The Cosmic Baryon and Metal Cycles Péroux, Céline; Howk, J. Christopher
Annual review of astronomy and astrophysics,
01/2020, Volume:
58, Issue:
1
Journal Article
Peer reviewed
Open access
Characterizing the relationship between stars, gas, and metals in galaxies is a critical component of understanding the cosmic baryon cycle. We compile contemporary censuses of the baryons in ...collapsed structures and their chemical makeup and dust content. We show the following:
The
mass density of the Universe is well determined to redshifts
and shows minor evolution with time. New observations of molecular hydrogen reveal its evolution mirrors that of the global star-formation rate density, implying a universal cosmic molecular gas depletion timescale. The low-redshift decline of the star-formation history is thus driven by the lack of molecular gas supply due to a drop in net accretion rate related to the decreased growth of dark matter halos.
The metal mass density in cold gas (
K) contains virtually all the metals produced by stars for
. At lower redshifts, the contributors to the total amount of metals are more diverse; at
, most of the observed metals are bound in stars. Overall, there is little evidence for a "missing metals problem" in modern censuses.
We characterize the dust content of neutral gas over cosmic time, finding the dust-to-gas and dust-to-metals ratios fall with decreasing metallicity. We calculate the cosmological dust mass density in the neutral gas up to
. There is good agreement between multiple tracers of the dust content of the Universe.
Without a source of new gas, our Galaxy would exhaust its supply of gas through the formation of stars. Ionized gas clouds observed at high velocity may be a reservoir of such gas, but their ...distances are key for placing them in the galactic halo and unraveling their role. We have used the Hubble Space Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the foreground of galactic stars. We show that iHVCs with 90 < lVLSRl £ 170 kilometers per second (where VLSR is the velocity in the local standard of rest frame) are within one galactic radius of the Sun and have enough mass to maintain star formation, whereas iHVCs with lVLSRl > 170 kilometers per second are at larger distances. These may be the next wave of infalling material.
We demonstrate the presence of an extended and massive circumgalactic medium (CGM) around Messier 31 using archival HST Cosmic Origins Spectrograph ultraviolet spectroscopy of 18 QSOs projected ...within two virial radii of M31 (R sub(vir) = 300 kpc). We detect absorption from Si III at -300 <, ~ v sub(LSR) <, ~ -150 km s super(-1) toward all three sightlines at R <, ~ 0.2R sub(vir), 3 of 4 sightlines at 0.8 <, ~ R/R sub(vir) <, ~ 1.1, and possibly 1 of 11 at 1.1 < R/R sub(vir) <, ~ 1.8. We present several arguments that the gas at these velocities observed in these directions originates from the M31 CGM rather than the Local Group or Milky Way CGM or Magellanic Stream. We show that the dwarf galaxies located in the CGM of M31 have very similar velocities over similar projected distances from M31. We find a non-trivial relationship only at these velocities between the column densities (N) of all the ions and R, whereby N decreases with increasing R. At R < 0.8R sub(vir), the covering fraction is close to unity for Si III and C IV (functionof sub(c) ~ 60%-97% at the 90% confidence level), but drops to functionof sub(c) <, ~ 10%-20% at R > ~ R sub(vir). We show that the M31 CGM gas is bound, multiphase, predominantly ionized, and is more highly ionized gas at larger R. We estimate using Si II, Si III, and Si IV, a CGM metal mass of > ~2 x 10 super(6) M sub(middot in circle) and gas mass of > ~3 x 10 super(9)(Z sub(middot in circle)/Z) M sub(middot in circle) within 0.2R sub(vir), and possibly a factor of ~10 larger within R sub(vir), implying substantial metal and gas masses in the CGM of M31.
