arXiv subjects

Glenn G. Kacprzak

Publications and source records attributed to Glenn G. Kacprzak.

At least 37 records · Page 2Linked to original sources

arXiv2025

The formation histories of massive and quiescent galaxies in the 3 < z < 4.5 Universe

We present the formation histories of 19 massive ($>3X10^{10}M_\odot$) quiescent (sSFR$<0.15Gyr^{-1}$) galaxy candidates at z~3.0-4.5 observed using JWST/NIRSpec. This completes the spectroscopic confirmation of the 24 K-selected quiescent galaxy sample from the ZFOURGE and 3DHST surveys (Schreiber et al. 2018a). Utilizing Prism $1-5μm$ spectroscopy, we confirm that all 12 sources that eluded confirmation by ground-based spectroscopy lie at z>3, resulting in a spectroscopically confirmed number density of $\sim1.4X10^{-5}Mpc^{-3}$ between $z\sim3-4$. Rest-frame U-V vs V-J color selections show high effectiveness in identifying quiescent galaxies, with a purity of~90%. Our analysis shows that parametric star-formation histories (SFHs) from FAST++ and binned SFHs from Prospector on average yield consistent results, revealing diverse formation and quenching times. The oldest galaxy formed $~6X10^{10}M_\odot$ by $z\sim10$ and has been quiescent for over 1 Gyr at z~3.2. We detect two galaxies with ongoing star formation and six with active galactic nuclei (AGN). We demonstrate that the choice of stellar population models, stellar libraries, and nebular or AGN contributions does not significantly affect the derived average SFHs of the galaxies. We demonstrate that extending spectral fitting beyond the rest-frame optical regime reduces the inferred average star formation rates in the earliest time bins of the SFH reconstruction. The assumed SFH prior influences the star formation rate at early times, where spectral diagnostic power is limited. Simulated z~3 quiescent galaxies from IllustrisTNG, SHARK, and Magneticum broadly match the average SFHs of the observed sample but struggle to capture the full diversity, particularly at early stages. Our results emphasize the need for mechanisms that rapidly build stellar mass and quench star formation within the first billion years of the Universe.

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arXiv2025

Spatially Resolved Galactic Winds at Cosmic Noon: Outflow Kinematics and Mass Loading in a Lensed Star-Forming Galaxy at $z=1.87$

We study the spatially resolved outflow properties of CSWA13, an intermediate mass ($M_*=10^{9}~\mathrm{M}_{\odot}$), gravitationally lensed star-forming galaxy at $z=1.87$. We use Keck/KCWI to map outflows in multiple rest-frame ultraviolet ISM absorption lines, along with fluorescent Si II$^*$ emission, and nebular emission from C III] tracing the local systemic velocity. The spatial structure of outflow velocity mirrors that of the nebular kinematics, which we interpret to be a signature of a young galactic wind that is pressurizing the ISM of the galaxy but is yet to burst out. From the radial extent of Si II$^*$ emission, we estimate that the outflow is largely encapsulated within $3.5$ kpc. We explore the geometry (e.g., patchiness) of the outflow by measuring the covering fraction at different velocities, finding that the maximum covering fraction is at velocities $v\simeq-150$ km$\,$s$^{-1}$. Using the outflow velocity ($v_{out}$), radius ($R$), column density ($N$), and solid angle ($Ω$) based on the covering fraction, we measure the mass loss rate $\log\dot{m}_{out}/(\mathrm{M}_{\odot}\text{yr}^{-1}) = 1.73\pm0.23$ and mass loading factor $\logη= 0.04\pm0.34$ for the low-ionization outflowing gas in this galaxy. These values are relatively large and the bulk of the outflowing gas is moving with speeds less than the escape velocity of the galaxy halo, suggesting that the majority of outflowing mass will remain in the circumgalactic medium and/or recycle back into the galaxy. The results support a picture of high outflow rates transporting mass and metals into the inner circumgalactic medium, providing the gas reservoir for future star formation.

