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Demystifying the Infrared Emission of Type-1 AGNs from z~0 to z~6
The accretion of supermassive black holes (SMBHs) is accompanied by large columns of dusty gas connected to the host galaxy interstellar medium, resulting in significant emission in the infrared (IR) spectral range (λ ∼1–1000 μm). IR observations of these systems provide a wealth of information to reveal the physics of active galactic nuclei (AGN) and its role in galaxy evolution. In this thesis, I present a systematic study to characterize and decipher the IR emission of Type-1 AGNs over very broad ranges of luminosity
(L_{AGN,bol} ∼ 10^8 –10^14 L_⊙) and redshift (z ∼0–6) from different perspectives: (1) we have demonstrated that the intrinsic IR SEDs of type-1 quasars at z ∼0–6 have variations from hot-/warm-dust-deficient populations to the normal population and characterized the similar AGN-heated far-IR SEDs among different AGN populations; (2) By adding UV-optical obscuration and IR-reprocessed emission of an extended distribution of large dust grains to the intrinsic AGN templates, we have successfully reconciled the IR behaviors of all
major populations of type-1 AGNs, including the strong polar dust emission found in several Seyfert-1 nuclei by mid-IR interferometry observations and the large SED variations among local Seyfert-1 nuclei, normal blue quasars, extremely red quasars at z ∼2–3,
AGNs with mid-IR excess emission at z ∼0.7–2, hot-dust-obscured galaxies at z ∼1.5–4, and dust-free quasars at z ∼ 6, which provided critical insights on how the diverse AGN dust environment can be reflected by the different IR SED shapes; (3) With an innovative
usage of the time-series data from asteroid/supernova-hunting surveys, we have developed the first mid-IR dust reverberation survey of quasars and put several important constraints on the AGN torus structures and supported the unification model; (4) Based on an accurate
knowledge of galaxy and AGN IR emission, we have shown the far-IR properties of quasar host galaxies at z ∼5–6 should be similar to the low-metallicity starbursting galaxy Haro 11 and studied the quasar star formation rates and typical stellar masss when the Universe
is only ∼1 Gyr old
The Intrinsic Far-infrared Continua of Type-1 Quasars
The range of currently proposed active galactic nucleus (AGN) far-infrared
templates results in uncertainties in retrieving host galaxy information from
infrared observations and also undermines constraints on the outer part of the
AGN torus. We discuss how to test and reconcile these templates. Physically,
the fraction of the intrinsic AGN IR-processed luminosity compared with that
from the central engine should be consistent with the dust-covering factor. In
addition, besides reproducing the composite spectral energy distributions
(SEDs) of quasars, a correct AGN IR template combined with an accurate library
of star-forming galaxy templates should be able to reproduce the IR properties
of the host galaxies, such as the luminosity-dependent SED shapes and aromatic
feature strengths. We develop tests based on these expected behaviors and find
that the shape of the AGN intrinsic far-IR emission drops off rapidly starting
at m and can be matched by an Elvis et al. (1994)-like template
with minor modification. Despite the variations in the near- to mid-IR bands,
AGNs in quasars and Seyfert galaxies have remarkably similar intrinsic far-IR
SEDs at - m, suggesting similar emission character of
the outermost region of the circumnuclear torus. The variations of the
intrinsic AGN IR SEDs among the type-1 quasar population can be explained by
the changing relative strengths of four major dust components with similar
characteristic temperatures, and there is evidence for compact AGN-heated dusty
structures at sub-kpc scales in the far-IR.Comment: Minor corrections to match the published version, 14 pages, 9
figures, 5 tables. The quasar intrinsic IR templates can be found at
http://u.arizona.edu/~jianwei/data/AGN_temp.ascii or in the published pape
Polar Dust, Nuclear Obscuration and IR SED Diversity in Type-1 AGNs
Despite the hypothesized similar face-on viewing angles, the infrared
emission of type-1 AGNs has diverse spectral energy distribution (SED) shapes
that deviate substantially from the well-characterized quasar templates.
