318 research outputs found
LBT and Spitzer Spectroscopy of Star-Forming Galaxies at 1 < z < 3: Extinction and Star Formation Rate Indicators
We present spectroscopic observations in the rest-frame optical and near- to
mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous
star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the
Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample
was selected to represent pure, actively star-forming systems, absent of active
galactic nuclei. The large lensing magnifications result in high
signal-to-noise spectra that can probe faint IR recombination lines, including
Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three
lensed galaxies with similar suites of unpublished data and observations from
the literature, resulting in the final sample of seven galaxies. We use the IR
recombination lines in conjunction with H-alpha observations to probe the
extinction, Av, of these systems, as well as testing star formation rate (SFR)
indicators against the SFR measured by fitting spectral energy distributions to
far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger
than previously known for a similar range of IR luminosities at these
redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of
extinction in the most IR luminous galaxies. We also measure extinction by
comparing SFR estimates from optical emission lines with those from far-IR
measurements. The comparison of results from these two independent methods
indicates a large variety of dust distribution scenarios at 1 < z < 3. Without
correcting for dust extinction, the H-alpha SFR indicator underestimates the
SFR; the size of the necessary correction depends on the IR luminosity and dust
distribution scenario. Individual SFR estimates based on the 6.2 micron PAH
emission line luminosity do not show a systematic discrepancy with extinction,
although a considerable, ~0.2 dex scatter is observed.Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 8
figure
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
Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b
GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multi-wavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 days or a planet with an orbital period between 2.5 and 4.0 days are excluded. Combined optical and near-infrared transmission spectroscopy favour an H/He dominated haze (mean molecular weight 1.080.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b
The Anticipated Supernova Associated with GRB090618
We use the cannonball model of gamma ray bursts (GRBs) and public data from
the first day of observations of GRB 090618 to predict its X-ray and optical
lightcurves until very late times, and, in particular, the emergence of a
photometric and spectroscopic signature of an SN akin to SN1998bw in its
optical afterglow with an anticipated peak brightness of magnitude 23 in the R
band around July 10, 2009, if extinction in the host galaxy can be neglected.Comment: 10 pages, 2 Figure
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
Reconstructing the \gamma-ray Photon Optical Depth of the Universe to z~4 from Multiwavelength Galaxy Survey Data
We reconstruct \gamma-ray opacity of the Universe out to z<3-4 using an
extensive library of 342 observed galaxy luminosity function surveys extending
to high redshifts. We cover the whole range from UV to mid-IR (0.15-25mic)
providing for the first time a robust empirical calculation of the
\gamma\gamma-optical depth out to several TeV. Here, we use the same database
as Helgason et al. 2012 where the EBL was reconstructed from luminosity
functions out to 4.5mic and was shown to recover observed galaxy counts to high
accuracy. We extend our earlier library of LFs to 25mic such that it covers the
energy range of pair production with \gamma-rays 1) in the entire Fermi/LAT
energy range, and 2) at higher TeV energies probed by ground-based Cherenkov
telescopes. In the absence of significant contributions to the cosmic diffuse
background from unknown populations, such as the putative Population III era
sources, the Universe appears to be largely transparent to \gamma-rays at all
Fermi/LAT energies out to z~2 whereas becoming opaque to TeV photons already at
z<0.2 and reaching \tau~10 at z=1. Comparing with the currently available
Fermi/LAT GRB and blazar data shows that there is room for significant
emissions originating in the first stars era.Comment: 5 pages, 5 figures. Published in ApJ Letter
Spatially resolved kinematics in the central 1 kpc of a compact star-forming galaxy at z=2.3 from ALMA CO observations
We present high spatial resolution (FWHM0.14'') observations of the
CO() line in GDS-14876, a compact star-forming galaxy at with
total stellar mass of . The spatially resolved
velocity map of the inner ~kpc reveals a continous velocity
gradient consistent with the kinematics of a rotating disk with km s and . The
gas-to-stellar ratios estimated from CO() and the dust continuum emission
span a broad range, and
, but are nonetheless consistent given the
uncertainties in the conversion factors. The dynamical modeling yields a
dynamical mass of which is
lower, but still consistent with the baryonic mass, (M=
M + M/M), if the smallest
CO-based gas fraction is assumed. Despite a low, overall gas fraction, the
small physical extent of the dense, star-forming gas probed by CO(),
smaller than the stellar size, implies a strong concentration
that increases the gas fraction up to
in the central 1 kpc. Such a gas-rich center, coupled with a high
star-formation rate, SFR 500 M yr, suggests that
GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong
nuclear starburst. Assuming its gas reservoir is depleted without
replenishment, GDS-14876 will quickly ( Myr) become a
compact quiescent galaxy that could retain some fraction of the observed
rotational support.Comment: Accepted for Publication in ApJL. Kinematic maps are shown in Figures
2 and
High-Velocity Outflows Without AGN Feedback: Eddington-Limited Star Formation in Compact Massive Galaxies
We present the discovery of compact, obscured star formation in galaxies at z
~ 0.6 that exhibit >1000 km/s outflows. Using optical morphologies from the
Hubble Space Telescope and infrared photometry from the Wide-field Infrared
Survey Explorer, we estimate star formation rate (SFR) surface densities that
approach Sigma_SFR ~ 3000 Msun/yr/kpc^2, comparable to the Eddington limit from
radiation pressure on dust grains. We argue that feedback associated with a
compact starburst in the form of radiation pressure from massive stars and ram
pressure from supernovae and stellar winds is sufficient to produce the
high-velocity outflows we observe, without the need to invoke feedback from an
active galactic nucleus.Comment: 6 pages, 4 figures, accepted for publication in ApJ Letter
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