Galactic Winds in Low-mass Galaxies McQuinn, Kristen. B. W.; van Zee, Liese; Skillman, Evan D.
Astrophysical journal/The Astrophysical journal,
11/2019, Volume:
886, Issue:
1
Journal Article
Peer reviewed
Open access
Stellar-feedback-driven outflows are predicted to play a fundamental role in the baryon cycle of low-mass galaxies. However, observational constraints of winds in nearby dwarf galaxies are limited, ...as outflows are transient, intrinsically low surface brightness features and thus difficult to detect. Using deep H observations, we search for winds in a sample of 12 nearby dwarfs (M* ∼ 107-109.3 M ) that host ongoing or recent starbursts. We detect features that we classify as winds in six galaxies, fountain candidates in five galaxies, and diffuse interstellar medium (ISM) in one system. Winds are found preferentially in galaxies with centrally concentrated star formation, while fountains are found in galaxies with spatially distributed star formation. We suggest that the concentration of star formation is a predictor for whether a low-mass galaxy will develop a wind. The spatial extent of all detected ionized gas is limited (<1/10 virial radius) and would still be considered the ISM by cosmological simulations. Our observations suggest that the majority of material expelled from dwarfs does not escape to the intergalactic medium but remains in the halo and may be recycled to the galaxies. Derived mass-loading factors range from 0.2 to 7 (with only a weak dependency on circular velocity or stellar mass), in tension with higher values in simulations needed to reproduce realistic low-mass galaxies and resolve discrepancies with ΛCDM. The sample is part of the panchromatic STARBurst IRegular Dwarf Survey-STARBIRDS-designed to characterize the starburst phenomenon in dwarf galaxies. We also report a previously uncatalogued nearby galaxy (J1118+7913).
CHAOS. III. GAS-PHASE ABUNDANCES IN NGC 5457 Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A. ...
Astrophysical journal/The Astrophysical journal,
10/2016, Volume:
830, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT We present Large Binocular Telescope observations of 109 H ii regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more ...temperature-sensitive auroral emission lines for 74 H ii regions, permitting the measurement of "direct" gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of TN ii with TS iii and TO iii, consistent with little or no intrinsic scatter; (2) a correlation of TS iii with TO iii, but with significant intrinsic dispersion; (3) overall agreement between TN ii, TS ii, and TO ii, as expected, but with significant outliers; (4) the correlations of TN ii with TS iii and TO iii match the predictions of photoionization modeling while the correlation of TS iii with TO iii is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation H ii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H ii regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 0.009 in O/H and 0.095 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of H ii regions in NGC 5457.
The chemical abundances of spiral galaxies, as probed by H ii regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large ...Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 H ii regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual H ii regions. We find that the dispersion in relationships is dependent on ionization, as characterized by , and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that N ii and S iii provide the most robust measures of electron temperature in low-ionization zones, while O iii provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of dex/Re with tot. = 0.08 for Rg/Re < 2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich H ii regions.
Abstract
Ultraviolet nebular emission lines are important for understanding the time evolution and nucleosynthetic origins of their associated elements, but the underlying trends of their relative ...abundances are unclear. We present UV spectroscopy of 20 nearby low-metallicity, high-ionization dwarf galaxies obtained using the
Hubble Space Telescope
. Building upon previous studies, we analyze the C/O relationship for a combined sample of 40 galaxies with significant detections of the UV O
+2
/C
+2
collisionally excited lines and direct-method oxygen abundance measurements. Using new analytic carbon ionization correction factor relationships, we confirm the flat trend in C/O versus O/H observed for local metal-poor galaxies. We find an average log(C/O) = −0.71 with an intrinsic dispersion of
σ
= 0.17 dex. The C/N ratio also appears to be constant at log(C/N) = 0.75, plus significant scatter (
σ
= 0.20 dex), with the result that carbon and nitrogen show similar evolutionary trends. This large and real scatter in C/O over a large range in O/H implies that measuring the UV C and O emission lines alone does not provide a reliable indicator of the O/H abundance. By modeling the chemical evolution of C, N, and O of individual targets, we find that the C/O ratio is very sensitive to both the detailed star formation history and to supernova feedback. Longer burst durations and lower star formation efficiencies correspond to low C/O ratios, while the escape of oxygen atoms in supernovae winds produces decreased effective oxygen yields and larger C/O ratios. Further, a declining C/O relationship is seen with increasing baryonic mass due to increasing effective oxygen yields.
