Specific Luminosity Research Articles

Long-term Study of the First Galactic Ultraluminous X-Ray Source Swift J0243.6+6124 Using NICER

We present the results obtained from detailed X-ray timing and spectral studies of X-ray pulsar Swift J0243.6+6124 during its giant and normal X-ray outbursts between 2017 and 2023 observed by the Neutron star Interior Composition Explorer (NICER). We focused on a timing analysis of the normal outbursts. A distinct break is found in the power density spectra of the source. The corresponding break frequency and slopes of the power laws around the break vary with luminosity, indicating a change in the accretion dynamics with the mass accretion rate. Interestingly, we detected quasiperiodic oscillations within a specific luminosity range, providing further insights into the underlying physical processes. We also studied the neutron star spin period evolution and a luminosity variation in the pulse profile during the recent 2023 outburst. The spectral analysis was conducted comprehensively for the giant and all other normal outbursts. We identified a double transition at luminosities of ≈7.5 × 1037 and 2.1 × 1038 erg s−1 in the evolution of continuum parameters like the photon index and cutoff energy with luminosity. This indicates three distinct accretion modes experienced by the source, mainly during the giant X-ray outburst. A soft blackbody component with a temperature of 0.08–0.7 keV is also detected in the spectra. The observed temperature undergoes a discontinuous transition when the pulsar evolves from a sub- to super-Eddington state. Notably, in addition to an evolving 6–7 keV iron line complex, a 1 keV emission line was observed during the super-Eddington state of the source, implying X-ray reflection from the accretion disk or outflow material.

Effects of heterogeneous data sets and time-lag measurement techniques on cosmological parameter constraints from Mg ii and C iv reverberation-mapped quasar data

ABSTRACT Previously, we demonstrated that Mg ii and C iv reverberation-mapped quasars (RM QSOs) are standardizable and that the cosmological parameters inferred using the broad-line region radius–luminosity (R–L) relation are consistent with those determined from better-established cosmological probes. With more data expected from ongoing and future spectroscopic and photometric surveys, it is imperative to examine how new QSO data sets of varied quality, with their own specific luminosity and time-delay distributions, can be best used to determine more restrictive cosmological parameter constraints. In this study, we test the effect of adding 25 OzDES Mg ii RM QSOs as well as 25 lower quality SDSS RM C iv QSOs, which increases the previous sample of RM QSOs by $\sim 36{{\ \rm per\ cent}}$. Although cosmological parameter constraints become tighter for some cosmological models after adding these new QSOs, the new combined data sets have increased differences between R–L parameter values obtained in different cosmological models and thus a lower standardizability for the larger Mg ii + C iv compilation. Different time-delay methodologies, particularly the ICCF and CREAM methods used for inferring time delays of SDSS RM QSOs, slightly affect cosmological and R–L relation parameter values, however, the effect is negligible for (smaller) compilations of robust time-delay detections. Our analysis indicates that increasing the sample size is not sufficient for tightening cosmological constraints and a quality cut is necessary to obtain a standardizable RM QSO sample.

FRB 20210405I: a nearby Fast Radio Burst localized to sub-arcsecond precision with MeerKAT

ABSTRACT We present the first sub-arcsecond localized Fast Radio Burst (FRB) detected using MeerKAT. FRB 20210405I was detected in the incoherent beam using the MeerTRAP pipeline on 2021 April 05 with a signal to noise ratio of 140.8 and a dispersion measure of 565.17 pc cm−3. It was detected while MeerTRAP was observing commensally with the ThunderKAT large survey project, and was sufficiently bright that we could use the ThunderKAT 8 s images to localize the FRB. Two different models of the dispersion measure in the Milky Way and halo suggest that the source is either right at the edge of the Galaxy, or outside. This highlights the uncertainty in the Milky Way dispersion measure models, particularly in the Galactic Plane, and the uncertainty of Milky Way halo models. Further investigation and modelling of these uncertainties will be facilitated by future detections and localizations of nearby FRBs. We use the combined localization, dispersion measure, scattering, specific luminosity, and chance coincidence probability information to find that the origin is most likely extra-galactic and identify the likely host galaxy of the FRB: 2MASS J1701249−4932475. Using SALT spectroscopy and archival observations of the field, we find that the host is a disc/spiral galaxy at a redshift of z = 0.066.

Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra

Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds, requiring a substantial sample size and systematic analysis methods. As of 2022, the Chandra data archive contains 37 high-resolution spectra of O, B, and WR stars, observed with the Chandra/HETGS, and of sufficient quality to fit the continua and emission-line profiles. Using a systematic approach to the data analysis, we explore morphological trends in the line profiles (i.e., O, Ne, Mg, and Si) and find that the centroid offsets of resolved lines versus wavelength can be separated in three empirically defined groups based on the amount of line broadening and centroid offset. Using Fe xvii (15.01, 17.05 Å) and Ne x α (12.13 Å) lines, which are prevalent among the sample stars, we find a well-correlated linear trend of increasing Full Width Half Maximum with faster wind terminal velocity. The H-like/He-like total line flux ratio for strong lines displays different trends with spectral class depending on ion species. Some of the sources in our sample have peculiar properties (e.g., magnetic and γ Cas-analog stars) and we find that these sources stand out as outliers from more regular trends. Finally, our spectral analysis is presented summarily in terms of X-ray spectral energy distributions in specific luminosity for each source, including tables of line identifications and fluxes.

Variation in optical and infrared properties of galaxies in relation to their surface brightness

Although it is now recognized that low surface brightness galaxies (LSBs) constitute a large fraction of the number density of galaxies, many of their properties are still poorly known. Based on only a few studies, LSBs are often considered to be “dust poor”, that is, with a very low amount of dust. For the first time, we use a large sample of LSBs and high surface brightness galaxies (HSBs) with deep observational data to study the variation of stellar and dust properties as a function of the surface brightness-surface mass density. Our sample consists of 1631 galaxies that were optically selected (with ugrizy-bands) at z < 0.1 from the North Ecliptic Pole (NEP) Wide field. We used the large multiwavelength set of ancillary data in this field ranging from UV to the far-infrared wavelengths. We measured the optical size and the surface brightness of the targets and analyzed their spectral energy distribution using the CIGALE fitting code. Based on the average r-band surface brightness (μ̄e), our sample consists of 1003 LSBs (μ̄e > 23 mag arcsec−2) and 628 HSBs (μ̄e ≤ 23 mag arcsec−2). We found that the specific star formation rate and specific infrared luminosity (total infrared luminosity per stellar mass) remain mostly flat as a function of surface brightness for both LSBs and HSBs that are star forming, but these characteristics decline steeply when the LSBs and HSBs are quiescent galaxies. The majority of LSBs in our sample have negligible dust attenuation (< 0.1 mag), and only about 4% of them show significant attenuation, with a mean V-band attenuation of 0.8 mag. We found that the LSBs with a significant attenuation also have a high r-band mass-to-light ratio (M/Lr > 3 M⊙/L⊙), making them outliers from the linear relation of surface brightness and stellar mass surface density. These outlier LSBs also show similarity to the extreme giant LSBs from the literature, indicating a possibly higher dust attenuation in giant LSBs. This work provides a large catalog of LSBs and HSBs as well as detailed measurements of several optical and infrared physical properties. Our results suggest that the dust content of LSBs is more varied than previously thought, with some of them having significant attenuation that makes them fainter than their intrinsic value. With these results, we will be able to make predictions on the dust content of the population of LSBs and how the presence of dust will affect their observations from current and upcoming surveys like JWST and LSST.

Periodic Radio Emission from the T8 Dwarf WISE J062309.94–045624.6

We present the detection of rotationally modulated, circularly polarized radio emission from the T8 brown dwarf WISE J062309.94−045624.6 between 0.9 and 2.0 GHz. We detected this high-proper-motion ultracool dwarf with the Australian SKA Pathfinder in 1.36 GHz imaging data from the Rapid ASKAP Continuum Survey. We observed WISE J062309.94−045624.6 to have a time and frequency averaged Stokes I flux density of 4.17 ± 0.41 mJy beam−1, with an absolute circular polarization fraction of 66.3% ± 9.0%, and calculated a specific radio luminosity of L ν ∼ 1014.8 erg s−1 Hz−1. In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multipeaked pulse structure, used dynamic spectra to place a lower limit of B > 0.71 kG on the dwarf’s magnetic field, and measured a P = 1.912 ± 0.005 hr periodicity, which we concluded to be due to rotational modulation. The luminosity and period we measured are comparable to those of other ultracool dwarfs observed at radio wavelengths. This implies that future megahertz to gigahertz surveys, with increased cadence and improved sensitivity, are likely to detect similar or later-type dwarfs. Our detection of WISE J062309.94−045624.6 makes this dwarf the coolest and latest-type star observed to produce radio emission.

Temporal Scattering, Depolarization, and Persistent Radio Emission from Magnetized Inhomogeneous Environments near Repeating Fast Radio Burst Sources

Abstract Some repeating fast radio burst (FRB) sources exhibit complex polarization behaviors, including frequency-dependent depolarization, variation of rotation measure (RM), and oscillating spectral structures of polarized components. Very recently, Feng et al. reported that active repeaters exhibit conspicuous frequency-dependent depolarization and a strong correlation between RM scatter (σ RM) and the temporal scattering time (τ s), σ RM ∝ τ s 1.0 ± 0.2 , both of which can be well described by multipath propagation through a magnetized inhomogeneous plasma screen. This observation strongly suggests that the temporal scattering and RM scatter originate from the same region. Besides, a particular finding of note in Feng et al. is that the FRBs with compact persistent radio sources (PRSs) tend to have extreme σ RM. In this work, we focus on some theoretical predictions of the relations among temporal scattering, depolarization by RM scatter, and PRSs contributed by the magnetized plasma environment close to a repeating FRB source. The behaviors of the RM scatter imply that the magnetized plasma environment is consistent with a supernova remnant or pulsar wind nebula, and the predicted σ RM–τ s relation is σ RM ∝ τ s ( 0.54 − 0.83 ) for different astrophysical scenarios. We further make a general discussion of PRSs that does not depend on specific astrophysical scenarios. We show that the specific luminosity of a PRS should have a positive correlation with the RM contributed by the plasma screen. This is consistent with the observations of FRB 121102 and FRB 190520B.

Inferring astrophysics and dark matter properties from 21 cm tomography using deep learning

ABSTRACT 21 cm tomography opens a window to directly study astrophysics and fundamental physics of early epochs in our Universe’s history, the Epoch of Reionization (EoR) and Cosmic Dawn (CD). Summary statistics such as the power spectrum omit information encoded in this signal due to its highly non-Gaussian nature. Here, we adopt a network-based approach for direct inference of CD and EoR astrophysics jointly with fundamental physics from 21 cm tomography. We showcase a warm dark matter (WDM) universe, where dark matter density parameter Ωm and WDM mass mWDM strongly influence both CD and EoR. Reflecting the three-dimensional nature of 21 cm light-cones, we present a new, albeit simple, 3D convolutional neural network (3D-21cmPIE-Net) for efficient parameter recovery at moderate training cost. On simulations we observe high-fidelity parameter recovery for CD and EoR astrophysics (R2 > 0.78–0.99), together with DM density Ωm (R2 > 0.97) and WDM mass (R2 > 0.61, significantly better for $m_\mathrm{WDM}\lt 3\!-\!4\,$ keV). For realistic mock observed light-cones that include noise and foreground levels expected for the Square Kilometre Array, we note that in an optimistic foreground scenario parameter recovery is unaffected, while for moderate, less optimistic foreground levels (occupying the so-called wedge) the recovery of the WDM mass deteriorates, while other parameters remain robust against increased foreground levels at R2 > 0.9. We further test the robustness of our network-based inference against modelling uncertainties and systematics by transfer learning between bare simulations and mock observations; we find robust recovery of specific X-ray luminosity and ionizing efficiency, while DM density and WDM mass come with increased bias and scatter.

How to increase the physics output per MW.h for FCC-ee?

The efficiency of colliders for physics is largely determined by their luminosity, while most of the energy consumed by high-energy e^+e^- colliders is proportional to the total beam current. Thus, the energy efficiency is mainly determined by the specific luminosity that needs to be maximized. One of the most effective ways to achieve this is by using the Crab waist collision scheme, which implies a large Piwinski angle (LPA). A distinctive feature of the FCC-ee is the great influence of beamstrahlung (radiation in the field of an opposite bunch) on beam dynamics. At low energies, this manifests itself in a significant increase in the energy spread and bunch length, at high energies, in a limitation of the beam lifetime. The collision of intense bunches with LPA and beamstrahlung can also lead to various kinds of instabilities limiting the luminosity. Here, we discuss the main aspects to consider when optimizing the parameters of the FCC-ee collider at different energies and explain the choice of basic parameters such as RF voltage, lattice functions at IP, bunch intensity, etc. We will also pay attention to open issues requiring further study and identify some key points for the next phase of this project.

