28 research outputs found
A search of CO emission lines in blazars: the low molecular gas content of BL Lac objects compared to quasars
BL Lacertae (Lac) objects that are detected at very high energies (VHE) are of fundamental importance to study multiple astrophysical processes, including the physics of jets, the properties of the extragalactic background light and the strength of the intergalactic magnetic field. Unfortunately, since most blazars have featureless optical spectra that preclude a redshift determination, a substantial fraction of these VHE extragalactic sources cannot be used for cosmological studies. To assess whether molecular lines are a viable way to establish distances, we have undertaken a pilot programme at the Institut of Millimétrique (IRAM) 30 m telescope to search for CO lines in three BL Lac objects with known redshifts. We report a positive detection of M⊙ towards 1ES 1959+650, but due to the poor quality of the baseline, this value is affected by a large systematic uncertainty. For the remaining two sources, W Comae and RGB J0710+591, we derive 3σ upper limits at, respectively, and 1.6 × 109 M⊙, assuming a line width of 150 km s−1 and a standard conversion factor α = 4 M⊙ (K km s−1 pc2)−1. If these low molecular gas masses are typical for blazars, blind redshift searches in molecular lines are currently unfeasible. However, deep observations are still a promising way to obtain precise redshifts for sources whose approximate distances are known via indirect methods. Our observations further reveal a deficiency of molecular gas in BL Lac objects compared to quasars, suggesting that the host galaxies of these two types of active galactic nuclei (AGN) are not drawn from the same parent population. Future observations are needed to assess whether this discrepancy is statistically significant, but our pilot programme shows how studies of the interstellar medium in AGN can provide key information to explore the connection between the active nuclei and the host galaxie
On the redshift of the blazar PKS0447-439
PKS0447-439 is one of the BL Lacertae objects that have been detected at very
high energy. There has been a recent report of a lower limit of z>1.246 for the
redshift of this blazar, challenging the current paradigm in which very
high-energy gamma-rays cannot freely propagate in the z>1 universe. In this
research note, we present a new MagE/Magellan spectrum of PKS0447-439 with
exquisite signal-to-noise (S/N>150 at 6500A). Our analysis confirms the
presence of the previously-reported absorption line at 6280A, which we
identify, however, with a known telluric absorption, invalidating the claim
that this blazar lies at z>1. Since no other extragalactic spectral features
are detected, we cannot establish a redshift based on our spectrum.Comment: 3 pages, 2 figures. Research note. A&A accepte
A search of CO emission lines in blazars: the low molecular gas content of BL Lac objects compared to quasars
BL Lacertae (Lac) objects that are detected at very-high energies (VHE) are
of fundamental importance to study multiple astrophysical processes, including
the physics of jets, the properties of the extragalactic background light and
the strength of the intergalactic magnetic field. Unfortunately, since most
blazars have featureless optical spectra that preclude a redshift
determination, a substantial fraction of these VHE extragalactic sources cannot
be used for cosmological studies. To assess whether molecular lines are a
viable way to establish distances, we have undertaken a pilot program at the
IRAM 30m telescope to search for CO lines in three BL Lac objects with known
redshifts. We report a positive detection of M_H2 ~ 3x10^8 Msun toward 1ES
1959+650, but due to the poor quality of the baseline, this value is affected
by a large systematic uncertainty. For the remaining two sources, W Comae and
RGB J0710+591, we derive 3sigma upper limits at, respectively, M_H2 < 8.0x10^8
Msun and M_H2 < 1.6x10^9 Msun, assuming a line width of 150 km/s and a standard
conversion factor alpha=4 M_sun/(K km/s pc^2). If these low molecular gas
masses are typical for blazars, blind redshift searches in molecular lines are
currently unfeasible. However, deep observations are still a promising way to
obtain precise redshifts for sources whose approximate distances are known via
indirect methods. Our observations further reveal a deficiency of molecular gas
in BL Lac objects compared to quasars, suggesting that the host galaxies of
these two types of active galactic nuclei (AGN) are not drawn from the same
parent population. Future observations are needed to assess whether this
discrepancy is statistically significant, but our pilot program shows how
studies of the interstellar medium in AGN can provide key information to
explore the connection between the active nuclei and the host galaxies.Comment: 8 pages, 3 figures. MNRAS accepte
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region
We present the first installment of HI sources extracted from the Arecibo
Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in 2005. Sources
have been extracted from 3-D spectral data cubes and then examined
interactively to yield global HI parameters. A total of 730 HI detections are
catalogued within the solid angle 11h44m < R.A.(J2000) < 14h00m and +12deg <
Dec.(J2000) < +16deg, and redshift range -1600 \kms < cz < 18000 \kms. In
comparison, the HI Parkes All-Sky Survey (HIPASS) detected 40 HI signals in the
same region. Optical counterparts are assigned via examination of digital
optical imaging databases. ALFALFA HI detections are reported for three
distinct classes of signals: (a) detections, typically with S/N > 6.5; (b) high
velocity clouds in the Milky Way or its periphery; and (c) signals of lower S/N
(to ~ 4.5) which coincide spatially with an optical object of known similar
redshift. Although this region of the sky has been heavily surveyed by previous
targeted observations based on optical flux-- or size-- limited samples, 69% of
the extracted sources are newly reported HI detections. The resultant
