Abstract
We present observations of CO(3−2) in 13 main-sequence
z
= 2.0–2.5 star-forming galaxies at
log
(
M
*
/
M
⊙
)
=
10.2
–
10.6
that span a wide range in metallicity (O/H) based on rest-optical ...spectroscopy. We find that
L
CO
(
3
−
2
)
′
/SFR decreases with decreasing metallicity, implying that the CO luminosity per unit gas mass is lower in low-metallicity galaxies at
z
∼ 2. We constrain the CO-to-H
2
conversion factor (
α
CO
) and find that
α
CO
inversely correlates with metallicity at
z
∼ 2. We derive molecular gas masses (
M
mol
) and characterize the relations among
M
*
, SFR,
M
mol
, and metallicity. At
z
∼ 2,
M
mol
increases and the molecular gas fraction (
M
mol
/
M
*
) decreases with increasing
M
*
, with a significant secondary dependence on SFR. Galaxies at
z
∼ 2 lie on a near-linear molecular KS law that is well-described by a constant depletion time of 700 Myr. We find that the scatter about the mean SFR−
M
*
, O/H−
M
*
, and
M
mol
−
M
*
relations is correlated such that, at fixed
M
*
,
z
∼ 2 galaxies with larger
M
mol
have higher SFR and lower O/H. We thus confirm the existence of a fundamental metallicity relation at
z
∼ 2, where O/H is inversely correlated with both SFR and
M
mol
at fixed
M
*
. These results suggest that the scatter of the
z
∼ 2 star-forming main sequence, mass–metallicity relation, and
M
mol
–
M
*
relation are primarily driven by stochastic variations in gas inflow rates. We place constraints on the mass loading of galactic outflows and perform a metal budget analysis, finding that massive
z
∼ 2 star-forming galaxies retain only 30% of metals produced, implying that a large mass of metals resides in the circumgalactic medium.
Abstract
We use medium-resolution JWST/NIRSpec observations from the Cosmic Evolution Early Release Science Survey to place the first constraints on dust attenuation and star formation based on ...Paschen lines for a sizable sample of 63 galaxies at redshifts
z
= 1.0–3.1. Our analysis indicates strong correlations between the Balmer decrement, H
α
/H
β
, and line ratios that include Paschen lines (i.e., Pa
α
/H
β
, Pa
β
/H
β
, and the Paschen decrement, Pa
α
/Pa
β
), suggesting that the former is sensitive to the overall dust obscuration toward H
ii
regions in high-redshift galaxies. The line ratios are used to derive nebular reddening,
E
(
B
−
V
)
neb
, and star formation rates (SFRs). There is marginal evidence that the SFRs deduced from Paschen lines may exceed by ≈25% those derived from Balmer lines alone, suggesting the presence of star formation that is optically thick in Balmer lines, though deeper observations are needed to confirm this result. Using the Paschen-line constraints on the bolometric SFRs, we reevaluate the relationship between dust obscuration and UV spectral slope, and find a reddening of the UV continuum that, on average, follows the SMC extinction curve. This analysis highlights the need for deeper spectroscopy of more representative samples to evaluate nebular dust attenuation and bolometric SFRs in high-redshift galaxies, and their relationship to the reddening of the UV continuum.
Abstract
We present results from the MOSFIRE Deep Evolution Field survey on broad flux from the nebular emission lines H
α
, N
ii
, O
iii
, H
β
, and S
ii
. The sample consists of 127 star-forming ...galaxies at 1.37 <
z
< 2.61 and 84 galaxies at 2.95 <
z
< 3.80. We decompose the emission lines using narrow and broad Gaussian components that we define as having FWHM < 275 km s
−1
and FWHM > 300 km s
−1
, respectively, for both individual galaxies and stacks. For individual galaxies, broad emission is detected at >3
σ
in <10% of galaxies and the broad flux accounts for 10%–70% of the total flux. In the stacks, we find a slight increase in broad to narrow flux ratio with mass but note that we cannot reliably detect broad emission with FWHM < 275 km s
−1
, which may be significant at low masses. When placed on the N2-BPT diagram (O
iii
/H
β
versus N
ii
/H
α
), the broad components of the stacks are shifted toward higher O
iii
/H
β
and N
ii
/H
α
ratios compared to the narrow component. We compare the location of the broad components to shock models and find that the broad component could be explained as a shocked outflow, but we do not rule out other possibilities, such as the presence of an AGN. We discuss the possible consequences of shocked emission on the galaxy location in emission line diagnostic diagrams and calculation of SFR. We attempt to estimate the mass outflow rate/star formation rate, but caution that our results strongly rely on the assumptions regarding the physical properties of the outflow.
