Luminosity Distribution Research Articles

The Cosmic History of Long Gamma-Ray Bursts

The cosmic formation rate of long gamma-ray bursts (LGRBs) encodes the evolution, across cosmic times, of the properties of their progenitors and of their environment. The LGRB formation rate and the luminosity function, with its redshift evolution, are derived by reproducing the largest sets of observations collected over the last four decades, namely the observer-frame prompt emission properties of the GRB samples detected by the Fermi and Compton Gamma Ray Observatory satellites and the redshift, luminosity, and energy distributions of the flux-limited, redshift-complete samples of GRBs detected by Swift. The model that best reproduces all these constraints consists of a GRB formation rate increasing with redshift ∝(1 + z)3.2, i.e., steeper than the star formation rate, up to z ∼ 3, followed by a decrease ∝(1 + z)−3. On top of this, our model also predicts a moderate evolution of the characteristic luminosity function break ∝(1 + z)0.6. Models with only luminosity or rate evolution are excluded at >5σ significance. The cosmic rate evolution of LGRBs is interpreted as their preference for occurring in environments with metallicity , consistent with theoretical models and host galaxy observations. The LGRB rate at z = 0, accounting for their collimation, is Gpc−3 yr−1 (68% confidence interval). This corresponds to ∼1% of broad-line Type Ibc supernovae producing a successful jet in the local universe. This fraction increases up to ∼7% at z ≥ 3. Finally, we estimate that at least ≈0.2−0.7 yr−1 of the Swift- and Fermi-detected bursts at z < 0.5 are jets observed slightly off-axis.

Optical emission-line luminosity function models for populations of supernova remnants

ABSTRACT We present a basic model for the calculation of the luminosity distribution of supernova remnant populations. We construct theoretical H$\rm \alpha \,$and joint [S ii]-H$\rm \alpha \,$luminosity functions for supernova remnants by combining prescriptions from a basic evolution model that provides the shock velocity and radius for SNRs of different age and pre-shock density, with shock excitation models that give the gas emissivity for shocks of different physical parameters. We assume a flat age distribution, and we explore the effect of different pre-shock density distributions or different magnetic parameters. We find a very good agreement between the shape of the model H$\rm \alpha \,$and the joint [S ii]-H$\rm \alpha \,$luminosity functions and those measured from SNR surveys in nearby galaxies.

Mass loss of massive helium star supernova progenitors shortly before explosion constrained by supernova radio properties

Abstract Mass loss of massive helium stars is not well understood even though it plays an essential role in determining their remnant neutron-star or black hole masses as well as ejecta mass of Type Ibc supernovae. Radio emission from Type Ibc supernovae is strongly affected by circumstellar matter properties formed by mass loss of their massive helium star progenitors. In this study, we estimate the rise time and peak luminosity distributions of Type Ibc supernovae in radio based on a few massive helium star mass-loss prescriptions and compare them with the observed distribution to constrain the uncertain massive helium star mass-loss rates. We find that massive helium stars in the luminosity range expected for ordinary Type Ibc supernova progenitors (4.6 ≲ log L/L⊙ ≲ 5.2) should generally have large mass-loss rates (≳ 10−6 M⊙ yr−1) in order to account for the observed rise time and peak luminosity distribution. Therefore, mass-loss prescriptions that predict significantly low mass-loss rates for helium stars in this luminosity range is inconsistent with the supernova radio observations. It is also possible that massive helium stars shortly before their explosion generally undergo mass-loss enhancement in a different way from the standard radiation-driven wind mechanism.

Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone

The evolution of magnetism in late-type dwarfs remains murky, as we can only weakly predict levels of activity for M dwarfs of a given mass and age. We report results from our spectroscopic survey of M dwarfs in the Southern Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite (TESS). As the TESS CVZs overlap with those of the James Webb Space Telescope, our targets constitute a legacy sample for studies of nearby M dwarfs. For 122 stars, we obtained at least one R ≈ 2000 optical spectrum with which we measure chromospheric Hα emission, a proxy for magnetic field strength. The fraction of active stars is consistent with what is expected for field M dwarfs; as in previous studies, we find that late-type M dwarfs remain active for longer than their early-type counterparts. While the TESS light curves for ≈20% of our targets show modulations consistent with rotation, TESS systematics are not well enough understood for confident measurements of rotation periods (P rot) longer than half the length of an observing sector. We report periods for 12 stars for which we measure P rot ≲ 15 days or find confirmation for the TESS-derived P rot in the literature. Our sample of 21 P rot, which includes periods from the literature, is consistent with our targets being spun-down field stars. Finally, we examine the Hα-to-bolometric luminosity distribution for our sample. Two stars are rotating fast enough to be magnetically saturated, but are not, hinting at the possibility that fast rotators may appear inactive in Hα.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.During the performance verification phase of the Spectrum-Roentgen-Gamma eROSITA telescope, the eROSITA Final Equatorial-Depth Survey (eFEDS) was carried out. It covers a 140 deg2field located at 126° &lt; RA &lt; 146° and–3° &lt; Dec &lt; + 6° with a nominal unvignetted exposure over the field of 2.2 ks. Five hundred and forty-two candidate clusters and groups were detected in this field, down to a flux limitFX~10–14erg s–1cm–2in the 0.5–2 keV band.Aims.In order to understand radio-mode feedback in galaxy clusters, we study the radio emission of brightest cluster galaxies (BCGs) of eFEDS clusters and groups, and we relate it to the X-ray properties of the host cluster.Methods.Using LOFAR, we identified 227 radio galaxies hosted in the BCGs of the 542 galaxy clusters and groups detected in eFEDS. We treated non-detections as radio upper limits. We analysed the properties of radio galaxies, such as redshift and luminosity distribution, offset from the cluster centre, largest linear size, and radio power. We studied their relation to the intracluster medium of the host cluster.Results.We find that BCGs with radio-loud active galactic nucleus (AGN) are more likely to lie close to the cluster centre than radioquiet BCGs. There is a clear relation between the cluster X-ray luminosity and the 144 MHz radio power of the BCG. Statistical tests indicate that this correlation is not produced by biases or selection effects in the radio band. We see no apparent link between largest linear size of the radio galaxy and the central density in the host cluster. Converting the radio luminosity into kinetic luminosity, we find that radiative losses of the intracluster medium are in an overall balance with the heating provided by the central AGN. Finally, we tentatively classify our objects into disturbed and relaxed based on different morphological parameters, and we show that the link between the AGN and the ICM apparently holds for both subsamples, regardless of the dynamical state of the cluster.

Stripped-envelope stars in different metallicity environments

Massive stars that become stripped of their hydrogen envelope through binary interaction or winds can be observed either as Wolf-Rayet stars, if they have optically thick winds, or as transparent-wind stripped-envelope stars. We approximate their evolution through evolutionary models of single helium stars, and compute detailed model grids in the initial mass range 1.5−70 M⊙ for metallicities between 0.01 and 0.04, from core helium ignition until core collapse. Throughout their lifetimes some stellar models expose the ash of helium burning. We propose that models that have nitrogen-rich envelopes are candidate WN stars, while models with a carbon-rich surface are candidate WC stars during core helium burning, and WO stars afterwards. We measure the metallicity dependence of the total lifetimes of our models and the duration of their evolutionary phases. We propose an analytic estimate of the wind’s optical depth to distinguish models of Wolf-Rayet stars from transparent-wind stripped-envelope stars, and find that the luminosity ranges at which WN-, WC-, and WO-type stars can exist is a strong function of metallicity. We find that all carbon-rich models produced in our grids have optically thick winds and match the luminosity distribution of observed populations. We construct population models and predict the numbers of transparent-wind stripped-envelope stars and Wolf-Rayet stars, and derive their number ratios at different metallicities. We find that as metallicity increases, the number of transparent-wind stripped-envelope stars decreases and the number of Wolf-Rayet stars increases. At high metallicities WC- and WO-type stars become more common. We apply our population models to nearby galaxies, and find that populations are more sensitive to the transition luminosity between Wolf-Rayet stars and transparent-wind helium stars than to the metallicity-dependent mass loss rates.

