arXiv subjects

Tetsuya Hashimoto

Publications and source records attributed to Tetsuya Hashimoto.

At least 55 records · Page 3Linked to original sources

arXiv2022

Metallicity-PAH Relation of MIR-selected Star-forming Galaxies in AKARI North Ecliptic Pole-wide Survey

We investigate the variation in the mid-infrared spectral energy distributions of 373 low-redshift ($z<0.4$) star-forming galaxies, which reflects a variety of polycyclic aromatic hydrocarbon (PAH) emission features. The relative strength of PAH emission is parameterized as $q_\mathrm{PAH}$, which is defined as the mass fraction of PAH particles in the total dust mass. With the aid of continuous mid-infrared photometric data points covering 7-24$μ$m and far-infrared flux densities, $q_\mathrm{PAH}$ values are derived through spectral energy distribution fitting. The correlation between $q_\mathrm{PAH}$ and other physical properties of galaxies, i.e., gas-phase metallicity ($12+\mathrm{log(O/H)}$), stellar mass, and specific star-formation rate (sSFR) are explored. As in previous studies, $q_\mathrm{PAH}$ values of galaxies with high metallicity are found to be higher than those with low metallicity. The strength of PAH emission is also positively correlated with the stellar mass and negatively correlated with the sSFR. The correlation between $q_\mathrm{PAH}$ and each parameter still exists even after the other two parameters are fixed. In addition to the PAH strength, the application of metallicity-dependent gas-to-dust mass ratio appears to work well to estimate gas mass that matches the observed relationship between molecular gas and physical parameters. The result obtained will be used to calibrate the observed PAH luminosity-total infrared luminosity relation, based on the variation of MIR-FIR SED, which is used in the estimation of hidden star formation.

astro-ph.GA↗

arXiv2022

The molecular gas kinematics in the host galaxy of non-repeating FRB 180924B

Fast radio bursts (FRBs) are millisecond-duration transients with large dispersion measures. The origin of FRBs is still mysterious. One of the methods to comprehend FRB origin is to probe the physical environments of FRB host galaxies. Mapping molecular-gas kinematics in FRB host galaxies is critical because it results in star formation that is likely connected to the birth of FRB progenitors. However, most previous works of FRB host galaxies have focused on its stellar component. Therefore, we, for the first time, report the molecular gas kinematics in the host galaxy of the non-repeating FRB 180924B at $z= 0.3216$. Two velocity components of the CO (3-2) emission line are detected in its host galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA): the peak of one component ($-155.40$ km s$^{-1}$) is near the centre of the host galaxy, and another ($-7.76$ km s$^{-1}$) is near the FRB position. The CO (3-2) spectrum shows asymmetric profiles with A$_{\rm peak}$ $=2.03\pm 0.39$, where A$_{\rm peak}$ is the peak flux density ratio between the two velocity components. The CO (3-2) velocity map also indicates an asymmetric velocity gradient from $-180$ km s$^{-1}$ to 8 km s$^{-1}$. These results indicate a disturbed kinetic structure of molecular gas in the host galaxy. Such disturbed kinetic structures are reported for repeating FRB host galaxies using HI emission lines in previous works. Our finding indicates that non-repeating and repeating FRBs could commonly appear in disturbed kinetic environments, suggesting a possible link between the gas kinematics and FRB progenitors.

astro-ph.GA↗

arXiv2022

Detection of a bright burst from the repeating FRB 20201124A at 2 GHz

We present a detection of a bright burst from FRB 20201124A, which is one of the most active repeating FRBs, based on S-band observations with the 64-m radio telescope at the Usuda Deep Space Center/JAXA. This is the first FRB observed by using a Japanese facility. Our detection at 2 GHz in February 2022 is the highest frequency for this FRB and the fluence of $>$ 189 Jy ms is one of the brightest bursts from this FRB source. We place an upper limit on the spectral index $α$ = -2.14 from the detection of the S band and non-detection of the X band at the same time. We compare an event rate of the detected burst with ones of the previous research, and suggest that the power-law of the luminosity function might be broken at lower fluence, and the fluences of bright FRBs distribute up to over 2 GHz with the power-law against frequency. In addition, we show the energy density of the burst detected in this work was comparable to the bright population of one-off FRBs. We propose that repeating FRBs can be as bright as one-off FRBs, and only their brightest bursts could be detected so some of repeating FRBs intrinsically might have been classified as one-off FRBs.

