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 .
Abstract
We present the first version release of SESAMME, a public, Python-based full spectrum fitting tool for Simultaneous Estimates of Star-cluster Age, Metallicity, Mass, and Extinction. SESAMME ...compares an input spectrum of a star cluster to a grid of stellar population models with an added nebular continuum component, using Markov Chain Monte Carlo methods to sample the posterior probability distribution in four dimensions: cluster age, stellar metallicity
Z
, reddening
E
(
B
−
V
), and a normalization parameter equivalent to a cluster mass. SESAMME is highly flexible in the stellar population models that it can use to model a spectrum; our testing and initial science applications use both BPASS and Starburst99. We illustrate the ability of SESAMME to recover accurate ages and metallicities even at a moderate signal-to-noise ratio (S/N ∼ 3–5 per wavelength bin) using synthetic, noise-added model spectra of young star clusters. Finally, we test the consistency of SESAMME with other age and metallicity estimates from the literature using a sample of Hubble Space Telescope/Cosmic Origins Spectrograph far-UV spectra toward young, massive clusters in M83 and NGC 1313. We find that, on the whole, SESAMME infers star cluster properties that are consistent with the literature in both low- and high-metallicity environments.
ABSTRACT
Super star cluster (SSC) A1 ($3.1\times 10^5\, \mathrm{M}_\odot$) in NGC 3125 has one of the strongest ($EW=4.6\pm 0.5\,$ Å) broad ($FWHM=1131\pm 40\,$ km s−1) He ii λ1640 emission lines in ...the nearby universe and constitutes an important template for interpreting observations of extreme He ii emitters out to redshifts of z ∼ 2 – 3. We use Cosmic Origins Spectrograph (COS) observations of A1 to show that there is no significant contamination of the He ii line with nebular emission and that the line is redshifted by 121 ± 17 km s−1 relative to ISM lines. We compare the COS G130M + G160M observations of A1 to recent binary BPASS and single-star Charlot & Bruzual (C&B) simple stellar population (SSP) models with very massive stars (VMS) of up to $300\, \mathrm{M}_\odot$. On the other hand, we suggest why BPASS models fail to reproduce A1’s He ii emission. On the other hand, a C&B model with Z = 0.008, age = 2.2 Myr, and VMS approaching the Eddington limit provides an excellent fit to the He ii emission and fits reasonably well C iii λ1175, N v λλ1238, 1241, and C iv λλ1548, 1551. We present O v λ1371 line-profile predictions showing that this line constitutes an important tracer of youth and VMS in galaxies. Finally, we discuss the presence of VMS in CDFS131717, a highly star-forming low-metallicity galaxy located at z = 3.071, which has a tentative detection of O v absorption and strong broad He ii emission. These features are rare and hint to the presence of short-lived VMS in the galaxy. Our results show the effect of the latest developments of stellar wind theory and the importance of accounting for VMS in models.
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 As the nearest confirmed Lyman continuum (LyC) emitter, Haro 11 is an exceptional laboratory for studying LyC escape processes crucial to cosmic reionization. Our new Hubble Space ...Telescope/Cosmic Origins Spectrograph G130M/1055 observations of its three star-forming knots now reveal that the observed LyC originates in Knots B and C, with 903–912 Å luminosities of 1.9 ± 1.5 × 10 40 erg s −1 and 0.9 ± 0.7 × 10 40 erg s −1 , respectively. We derive local escape fractions f esc,912 = 3.4% ± 2.9% and 5.1% ± 4.3% for Knots B and C, respectively. Our Starburst99 modeling shows dominant populations on the order of ∼1–4 Myr and 1–2 × 10 7 M ⊙ in each knot, with the youngest population in Knot B. Thus, the knot with the strongest LyC detection has the highest LyC production. However, LyC escape is likely less efficient in Knot B than in Knot C due to higher neutral gas covering. Our results therefore stress the importance of the intrinsic ionizing luminosity, and not just the escape fraction, for LyC detection. Similarly, the Ly α escape fraction does not consistently correlate with LyC flux, nor do narrow Ly α red peaks. High observed Ly α luminosity and low Ly α peak velocity separation, however, do correlate with higher LyC escape. Another insight comes from the undetected Knot A, which drives the Green Pea properties of Haro 11. Its density-bounded conditions suggest highly anisotropic LyC escape. Finally, both of the LyC-leaking Knots, B and C, host ultraluminous X-ray sources (ULXs). While stars strongly dominate over the ULXs in LyC emission, this intriguing coincidence underscores the importance of unveiling the role of accretors in LyC escape and reionization.
