21 research outputs found
Nuclear Activity in the Low Metallicity Dwarf Galaxy SDSS J0944-0038: A Glimpse into the Primordial Universe
Local low metallicity dwarf galaxies are relics of the early universe and
hold clues into the origins of supermassive black holes (SMBHs). In recent
work, coronal lines have been used to unveil a population of candidate
accreting black holes in dwarf galaxies with gas phase metallicities and
stellar masses well below the host galaxies of any previously known AGNs. Using
MUSE/VLT observations, we report the detection of [Fe X] 6374 coronal
line emission and a broad H line in the nucleus of SDSS
J094401.87003832.1, a nearby () metal poor dwarf galaxy at least
fifty times less massive than the LMC. The [Fe X] 6374 emission is
compact and centered on the brightest nuclear source, with a spatial extent of
100 pc. The [Fe X] luminosity is erg s,
within the range seen in previously identified AGNs in the dwarf galaxy
population. This line has never been observed in gas ionized by hot stars.
While it can be produced in supernova ejecta, the [Fe X] flux from SDSS
J094401.87003832.1 has persisted over the ~19 year time period between the
SDSS and MUSE observations, ruling out supernovae as the origin for the
emission. The FWHM of the broad component of the H line is
km s and its luminosity is erg s,
lower than the broad line luminosities of previously identified low mass broad
line AGNs. These observations, together with previously reported
multi-wavelength observations, can most plausibly be explained by the presence
of an accreting intermediate mass black hole in a primordial galaxy analog.
However, we cannot rule out the possibility that current stellar population
models of metal poor stars significantly under-predict the stellar ionizing
photon flux, and that metal poor stars can produce an extreme ionizing spectrum
similar to that produced by AGNs.Comment: 12 pages, 5 figures, 1 table, submitted to ApJL. Comments welcom
Relics of Supermassive Black Hole Seeds: The Discovery of an Accreting Black Hole in an Optically Normal, Low Metallicity Dwarf Galaxy
The detection and characterization of supermassive black holes (SMBHs) in
local low mass galaxies is crucial to our understanding of the origins of
SMBHs. This statement assumes that low mass galaxies have had a relatively
quiet cosmic history, so that their black holes have not undergone significant
growth and therefore can be treated as relics of the original SMBH seeds. While
recent studies have found optical signatures of active galactic nuclei (AGNs)
in a growing population of dwarf galaxies, these studies are biased against low
metallicity and relatively merger-free galaxies, thus missing precisely the
demographic in which to search for the relics of SMBH seeds. Here, we report
the detection of the [\ion{Si}{6}]1.963~m coronal line (CL), a robust
indicator of an AGN in the galaxy SDSS~J160135.95+311353.7, a nearby
() low metallicity galaxy with a stellar mass approximately an order
of magnitude lower than the LMC (~M) and no
optical evidence for an AGN. The AGN bolometric luminosity implied by the CL
detection is ~erg~s, precisely what is predicted from
its near-infrared continuum emission based on well-studied AGNs. Our results
are consistent with a black hole of mass ~M, in line with
expectations based on its stellar mass. This is the first time a near-infrared
CL has been detected in a low mass, low metallicity galaxy with no optical
evidence for AGN activity, providing confirmation of the utility of infrared
CLs in finding AGNs in low mass galaxies when optical diagnostics fail. These
observations highlight a powerful avenue of investigation to hunt for low mass
black holes in the JWST era.Comment: 11 pages, 3 figures, accepted to ApJ
An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Sub-Solar Water Abundance
We present an optical-to-infrared transmission spectrum of the inflated
sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite
(TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic
grism, and the Spitzer Space Telescope (Spitzer) at 3.6 m, in addition to
a Spitzer 4.5 m secondary eclipse. The precise HST transmission spectrum
notably reveals a low-amplitude water feature with an unusual shape. Based on
free retrieval analyses with varying molecular abundances, we find strong
evidence for water absorption. Depending on model assumptions, we also find
tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water
abundance is generally solar (0.001--0.7 solar
over a range of model assumptions), several orders of magnitude lower than
expected from planet formation models based on the solar system metallicity
trend. We also consider chemical equilibrium and self-consistent 1D
radiative-convective equilibrium model fits and find they too prefer low
metallicities (, consistent with the free retrieval
results). However, all the retrievals should be interpreted with some caution
since they either require additional absorbers that are far out of chemical
equilibrium to explain the shape of the spectrum or are simply poor fits to the
data. Finally, we find the Spitzer secondary eclipse is indicative of full heat
redistribution from KELT-11b's dayside to nightside, assuming a clear dayside.