astro-ph.HE↗

arXiv2022

Diverse Properties of Molecular Gas in the Host Galaxies of Fast Radio Bursts

We report the properties of molecular gas in a sample of six host galaxies of fast radio bursts (FRBs) obtained from CO observations with the Atacama Large Millimeter/submillimeter Array (FRBs 20180924B, 20190102C, and 20190711A) and results of one non-detection in a dwarf galaxy (FRB20121102A) and two events detected in M81 (FRB20200120E) and the Milky Way (FRB20200428A). The CO observations resulted in the detection of CO(3-2) emission in the FRB20180924B host and non-detections of CO(3-2) and CO(2-1) emission in the hosts of FRB20190102C and FRB20190711A, respectively. The derived molecular gas mass and 3$σ$ upper limit is $(2.4 \pm 0.2) \times 10^9$ $M_{\odot}$, $<3.8 \times 10^8$ $M_{\odot}$, and $<6.7 \times 10^9$ $M_{\odot}$ for the hosts of FRB20180924B, FRB20190102C, and FRB20190711A, respectively. We found diversity in molecular gas properties (gas mass, gas depletion time, and gas fraction to stellar mass) in the sample. Compared to other star-forming galaxies, the FRB20180924B host is gas-rich (the larger molecular gas fraction), and the hosts of FRB20190102C and FRB20200120E are gas-poor with a shorter depletion time for their stellar mass and star-formation rate. Our findings suggest that FRBs arise from multiple progenitors or single progenitors that can exist in a wide range of galaxy environments. Statistical analysis shows a significant difference in the distribution of molecular gas fraction between the FRB hosts and local star-forming galaxies. However, the difference is not substantial when an outlier, the FRB20200120E host, is excluded, and analysis with a larger sample is needed.

astro-ph.GA↗

arXiv2022

Detection Rate of Fast Radio Bursts in the Milky Way with BURSTT

Fast radio bursts (FRBs) are intense bursts of radio emission with durations of milliseconds. Although researchers have found them happening frequently all over the sky, they are still in the dark to understand what causes the phenomena because the existing radio observatories have encountered certain challenges during the discovery of FRB progenitors. The construction of Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is being proposed to solve these challenges. We simulate mock Galactic FRB-like events by applying a range of spatial distributions, pulse widths and luminosity functions. The effect of turbulent Interstellar Medium (ISM) on the detectability of FRB-like events within the Milky Way plane is considered to estimate the dispersion measure and pulse scattering of mock events. We evaluate the fraction of FRB-like events in the Milky Way that are detectable by BURSTT and compare the result with those by Survey for Transient Astronomical Radio Emission 2 (STARE2) and Galactic Radio Explorer (GReX). We find that BURSTT could increase the detection rate by more than two orders of magnitude compared with STARE2 and GReX, depending on the slope of luminosity function of the events. We also investigate the influence of the specifications of BURSTT on its detection improvement. This leads to the fact that greatly higher sensitivity and improved coverage of the Milky Way plane have significant effects on the detection improvement of BURSTT. We find that the upgrade version of BURSTT, BURSTT-2048 could increase the detection rate of faint Galactic FRB-like events by a factor of 3.

astro-ph.HE↗

arXiv2022

BURSTT: Bustling Universe Radio Survey Telescope in Taiwan

Fast Radio Bursts (FRBs) are bright millisecond-duration radio transients that appear about 1,000 times per day, all-sky, for a fluence threshold 5 Jy ms at 600 MHz. The FRB radio-emission physics and the compact objects involved in these events are subjects of intense active debate. To better constrain source models, the Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is optimized to discover and localize a large sample of rare, high-fluence, nearby FRBs. This is the population most amenable to multi-messenger, multi-wavelength follow-up, allowing deeper understanding of source mechanisms. BURSTT will provide horizon-to-horizon sky coverage with a half power field-of-view (FoV) of $\sim$10$^{4}$ deg$^{2}$, a 400 MHz effective bandwidth between 300-800 MHz, and sub-arcsecond localization, made possible using outrigger stations hundreds to thousands of km from the main array. Initially, BURSTT will employ 256 antennas. After tests of various antenna designs and optimization of system performance we plan to expand to 2048 antennas. We estimate that BURSTT-256 will detect and localize $\sim$100 bright ($\geq$100 Jy ms) FRBs per year. Another advantage of BURSTT's large FoV and continuous operation will be greatly enhanced monitoring of FRBs for repetition. The current lack of sensitive all-sky observations likely means that many repeating FRBs are currently cataloged as single-event FRBs.

