arXiv subjects

Alison L. Coil

Publications and source records attributed to Alison L. Coil.

At least 19 recordsLinked to original sources

arXiv2026

What becomes of JWST/NIRCam-selected high-redshift massive galaxies?

Early JWST/NIRCam surveys revealed a puzzling population of high-redshift massive galaxy candidates largely absent from previous rest-frame UV surveys. Spectroscopic follow-up has both confirmed and contested these candidates, whose potential overabundance may challenge traditional models of galaxy formation. In this study we evaluate the reliability of the photometric selections used to identify these candidates in observational data by applying them to galaxies in the TNG300 simulation with synthetic dust-attenuated photometry. Among the five observational selection criteria considered, we find that the selection presented by P\'erez-Gonz\'alez et al. is the most reliable and inclusive. Nevertheless, only 1 of the 18 galaxies at $z\sim5$ with $M_{\star} \geq 10^{11}~\mathrm{M_{\odot}}$ in the simulation satisfies this selection; the remaining 17 galaxies are on average $\sim0.5$ mag bluer than the color selection under the adopted dust model. We construct an improved JWST/NIRCam color-magnitude selection that provides a more complete census of massive galaxies at $z\sim5$ in TNG300 while excluding dusty, low-mass galaxies identified by criteria from the observational literature. We investigate the descendants of the most massive NIRCam-selected galaxies at $z=7,~4,$ and $2$ in TNG300, finding that they rarely evolve into the most massive galaxies by $z=0$. In general only the high-redshift massive galaxies that undergo substantial late-time ($z\lesssim0.2$) merger-driven growth become the most massive galaxies in the Universe today. Together these results suggest that current observational JWST/NIRCam selections are not identifying the most massive high-redshift galaxies, and caution against interpreting high-redshift massive galaxies as direct progenitors of the most massive galaxies at $z=0$.

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arXiv2026

Astronomical Advantages of a Boost Mission to Facilitate HST Science into the 2030s: Imaging the Circumgalactic Medium of Galaxies

We present the case for imaging ultraviolet line emission from highly ionized metals and HI Lya in the circumgalactic medium of galaxies, should the Hubble Space Telescope receive an orbital boost. Hubble can uniquely probe emission lines with ionization potentials between 13 and 200 electron-volts (Lya, CIV, OVI, NeVIII, etc). Spatial mapping of the diffuse material traced by these transitions is critical to constraining the physics of feedback and the energetic exchange between galaxies and their circumgalactic environments, as well as basic morphologies of the dominant mass component. Deep high-resolution mapping of these features will not be possible with any other observatory, existing or planned, until HWO is launched, which leaves HST as a critical observatory to test key science drivers for HWO. If HST receives an orbital boost, it can (a) provide the first statistical constraints on the spatial distribution of warm-hot CGM and (b) provide important avenues for science case development, as well as target/pointing selection, for HWO's upcoming spectroscopic facilities.

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arXiv2026

A Shocked Wind Interpretation of an Odd Radio Circle

Odd Radio Circles (ORCs) are a new class of extragalactic object, with large rings of faint radio continuum emission typically spanning 100s of kpc; their origins are unknown. Previous optical spectroscopy of the central galaxy in ORC4, a classic isolated ORC, revealed spatially-extended ionized gas with strong [OII] emission and line ratios consistent with LINER emission. We present new Keck/KCWI+KCRM integral field spectroscopy covering multiple strong optical emission lines to measure the extent, morphology, and spatially-resolved kinematics and line ratios of the ionized and neutral gas in the ORC4 central galaxy. We find that [OII] is the strongest optical emission line in this massive, old galaxy, and the [OII] emission is detected to larger radial extent than the other optical lines. The gas kinematics show strong spatial asymmetries, high velocity gradients (>100 km/s), and high velocity dispersion (~200 km/s). The emission line ratios are most consistent with shock models with shock velocities of ~200-300 km/s and are not fit well by stellar or AGN photoionization models. These findings are consistent with a model in which the gas in the ORC4 central galaxy is the result of shock ionization in and around the central galaxy, likely due to mixing and cooling of gas associated with the event that created the large-scale radio ring of emission that identified this source as an ORC.

