arXiv subjects

J. Xavier Prochaska

Publications and source records attributed to J. Xavier Prochaska.

At least 73 records · Page 4Linked to original sources

arXiv2024

Investigating the sightline of a highly scattered FRB through a filamentary structure in the local Universe

Fast radio bursts (FRBs) are unique probes of extragalactic ionized baryonic structure as each signal, through its burst properties, holds information about the ionized matter it encounters along its sightline. FRB 20200723B is a burst with a scattering timescale of $τ_\mathrm{400\,MHz} >$1 second at 400 MHz and a dispersion measure of DM $\sim$ 244 pc cm$^{-3}$. Observed across the entire CHIME/FRB frequency band, it is the single-component burst with the largest scattering timescale yet observed by CHIME/FRB. The combination of its high scattering timescale and relatively low dispersion measure present an uncommon opportunity to use FRB 20200723B to explore the properties of the cosmic web it traversed. With an $\sim$arcminute-scale localization region, we find the most likely host galaxy is NGC 4602 (with PATH probability $P(O|x)=0.985$), which resides $\sim$30 Mpc away within a sheet filamentary structure on the outskirts of the Virgo Cluster. We place an upper limit on the average free electron density of this filamentary structure of $\langle n_e \rangle < 4.6^{+9.6}_{-2.0} \times 10^{-5}$ cm$^{-3}$, broadly consistent with expectations from cosmological simulations. We investigate whether the source of scattering lies within the same galaxy as the FRB, or at a farther distance from an intervening structure along the line of sight. Comparing with Milky Way pulsar observations, we suggest the scattering may originate from within the host galaxy of FRB 20200723B.

astro-ph.HE↗

arXiv2024

The Metallicity Mapping of the Ionized Diffuse Gas at the Milky Way Disk-halo Interface

Metals in the diffuse, ionized gas at the boundary between the Milky Way's interstellar medium (ISM) and circumgalactic medium (CGM), known as the disk-halo interface (DHI), are valuable tracers of the feedback processes that drive the Galactic fountain. However, metallicity measurements in this region are challenging due to obscuration by the Milky Way ISM and uncertain ionization corrections that affect the total hydrogen column density. In this work, we constrain the ionization corrections to neutral hydrogen column densities using precisely measured electron column densities from the dispersion measure of pulsars that lie in the same globular clusters as UV-bright targets with high-resolution absorption spectroscopy. We address the blending of absorption lines with the ISM by jointly fitting Voigt profiles to all absorption components. We present our metallicity estimates for the DHI of the Milky Way based on detailed photoionization modeling to the absorption from ionized metal lines and ionization-corrected total hydrogen columns. Generally, the gas clouds show a large scatter in metallicity, ranging between $0.04-3.2\ Z_{\odot}$, implying that the DHI consists of a mixture of gaseous structures having multiple origins. We estimate the inflow and outflow timescales of the DHI ionized clouds to be $6 - 35$ Myr. We report the detection of an infalling cloud with super-solar metallicity that suggests a Galactic fountain mechanism, whereas at least one low-metallicity outflowing cloud ($Z < 0.1\ Z_{\odot}$) poses a challenge for Galactic fountain and feedback models.

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arXiv2024

MAMMOTH-Subaru. II. Diverse Populations of Circumgalactic Ly$α$ Nebulae at Cosmic Noon