A comparative study of luminosity functions and event rate densities of long GRBs with non-parametric method

ABSTRACT In this work, we restudy the dependence of luminosity function and event rates for different gamma-ray burst samples on the criteria of sample selection and threshold effect. To compare with many previous studies, we have chosen two samples including 88 and 118 long bursts with known redshift and peak flux over 2.6 ph cm−2 s−1, from which 79 bursts are picked out to constitute our complete sample. It is found that the evolution of luminosity with redshift can be expressed by L∝(1 + z)k with a diverse k relied more on the sample selection. Interestingly, the cumulative distributions of either non-evolving luminosities or redshifts are found to be also determined by the sample selection rather than the instrumental sensitivity. Nevertheless, the non-evolving luminosities of our samples are similarly distributed with a comparable break luminosity of L0 ∼ 1051 erg s−1. Importantly, we verify with a K-S test that three cases of event rates for the two burst samples evolve with redshift similarly except a small discrepancy due to sampling differences at low-redshift of z &amp;lt; 1, in which all event rates show an excess of Gaussian profile instead of monotonous decline no matter whether the sample is complete. Most importantly, it is found that the burst rates violate the star formation rate at low redshift, while both of them are good in agreement with each other in the higher-redshift regions as many authors discovered previously. Therefore, we predict that two types of long bursts are favored in terms of their associations with both the star formation and the cosmic metallicity.

The Habitable Zones of Rapidly Rotating Main Sequence A/F Stars

Abstract We investigate how rapid stellar rotation commonly seen in A/F stars can influence planet habitability. Specifically, we model how rapid rotation influences a planet’s irradiation and determine the location of the habitable zone for stars in the mass range 1.3 M ⊙ ≤ M ⋆ ≤ 2.2 M ⊙. Rapid stellar rotation can dramatically change a star’s luminosity and spectral energy distribution, and therefore can affect the habitability of any surrounding planets. Stars of mass M ⋆ ≳ 1.3 M ⊙ commonly rotate near their breakup speeds, which causes two effects relevant to planet habitability. First, these stars flatten into oblate spheroids with shorter polar radii and elongated equatorial radii. Second, rapid rotation induces a pole-to-equator temperature gradient on the surface of these stars. Using a 1D climate model, we calculate the inner and outer edges of the habitable zone of well-known rapid rotators and average theoretical stars in our stellar mass range. We find that, in general, rapid rotation causes the habitable zone to reside closer in than for a nonrotating equivalent star. We also find that gravity darkening dramatically reduces stellar UV emission, which combats the common assumption that high-mass stars emit too much UV light for habitable worlds. Overall, we determine that rapid stellar rotation has important consequences for the overall habitability of a system and must be accounted for both when modeling exoplanet environments and in observation of planets around high-mass stars.

Radio AGN in nearby dwarf galaxies: the important role of AGN in dwarf galaxy evolution

ABSTRACT We combine deep optical and radio data, from the Hyper Suprime-Cam and the Low-Frequency Array (LOFAR), respectively, to study 78 radio active galactic nuclei (AGN) in nearby (z &amp;lt; 0.5) dwarf galaxies. Comparison to a control sample, matched in stellar mass and redshift, indicates that the AGN and controls reside in similar environments, show similar star formation rates (which trace gas availability) and exhibit a comparable incidence of tidal features (which indicate recent interactions). We explore the AGN properties by combining the predicted gas conditions in dwarfs from a cosmological hydrodynamical simulation with a Monte Carlo suite of simulated radio sources, based on a semi-analytical model for radio-galaxy evolution. In the subset of LOFAR-detectable simulated sources, which have a similar distribution of radio luminosities as our observed AGN, the median jet powers, ages, and accretion rates are ∼1035 W, ∼5 Myr, and ∼10−3.4 M⊙ yr−1, respectively. The median mechanical energy output of these sources is ∼100 times larger than the median binding energy expected in dwarf gas reservoirs, making AGN feedback plausible. Since special circumstances (in terms of environment, gas availability, and interactions) are not necessary for the presence of AGN, and the central gas masses are predicted to be an order of magnitude larger than that required to fuel the AGN, AGN triggering in dwarfs is likely to be stochastic and a common phenomenon. Together with the plausibility of energetic feedback, this suggests that AGN could be important drivers of dwarf galaxy evolution, as is the case in massive galaxies.

