-density
relation exponent gamma=1.1 +/- 0.1 (1 sigma). Our results are consistent with
previous observations that indicate there may be additional sources of heating
in the IGM at z<4.Comment: 15 pages, 14 figures, matches version accepted for publication on
MNRA
The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
We analyze the physical conditions of the cool, photoionized (T
K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density
measurements for 44 gaseous halos within 160 kpc of galaxies at . These data are well described by simple photoionization models, with
the gas highly ionized (n/n) by the
extragalactic ultraviolet background (EUVB). Scaling by estimates for the
virial radius, R, we show that the ionization state (tracked by the
dimensionless ionization parameter, U) increases with distance from the host
galaxy. The ionization parameters imply a decreasing volume density profile
n = (10)(R/R. Our derived
gas volume densities are several orders of magnitude lower than predictions
from standard two-phase models with a cool medium in pressure equilibrium with
a hot, coronal medium expected in virialized halos at this mass scale. Applying
the ionization corrections to the HI column densities, we estimate a lower
limit to the cool gas mass M
M for the volume within R R. Allowing for an
additional warm-hot, OVI-traced phase, the CGM accounts for at least half of
the baryons purported to be missing from dark matter halos at the 10
M scale.Comment: 19 pages, 12 Figures, and a 37-page Appendix with 36 additional
figures. Accepted to ApJ June 21 201
- …