Circumgalactic Lyman-alpha (Ly$α$) nebulae are gaseous halos around galaxies exhibiting luminous extended Ly$α$ emission. This work investigates Ly$α$ nebulae from deep imaging of $\sim12~\mathrm{deg}^2$ sky, targeted by the MAMMOTH-Subaru survey. Utilizing the wide-field capability of Hyper Suprime-Cam (HSC), we present one of the largest blind Ly$α$ nebula selections, including QSO nebulae, Ly$α$ blobs, and radio galaxy nebulae down to typical $2σ$ Ly$α$ surface brightness of $(5-10)\times10^{-18}\mathrm{~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$. The sample contains 117 nebulae with Ly$α$ sizes of 40 - 400 kpc, and the most gigantic one spans about 365 kpc, referred to as the Ivory Nebula. Combining multiwavelength data, we investigate diverse nebula populations and associated galaxies. We find a small fraction of Ly$α$ nebulae have QSOs ($\sim7\%$), luminous infrared galaxies ($\sim1\%$), and radio galaxies ($\sim 2\%$). Remarkably, among the 28 enormous Ly$α$ nebulae (ELANe) exceeding 100 kpc, about 80\% are associated with UV-faint galaxies ($M_\mathrm{UV} > -22$), categorized as Type II ELANe. We underscore that Type II ELANe constitute the majority but remain largely hidden in current galaxy and QSO surveys. Dusty starburst and obscured AGN activity are proposed to explain the nature of Type II ELANe. The SED of stacking all Ly$α$ nebulae also reveals signs of massive dusty star-forming galaxies with obscured AGNs. We propose a model to explain the dusty nature where the diverse populations of Ly$α$ nebulae capture massive galaxies at different evolutionary stages undergoing violent assembling. Ly$α$ nebulae provide critical insights into the formation and evolution of today's massive cluster galaxies at cosmic noon.

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arXiv2024

The Environments of Fast Radio Bursts Viewed Using Adaptive Optics

We present GeMS/GSAOI observations of five fast radio burst (FRB) host galaxies with sub-arcsecond localizations. We examine and quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 r_e and in fainter regions of the host. When combined with the FRB sample from Mannings et al. (2021), we find that FRBs are statistically distinct from Ca-rich transients in terms of light and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, in combination with the combined FRB sample trace the distribution of stellar mass, points towards a possible similarity of the environments of CC-SNe and FRBs. We also find that 4/5 FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to the spiral structure of their hosts, with a median distance of 0.53 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes.

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arXiv2024

FRB Line-of-sight Ionization Measurement From Lightcone AAOmega Mapping Survey: the First Data Release

This paper presents the first public data release (DR1) of the FRB Line-of-sight Ionization Measurement From Lightcone AAOmega Mapping (FLIMFLAM) Survey, a wide field spectroscopic survey targeted on the fields of 10 precisely localized Fast Radio Bursts (FRBs). DR1 encompasses spectroscopic data for 10,468 galaxy redshifts across 10 FRBs fields with z<0.4, covering approximately 26 deg^2 of the sky in total. FLIMFLAM is composed of several layers, encompassing the `Wide' (covering ~ degree or >10 Mpc scales), `Narrow', (several-arcminute or ~ Mpc) and integral field unit (`IFU'; ~ arcminute or ~ 100 kpc ) components. The bulk of the data comprise spectroscopy from the 2dF-AAOmega on the 3.9-meter Anglo-Australian Telescope, while most of the Narrow and IFU data was achieved using an ensemble of 8-10-meter class telescopes. We summarize the information on our selected FRB fields, the criteria for target selection, methodologies employed for data reduction, spectral analysis processes, and an overview of our data products. An evaluation of our data reveals an average spectroscopic completeness of 48.43%, with over 80% of the observed targets having secure redshifts. Additionally, we describe our approach on generating angular masks and calculating the target selection functions, setting the stage for the impending reconstruction of the matter density field.

