84 research outputs found
Completing the Census of AGN in GOODS-S/HUDF: New Ultra-Deep Radio Imaging and Predictions for JWST
A global understanding of Active Galactic Nuclei (AGN) and their host
galaxies hinges on completing a census of AGN activity without selection biases
down to the low-luminosity regime. Toward that goal, we identify AGN within
faint radio populations at cosmic noon selected from new ultra-deep, high
resolution imaging from the Karl G. Jansky Very Large Array at 6 and 3 GHz.
These radio data are spatially coincident with the ultra-deep legacy surveys in
the GOODS-S/HUDF region, particularly the unparalleled Chandra 7 Ms X-ray
imaging. Combined, these datasets provide a unique basis for a thorough census
of AGN, allowing simultaneous identification via (1) high X-ray luminosity; (2)
hard X-ray spectra; (3) excess X-ray relative to 6 GHz; (4) mid-IR colors; (5)
SED fitting; (6) radio excess via the radio-infrared relation; (7) flat radio
spectra via multi-band radio; and (8) optical spectroscopy. We uncover AGN in
fully half our faint radio sample, indicating a source density of one AGN
arcmin, with a similar number of radio-undetected AGN identified via
X-ray over the same area. Our radio-detected AGN are majority radio-quiet, with
radio emission consistent with being powered predominantly by star formation.
Nevertheless, we find AGN radio signatures in our sample: with radio
excess indicating radio-loud activity and of radio-quiet AGN
candidates with flat or inverted radio spectra. The latter is a lower limit,
pending our upcoming deeper 3 GHz survey. Finally, despite these extensive
datasets, this work is likely still missing heavily obscured AGN. We discuss in
detail this elusive population and the prospects for completing our AGN census
with JWST/MIRI.Comment: Accepted for publication in ApJ. 30 pages, 13 figures, 2 tables, 2
appendices. Minor update to fix typos and better match published versio
Probing Obscured Massive Black Hole Accretion and Growth since Cosmic Dawn
Most of the stars today reside in galactic spheroids, whose properties are tightly tied to the supermassive black holes (MBHs) at their centers, implying that the accretion activity onto MBHs leaves a lasting imprint on the evolution of their host galaxies. Despite the importance of this so-called MBH-galaxy co-evolution, the physical mechanisms responsible for driving this relationship - such as the dominant mode of energetic feedback from active galactic nuclei (AGN) - remain a poorly understand aspect of galaxy assembly. A key challenge for identifying and characterizing AGN during the peak epoch of galaxy assembly and beyond is the presence of large columns of gas and dust, which fuels the growth of their MBHs but effectively obscures them from view in optical and X-ray studies. The high sensitivity of the ngVLA will capture emission from AGN in an extinction-free manner out to z ∼ 6 and beyond. At lower-redshifts (z ∼ 2), the high angular resolution of the ngVLA will enable spatially-resolved studies capable of localizing the sites of actively growing MBHs within their host galaxies during the peak epoch of cosmic assembly
Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks
Luminous debris disks of warm dust in the terrestrial planet zones around
solar-like stars are recently found to vary, indicative of ongoing large-scale
collisions of rocky objects. We use Spitzer 3.6 and 4.5 {\mu}m time-series
observations in 2012 and 2013 (extended to 2014 in one case) to monitor 5 more
debris disks with unusually high fractional luminosities ("extreme debris
disk"), including P1121 in the open cluster M47 (80 Myr), HD 15407A in the AB
Dor moving group (80 Myr), HD 23514 in the Pleiades (120 Myr), HD 145263 in the
Upper Sco Association (10 Myr), and the field star BD+20 307 (>1 Gyr). Together
with the published results for ID8 in NGC 2547 (35 Myr), this makes the first
systematic time-domain investigation of planetary impacts outside the solar
system. Significant variations with timescales shorter than a year are detected
in five out of the six extreme debris disks we have monitored. However,
different systems show diverse sets of characteristics in the time domain,
including long-term decay or growth, disk temperature variations, and possible
periodicity.Comment: 50 pages, 14 figures, 9 tables; Accepted for publication in the
Astrophysical Journa
Large Impacts around a Solar Analog Star in the Era of Terrestrial Planet Formation
The final assembly of terrestrial planets occurs via massive collisions,
which can launch copious clouds of dust that are warmed by the star and glow in
the infrared. We report the real-time detection of a debris-producing impact in
the terrestrial planet zone around a 35-million year-old solar analog star. We
observed a substantial brightening of the debris disk at 3-5 {\mu}m, followed
by a decay over a year, with quasi-periodic modulations of the disk flux. The
behavior is consistent with the occurrence of a violent impact that produced
vapor out of which a thick cloud of silicate spherules condensed that were
ground into dust by collisions. These results demonstrate how the time domain
can become a new dimension for the study of terrestrial planet formation.Comment: 25 pages, 7 figures (fixed a typo in name
Cosmic evolution of radio-excess active galactic nuclei in quiescent and star-forming galaxies across 0 < z < 4