astro-ph.IM↗

arXiv2022

Galaxy source counts at 7.7 $μ$m, 10 $μ$m and 15 $μ$m with the James Webb Space Telescope

We present mid-infrared galaxy number counts based on the Early Release Observations obtained by the James Webb Space Telescope (JWST) at 7.7-, 10- and 15-$μ$m (F770W, F1000W and F1500W, respectively) bands of the Mid-Infrared Instrument (MIRI). Due to the superior sensitivity of JWST, the 80 percent completeness limits reach 0.32, 0.79 and 2.0 $μ$Jy in F770W, F1000W and F1500W filters, respectively, i.e., $\sim$100 times deeper than previous space infrared telescopes such as Spitzer or AKARI. The number counts reach much deeper than the broad bump around $0.05\sim0.5$ mJy due to polycyclic aromatic hydrocarbon (PAH) emissions. An extrapolation towards fainter flux from the evolutionary models in the literature agrees amazingly well with the new data, where the extrapolated faint-end of infrared luminosity functions combined with the cosmic star-formation history to higher redshifts can reproduce the deeper number counts by JWST. Our understanding of the faint infrared sources has been confirmed by the observed data due to the superb sensitivity of JWST.

astro-ph.GA↗

arXiv2022

Constraining the Hubble constant and its lower limit from the proper motion of extragalactic radio jets

The Hubble constant ($H_{0}$) is a measurement to describe the expansion rate of the Universe in the current era. However, there is a $4.4σ$ discrepancy between the measurements from the early Universe and the late Universe. In this research, we propose a model-free and distance-free method to constrain $H_{0}$. Combining Friedman-Lemaître-Robertson-Walker cosmology with geometrical relation of the proper motion of extragalactic jets, the lower limit ($H_{\rm 0,min}$) of $H_{0}$ can be determined using only three cosmology-free observables: the redshifts of the host galaxies, as well as the approaching and receding angular velocities of radio jets. Using these, we propose to use the Kolmogorov-Smirnov test (K-S test) between cumulative distribution functions of $H_{\rm 0,min}$ to differentiate cosmology. We simulate 100, 200, and 500 extragalactic jets with 3 levels of accuracy of the proper motion ($μ_{a}$ and $μ_{r}$), at $10\%$, $5\%$, and $1\%$, corresponding to the accuracies of the current and future radio interferometers. We perform K-S tests between the simulated samples as theoretical distributions with different $H_{0}$ and power-law index of velocity distribution of jets and mock observational data. Our result suggests increasing sample sizes leads to tighter constraints on both power-law index and the Hubble constant at moderate accuracy (i.e., $10\%$ and $5\%$) while at $1\%$ accuracy, increasing sample sizes leads to tighter constraints on power-law index more. Improving accuracy results in better constraints in the Hubble constant compared with the power-law index in all cases but it alleviates the degeneracy.

astro-ph.CO↗

arXiv2022

Can luminous Lyman alpha emitters at $z$ $\simeq$ 5.7 and $z$ $\simeq$ 6.6 suppress star formation?

Addressing how strong UV radiation affects galaxy formation is central to understanding their evolution. The quenching of star formation via strong UV radiation (from starbursts or AGN) has been proposed in various scenes to solve certain astrophysical problems. Around luminous sources, some evidence of decreased star formation has been found but is limited to a handful of individual cases. No direct, conclusive evidence on the actual role of strong UV radiation in quenching star formation has been found. Here we present statistical evidence of decreased number density of faint (AB magnitude $\geq$ 24.75 mag) Lyαemitters (LAEs) around bright (AB magnitude < 24.75 mag) LAEs even when the radius goes up to 10 pMpc for $z$ $\simeq$ 5.7 LAEs. A similar trend is found for z $\simeq$ 6.6 LAEs but only within 1 pMpc radius from the bright LAEs. We use a large sample of 1077 (962) LAEs at $z$ $\simeq$ 5.7 ($z$ $\simeq$ 6.6) selected in total areas of 14 (21) deg$^2$ with Subaru/Hyper Suprime-Cam narrow-band data, and thus, the result is of statistical significance for the first time at these high redshift ranges. A simple analytical calculation indicates that the radiation from the central LAE is not enough to suppress LAEs with AB mag $\geq$ 24.75 mag around them, suggesting additional physical mechanisms we are unaware of are at work. Our results clearly show that the environment is at work for the galaxy formation at $z$ $\sim$ 6 in the Universe.