These potentially unusual results for KELT-11b's composition are suggestive of
new challenges on the horizon for atmosphere and formation models in the face
of increasingly precise measurements of exoplanet spectra.Comment: Accepted to The Astronomical Journal. 31 pages, 20 figures, 7 table
EarthFinder Probe Mission Concept Study: Characterizing nearby stellar exoplanet systems with Earth-mass analogs for future direct imaging
EarthFinder is a NASA Astrophysics Probe mission concept selected for study
as input to the 2020 Astrophysics National Academies Decadal Survey. The
EarthFinder concept is based on a dramatic shift in our understanding of how
PRV measurements should be made. We propose a new paradigm which brings the
high precision, high cadence domain of transit photometry as demonstrated by
Kepler and TESS to the challenges of PRV measurements at the cm/s level. This
new paradigm takes advantage of: 1) broad wavelength coverage from the UV to
NIR which is only possible from space to minimize the effects of stellar
activity; 2) extremely compact, highly stable, highly efficient spectrometers
(R>150,000) which require the diffraction-limited imaging possible only from
space over a broad wavelength range; 3) the revolution in laser-based
wavelength standards to ensure cm/s precision over many years; 4) a high
cadence observing program which minimizes sampling-induced period aliases; 5)
exploiting the absolute flux stability from space for continuum normalization
for unprecedented line-by-line analysis not possible from the ground; and 6)
focusing on the bright stars which will be the targets of future imaging
missions so that EarthFinder can use a ~1.5 m telescope.Comment: NASA Probe Mission concept white paper for 2020 Astrophysics National
Academies Decadal Surve
EarthFinder Probe Mission Concept Study: Characterizing nearby stellar exoplanet systems with Earth-mass analogs for future direct imaging
EarthFinder is a NASA Astrophysics Probe mission concept selected for study as input to the 2020 Astrophysics National Academies Decadal Survey. The EarthFinder concept is based on a dramatic shift in our understanding of how PRV measurements should be made. We propose a new paradigm which brings the high precision, high cadence domain of transit photometry as demonstrated by Kepler and TESS to the challenges of PRV measurements at the cm/s level. This new paradigm takes advantage of: 1) broad wavelength coverage from the UV to NIR which is only possible from space to minimize the effects of stellar activity; 2) extremely compact, highly stable, highly efficient spectrometers (R>150,000) which require the diffraction-limited imaging possible only from space over a broad wavelength range; 3) the revolution in laser-based wavelength standards to ensure cm/s precision over many years; 4) a high cadence observing program which minimizes sampling-induced period aliases; 5) exploiting the absolute flux stability from space for continuum normalization for unprecedented line-by-line analysis not possible from the ground; and 6) focusing on the bright stars which will be the targets of future imaging missions so that EarthFinder can use a ~1.5 m telescope
A planet within the debris disk around the pre-main-sequence star AU Microscopii
AU Microscopii (AU Mic) is the second closest pre main sequence star, at a
distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses
a relatively rare and spatially resolved3 edge-on debris disk extending from
about 35 to 210 astronomical units from the star, and with clumps exhibiting
non-Keplerian motion. Detection of newly formed planets around such a star is
challenged by the presence of spots, plage, flares and other manifestations of
magnetic activity on the star. Here we report observations of a planet
transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of
8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4
Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 sigma
confidence. Our observations of a planet co-existing with a debris disk offer
the opportunity to test the predictions of current models of planet formation
and evolution.Comment: Nature, published June 24th [author spelling name fix
The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report
The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument