The 5'-3' exoribonuclease Pacman (Xrn1) regulates expression of the heat shock protein Hsp67Bc and the microRNA miR-277-3p in Drosophila wing imaginal discs

Pacman/Xrn1 is a highly conserved exoribonuclease known to play a critical role in gene regulatory events such as control of mRNA stability, RNA interference and regulation via miRNAs. Although Pacman has been well studied in Drosophila tissue culture cells, the biologically relevant cellular pathways controlled by Pacman in natural tissues are unknown. This study shows that a hypomorphic mutation in pacman (pcm5) results in smaller wing imaginal discs. These tissues, found in the larva, are known to grow and differentiate to form wing and thorax structures in the adult fly. Using microarray analysis, followed by quantitative RT-PCR, we show that eight mRNAs were increased in level by >2 fold in the pcm5 mutant wing discs compared to the control. The levels of pre mRNAs were tested for five of these mRNAs; four did not increase in the pcm5 mutant, showing that they are regulated at the post-transcriptional level and therefore could be directly affected by Pacman. These transcripts include one that encodes the heat-shock protein Hsp67Bc, which is upregulated 11.9-fold at the post-transcriptional level and 2.3-fold at the protein level. One miRNA, miR-277-3p, is 5.6-fold downregulated at the post-transcriptional level in mutant discs, suggesting that Pacman affects its processing in this tissue. Together, these data show that a relatively small number of mRNAs and miRNAs substantially change in abundance in pacman mutant wing imaginal discs. Since Hsp67Bc is known to regulate autophagy and protein synthesis, it is possible that Pacman may control the growth of wing imaginal discs by regulating these processes

The accretion disc in the quasar SDSS J0924+0219

We present single-epoch multi-wavelength optical-NIR observations of the "anomalous" lensed quasar SDSS J0924+0219, made using the Magellan 6.5-metre Baade telescope at Las Campanas Observatory, Chile. The data clearly resolve the anomalous bright image pair in the lensed system, and exhibit a strong decrease in the anomalous flux ratio with decreasing wavelength. This is interpreted as a result of microlensing of a source of decreasing size in the core of the lensed quasar. We model the radius of the continuum emission region, sigma, as a power-law in wavelength, sigma lambda^zeta. We place an upper limit on the Gaussian radius of the u'-band emission region of 3.04E16 h70^{-1/2} (/M_sun)^{1/2} cm, and constrain the size-wavelength power-law index to zeta<1.34 at 95% confidence. These observations rule out an alpha-disc prescription for the accretion disc in SDSS J0924+0219 with 94% confidence.Comment: 8 pages, 5 figures. Accepted for publication in MNRA

Major Substructure in the M31 Outer Halo: the South-West Cloud

We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo of M31. The South-West Cloud lies at a projected distance of ~100 kpc from the centre of M31, and extends for at least ~50 kpc in projection. We use Pan-Andromeda Archaeological Survey photometry of red giant branch stars to determine a distance to the South-West Cloud of 793 +/- 45 kpc. The metallicity of the cloud is found to be [Fe/H] = -1.3 +/- 0.1. This is consistent with the coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities determined using an independent technique of [Fe/H] = -1.35 +/- 0.15. We measure a brightness for the Cloud of M_V = -12.1 mag; this is ~75 per cent of the luminosity implied by the luminosity-metallicity relation. Under the assumption that the South-West Cloud is the visible remnant of an accreted dwarf satellite, this suggests that the progenitor object was amongst M31's brightest dwarf galaxies prior to disruption.Comment: 13 pages, 9 figures, accepted for publication in MNRA