Context. Radio-excess active galactic nuclei (radio-AGNs) are essential to our understanding of both the physics of black hole (BH) accretion and the interaction between BHs and host galaxies. Recent deep and wide radio continuum surveys have made it possible to study radio-AGNs down to lower luminosities and up to higher redshifts than previous studies, and are providing new insights into the abundance and physical origin of radio-AGNs.Aims. Here we focus on the cosmic evolution, physical properties, and AGN-host galaxy connections of radio-AGNs selected from a total sample of ∼400 000 galaxies at 0 < z < 4 in the GOODS-N and COSMOS fields.Methods. Combining the deep radio continuum data with multi-band, de-blended far-infrared, and submillimeter data, we were able to identify 983 radio-AGNs out of the entire galaxy sample through radio excess relative to the far-infrared–radio relation.Results. We studied the cosmic evolution of 1.4 GHz radio luminosity functions (RLFs) for both star-forming galaxies (SFGs) and radio-AGNs, which can be well described by a pure luminosity evolution of L⋆ ∝ (1 + z)−0.34 × z + 3.57 and a pure density evolution of Φ⋆ ∝ (1 + z)−0.77 × z + 2.69, respectively. We derived the turnover luminosity, above which the number density of radio-AGNs surpasses that of SFGs. We show that this crossover luminosity increases with increasing redshifts, from 1022.9 W Hz−1 at z ∼ 0 to 1025.2 W Hz−1 at z ∼ 4. At the full redshift range of 0 < z < 4, we further derive the probability (pradio) of SFGs and quiescent galaxies (QGs) hosting a radio-AGN, as a function of stellar mass (M⋆), radio luminosity (LR), and redshift (z), which yields pradio ∝ (1+z)3.08 M⋆1.06 LR−0.77 for SFGs, and pradio ∝ (1+z)2.47 M⋆1.41 LR−0.60 for QGs, respectively.Conclusions. The quantitative relation for the probabilities of galaxies hosting a radio-AGN indicates that radio-AGNs in QGs prefer to reside in more massive galaxies with higher LR than those in SFGs. The fraction of radio-AGN increases toward higher redshift in both SFGs and QGs, with a more rapid increase in SFGs
JWST and ALMA imaging of dust-obscured, massive substructures in a typical star-forming disk galaxy
We present an identification of dust-attenuated star-forming galactic-disk
substructures in a typical star-forming galaxy (SFG), UDF2, at . To
date, substructures containing significant buildup of stellar mass and actively
forming stars have yet to be found in typical (i.e., main-sequence) SFGs at . This is due to the strong dust attenuation common in massive galaxies at
the epoch and the scarcity of high-resolution, high-sensitivity
extinction-independent imaging. To search for disk substructures, we subtracted
the central stellar-mass disk from the JWST/NIRCam rest-frame 1.2 m image
( resolution) and subtracted, in the visibility plane, the central
starburst disk from ALMA rest-frame 240 m observations (
resolution). The residual images revealed substructures at rest-frame 1.2
m co-located with those found at rest-frame 240 m, kpc
away from the galactic center. The largest substructure contains % of
the total stellar mass and % of the total SFR of the galaxy. While
UDF2 exhibits a kinematically-ordered velocity field of molecular gas
consistent with a secularly evolving disk, more sensitive observations are
required to characterize the nature and the origin of this substructure (spiral
arms, minor merger, or other types of disk instabilities). UDF2 resides in an
overdense region ( massive galaxies within 70 kpc projected
distance at ) and the substructures may be associated with
interaction-induced instabilities. Importantly, a statistical sample of such
substructures identified with JWST and ALMA could play a key role in bridging
the gap between the bulge-forming starburst and the rest of the galaxy.Comment: 7 pages, 5 figures; ApJL, accepte
SXDF-ALMA 2 Arcmin^2 Deep Survey: Resolving and Characterizing the Infrared Extragalactic Background Light Down to 0.5 mJy
We present a multi-wavelength analysis of five submillimeter sources (S_1.1mm
= 0.54-2.02 mJy) that were detected during our 1.1-mm-deep continuum survey in
the SXDF-UDS-CANDELS field (2 arcmin^2, 1sigma = 0.055 mJy beam^-1) using the
Atacama Large Millimeter/submillimeter Array (ALMA). The two brightest sources
correspond to a known single-dish (AzTEC) selected bright submillimeter galaxy
(SMG), whereas the remaining three are faint SMGs newly uncovered by ALMA. If
we exclude the two brightest sources, the contribution of the ALMA-detected
faint SMGs to the infrared extragalactic background light is estimated to be ~
4.1^{+5.4}_{-3.0} Jy deg^{-2}, which corresponds to ~ 16^{+22}_{-12}% of the
infrared extragalactic background light. This suggests that their contribution
to the infrared extragalactic background light is as large as that of bright
SMGs. We identified multi-wavelength counterparts of the five ALMA sources. One
of the sources (SXDF-ALMA3) is extremely faint in the optical to near-infrared
region despite its infrared luminosity (L_IR ~ 1e12 L_sun or SFR ~ 100 M_sun
yr^{-1}). By fitting the spectral energy distributions (SEDs) at the
optical-to-near-infrared wavelengths of the remaining four ALMA sources, we
obtained the photometric redshifts (z_photo) and stellar masses (M_*): z_photo
~ 1.3-2.5, M_* ~ (3.5-9.5)e10 M_sun. We also derived their star formation rates
(SFRs) and specific SFRs (sSFRs) as ~ 30-200 M_sun yr^{-1} and ~ 0.8-2
Gyr^{-1}, respectively. These values imply that they are main-sequence
star-forming galaxies.Comment: PASJ accepted, 15 pages, 6 figures, 2 table
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