Motivated by the commonly-seen UV-optical obscuration and the discovery of
parsec-scale mid-IR polar dust emission in some nearby AGNs, we develop
semi-empirical SED libraries for reddened type-1 AGNs built on the quasar
intrinsic templates, assuming low-level extinction caused by an extended
distribution of large dust grains. We demonstrate that this model can reproduce
the nuclear UV-to-IR SED and the strong mid-IR polar dust emission of NGC 3783,
the type-1 AGN with the most relevant and robust observational constraints. In
addition, we compile 64 low- Seyfert-1 nuclei with negligible mid-IR star
formation contamination and satisfactorily fit the individual IR SEDs as well
as the composite UV to mid-IR composite SEDs. Given the success of these fits,
we characterize the possible infrared SED of AGN polar dust emission and
utilize a simple but effective strategy to infer its prevalence among type-1
AGNs. The SEDs of high- peculiar AGNs, including the extremely red quasars,
mid-IR warm-excess AGNs, and hot dust-obscured galaxies, can be also reproduced
by our model. These results indicate that the IR SEDs of most AGNs, regardless
of redshift or luminosity, arise from similar circumnuclear torus properties
but differ mainly due to the optical depths of extended obscuring dust
components.Comment: 37 pages, 22 figures, 5 tables; accepted for publication in The
Astrophysical Journal; the AGN templates can be retrieved from
https://github.com/karlan/AGN_template
Dust in Active Galactic Nuclei: Anomalous Silicate to Optical Extinction Ratios?
Dust plays a central role in the unification theory of active galactic nuclei
(AGNs). However, little is known about the nature (e.g., size, composition) of
the dust which forms a torus around the AGN. In this Letter we report a
systematic exploration of the optical extinction (A_V) and the silicate
absorption optical depth (\Delta\tau9.7) of 110 type 2 AGNs. We derive A_V from
the Balmer decrement based on the Sloan Digital Sky Survey data, and
\Delta\tau9.7 from the Spitzer/Infrared Spectrograph data. We find that with a
mean ratio of A_V/\Delta\tau9.7 ~ 5.5, the optical-to-silicate extinction
ratios of these AGNs are substantially lower than that of the Galactic diffuse
interstellar medium (ISM) for which A_V/\Delta\tau9.7 ~ 18.5. We argue that the
anomalously low A_V/\Delta\tau9.7 ratio could be due to the predominance of
larger grains in the AGN torus compared to that in the Galactic diffuse ISM.Comment: ApJL, 792, L9, in prin
Dust-Deficient Palomar-Green Quasars and the Diversity of AGN Intrinsic IR Emission
To elucidate the intrinsic broadband infrared (IR) emission properties of
active galactic nuclei (AGNs), we analyze the spectral energy distributions
(SEDs) of 87 z<0.5 Palomar-Green (PG) quasars. While the Elvis AGN template
with a moderate far-IR correction can reasonably match the SEDs of the AGN
components in ~60% of the sample (and is superior to alternatives such as that
by Assef), it fails on two quasar populations: 1) hot-dust-deficient (HDD)
quasars that show very weak emission thoroughly from the near-IR to the far-IR,
and 2) warm-dust-deficient (WDD) quasars that have similar hot dust emission as
normal quasars but are relatively faint in the mid- and far-IR. After building
composite AGN templates for these dust-deficient quasars, we successfully fit
the 0.3-500 {\mu}m SEDs of the PG sample with the appropriate AGN template, an
infrared template of a star-forming galaxy, and a host galaxy stellar template.
20 HDD and 12 WDD quasars are identified from the SED decomposition, including
seven ambiguous cases. Compared with normal quasars, the HDD quasars have AGN
with relatively low Eddington ratios and the fraction of WDD quasars increases
with AGN luminosity. Moreover, both the HDD and WDD quasar populations show
relatively stronger mid-IR silicate emission. Virtually identical SED
properties are also found in some quasars from z = 0.5 to 6. We propose a
conceptual model to demonstrate that the observed dust deficiency of quasars
can result from a change of structures of the circumnuclear tori that can occur
at any cosmic epoch.Comment: minor corrections to match the published versio
Long Fading Mid-Infrared Emission in Transient Coronal Line Emitters: Dust Echo of Tidal Disruption Flare
The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between and erg~s
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times erg s and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment
ViT-A*: Legged Robot Path Planning using Vision Transformer A*
Legged robots, particularly quadrupeds, offer
promising navigation capabilities, especially in scenarios requiring traversal over diverse terrains and obstacle avoidance.
This paper addresses the challenge of enabling legged robots
to navigate complex environments effectively through the integration of data-driven path-planning methods. We propose
an approach that utilizes differentiable planners, allowing the
learning of end-to-end global plans via a neural network for
commanding quadruped robots. The approach leverages 2D
maps and obstacle specifications as inputs to generate a global
path. To enhance the functionality of the developed neural
network-based path planner, we use Vision Transformers (ViT)
for map pre-processing, to enable the effective handling of
larger maps. Experimental evaluations on two real robotic
quadrupeds (Boston Dynamics Spot and Unitree Go1) demonstrate the effectiveness and versatility of the proposed approach
in generating reliable path plans
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