11 research outputs found
Atomic Data Revisions for Transitions Relevant to Observations of Interstellar, Circumgalactic, and Intergalactic Matter
Measurements of element abundances in galaxies from astrophysical spectroscopy depend sensitively on the atomic data used. With the goal of making the latest atomic data accessible to the community, we present a compilation of selected atomic data for resonant absorption lines at wavelengths longward of 911.753 Å (the H I Lyman limit), for key heavy elements (heavier than atomic number 5) of astrophysical interest. In particular, we focus on the transitions of those ions that have been observed in the Milky Way interstellar medium (ISM), the circumgalactic medium (CGM) of the Milky Way and/or other galaxies, and the intergalactic medium (IGM). We provide wavelengths, oscillator strengths, associated accuracy grades, and references to the oscillator strength determinations. We also attempt to compare and assess the recent oscillator strength determinations. For about 22% of the lines that have updated oscillator strength values, the differences between the former values and the updated ones are ≳ 0.1 dex. Our compilation will be a useful resource for absorption line studies of the ISM, as well as studies of the CGM and IGM traced by sight lines to quasars and gamma-ray bursts. Studies (including those enabled by future generations of extremely large telescopes) of absorption by galaxies against the light of background galaxies will also benefit from our compilation
Detection of Dust in High-Velocity Cloud Complex C -- Enriched Gas Accreting onto the Milky Way
We present the detection of dust depletion in Complex C, a massive,
infalling, low-metallicity high-velocity cloud in the northern Galactic
hemisphere that traces the ongoing accretion of gas onto the Milky Way. We
analyze a very high signal-to-noise HST/COS spectrum of AGN Mrk 817 formed by
coadding 165 individual exposures taken under the AGN STORM 2 program, allowing
us to determine dust-depletion patterns in Complex C at unprecedented
precision. By fitting Voigt components to the O I, S II, N I, Si II, Fe II, and
Al II absorption and applying ionization corrections from customized Cloudy
photoionization models, we find sub-solar elemental abundance ratios of
[Fe/S]=-0.42+/-0.08, [Si/S]=-0.29+/-0.05, and [Al/S]=-0.53+/-0.08. These ratios
indicate the depletion of Fe, Si, and Al into dust grains, since S is mostly
undepleted. The detection of dust provides an important constraint on the
origin of Complex C, as dust grains indicate the gas has been processed through
galaxies, rather than being purely extragalactic. We also derive a low
metallicity of Complex C of [S/H]=-0.51+/-0.16 (31% solar), confirming earlier
results from this sightline. We discuss origin models that could explain the
presence of dust in Complex C, including Galactic fountain models, tidal
stripping from the Magellanic Clouds or other satellite galaxies, and
precipitation of coronal gas onto dust-bearing ``seed" clouds.Comment: 8 pages, 3 figures, accepted for publication in ApJ Letters. This
version has been updated with proof correction
Diverse metallicities of Fermi bubble clouds indicate dual origins in the disk and halo
The Galactic Center is surrounded by two giant plasma lobes known as the
Fermi Bubbles, extending ~10 kpc both above and below the Galactic plane.
Spectroscopic observations of Fermi Bubble directions at radio, ultraviolet,
and optical wavelengths have detected multi-phase gas clouds thought to be
embedded within the bubbles referred to as Fermi Bubble high-velocity clouds
(FB HVCs). While these clouds have kinematics that can be modeled by a
biconical nuclear wind launched from the Galactic center, their exact origin is
unknown because, until now, there has been little information on their
heavy-metal abundance (metallicity). Here we show that FB HVCs have a wide
range of metallicities from <20% solar to ~320% solar. This result is based on
the first metallicity survey of FB HVCs. These metallicities challenge the
previously accepted tenet that all FB HVCs are launched from the Galactic
center into the Fermi Bubbles with solar or super-solar metallicities. Instead,
we suggest that FB HVCs originate in both the Milky Way's disk and halo. As
such, some of these clouds may characterize circumgalactic medium that the
Fermi Bubbles expand into, rather than material carried outward by the nuclear
wind, changing the canonical picture of FB HVCs. More broadly, these results
reveal that nuclear outflows from spiral galaxies can operate by sweeping up
gas in their halos while simultaneously removing gas from their disks.Comment: This version of the article has been accepted for publication on
Nature Astronomy after peer review. This version is not the Version of Record
(https://doi.org/10.1038/s41550-022-01720-0) and does not reflect
post-acceptance improvements, or any correction
Observations of a Magellanic Corona
The Large and Small Magellanic Clouds (LMC/SMC) are the closest major
satellite galaxies of the Milky Way. They are likely on their first passage on
an infalling orbit towards our Galaxy (Besla et al. 2007) and trace the ongoing
dynamics of the Local Group (D'Onghia & Fox 2016). Recent measurements of a
high mass for the LMC (M_halo = 10^(11.1-11.4) solar masses; Penarrubia et al.