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arXiv2025

Star Formation Histories and Stellar Dynamics in the Central Galaxies of RX J0820.9+0752, A1835, and PKS 0745-191

We present Keck Cosmic Web Imager observations of stellar populations in three galaxies lying at the centers of cooling flow clusters. All three host rich molecular gas reservoirs and show prominent Balmer absorption from $30-100$ Myr-old stars consistent with long lasting star formation. Two systems, A1835 and PKS 0745$-$191, have spatially extended young stellar populations in their centers with recent star formation rates of 100 M$_{\odot}$ yr$^{-1}$ and 8 M$_{\odot}$ yr$^{-1}$, respectively. In A1835 we uncover a blueshifted clump of young stars moving at high speed with respect to the gas and central galaxy. We suggest these stars formed in a gaseous outflow and have since detached from their natal gas and are now falling inward. This result indicates that star formation is proceeding in a dynamically complex environment shaped by the central galaxy's motion relative to cooling clouds and the feedback from radio jets. In RX J0820.9+0752 intermediate-age stars are found in a filament outside the nucleus with no discernible star formation at the center of the galaxy. All projected galaxies consist of old stellar populations with deep D4000 breaks and lack detectable warm gas. While they may interact gravitationally with the central galaxy, they cannot have donated the upward of $10^{10}~ M_{\odot}$ of molecular gas found in these systems. These results highlight the importance of analyzing spatially resolved stellar kinematics and star formation histories in brightest cluster galaxies, an approach that remains relatively understudied.

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arXiv2025

A XRISM Observation of the Archetypal Radio-Mode Feedback System Hydra-A: Measurements of Atmospheric Motion and Constraints on Turbulent Dissipation

We present XRISM Resolve observations centered on Hydra-A, a redshift z = 0.054 brightest cluster galaxy which hosts one of the largest and most powerful FR-I radio sources in the nearby Universe. We examine the effects of its high jet power on the velocity structure of the cluster's hot atmosphere. Hydra-A's central radio jets have inflated X-ray cavities with energies upward of $10^{61}$ erg. They reach altitudes of 225 kpc from the cluster center, well beyond the atmosphere's central cooling region. Resolve's $3\times3$ arcmin field-of-view covers $190\times190$ kpc, which encompasses most of the cooling volume. We find a one dimensional atmospheric velocity dispersion across the volume of $164\pm10$ km/s. The fraction in isotropic turbulence or unresolved bulk velocity is unknown. Assuming pure isotropic turbulence, the turbulent kinetic energy is $2.5 \%$ of the thermal energy radiated away over the cooling timescale, implying that kinetic energy must be supplied continually to offset cooling. While Hydra-A's radio jets are powerful enough to supply kinetic energy to the atmosphere at the observed level, turbulent dissipation alone would struggle to offset cooling throughout the cooling volume. The central galaxy's radial velocity is similar to the atmospheric velocity, with an offset of $-37 \pm 23$ km/s.

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arXiv2025

JWST Discovery of Warm Dust in the Circumgalactic Medium of the Makani Galaxy

We report the detection of near- and mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs) out to ~ 35 kpc in the Makani Galaxy, a compact massive galaxy with a record-breaking 100-kpc scale starburst-driven wind at redshift z = 0.459. The NIRCam and MIRI observations with JWST take advantage of a coincidental match between the PAH spectral features at 3.3, 7.7, and (11.3 + 12.2) microns in Makani and the bandpasses of the MIRI and NIRCam filters. The warm dust is not only detected in the cool-gas tracers of the galactic wind associated with the more recent (7 Myr) starburst episode, but also in the outer warm-ionized gas wind produced by the older (0.4 Gyr) episode. The presence of PAHs in the outer wind indicates that the PAHs have survived the long (R/v ~ 10^8 yrs) journey to the halo despite the harsh environment of the galactic wind. The measured F1800W/F1130W flux ratios in the unresolved nucleus, inner halo (R = 10 - 20 kpc), and outer halo (R = 20 - 35 kpc), tracers of the PAH (11.3 + 12.2)/7.7 ratios, indicate decreasing starlight intensity incident on the PAHs, decreasing PAH sizes, and increasing PAH ionization fractions with increasing distance from the nucleus. These data provide the strongest evidence to date that the ejected dust of galactic winds survives the long journey to the CGM, but is eroded along the way.