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arXiv2024

DUVET: sub-kiloparsec resolved star formation driven outflows in a sample of local starbursting disk galaxies

We measure resolved (kiloparsec-scale) outflow properties in a sample of 10 starburst galaxies from the DUVET (Deep near-UV observations of Entrained gas in Turbulent galaxies) sample, using Keck/KCWI observations of H$β$ and [OIII]~$λ$5007. We measure $\sim460$ lines-of-sight that contain outflows, and use these to study scaling relationships of outflow velocity ($v_{\rm out}$), mass-loading factor ($η$; mass outflow rate per SFR) and mass flux ($\dotΣ_{\rm out}$; mass outflow rate per area) with co-located SFR surface density ($Σ_{\rm SFR}$) and stellar mass surface density ($Σ_{\ast}$). We find strong, positive correlations of $\dotΣ_{\rm out} \propto Σ_{\rm SFR}^{1.2}$ and $\dotΣ_{\rm out} \propto Σ_{\ast}^{1.5}$. We also find shallow correlations between $v_{\rm out}$ and both $Σ_{\rm SFR}$ and $Σ_{\ast}$. Our resolved observations do not suggest a threshold in outflows with $Σ_{\rm SFR}$, but rather we find that the local specific SFR ($Σ_{\rm SFR}/Σ_\ast$) is a better predictor of where outflows are detected. We find that outflows are very common above $Σ_{\rm SFR}/Σ_\ast\gtrsim 0.1$~Gyr$^{-1}$ and rare below this value. We argue that our results are consistent with a picture in which outflows are driven by supernovae, and require more significant injected energy in higher mass surface density environments to overcome local gravity. The correlations we present here provide a statistically robust, direct comparison for simulations and higher redshift results from JWST.

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arXiv2024

Detection of gas inflow during the onset of a starburst in a low-mass galaxy at z=2.45

The baryon cycle is crucial for understanding galaxy formation, as gas inflows and outflows vary throughout a galaxy's lifetime and affect its star formation rate. Despite the necessity of accretion for galaxy growth at high redshifts, direct observations of inflowing gas have proven elusive especially at $z\gtrsim2$. We present spectroscopic analysis of a galaxy at redshift $z=2.45$ which exhibits signs of inflow in several ultraviolet interstellar absorption lines, with no clear outflow signatures. The absorption lines are redshifted by $\sim$250 km sec$^{-1}$ with respect to the systemic redshift, and C IV shows a prominent inverse P-Cygni profile. Simple stellar population models suggest that this galaxy has a low metallicity ($\sim$5% solar), with a very young starburst of age $\sim$4 Myr dominating the ultraviolet luminosity. The gas inflow velocity and nebular velocity dispersion suggest an approximate halo mass of order $\sim 10^{11}M_{\odot}$, a regime in which simulations predict that bursty star formation is common at this redshift. We conclude that this system is likely in the beginning of a cycle of bursty star formation, where inflow and star formation rates are high, but where supernovae and other feedback processes have not yet launched strong outflows. In this scenario, we expect the inflow-dominated phase to be observable (e.g., with net redshifted ISM absorption) for only a short timescale after a starburst onset. This result represents a promising avenue for probing the full baryon cycle, including inflows, during the formative phases of low-mass galaxies at high redshifts.

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arXiv2024

Signatures of gas flows-II: Connecting the kinematics of the multiphase circumgalactic medium to galaxy rotation

