Abstract
Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFRs) and fueling of ...active galactic nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive (
M
*
> 10
10
M
⊙
) major (1 <
M
1
/
M
2
< 4) spectroscopic galaxy pairs at 0.5 <
z
< 3.0 with Δ
V
< 5000 km s
−1
(1000 km s
−1
) and projected separation <150 kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of
1.23
−
0.09
+
0.08
in the closest projected separation bin (<25 kpc) relative to a stellar mass-, redshift-, and environment-matched control sample of isolated galaxies. We find that the level of SFR enhancement is a factor of ∼1.5 higher at 0.5 <
z
< 1 than at 1 <
z
< 3 in the closest projected separation bin. Among a sample of visually identified mergers, we find an enhancement of a factor of
1.86
−
0.18
+
0.29
(∼3
σ
) for coalesced systems. For this visually identified sample, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40
−
0.37
+
0.62
versus
1.58
−
0.20
+
0.29
for 0.5 <
z
< 1.6 and 1.6 <
z
< 3.0, respectively). The SFR enhancements seen in our interactions and mergers are all lower than the level seen in local samples at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.
ABSTRACT
We present 10 main-sequence ALPINE galaxies (log (M/M⊙) = 9.2−11.1 and ${\rm SFR}=23-190\, {\rm M_{\odot }\, yr^{-1}}$) at z ∼ 4.5 with optical O ii measurements from Keck/MOSFIRE ...spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multiwavelength sample at these redshifts, combining various measurements in the ultraviolet, optical, and far-infrared including C ii158 $\mu$m line emission and dust continuum from ALMA and H α emission from Spitzer photometry. For the first time, this unique sample allows us to analyse the relation between O ii and total star-formation rate (SFR) and the interstellar medium (ISM) properties via O ii/C ii and O ii/H α luminosity ratios at z ∼ 4.5. The O ii−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around $50{{\ \rm per\ cent}}$ solar. To explain the measured dust-corrected luminosity ratios of $\log (L_{\rm OII}/L_{\rm CII}) \sim 0.98^{+0.21}_{-0.22}$ and $\log (L_{\rm OII}/L_{\rm H\alpha }) \sim -0.22^{+0.13}_{-0.15}$ for our sample, ionization parameters log (U) < −2 and electron densities $\log (\rm n_e / {\rm cm^{-3}}) \sim 2.5-3$ are required. The former is consistent with galaxies at z ∼ 2−3, however lower than at z > 6. The latter may be slightly higher than expected given the galaxies’ specific SFR. The analysis of this pilot sample suggests that typical log (M/M⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the epoch of reionization at z > 6.
Abstract
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at
z
= 3–9 using early James Webb Space Telescope (JWST) ...CEERS NIRCam observations. Our sample consists of 850 galaxies at
z
> 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at
z
> 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at
z
= 3, and this fraction drops to ∼30% at
z
= 6–9, while galaxies with spheroids make up ∼30%–40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%–50%), while those that are purely irregular increases from ∼12% to ∼20% at
z
> 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.
Abstract
We present rest-frame optical emission-line flux ratio measurements for five
z
> 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 ...Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable
relative
flux calibration of emission lines that are closely separated in wavelength, despite the uncertain
absolute
spectrophotometry of the current version of the reductions. Compared to
z
∼ 3 galaxies in the literature, the
z
> 5 galaxies have similar O
iii
λ
5008/H
β
ratios, similar O
iii
λ
4364/H
γ
ratios, and higher (∼0.5 dex) Ne
III
λ
3870/O
II
λ
3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured Ne
III
λ
3870/O
II
λ
3728, O
iii
λ
4364/H
γ
, and O
iii
λ
5008/H
β
emission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization (
log
(
Q
)
≃
8
−
9
, units of cm s
−1
), low metallicity (
Z
/
Z
⊙
≲ 0.2), and very high pressure (
log
(
P
/
k
)
≃
8
−
9
, units of cm
−3
). The combination of O
iii
λ
4364/H
γ
and O
iii
λ
(4960 + 5008)/H
β
line ratios indicate very high electron temperatures of
4.1
<
log
(
T
e
/
K
)
<
4.4
, further implying metallicities of
Z
/
Z
⊙
≲ 0.2 with the application of low-redshift calibrations for “
T
e
-based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn.
