The contribution of starbursts and normal galaxies to infrared luminosity functions at z < 2

We present a parameter-less approach to predict the shape of the infrared (IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and relies on only three observables: (1) the redshift evolution of the stellar mass function for star-forming galaxies, (2) the evolution of the specific star formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian decomposition of the sSFR-distribution at fixed stellar mass into a contribution (assumed redshift- and mass-invariant) from main-sequence and starburst activity. This self-consistent and simple framework provides a powerful tool for predicting cosmological observables: observed IR LFs are successfully matched at all z < 2, suggesting a constant or only weakly redshift-dependent contribution (8-14%) of starbursts to the star formation rate density. We separate the contributions of main-sequence and starburst activity to the global IR LF at all redshifts. The luminosity threshold above which the starburst component dominates the IR LF rises from log(LIR/Lsun) = 11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR in main-sequence galaxies.Comment: 7 pages, 4 figures & 1 table. Accepted for publication in ApJL. Minor typos corrected in v2 following receipt of proof

Interferometric CO observations of the ultraluminous IRAS galaxies ARP 220, IC 694/NGC 3690, NGC 6420 and NGC 7469

High resolution CO observations of the IRAS galaxies Arp 220, IC 694/NGC 3690, NGC 6240 and NGC 7469 were made with the Millimeter Wave Interferometer of the Owen Valley Radio Observatory. These yield spatial information on scales of 1 to 5 kpc and allow the separation of compact condensations from the more extended emission in the galaxies. In the case of the obviously interacting system IC 694/NGC 3690 the contributions of each component can be discerned. For that galaxy, and also for Arp 220, the unusually high lumonisities may be produced by nonthermal processes rather than by intense bursts of star formation

Ultraslow light in inhomogeneously broadened media

We calculate the characteristics of ultraslow light in an inhomogeneously broadened medium. We present analytical and numerical results for the group delay as a function of power of the propagating pulse. We apply these results to explain the recently reported saturation behavior [Baldit {\it et al.}, \prl {\bf 95}, 143601 (2005)] of ultraslow light in rare earth ion doped crystal.Comment: 4 pages, 5 figure

The contribution of starbursts and normal galaxies to IR luminosity functions and the molecular gas content of the Universe at z<2

We present a parameter-less approach capable of predicting the shape of the infrared luminosity function at redshifts z ≤2. It relies on three observables: (1) the redshift evolution of the stellar mass function for star-forming galaxies, (2) the evolution of the specific star formation rate of main-sequence galaxies, and (3) the double-Gaussian decomposition of the specific star formation rate distribution at fixed stellar mass into the contributions (assumed to be redshift- and mass-invariant) from main-sequence and starburst activity. Using this self-consistent and simple framework, we identify the contributions of main-sequence and starburst activity to the global infrared luminosity function and find a constant or only weakly redshift-dependent contribution (8–14%) of starbursts to the star formation rate density at z ≤2. Over the same redshift range, we also infer the evolution of the cosmic abundance of molecular gas in star-forming galaxies, based on the relations between star formation rate and molecular gas mass followed by normal and starburst galaxies

The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6

We examine the evolution of the IGM Ly-alpha optical depth distribution using the transmitted flux probability distribution function (PDF) in a sample of 63 QSOs spanning absorption redshifts 1.7 < z < 5.8. The data are compared to two theoretical optical depth distributions: a model distribution based on the density distribution of Miralda-Escude et al. (2000) (MHR00), and a lognormal distribution. We assume a uniform UV background and an isothermal IGM for the MHR00 model, as has been done in previous works. Under these assumptions, the MHR00 model produces poor fits to the observed flux PDFs at redshifts where the optical depth distribution is well sampled, unless large continuum corrections are applied. However, the lognormal optical depth distribution fits the data at all redshifts with only minor continuum adjustments. We use a simple parametrization for the evolution of the lognormal parameters to calculate the expected mean transmitted flux at z > 5.4. The lognormal optical depth distribution predicts the observed Ly-alpha and Ly-beta effective optical depths at z > 5.7 while simultaneously fitting the mean transmitted flux down to z = 1.6. If the evolution of the lognormal distribution at z < 5 reflects a slowly-evolving density field, temperature, and UV background, then no sudden change in the IGM at z ~ 6 due to late reionization appears necessary. We have used the lognormal optical depth distribution without any assumption about the underlying density field. If the MHR00 density distribution is correct, then a non-uniform UV background and/or IGM temperature may be required to produce the correct flux PDF. We find that an inverse temperature-density relation greatly improves the PDF fits, but with a large scatter in the equation of state index. [Abridged]Comment: 45 pages, 16 figures, submitted to Ap

Entanglement generation in persistent current qubits

In this paper we investigate the generation of entanglement between two persistent current qubits. The qubits are coupled inductively to each other and to a common bias field, which is used to control the qubit behaviour and is represented schematically by a linear oscillator mode. We consider the use of classical and quantum representations for the qubit control fields and how fluctuations in the control fields tend to suppress entanglement. In particular, we demonstrate how fluctuations in the bias fields affect the entanglement generated between persistent current qubits and may limit the ability to design practical systems.Comment: 7 pages, 4 figures, minor changes in reply to referees comment

Further evidence for a quasar-driven jet impacting its neighbour galaxy: the saga of HE0450-2958 continues

HE0450-2958, an interacting quasar-starburst galaxy pair at z = 0.285, is one of the best known examples of strong star formation activity in the presence of a quasardriven jet. We present new multi-band JVLA-imaging covering 1 to 6 GHz and reaching an angular resolution of up to 0” . 6 (a 6-fold improvement over existing radio data). We confirm the previous detection of a spatially extended radio component around the quasar indicating that there is on-going star formation activity in the quasar host galaxy. For the first time, we directly detect a jet-like bipolar outflow from the quasar aligned with its companion star-forming galaxy (SFG) and several blobs of ionized gas in its vicinity identified in previous studies. Within the companion SFG we find evidence for a flattening of the synchrotron spectral index towards the point of intersection with the jet axis, further suggesting that the outflow may actually be impacting its interstellar medium (ISM). We discuss two possible mechanisms that could have triggered the starburst in the companion SFG: a wet-dry merger with the quasar and jet-induced star formation. While triggering through interaction-driven gas dynamics cannot be excluded with current data, our new observations make HE0450-2958 a strong candidate for jet-induced star formation, and one of the rare links between local systems (like Minkowski’s Object or Centaurus A) and the high-z regime where radio-optical alignments suggest that this phenomenon could be more common