We present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project. In contrast to most extant simulations of galaxy formation, which concentrate computational resources on ...galactic disks and spheroids with fluid and particle elements of fixed mass, the FOGGIE simulations focus on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies. Using the Enzo code and a new refinement scheme, FOGGIE reaches spatial resolutions of 381 comoving h−1 pc and resolves extremely low masses ( 1-100 ) out to 100 comoving h−1 kpc from the central halo. At these resolutions, cloud and filament-like structures giving rise to simulated absorption are smaller, and better resolved, than the same structures simulated with standard density-dependent refinement. Most of the simulated absorption arises in identifiable and well-resolved structures with masses 104 , well below the mass resolution of typical zoom simulations. However, integrated quantities such as mass surface density and ionic covering fractions change at only the 30% level as resolution is varied. These relatively small changes in projected quantities-even when the sizes and distribution of absorbing clouds change dramatically-indicate that commonly used observables provide only weak constraints on the physical structure of the underlying gas. Comparing the simulated absorption features to the KODIAQ (Keck Observatory Database of Ionized Absorption toward Quasars) survey of z ∼ 2-3.5 Lyman limit systems, we show that high-resolution FOGGIE runs better resolve the internal kinematic structure of detected absorption and better match the observed distribution of absorber properties. These results indicate that circumgalactic medium resolution is key in properly testing simulations of galaxy evolution with circumgalactic observations.
THE H i CONTENT OF THE UNIVERSE OVER THE PAST 10 GYR Neeleman, Marcel; Prochaska, J. Xavier; Ribaudo, Joseph ...
Astrophysical journal/The Astrophysical journal,
02/2016, Volume:
818, Issue:
2
Journal Article
Peer reviewed
Open access
ABSTRACT We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly absorbers (DLAs) at low redshift ( ). Our statistical ...sample includes 463 quasars with spectral coverage spanning a total redshift path or an absorption path . Within this survey path, we identify 4 DLAs defined as absorbers with H i column density cm−2, which implies an incidence per absorption length at a median survey path redshift of z = 0.623. While our estimate of is lower than earlier estimates at from H i 21 cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the frequency distribution function , but the observed distribution agrees with previous estimates at . Adopting the shape of , we infer an H i mass density at of . This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z H i 21 cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyr.
ABSTRACT
We model the kinematics of the high- and intermediate-velocity clouds (HVCs and IVCs) observed in absorption towards a sample of 55 Galactic halo stars with accurate distance measurements. ...We employ a simple model of a thick disc whose main free parameters are the gas azimuthal, radial, and vertical velocities (vϕ, vR, and vz), and apply it to the data by fully accounting for the distribution of the observed features in the distance–velocity space. We find that at least two separate components are required to reproduce the data. A scenario where the HVCs and the IVCs are treated as distinct populations provides only a partial description of the data, which suggests that a pure velocity-based separation may give a biased vision of the gas physics at the Milky Way’s disc–halo interface. Instead, the data are better described by a combination of an inflow component and an outflow component, both characterized by rotation with vϕ comparable to that of the disc and vz of $50\!-\!100\, {\rm km\, s}^{-1}$. Features associated with the inflow appear to be diffused across the sky, while those associated with the outflow are mostly confined within a bicone pointing towards (l = 220°, b = +40°) and (l = 40°, b = −40°). Our findings indicate that the lower ($|z| \lesssim 10\, {\rm kpc}$) Galactic halo is populated by a mixture of diffuse inflowing gas and collimated outflowing material, which are likely manifestations of a galaxy-wide gas cycle triggered by stellar feedback, that is, the galactic fountain.
Outflowing winds of multiphase plasma have been proposed to regulate the buildup of galaxies, but key aspects of these outflows have not been probed with observations. By using ultraviolet absorption ...spectroscopy, we show that "warm-hot" plasma at 10 5.5 kelvin contains 10 to 150 times more mass than the cold gas in a post-star burst galaxy wind. This wind extends to distances > 68 kiloparsecs, and at least some portion of it will escape. Moreover, the kinematical correlation of the cold and warm-hot phases indicates that the warm-hot plasma is related to the interaction of the cold matter with a hotter (unseen) phase at »10⁶ kelvin. Such multiphase winds can remove substantial masses and alter the evolution of post-star burst galaxies.