Abstract
The study of galaxy evolution hinges on our ability to interpret multiwavelength galaxy observations in terms of their physical properties. To do this, we rely on spectral energy ...distribution (SED) models, which allow us to infer physical parameters from spectrophotometric data. In recent years, thanks to wide and deep multiwave band galaxy surveys, the volume of high-quality data have significantly increased. Alongside the increased data, algorithms performing SED fitting have improved, including better modeling prescriptions, newer templates, and more extensive sampling in wavelength space. We present a comprehensive analysis of different SED-fitting codes including their methods and output with the aim of measuring the uncertainties caused by the modeling assumptions. We apply 14 of the most commonly used SED-fitting codes on samples from the CANDELS photometric catalogs at
z
∼ 1 and
z
∼ 3. We find agreement on the stellar mass, while we observe some discrepancies in the star formation rate (SFR) and dust-attenuation results. To explore the differences and biases among the codes, we explore the impact of the various modeling assumptions as they are set in the codes (e.g., star formation histories, nebular, dust and active galactic nucleus models) on the derived stellar masses, SFRs, and
A
V
values. We then assess the difference among the codes on the SFR–stellar mass relation and we measure the contribution to the uncertainties by the modeling choices (i.e., the modeling uncertainties) in stellar mass (∼0.1 dex), SFR (∼0.3 dex), and dust attenuation (∼0.3 mag). Finally, we present some resources summarizing best practices in SED fitting.
Galaxy interactions and mergers are thought to play an important role in the evolution of galaxies. Studies in the nearby universe show a higher fraction of active galactic nuclei (AGNs) in ...interacting and merging galaxies than in their isolated counterparts, indicating that such interactions are important contributors to black hole growth. To investigate the evolution of this role at higher redshifts, we have compiled the largest known sample of major spectroscopic galaxy pairs (2381 with ΔV < 5000 km s−1) at 0.5 < z < 3.0 from observations in the COSMOS and CANDELS surveys. We identify X-ray and IR AGNs among this kinematic pair sample, a visually identified sample of mergers and interactions, and a mass-, redshift-, and environment-matched control sample for each in order to calculate AGN fractions and the level of AGN enhancement as a function of relative velocity, redshift, and X-ray luminosity. While we see a slight increase in AGN fraction with decreasing projected separation, overall, we find no significant enhancement relative to the control sample at any separation. In the closest projected separation bin (< 25 kpc, ΔV < 1000 km s−1), we find enhancements of a factor of and for X-ray and IR-selected AGNs, respectively. While we conclude that galaxy interactions do not significantly enhance AGN activity on average over 0.5 < z < 3.0 at these separations, given the errors and the small sample size at the closest projected separations, our results would be consistent with the presence of low-level AGN enhancement.
A complete understanding of how galaxies form and evolve over cosmic time remains a fundamental goal of astrophysics. Several key processes drive galaxy evolution, all of which require further ...investigation to fully constrain and understand how they combine to affect the life cycles and evolution of galaxies into the forms we observe today. With three closely related, but independent projects my PhD research provides valuable insight into understanding the processes driving star formation in the early universe through an analysis of the gas content, distribution, and the bulk motion of the gas in star forming galaxies at high redshift. In my first project we investigated for the first time the ISM properties of high-z galaxy population via the currently largest sample of 10 typical main-sequence galaxies at z∼4.5 with optical OII measurements from Keck/MOSFIRE spectroscopy and Subaru/MOIRCS narrow-band imaging. I find that the OII−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around 50% solar. The analysis of this pilot sample suggests that typical log(M/M⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the Epoch of Reionization at z > 6. For my second project we provide a detailed analysis of a massive, M∗ = 1.31 ± 0.20 x1011 M⊙, star forming galaxy at z=2.47 using resoled CO(3-2) ALMA observations, MOSFIRE Hα spectroscopy, and ancillary data. We find that our galaxy although originally thought to be a starburst galaxy from the Herschel data, is a highly obscured main sequence galaxy with an AGN fraction of 0.6. In my final project we aim to place constraints on merger activity through a kinematic analysis of Hα emission of starburst galaxies at z∼1.5 observed with MOSFIRE on the Keck telescope. From these data I was able to reduce 37 masks of 9 nights of observations, which resulted in the measurement of spectroscopic redshifts for 217 galaxies both on and above the galaxy main sequence. Visual morphological analysis on an initial selection of these galaxies show that the morphology is overall regular with a mixture of disks and spheroids, with evidence of a few possible merging systems.