positional accuracy of HI sources is 20" (median). The median redshift of the
sample is ~7000 \kms and its distribution reflects the known local large scale
structure including the Virgo cluster. Several extended HI features are found
in the vicinity of the Virgo cluster. A small percentage (6%) of HI detections
have no identifiable optical counterpart, more than half of which are high
velocity clouds in the Milky Way vicinity; the remaining 17 objects do not
appear connected to or associated with any known galaxy.Comment: Astronomical Journal, in pres
Response to Comment on “Plant diversity increases with the strength of negative density dependence at the global scale”
Hülsmann and Hartig suggest that ecological mechanisms other than specialized natural enemies or intraspecific competition contribute to our estimates of conspecific negative density dependence (CNDD). To address their concern, we show that our results are not the result of a methodological artifact and present a null-model analysis that demonstrates that our original findings—(i) stronger CNDD at tropical relative to temperate latitudes and (ii) a latitudinal shift in the relationship between CNDD and species abundance—persist even after controlling for other processes that might influence spatial relationships between adults and recruits
A VERITAS/Breakthrough Listen Search for Optical Technosignatures
The Breakthrough Listen Initiative is conducting a program using multiple
telescopes around the world to search for "technosignatures": artificial
transmitters of extraterrestrial origin from beyond our solar system. The
VERITAS Collaboration joined this program in 2018, and provides the capability
to search for one particular technosignature: optical pulses of a few
nanoseconds duration detectable over interstellar distances. We report here on
the analysis and results of dedicated VERITAS observations of Breakthrough
Listen targets conducted in 2019 and 2020 and of archival VERITAS data
collected since 2012. Thirty hours of dedicated observations of 136 targets and
249 archival observations of 140 targets were analyzed and did not reveal any
signals consistent with a technosignature. The results are used to place limits
on the fraction of stars hosting transmitting civilizations. We also discuss
the minimum-pulse sensitivity of our observations and present VERITAS
observations of CALIOP: a space-based pulsed laser onboard the CALIPSO
satellite. The detection of these pulses with VERITAS, using the analysis
techniques developed for our technosignature search, allows a test of our
analysis efficiency and serves as an important proof-of-principle.Comment: 15 pages, 7 figure
VERITAS discovery of very high energy gamma-ray emission from S3 1227+25 and multiwavelength observations
We report the detection of very high energy gamma-ray emission from the
blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging
Telescope Array System (VERITAS). VERITAS observations of the source were
triggered by the detection of a hard-spectrum GeV flare on May 15, 2015 with
the Fermi-Large Area Telescope (LAT). A combined five-hour VERITAS exposure on
May 16th and May 18th resulted in a strong 13 detection with a
differential photon spectral index, = 3.8 0.4, and a flux level
at 9% of the Crab Nebula above 120 GeV. This also triggered target of
opportunity observations with Swift, optical photometry, polarimetry and radio
measurements, also presented in this work, in addition to the VERITAS and
Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period
finds evidence of a shortest variability timescale of = 6.2
0.9 hours, indicating emission from compact regions within the jet, and the
combined gamma-ray spectrum shows no strong evidence of a spectral cut-off. An
investigation into correlations between the multiwavelength observations found
evidence of optical and gamma-ray correlations, suggesting a single-zone model
of emission. Finally, the multiwavelength spectral energy distribution is well
described by a simple one-zone leptonic synchrotron self-Compton radiation
model.Comment: 18 pages, 6 figures. Accepted for publication in the Astrophysical
Journal (ApJ
Genome-Wide Association Study of Susceptibility to Idiopathic Pulmonary Fibrosis
Rationale: Idiopathic pulmonary fibrosis (IPF) is a complex lung disease characterised by scarring of the lung that is believed to result from an atypical response to injury of the epithelium. Genome-wide association studies have reported signals of association implicating multiple pathways including host defence, telomere maintenance, signalling and cell-cell adhesion. Objectives: To improve our understanding of factors that increase IPF susceptibility by identifying previously unreported genetic associations. Methods and measurements: We conducted genome-wide analyses across three independent studies and meta-analysed these results to generate the largest genome-wide association study of IPF to date (2,668 IPF cases and 8,591 controls). We performed replication in two independent studies (1,456 IPF cases and 11,874 controls) and functional analyses (including statistical fine-mapping, investigations into gene expression and testing for enrichment of IPF susceptibility signals in regulatory regions) to determine putatively causal genes. Polygenic risk scores were used to assess the collective effect of variants not reported as associated with IPF. Main results: We identified and replicated three new genome-wide significant (P<5×10−8) signals of association with IPF susceptibility (associated with altered gene expression of KIF15, MAD1L1 and DEPTOR) and confirmed associations at 11 previously reported loci. Polygenic risk score analyses showed that the combined effect of many thousands of as-yet unreported IPF susceptibility variants contribute to IPF susceptibility. Conclusions: The observation that decreased DEPTOR expression associates with increased susceptibility to IPF, supports recent studies demonstrating the importance of mTOR signalling in lung fibrosis. New signals of association implicating KIF15 and MAD1L1 suggest a possible role of mitotic spindle-assembly genes in IPF susceptibility