Humans have more than doubled the amount of reactive nitrogen (Nr) added to the biosphere, yet most of what is known about its accumulation and ecological effects is derived from studies of heavily ...populated regions. Nitrogen (N) stable isotope ratios (¹⁵N:¹⁴ N) in dated sediments from 25 remote Northern Hemisphere lakes show a coherent signal of an isotopically distinct source of N to ecosystems beginning in 1895 ± 10 years (±1 standard deviation). Initial shifts in N isotope composition recorded in lake sediments coincide with anthropogenic CO₂ emissions but accelerate with widespread industrial Nr production during the past half century. Although current atmospheric Nr deposition rates in remote regions are relatively low, anthropogenic N has probably influenced watershed N budgets across the Northern Hemisphere for over a century.
We present results on the dust attenuation curve of z, ~ 2 galaxies using early observations from the MOSFIRE Deep Evolution Field survey. Our sample consists of 224 star-forming galaxies with z ...sub(spec) = 1.36-2.59 and high signal-to-noise ratio measurements of H alpha and H beta obtained with Keck/MOSFIRE. We construct composite spectral energy distributions (SEDs) of galaxies in bins of Balmer decrement to measure the attenuation curve. We find a curve that is similar to the SMC extinction curve at lambda gap 2500 A. At shorter wavelengths, the shape is identical to that of the Calzetti et al. relation, but with a lower normalization. Hence, the new attenuation curve results in star formation rates (SFRs) that are approximately 20% lower, and stellar masses that are Delta log(M super(*)/M sub(middot in circle))Asymptotically = to 0.16 dex lower, than those obtained with the Calzetti relation. We find that the difference in the total attenuation of the ionized gas and stellar continuum correlates strongly with SFR, such that for dust-corrected SFRs gap 20 M sub(middot in circle) yr super(-1), assuming a Chabrier initial mass function, the nebular emission lines suffer an increasing degree of obscuration relative to the continuum. A simple model that can account for these trends is one in which the UV through optical stellar continuum is dominated by a population of less-reddened stars, while the nebular line and bolometric luminosities become increasingly dominated by dustier stellar populations for galaxies with large SFRs, as a result of the increased dust enrichment that accompanies such galaxies. Consequently, UV- and SED-based SFRs may underestimate the total SFR at even modest levels of approximately 20 M sub(middot in circle)yr super(-1).
ABSTRACT We present gas kinematics for 178 star-forming galaxies at from the MOSFIRE Deep Evolution Field survey. We have developed models to interpret the kinematic measurements from fixed-angle ...multi-object spectroscopy, using structural parameters derived from Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey Hubble Space Telescope/F160W imaging. For 35 galaxies, we measure resolved rotation with a median of . We derive dynamical masses from the kinematics and sizes and compare them to baryonic masses, with gas masses estimated from dust-corrected star formation rates (SFRs) and the Kennicutt-Schmidt relation. When assuming that galaxies with and without observed rotation have the same median , we find good agreement between the dynamical and baryonic masses, with a scatter of and a median offset of . This comparison implies a low dark matter fraction (8% within an effective radius) for a Chabrier initial mass function (IMF), and disfavors a Salpeter IMF. Moreover, the requirement that / should be independent of inclination yields a median value of for galaxies without observed rotation. If, instead, we treat the galaxies without detected rotation as early-type galaxies, the masses are also in reasonable agreement ( , ). The inclusion of gas masses is critical in this comparison; if gas masses are excluded, there is an increasing trend of / with higher specific SFR (SSFR). Furthermore, we find indications that decreases with increasing SSFR for our full sample, which may reflect disk settling. We also study the Tully-Fisher relation and find that at fixed stellar mass was higher at earlier times. At fixed baryonic mass, we observe the opposite trend. Finally, the baryonic and dynamical masses of the active galactic nuclei in our sample are also in excellent agreement, suggesting that the kinematics trace the host galaxies.
