22 research outputs found
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.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Machine Learning Classification of Repeating FRBs from FRB121102
Fast Radio Bursts (FRBs) are mysterious bursts in the millisecond timescale
at radio wavelengths. Currently, there is little understanding about the
classification of repeating FRBs, based on difference in physics, which is of
great importance in understanding their origin. Recent works from the
literature focus on using specific parameters to classify FRBs to draw
inferences on the possible physical mechanisms or properties of these FRB
subtypes. In this study, we use publicly available 1652 repeating FRBs from
FRB121102 detected with the Five-hundred-meter Aperture Spherical Telescope
(FAST), and studied them with an unsupervised machine learning model. By
fine-tuning the hyperparameters of the model, we found that there is an
indication for four clusters from the bursts of FRB121102 instead of the two
clusters ("Classical" and "Atypical") suggested in the literature. Wherein, the
"Atypical" cluster can be further classified into three sub-clusters with
distinct characteristics. Our findings show that the clustering result we
obtained is more comprehensive not only because our study produced results
which are consistent with those in the literature but also because our work
uses more physical parameters to create these clusters. Overall, our methods
and analyses produced a more holistic approach in clustering the repeating FRBs
of FRB121102.Comment: 24 pages, 14 figure
Galaxy source counts at 7.7 m, 10 m and 15 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-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 Jy in F770W, F1000W and
F1500W filters, respectively, i.e., 100 times deeper than previous space
infrared telescopes such as Spitzer or AKARI. The number counts reach much
deeper than the broad bump around 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.Comment: 6 pages, 8 figures. Accepted for publication in MNRA
A Dyson Sphere around a black hole
The search for extraterrestrial intelligence (SETI) has been conducted for
nearly 60 years. A Dyson Sphere, a spherical structure that surrounds a star
and transports its radiative energy outward as an energy source for an advanced
civilisation, is one of the main targets of SETI. In this study, we discuss
whether building a Dyson Sphere around a black hole is effective. We consider
six energy sources: (i) the cosmic microwave background, (ii) the Hawking
radiation, (iii) an accretion disk, (iv) Bondi accretion, (v) a corona, and
(vi) relativistic jets. To develop future civilisations (for example, a Type II
civilisation), () is expected to
be needed. Among (iii) to (vi), the largest luminosity can be collected from an
accretion disk, reaching , enough to maintain a Type
II civilisation. Moreover, if a Dyson Sphere collects not only the
electromagnetic radiation but also other types of energy (e.g., kinetic energy)
from the jets, the total collected energy would be approximately 5 times
larger. Considering the emission from a Dyson Sphere, our results show that the
Dyson Sphere around a stellar-mass black hole in the Milky Way (
away from us) is detectable in the ultraviolet,
optical, near-infrared(), and mid-infrared() wavelengths via the waste heat
radiation using current telescopes such as Galaxy Evolution Explorer
Ultraviolet Sky Surveys. Performing model fitting to observed spectral energy
distributions and measuring the variability of radial velocity may help us to
identify these possible artificial structures.Comment: This paper has been accepted for publication in MNRA
Extreme damped Lyman- absorption in young star-forming galaxies at
The onset of galaxy formation is thought to be initiated by the infall of
neutral, pristine gas onto the first protogalactic halos. However, direct
constraints on the abundance of neutral atomic hydrogen (HI) in galaxies have
been difficult to obtain at early cosmic times. Here we present spectroscopic
observations with JWST of three galaxies at redshifts , about
Myr after the Big Bang, that show strong damped Lyman-
absorption ( cm) from HI in their local
surroundings, an order of magnitude in excess of the Lyman- absorption
caused by the neutral intergalactic medium at these redshifts. Consequently,
these early galaxies cannot be contributing significantly to reionization, at
least at their current evolutionary stages. Simulations of galaxy formation
show that such massive gas reservoirs surrounding young galaxies so early in
the history of the universe is a signature of galaxy formation in progress.Comment: Submitte
Spatially Resolved Stellar Populations of Galaxies in WHL0137-08 and MACS0647+70 Clusters as Revealed by JWST: How do Galaxies Grow and Quench Over Cosmic Time?