The multiphase CGM hosts critical processes that affect galaxy evolution such as accretion and outflows. We searched for evidence of these phenomena by using the EW co-rotation fraction ($f_{\rm EWcorot}$) to study the kinematic connection between the multiphase CGM and host galaxy rotation. We examined CGM absorption from HST/COS (including, but not limited to, SiII, CII, SiIII, CIII, and OVI) within $21\leq D\leq~276$ kpc of 27 galaxies. We find the median $f_{\rm EWcorot}$ for all ions is consistent within errors and the $f_{\rm EWcorot}$ increases with increasing N(HI). The $f_{\rm EWcorot}$ of lower ionization gas decreases with increasing $D/R_{\rm vir}$ while OVI and HI are consistent with being flat. The $f_{\rm EWcorot}$ varies minimally as a function of azimuthal angle and is similar for all ions at a fixed azimuthal angle. The larger number of OVI detections enabled us to investigate where the majority of co-rotating gas is found. Highly co-rotating OVI primarily resides along the galaxies' major axis. Looking at the $f_{\rm EWcorot}$ as a function of ionization potential (${d{f_{\rm EWcorot}}}/{d{(eV)}}$), we find a stronger co-rotation signature for lower-ionization gas. There are suggestions of a connection between the CGM metallicity and major axis co-rotation where low-ionization gas with higher $f_{\rm EWcorot}$ exhibits lower metallicity and may trace large-scale filamentary inflows. Higher ionization gas with higher $f_{\rm EWcorot}$ exhibits higher metallicity and may instead trace co-planar recycled gas accretion. Our results stress the importance of comparing absorption originating from a range of ionization phases to differentiate between various gas flow scenarios.

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arXiv2024

An emission map of the disk-circumgalactic medium transition in starburst IRAS 08339+6517

Most of a galaxy's mass is located out to hundreds of kiloparsecs beyond its stellar component. This diffuse reservoir of gas, the circumgalactic medium (CGM), acts as the interface between a galaxy and the cosmic web that connects galaxies. We present kiloparsec-scale resolution integral field spectroscopy of emission lines that trace cool ionized gas from the center of a nearby galaxy to 30 kpc into its CGM. We find a smooth surface brightness profile with a break in slope at twice the 90% stellar radius. The gas also transitions from being photoionized by HII star-forming regions in the disk to being ionized by shocks or the extragalactic UV background at larger distances. These changes represent the boundary between the interstellar medium (ISM) and the CGM, revealing how the dominant reservoir of baryonic matter directly connects to its galaxy.

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arXiv2024

The Carousel Lens: A Well-Modeled Strong Lens with Multiple Lensed Sources

Over the past few years alone, the lensing community has discovered thousands of strong lens candidates, and spectroscopically confirmed hundreds of them. In this time of abundance, it becomes pragmatic to focus our time and resources on the few extraordinary systems, in order to most efficiently study the universe. In this paper, we present such a system: DESI-090.9854-35.9683, a cluster-scale lens at $z_{\rm l} = 0.49$, with seven observed lensed sources around the core, and additional lensed sources further out in the cluster. From the number and the textbook configuration of the lensed images, a tight constraint on the mass potential of the lens is possible. This would allow for detailed analysis on the dark and luminous matter content within galaxy clusters, as well as a probe into dark energy and high-redshift galaxies. We present our spatially resolved kinematic measurements of this system from the Very Large Telescope Multi Unit Spectroscopic Explorer, which confirm five of these source galaxies (in ascending order, at $z_{\rm s} = 0.962, 0.962, 1.166, 1.432,$ and $1.432$). With previous Hubble Space Telescope imaging in the F140W and F200LP bands, we also present a simple two power-law profile flux-based lens model that, for a cluster lens, well models the five lensed arc families with redshifts. We determine the mass to be $M(< θ_{\rm E}) = 4.78\times10^{13} M_{\odot}$ for the primary mass potential. From the model, we extrapolate the redshift of one of the two source galaxies not yet spectroscopically confirmed to be at $z_{\rm s}=4.52^{+1.03}_{-0.71}$.

