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.
ABSTRACT We report new observations from a systematic, spectroscopic, ultraviolet absorption-line survey that maps the spatial and kinematic properties of the high velocity gas in the Galactic Center ...(GC) region. We examine the hypothesis that this gas traces the biconical nuclear outflow. We use an ultraviolet spectra of 47 background QSOs and halo stars projected inside and outside the northern Fermi Bubble from the Hubble Space Telescope to study the incidence of high velocity absorption around it. We use five lines of sight inside the northern Fermi Bubble to constrain the velocity and column densities of outflowing gas traced by O i, Al ii, C ii, C iv, Si ii, Si iii, Si iv, and other species. We find that all five lines of sight inside the northern Fermi Bubble exhibit blueshifted high velocity absorption components, whereas only 9 out of the 42 lines of sight outside the northern Fermi Bubble exhibit blueshifted high velocity absorption components. The observed outflow velocity profile decreases with Galactic latitude and radial distance (R) from the GC. The observed blueshifted velocities change from at R 2.3 kpc to at R 6.5 kpc. We derive the metallicity of the entrained gas along the 1H1613-097 sightline, one that passes through the center of the northern Fermi Bubble, finding O/H −0.54 0.15. A simple kinematic model, tuned to match the observed absorption component velocities along the five lines of sight inside the Bubble, constrains the outflow velocities to 1000-1300 , and the age of the outflow to be ∼6-9 Myr. We estimate a minimum mass outflow rate for the nuclear outflow to be . Combining the age and mass outflow rates, we determine a minimum mass of total UV-absorbing cool gas entrained in the Fermi Bubbles to be .
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.
Abstract
We characterize the chemical and physical conditions in an outflowing high-velocity cloud (HVC) in the inner Galaxy. We report a supersolar metallicity of O/H = +0.36 ± 0.12 for the HVC at
v
...LSR
= 125.6 km s
−1
toward the star HD 156359 (
l
= 328.°7,
b
= −14.°5,
d
= 9 kpc,
z
= −2.3 kpc). Using archival observations from the Far-Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope Imaging Spectrograph, and the European Southern Observatory Fiber-fed Extended Range Optical Spectrograph we measure high-velocity absorption in H
i
, O
i
, C
ii
, N
ii
, Si
ii
, Ca
ii
, Si
iii
, Fe
iii
, C
iv
, Si
iv
, N
v
, and O
vi
. We measure a low H
i
column density of log
N
(H
i
) = 15.54 ± 0.05 in the HVC from multiple unsaturated H
i
Lyman series lines in the FUSE data. We determine a low dust depletion level in the HVC from the relative strength of silicon, iron, and calcium absorption relative to oxygen, with Si/O = −0.33 ± 0.14, Fe/O = −0.30 ± 0.20, and Ca/O = −0.56 ± 0.16. Analysis of the high-ion absorption using collisional ionization models indicates that the hot plasma is multiphase, with the C
iv
and Si
iv
tracing 10
4.9
K gas and N
v
and O
vi
tracing 10
5.4
K gas. The cloud’s metallicity, dust content, kinematics, and close proximity to the disk are all consistent with a Galactic wind origin. As the HD 156359 line of sight probes the inner Galaxy, the HVC appears to be a young cloud caught in the act of being entrained in a multiphase Galactic outflow and driven out into the halo.
Abstract
Using new ultraviolet (UV) spectra of five background quasars from the Cosmic Origins Spectrograph on the Hubble Space Telescope, we analyze the low-latitude (
) regions of the Fermi ...Bubbles, the giant gamma-ray-emitting lobes at the Galactic Center. We combine these data with previous UV and atomic hydrogen (H
i
) data sets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the Fermi Bubbles. We find that the number of UV absorption components per sight line decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble H
i
clouds are accelerated up to
b
∼ 7°, whereas when we model the UV Fermi Bubbles clouds’ deprojected flow velocities, we find that they are flat or even accelerating with distance from the Galactic center. This trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the Fermi Bubbles or has an acceleration phase followed by a coasting phase. Finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding ∼30°, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray-defined Fermi Bubbles. These anomalous-velocity clouds are likely in front of the Fermi Bubbles and could be remnants from past nuclear outflows. Overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies.
Abstract
We present results of a study comparing the relative velocity of Ly
α
absorbers to the rotation velocity of nearby galaxy disks in the local universe (
z
≤ 0.03). We have obtained rotation ...curves via long-slit spectroscopy of eight galaxies with the Southern African Large Telescope, and combine this data set with an additional 16 galaxies with data from the literature. Each galaxy appears within 3
R
vir
of a QSO sightline with archival Cosmic Origin Spectrograph spectra. We study the velocity orientation of absorbers with respect to nearby galaxy’s rotation, and compare with results from both the Steidel et al. monolithic halo model and a new cylindrical Navarro–Frenk–White galaxy halo model to interpret these data in the context of probing 3D galaxy halos via 1D QSO absorption-line spectroscopy. Relative to these models, we find that up to 59% ± 5% of Ly
α
absorbers have velocities consistent with corotation. We find the Ly
α
corotation fraction to decrease with galaxy luminosity (
L
*) and impact parameter in a model-independent fashion. We report that both anti-rotating absorbers and those found near luminous galaxies (
L
≳ 0.5
L
*) mostly have low Doppler
b
-parameters (
b
≲ 50 km s
−1
). Absorbers consistent with corotation show a wide range of Doppler
b
-parameters. Finally, we find a strong anticorrelation between corotation fraction and galaxy inclination, which is at odds with recent metal-line kinematic studies and suggests the kinematic and geometric distribution of the circumgalactic medium is complex and multiphase.