Comparison of interstellar medium (ISM) absorption in the UV spectrum of LS 4825, a B1 Ib−II star d = 21 5 kpc from the Sun toward l = 1 67 and b = −6 63, with ISM absorption toward an aligned ...foreground star at d < 7.0 1.7 kpc, allows us to isolate and study gas associated with the Milky Way nuclear wind. Spectra from the Space Telescope Imaging Spectrograph show low-ionization absorption out to d < 7 kpc (e.g., O i, C ii, Mg ii, Si ii, Fe ii, S ii) only between 0 and 40 km s−1, while absorption at d > 7 kpc, ∼1 kpc below the Galactic plane, is complex and spans −290 to +94 km s−1. The intermediate and high ions Si iii, C iv, Si iv, and N v show extremely strong absorption with multiple components from −283 to 107 km s−1, implying that the ISM ∼1 kpc below the Galactic center has a substantial reservoir of plasma and more gas containing C iv and N v than in the Carina OB1 association at z = 0 kpc. Abundances and physical conditions are presented for many absorption components. The high ion absorption traces cooling transition temperature plasma probably driven by the outflowing hot gas, while the extraordinarily large thermal pressure, p/k ∼ 105 cm−3 K−1, in an absorption component at −114 km s−1 probably arises from the ram pressure of the outflowing hot gas. The observations are consistent with a flow whose ionization structure in the high ions can be understood through a combination of nonequilibrium radiative cooling and turbulent mixing.
Abstract We analyze the far-ultraviolet (1130−1770 Å rest frame) spectroscopy of 20 young (<50 Myr) and massive (>10 4 M ⊙ ) star clusters (YSCs) in 11 nearby star-forming galaxies. We probe the ...interstellar gas intervening along the line of sight, detecting several metal absorption lines of a wide range of ionization potentials, from 6.0 to 77.5 eV. Multiple-component Voigt fits to the absorption lines are used to study the kinematics of the gas. We find that nearly all targets in the sample feature gas outflowing from 30 up to 190 km s −1 , often in both the neutral and ionized phases. The outflow velocities correlate with the underlying stellar population properties directly linked to the feedback: the mass of the YSCs, the photon production rate, and the instantaneous mechanical luminosity produced by stellar winds and supernovae. We detect a neutral inflow in four targets, which we interpret as likely not associated with the star cluster but tracing larger-scale gas kinematics. A comparison between the outflows’ energy and that produced by the associated young stellar populations suggests an average coupling efficiency of 10% with a broad scatter. Our results extend the relation found in previous works between galactic outflows and the host galaxy star formation rate to smaller scales, pointing toward the key role that clustered star formation and feedback play in regulating galaxy growth.