Predicting far-infrared maps of galaxies via machine learning techniques

Context. The ultraviolet (UV) to sub-millimetre spectral energy distribution of galaxies can be roughly divided into two sections: the stellar emission (attenuated by dust) at UV to near-infrared wavelengths and dust emission at longer wavelengths. In Dobbels et al. (2020, A&A, 634, A57), we show that these two sections are strongly related, and we can predict the global dust properties from the integrated UV to mid-infrared emission with the help of machine learning techniques. Aims. We investigate if these machine learning techniques can also be extended to resolved scales. Our aim is to predict resolved maps of the specific dust luminosity, specific dust mass, and dust temperature starting from a set of surface brightness images from UV to mid-infrared wavelengths. Methods. We used a selection of nearby galaxies retrieved from the DustPedia sample, in addition to M31 and M33. These were convolved and resampled to a range of pixel sizes, ranging from 150 pc to 3 kpc. We trained a random forest model which considers each pixel individually. Results. We find that the predictions work well on resolved scales, with the dust mass and temperature having a similar root mean square error as on global scales (0.32 dex and 3.15 K on 18″ scales respectively), and the dust luminosity being noticeably better (0.11 dex). We find no significant dependence on the pixel scale. Predictions on individual galaxies can be biased, and we find that about two-thirds of the scatter can be attributed to scatter between galaxies (rather than within galaxies). Conclusions. A machine learning approach can be used to create dust maps, with its resolution being only limited to the input bands, thus achieving a higher resolution than Herschel. These dust maps can be used to improve global estimates of dust properties, they can lead to a better estimate of dust attenuation, and they can be used as a constraint on cosmological simulations that trace dust.

X-Ray Constraints on the Hot Gas Content of Early-type Galaxies in Virgo

Abstract We present a systematic study of the diffuse hot gas around early-type galaxies (ETGs) residing in the Virgo cluster, based on archival Chandra observations. Our representative sample consists of 79 galaxies with low-to-intermediate stellar masses (M * ≈ 109−11 M ⊙), a mass range that has not been extensively explored with X-ray observations thus far. We detect diffuse X-ray emission in only eight galaxies and find that in five cases a substantial fraction of the detected emission can be unambiguously attributed to truly diffuse hot gas, based on their spatial distribution and spectral properties. For the individually nondetected galaxies, we constrain their average X-ray emission by performing a stacking analysis, finding a specific X-ray luminosity of L X / M * ∼ 10 28 erg s − 1 M ⊙ − 1 , which is consistent with unresolved stellar populations. The apparent paucity of truly diffuse hot gas in these low- and intermediate-mass ETGs may be the result of efficient ram pressure stripping by the hot intracluster medium. However, we also find no significant diffuse hot gas in a comparison sample of 57 field ETGs of similar stellar masses, for which archival Chandra observations with similar sensitivity are available. This points to the alternative possibility that galactic winds evacuate the hot gas from the inner region of low- and intermediate-mass ETGs, regardless of the galactic environment. Nevertheless, we do find strong morphological evidence for ongoing ram pressure stripping in two galaxies (NGC 4417 and NGC 4459). A better understanding of the roles of ram pressure stripping and galactic winds in regulating the hot gas content of ETGs invites sensitive X-ray observations for a large galaxy sample.

Constraints on the sub-pc environment of the nearby Type Iax SN 2014dt from deep X-ray and radio observations

ABSTRACT We present X-ray and radio observations of what may be the closest Type Iax supernova (SN) to date, SN 2014dt (d = 12.3–19.3 Mpc), and provide tight constraints on the radio and X-ray emission. We infer a specific radio luminosity $L_R\lt (1.0\!-\!2.4)\times 10^{25}\, \rm {erg\, s^{-1}\, Hz^{-1}}$ at a frequency of 7.5 GHz and a X-ray luminosity $L_X\lt 1.4\times 10^{38}\, \rm {erg\, s^{-1}}$ (0.3–10 keV) at ∼38–48 d post-explosion. We interpret these limits in the context of Inverse Compton (IC) emission and synchrotron emission from a population of electrons accelerated at the forward shock of the explosion in a power-law distribution $N_e(\gamma _e)\propto \gamma _e^{-p}$ with p = 3. Our analysis constrains the progenitor system mass-loss rate to be $\dot{M}\lt 5.0 \times 10^{-6} \rm {M_{\odot }\, yr^{-1}}$ at distances $r\lesssim 10^{16}\, \rm {cm}$ for an assumed wind velocity $v_w=100\, \rm {km\, s^{-1}}$, and a fraction of post-shock energy into magnetic fields and relativistic electrons of ϵB = 0.01 and ϵe = 0.1, respectively. This result rules out some of the parameter space of symbiotic giant star companions, and it is consistent with the low mass-loss rates expected from He-star companions. Our calculations also show that the improved sensitivity of the next-generation Very Large Array (ngVLA) is needed to probe the very low-density media characteristic of He stars that are the leading model for binary stellar companions of white dwarfs giving origin to Type Iax SNe.