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arXiv2025

Selection of Dwarf Galaxies Hosting AGNs: A Measure of Bias and Contamination using Unsupervised Machine Learning Techniques

Identifying AGNs in dwarf galaxies is critical for understanding black hole formation but remains challenging due to their low luminosities, low metallicities, and star formation-driven emission that can obscure AGN signatures. Machine learning (ML) techniques, particularly unsupervised methods, offer new ways to address these challenges by uncovering patterns in complex data. In this study, we apply Self-Organizing Maps (SOMs) to explore the SED manifold of dwarf galaxies and evaluate AGN selection biases across diagnostics. We train a 51 by 51 SOM on 30,344 dwarf galaxies (redshift less than 0.055 and stellar mass below 10 to the 9.5 solar masses) from the NSA catalog using nine-band photometry from near-UV to mid-infrared. A set of 438 previously identified dwarf AGNs, selected via various methods, was mapped onto the SOM. AGNs identified by different methods occupy distinct and partially overlapping regions in SED space, reflecting selection biases tied to host properties. BPT selected AGNs cluster in higher-mass regions, while X-ray and variability-selected AGNs show broader distributions. WISE-selected AGNs are concentrated in lower-mass regions and form two clumps: one associated with bluer, starburst-like systems and the other with redder, more AGN-like SEDs. This separation may help distinguish true AGN hosts from starburst contaminants in WISE-selected samples. AGNs selected via traditional emission-line, broad-line, and WISE methods tend to avoid SOM regions linked to strong star formation. In contrast, a subset of AGNs in low-mass galaxies occupy regions indicative of high AGN luminosity relative to stellar content, highlighting luminous AGNs in faint hosts. These results demonstrate the utility of manifold learning for improving AGN selection in the low-mass regime.

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arXiv2025

Quantifying the Impact of Incompleteness on Identifying and Interpreting Galaxy Protocluster Populations with the TNG-Cluster Simulation

We use the TNG-Cluster simulation to investigate how stellar mass and star formation rate (SFR) incompleteness affect the identification of density peaks within galaxy protoclusters at different redshifts. Our analysis focuses on a sample of $352$ protoclusters, defined as the progenitor populations of galaxies that reside within the virialized region of $z=0$ clusters with $M_{\rm{200}}^{z=0}\sim10^{14.3-15.5}~{\rm M}_{\odot}$. For comparison, we define our "baseline" protocluster population as galaxies with ${M}_{\star}> 10^{8.5}~{\rm M}_{\odot}$ at any redshift. We find that ${M}_{\star}$-limited (${M}_{\star} > 10^{9.5}~{\rm M}_{\odot}$) and SFR-limited ($\rm{SFR} > 10~{\rm M}_{\odot} \mathrm{yr}^{-1}$) subpopulations recover the baseline highest galaxy density peak in roughly $\sim60\%$ of cases within an accuracy of $1.0$ pMpc (corresponding to an angular scale of $\sim 2-2.5$ arcmin) at $z > 2$. This recovery fraction drops to $\sim40-50\%$ when restricting to galaxies with ${M}_{\star} > 10^{10.0}~{\rm M}_{\odot}$. We find that the baseline highest galaxy density peaks typically coincide with the highest dark matter and stellar mass density peaks, with separations less than $0.5$ pMpc in $\sim60-75\%$ of cases at $z>2$. This agreement drops to $\sim45-50\%$ when restricting to galaxies with ${M}_{\star} > 10^{10.0}~{\rm M}_{\odot}$. These results indicate that identifying the densest regions of protoclusters -- i.e., the core -- is highly sensitive to stellar mass and SFR completeness limits. Nevertheless, at $z>2$ we find that the baseline highest galaxy density peaks are generally sites of enhanced star formation and accelerated mass growth relative to the remainder of the protocluster, consistent with some observational studies.

