Abstract
We investigate the nature of the relation among stellar mass, star formation rate, and gas-phase metallicity (the
–SFR–
Z
relation) at high redshifts using a sample of 260 star-forming ...galaxies at
z
∼ 2.3 from the MOSDEF survey. We present an analysis of the high-redshift
–SFR–
Z
relation based on several emission-line ratios for the first time. We show that a
–SFR–
Z
relation clearly exists at
z
∼ 2.3. The strength of this relation is similar to predictions from cosmological hydrodynamical simulations. By performing a direct comparison of stacks of
z
∼ 0 and
z
∼ 2.3 galaxies, we find that
z
∼ 2.3 galaxies have ∼0.1 dex lower metallicity at fixed
and SFR. In the context of chemical evolution models, this evolution of the
–SFR–
Z
relation suggests an increase with redshift of the mass-loading factor at fixed
, as well as a decrease in the metallicity of infalling gas that is likely due to a lower importance of gas recycling relative to accretion from the intergalactic medium at high redshifts. Performing this analysis simultaneously with multiple metallicity-sensitive line ratios allows us to rule out the evolution in physical conditions (e.g., N/O ratio, ionization parameter, and hardness of the ionizing spectrum) at fixed metallicity as the source of the observed trends with redshift and with SFR at fixed
at
z
∼ 2.3. While this study highlights the promise of performing high-order tests of chemical evolution models at high redshifts, detailed quantitative comparisons ultimately await a full understanding of the evolution of metallicity calibrations with redshift.
We use extensive spectroscopy from the MOSFIRE Deep Evolution Field survey to investigate the relationships between rest-frame optical emission line equivalent widths (W) and a number of galaxy and ...interstellar medium (ISM) characteristics for a sample of 1134 star-forming galaxies at redshifts 1.4 z 3.8. We examine how the equivalent widths of , , λλ4960, 5008, + Hβ, , and , depend on stellar mass, UV slope, age, star formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 and /Hβ), gas-phase metallicity, and ionizing photon production efficiency ( ion). The trend of increasing W with decreasing stellar mass is strongest for (and +Hβ). More generally, the equivalent widths of all the lines increase with redshift at a fixed stellar mass or fixed gas-phase metallicity, suggesting that high equivalent width galaxies are common at high redshift. This redshift evolution in equivalent widths can be explained by the increase in SFR and decrease in metallicity with redshift at a fixed stellar mass. Consequently, the dependence of W on sSFR is largely invariant with redshift, particularly when examined for galaxies of a given metallicity. Our results show that high equivalent width galaxies, specifically those with high , have low stellar masses, blue UV slopes, young ages, high sSFRs, ISM line ratios indicative of high ionization parameters, high ion, and low metallicities. As these characteristics are often attributed to galaxies with high ionizing escape fractions, galaxies with high W are likely candidates for the population that dominates cosmic reionization.
We investigate the infrared (IR) contribution from supermassive black hole activity versus host galaxy emission in the mid- to far-IR spectrum for a large sample of X-ray bright active galactic ...nuclei (AGN) residing in dusty, star-forming host galaxies. We select 703 AGN with erg s−1 at 0.1 < z < 5 from the Chandra XBoötes X-ray Survey with rich multiband observations in the optical to far-IR. This is the largest sample to date of X-ray AGN with mid- and far-IR detections that uses spectral energy distribution (SED) decomposition to determine intrinsic AGN and host galaxy IR luminosities. We determine weak or nonexistent relationships when averaging star formation activity as a function of AGN activity, but see stronger positive trends when averaging LX in bins of star-forming activity for AGN at low redshifts. We estimate an average dust covering factor (CF) of 33% based on IR SEDs and bolometric AGN luminosity, corresponding to a Type 2 AGN population of roughly a third. We also see a population of AGN that challenge the inclination-based unification model with individual dust CFs that contradict the nuclear obscuration expected from observed X-ray hardness ratios. We see no strong connection between AGN fractions in the IR and corresponding total IR, 24 m, or X-ray luminosities. The average rest-frame AGN contribution as a function of IR wavelength shows significant (∼80%) contributions in the mid-IR that trail off at λ > 30 m. Additionally, we provide a relation between observed LX and pure AGN IR output for high-z AGN, allowing future studies to estimate AGN IR contribution using only observed X-ray flux density estimates.