Abstract
Mrk 71 is a low-metallicity (
Z
= 0.16
Z
☉
) starburst region in the local dwarf galaxy NGC 2366, hosting two super star clusters (SSCs A and B), and it is recognized as a Green Pea (GP) ...analog with SSC A responsible for the GP properties. We present STIS and FOS far-ultraviolet (FUV) spectra of the embedded SSC Mrk 71-A obtained with the Hubble Space Telescope. The STIS FUV spectrum shows the characteristic features of very massive stars (VMS; masses >100
M
⊙
) and we derive an age of 1 ± 1 Myr by comparison with the Charlot & Bruzual suite of spectral population synthesis models with upper mass limits of 300 and 600
M
⊙
. We compare the STIS spectrum with all known SSC spectra exhibiting VMS signatures: NGC 5253-5, R136a, NGC 3125-A1, and the
z
= 2.37 Sunburst cluster. We find that the cluster mass-loss rates and wind velocities, as characterized by the C
iv
P Cygni profiles and the He
ii
emission line strengths, are very similar over
Z
= 0.16–0.4 Z
☉
. This agrees with predictions that the optically thick winds of VMS will be enhanced near the Eddington limit and show little metallicity dependence. We find very strong damped Ly
α
absorption with
N
(H
i
) =10
22.2
cm
−2
associated with Mrk 71-A. We discuss the natal environment of this young SSC in terms of radiatively driven winds, catastrophic cooling, and recent models where the cluster is surrounded by highly pressurized clouds with large neutral columns.
Abstract In the current JWST era, rest-frame UV spectra play a crucial role in enhancing our understanding of the interstellar medium (ISM) and stellar properties of the first galaxies in the epoch ...of reionization ( z > 6). Here, we compare well-known and reliable optical diagrams sensitive to the main ionization source (i.e., star formation, SF; active galactic nuclei, AGN; and shocks) to UV counterparts proposed in the literature—the so-called “UV–BPT diagrams”—using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY), which is the largest high-quality, high-resolution, and broad-wavelength range atlas of far-UV spectra for 45 local star-forming galaxies. In particular, we explore where CLASSY UV line ratios are located in the different UV diagnostic plots, taking into account state-of-the-art photoionization and shock models, and, for the first time, the measured ISM and stellar properties (e.g., gas-phase metallicity, ionization parameter, carbon abundance, and stellar age). We find that the combination of C iii λ λ 1907,9 He ii λ 1640 and O iii λ 1666 can be a powerful tool to separate between SF, shocks, and AGN at subsolar metallicities. We also confirm that alternative diagrams without O iii λ 1666 still allow us to define an SF-locus, with some caveats. Diagrams including C iv λ λ 1548,51 should be taken with caution given the complexity of this doublet profile. Finally, we present a discussion detailing the ISM conditions required to detect UV emission lines, visible only in low gas-phase metallicity (12 + log(O/H) ≲ 8.3) and high ionization parameter (log( U ) ≳ −2.5) environments. Overall, CLASSY and our UV toolkit will be crucial in interpreting the spectra of the earliest galaxies that JWST is currently revealing.
Abstract
We present a first look at the MRS observations of the nucleus of the nearby galaxy M83, taken with MIRI on board JWST. The observations show a rich set of emission features from the ionized ...gas, warm molecular gas, and dust. To begin dissecting the complex processes in this part of the galaxy, we divide the observations into four different regions. We find that the strength of the emission features varies strongly from region to region, with the southeast region displaying the weakest features tracing the dust continuum and interstellar medium (ISM) properties. Comparison between the cold molecular gas traced by the
12
CO (1–0) transition with the Atacama Large Millimeter/submillimeter Array and the H
2
S(1) transition shows a similar spatial distribution. This is in contrast to the distribution of the much warmer H
2
emission from the S(7) transition found to be concentrated around the optical nucleus. We use the rotational emission lines and model the H
2
excitation to estimate a total molecular gas mass accounting for the warm H
2
component of
M
(>50 K)
H
2
= 67.90 (±5.43) × 10
6
M
⊙
. We compare this value to the total gas mass inferred by probing the cold H
2
gas through the
12
CO (1–0) emission,
M
(CO)
H
2
= 17.15 × 10
6
M
⊙
. We estimate that ∼75% of the total molecular gas mass is contained in the warm H
2
component. We also identify O
iv
25.89
μ
m and Fe
ii
25.99
μ
m emission. We propose that the diffuse Fe
ii
25.99
μ
m emission might be tracing shocks created during the interactions between the hot wind produced by the starburst and the much cooler ISM above the galactic plane. More detailed studies are needed to confirm such a scenario.
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