Host galaxy properties of X-ray active galactic nuclei in the local Universe

We study the host galaxy properties of active galactic nuclei (AGN) that have been detected in X-rays in the nearby Universe (z &lt; 0.2). For that purpose, we use the catalogue provided by the ROSAT-2RXS in the 0.1–2.4 keV energy band, one of the largest X-ray datasets with spectroscopic observations. Our sample consists of ∼900 X-ray AGN. The catalogue provides classification of the sources into type 1 and 2 based on optical spectra. Approximately 25% of the AGN are type 2. We use the available optical, near-IR, and mid-IR photometry to construct spectral energy distributions (SEDs). We measure the stellar mass (M*) and star formation rate (SFR) of the AGN by fitting these SEDs with the X-CIGALE code. We compare the M* and SFR of the two AGN populations, taking their different redshift and luminosity distributions into account. Based on our results, type 2 AGN tend to live in more massive galaxies compared to their type 1 counterparts (log [M∗(M⊙)] = 10.49−0.10+0.16 vs. 10.23−0.08+0.05), in agreement with previous studies at higher redshifts. In terms of SFRs, our analysis shows that, in the nearby Universe, the number of X-ray AGN that live in quiescent systems is higher compared to at higher redshifts, in accordance with previous studies in the local Universe. However, the majority of AGN (∼75%) live inside or above the main sequence.

The low-end of the black hole mass function at cosmic dawn

ABSTRACT Understanding the formation and growth of supermassive black holes (SMBHs) at high redshift represents a major challenge for theoretical models. In this work, we investigate the early evolution of the first SMBHs by constraining their distribution in mass and luminosity at z &amp;gt; 4. In particular, we focus on the poorly explored low-mass end of the nuclear black hole (BH) distribution down to z ≃ 4, and explore its connection with the nature of the first BH seeds and the processes governing their mass growth. To this aim, we have developed CAT (Cosmic Archaeology Tool), a new semi-analytic model that describes the formation of the first stars and BHs in a self-consistent way and follows the co-evolution of nuclear BHs and their host galaxies for a representative population at z &amp;gt; 4. We find that current observational constraints favour models where the growth of BH seeds is Eddington limited and occurs at the Bondi–Hoyle–Lyttleton rate or where super-Eddington accretion occurs via a slim disc during gas-rich galaxy mergers. The main difference between these two model variants lies at the low end of the predicted mass and luminosity functions at 4 ≤ z ≤ 6, where a clear gap appears in the first model, reflecting the stunted growth of light BH seeds formed as remnants of the first stars. Detecting this signature will be extremely challenging even for the future generation of space observatories, such as JWST, Athena, and Lynx.

New Probability Distributions in Astrophysics: X. Truncation and Mass-Luminosity Relationship for the Fr&amp;#232;chet Distribution

The Frèchet distribution has aided the modelling of scientific data in many contexts. We demonstrate how it can be adapted to model astrophysical data. We analyze the truncated version of the Frèchet distribution deriving the probability density function (PDF), the distribution function, the average value, the rth moment about the origin, the median, the random generation of values and the maximum likelihood estimator, which allows us to derive the two unknown parameters. This first PDF in the regular and truncated version is then applied to model the mass of the stars. A canonical transformation from the mass to the luminosity allows us to derive a new PDF, which is derived in its regular and truncated version. Finally, we apply this new PDF model on the distribution in luminosity of NGC 2362.

Measurement of the Dark Matter Velocity Dispersion with Galaxy Stellar Masses, UV Luminosities, and Reionization

The root-mean-square of non-relativistic warm dark matter particle velocities scales as vhrms(a)=vhrms(1)/a , where a is the expansion parameter of the universe. This velocity dispersion results in a cut-off of the power spectrum of density fluctuations due to dark matter free-streaming. Let kfs (teq) be the free-streaming comoving cut-off wavenumber at the time of equal densities of radiation and matter. We obtain , and , at 68% confidence, from the observed distributions of galaxy stellar masses and rest frame ultra-violet luminosities. This result is consistent with reionization. From the velocity dispersion cut-off mass we obtain the limits vhrms(1)kfs (teq) >1.5 Mpc-1. These results are in agreement with previous measurements based on spiral galaxy rotation curves, and on the formation of first galaxies and reionization. These measured parameters determine the temperature-to-mass ratio of warm dark matter. This ratio happens to be in agreement with the no freeze-in and no freeze-out warm dark matter scenario of spin 0 dark matter particles decoupling early on from the standard model sector. Spin 1/2 and spin 1 dark matter are disfavored if nature has chosen the no freeze-in and no freeze-out scenario. An extension of the standard model of quarks and leptons, with scalar dark matter that couples to the Higgs boson that is in agreement with all current measurements, is briefly reviewed. Discrepancies with limits on dark matter particle mass that can be found in the literature are addressed.