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arXiv2024

Gravitational Lensing Reveals Cool Gas within 10-20 kpc around a Quiescent Galaxy

While quiescent galaxies have comparable amounts of cool gas in their outer circumgalactic medium (CGM) compared to star-forming galaxies, they have significantly less interstellar gas. However, open questions remain on the processes causing galaxies to stop forming stars and stay quiescent . Theories suggest dynamical interactions with the hot corona prevent cool gas from reaching the galaxy, therefore predicting the inner regions of quiescent galaxy CGMs are devoid of cool gas. However, there is a lack of understanding of the inner regions of CGMs due to the lack of spatial information in quasar-sightline methods. We present integral-field spectroscopy probing 10--20~kpc (2.4--4.8 R\textsubscript{e}) around a massive quiescent galaxy using a gravitationally lensed star-forming galaxy. We detect absorption from Magnesium (MgII) implying large amounts of cool atomic gas (10\textsuperscript{8.4} -- 10\textsuperscript{9.3} M\textsubscript{$\odot$} with T$\sim$10\textsuperscript{4} Kelvin), in comparable amounts to star-forming galaxies. Lens modeling of Hubble imaging also reveals a diffuse asymmetric component of significant mass consistent with the spatial extent of the MgII absorption, and offset from the galaxy light profile. This study demonstrates the power of galaxy-scale gravitational lenses to not only probe the gas around galaxies, but to also independently probe the mass of the CGM due to it's gravitational effect.

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arXiv2024

Signatures of gas flows-I: Connecting the kinematics of the HI circumgalactic medium to galaxy rotation

The CGM hosts many physical processes with different kinematic signatures that affect galaxy evolution. We address the CGM-galaxy kinematic connection by quantifying the fraction of HI that is aligned with galaxy rotation with the equivalent width co-rotation fraction, $f_{\rm EWcorot}$. Using 70 quasar sightlines having HST/COS HI absorption (${12<\log (N(HI)/{\rm cm}^{-2})<20}$) within $5R_{\rm vir}$ of $z<0.6$ galaxies we find that $f_{\rm EWcorot}$ increases with increasing HI column density. $f_{\rm EWcorot}$ is flat at $\sim0.6$ within $R_{\rm vir}$ and decreases beyond $R_{\rm vir}$ to $f_{\rm EWcorot}$$\sim0.35$. $f_{\rm EWcorot}$ also has a flat distribution with azimuthal and inclination angles within $R_{\rm vir}$, but decreases by a factor of two outside of $R_{\rm vir}$ for minor axis gas and by a factor of two for edge-on galaxies. Inside $R_{\rm vir}$, co-rotation dominated HI is located within $\sim 20$ deg of the major and minor axes. We surprisingly find equal amounts of HI absorption consistent with co-rotation along both major and minor axes within $R_{\rm vir}$. However, this co-rotation disappears along the minor axis beyond $R_{\rm vir}$, suggesting that if this gas is from outflows, then it is bound to galaxies. $f_{\rm EWcorot}$ is constant over two decades of halo mass, with no decrease for log(M$_{\rm h}/M_{\odot})>12$ as expected from simulations. Our results suggest that co-rotating gas flows are best found by searching for higher column density gas within $R_{\rm vir}$ and near the major and minor axes.

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arXiv2024

AGEL: Is the Conflict Real? Investigating Galaxy Evolution Models using Strong Lensing at 0.3 < z < 0.9

Observed evolution of the total mass distribution with redshift is crucial to testing galaxy evolution theories. To measure the total mass distribution, strong gravitational lenses complement the resolved dynamical observations currently limited to $z \lesssim 0.5$. Here we present the lens models for a pilot sample of seven galaxy-scale lenses from the ASTRO3D Galaxy Evolution with Lenses (AGEL) survey. The AGEL lenses, modeled using HST/WFC3-F140W images with Gravitational Lens Efficient Explorer (GLEE) software, have deflector redshifts between $0.3 < z_{\rm defl} < 0.9$. Assuming a power-law density profile with slope $γ$, we measure the total density profile for the deflector galaxies via lens modeling. We also measure the stellar velocity dispersions ($σ_{\rm obs}$) for four lenses and obtain $σ_{\rm obs}$ from SDSS-BOSS for the remaining lenses to test our lens models by comparing observed and model-predicted velocity dispersions. For the seven AGEL lenses, we measure an average density profile slope of $-1.95 \pm 0.09$ and a $γ$--$z$ relation that does not evolve with redshift at $z<1$. Although our result is consistent with some observations and simulations, it differs from other studies at $z<1$ that suggest the $γ$--$z$ relation evolves with redshift. The apparent conflicts among observations and simulations may be due to a combination of 1) systematics in the lensing and dynamical modeling; 2) challenges in comparing observations with simulations; and 3) assuming a simple power-law for the total mass distribution. By providing more lenses at $z_{\rm defl} > 0.5$, the AGEL survey will provide stronger constraints on whether the mass profiles evolve with redshift as predicted by current theoretical models.

