314 research outputs found
Observations of molecules in high redshift galaxies
I present an overview of the molecular gas observations in high redshift galaxies. This field has seen tremendous progress in the past few years, with an increased number of detections of other molecules than CO. The molecular line observations are done towards different classes of massive starbursts, including submillimeter galaxies, quasars, and massive gas-rich disks. I will highlight results of detections of HCN, HCO+, and other small molecules, as well as the Spitzer detections of PAHs. Additionally, I will discuss about the excitation of CO and other species in the high-z galaxies and put this in the context of new telescopes such as ALMA
The SCUBA-2 850 follow-up of WISE-selected, luminous dust-obscured quasars
Hot dust-obscured galaxies (Hot DOGs) are a new population recently
discovered in the \wise All-Sky survey. Multiwavelength follow-up observations
suggest that they are luminous, dust-obscured quasars at high redshift. Here we
present the JCMT SCUBA-2 850 follow-up observations of 10 Hot DOGs.
Four out of ten Hot DOGs have been detected at level. Based on the
IR SED decomposition approach, we derive the IR luminosities of AGN torus and
cold dust components. Hot DOGs in our sample are extremely luminous with most
of them having . The torus emissions
dominate the total IR energy output. However, the cold dust contribution is
still non-negligible, with the fraction of the cold dust contribution to the
total IR luminosity being dependent on the choice of torus
model. The derived cold dust temperatures in Hot DOGs are comparable to those
in UV bright quasars with similar IR luminosity, but much higher than those in
SMGs. Higher dust temperatures in Hot DOGs may be due to the more intense
radiation field caused by intense starburst and obscured AGN activities.
Fourteen and five submillimeter serendipitous sources in the 10 SCUBA-2 fields
around Hot DOGs have been detected at and levels,
respectively. By estimating their cumulative number counts, we confirm the
previous argument that Hot DOGs lie in dense environments. Our results support
the scenario in which Hot DOGs are luminous, dust-obscured quasars lying in
dense environments, and being in the transition phase between extreme starburst
and UV-bright quasars.Comment: 26 pages, 7 figures, PASP accepte
The effect of recessions on firms’ boundaries
The economic theory of the firm offers conflicting predictions of how the two major effects of recessions, changes in demand and access to credit, affect firm boundaries. Using data on Norwegian firms in the recent recession, we find support for both increased and reduced vertical integration of core activities in response to such changes. Further, we find that access to credit negatively moderates the effect of reductions in demand on vertical integration. The latter finding may highlight a possible explanation for the conflicting theoretical predictions
Stacking of interferometric data
Radio and mm observations play an important role in determining the star formation properties of high redshift galaxies. However, most galaxies at high redshift are too faint to be detected individually at these wavelengths. A way to study this population of galaxies is to use stacking. By averaging the emission of a large number of galaxies detected in optical or near infrared surveys, we can achieve statistical detection. We investigate methods for stacking data from interferometric surveys. Interferometry poses unique challenges in stacking due to the nature of imaging of this data. We have compared directly stacking the uv data with stacking of the imaged data, the latter being the typically used approach. Using simulated data, we find that uv-stacking may provide around 50% less noise and that image based stacking systematically loses around 10% of the flux
Structure and morphology of X-ray selected AGN hosts at 1<z<3 in CANDELS-COSMOS field
We analyze morphologies of the host galaxies of 35 X-ray selected active
galactic nucleus (AGNs) at in the Cosmic Evolution Survey (COSMOS)
field using Hubble Space Telescope/WFC3 imaging taken from the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We build a control
sample of 350 galaxies in total, by selecting ten non-active galaxies drawn
from the same field with the similar stellar mass and redshift for each AGN
host. By performing two dimensional fitting with GALFIT on the surface
brightness profile, we find that the distribution of Srsic index (n) of
AGN hosts does not show a statistical difference from that of the control
sample. We measure the nonparametric morphological parameters (the asymmetry
index A, the Gini coefficient G, the concentration index C and the M20 index)
based on point source subtracted images. All the distributions of these
morphological parameters of AGN hosts are consistent with those of the control
sample. We finally investigate the fraction of distorted morphologies in both
samples by visual classification. Only 15% of the AGN hosts have highly
distorted morphologies, possibly due to a major merger or interaction. We find
there is no significant difference in the distortion fractions between the AGN
host sample and control sample. We conclude that the morphologies of X-ray
selected AGN hosts are similar to those of nonactive galaxies and most AGN
activity is not triggered by major merger.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
LineStacker: A spectral line stacking tool for interferometric data
LineStacker is a new open access and open source tool for stacking of
spectral lines in interferometric data. LineStacker is an ensemble of CASA
tasks, and can stack both 3D cubes or already extracted spectra. The algorithm
is tested on increasingly complex simulated data sets, mimicking Atacama Large
Millimeter/submillimeter Array and Karl G. Jansky Very Large Array observations
of [CII] and CO(3-2) emission lines, from and galaxies
respectively. We find that the algorithm is very robust, successfully
retrieving the input parameters of the stacked lines in all cases with an
accuracy \%. However, we distinguish some specific situations
showcasing the intrinsic limitations of the method. Mainly that high
uncertainties on the redshifts () can lead to poor signal to
noise ratio improvement, due to lines being stacked on shifted central
frequencies. Additionally we give an extensive description of the embedded
statistical tools included in LineStacker: mainly bootstrapping, rebinning and
subsampling. Velocity rebinning {is applied on the data before stacking and}
proves necessary when studying line profiles, in order to avoid artificial
spectral features in the stack. Subsampling is useful to sort the stacked
sources, allowing to find a subsample maximizing the searched parameters, while
bootstrapping allows to detect inhomogeneities in the stacked sample.