Measurement of the Dark Matter Velocity Dispersion with Dwarf Galaxy Rotation Curves

Warm dark matter has, by definition, a velocity dispersion. Let vhms(a)=vhms(1)/a be the root-mean-square velocity of non-relativistic warm dark matter particles in the early universe at expansion parameter a. vhms(1) is an adiabatic invariant. We obtain vhms(1) in the core of 11 dwarf galaxies dominated by dark matter, from their observed rotation curves, up to a rotation and relaxation correction. We obtain a mean 0.490 km/s and standard deviation 0.160 km/s, with a distribution peaked at the lower end. We apply a mild, data driven, rotation and relaxation correction that obtains the adiabatic invariant in the core of the galaxies: vhms(1)=0.406 ± 0.069 km/s. These two small relative standard deviations justify the prediction that the adiabatic invariant vhms(1) in the core of the galaxies is of cosmological origin if dark matter is warm. This result is in agreement with measurements of vhms(1) based on spiral galaxy rotation curves, galaxy ultra-violet luminosity distributions, galaxy stellar mass distributions, the formation of first galaxies, reionization, and the velocity dispersion cut-off mass.

Maximum luminosities of normal stripped-envelope supernovae are brighter than explosion models allow

Context. Stripped-envelope supernovae (SE SNe) of Type Ib and Type Ic are thought to be the result of explosions of massive stars that have lost their outer envelopes. The favored explosion mechanism is via core-collapse, with the shock later revived by neutrino heating. However, there is an upper limit to the amount of radioactive 56Ni that such models can accommodate. Recent studies in the literature point to a tension between the maximum luminosity from such simulations and the observations. Aims. We used a well-characterized sample of SE SNe from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to scrutinize the observational caveats regarding estimates of the maximum luminosity (and thus the amount of ejected radioactive nickel) for the sample members. Methods. We employed the strict selection criteria for the BTS to collect a sample of spectroscopically classified normal Type Ibc SNe, for which we used the ZTF light curves to determine the maximum luminosity. We culled the sample further based on data quality, shape of the light curves, distances, and colors. Then we examined the uncertainties that may affect the measurements. The methodology of the sample construction based on this BTS sample can be used for other future investigations. Results. We analyzed the observational data, consisting of optical light curves and spectra, for the selected sub-samples. In total, we used 129 Type Ib or Type Ic BTS SNe with an initial rough luminosity distribution peaking at Mr = −17.61 ± 0.72, and where 36% are apparently brighter than the theoretically predicted maximum brightness of Mr = −17.8. When we further culled this sample to ensure that the SNe are normal Type Ibc with good LC data within the Hubble flow, the sample of 94 objects gives Mr = −17.64 ± 0.54. A main uncertainty in absolute magnitude determinations for SNe is the host galaxy extinction correction, but the reddened objects only get more luminous after corrections. If we simply exclude red objects, or those with unusual or uncertain colors, then we are left with 14 objects at Mr = −17.90 ± 0.73, whereof a handful are most certainly brighter than the suggested theoretical limit. The main result of this study is thus that normal SNe Ibc do indeed reach luminosities above 1042.6 erg s−1, which is apparently in conflict with existing explosion models.

X-ray source population in the polar ring galaxy NGC 660 as observed by Chandra

We present Chandra observations of the nearby polar ring galaxy NGC 660 to study its X-ray source population. Based on our analysis, we detected a total of 23 X-ray sources in the 0.5−8 keV band, with luminosities ranging from ∼1037 to ∼1039 erg s−1. Twenty-two of these sources are located off-nuclear and have luminosities below the ultraluminous X-ray source (ULX) threshold value of L 0.5−8 keV < 1039 erg s−1, suggesting that they are likely to be X-ray binary (XRB) candidates. The remaining source is located at the center of the galaxy, suggesting it is an active galactic nucleus (AGN). However, we estimated that four of the detected sources could be associated with background objects. Based on the source count rates in each of the Chandra observations, we found evidence for variability in nine of the 23 sources, including the AGN. However, further investigation with spectral analysis suggested no significant differences in the AGN luminosities between the observations. The X-ray luminosity distribution of the galaxy was found to be generally lower than that expected from previous studies on star forming and collisional ring galaxies. No ULX was also detected in the galaxy, in contrast with what was expected from the galaxyʼs SFR and metallicity (i.e., SFR = 14.43 ± 0.19 M ⊙ yr−1 and Z = 0.94 ± 0.01 Z ⊙, respectively). These results suggest a deficit in the X-ray sources detected. Based on source hardness ratio distribution, we found evidence that the fainter sources have a harder source spectrum, indicating higher absorption. This further suggests that there could be more X-ray sources that were not detected in the galaxy due to significant obscuration.

