The apparent detection of an exoplanet orbiting Fomalhaut was announced in 2008. However, subsequent observations of Fomalhaut b raised questions about its status: Unlike other exoplanets, it is ...bright in the optical and nondetected in the infrared, and its orbit appears to cross the debris ring around the star without the expected gravitational perturbations. We revisit previously published data and analyze additional Hubble Space Telescope (HST) data, finding that the source is likely on a radial trajectory and has faded and become extended. Dynamical and collisional modeling of a recently produced dust cloud yields results consistent with the observations. Fomalhaut b appears to be a directly imaged catastrophic collision between two large planetesimals in an extrasolar planetary system. Similar events should be very rare in quiescent planetary systems of the age of Fomalhaut, suggesting that we are possibly witnessing the effects of gravitational stirring due to the orbital evolution of hypothetical planet(s) around the star.
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 ∼20 m and can be matched by an Elvis et al.-like template with a 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 λ ∼ 20-100 m, suggesting a 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-kiloparsec scales in the far-IR.
Abstract
We characterize the stellar mass of J2239+0207, a
z
∼ 6.25 sub-Eddington quasar (
M
1450
= −24.6), using dedicated JWST/NIRCam medium-band observations of a nearby point-spread function star ...to remove the central point source and reveal the underlying galaxy emission. We detect the host galaxy in two bands longward of the Balmer break, obtaining a stellar mass of ∼10
10
M
⊙
, more than an order of magnitude less than this quasar’s existing measured C
ii
dynamical mass. We additionally calculate the mass of J2239+0207's central supermassive black hole using JWST/NIRSpec integral field unit observations, and determine that the black hole is ∼15 times more massive than predicted by the local
M
BH
–
M
*
relation, similar to many high-redshift quasars with dynamical masses determined via millimeter-wave line widths. We carefully consider potential selection effects at play, and find that even when
z
∼ 6 quasars are compared to a local sample with similarly determined dynamical masses, many of the high-redshift quasars appear to possess overmassive black holes. We conclude
z
∼ 6 quasars are likely to have a larger spread about the
M
BH
–
M
*
relation than observed in the local Universe.
Hiding Dust around ϵ Eridani Wolff, Schuyler Grace; Gáspár, András; H. Rieke, George ...
The Astronomical journal,
03/2023, Letnik:
165, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
With a Jupiter-like exoplanet and a debris disk with both asteroid and Kuiper Belt analogs,
ϵ
Eridani has a fascinating resemblance to our expectations for a young solar system. We present a ...deep Hubble Space Telescope/Space Telescope Imaging Spectrograph coronographic data set using eight orbit visits and the point-spread function calibrator
δ
Eridani. While we were unable to detect the debris disk, we place stringent constraints on the scattered light surface brightness of
∼
4
μ
Jy
arcsec
−
2
.
We combine this scattered light detection limit with a reanalysis of archival near- and mid-infrared observations and a dynamical model of the full planetary system to refine our model of the
ϵ
Eridani debris disk components. Radiative transfer modeling suggests an asteroid belt analog inside of 3 au, an intermediate disk component in the 6–37 au region, and a Kuiper Belt analog colocated with the narrow belt observed in the millimeter (69 au). Modeling also suggests a large minimum grain size requiring either very porous grains or a suppression of small grain production, and a radially stratified particle size distribution. The inner disk regions require a steep power-law slope (
s
−3.8
where
s
is the grain size) weighted toward smaller grains and the outer disk prefers a shallower slope (
s
−3.4
) with a minimum particle size of >2
μ
m. These conclusions will be enhanced by upcoming coronagraphic observations of the system with the James Webb Space Telescope, which will pinpoint the radial location of the dust belts and further diagnose the dust particle properties.
We present estimates of black hole accretion rates (BHARs) and nuclear, extended, and total star formation rates for a complete sample of Seyfert galaxies. Using data from the Spitzer Space ...Telescope, we measure the active galactic nucleus (AGN) luminosity using the OIV lambda25.89 mum emission line and the star-forming luminosity using the 11.3 mum aromatic feature and extended 24 mum continuum emission. We find that black hole growth is strongly correlated with nuclear (r < 1 kpc) star formation, but only weakly correlated with extended (r > 1 kpc) star formation in the host galaxy. In particular, the nuclear star formation rate (SFR) traced by the 11.3 mum aromatic feature follows a relationship with the BHAR of the form SFR is proportional to M sub(BH) super(0.8), with an observed scatter of 0.5 dex. This SFR-BHAR relationship persists when additional star formation in physically matched r = 1 kpc apertures is included, taking the form SFR is proportional to M sub(BH) super(0.6). However, the relationship becomes almost indiscernible when total SFRs are considered. This suggests a physical connection between the gas on sub-kiloparsec and sub-parsec scales in local Seyfert galaxies that is not related to external processes in the host galaxy. It also suggests that the observed scaling between star formation and black hole growth for samples of AGNs will depend on whether the star formation is dominated by a nuclear or an extended component. We estimate the integrated black hole and bulge growth that occurs in these galaxies and find that an AGN duty cycle of 5%-10% would maintain the ratio between black hole and bulge masses seen in the local universe.