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arXiv2024

Unveiling the Complex Circumgalactic Medium: A Comparative Study of Merging and Non-Interacting Galaxy Groups

While most galaxies live in group environments where they undergo an accelerated evolution, the characteristics of their circumgalactic medium (CGM) remain uncertain. We present an analysis of the CGM of two galaxy groups in different stages of interaction: (G1) a close pair of galaxies ($z=0.043$) separated by 87 kpc that do not show signs of interactions and (G2) four merging galaxies ($z=0.098$) separated by 10 kpc. We present spatially-resolved Keck/KCWI galaxy observations and HST/COS quasar spectra (G1 at 48 kpc and G2 at 100 kpc away) to quantify both the resolved galaxy and CGM properties in these two different group environments. G1 contains two typical star-forming galaxies with no evidence of strong outflows. G2 contains two star-forming, one post-starburst and one quiescent galaxy. Both groups have a range of CGM detected metal lines (HI, CII, SiII, SiIII, NV and OVI). Despite G2 being twice as far from the quasar, G2 has $\log (N(HI)/{\rm cm}^{-2})=17.33$, compared to $\log (N(HI)/{\rm cm}^{-2})=16.43$ for G1. We find that the CGM of the merging galaxies (G2) is more kinematically complex, is in a higher ionisation state, spans a wider range of metallicities and column densities, has smaller cloud sizes, and is inconsistent with the simple superposition model that seems to match well with G1. We conclude that the complexity of the CGM in merging galaxies surpasses that of not strongly interacting galaxies, suggesting that mergers play a significant role in shaping the intricate structure of the CGM.

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arXiv2024

A massive galaxy that formed its stars at $z \sim 11$

The formation of galaxies by gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental paradigm underpinning modern astrophysics and predicts a strong decline in the number of massive galaxies at early cosmic times. Extremely massive quiescent galaxies (stellar masses $>10^{11}$ M$_\odot$) have now been observed as early as 1-2 billions years after the Big Bang; these are extremely constraining on theoretical models as they form 300-500 Myr earlier and only some models can form massive galaxies this early. Here we report on the spectroscopic observations with the James Webb Space Telescope of a massive quiescent galaxy ZF-UDS-7329 at redshift 3.205 $\pm$ 0.005 that eluded deep ground-based spectrscopy, is significantly redder than typical and whose spectrum reveals features typical of much older stellar populations. Detailed modelling shows the stellar population formed around 1.5 billion years earlier in time (z ~ 11) at an epoch when dark matter halos of sufficient hosting mass have not yet assembled in the standard scenario. This observation may point to the presence of undetected populations of early galaxies and the possibility of significant gaps in our understanding of early stellar populations, galaxy formation and/or the nature of dark matter.

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arXiv2024

DUVET: Resolved direct metallicity measurements in the outflow of starburst galaxy NGC 1569