Abstract
We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of M
halo ≈ 1010 M⊙ at z = 0, in order to understand the relationship among halo ...assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (fire) project and are performed at extremely high resolution (m
baryon = 500 M⊙, m
dm = 2500 M⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M
*/M⊙ ≈ 105 − 107). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity V
max, both of which are tightly linked to halo formation time. Much of this dependence of M
* on a second parameter (beyond M
halo) is a direct consequence of the M
halo ∼ 1010 M⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M
⋆ ≳ 2 × 106 M⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r
1/2. Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M
⋆ ≈ 2 × 106 − 2 × 10− 4 M
halo is broadly consistent with previous work and provides a testable prediction of fire feedback models in Λcold dark matter.
Abstract
Stellar population models produce radiation fields that ionize oxygen up to O
+2
, defining the limit of standard H
ii
region models (<54.9 eV). Yet, some extreme emission-line galaxies, or ...EELGs, have surprisingly strong emission originating from much higher ionization potentials. We present UV HST/COS and optical LBT/MODS spectra of two nearby EELGs that have very high-ionization emission lines (e.g., He
ii
λλ
1640,4686 C
iv
λλ
1548,1550, Fe
v
λ
4227, Ar
iv
λλ
4711,4740). We define a four-zone ionization model that is augmented by a very high-ionization zone, as characterized by He
+2
(>54.4 eV). The four-zone model has little to no effect on the measured total nebular abundances, but does change the interpretation of other EELG properties: we measure steeper central ionization gradients; higher volume-averaged ionization parameters; and higher central
T
e
,
n
e
, and log
U
values. Traditional three-zone estimates of the ionization parameter can underestimate the average log
U
by up to 0.5 dex. Additionally, we find a model-independent dichotomy in the abundance patterns, where the
α
/H abundances are consistent but N/H, C/H, and Fe/H are relatively deficient, suggesting these EELGs are
α
/Fe-enriched by more than three times. However, there still is a high-energy ionizing photon production problem (HEIP
3
). Even for such
α
/Fe enrichment and very high log
U
s, photoionization models cannot reproduce the very high-ionization emission lines observed in EELGs.
CHAOS. II. GAS-PHASE ABUNDANCES IN NGC 5194 Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A. ...
Astrophysical journal/The Astrophysical journal,
07/2015, Volume:
808, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT We have observed NGC 5194 (M51a) as part of the CHemical Abundances of Spirals project. Using the Multi Object Double Spectrographs on the Large Binocular Telescope we are able to measure ...one or more of the temperature-sensitive auroral lines (O iii λ4363, N ii λ5755, S iii λ6312) and thus measure "direct" gas-phase abundances in 29 individual H ii regions. O iii λ4363 is only detected in two H ii regions, both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC 5194 and find excellent agreement ( ) for all but one region. We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC 5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter ( ≤ 0.08 dex), most of which can be attributed to random error and not to intrinsic dispersion. The gas-phase abundance gradient is consistent with the gradients observed in other interacting galaxies, which tend to be shallower than gradients measured in isolated galaxies. The N/O ratio ( ) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10), relative to primary production mechanisms than predicted by theoretical models.
Abstract
We analyze the rest-frame near-UV and optical nebular spectra of three
z
> 7 galaxies from the Early Release Observations taken with the Near-Infrared Spectrograph (NIRSpec) on the James ...Webb Space Telescope (JWST). These three high-
z
galaxies show the detection of several strong emission nebular lines, including the temperature-sensitive O
iii
λ
4363 line, allowing us to directly determine the nebular conditions and abundances for O/H, C/O, and Ne/O. We derive O/H abundances and ionization parameters that are generally consistent with other recent analyses. We analyze the mass–metallicity relationship (i.e., slope) and its redshift evolution by comparing between the three
z
> 7 galaxies and local star-forming galaxies. We also detect the C
iii
λλ
1907, 1909 emission in a
z
> 8 galaxy from which we determine the most distant C/O abundance to date. This valuable detection of log(C/O) = −0.83 ± 0.38 provides the first test of C/O redshift evolution out to high redshift. For neon, we use the high-ionization Ne
iii
λ
3869 line to measure the first Ne/O abundances at
z
> 7, finding no evolution in this
α
-element ratio. We explore the tentative detection of Fe
ii
and Fe
iii
lines in a
z
> 8 galaxy, which would indicate a rapid buildup of metals. Importantly, we demonstrate that properly flux-calibrated and higher-S/N spectra are crucial to robustly determine the abundance pattern in
z
> 7 galaxies with NIRSpec/JWST.
We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10 super(4) < M sub(sstarf) < 10 super(9) M sub(middot in circle)). The SFHs are ...derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted "true fossils" identified by Bovill & Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., K.K.R 25).
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