A MeerKAT survey of nearby nova-like cataclysmic variables

ABSTRACT We present the results of MeerKAT radio observations of 11 nearby nova-like cataclysmic variables (CVs). We have detected radio emission from IM Eri, RW Sex, V3885 Sgr, and V603 Aql. While RW Sex, V3885 Sgr, and V603 Aql had been previously detected, this is the first reported radio detection of IM Eri. Our observations have doubled the sample of non-magnetic CVs with sensitive radio data. We observe that at our radio detection limits, a specific optical luminosity ${\gtrsim}2.2\times 10^{18}\,$ erg s−1 Hz−1 (corresponding to MV ≲ 6.0) is required to produce a radio detection. We also observe that the X-ray and radio luminosities of our detected nova-like CVs are on an extension of the $L_X\propto L_R^{\sim 0.7}$ power law originally proposed for non-pulsating neutron star low-mass X-ray binaries. We find no other correlations between the radio emission and emission in other wavebands or any other system parameters for the existing sample of radio-detected non-magnetic CVs. We measure in-band (0.9–1.7 GHz) radio spectral indices that are consistent with reports from earlier work. Finally, we constructed broad spectral energy distributions for our sample from published multiwavelength data, and use them to place constraints on the mass transfer rates of these systems.

Physicochemical quality and sensory acceptance of toasts with partial replacement of wheat flour by maize biomass flour.

The aim of this study was to assess physicochemical and sensory viability of toasts developed from the partial replacement of wheat flour (WF) by maize biomass flour (MBF). Different levels of MBF (0, 5, 10, 15 and 20g 100g-1) were used. Data obtained were evaluated by univariate and multivariate analyses. The level of replacement of WF by MBF influenced all physicochemical properties of the toast. Moisture (5.67-7.12g 100g-1), hardness (56.67-131.66N), chroma of crust and crumb (29.86-30.27 and 19.76-25.83, respectively), and hue angle of crust and crumb (60.32°-64.79° and 81.41°-82.06°, respectively) were increased; and area (2286.4-1658.1mm2), specific volume (3.47-1.83mLg-1) and luminosity of crust and crumb (62.39-59.67 and 65.49-62.54, respectively) were decreased as the level of substitution of WF by MBF increased. The toasts did not present microbiological risk. The formulations with higher sensory acceptance were 5 and 15g 100g-1 of MBF, being considered rich in proteins (16.25 and 15.43g 100g-1, respectively) and rich in dietary fibers (12.10 and 16.02g 100g-1, respectively), therefore with high nutritional and functional values. The production of toasts with partial replacement of WF by MBF is feasible in relation to physicochemical and sensory characteristics, which it may stimulate exploitation of this by-product and sustainable production of baked goods.

LEGUS and Hα-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Age

Abstract We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449, based on multiband imaging observations taken as part of the LEGUS and H α -LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages, and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of H α measurements, the role of stochasticity for low-mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age dating of clusters. A comparison with ages derived from stellar color–magnitude diagrams for partially resolved clusters shows reasonable agreement, but large scatter in some cases. The fraction of light found in clusters relative to the total light (i.e., T L ) in the U, B, and V filters in 25 different ≈ kiloparsec-size regions throughout NGC 4449 correlates with both the specific region luminosity, R L , and the dominant age of the underlying stellar population in each region. The observed cluster age distribution is found to decline over time as dN/dτ ∝ τ γ , with γ = −0.85 ± 0.15, independent of cluster mass, and is consistent with strong, early cluster disruption. The mass functions of the clusters can be described by a power law with dN/dM ∝ M β and β = −1.86 ± 0.2, independent of cluster age. The mass and age distributions are quite resilient to differences in age-dating methods. There is tentative evidence for a factor of 2–3 enhancement in both the star and cluster formation rate ≈100–300 Myr ago, indicating that cluster formation tracks star formation generally. The enhancement is probably associated with an earlier interaction event.

Near-Surface Plasma Formed by Dual-Pulse Laser Action at Two Wavelengths on Titanium in Air

Spectra and structures of near-surface plasma torches were studied experimentally by measuring the specific mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for specific mass loss, 3–6 μs. The results were important for enhancing the efficiency of laser emission spectral analysis and laser-plasma processing of materials.