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arXiv2024

Extremes of Dissolved Oxygen in the California Current System

Dissolved oxygen (DO) is a non-conservative tracer of interactions at the air-sea interface, respiration and photosynthesis, and advection. In this manuscript, we study extremes in the degree of oxygen saturation (SO), the ratio of DO to the maximum concentration given the water's temperature, salinity, and depth with SO=1 critically saturated. We perform the analysis with the California Underwater Glider Network (CUGN), which operates gliders on four lines that extend from the California coast to several hundred kilometers offshore, profiling to 500m depth every 3km. Since ~2017, the gliders have been equipped with a Sea-Bird 63 optode sensor to measure the DO content. We find that parcels with SO>1.1, hyperoxic extrema, occur primarily near-shore in the upper 50m of the water column and during non-winter months. Along Line 90 which originates in San Diego, these hyperoxic events occur primarily in stratified waters with shallow mixed layers. We hypothesize that photosynthesis elevates DO in sub-surface water that can not rapidly ventilate with the surface. Along the three other lines, hyperoxic extrema occur almost exclusively at the surface and are correlated with elevated Chl-a fluorescence suggesting they are primarily driven by blooms of photosynthesis. We also examine hypoxic extrema, finding that parcels with SO<0.9 and z<50m occur most frequently along the northernmost line where upwelling has greatest impact.

physics.ao-ph↗

arXiv2024

On the Peril of Inferring Phytoplankton Properties from Remote-Sensing Observations

Since 1978, sensors on remote-sensing satellites have provided global, multi-band images at optical wavelengths to assess ocean color. In parallel, sophisticated radiative transfer models account for attenuation and emission by the Earth's atmosphere and ocean, thereby estimating the water-leaving radiance or and remote-sensing reflectance Rrs. From these Rrs measurements, estimates of the absorption and scattering by seawater are inferred. We emphasize an inherent, physical degeneracy in the radiative transfer equation that relates Rrs to the absorption and backscattering coefficients a and b_b, aka inherent optical properties (IOPs). Because Rrs depends solely on the ratio of b_b to a, meaning one cannot retrieve independent functions for the non-water IOPs, a_nw and b_bnw, without a priori knowledge. Moreover, water generally dominates scattering at blue wavelengths and absorption at red wavelengths, further limiting retrievals of IOPs in the presence of noise. We demonstrate that all previous and current multi-spectral satellite observations lack the statistical power to measure more than 3 parameters total to describe a_nw and b_bnw. Due to the ubiquitous exponential-like absorption by color dissolved organic matter at short wavelengths (l<500nm), multi-spectral Rrs do not permit the detection of phytoplankton absorption a_ph without very strict priors. Furthermore, such priors lead to biased and uncertain retrievals of a_ph. Hyperspectral observations may recover a 4th and possibly 5th parameter describing only one or two aspects of the complexity of a_ph. These results cast doubt on decades of literature on IOP retrievals, including estimates of phytoplankton growth and biomass. We further conclude that NASA/PACE will greatly enhance our ability to measure the phytoplankton biomass of Earth, but challenges remain in resolving the IOPs.

physics.ao-ph↗

arXiv2024

A New Measurement of the Mean Transmitted Flux in the Lyman-alpha and Lyman-beta Forest

We present new measurements of the mean transmitted flux in the hydrogen Ly$\rm α$ and a relative transmitted flux measurement in Ly$\rm β$ using 27,008 quasar spectra from the Fourteenth Data Release (DR14) of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). Individual spectra are first combined into 16 composites with mean redshifts in the range of $2.8 \rm{4.0}$ on $τ_{\rm{Lyα}}$, and our determinations of $Δτ_{\rm{Lyβ}}$, are dominated by systematic errors, likely arising from bias and uncertainties in estimates of the quasar continuum. Our $τ_{\rm{Lyα}}$ values show a smooth increase by a factor of 5 over the redshift range $z=2.4-4.4$.

astro-ph.GA↗

arXiv2024

The COS-Holes Survey: Connecting Galaxy Black Hole Mass with the State of the CGM