We analyze a sample of 62600 Spitzer MIPS 24 km sources brighter than 680 kJy and located in the Chandra Deep Field-South to characterize the evolution of the comoving infrared (IR) energy density of ...the universe up to z 6 1. Using published ancillary optical data, we first obtain a nearly complete redshift determination for the 24 km objects associated with R 24 mag counterparts at z 1. These sources represent 655%-60% of the total MIPS 24 km population with f sub(24)k sub(m) 80 kJy, the rest of the sample likely lying at higher redshifts. We then determine an estimate of their total IR luminosities using various libraries of IR spectral energy distributions. We find that the 24 km population at 0.5 z 1 is dominated by "luminous infrared galaxies" (i.e., 10 super(11) L sub( ), L sub(IR) , 10 super(12) L sub( )), the counterparts of which appear to be also luminous at optical wavelengths and tend to be more massive than the majority of optically selected galaxies. A significant number of fainter sources (5 x 10 super(10) L sub( )L sub(IR) , 10 super(11) L sub( ))are also detected at similar distances. We finally derive 15 km and total IR luminosity functions (LFs) up to z 6 1. In agreement with the previous results from the Infrared Space Observatory (ISO) and SCUBA and as expected from the MIPS source number counts, we find very strong evolution of the contribution of the IR-selected population with look-back time. Pure evolution in density is firmly excluded by the data, but we find considerable degeneracy between strict evolution in luminosity and a combination of increases in both density and luminosity L IR a (1 + z) super(3.2) super(+) sub(-) super(0) sub(0) super(.) sub(.) super(7) sub(2) hIR a (1 + z) super(0.7) super(+) sub(-) super(0) sub(0) super(.) sub(.) super(6) sub(2). A significant steepening of the faint-end slope of the IR luminosity function is also unlikely, as it would overproduce the faint 24 km source number counts. Our results imply that the comoving IR energy density of the universe evolves as (1 + z) super(3.9c0.4) up to z 6 1 and that galaxies luminous in the infrared (i.e., L sub(IR) . 10 super(11) L sub( )) are responsible for 70% c 15% of this energy density at z 6 1. Taking into account the contribution of the UV luminosity evolving as (1 + z)6 super(2.5), we infer that these IR-luminous sources dominate the star-forming activity beyond z 6 0.7. The uncertainties affecting these conclusions are largely dominated by the errors in the k-corrections used to convert 24 km fluxes into luminosities.
The continued operation of the Wide-field Infrared Survey Explorer (WISE), combined with several ground-based optical transient surveys (e.g., CRTS, ASAS-SN, and PTF), offers an unprecedented ...opportunity to explore the dust structures in luminous active galactic nuclei (AGNs). We use these data for a mid-IR dust reverberation mapping (RM) study of 87 archetypal Palomar-Green quasars at z 0.5. To cope with various contaminations of the photometry data and the sparse time sampling of the light curves, procedures to combine these data sets and retrieve the dust RM signals have been developed. We find that ∼70% of the sample (with a completeness correction up to 95%) has convincing mid-IR time lags in the WISE W1 (∼3.4 m) and W2 (∼4.5 m) bands, and they are proportional to the square root of the AGN luminosity. Combined with previous K-band (∼2.2 m) RM results in the literature, the inferred dust emission size ratios are R K : R W 1 : R W 2 = 0.6 : 1 : 1.2 . Under simple assumptions, we put preliminary constraints on the projected dust surface density at these bands and reveal the possibly different torus structures among hot-dust-deficient, warm-dust-deficient, and normal quasars from the reverberation signals. With multi-epoch Spitzer data and later WISE photometry, we also explore AGN IR variability at 10-24 m over a 5 yr timescale. Except for blazars and flat-spectrum radio sources, the majority of AGNs have typical variation amplitudes at 24 m of no more than 10% of that in the W1 band, indicating that the dust reverberation signals damp out quickly at longer wavelengths. In particular, steep-spectrum radio quasars also lack strong 24 m variability, consistent with the unification picture of radio-loud AGNs.