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arXiv2025

Velocity Structure Correlations between the Nebular, Molecular, and Atmospheric Gases in the Cores of Four Cool Core Clusters

We investigate the velocity structure of nebular gas in the central galaxies of four clusters: Abell 1835, PKS 0745-191, Abell 262, and RXJ0820.9+0752, using data from the Keck Cosmic Web Imager (KCWI). Velocity structure functions (VSFs) of the [OII] emission line are compared to VSFs of molecular clouds observed with the Atacama Large Millimeter/submillimeter Array (ALMA). Apart from Abell 262 where the gas is located in a circumnuclear disk, the nebular gas in the remaining galaxies lies in off-nuclear filamentary structures with VSFs steeper than the Kolmogorov slope. This steepening may be plausibly attributed to gravity although other factors, such as magnetic stresses and bulk motion,} may be significant. The VSFs of CO and [OII] emission are similar in RXJ0820 and Abell 262, indicating close coupling of the nebular and molecular gases. In contrast, the nebular and molecular gases are differentiated on most scales in PKS 0745 and Abell 1835. This discrepancy is likely due to the radio-AGN churning the gas. We compare the scale-dependent velocity amplitudes of the hot atmospheres constrained by X-ray surface brightness fluctuation analysis using Chandra observations to the nebular VSFs. The large-scale consistency in Abell 1835 and RXJ0820 is consistent with condensation from the hot atmospheres. {We explore substantial systematic biases, including projection effects, windowing, and smoothing effects when comparing VSFs using different telescopes and instruments.

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arXiv2024

The importance of gas starvation in driving satellite quenching in galaxy groups at $z\sim 0.8$

We present results from a Keck/DEIMOS survey to study satellite quenching in group environments at $z \sim 0.8$ within the Extended Groth Strip (EGS). We target $11$ groups in the EGS with extended X-ray emission. We obtain high-quality spectroscopic redshifts for group member candidates, extending to depths over an order of magnitude fainter than existing DEEP2/DEEP3 spectroscopy. This depth enables the first spectroscopic measurement of the satellite quiescent fraction down to stellar masses of $\sim 10^{9.5}~{\rm M}_{\odot}$ at this redshift. By combining an infall-based environmental quenching model, constrained by the observed quiescent fractions, with infall histories of simulated groups from the IllustrisTNG100-1-Dark simulation, we estimate environmental quenching timescales ($τ_{\mathrm{quench}}$) for the observed group population. At high stellar masses (${M}_{\star}=10^{10.5}~{\rm M}_{\odot}$) we find that $τ_{\mathrm{quench}} = 2.4\substack{+0.2 \\ -0.2}$ Gyr, which is consistent with previous estimates at this epoch. At lower stellar masses (${M}_{\star}=10^{9.5}~{\rm M}_{\odot}$), we find that $τ_{\mathrm{quench}}=3.1\substack{+0.5 \\ -0.4}$ Gyr, which is shorter than prior estimates from photometry-based investigations. These timescales are consistent with satellite quenching via starvation, provided the hot gas envelope of infalling satellites is not stripped away. We find that the evolution in the quenching timescale between $0 \lt z \lt 1$ aligns with the evolution in the dynamical time of the host halo and the total cold gas depletion time. This suggests that the doubling of the quenching timescale in groups since $z\sim1$ could be related to the dynamical evolution of groups or a decrease in quenching efficiency via starvation with decreasing redshift.