LineStacker is a useful tool for extracting the most from spectral observations
of various types.Comment: Resubmitted to MNRAS after referee repor
ALMA detects molecular gas in the halo of the powerful radio galaxy TXS 0828+193
Both theoretical and observational results suggest that high-redshift radio
galaxies (HzRGs) inhabit overdense regions of the universe and might be the
progenitors of local, massive galaxies residing in the centre of galaxy
clusters. In this paper we present CO(3-2) line observations of the HzRG TXS
0828+193 (z=2.57) and its environment using the Atacama Large
Millimeter/submillimeter Array. In contrast to previous observations, we detect
CO emission associated with the HzRG and derive a molecular gas mass of
. Moreover, we confirm the presence of
a previously detected off-source CO emitting region (companion #1), and detect
three new potential companions. The molecular gas mass of each companion is
comparable to that of the HzRG. Companion #1 is aligned with the axis of the
radio jet and has stellar emission detected by Spitzer. Thus this source might
be a normal star-forming galaxy or alternatively a result of jet-induced star
formation. The newly found CO sources do not have counterparts in any other
observing band and could be high-density clouds in the halo of TXS 0828+193 and
thus potentially linked to the large-scale filamentary structure of the cosmic
web.Comment: Accepted by MNRAS; 9 pages, 4 figure
A merger in the dusty, galaxy A1689-zD1?
The gravitationally-lensed galaxy A1689-zD1 is one of the most distant
spectroscopically confirmed sources (). It is the earliest known galaxy
where the interstellar medium (ISM) has been detected; dust emission was
detected with the Atacama Large Millimetre Array (ALMA). A1689-zD1 is also
unusual among high-redshift dust emitters as it is a sub-L* galaxy and is
therefore a good prospect for the detection of gaseous ISM in a more typical
galaxy at this redshift. We observed A1689-zD1 with ALMA in bands 6 and 7 and
with the Green Bank Telescope (GBT) in band . To study the structure of
A1689-zD1, we map the mm thermal dust emission and find two spatial components
with sizes about \,kpc (lensing-corrected). The rough spatial
morphology is similar to what is observed in the near-infrared with {\it HST}
and points to a perturbed dynamical state, perhaps indicative of a major merger
or a disc in early formation. The ALMA photometry is used to constrain the
far-infrared spectral energy distribution, yielding a dust temperature (--\,K for ). We do not detect the CO(3-2) line
in the GBT data with a 95\% upper limit of 0.3\,mJy observed. We find a slight
excess emission in ALMA band~6 at 220.9\,GHz. If this excess is real, it is
likely due to emission from the [CII] 158.8\,m line at . The stringent upper limits on the [CII]/ luminosity ratio
suggest a [CII] deficit similar to several bright quasars and massive
starbursts.Comment: 9 pages, accepted to MNRAS, in pres
ALMA Reveals a Gas-rich, Maximum Starburst in the Hyperluminous, Dust-obscured Quasar W0533-3401 at z similar to 2.9
We present ALMA observations and multiwavelength spectral energy distribution analysis in a Wide-field Infrared Survey Explorer-selected, hyperluminous dust-obscured quasar W0533-3401 at z = 2.9. We derive the physical properties of each of its components, such as molecular gas, stars, dust, and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO (3-2) line are detected. The derived molecular gas mass M-gas = 8.4 x 10(10) M-circle dot and its fraction f(gas) = 0.7 suggest that W0533-3401 is gas-rich. The star formation rate (SFR) has been estimated to be similar to 3000-7000M(circle dot) yr(-1) by using different methods. The high values of SFR and specific SFR suggest that W0533-3401 is a maximum starburst. The corresponding gas depletion timescales are very short (t(depl) similar to 12-28 Myr). The CO (3-2) emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow, or merger. Finally, we infer the black hole mass growth rate of W0533-3401 ((M)over dot(BH) = 49 M-circle dot yr(-1)), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio M-BH/M-* of W0533-3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving toward the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that W0533-3401, with both a gas-rich maximum starburst and a rapid black hole growth, is experiencing a short transition phase toward an unobscured quasar
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