We use Hubble Space Telescope (HST) NICMOS continuum and Paa observations to study the near-infrared and star formation properties of a representative sample of 30 local (d 635-75 Mpc) luminous ...infrared galaxies (LIRGs, infrared 8-1000 km luminosities of log L sub(IR) = 11-11.9 L sub( )). The data provide spatial resolutions of 25-50 pc and cover the central 63.3-7.1 kpc regions of these galaxies. About half of the LIRGs show compact (61-2 kpc) Paa emission with a high surface brightness in the form of nuclear emission, rings, and minispirals. The rest of the sample show Paa emission along the disk and the spiral arms extending over scales of 3-7 kpc and larger. About half of the sample contains H II regions with Ha luminosities significantly higher than those observed in normal galaxies. There is a linear empirical relationship between the mid-IR 24 km and hydrogen recombination (extinction-corrected Paa) luminosity for these LIRGs, and the H II regions in the central part of M51. This relation holds over more than four decades in luminosity, suggesting that the mid-IR emission is a good tracer of the star formation rate (SFR). Analogous to the widely used relation between the SFR and total IR luminosity of R. Kennicutt, we derive an empirical calibration of the SFR in terms of the monochromatic 24 km luminosity that can be used for luminous, dusty galaxies.
Abstract
We probe the dusty environment of the archetypical Type 1 active galactic nucleus (AGN) in NGC 4151 with comprehensive IR reverberation mapping over several decades, in the
J
(∼1.22
μ
m),
H
...(∼1.63
μ
m),
K
(∼2.19
μ
m),
L
(∼3.45
μ
m), and
N
bands (∼10.6
μ
m), plus multiple measurements at 20–40
μ
m. At 1–4
μ
m, the hot dust reverberation signals come from two distinct dust populations at separate radii (∼0.033 pc and ∼0.076 pc), with temperatures of ∼1500–2500 K and ∼900–1000 K, consistent with the expected properties of sublimating graphite and silicate dust grains. The domination of the torus infrared output by carbon and silicate grains near their sublimation temperatures and radii may account for the general similarity of AGN near-IR spectral energy distributions. The torus inner edge defined by the hottest dust remains at roughly the same radius independent of the AGN optical luminosity over ∼25 yr. The emission by hot dust warmed directly by the optical/UV AGN output has increased gradually by ∼4% yr
−1
, indicating a possibly growing torus. A third dust component at ∼700 K does not seem to participate directly in the IR reverberation behavior, and its emission may originate deep in the circumnuclear torus. We find a reverberation signal at ∼10
μ
m with an inferred radius for the warm dust of ∼2.2–3.1 pc. The lack of variability at 20–40
μ
m indicates that the far-IR emission comes from even more extended regions. The torus properties revealed by dust reverberation analysis are inconsistent with predictions from pure clumpy torus models. Instead, the longer-wavelength emission possibly originates in a flared torus or the polar wind.
We have discovered a remarkable warm (130-160 K) molecular hydrogen tail with a H{sub 2} mass of approximately 4 x 10{sup 7} M{sub sun} extending 20 kpc from a cluster spiral galaxy, ESO 137-001, in ...Abell 3627. At least half of this gas is lost permanently to the intracluster medium, as the tail extends beyond the tidal radius of the galaxy. We also detect a hot (400-550 K) component in the tail that is approximately 1% of the mass. The large H{sub 2} line to IR continuum luminosity ratio in the tail indicates that star formation is not a major excitation source and that the gas is possibly shock-heated. This discovery confirms that the galaxy is currently undergoing ram-pressure stripping, as also indicated by its previously discovered X-ray and H{alpha} tails. We estimate that the galaxy is losing its warm H{sub 2} gas at a rate of {approx}2-3 M{sub sun} yr{sup -1}. The true mass-loss rate is likely higher if we account for cold molecular gas and atomic gas. We predict that the galaxy will lose most of its gas in a single pass through the core and place a strong upper limit on the ram-pressure timescale of 1 Gyr. We also study the star-forming properties of the galaxy and its tail. We identify most of the previously discovered external H{alpha} sources within the tail in our 8 {mu}m data but not in our 3.6 {mu}m data; IRS spectroscopy of the region containing these H{alpha} sources also reveals aromatic features typically associated with star formation. From the positions of these H II regions, it appears that star formation is not occurring throughout the molecular hydrogen tail but only immediately downstream of the galaxy. Some of these H II regions lie outside the tidal radius of the galaxy, indicating that ram-pressure stripping can be a source of intracluster stars.
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