We present an analysis of \textit{HST}/COS/G160M observations of CIV in the inner circumgalactic medium (CGM) of a novel sample of eight z$\sim$0, L$\approx$L$^{\star}$ galaxies, paired with UV-bright QSOs at impact parameters ($R_\mathrm{proj}$) between 25-130 kpc. The galaxies in this stellar-mass-controlled sample (log$_{10}$M$_{\star}$/M$_{\odot}$ $\sim$ 10.2-10.9 M$_{\odot}$) host super-massive black holes (SMBHs) with dynamically-measured masses spanning log$_{10}$M$_\mathrm{BH}$/M$_{\odot}$ $\sim$ 6.8-8.4; this allows us to compare our results with models of galaxy formation where the integrated feedback history from the SMBH alters the CGM over long timescales. We find that the \ion{C}{IV} column density measurements (N$_{\rm C IV}$) (average log$_{10}$N$_{\rm C IV, CH}$ = 13.94$\pm$0.09 cm$^{-2}$) are largely consistent with existing measurements from other surveys of N$_{\rm C IV}$ in the CGM (average log$_{10}$N$_{\rm C IV, Lit}$ = 13.90$\pm$0.08 cm$^{-2}$), but do not show obvious variation as a function of the SMBH mass. In contrast, specific star-formation rate (sSFR) is highly correlated with the ionized content of the CGM. We find a large spread in sSFR for galaxies with log$_{10}$M$_\mathrm{BH}$/M$_{\odot}$ $>$ 7.0, where the CGM \ion{C}{IV} content shows clear dependence on galaxy sSFR but not M$_\mathrm{BH}$. Our results do not indicate an obvious causal link between CGM CIV and the mass of the galaxy's SMBH; however through comparisons to the EAGLE, Romulus25, $\&$ IllustrisTNG simulations, we find that our sample is likely too small to constrain such causality.

astro-ph.GA↗

arXiv2024

Probing the impact of radio-mode feedback on the properties of the cool circumgalactic medium

We explore the influence of radio-mode feedback on the properties of the cool circumgalactic medium (CGM). To this end, we assemble a statistical sample of approximately 30,000 radio galaxies with background quasars by combining optical spectroscopic measurements of luminous red galaxies (LRGs) and quasars from the year 1 dataset of Dark Energy Spectroscopic Instrument (DESI) and radio sources from the LOw-Frequency ARray Two-metre Sky Survey (LoTSS) DR2 catalog and the Very Large Array Sky Survey (VLASS) quick look catalog. Galaxies with similar optical properties but with no radio counterparts in LoTSS and VLASS are selected as the control group. We measure the cool CGM properties of radio galaxies and their control samples traced by MgII absorption lines, including covering fraction, rest equivalent width, and gas kinematics. Our results show no significant difference in the properties of gas around radio galaxies and their control sample, indicating that the operating radio-mode feedback of massive galaxies does not produce detectable effects on the properties of the cool CGM. Finally, we show that the CGM of radio galaxies contain a non-negligible amount of cool gas with approximately 10^10 solar masses. This abundance can place a stringent constraint on the radio-mode feedback models.

astro-ph.GA↗

arXiv2024

Mapping Obscured Star Formation in the Host Galaxy of FRB 20201124A

We present high-resolution 1.5 $-$ 6 GHz Karl G. Jansky Very Large Array (VLA) and Hubble Space Telescope (HST) optical and infrared observations of the extremely active repeating fast radio burst (FRB) FRB 20201124A and its barred spiral host galaxy. We constrain the location and morphology of star formation in the host and search for a persistent radio source (PRS) coincident with FRB 20201124A. We resolve the morphology of the radio emission across all frequency bands and measure a star formation rate SFR $\approx 8.9\,M_{\odot}$ yr$^{-1}$, approximately $\approx 2.5-6$ times larger than optically-inferred SFRs, demonstrating dust-obscured star formation throughout the host. Compared to a sample of all known FRB hosts with radio emission, the host of FRB 20201124A has the most significantly obscured star formation. While HST observations show the FRB to be offset from the bar or spiral arms, the radio emission extends to the FRB location. We propose that the FRB progenitor could have formed in situ (e.g., a magnetar born from a massive star explosion). It is still plausible, although less likely, that the progenitor of FRB 20201124A migrated from the central bar of the host. We further place a limit on the luminosity of a putative PRS at the FRB position of $L_{\rm 6.0 \ GHz}$ $\lesssim$ 1.8 $\times 10^{27}$ erg s$^{-1}$ Hz$^{-1}$, among the deepest PRS luminosity limits to date. However, this limit is still broadly consistent with both magnetar nebulae and hypernebulae models assuming a constant energy injection rate of the magnetar and an age of $\gtrsim 10^{5}$ yr in each model, respectively.

