The Mass Inflow and Outflow Rates of the Milky Way Fox, Andrew J.; Richter, Philipp; Ashley, Trisha ...
Astrophysical journal/The Astrophysical journal,
10/2019, Volume:
884, Issue:
1
Journal Article
Peer reviewed
Open access
We present new calculations of the mass inflow and outflow rates around the Milky Way (MW), derived from a catalog of ultraviolet metal-line high-velocity clouds (HVCs). These calculations are ...conducted by transforming the HVC velocities into the Galactic standard of rest (GSR) reference frame, identifying inflowing (vGSR < 0 km s−1) and outflowing (vGSR > 0 km s−1) populations, and using observational constraints on the distance, metallicity, dust content, covering fractions, and total silicon column density of each population. After removing HVCs associated with the Magellanic Stream and the Fermi Bubbles, we find inflow and outflow rates in cool (T ∼ 104 K) ionized gas of dMin/dt (0.53 0.23)(d/12 kpc)(Z/0.2Z )−1 M yr−1 and dMout/dt (0.16 0.07)(d/12 kpc)(Z/0.5Z )−1 M yr−1. The apparent excess of inflowing over outflowing gas suggests that the MW is currently in an inflow-dominated phase, but the presence of substantial mass flux in both directions supports a Galactic fountain model, in which gas is constantly recycled between the disk and the halo. We also find that the metal flux in both directions (in and out) is indistinguishable. By comparing the outflow rate to the Galactic star formation rate, we present the first estimate of the mass loading factor ( HVC) of the disk-wide MW wind, finding HVC (0.10 0.06)(d/12 kpc)(Z/0.5Z )−1. Including the contributions from low- and intermediate-velocity clouds and from hot gas would increase these inflow and outflow estimates.
We present the results from our COS circumgalactic medium (CGM) compendium (CCC), a survey of the CGM at z 1 using H i-selected absorbers with 15 < < 19. We focus here on 82 partial Lyman limit ...systems (pLLSs, 16.2 ≤ < 17.2) and 29 LLSs (17.2 ≤ < 19). Using Bayesian techniques and Markov Chain Monte Carlo sampling of a grid of photoionization models, we derive the posterior probability distribution functions (PDFs) for the metallicity of each absorber in CCC. We show that the combined pLLS metallicity PDF at z 1 has two main peaks at −1.7 and −0.4, with a strong dip at −1. The metallicity PDF of the LLSs might be more complicated than a unimodal or bimodal distribution. The pLLSs and LLSs probe a similar range of metallicities −3 +0.4, but the fraction of very metal-poor absorbers with −1.4 is much larger for the pLLSs than the LLSs. In contrast, absorbers with ≥ 19 have mostly −1 0 at z 1. The metal-enriched gas probed by pLLSs and LLSs confirms that galaxies that have been enriching their CGM over billions of years. Surprisingly, despite this enrichment, there is also abundant metal-poor CGM gas (41%-59% of the pLLSs have −1.4), representing a reservoir of near-pristine gas around z 1 galaxies. We compare our empirical results to recent cosmological zoom simulations, finding some discrepancies, including an overabundance of metal-enriched CGM gas in simulations.
We characterize the metallicities and physical properties of cool, photoionized gas in a sample of 152 z 1 strong Ly forest systems (SLFSs, absorbers with 15 < log NH i < 16.2). The sample is drawn ...from our Cosmic Origins Spectrograph (COS) circumgalactic medium compendium (CCC), an ultraviolet survey of H i-selected circumgalactic gas around z 1 galaxies that targets 261 absorbers with 15 < log NH i < 19. We show that the metallicity probability distribution function of the SLFSs at z 1 is unimodal, skewed to low metallicities with a mean and median of X/H = −1.47 and −1.18 dex. Very metal-poor gas with X/H < −1.4 represents about half of the population of absorbers with 15 < log NH i 18, while it is rare at higher NH i. Thus, there are important reservoirs of primitive (though not pristine) diffuse ionized gas around z 1 galaxies. The photoionized gas around z 1 galaxies is highly inhomogeneous based on the wide range of metallicities observed (−3 X/H +0.4) and the fact that there are large metallicity variations (factors of 2 to 25) for most of the closely spaced absorbers (Δv 300 km s−1) along the same sightlines. These absorbers show a complex evolution with redshift and H i column density, and we identify subtle cosmic evolution effects that affect the interpretation of metallicity distributions and comparison with other absorber samples. We discuss the physical conditions and cosmic baryon and metal budgets of the CCC absorbers. Finally, we compare the CCC results to recent cosmological zoom simulations and explore the origins of the 15 < log NH i < 19 absorbers within the Evolution and Assembly of GaLaxies and their Environments (EAGLE) high-resolution simulations.