Using data from the MOSFIRE Deep Evolution Field (MOSDEF) survey, we present a census of active galactic nucleus (AGN)-driven ionized outflows in a sample of 159 AGNs at 1.4 ≤ z ≤ 3.8. The sample ...spans AGN bolometric luminosities of 1044-47 erg s−1 and includes both quiescent and star-forming galaxies extending across 3 orders of magnitude in stellar mass. We identify and characterize outflows from the Hβ, O iii, H , and N ii emission line spectra. We detect outflows in 17% of the AGNs, seven times more often than in a mass-matched sample of inactive galaxies in MOSDEF. The outflows are fast and galaxy-wide, with velocities of ∼400-3500 km s and spatial extents of 0.3-11.0 kpc. The incidence of outflows among AGNs is independent of the stellar mass of the host galaxy, with outflows detected in both star-forming and quiescent galaxies. This suggests that outflows exist across different phases in galaxy evolution. We investigate relations between outflow kinematic, spatial, and energetic properties and both AGN and host galaxy properties. Our results show that AGN-driven outflows are widespread in galaxies along the star-forming main sequence. The mass-loading factors of the outflows are typically 0.1-1 and increase with AGN luminosity, capable of exceeding unity at . In these more luminous sources, the ionized outflow alone is likely sufficient to regulate star formation and, when combined with outflowing neutral and molecular gas, may be able to quench star formation in their host galaxies.
ABSTRACT
We present detections of O iii λ4363 and direct-method metallicities for star-forming galaxies at z = 1.7–3.6. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) ...survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at z > 1, spanning 7.5 < 12+log(O/H) < 8.2 and log(M*/M⊙) = 7–10. We find that strong-line calibrations based on local analogues of high-redshift galaxies reliably reproduce the metallicity of the z > 1 sample on average. We construct the first mass–metallicity relation at z > 1 based purely on direct-method O/H, finding a slope that is consistent with strong-line results. Direct-method O/H evolves by ≲0.1 dex at fixed M* and star formation rate from z ∼ 0 to 2.2. We employ photoionization models to constrain the ionization parameter and ionizing spectrum in the high-redshift sample. Stellar models with supersolar O/Fe and binary evolution of massive stars are required to reproduce the observed strong-line ratios. We find that the z > 1 sample falls on the z ∼ 0 relation between ionization parameter and O/H, suggesting no evolution of this relation from z ∼ 0 to z ∼ 2. These results suggest that the offset of the strong-line ratios of this sample from local excitation sequences is driven primarily by a harder ionizing spectrum at fixed nebular metallicity compared to what is typical at z ∼ 0, naturally explained by supersolar O/Fe at high redshift caused by rapid formation time-scales. Given the extreme nature of our z > 1 sample, the implications for representative z ∼ 2 galaxy samples at ∼1010 M⊙ are unclear, but similarities to z > 6 galaxies suggest that these conclusions can be extended to galaxies in the epoch of reionization.
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.