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arXiv2024

Diverse pathways for supermassive black hole-galaxy coevolution

Supermassive black holes (SMBHs) are observed in diverse galaxy populations across time yet a clear understanding of how they coevolve with their hosts has not been reached. Physically-motivated models of SMBH accretion and feedback vary widely between galaxy formation simulations due to the difficulty of modeling the range of scales important for galactic and SMBH processes. Here we use observational data to build an empirical model for SMBH growth. We apply observed specific accretion rate probability distributions as a function of galaxy star formation rate between $z = 0-2$ to the UniverseMachine galaxy formation model to determine SMBH accretion rates based on galaxy properties. We use observed $z = 0$ SMBH-stellar mass relations for the quiescent and star-forming populations to provide the local boundary conditions for SMBH growth histories. We then track the coevolutionary histories of galaxy stellar mass and their SMBHs backwards in time to $z = 2$. We find that the most massive SMBHs at $z = 0$ have grown very little of their total mass between $z = 0-2$, indicating early SMBH mass assembly for these systems. Conversely, lower mass SMBHs at $z = 0$ assembled their mass gradually across $z = 0-2$. This results in substantial evolution of the SMBH-stellar mass relation, shifting to higher normalization and shallower slope with increasing redshift. We find that the substantial scatter observed in the $z = 0$ SMBH-stellar mass relation results in the diversity of growth pathways found in our model, with some galaxies assembling their stellar mass before their SMBHs and others doing the opposite.

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arXiv2024

X-ray AGN in Boötes: The lack of growth of the most massive black holes since z=4

Supermassive Black Holes (BHs) are known to efficiently grow through gas accretion, but even sustained and intense mass build-up through this mechanism struggles to explain the assembly of the most massive BHs observed in the local Universe. Using the Chandra Deep-Wide Field Survey (CDFWS) in the Boötes field, we measure BH--galaxy assembly in massive galaxies ($M_\star\gtrsim10^{10}\rm M_\odot$) through the AGN fraction and specific Black Hole accretion rate (sBHAR) distribution as a function of redshift and stellar mass. We determine stellar masses and star formation rates for a parent sample of optically selected galaxies as well as those with X-ray detections indicating the presence of an AGN through Spectral Energy Distribution (SED) fitting. We derive a redshift-dependent mass completeness limit and extract X-ray information for every galaxy as to provide a comprehensive picture of the AGN population in massive galaxies. While X-ray AGN samples are dominated by moderately massive host galaxies of $M_{\star} \geqslant 10^{10}\rm M_{\odot}$, we do not find a strong stellar mass dependence in AGN fraction (to limits in sBHAR), indicating a bias towards massive galaxies in the observed samples. We derive BH-galaxy growth tracks over time, which reveal that while most BH mass has been accumulated since $z=4$ for lower mass BHs, the assembly of the most massive BHs is more complex, with little to no relative mass gain since $z=4$, implying that rapid and intense growth episodes prior to $z=4$ were necessary to form these massive BHs.

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arXiv2024

Application of Manifold Learning to Selection of Different Galaxy Populations and Scaling Relation Analysis

The growing volume of data produced by large astronomical surveys necessitates the development of efficient analysis techniques capable of effectively managing high-dimensional datasets. This study addresses this need by demonstrating some applications of manifold learning and dimensionality reduction techniques, specifically the Self-Organizing Map (SOM), on the optical+NIR SED space of galaxies, with a focus on sample comparison, selection biases, and predictive power using a small subset. To this end, we utilize a large photometric sample from the five CANDELS fields and a subset with spectroscopic measurements from the KECK MOSDEF survey in two redshift bins at $z\sim1.5$ and $z\sim2.2$. We trained SOM with the photometric data and mapped the spectroscopic data onto it as our study case. We found that MOSDEF targets do not cover all SED shapes existing in the SOM. Our findings reveal that Active Galactic Nuclei (AGN) within the MOSDEF sample are mapped onto the more massive regions of the SOM, confirming previous studies and known selection biases towards higher-mass, less dusty galaxies. Furthermore, SOM were utilized to map measured spectroscopic features, examining the relationship between metallicity variations and galaxy mass. Our analysis confirmed that more massive galaxies exhibit lower [OIII]/H$β$ and [OIII]/[OII] ratios and higher H$α$/H$β$ ratios, consistent with the known mass-metallicity relation. These findings highlight the effectiveness of SOM in analyzing and visualizing complex, multi-dimensional datasets, emphasizing their potential in data-driven astronomical studies.