astro-ph.GA↗

arXiv2022

On the relation between duration and energy of non-repeating fast radio bursts: census with the CHIME data

A correlation between the intrinsic energy and the burst duration of non-repeating fast radio bursts (FRBs) has been reported. If it exists, the correlation can be used to estimate intrinsic energy from the duration, and thus can provide us with a new distance measure for cosmology. However, the correlation suffered from small number statistics (68 FRBs) and was not free from contamination by latent repeating populations, which might not have such a correlation. How to separate/exclude the repeating bursts from the mixture of all different types of FRBs is essential to see this property. Using a much larger sample from the new FRB catalogue (containing 536 FRBs) recently released by the CHIME/FRB project, combined with a new classification method developed based on unsupervised machine learning, we carried out further scrutiny of the relation. We found that there is a weak correlation between the intrinsic energy and duration for non-repeating FRBs at z < 0.3 with Kendall's tau correlation coefficient of 0.239 and significance of 0.001 (statistically significant), whose slope looks similar to that of gamma-ray bursts. This correlation becomes weaker and insignificant at higher redshifts (z > 0.3), possibly due to the lack of the faint FRBs at high-z and/or the redshift evolution of the correlation. The scattering time in the CHIME/FRB catalogue shows an intriguing trend: it varies along the line obtained from linear fit on the energy versus duration plane between these two parameters. A possible cosmological application of the relation must wait for faint FRBs at high-z.

astro-ph.CO↗

arXiv2022

ALMA [O III] and [C II] Detections of A1689-zD1 at $z=7.13$

A1689-zD1 is one of the most distant galaxies, discovered with the aid of gravitational lensing, providing us with an important opportunity to study galaxy formation in the very early Universe. In this study, we report the detection of [C II]158$μ$m and [O III]88$μ$m emission lines of A1689-zD1 in the ALMA Bands 6 and 8. We measure the redshift of this galaxy as $z_{\rm{sys}}=7.133\pm0.005$ based on the [C II] and [O III] emission lines, consistent with that adopted by Bakx et al. (2021). The observed $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ ratio is $2.09\pm0.09$, higher than most of the local galaxies, but consistent with other $z\sim7$ galaxies. The moderate-spatial resolution of ALMA data provided us with a precious opportunity to investigate spatial variation of $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$. In contrast to the average value of 2.09, we find a much higher $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ of $\sim 7$ at the center of the galaxy. This spatial variation of $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ was seldom reported for other high-z galaxies. It is also interesting that the peak of the ratio does not overlap with optical peaks. Possible physical reasons include a central AGN, shock heating from merging, and starburst. Our moderate-spatial resolution data also reveals that in addition to the observed two clumps shown in previous HST images, there is a redshifted segment to the west of the northern optical clump. Such a structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected materials, or that the northern redshifted materials being from a third more highly obscured region of the galaxy.

astro-ph.GA↗

arXiv2022

Energy functions of fast radio bursts derived from the first CHIME/FRB catalogue

Fast radio bursts (FRBs) are mysterious millisecond pulses in radio, most of which originate from distant galaxies. Revealing the origin of FRBs is becoming central in astronomy. The redshift evolution of the FRB energy function, i.e., the number density of FRB sources as a function of energy, provides important implications for the FRB progenitors. Here we show the energy functions of FRBs selected from the recently released Canadian Hydrogen Intensity Mapping Experiment (CHIME) catalogue using the $V_{\rm max}$ method. The $V_{\rm max}$ method allows us to measure the redshift evolution of the energy functions as it is without any prior assumption on the evolution. We use a homogeneous sample of 164 non-repeating FRB sources, which are about one order of magnitude larger than previously investigated samples. The energy functions of non-repeating FRBs show Schechter function-like shapes at $z\lesssim1$. The energy functions and volumetric rates of non-repeating FRBs decrease towards higher redshifts similar to the cosmic stellar-mass density evolution: there is no significant difference between the non-repeating FRB rate and cosmic stellar-mass density evolution with a 1\% significance threshold, whereas the cosmic star-formation rate scenario is rejected with a more than 99\% confidence level. Our results indicate that the event rate of non-repeating FRBs is likely controlled by old populations rather than young populations which are traced by the cosmic star-formation rate density. This suggests old populations such as old neutron stars and black holes as more likely progenitors of non-repeating FRBs.