Abstract
We present rest-optical spectroscopic properties of a sample of four galaxies in the Atacama Large Millimeter/submillimeter Array Hubble Ultra Deep Field (ALMA HUDF). These galaxies span the ...redshift range
and the stellar mass range
. They have existing far-infrared and radio measurements of dust-continuum and molecular gas emission from which bolometric star formation rates (SFRs), dust masses, and molecular gas masses have been estimated. We use new
H
- and
K
-band near-infrared spectra from the Keck/Multi-object Spectrometer for Infrared Exploration (MOSFIRE) to estimate SFRs from dust-corrected H
α
emission (SFR(H
α
)) and gas-phase oxygen abundances from the ratio N
ii
/H
α
. We find that the dust-corrected SFR(H
α
) is systematically lower than the bolometric SFR by a factor of several, and measure gas-phase oxygen abundances in a narrow range,
(
). Relative to a large
z
∼ 2 comparison sample from the MOSFIRE Deep Evolution Field (MOSDEF) survey, the ALMA HUDF galaxies scatter roughly symmetrically around the best-fit linear mass–metallicity relation, providing tentative evidence for a flattening in the SFR dependence of metallicity at high stellar mass. Combining oxygen abundances with estimates of dust and molecular gas masses, we show that there is no significant evolution in the normalization of the dust-to-gas ratio (DGR) versus metallicity relation from
z
∼ 0 to
z
∼ 2. This result is consistent with some semi-analytic models and cosmological simulations describing the evolution of dust in galaxies. Tracing the actual form of the DGR versus metallicity relation at high redshift now requires combined measurements of dust, gas, and metallicity over a significantly wider range in metallicity.
We present new results on the kinematics and spatial distribution of metal-enriched gas within {approx}125 kpc of star-forming ('Lyman break') galaxies at redshifts 2 {approx_lt} z {approx_lt} 3. In ...particular, we focus on constraints provided by the rest-frame far-ultraviolet (far-UV) spectra of faint galaxies, and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with (z) = 2.3 {+-} 0.3 and with both rest-frame far-UV and H{alpha} spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Ly{alpha} emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1''-15'') angular pairs of z {approx} 2-3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3-125 kpc (physical) at (z) = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Ly{alpha} emission lines, as well as the observed variation of absorption line strength (H I and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with v{sub out}(r) increasing with r (i.e., the highest velocities are located at the largest galactocentric distances r). The inferred radial dependence of the covering fraction of cool gas (which modulates the absorption line strength) is f{sub c} (r) {proportional_to} r {sup -{gamma}} with 0.2 {approx_lt} {gamma} {approx_lt} 0.6 depending on transition. We discuss the results of the observations in the context of 'cold accretion', in which cool gas is accreting via filamentary streams directly onto the central regions of galaxies. At present, we find little observational evidence for cool infalling material, while evidence supporting the large-scale effects of superwind outflows is strong. This 'pilot' study using faint galaxy spectra demonstrates the potential of using galaxies to trace baryons within galaxies, in the circumgalactic medium, and ultimately throughout the intergalactic medium.
Abstract
We analyze the rest-optical emission-line ratios of star-forming galaxies at 2.7 ≤
z
< 6.5 drawn from the Cosmic Evolution Early Release Science (CEERS) Survey and their relationships with ...stellar mass (
M
*
). Our analysis includes both line ratios based on the N
ii
λ
6583 feature (N
ii
λ
6583/H
α
, (O
iii
λ
5007/H
β
)/(N
ii
λ
6583/H
α
) (O3N2), and N
ii
λ
6583/O
ii
λ
3727) and those featuring
α
-elements (O
iii
λ
5007/H
β
, O
iii
λ
5007/O
ii
λ
3727 (O
32
), (O
iii
λλ
4959, 5007 + O
ii
λ
3727)/H
β
(R
23
), and Ne
iii
λ
3869/O
ii
λ
3727). Given the typical flux levels of N
ii
λ
6583 and Ne
iii
λ
3869, which are undetected in the majority of individual CEERS galaxies at 2.7 ≤
z
< 6.5, we construct composite spectra in bins of
M
*
and redshift. Using these composite spectra, we compare the relationships between emission-line ratios and
M
*
at 2.7 ≤
z
< 6.5 with those observed at lower redshift. While there is significant evolution toward higher excitation (e.g., higher O
iii
λ
5007/H
β
, O
32
, O3N2) and weaker nitrogen emission (e.g., lower N
ii
λ
6583/H
α
and N
ii
λ
6583/O
ii
λ
3727) between
z
∼ 0 and
z
∼ 3, we find in most cases that there is no significant evolution in the relationship between line ratio and
M
*
beyond
z
∼ 3. The Ne
iii
λ
3869/O
ii
λ
3727 ratio is anomalous in showing evidence for significant elevation at 4.0 ≤
z
< 6.5 at fixed mass, relative to
z
∼ 3.3. Collectively, however, our empirical results suggest no significant evolution in the mass–metallicity relationship at 2.7 ≤
z
< 6.5. Representative galaxy samples and metallicity calibrations based on existing and upcoming JWST/NIRSpec observations will be required to translate these empirical scaling relations into ones tracing chemical enrichment and gas cycling and to distinguish among descriptions of feedback in galaxy formation simulations at
z
> 3.
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