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arXiv2024

Complex Velocity Structure of Nebular Gas in Active Galaxies Centred in Cooling X-ray Atmospheres

[OII] emission maps obtained with the Keck Cosmic Web Imager (KCWI) are presented for four galaxies centered in cooling X-ray cluster atmospheres. Nebular emission extending tens of kpc is found in systems covering a broad range of atmospheric cooling rates, cluster masses, and dynamical states. Abell 262's central galaxy hosts a kpc-scale disk. The nebular gas in RXJ0820.9+0752 is offset and redshifted with respect to the central galaxy by $10-20$ kpc and 150 km s$^{-1}$, respectively. The nebular gases in PKS 0745-191 and Abell 1835 are being churned to higher velocity dispersion by X-ray bubbles and jets. The churned gas is enveloped by larger scale, lower velocity dispersion (quiescent) nebular emission. The mean line-of-sight speeds of the churned gas, quiescent gas, and the central galaxy each differ by up to $\sim 150$ km s$^{-1}$; nebular speeds upward of $800$ km s$^{-1}$ are found. Gases with outwardly-rising speeds upward of several hundred km s$^{-1}$ are consistent with being advected behind and being lifted by the rising bubbles. The peculiar motion between the galaxy, nebular gas, and perhaps the hot atmosphere from which it presumably condensed is affecting the bubble dynamics, and may strongly affect thermally unstable cooling, the dispersal of jet energy, and the angular momentum of gas accreting onto the galaxies and their nuclear black holes.

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arXiv2024

Stacking and Analyzing $z\approx 2$ MOSDEF Galaxies by Spectral Types: Implications for Dust Geometry and Galaxy Evolution

We examine star-formation and dust properties for a sample of 660 galaxies at $1.37\leq z\leq 2.61$ in the MOSDEF survey by dividing them into groups with similarly-shaped spectral energy distributions (SEDs). For each group, we combine the galaxy photometry into a finely-sampled composite SED, and stack their spectra. This method enables the study of more complete galaxy samples, including galaxies with very faint emission lines. We fit these composite SEDs with Prospector to measure the stellar attenuation and SED-based star-formation rates (SFRs). We also derive emission-line properties from the spectral stacks, including Balmer decrements, dust-corrected SFRs, and metallicities. We find that stellar attenuation correlates most strongly with mass, while nebular attenuation correlates strongly with both mass and SFR. Furthermore, the excess of nebular compared to stellar attenuation correlates most strongly with SFR. The highest SFR group has 2 mag of excess nebular attenuation. Our results are consistent with a model in which star-forming regions become more dusty as galaxy mass increases. To explain the increasing excess nebular attenuation, we require a progressively larger fraction of star formation to occur in highly-obscured regions with increasing SFR. This highly-obscured star formation could occur in dusty clumps or central starbursts. Additionally, as each galaxy group represents a different evolutionary stage, we study their locations on the UVJ and SFR-mass diagrams. As mass increases, metallicity and dust attenuation increase, while sSFR decreases. However, the most massive group moves towards the quiescent region of the UVJ diagram, while showing less obscuration, potentially indicating removal of dust.