astro-ph.HE↗

arXiv2021

Upper limits on Einstein's weak equivalence principle placed by uncertainties of dispersion measures of fast radio bursts

Fast radio bursts (FRBs) are astronomical transients with millisecond timescales occurring at cosmological distances. The observed time lag between different energies of each FRB is well described by the inverse-square law of the observed frequency, i.e., dispersion measure. Therefore, FRBs provide one of the ideal laboratories to test Einstein's weak equivalence principle (WEP): the hypothetical time lag between photons with different energies under a gravitational potential. If WEP is violated, such evidence should be exposed within the observational uncertainties of dispersion measures, unless the WEP violation also depends on the inverse-square of the observed frequency. In this work, we constrain the difference of gamma parameters ($Δγ$) between photons with different energies using the observational uncertainties of FRB dispersion measures, where $Δγ=0$ for Einstein's general relativity. Adopting the averaged 'Shapiro time delay' for cosmological sources, FRB 121002 at $z=1.6\pm0.3$ and FRB 180817.J1533+42 at $z=1.0\pm0.2$ place the most stringent constraints of $\logΔγ<-20.8\pm0.1$ and $\log(Δγ/r_{E}) < -20.9\pm0.2$, respectively, where $r_{E}$ is the energy ratio between the photons. The former is about three orders of magnitude lower than those of other astrophysical sources in previous works under the same formalization of the Shapiro time delay while the latter is comparable to the tightest constraint so far.

gr-qc↗

arXiv2021

Constraining violations of the Weak Equivalence Principle Using CHIME FRBs

Einstein's General Relativity (GR) is the basis of modern astronomy and astrophysics. Testing the validity of basic assumptions of GR is important. In this work, we test a possible violation of the Weak Equivalence Principle (WEP), i.e., there might be a time-lag between photons of different frequencies caused by the effect of gravitational fields if the speeds of photons are slightly different at different frequencies. We use Fast Radio Bursts (FRBs) , which are astronomical transients with millisecond timescales detected in the radio frequency range. Being at cosmological distances, accumulated time delay of FRBs can be caused by the plasma in between an FRB source and an observer, and by gravitational fields in the path of the signal. We segregate the delay due to dispersion and gravitational field using the post-Newtonian formalism (PPN) parameter $Δγ$, which defines the space-curvature due to gravity by a unit test mass. We did not detect any time-delay from FRBs but obtained tight constraints on the upper limit of $Δγ$. For FRB20181117C with $z = 1.83 \pm 0.28$ and $ν_{obs}$ = $676.5\,{\rm MHz}$, the best possible constraint is obtained at log($Δγ$) = $-21.58 ^{+0.10}_{-0.12}$ and log($Δγ$/$r_{\rm E}$) = $-21.75 ^{+0.10}_{-0.14}$, respectively, where $r_{\rm E}$ is the energy ratio of two photons of the same FRB signal. This constraint is about one order of magnitude better than the previous constraint obtained with FRBs, and five orders tighter than any constraint obtained using other cosmological sources.

gr-qc↗

arXiv2021

Uncloaking hidden repeating fast radio bursts with unsupervised machine learning

The origins of fast radio bursts (FRBs), astronomical transients with millisecond timescales, remain unknown. One of the difficulties stems from the possibility that observed FRBs could be heterogeneous in origin; as some of them have been observed to repeat, and others have not. Due to limited observing periods and telescope sensitivities, some bursts may be misclassified as non-repeaters. Therefore, it is important to clearly distinguish FRBs into repeaters and non-repeaters, to better understand their origins. In this work, we classify repeaters and non-repeaters using unsupervised machine learning, without relying on expensive monitoring observations. We present a repeating FRB recognition method based on the Uniform Manifold Approximation and Projection (UMAP). The main goals of this work are to: (i) show that the unsupervised UMAP can classify repeating FRB population without any prior knowledge about their repetition, (ii) evaluate the assumption that non-repeating FRBs are contaminated by repeating FRBs, and (iii) recognise the FRB repeater candidates without monitoring observations and release a corresponding catalogue. We apply our method to the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) database. We found that the unsupervised UMAP classification provides a repeating FRB completeness of 95 per cent and identifies 188 FRB repeater source candidates from 474 non-repeater sources. This work paves the way to a new classification of repeaters and non-repeaters based on a single epoch observation of FRBs.