astro-ph.HE↗

arXiv2024

A pulsar-like swing in the polarisation position angle of a nearby fast radio burst

Fast radio bursts (FRBs) last for milliseconds and arrive at Earth from cosmological distances. While their origin(s) and emission mechanism(s) are presently unknown, their signals bear similarities with the much less luminous radio emission generated by pulsars within our Galaxy and several lines of evidence point toward neutron star origins. For pulsars, the linear polarisation position angle (PA) often exhibits evolution over the pulse phase that is interpreted within a geometric framework known as the rotating vector model (RVM). Here, we report on a fast radio burst, FRB 20221022A, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and localized to a nearby host galaxy ($\sim 65\; \rm{Mpc}$), MCG+14-02-011. This one-off FRB displays a $\sim 130$ degree rotation of its PA over its $\sim 2.5\; \rm{ms}$ burst duration, closely resembling the "S"-shaped PA evolution commonly seen from pulsars and some radio magnetars. The PA evolution disfavours emission models involving shocks far from the source and instead suggests magnetospheric origins for this source which places the emission region close to the FRB central engine, echoing similar conclusions drawn from tempo-polarimetric studies of some repeating sources. This FRB's PA evolution is remarkably well-described by the RVM and, although we cannot determine the inclination and magnetic obliquity due to the unknown period/duty cycle of the source, we can dismiss extremely short-period pulsars (e.g., recycled millisecond pulsars) as potential progenitors. RVM-fitting appears to favour a source occupying a unique position in the period/duty cycle phase space that implies tight opening angles for the beamed emission, significantly reducing burst energy requirements of the source.

astro-ph.HE↗

arXiv2024

A survey of Ly$α$ emission around Damped Ly$α$ absorbers at $z \approx 2$ with the Keck Cosmic Web Imager

We present Keck Cosmic Web Imager (KCWI) Ly$α$ integral field spectroscopy of the fields surrounding 14 Damped Ly$α$ absorbers (DLAs) at $z \approx 2$. Of these 14 DLAs, 9 have high metallicities ([M/H]$~> -0.3$), and 4 of those 9 feature a CO-emitting galaxy at an impact parameter $\lesssim 30$ kpc. Our search reaches median Ly$α$ line flux sensitivities of $\sim 2 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ over apertures of $\sim6$ kpc and out to impact parameters of $\sim50$ kpc. We recover the Ly$α$ flux of three known Ly$α$-emitting H I-selected galaxies in our sample. In addition, we find two Ly$α$ emitters at impact parameters of $\approx 50-70$ kpc from the high metallicity DLA at $z \approx 1.96$ toward QSO B0551-366. This field also contains a massive CO-emitting galaxy at an impact parameter of $\approx 15$ kpc. Apart from the field with QSO B0551-366, we do not detect significant Ly$α$ emission in any of the remaining 8 high-metallicity DLA fields. Considering the depth of our observations and our ability to recover previously known Ly$α$ emitters, we conclude that H I-selected galaxies associated with high-metallicity DLAs at $z \approx 2$ are dusty, and therefore might feature low Ly$α$ escape fractions. Our results indicate that complementary approaches -- using Ly$α$, CO, H$α$, and [C II] 158$μ$m emission -- are necessary to identify the wide range of galaxy types associated with $z \approx 2$ DLAs.