We study the spatially resolved stellar populations of 444 galaxies at
in two clusters (WHL0137-08 and MACS0647+70) and a blank field,
combining imaging data from HST and JWST to perform spatially resolved spectral
energy distribution (SED) modeling using pixedfit. The high spatial resolution
of the imaging data combined with magnification from gravitational lensing in
the cluster fields allows us to resolve some galaxies to sub-kpc scales (for
109 of our galaxies). At redshifts around cosmic noon and higher (), we find mass doubling times to be independent of radius,
inferred from flat specific star formation rate (sSFR) radial profiles and
similarities between the half-mass and half-SFR radii. At lower redshifts
(), a significant fraction of our star-forming
galaxies show evidence for nuclear starbursts, inferred from centrally elevated
sSFR, and a much smaller half-SFR radius compared to the half-mass radius. At
later epochs, we find more galaxies suppress star formation in their center but
are still actively forming stars in the disk. Overall, these trends point
toward a picture of inside-out galaxy growth consistent with theoretical models
and simulations. We also observe a tight relationship between the central mass
surface density and global stellar mass with dex scatter. Our
analysis demonstrates the potential of spatially resolved SED analysis with
JWST data. Future analysis with larger samples will be able to further explore
the assembly of galaxy mass and the growth of their structuresComment: 31 pages, 18 figures, accepted for publication in ApJ. Some examples
and tutorials of spatially resolved SED analysis will be available at
https://github.com/aabdurrouf/JWST-HST_resolvedSEDfit
Extinction-free Census of AGNs in the AKARI/IRC North Ecliptic Pole Field from 23-band Infrared Photometry from Space Telescopes
In order to understand the interaction between the central black hole and the whole galaxy or their co-evolution history along with cosmic time, a complete census of active galactic nuclei (AGN) is crucial. However, AGNs are often missed in optical, UV and soft X-ray observations since they could be obscured by gas and dust. A mid-infrared (mid-IR) survey supported by multiwavelength data is one of the best ways to find obscured AGN activities because it suffers less from extinction. Previous large IR photometric surveys, e.g., WISE and Spitzer, have gaps between the mid-IR filters. Therefore, star forming galaxy (SFG)-AGN diagnostics in the mid-IR were limited. The AKARI satellite has a unique continuous 9-band filter coverage in the near to mid-IR wavelengths. In this work, we take advantage of the state-of-the-art spectral energy distribution (SED) modelling software, CIGALE, to find AGNs in mid-IR. We found 126 AGNs in the NEP-Wide field with this method. We also investigate the energy released from the AGN as a fraction of the total IR luminosity of a galaxy. We found that the AGN contribution is larger at higher redshifts for a given IR luminosity. With the upcoming deep IR surveys, e.g., JWST, we expect to find more AGNs with our method
Two lensed star candidates at behind the galaxy cluster MACS J0647.7+7015
We report the discovery of two extremely magnified lensed star candidates
behind the galaxy cluster MACS J0647.7+7015, in recent multi-band James Webb
Space Telescope (JWST) NIRCam observations. The candidates are seen in a
previously known, dropout giant arc that straddles the
critical curve. The candidates lie near the expected critical curve position
but lack clear counter images on the other side of it, suggesting these are
possibly stars undergoing caustic crossings. We present revised lensing models
for the cluster, including multiply imaged galaxies newly identified in the
JWST data, and use them to estimate a background macro-magnification of at
least and at the positions of the two candidates,
respectively. With these values, we expect effective, caustic-crossing
magnifications of for the two star candidates. The Spectral Energy
Distributions (SEDs) of the two candidates match well spectra of B-type stars
with best-fit surface temperatures of K, and K,
respectively, and we show that such stars with masses M
and M, respectively, can become sufficiently magnified to
be observed. We briefly discuss other alternative explanations and conclude
these are likely lensed stars, but also acknowledge that the less magnified
candidate may instead be or reside in a star cluster. These star candidates
constitute the second highest-redshift examples to date after Earendel at
, establishing further the potential of studying extremely
magnified stars to high redshifts with the JWST. Planned visits including
NIRSpec observations will enable a more detailed view of the candidates already
in the near future.Comment: 12 pages, 5 figures, 2 tables. Fixed Fig 3. comments are welcom
Spatially resolved stellar populations of 0.3 < z < 6.0 Galaxies in WHL 0137–08 and MACS 0647+70 clusters as revealed by JWST: How do galaxies grow and quench over cosmic time?
We study the spatially resolved stellar populations of 444 galaxies at 0.3 < z < 6.0 in two clusters (WHL 0137–08 and MACS 0647+70) and a blank field, combining imaging data from the Hubble Space Telescope and JWST to perform spatially resolved spectral energy distribution (SED) modeling using piXedfit. The high spatial resolution of the imaging data combined with magnification from gravitational lensing in the cluster fields allows us to resolve a large fraction of our galaxies (109) to subkiloparsec scales. At redshifts around cosmic noon and higher (2.5 ≲ z ≲ 6.0), we find mass-doubling times to be independent of radius, inferred from flat specific star formation rate (sSFR) radial profiles and similarities between the half-mass and half-SFR radii. At lower redshifts (1.5 ≲ z ≲ 2.5), a significant fraction of our star-forming galaxies shows evidence for nuclear starbursts, inferred from a centrally elevated sSFR and a much smaller half-SFR radius compared to the half-mass radius. At later epochs, we find more galaxies suppress star formation in their centers but are still actively forming stars in the disk. Overall, these trends point toward a picture of inside-out galaxy growth consistent with theoretical models and simulations. We also observe a tight relationship between the central mass surface density and global stellar mass with ∼0.38 dex scatter. Our analysis demonstrates the potential of spatially resolved SED analysis with JWST data. Future analysis with larger samples will be able to further explore the assembly of galaxy mass and the growth of their structures.A. and T.H. are funded by a grant for JWST-GO-01433 provided by STScI under NASA contract NAS5-03127. The CosmicDawn Center is funded by the Danish National
Research Foundation (DNRF) under grant #140. P.D. acknowledges support from the NWO grant 016.VIDI.189.162 (“ODIN”) and from the European Commission’s and University of Groningen’s CO-FUND Rosalind Franklin program. R.A.W. acknowledges support from NASA JWST Interdisciplinary Scientist grants NAG5-12460, NNX14AN10G, and 80NSSC18K0200 from GSFC. A.Z. and A.K.M. acknowledge support by grant 2020750 from the United States–Israel Binational Science Foundation (BSF) and grant 2109066 from the United States National Science Foundation (NSF), and by
the Ministry of Science & Technology, Israel. M.O. acknowledges support from JSPS KAKENHI grant Nos. JP22H01260, JP20H05856, JP20H00181, and JP22K21349. A.A. acknowledges support from the Swedish Research Council (Vetenskapsrådet project grants 2021-05559). E.V. acknowledges financial support through grants PRIN-MIUR 2017WSCC32, 2020SKSTHZ, and the INAF GO Grant 2022 (P.I. E. Vanzella).Peer reviewe