We derive new self-consistent theoretical UV, optical, and IR diagnostics for the interstellar medium (ISM) pressure and electron density in the ionized nebulae of star-forming galaxies. Our UV ...diagnostics utilize the intercombination, forbidden, and resonance lines of silicon, carbon, aluminum, neon, and nitrogen. We also calibrate the optical and IR forbidden lines of oxygen, argon, nitrogen, and sulfur. We show that line ratios used as ISM pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas. In addition, the traditional electron density diagnostic S ii λ6731/S ii λ6717 is strongly dependent on the gas-phase metallicity. We show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae. The S ii and O ii ratios are produced in different zones and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant. We review the temperature and density distributions observed within H ii regions and discuss the implications of these distributions on measuring the electron density of the gas. Many H ii regions contain radial variations in density. We suggest that the ISM pressure is a more meaningful quantity to measure in H ii regions or galaxies. Specific combinations of line ratios can cover the full range of ISM pressures (4 < log(P/k) < 9). As H ii regions become resolved at increasingly high redshift through the next generation of telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day.
ABSTRACT Using Spitzer observations of classical Cepheids we have measured the true average distance modulus of the Small Magellanic Cloud (SMC) to be mag (corresponding to kpc), which is 0.48 0.01 ...mag more distant than the LMC. This is in agreement with previous results from Cepheid observations, as well as with measurements from other indicators such as RR Lyrae stars and the tip of the red giant branch. Utilizing the properties of the mid-infrared Leavitt Law we measured precise distances to individual Cepheids in the SMC, and have confirmed that the galaxy is tilted and elongated such that its eastern side is up to 20 kpc closer than its western side. This is in agreement with the results from red clump stars and dynamical simulations of the Magellanic Clouds and Stream.
ABSTRACT We present the first results from MMT and Keck spectroscopy for a large sample of emission-line galaxies selected from our narrowband imaging in the Subaru Deep Field. We measured the weak O ...iii λ4363 emission line for 164 galaxies (66 with at least 3 detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Because the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with O iii λ4363 line strength. Our temperature-based metallicity study is the first to span Gyr of cosmic time and dex in stellar mass for low-mass galaxies, -9.0. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass-gas metallicity relation and its dependence on dust-corrected star formation rate (SFR). The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass-metallicity relation is consistent with Andrews & Martini at , and evolves toward lower abundances at a given stellar mass, . We find that galaxies with lower metallicities have higher SFRs at a given stellar mass and redshift, although the scatter is large ( dex) and the trend is weaker than seen in local studies. We also compare our mass-metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We identified 16 extremely metal-poor galaxies with abundances of less than a tenth of solar; our most metal-poor galaxy at is similar to I Zw 18.
Abstract
We report the discovery of an accreting supermassive black hole at
z
= 8.679. This galaxy, denoted here as CEERS_1019, was previously discovered as a Ly
α
-break galaxy by Hubble with a Ly
α
...redshift from Keck. As part of the Cosmic Evolution Early Release Science (CEERS) survey, we have observed this source with JWST/NIRSpec, MIRI, NIRCam, and NIRCam/WFSS and uncovered a plethora of emission lines. The H
β
line is best fit by a narrow plus a broad component, where the latter is measured at 2.5
σ
with an FWHM ∼1200 km s
−1
. We conclude this originates in the broadline region of an active galactic nucleus (AGN). This is supported by the presence of weak high-ionization lines (N V, N IV, and C III), as well as a spatial point-source component. The implied mass of the black hole (BH) is log (
M
BH
/
M
⊙
) = 6.95 ± 0.37, and we estimate that it is accreting at 1.2 ± 0.5 times the Eddington limit. The 1–8
μ
m photometric spectral energy distribution shows a continuum dominated by starlight and constrains the host galaxy to be massive (log M/M
⊙
∼9.5) and highly star-forming (star formation rate, or SFR ∼ 30 M
⊙
yr
−1
; log sSFR ∼ − 7.9 yr
−1
). The line ratios show that the gas is metal-poor (
Z
/
Z
⊙
∼ 0.1), dense (
n
e
∼ 10
3
cm
−3
), and highly ionized (log
U
∼ − 2.1). We use this present highest-redshift AGN discovery to place constraints on BH seeding models and find that a combination of either super-Eddington accretion from stellar seeds or Eddington accretion from very massive BH seeds is required to form this object.