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arXiv2024

Not so windy after all: MUSE disentangles AGN-driven winds from merger-induced flows in rapidly-transitioning galaxies

Post-starburst galaxies are believed to be in a rapid transition between major merger starbursts and quiescent ellipticals, where AGN feedback is suggested as one of the processes responsible for the quenching. To study the role of AGN feedback, we constructed a sample of post-starburst candidates with AGN and indications of ionized outflows. We use MUSE/VLT observations to resolve the properties of the stars and multi-phased gas in five of them. All the galaxies show signatures of interaction/merger in their stellar or gas properties, with some galaxies at an early stage of interaction with companions at distances $\sim$50 kpc, suggesting that optical post-starburst signatures may be present well before the final starburst and coalescence. We detect narrow and broad kinematic components in multiple transitions in all the galaxies. Our detailed analysis of their kinematics and morphology suggests that, contrary to our expectation, the properties of the broad kinematic components are inconsistent with AGN-driven winds in 3 out of 5 galaxies. The two exceptions are also the only galaxies in which spatially-resolved NaID P-Cygni profiles are detected. In some cases, the observations are more consistent with interaction-induced galactic-scale flows, an often overlooked process. These observations raise the question of how to interpret broad kinematic components in interacting and perhaps also in active galaxies, in particular when spatially-resolved observations are not available or cannot rule out merger-induced galactic-scale motions. We suggest that NaID P-Cygni profiles are more effective outflow tracers, and use them to estimate the energy that is carried by the outflow.

astro-ph.GA↗

arXiv2024

HI, FRB, what's your z: The first FRB host galaxy redshift from radio observations

Identification and follow up observations of the host galaxies of fast radio bursts (FRBs) not only help us understand the environments in which the FRB progenitors reside, but also provide a unique way of probing the cosmological parameters using the dispersion measures of FRBs and distances to their origin. A fundamental requirement is an accurate distance measurement to the FRB host galaxy, but for some sources viewed through the Galactic plane, optical/NIR spectroscopic redshifts are extremely difficult to obtain due to dust extinction. Here we report the first radio-based spectroscopic redshift measurement for an FRB host galaxy, through detection of its neutral hydrogen (HI) 21-cm emission using MeerKAT observations. We obtain an HI-based redshift of z = 0.0357 for the host galaxy of FRB 20230718A, an apparently non-repeating FRB detected in the CRAFT survey and localized at a Galactic latitude of -0.367 deg. Our observations also reveal that the FRB host galaxy is interacting with a nearby companion, which is evident from the detection of an HI bridge connecting the two galaxies. A subsequent optical spectroscopic observation confirmed an FRB host galaxy redshift of 0.0359 +- 0.0004. This result demonstrates the value of HI to obtain redshifts of FRBs at low Galactic latitudes and redshifts. Such nearby FRBs whose dispersion measures are dominated by the Milky Way can be used to characterise these components and thus better calibrate the remaining cosmological contribution to dispersion for more distant FRBs that provide a strong lever arm to examine the Macquart relation between cosmological DM and redshift.

astro-ph.GA↗

arXiv2023

Machine-Learning Enhanced Photometric Analysis of the Extremely Bright GRB 210822A

