200 research outputs found
Investigative Study on Preprint Journal Club as an Effective Method of Teaching Latest Knowledge in Astronomy
As recent advancements in physics and astronomy rapidly rewrite textbooks,
there is a growing need in keeping abreast of the latest knowledge in these
fields. Reading preprints is one of the effective ways to do this. By having
journal clubs where people can read and discuss journals together, the benefits
of reading journals become more prevalent. We present an investigative study of
understanding the factors that affect the success of preprint journal clubs in
astronomy, more commonly known as Astro-ph/Astro-Coffee (hereafter called AC).
A survey was disseminated to understand how institutions from different
countries implement AC. We interviewed 9 survey respondents and from their
responses we identified four important factors that make AC successful:
commitment (how the organizer and attendees participate in AC), environment
(how conducive and comfortable AC is conducted), content (the discussed topics
in AC and how they are presented), and objective (the main goal/s of conducting
AC). We also present the format of our AC, an elective class which was
evaluated during the Spring Semester 2020 (March 2020 - June 2020). Our
evaluation with the attendees showed that enrollees (those who are enrolled and
are required to present papers regularly) tend to be more committed in
attending compared to audiences (those who are not enrolled and are not
required to present papers regularly). In addition, participants tend to find
papers outside their research field harder to read. Finally, we showed an
improvement in the weekly number of papers read after attending AC of those who
present papers regularly, and a high satisfaction rating of our AC. We
summarize the areas of improvement in our AC implementation, and we encourage
other institutions to evaluate their own AC in accordance with the four
aforementioned factors to assess the effectiveness of their AC in reaching
their goals.Comment: Accepted for publication in PRPER. A summary video is available at
http://www.youtube.com/watch?v=fzy2I_xA_dU&ab_channel=NthuCosmolog
Can luminous Lyman alpha emitters at 5.7 and 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
24.75 mag) Ly\alpha emitters (LAEs) around bright (AB magnitude < 24.75 mag)
LAEs even when the radius goes up to 10 pMpc for 5.7 LAEs. A
similar trend is found for z 6.6 LAEs but only within 1 pMpc radius
from the bright LAEs. We use a large sample of 1077 (962) LAEs at
5.7 ( 6.6) selected in total areas of 14 (21) deg 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 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 6 in the Universe.Comment: Accepted for publication at 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
Photometric Redshifts in the North Ecliptic Pole Wide Field based on a Deep Optical Survey with Hyper Suprime-Cam
The space infrared telescope has performed near- to mid-infrared
(MIR) observations on the North Ecliptic Pole Wide (NEPW) field (5.4 deg)
for about one year. took advantage of its continuous nine photometric
bands, compared with NASA's and WISE space telescopes, which had only
four filters with a wide gap in the MIR. The NEPW field lacked deep and
homogeneous optical data, limiting the use of nearly half of the IR sources for
extra-galactic studies owing to the absence of photometric redshifts
(photo-zs). To remedy this, we have recently obtained deep optical imaging over
the NEPW field with 5 bands (, , , , and ) of the Hyper
Suprime-Camera (HSC) on the Subaru 8m telescope. We optically identify AKARI-IR
sources along with supplementary and WISE data as well as
pre-existing optical data. In this work, we derive new photo-zs using a
template-fitting method code ( ) and reliable photometry
from 26 selected filters including HSC, , CFHT, Maidanak, KPNO,
and WISE data. We take 2026 spectroscopic redshifts (spec-z) from all
available spectroscopic surveys over the NEPW to calibrate and assess the
accuracy of the photo-zs. At z < 1.5, we achieve a weighted photo-z dispersion
of = 0.053 with = 11.3% catastrophic errors.Comment: 20 pages, 13 figures, accepted for publication in MNRAS. For summary
video, please see http://youtu.be/hjNJRCoBIg
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
Search for Optically Dark Infrared Galaxies without Counterparts of Subaru Hyper Suprime-Cam in the AKARI North Ecliptic Pole Wide Survey Field
We present the physical properties of AKARI sources without optical counterparts in optical images from the Hyper Suprime-Cam (HSC) on the Subaru telescope. Using the AKARI infrared (IR) source catalog and HSC optical catalog, we select 583 objects that do not have HSC counterparts in the AKARI North Ecliptic Pole wide survey field (~5 deg2). Because the HSC limiting magnitude is deep (gAB ~ 28.6), these are good candidates for extremely red star-forming galaxies (SFGs) and/or active galactic nuclei (AGNs), possibly at high redshifts. We compile multiwavelength data out to 500 μm and use them for fitting the spectral energy distribution with CIGALE to investigate the physical properties of AKARI galaxies without optical counterparts. We also compare their physical quantities with AKARI mid-IR selected galaxies with HSC counterparts. The estimated redshifts of AKARI objects without HSC counterparts range up to z ~ 4, significantly higher than for AKARI objects with HSC counterparts. We find that (i) 3.6 – 4.5 μm color, (ii) AGN luminosity, (iii) stellar mass, (iv) star formation rate, and (v) V-band dust attenuation in the interstellar medium of AKARI objects without HSC counterparts are systematically larger than those of AKARI objects with counterparts. These results suggest that our sample includes luminous, heavily dust-obscured SFGs/AGNs at z ~ 1–4 that are missed by previous optical surveys, providing very interesting targets for the coming era of the James Webb Space Telescope
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