Young star cluster populations in the E-MOSAICS simulations

ABSTRACT We present an analysis of young star clusters (YSCs) that form in the E-MOSAICS cosmological, hydrodynamical simulations of galaxies and their star cluster populations. Through comparisons with observed YSC populations, this work aims to test models for YSC formation and obtain an insight into the formation processes at work in part of the local galaxy population. We find that the models used in E-MOSAICS for the cluster formation efficiency and high-mass truncation of the initial cluster mass function ($M_\rm {c,\ast }$) both quantitatively reproduce the observed values of cluster populations in nearby galaxies. At higher redshifts (z ≥ 2, near the peak of globular cluster formation) we find that, at a constant star formation rate (SFR) surface density, $M_\rm {c,\ast }$ is larger than at z = 0 by a factor of four due to the higher gas fractions in the simulated high-redshift galaxies. Similar processes should be at work in local galaxies, offering a new way to test the models. We find that cluster age distributions may be sensitive to variations in the cluster formation rate (but not SFR) with time, which may significantly affect their use in tests of cluster mass-loss. By comparing simulations with different implementations of cluster formation physics, we find that (even partially) environmentally independent cluster formation is inconsistent with the brightest cluster-SFR and specific luminosity-$\Sigma _\rm {SFR}$ relations, whereas these observables are reproduced by the fiducial, environmentally varying model. This shows that models in which a constant fraction of stars form in clusters are inconsistent with observations.

Revealing the differences in the SMBH accretion rate distributions of starburst and non-starburst galaxies

We infer and compare the specific X-ray luminosity distributions for a sample of massive (i.e. $\log_{10} (M*/M\odot) > 10.5$) galaxies split according to their far-infrared-derived star-forming properties (i.e., starburst and non-starburst) and redshift. We model each distribution as a power-law with an upper and lower turnover, and adopt a maximum likelihood method to include information from non-detections in the form of upper limits. When we use our inferred distributions to calculate the ratios of high to low sLx AGN (corresponding to above and below $0.1\lambda_{\text{Edd}}$, respectively) we find that starbursts have significantly higher proportions of high sLx AGN compared to their non-starburst counterparts. These findings help explain the increase in average X-ray luminosity in bins of increasing SFR reported by previous studies.

Detection of an OH 1665 MHz Maser in M33

We report one OH 1665-MHz detection in new observations with the NSF's Karl G. Jansky Very Large Array. To the authors' knowledge, this is the first OH maser detection in M33. The source occurs at a position of $\alpha=23.50069(9)^{\circ}$ and $\delta = 30.67984(9)^{\circ}$ (J2000) and is unresolved at the beam size ($9.7$). Two H$\alpha$ sources from the Moody et al. (2017) catalogue --- C1-1 and C1-2 --- are consistent within the beam size. We find a peak flux density of 24.1 mJy in a 1.5 km s$^{-1}$ channel. At the distance of M33, the source's specific luminosity is consistent with the brightest Galactic OH 1665-MHz masers.

Observational Constraints on Correlated Star Formation and Active Galactic Nuclei in Late-stage Galaxy Mergers

Abstract Galaxy mergers are capable of triggering both star formation and active galactic nuclei (AGNs) and therefore may represent an important pathway in the co-evolution of galaxies and supermassive black holes (SMBHs). However, correlated enhancements of merger-induced star formation and AGN triggering may be hidden by the variable conditions and timescales during which they occur. In Paper I, we presented evidence of merger-triggered AGN in a sample of six late-stage galaxy mergers ( 2 – 8 kpc nuclear separations). In this follow-up work, we use multi-wavelength Hubble Space Telescope imaging and additional archival data to examine their star-forming properties to test for merger-triggered star formation and if it is correlated with SMBH growth. We find that the morphological asymmetries are correlated with enhanced specific star formation rates, indicating the presence of merger-triggered star formation. Additionally, the stellar populations become younger with increasing radius from the nucleus, indicating that the merger-induced star formation primarily occurs on global scales. However, we also find that the star formation rate enhancements are consistent with or lower than those of larger separation galaxy pair samples. This result is consistent with simulations predicting a decline of the global star formation rates in late-stage galaxy mergers with < 10 kpc nuclear separations. Finally, we find that enhancements in specific star formation rate and AGN luminosity are positively correlated, but that an average temporal delay of ≳ 10 8 years likely exists between the peak of global star formation and the onset of AGN triggering in 80% of the systems.