Abstract
We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy ...SGAS J111020.0+645950.8 at a redshift of
z
= 2.481. The physical size scales that we probe, radii
r
= 30–50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with
pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of
galaxies. In this galaxy, star-forming regions smaller than 100 pc—physical scales not usually resolved at these redshifts by current telescopes—are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of the order of 1 kpc. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time.
We constrain the slope of the star formation rate (SFR; log Psi) to stellar mass (log M sub(*)) relation down to log(M sub(*)/M sub(middot in circle)) = 8.4 (log(M sub(*)/M sub(middot in circle)) = ...9.2) at z = 0.5 (z = 2.5) with a mass-complete sample of 39,106 star-forming galaxies selected from the 3D-HST photometric catalogs, using deep photometry in the CANDELS fields. For the first time, we find that the slope is dependent on stellar mass, such that it is steeper at low masses (log Psi is proportional to log M sub(*)) than at high masses (log Psi is proportional to (0.3-0.6) log M sub(*)). These steeper low-mass slopes are found for three different star formation indicators: the combination of the ultraviolet (UV) and infrared (IR), calibrated from a stacking analysis of Spitzer/MIPS 24 mu m imaging; beta -corrected UV SFRs; and H alpha SFRs. The normalization of the sequence evolves differently in distinct mass regimes as well: for galaxies less massive than log(M sub(*)/M sub(middot in circle)) < 10 the specific SFR (Psi/M sub(*)) is observed to be roughly self-similar with Psi/M sub(*) is proportional to (1 + z) super(1.9), whereas more massive galaxies show a stronger evolution with Psi/M sub(*) is proportional to (1 + z) super(2.2-3.5) for log(M sub(*)/M sub(middot in circle)) = 10.2-11.2. The fact that we find a steep slope of the star formation sequence for the lower mass galaxies will help reconcile theoretical galaxy formation models with the observations.
We present a detailed analysis of multi-wavelength Hubble Space Telescope/Wide Field Camera 3 (WFC3) imaging and Keck/OSIRIS near-infrared adaptive optics-assisted integral field spectroscopy for a ...highly magnified lensed galaxy at z = 1.70. This young starburst is representative of ultraviolet-selected star-forming galaxies (SFGs) at z ~ 2 and contains multiple individual star-forming regions. Due to the lensing magnification, we can resolve spatial scales down to 100 pc in the source plane of the galaxy. The velocity field shows disturbed kinematics suggestive of an ongoing interaction and there is a clear signature of a tidal tail. We constrain the age, reddening, star formation rate, and stellar mass of the star-forming clumps from spectral energy distribution (SED) modeling of the WFC3 photometry and measure their H alpha luminosity, metallicity, and outflow properties from the OSIRIS data. With strong star-formation-driven outflows in four clumps, RCSGA0327 is the first high-redshift SFG at stellar mass <10 super(10) M sub(middot in circle) with spatially resolved stellar winds. We compare the H alpha luminosities, sizes, and dispersions of the star-forming regions with other high-z clumps as well as local giant H II regions and find no evidence for increased clump star formation surface densities in interacting systems, unlike in the local universe. Spatially resolved SED modeling unveils an established stellar population at the location of the largest clump and a second mass concentration near the edge of the system that is not detected in H alpha emission. This suggests a picture of an equal-mass mixed major merger, which has not triggered a new burst of star formation or caused a tidal tail in the gas-poor component.
Abstract
Far-ultraviolet (FUV; ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, ...feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N
1500 Å
≳ 5/resel), high-resolution (
R
∼ 15,000) FUV spectral database of 45 nearby (0.002 <
z
< 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < log
M
⋆
(
M
⊙
) < 10.1), star formation rate (−2.0 < log SFR (
M
⊙
yr
−1
) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O
32
< 38.0), reddening (0.02 <
E
(
B
−
V
) < 0.67), and nebular density (10 <
n
e
(cm
−3
) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with the
z
∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to
z
≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
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