Abstract
Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field survey, we investigate the role of the local environment in the gas-phase metallicity of galaxies. The local environment ...measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, N
ii
λ
6584 and H
α
, we measure gas-phase oxygen abundances of 167 galaxies at 1.37 ≤
z
≤ 1.7 and 303 galaxies at 2.09 ≤
z
≤ 2.61, located in diverse environments. We find that at
z
∼ 1.5, the average metallicity of galaxies in overdensities with
M
*
∼ 10
9.8
M
⊙
, 10
10.2
M
⊙,
and 10
10.8
M
⊙
is higher relative to their field counterparts by 0.094 ± 0.051, 0.068 ± 0.028, and 0.052 ± 0.043 dex, respectively. However, this metallicity enhancement does not exist at higher redshift,
z
∼ 2.3, where, compared to the field galaxies, we find 0.056 ± 0.043, 0.056 ± 0.028, and 0.096 ± 0.034 dex lower metallicity for galaxies in overdense environments with
M
*
∼ 10
9.8
M
⊙
, 10
10.2
M
⊙
and 10
10.7
M
⊙
, respectively. Our results suggest that, at 1.37 ≤
z
≤ 2.61, the variation of mass–metallicity relation with local environment is small (<0.1 dex), and reverses at
z
∼ 2. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the universe evolves to lower redshifts (
z
≲ 2), the shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.
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 constrain the emission mechanisms responsible for the prodigious electromagnetic output generated by active galactic nuclei (AGNs) and their host galaxies with a novel state-of-the-art ...AGN radio-to-X-ray spectral energy distribution model fitting code (ARXSED). ARXSED combines multiple components to fit the spectral energy distributions (SEDs) of AGNs and their host galaxies. Emission components include radio structures such as lobes and jets, infrared emission from the AGN torus, visible-to-X-ray emission from the accretion disk, and radio-to-ultraviolet emission from the host galaxy. Applying ARXSED to the radio SEDs of 20 3CRR quasars at 1 <
z
< 2 verifies the need for more than a simple power law when compact radio structures are present. The nonthermal emission contributes 91%–57% of the observed-frame 1.25 mm to 850
μ
m flux, and this component must be accounted for when using these wavelengths to estimate star formation properties. We predict the presence of strong radio-linked X-ray emission in more than half the sample sources. ARXSED estimates median (and the associated first and third quartile ranges) BH mass of
2.9
1.7
6.0
×
10
9
M
☉
, logarithm of Eddington ratio of
−
1.0
−
1.2
−
0.6
, and spin of
0.98
0.94
0.99
for our sample. The inferred AGN torus and accretion disk parameters agree with those estimated from spectroscopic analyses of similar samples in the literature. We present the median intrinsic SED of the luminous radio-loud quasars at 1 <
z
≲ 2; this SED represents a significant improvement in the way each component is modeled.
Abstract While supermassive black holes (SMBHs) are widely observed in the nearby and distant Universe, their origin remains debated with two viable formation scenarios with light and heavy seeds. In ...the light seeding model, the seed of the first SMBHs form from the collapse of massive stars with masses of 10–100 M ⊙ , while the heavy seeding model posits the formation of 10 4–5 M ⊙ seeds from direct collapse. The detection of SMBHs at redshifts z ≳ 10, edging closer to their formation epoch, provides critical observational discrimination between these scenarios. Here, we focus on the JWST-detected galaxy, GHZ 9, at z ≈ 10 that is lensed by the foreground cluster, A2744. Based on 2.1 Ms deep Chandra observations, we detect a candidate X-ray active galactic nucleus (AGN), which is spatially coincident with the high-redshift galaxy, GHZ 9. The SMBH candidate is inferred to have a bolometric luminosity of ( 1.0 − 0.4 + 0.5 ) × 10 46 erg s − 1 , which corresponds to a black hole (BH) mass of ( 8.0 − 3.2 + 3.7 ) × 10 7 M ⊙ assuming Eddington-limited accretion. This extreme mass at such an early cosmic epoch suggests the heavy seed origin for this BH candidate. Based on the Chandra and JWST discoveries of extremely high-redshift quasars, we have constructed the first simple AGN luminosity function extending to z ≈ 10. Comparison of this luminosity function with theoretical models indicates an overabundant z ≈ 10 SMBH population, consistent with a higher-than-expected seed formation efficiency.
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