Abstract The Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey program was designed specifically to include Near Infrared Slitless Spectroscopic observations (NGDEEP-NISS) to ...detect multiple emission lines in as many galaxies as possible and across a wide redshift range using the Near Infrared Imager and Slitless Spectrograph. We present early results obtained from the first set of observations (Epoch 1, 50% of the allocated orbits) of this program (NGDEEP-NISS1). Using a set of independently developed calibration files designed to deal with a complex combination of overlapping spectra, multiple position angles, and multiple cross filters and grisms, in conjunction with a robust and proven algorithm for quantifying contamination from overlapping dispersed spectra, NGDEEP-NISS1 has achieved a 3 σ sensitivity limit of 2 × 10 −18 erg s −1 cm −2 . We demonstrate the power of deep wide field slitless spectroscopy (WFSS) to characterize the star formation rates, and metallicity (O iii /H β ), and dust content, of galaxies at 1 < z < 3.5. The latter showing intriguing initial results on the applicability and assumptions made regarding the use of Case B recombination. Further, we identify the presence of active galactic nuclei and infer the mass of their supermassive black holes using broadened restframe Mg ii and H β emission lines. The spectroscopic results are then compared with the physical properties of galaxies extrapolated from fitting spectral energy distribution models to photometry alone. The results clearly demonstrate the unique power and efficiency of WFSS at near-infrared wavelengths over other methods to determine the properties of galaxies across a broad range of redshifts.
Abstract We present the first results from the Web Epoch of Reionization Ly α Survey (WERLS), a spectroscopic survey of Ly α emission using Keck I/MOSFIRE and LRIS. WERLS targets bright ( J < 26) ...galaxy candidates with photometric redshifts of 5.5 ≲ z ≲ 8 selected from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11 z ∼ 7–8 Ly α emitters (LAEs; three secure and eight tentative candidates) detected in the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield is ∼13%, which is broadly consistent with expectations assuming some loss from redshift uncertainty, contamination from sky OH lines, and that the Universe is approximately half-ionized at this epoch, whereby observable Ly α emission is unlikely for galaxies embedded in a neutral intergalactic medium. Our targets are selected to be UV-bright, and span a range of absolute UV magnitudes with −23.1 < M UV < −19.8. With two LAEs detected at z = 7.68, we also consider the possibility of an ionized bubble at this redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for pinpointing beacons of reionization and mapping the large-scale distribution of mass relative to the ionization state of the Universe.
We analyze the evolution of massive (log$_{10}$ $M_\star/M_\odot$ $>10$)
galaxies at $z \sim$ 4--8 selected from the JWST Cosmic Evolution Early Release
Science (CEERS) survey. We infer the physical ...properties of all galaxies in the
CEERS NIRCam imaging through spectral energy distribution (SED) fitting with
dense basis to select a sample of high redshift massive galaxies. Where
available we include constraints from additional CEERS observing modes,
including 18 sources with MIRI photometric coverage, and 28 sources with
spectroscopic confirmations from NIRSpec or NIRCam wide-field slitless
spectroscopy. We sample the recovered posteriors in stellar mass from SED
fitting to infer the volume densities of massive galaxies across cosmic time,
taking into consideration the potential for sample contamination by active
galactic nuclei (AGN). We find that the evolving abundance of massive galaxies
tracks expectations based on a constant baryon conversion efficiency in dark
matter halos for $z \sim$ 1--4. At higher redshifts, we observe an excess
abundance of massive galaxies relative to this simple model. These higher
abundances can be explained by modest changes to star formation physics and/or
the efficiencies with which star formation occurs in massive dark matter halos,
and are not in tension with modern cosmology.
![The ALPINE-ALMA [C ii ] su...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711_1365-8711_1365-2966/small "The ALPINE-ALMA [C ii ] survey: Investigation of 10 galaxies at z ∼ 4.5 with [O ii ] and [C ii ] line emission − ISM properties and [O ii ]−SFR relation")
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