Observing the circumgalactic medium (CGM) in emission provides 3D maps of the spatial and kinematic extent of the gas that fuels galaxies and receives their feedback. We present mock emission-line ...maps of highly resolved CGM gas from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project and link these maps back to physical and spatial properties of the gas. In particular, we examine the ionization source leading to most O vi emission and how resolution affects the physical properties of the gas generating the emission. Finally, when increasing the spatial resolution alone, the total luminosity of the line emission increases by an order of magnitude for some lines considered. Current integral field unit instruments like Keck Cosmic Web Imager and Multi Unit Spectroscopic Explorer should be able to detect the brightest knots and filaments of such emission, and use this to infer the bulk kinematics of the CGM gas with respect to the galaxy. We conclude that the spatial resolution of simulated CGM gas can significantly influence the distribution of gas temperatures, densities, and metallicities that contribute to a given observable region. Greater spatial resolution than has been typically included in cosmological simulations to date is needed to properly interpret observations in terms of the underlying gas structure driving emission.
ABSTRACT
We present an analysis of the metallicity distribution of the dense circumgalactic medium (CGM) of galaxies at 0.1 ≲
z
≲ 1.1 as probed by partial Lyman limit systems (pLLSs, 16.1 < log
... < 17.2) and LLSs (17.2 ≤ log
< 17.7 in our sample). The new H
i
-selected sample, drawn from our
Hubble Space Telescope
COS G140L snapshot survey of 61 QSOs, has 20 pLLSs and 10 LLSs. Combined with our previous survey, we have a total of 44 pLLSs and 11 LLSs. We find that the metallicity distribution of the pLLSs is bimodal at
z
≲ 1, with a minimum at X/H = −1. The low-metallicity peak comprises (57 ± 8)% of the pLLSs and is centered at X/H ≃ −1.87(1.3% solar metallicity), while the high-metallicity peak is centered at X/H ≃ −0.32 (48% solar metallicity). Although the sample of LLSs is still small, there is some evidence that the metallicity distributions of the LLSs and pLLSs are different, with a far lower fraction of very metal-poor (X/H < −1.4) LLSs than pLLSs. The fraction of LLSs with X/H < −1 is similar to that found in pLLSs (∼56%). However, higher H
i
column density absorbers (log
> 19.0) show a much lower fraction of metal-poor gas; therefore, the metallicity distribution of gas in and around galaxies depends sensitively on
N
H
i
at
z
≲ 1. We interpret the high-metallicity (X/H ≥ −1) pLLSs and LLSs as arising in outflows, recycling winds, and tidally stripped gas around galaxies. The low-metallicity pLLSs and LLSs imply that the CGM of
z
≲ 1 galaxies hosts a substantial mass of cool, dense, low-metallicity gas that may ultimately accrete onto the galaxies.
Abstract
We describe the survey for galaxies in the fields surrounding nine sightlines to far-UV bright,
z
∼ 1 quasars that define the COS Absorption Survey of Baryon Harbors (CASBaH) program. The ...photometry and spectroscopy that comprise the data set come from a mixture of public surveys (SDSS, DECaLS) and our dedicated efforts on private facilities (Keck, MMT, LBT). We report the redshifts and stellar masses for 5902 galaxies within ≈10 comoving-Mpc of the sightlines with a median of
and
. This data set, publicly available as the CASBaH
specDB
, forms the basis of several recent and ongoing CASBaH analyses. Here, we perform a clustering analysis of the galaxy sample with itself (auto-correlation) and against the set of O
vi
absorption systems (cross-correlation) discovered in the CASBaH quasar spectra with column densities
. For each, we describe the measured clustering signal with a power-law correlation function
and find that
for the auto-correlation and
for galaxy–O
vi
cross-correlation. We further estimate a bias factor of
from the galaxy–galaxy auto-correlation, indicating the galaxies are hosted by halos with mass
. Finally, we estimate an O
vi
–galaxy bias factor
from the cross-correlation which is consistent with O
vi
absorbers being hosted by dark matter halos with typical mass
. Future works with upcoming data sets (e.g., CGM
2
) will improve upon these results and will assess whether any of the detected O
vi
arises in the intergalactic medium.
Abstract
This study addresses how the incidence rate of strong O
vi
absorbers in a galaxy’s circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in ...the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O
vi
absorption within 400 projected kpc and 300 km s
−1
of 52 galaxies with
M
*
∼ 3 × 10
10
M
⊙
. The galaxies have redshifts 0.12 <
z
< 0.6, stellar masses 10
10.1
M
⊙
<
M
*
< 10
10.9
M
⊙
, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O
vi
absorption (
N
O
VI
≥ 10
14.3
cm
−2
) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O
vi
covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3
σ
-equivalent statistical significance. On average, the CGM of star-forming galaxies with
M
*
∼ 3 × 10
10
M
⊙
contains more O
vi
than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass.
Abstract
We combine data sets from the CGM
2
and CASBaH surveys to model a transition point,
R
cross
, between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data ...consist of 7244 galaxies at
z
< 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01–20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H
i
Ly
α
. Our best-fitting model is a two-component model that combines a 3D absorber–galaxy cross-correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of
R
cross
as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 10
8
≤
M
⋆
/
M
⊙
≤ 10
10.5
, we find that
R
cross
(
M
⋆
) ≈ 2.0 ± 0.6
R
vir
. Additionally, we find excellent agreement between
R
cross
(
M
⋆
) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at
z
< 0.5 that distribute
T
≈ 10
4
K gas to distances beyond the virial radius.
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.
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