A GPU-Enabled, High-Resolution Cosmological Microlensing Parameter Survey

In the era of synoptic surveys, the number of known gravitationally lensed quasars is set to increase by over an order of magnitude. These new discoveries will enable a move from single-quasar studies to investigations of statistical samples, presenting new opportunities to test theoretical models for the structure of quasar accretion discs and broad emission line regions (BELRs). As one crucial step in preparing for this influx of new lensed systems, a large-scale exploration of microlensing convergence-shear parameter space is warranted, requiring the computation of O(10^5) high resolution magnification maps. Based on properties of known lensed quasars, and expectations from accretion disc/BELR modelling, we identify regions of convergence-shear parameter space, map sizes, smooth matter fractions, and pixel resolutions that should be covered. We describe how the computationally time-consuming task of producing ~290000 magnification maps with sufficient resolution (10000^2 pixel/map) to probe scales from the inner edge of the accretion disc to the BELR can be achieved in ~400 days on a 100 teraflop/s high performance computing facility, where the processing performance is achieved with graphics processing units. We illustrate a use-case for the parameter survey by investigating the effects of varying the lens macro-model on accretion disc constraints in the lensed quasar Q2237+0305. We find that although all constraints are consistent within their current error bars, models with more densely packed microlenses tend to predict shallower accretion disc radial temperature profiles. With a large parameter survey such as the one described here, such systematics on microlensing measurements could be fully explored.Comment: 30 pages, 3 figures, accepted for publication in Ap

Differential microlensing measurements of quasar broad-line kinematics in Q2237+0305

The detailed workings of the central engines of powerful quasars remain a mystery. This is primarily due to the fact that, at their cosmological distances, the inner regions of these quasars are spatially unresolvable. Reverberation mapping is now beginning to unlock the physics of the Broad Emission Line Region (BELR) in nearby, low-luminosity quasars, however it is still unknown whether this gas is dominated by virial motion, by outflows, or infall. The challenge is greater for more distant, powerful sources due to the very long response time of the BELR to changes in the continuum. We present a new technique for probing the kinematic properties of the BELR and accretion disk of high-z quasars using differential microlensing, and show how substantial information can be gained through a single observation of a strongly-lensed quasar using integral field spectroscopy. We apply this technique to GMOS IFU observations of the multiply-imaged quasar Q2237+0305, and find that the observed microlensing signature in the CIII] broad emission line favours gravitationally-dominated dynamics over an accelerating outflow

Disc orientations in pre-main-sequence multiple systems. A study in southern star formation regions

Classical T Tauri stars are encircled by accretion discs most of the time unresolved by conventional imaging observation. However, numerical simulations show that unresolved aperture linear polarimetry can be used to extract information about the geometry of the immediate circumstellar medium that scatter the starlight. Monin, Menard & Duchene (1998) previously suggested that polarimetry can be used to trace the relative orientation of discs in young binary systems in order to shed light on the stellar and planet formation process. In this paper, we report on new VLT/FORS1 optical linear polarisation measurements of 23 southern binaries spanning a range of separation from 0.8'' to 10''. In each field, the polarisation of the central binary is extracted, as well as the polarisation of nearby stars in order to estimate the local interstellar polarisation. We find that, in general, the linear polarisation vectors of individual components in binary systems tend to be parallel to each other. The amplitude of their polarisations are also correlated. These findings are in agreement with our previous work and extend the trend to smaller separations. They are also similar to other studies, e.g., Donar et al. 1999; Jensen et al. 2000, 2004; Wolf et al. 2001. However, we also find a few systems showing large differences in polarisation level, possibly indicating different inclinations to the line-of-sight for their discs.Comment: 13 pages, 11 figures, accepted in Astronomy and Astrophysics. accepted in Astronomy and Astrophysics (A&A

Correlations Between Central Massive Objects And Their Host Galaxies: From Bulgeless Spirals to Ellipticals

Recent observations by Ferrarese et al. (2006) and Wehner et al. (2006) reveal that a majority of galaxies contain a central massive object (CMO), either a supermassive black hole (SMBH) or a compact stellar nucleus, regardless of the galaxy mass or morphological type, and that there is a tight relation between the masses of CMOs and those of the host galaxies. Several recent studies show that feedback from black holes can successfully explain the \msigma correlation in massive elliptical galaxies that contain SMBHs. However, puzzles remain in spirals or dwarf spheroids that do not appear to have black holes but instead harbor a compact central stellar cluster. Here we use three-dimensional, smoothed particle hydrodynamics simulations of isolated galaxies to study the formation and evolution of CMOs in bulgeless disk galaxies, and simulations of merging galaxies to study the transition of the CMO--host mass relation from late-type bulgeless spirals to early-type ellipticals. Our results suggest that the observed correlations may be established primarily by the depletion of gas in the central region by accretion and star-formation, and may hold for all galaxy types. A systematic search for CMOs in the nuclei of bulgeless disk galaxies would offer a test of this conclusion. (Abridged)Comment: 11 pages, 8 figures, accepted to Ap