astro-ph.HE↗

arXiv2021

The evolution of merger fraction of galaxies at z < 0.6 depending on the star formation mode in the AKARI NEP Wide field

We study the galaxy merger fraction and its dependence on star formation mode in the5.4 square degrees of the North Ecliptic Pole-Wide field. We select 6352 galaxies withAKARI 9μm detections, and identify mergers among them using the Gini coefficientand M20derived from the Subaru/HSC optical images. We obtain the total infraredluminosity and star formation rate of galaxies using the spectral energy distributiontemplates based on one band, AKARI 9μm. We classify galaxies into three differentstar formation modes (i.e. starbursts, main sequence, and quiescent galaxies) andcalculate the merger fractions for each. We find that the merger fractions of galaxiesincrease with redshift atz<0.6. The merger fractions of starbursts are higher thanthose of main sequence and quiescent galaxies in all redshift bins. We also examinethe merger fractions of far-infrared detected galaxies which have at least one detectionfromHerschel/SPIRE. We find thatHerscheldetected galaxies have higher mergerfraction compared to non-Herscheldetected galaxies, and bothHerscheldetected andnon-Herscheldetected galaxies show clearly different merger fractions depending onthe star formation modes.

astro-ph.GA↗

arXiv2021

Environmental Effects on AGN activity via Extinction-free Mid-Infrared Census

How does the environment affect active galactic nucleus (AGN) activity? We investigated this question in an extinction-free way, by selecting 1120 infrared galaxies in the $AKARI$ North Ecliptic Pole Wide field at redshift $z$ $\leq$ 1.2. A unique feature of the $AKARI$ satellite is its continuous 9-band infrared (IR) filter coverage, providing us with an unprecedentedly large sample of IR spectral energy distributions (SEDs) of galaxies. By taking advantage of this, for the first time, we explored the AGN activity derived from SED modelling as a function of redshift, luminosity, and environment. We quantified AGN activity in two ways: AGN contribution fraction (ratio of AGN luminosity to the total IR luminosity), and AGN number fraction (ratio of number of AGNs to the total galaxy sample). We found that galaxy environment (normalised local density) does not greatly affect either definitions of AGN activity of our IRG/LIRG samples (log ${\rm L}_{\rm TIR}$ $\leq$ 12). However, we found a different behavior for ULIRGs (log ${\rm L}_{\rm TIR}$ $>$ 12). At our highest redshift bin (0.7 $\lesssim$ z $\lesssim$ 1.2), AGN activity increases with denser environments, but at the intermediate redshift bin (0.3 $\lesssim$ z $\lesssim$ 0.7), the opposite is observed. These results may hint at a different physical mechanism for ULIRGs. The trends are not statistically significant (p $\geq$ 0.060 at the intermediate redshift bin, and p $\geq$ 0.139 at the highest redshift bin). Possible different behavior of ULIRGs is a key direction to explore further with future space missions (e.g., $JWST$, $Euclid$, $SPHEREx$).

astro-ph.GA↗

arXiv2021

Far-infrared star-formation rates of six GRB host galaxies with ALMA

Gamma-Ray Bursts (GRBs) can be a promising tracer of cosmic star-formation rate history (CSFRH). In order to reveal the CSFRH using GRBs, it is important to understand whether they are biased tracers or not. For this purpose, it is crucial to understand properties of GRB host galaxies, in comparison to field galaxies. In this work, we report ALMA far-infrared (FIR) observations of six $z\sim2$ IR-bright GRB host galaxies, which are selected for the brightness in IR. Among them, four host galaxies are detected for the first time in the rest-frame FIR. In addition to the ALMA data, we collected multi-wavelength data from previous studies for the six GRB host galaxies. Spectral energy distribution (SED) fitting analyses were performed with \texttt{CIGALE} to investigate physical properties of the host galaxies, and to test whether active galactic nucleus (AGN) and radio components are required or not. Our results indicate that the best-fit templates of five GRB host galaxies do not require an AGN component, suggesting the absence of AGNs. One GRB host galaxy, 080207, shows a very small AGN contribution. While derived stellar masses of the three host galaxies are mostly consistent with those in previous studies, interestingly the value of star-formation rates (SFRs) of all six GRB hosts are inconsistent with previous studies. Our results indicate the importance of rest-frame FIR observations to correctly estimate SFRs by covering thermal emission from cold dust heated by star formation.

astro-ph.GA↗