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arXiv2024

The Outflowing [OII] Nebulae of Compact Starburst Galaxies at z $\sim$ 0.5

High-velocity outflows are ubiquitous in compact, massive (M$_* \sim$ 10$^{11}$ M$_{\odot}$), z $\sim$ 0.5 galaxies with extreme star formation surface densities ($Σ_{SFR} \sim$ 2000 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$). We have previously detected and characterized these outflows using MgII absorption lines. To probe their full extent, we present Keck/KCWI integral field spectroscopy of the [OII] and MgII emission nebulae surrounding all of the 12 galaxies in this study. We find that [OII] is more effective than MgII in tracing low surface brightness, extended emission in these galaxies. The [OII] nebulae are spatially extended beyond the stars, with radial extent R$_{90}$ between 10 and 40 kpc. The nebulae exhibit non-gravitational motions, indicating galactic outflows with maximum blueshifted velocities ranging from -335 to -1920 km s$^{-1}$. The outflow kinematics correlate with the bursty star formation histories of these galaxies. Galaxies with the most recent bursts of star formation (within the last $<$ 3 Myr) exhibit the highest central velocity dispersions ($σ>$ 400 km s$^{-1}$), while the oldest bursts have the lowest-velocity outflows. Many galaxies exhibit both high-velocity cores and more extended, slower-moving gas indicative of multiple outflow episodes. The slower, larger outflows occurred earlier and have decelerated as they propagate into the CGM and mix on timescales $>$ 50 Myr.

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arXiv2024

Ly$α$ Halo Properties and Dust in the Circumgalactic Medium of $z \sim 2$ Star-forming Galaxies

We present Keck Cosmic Web Imager IFU observations around extended Ly$α$ halos of 27 typical star-forming galaxies with redshifts $2.0 < z < 3.2$ drawn from the MOSFIRE Deep Evolution Field survey. We examine the average Ly$α$ surface-brightness profiles in bins of star-formation rate (SFR), stellar mass ($M_*$), age, stellar continuum reddening, SFR surface density ($\rm Σ_{SFR}$), and $\rm Σ_{SFR}$ normalized by stellar mass ($\rm Σ_{sSFR}$). The scale lengths of the halos correlate with stellar mass, age, and stellar continuum reddening; and anti-correlate with star-formation rate, $\rm Σ_{SFR}$, and $\rm Σ_{sSFR}$. These results are consistent with a scenario in which the down-the-barrel fraction of Ly$α$ emission is modulated by the low-column-density channels in the ISM, and that the neutral gas covering fraction is related to the physical properties of the galaxies. Specifically, we find that this covering fraction increases with stellar mass, age, and $E(B-V)$; and decreases with SFR, $\rm Σ_{SFR}$ and $\rm Σ_{sSFR}$. We also find that the resonantly scattered Ly$α$ emission suffers greater attenuation than the (non-resonant) stellar continuum emission, and that the difference in attenuation increases with stellar mass, age, and stellar continuum reddening, and decreases with $\rm Σ_{sSFR}$. These results imply that more reddened galaxies have more dust in their CGM.

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arXiv2024

The MOSDEF Survey: Properties of Warm Ionised Outflows at $z=$ 1.4-3.8

We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field survey to investigate the kinematics and energetics of ionised gas outflows. Using a sample of 598 star-forming galaxies at redshift 1.4 < $z$ < 3.8, we decompose $\rm{H}α$ and [OIII] emission lines into narrow and broad components, finding significant detections of broad components in 10% of the sample. The ionised outflow velocity from individual galaxies appears independent of galaxy properties, such as stellar mass, star-formation rate (SFR), and star-formation-rate surface density ($Σ_{\rm SFR}$). Adopting a simple outflow model, we estimate the mass-, energy- and momentum-loading factors of the ionised outflows, finding modest values with averages of 0.33, 0.04, and 0.22, respectively. The larger momentum- than energy-loading factors, for the adopted physical parameters, imply that these ionised outflows are primarily momentum-driven. We further find a marginal correlation (2.5$σ$) between the mass-loading factor and stellar mass in agreement with predictions by simulations, scaling as $η_{m}$ $\propto M_{\star}^{-0.45}$. This shallow scaling relation is consistent with these ionised outflows being driven by a combination of mechanical energy generated by supernovae explosions and radiation pressure acting on dusty material. In a majority of galaxies, the outflowing material does not appear to have sufficient velocity to escape the gravitational potential of their host, likely recycling back at later times. Together, these results suggest that the ionised outflows traced by nebular emission lines are negligible, with the bulk of mass and energy carried out in other gaseous phases.

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