2016, Erkal et al. 2018, 2019, Kallivayalil et al. 2018) imply the LMC should
host a Magellanic Corona: a collisionally ionized, warm-hot gaseous halo at the
virial temperature (10^(5.3-5.5) K) initially extending out to the virial
radius (100-130 kpc). Such a Corona would have shaped the formation of the
Magellanic Stream (Lucchini et al. 2020), a tidal gas structure extending over
200 degrees across the sky (D'Onghia & Fox 2016, Besla et al. 2012, Nidever et
al. 2010) that is bringing in metal poor gas to the Milky Way (Fox et al.
2014). No observational evidence for such an extended Corona has been published
previously, with detections of highly ionized gas only reported in directions
directly toward the LMC, where winds from the LMC disk may dominate (deBoer &
Savage 1980, Wakker et al. 1998). Here we show evidence for this Magellanic
Corona with a potential direct detection in highly ionized oxygen (O^+5), and
indirectly via triply-ionized carbon and silicon, seen in ultraviolet
absorption toward background quasars. We find that the Magellanic Corona is
part of a pervasive multiphase Magellanic circumgalactic medium (CGM) seen in
many ionization states with a declining projected radial profile out to at
least 35 kpc from the LMC and a total ionized CGM mass of
log_10(M_HII;CGM/solar masses) = 9.1 +/- 0.2. The evidence for the Magellanic
Corona is a crucial step forward in characterizing the Magellanic Group and its
nested evolution with the Local Group.Comment: View published, open access version here:
https://www.nature.com/articles/s41586-022-05090-5 Main Text: 7 Pages, 4
Figures Methods: 19 Pages, 7 Extended Data Figures, 3 Extended Data Table
Probing Structure in Cold Gas at with Gravitationally Lensed Quasar Sight Lines
Absorption spectroscopy of gravitationally lensed quasars (GLQs) enables
study of spatial variations in the interstellar and/or circumgalactic medium of
foreground galaxies. We report observations of 4 GLQs, each with two images
separated by 0.8-3.0", that show strong absorbers at redshifts
0.41.3 in their spectra, including some at the lens redshift
with impact parameters 1.5-6.9 kpc. We measure H I Lyman lines along two sight
lines each in five absorbers (10 sight lines in total) using HST STIS, and
metal lines using Magellan Echellette or Sloan Digital Sky Survey. Our data
have doubled the lens galaxy sample with measurements of H I column densities
() and metal abundances along multiple sight lines. Our data,
combined with the literature, show no strong correlation between absolute
values of differences in , , or [Fe/H] and the
sight line separations at the absorber redshifts for separations of 0-8 kpc.
The estimated abundance gradients show a tentative anti-correlation with
abundances at galaxy centers. Some lens galaxies show inverted gradients,
possibly suggesting central dilution by mergers or infall of metal-poor gas.
[Fe/H] measurements and masses estimated from GLQ astrometry suggest the lens
galaxies lie below the total mass-metallicity relation for early-type galaxies
as well as measurements for quasar-galaxy pairs and gravitationally lensed
galaxies at comparable redshifts. This difference may arise in part from the
dust depletion of Fe. Higher resolution measurements of H and metals
(especially undepleted elements) for more GLQ absorbers and accurate lens
redshifts are needed to confirm these trends.Comment: 59 pages, 18 figures, accepted for publication in the Astrophysical
Journa
Metal-enriched galaxies in the first ∼1 billion years: evidence of a smooth metallicity evolution at z ∼ 5
International audienceWe present seven new abundance measurements of the elements O, C, and Si at z > 4.5, doubling the existing sample of weakly depleted elements in gas-rich galaxies, in order to constrain the first ∼1 billion years of cosmic metal evolution. These measurements are based on quasar spectra of damped Lyman α absorbers (DLAs) and sub-DLAs obtained with the Magellan Inamori Kyocera Echelle (MIKE) and Magellan Echellette (MagE) spectrographs on Magellan-South, and the X-Shooter spectrograph on the Very Large Telescope. We combine these new measurements with those drawn from the literature to estimate the N_{H I}-weighted binned mean metallicity of -1.51 ± 0.18 at z = 4.8. This metallicity value is in excellent agreement with the prediction from lower redshift DLAs, supporting the interpretation that the metallicity evolution is smooth at z ∼ 5, rather than showing a sudden decline at z > 4.7. Furthermore, the metallicity evolution trends for the DLAs and sub-DLAs are similar within our uncertainties. We also find that the [C/O] ratios for z ∼ 5 DLAs are consistent with those of the very metal-poor DLAs. Additionally, using [C/O] and [Si/O] to constrain the nucleosynthesis models, we estimate that the probability distributions of the progenitor star masses for three relatively metal-poor DLAs are centred around 12-17 M⊙. Finally, the z ∼ 5 absorbers show a different metallicity-velocity dispersion relation than lower redshift DLAs, suggesting that they may be tracing a different population of galaxies
Caught in the Act: A Metal-rich High-velocity Cloud in the Inner Galaxy
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