ABSTRACT
Intermediate- and high-velocity clouds (IVCs, HVCs) are a potential source of fuel for star formation in the Milky Way (MW), but their origins and fates depend sensitively on their ...distances. We search for IVCs and HVCs in HST high-resolution ultraviolet spectra of 55 halo stars at vertical heights $|z|\gtrsim \,1$ kpc. We show that IVCs (40 ≤ |$v$LSR| < 90 ${\rm km\, s}^{-1}$) have a high detection rate – the covering factor, fc – that is about constant (fc = 0.90 ± 0.04) from $z$ = 1.5 to 14 kpc, implying IVCs are essentially confined to |$z$| ≲ 1.5 kpc. For the HVCs (90 ≤ |$v$LSR| ≲ 170 ${\rm km\, s}^{-1}$), we find fc increases from fc ≃ 0.14 ± 0.10 at |$z$| ≲ 2–3 kpc to fc = 0.60 ± 0.15 at 6 ≲ |$z$| ≲ 14 kpc, the latter being similar to that found towards QSOs. In contrast, the covering factor of very high-velocity clouds (VHVCs; |$v$LSR| ≳ 170 ${\rm km\, s}^{-1}$) is $f_c \lt 0.04$ in the stellar sample compared to 20 per cent towards QSOs, implying these clouds must be at d ≳ 10–15 kpc (|$z$| ≳ 10 kpc). Gas clouds with |$v$LSR| > 40 ${\rm km\, s}^{-1}$ at |b| ≳ 15° have therefore |$v$LSR| decreasing with decreasing |$z$|. Our findings are consistent with a Galactic rain and/or fountain origin for these clouds. In the latter scenario, VHVCs may mostly serve as fuel for the MW halo. In view of their high covering factors and since all the IVCs and some HVCs are found in the thick disc, they appear good candidates as gas reservoirs to help sustain star formation in the MW.
Project AMIGA: The Circumgalactic Medium of Andromeda Lehner, Nicolas; Berek, Samantha C.; Howk, J. Christopher ...
Astrophysical journal/The Astrophysical journal,
09/2020, Volume:
900, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
Project AMIGA (Absorption Maps In the Gas of Andromeda) is a survey of the circumgalactic medium (CGM) of Andromeda (M31,
≃ 300 kpc) along 43 QSO sightlines at impact parameters 25 ≤
R
... ≤ 569 kpc (25 at
R
≲
). We use ultraviolet absorption measurements of Si
ii
, Si
iii
, Si
iv
, C
ii
, and C
iv
from the Hubble Space Telescope/Cosmic Origins Spectrograph and O
vi
from the Far Ultraviolet Spectroscopic Explorer to provide an unparalleled look at how the physical conditions and metals are distributed in the CGM of M31. We find that Si
iii
and O
vi
have a covering factor near unity for
R
≲ 1.2
and ≲1.9
, respectively, demonstrating that M31 has a very extended ∼10
4
–10
5.5
K ionized CGM. The metal and baryon masses of the 10
4
–10
5.5
K CGM gas within
are ≳10
8
and ≳4 × 10
10
(
Z
/0.3
Z
⊙
)
−1
M
⊙
, respectively. There is not much azimuthal variation in the column densities or kinematics, but there is with
R
. The CGM gas at
R
≲ 0.5
is more dynamic and has more complicated, multiphase structures than at larger radii, perhaps a result of more direct impact of galactic feedback in the inner regions of the CGM. Several absorbers are projected spatially and kinematically close to M31 dwarf satellites, but we show that those are unlikely to give rise to the observed absorption. Cosmological zoom simulations of ∼
L
* galaxies have O
vi
extending well beyond
as observed for M31 but do not reproduce well the radial column density profiles of the lower ions. However, some similar trends are also observed, such as the lower ions showing a larger dispersion in column density and stronger dependence on
R
than higher ions. Based on our findings, it is likely that the Milky Way has a ∼10
4
–10
5.5
K CGM as extended as for M31 and their CGM (especially the warm–hot gas probed by O
vi
) are overlapping.
Observed dust surface density across cosmic times Péroux, Céline; De Cia, Annalisa; Howk, J Christopher
Monthly Notices of the Royal Astronomical Society,
05/2023, Volume:
522, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
Our ability to interpret observations of galaxies and trace their stellar, gas, and dust content over cosmic time critically relies on our understanding of how the dust abundance and ...properties vary with environment. Here, we compute the dust surface density across cosmic times to put novel constraints on simulations of the build-up of dust. We provide observational estimates of the dust surface density consistently measured through depletion methods across a wide range of environments, going from the Milky Way up to z = 5.5 galaxies. These conservative measurements provide complementary estimates to extinction-based observations. In addition, we introduce the dust surface density distribution function – in analogy with the cold gas column density distribution functions. We fit a power law of the form log f(ΣDust) = −1.92 × log ΣDust − 3.65, which proves slightly steeper than that for neutral gas and metal absorbers. This observed relation, which can be computed by simulations predicting resolved dust mass functions through 2D projection, provides new constraints on modern dust models.
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