In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that ...pass through or within 30degrees of the 21 cm emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross-section of the Magellanic System is approximately 11,000 deg super(2), or around one-quarter of the entire sky. Using observations of the Si III/Si II ratio together with Cloudy photoionization modeling, we calculate the total gas mass (atomic plus ionized) of the Magellanic System to be approximately 2.0 x 10 super(9) M sub(middot in circle) (d/55 kpc) super(2), with the ionized gas contributing around three times as much mass as the atomic gas. This is larger than the current-day interstellar HI mass of both Magellanic Clouds combined, indicating that they have lost most of their initial gas mass.
Simulations of the formation of large-scale structures predict that dark matter, low density highly ionized gas, and galaxies form 10 to 40 Mpc scale filaments. These structures are easily recognized ...in the distribution of galaxies. Here we use Ly alpha absorption lines to study the gas in 30 x 6 Mpc filament at cz ~ 3500km s super(-1), defined using a new catalog of nearby (cz < 10,000 km s super(-1)) galaxies, which is complete down to a luminosity of about 0.05 Llow * for the region of space analyzed here. Using Hubble Space Telescope spectra of 24 active galactic nuclei, we sample the gas in this filament. All of our sightlines pass outside the virial radius of any known filament galaxy. Within 500 kpc of the filament axis the detection rate is ~80%, but no detections are seen more than 2.1 Mpc from the filament axis. The width of the Ly alpha lines correlates with filament impact parameter and the four BLAs in our sample occur within 400 kpc of the filament axis, indicating increased temperature and/or turbulence. Comparing to simulations, we find that the recent Haardt & Madau extragalactic ionizing background predicts a factor of 3-5 too few ionizing photons. Using a more intense radiation field matches the hydrogen density profile within 2.1 Mpc of the filament axis, but the simulations still overpredict the detection rate between 2.1 and 5 Mpc from the axis. The baryonic mass inside filament galaxies is 1.4 x 10 super(13) M sub(middot in circle), while the mass of filament gas outside galaxy halos is found to be 5.2 x 10 super(13) M sub(middot in circle).
Giant lobes of plasma extend approximate55degrees above and below the Galactic center, glowing in emission from gamma rays (the Fermi Bubbles) to microwaves and polarized radio waves. We use ...ultraviolet absorption-line spectra from the Hubble Space Telescope to constrain the velocity of the outflowing gas within these regions, targeting the quasar PDS 456 (scriptl b = 10degrees.4, +11degrees.2). This sightline passes through a clear biconical structure seen in hard X-ray and gamma-ray emission near the base of the northern Fermi Bubble. We report two high-velocity metal absorption components, at upsilon sub(LSR) = -235 and +250 km s super(-1), which cannot be explained by co-rotating gas in the Galactic disk or halo. Their velocities are suggestive of an origin on the front and back side of an expanding biconical outflow emanating from the Galactic center. We develop simple kinematic biconical outflow models that can explain the observed profiles with an outflow velocity of > ~900 km s super(-1) and a full opening angle of approximate110degrees (matching the X-ray bicone). This indicates Galactic center activity over the last approximate2.5-4.0 Myr, in line with age estimates of the Fermi Bubbles. The observations illustrate the use of UV spectroscopy to probe the properties of swept-up gas venting into the Fermi Bubbles.
Abstract
High-velocity clouds (HVCs) are multiphase gas structures whose velocities (∣
v
LSR
∣ ≥ 100 km s
−1
) are too high to be explained by Galactic disk rotation. While large HVCs are well ...characterized, compact and small HVCs (with H
i
angular sizes of a few degrees) are poorly understood. Possible origins for such small clouds include Milky Way (MW) halo gas or fragments of the Magellanic System, but neither their origin nor their connection to the MW halo has been confirmed. We use new Hubble Space Telescope/Cosmic Origins Spectrograph UV spectra and Green Bank Telescope H
i
spectra to measure the metallicities of five small HVCs in the southern Galactic sky projected near the Magellanic System. We build a set of distance-dependent Cloudy photoionization models for each cloud and calculate their ionization-corrected metallicities. All five small HVCs have oxygen metallicities ≤0.17
Z
⊙
, indicating they do not originate in the disk of the MW. Two of the five have metallicities of 0.16–0.17
Z
⊙
, similar to the Magellanic Stream, suggesting these clouds are fragments of the Magellanic System. The remaining three clouds have much lower metallicities of 0.02–0.04
Z
⊙
. While the origin of these low-metallicity clouds is unclear, they could be gaseous minihalos or gas stripped from dwarf galaxies by ram pressure or tidal interactions. These results suggest that small HVCs do not all reside in the inner MW halo or the Magellanic System, but instead can trace more distant structures.
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