Red supergiants in M31: the Humphreys–Davidson limit at high metallicity

ABSTRACT The empirical upper limit to red supergiant (RSG) luminosity, known as the Humphreys–Davidson (HD) limit, has been commonly explained as being caused by the stripping of stellar envelopes by metallicity-dependent line-driven winds. As such, the theoretical expectation is that the HD limit should be higher at lower metallicity, where weaker mass-loss rates mean that higher initial masses are required for an envelope to be stripped. In this paper, we test this prediction by measuring the luminosity function of RSGs in M31 and comparing it to those in the LMC and SMC. We find that log (Lmax/L⊙) = 5.53 ± 0.03 in M31 (Z ≳ Z⊙), consistent with the limit found for both the LMC (Z ∼ 0.5 Z⊙) and SMC (Z ∼ 0.25 Z⊙), while the RSG luminosity distributions in these three galaxies are consistent to within 1σ. We therefore find no evidence for a metallicity dependence on both the HD limit and the RSG luminosity function, and conclude that line-driven winds on the main sequence are not the cause of the HD limit.

Polarized image of a Schwarzschild black hole with a thin accretion disk as photon couples to Weyl tensor

We have studied polarized image of a Schwarzschild black hole with an equatorial thin accretion disk as photon couples to Weyl tensor. The birefringence of photon originating from the coupling affect the black hole shadow, the thin disk pattern and its luminosity distribution. We also analyze the observed polarized intensity in the sky plane. The observed polarized intensity in the bright region is stronger than that in the darker region. The stronger effect of the coupling on the observed polarized vector appears only in the bright region close to black hole. These features in the polarized image could help us to understand black hole shadow, the thin accretion disk and the coupling between photon and Weyl tensor.

Lyα Line Properties at z = 3.78 and Their Environmental Dependence: A Case Study around a Massive Protocluster

Abstract Lyα-emitting galaxies (LAEs) are easily detectable in the high-redshift universe and are potentially efficient tracers of large-scale structure at early epochs, as long as their observed properties do not depend strongly on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift z ≃ 3.78. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Lyα luminosity distribution is well represented by a Schechter function with log ( L * / erg s − 1 ) = 43.26 − 0.22 + 0.20 and log ( ϕ * / Mpc − 3 ) = − 3.40 − 0.04 + 0.03 with α = −1.5. Fitting the equivalent width distribution as an exponential, we find a scale factor of ω = 79 − 15 + 15 Å. We also measured the Lyα luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for L* and ω. Hence, despite having a mean overdensity more than 2× that of the general field, the shapes of the Lyα luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Lyα luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Lyα escape fraction and suggests that LAEs at lower redshift can be on average significantly more dusty that their counterparts at higher redshift.

The fast radio burst population evolves, consistent with the star formation rate

ABSTRACT Fast radio bursts (FRBs) are extremely powerful sources of radio waves observed at cosmological distances. We use a sophisticated model of FRB observations – presented in detail in a companion paper – to fit FRB population parameters using large samples of FRBs detected by ASKAP and Parkes, including seven sources with confirmed host galaxies. Our fitted parameters demonstrate that the FRB population evolves with redshift in a manner consistent with, or faster than, the star formation rate (SFR), ruling out a non-evolving population at better than 98 per cent CL (depending on modelling uncertainties). Our estimated maximum FRB energy is $\log _{10} E_{\rm max} [{\rm erg}] = 41.70_{-0.06}^{+0.53}$ (68 per cent CL) assuming a 1 GHz emission bandwidth, with slope of the cumulative luminosity distribution $\gamma =-1.09_{-0.10}^{+0.14}$. We find a log-mean host DM contribution of $129_{-48}^{+66}$ pc cm−3 on top of a typical local (interstellar medium and halo) contribution of ∼80 pc cm−3, which is higher than most literature values. These results are insensitive to assumptions of the FRB spectral index, and are consistent with the model of FRBs arising as the high-energy limit of magnetar bursts, but allow for FRB progenitors that evolve faster than the SFR.