We present the results of direct-method metallicity measurements in the disk and outflow of the low-metallicity starburst galaxy NGC 1569. We use Keck Cosmic Web Imager observations to map the galaxy across 54$\arcsec$ (800 pc) along the major axis and 48$\arcsec$ (700 pc) along the minor axis with a spatial resolution of 1$\arcsec$ ($\sim$15 pc). We detect common strong emission lines ([\ion{O}{III}] $λ$5007, H$β$, [\ion{O}{II}] $λ$3727) and the fainter [\ion{O}{III}] $λ$4363 auroral line, which allows us to measure electron temperature ($T_e$) and metallicity. Theory suggests that outflows drive metals out of the disk driving observed trends between stellar mass and gas-phase metallicity. Our main result is that the metallicity in the outflow is similar to that of the disk, $Z_{\rm out} / Z_{\rm ISM} \approx 1$. This is consistent with previous absorption line studies in higher mass galaxies. Assumption of a mass-loading factor of $\dot{M}_{\rm out}/{\rm SFR}\sim3$ makes the metal-loading of NGC 1569 consistent with expectations derived from the mass-metallicity relationship. Our high spatial resolution metallicity maps reveal a region around a supermassive star cluster (SSC-B) with distinctly higher metallicity and higher electron density, compared to the disk. Given the known properties of SSC-B the higher metallicity and density of this region are likely the result of star formation-driven feedback acting on the local scale. Overall, our results are consistent with the picture in which metal-enriched winds pollute the circumgalactic medium surrounding galaxies, and thus connect the small-scale feedback processes to large-scale properties of galaxy halos.

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arXiv2024

Cloud-by-cloud Multiphase Investigation of the Circumgalactic Medium of Low-redshift Galaxies

The pervasive presence of warm gas in galaxy halos suggests that the circumgalactic medium (CGM) is multiphase in its ionization structure and complex in its kinematics. Some recent state-of-the-art cosmological galaxy simulations predict an azimuthal dependence of CGM metallicities. We investigate the presence of such a trend by analyzing the distribution of gas properties in the CGM around 47 $z <$ 0.7 galaxies from the Multiphase Galaxy Halos Survey determined using a cloud-by-cloud, multiphase, ionization modelling approach. We identify three distinct populations of absorbers: cool clouds ($T \sim$ 10$^{4.1}$ K) in photoionization equilibrium, warm-hot collisionally ionized clouds ($T \sim$ 10$^{4.5-5}$ K) affected by time-dependent photoionization, and hotter clouds ($T \sim$ 10$^{5.4-6}$ K) with broad OVI and Lya absorption consistent with collisional ionization. We find that fragmentation can play a role in the origin of cool clouds, that warm-hot clouds are out of equilibrium due to rapid cooling, and that hotter clouds are representative of virialized halo gas in all but the lowest mass galaxies. The metallicities of clouds do not depend on the azimuthal angle or other galaxy properties for any of these populations. At face value, this disagrees with the simplistic model of the CGM with bipolar outflows and cold-mode planar accretion. However, the number of clouds per sightline is significantly larger close to the minor and major axes. This implies that the processes of outflows and accretion are contributing to these CGM cloud populations, and our sightlines are probing gas of mixed origins at all azimuthal angles in these low redshift galaxies.

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arXiv2024

MOSEL survey: Spatially offset Lyman-continuum emission in a new emitter at z=3.088

We present the discovery of a unique Lyman-continuum (LyC) emitter at z=3.088. The LyC emission were detected using the Hubble Space Telescope (HST) WFC3/UVIS F336W filter, covering a rest-frame wavelength range of 760-900 Angstrom. The peak signal-to-noise ratio (SNR) of LyC emission is 3.9 in a r=0.24'' aperture and is spatially offset by 0.29''+/-0.04'' (~ 2.2+/-0.3 kpc) from the rest-UV emission peak (F606W). By combining imaging and spectroscopic data from the James Webb Space Telescope (JWST) JADES, FRESCO and JEMS surveys, along with VLT/MUSE data from the MXDF survey, we estimate that the probability of random alignment with an interloper galaxy causing the LyC emission is less than 6x10^-5. The interstellar medium (ISM) conditions in the galaxy are similar to other LyC emitters at high redshift (12+log(O/H)=7.79+/-0.06, logU =-3.27+/-0.14, O32 = 3.65+/-0.22), although the single-peaked Lyman-alpha profile and lack of rest-UV emission lines suggest an optically thick ISM. We think that LyC photons are leaking through a narrow cone of optically thin neutral ISM, most likely created by a past merger (as evidenced by medium-band F210M and F182M images). Using the escape fraction constraints from individual leakers and a simple model, we estimate that the opening half-angle of ionization cones can be as low as 16^deg (2% ionised fraction) to reproduce some of the theoretical constraints on the average escape fraction for galaxies. The narrow opening angle required can explain the low number density of confirmed LyC leakers.