We present analytical and numerical models of the bright long GRB 210822A at $z=1.736$. The intrinsic extreme brightness exhibited in the optical, which is very similar to other bright GRBs (e.g., GRBs 080319B, 130427A, 160625A 190114C, and 221009A), makes GRB 210822A an ideal case for studying the evolution of this particular kind of GRB. We use optical data from the RATIR instrument starting at $T+315.9$ s, with publicly available optical data from other ground-based observatories, as well as Swift/UVOT, and X-ray data from the Swift/XRT instrument. The temporal profiles and spectral properties during the late stages align consistently with the conventional forward shock model, complemented by a reverse shock element that dominates optical emissions during the initial phases ($T<300$ s). Furthermore, we observe a break at $T=80000$s that we interpreted as evidence of a jet break, which constrains the opening angle to be about $θ_\mathrm{j}=(3-5)$ degrees. Finally, we apply a machine-learning technique to model the multi-wavelength light curve of GRB 210822A using the AFTERGLOWPY library. We estimate the angle of sight $θ_{obs}=(6.4 \pm 0.1) \times 10^{-1}$ degrees, the energy $E_0=(7.9 \pm 1.6)\times 10^{53}$ ergs, the electron index $p=2.54 \pm 0.10$, the thermal energy fraction in electrons $ε_\mathrm{e}=(4.63 \pm 0.91) \times 10^{-5}$ and in the magnetic field $ε_\mathrm{B}= (8.66 \pm 1.01) \times 10^{-6}$, the efficiency $χ= 0.89 \pm 0.01$, and the density of the surrounding medium $n_\mathrm{0} = 0.85 \pm 0.01 cm^{-3}$.

astro-ph.HE↗

arXiv2023

A Fast Radio Burst in a Compact Galaxy Group at $z$~1

FRB 20220610A is a high-redshift Fast Radio Burst (FRB) that has not been observed to repeat. Here, we present rest-frame UV and optical $\textit{Hubble Space Telescope}$ observations of the field of FRB 20220610A. The imaging reveals seven extended sources, one of which we identify as the most likely host galaxy with a spectroscopic redshift of $z$=1.017. We spectroscopically confirm at least three additional sources to be at the same redshift, and identify the system as a compact galaxy group with possible signs of interaction among group members. We determine the host of FRB 20220610A to be a star-forming galaxy with stellar mass of $\approx10^{9.7}\,M_{\odot}$, mass-weighted age of $\approx2.6$~Gyr, and star formation rate (integrated over the last 100 Myr) of $\approx1.7$~M$_{\odot}$~yr$^{-1}$. These host properties are commensurate with the star-forming field galaxy population at z~1 and trace their properties analogously to the population of low-$z$ FRB hosts. Based on estimates of the total stellar mass of the galaxy group, we calculate a fiducial contribution to the observed Dispersion Measure (DM) from the intragroup medium of $\approx 110-220$ $\rm pc \, cm^{-3}$ (rest-frame). This leaves a significant excess of $500^{+272}_{-109}$ $\rm pc \, cm^{-3}$ (in the observer frame), with additional sources of DM possibly originating from the circumburst environment, host galaxy interstellar medium, and/or foreground structures along the line of sight. Given the low occurrence rates of galaxies in compact groups, the discovery of an FRB in such a group demonstrates a rare and novel environment in which FRBs can occur.

astro-ph.GA↗

arXiv2023

Limits on Optical Counterparts to the Repeating FRB 20180916B from High-speed Imaging with Gemini-N/'Alopeke

We report on contemporaneous optical observations at ~10 ms timescales from the fast radio burst (FRB) 20180916B of two repeat bursts (FRB 20201023, FRB 20220908) taken with the 'Alopeke camera on the Gemini North telescope. These repeats have radio fluences of 2.8 and 3.5 Jy ms, respectively, approximately in the lower 50th percentile for fluence from this repeating burst. The 'Alopeke data reveal no significant optical detections at the FRB position and we place 3-sigma upper limits to the optical fluences of <8.3e-3 and <7.7e-3 Jy ms after correcting for line-of-sight extinction. Together, these yield the most sensitive limits to the optical-to-radio fluence ratio of an FRB on these timescales with eta < 3e-3 by roughly an order of magnitude. These measurements rule out progenitor models where FRB 20180916B has a similar fluence ratio to optical pulsars similar to the Crab pulsar or optical emission is produced as inverse Compton radiation in a pulsar magnetosphere or young supernova remnant. Our ongoing program with 'Alopeke on Gemini-N will continue to monitor repeating FRBs, including FRB 20180916B, to search for optical counterparts on ms timescales.

astro-ph.HE↗