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arXiv2024

The Mass Density of MgII Absorbers from the Australian Dark Energy Survey

We present an all-southern sky survey for MgII doublet absorbers in 951 z < 4 AGN/quasar spectra from the Australian Dark Energy Survey (OzDES). The spectral resolution ranges from R = 1400-1700 over the wavelengths 3700 A-8800 A. The survey has a 5sigma detection completeness of 50% and above for rest-frame equivalent widths W_r(2796) >= 0.3 A. We studied 656 MgII absorption systems over the redshift range 0.33 < z < 2.19 with equivalent widths 0.3 < W_r(2796) < 3.45 A. The equivalent width distribution is well fit by an exponential function with W* = 0.76 +/- 0.04 A and the redshift path density exhibits very little evolution. Overall, our findings are consistent with the large, predominantly northern-sky, surveys of MgII absorbers. We developed and implemented a Monte Carlo model informed by a high-resolution MgII survey for determining the MgII mass density, Omega_MgII. We found Omega_MgII ~ 5 x 10^-7 with no evidence of evolution over a ~7 Gyr time span following Cosmic Noon. Incorporating measurements covering 2.0 < z < 6.4 from the literature, we extended our insights into MgII mass density evolution from the end of reionization well past the Cosmic Noon epoch. The presented Monte Carlo model has potential for advancing our knowledge of the evolution of mass densities of metal-ions common to quasar absorption line studies, as it exploits the efficiency of large low-resolution surveys while requiring only small samples from expensive high-resolution surveys.

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arXiv2024

A population of faint, old, and massive quiescent galaxies at 3 < z < 4 revealed by JWST NIRSpec Spectroscopy

Here we present a sample of 12 massive quiescent galaxy candidates at z~3-4 observed with the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These galaxies were pre-selected from the Hubble Space Telescope imaging and 10 of our sources were unable to be spectroscopically confirmed by ground based spectroscopy. By combining spectroscopic data from NIRSpec with multi-wavelength imaging data from the JWST Near Infrared Camera (NIRCam), we analyse their stellar populations and their formation histories. We find that all of our galaxies classify as quiescent based on the reconstruction of their star formation histories but show a variety of quenching timescales and ages. All our galaxies are massive ($\sim0.1-1.2 \times 10^{11} M\odot$), with masses comparable to massive galaxies in the local Universe. We find that the oldest galaxy in our sample formed $\sim1.0\times10^{11} M\odot$ of mass within the first few hundred million years of the Universe and has been quenched for more than a billion years by the time of observation at z$\sim$3.2 ($\sim$2 billion years after the Big Bang). Our results point to very early formation of massive galaxies requiring a high conversion rate of baryons to stars in the early Universe.

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arXiv2023

MOSEL survey: JWST reveals major mergers/strong interactions drive the extreme emission lines in the early universe

Extreme emission line galaxies (EELGs), where nebular emissions contribute 30-40% of the flux in certain photometric bands, are ubiquitous in the early universe (z>6). We utilise deep NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to investigate the properties of companion galaxies (projected distance <40 kpc, |dv|<10,000 km/s) around EELGs at z~3. Tests with TNG100 simulation reveal that nearly all galaxies at z=3 will merge with at least one companion galaxy selected using similar parameters by z=0. The median mass ratio of the most massive companion and the total mass ratio of all companions around EELGs is more than 10 times higher than the control sample. Even after comparing with a stellar mass and stellar mass plus specific SFR-matched control sample, EELGs have three-to-five times higher mass ratios of the brightest companion and total mass ratio of all companions. Our measurements suggest that EELGs are more likely to be experiencing strong interactions or undergoing major mergers irrespective of their stellar mass or specific SFRs. We suspect that gas cooling induced by strong interactions and/or major mergers could be triggering the extreme emission lines, and the increased merger rate might be responsible for the over-abundance of EELGs at z>6.

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