Deep Photometry in a Remote M31 Major Axis Field Near G1

We present photometry from Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 parallel imagery of a remote M31 field at a projected distance of about 34 kpc from the nucleus near the SW major axis. This field is near the globular cluster G1, and near one of the candidate tidal plumes identified by Ferguson et al. (2002). The F606W (V) and F814W (I) images were obtained in parallel with Space Telescope Imaging Spectrograph spectroscopy of G1 (GO-9099) and total 7.11 hours of integration time -- the deepest HST field in the outer disk of M31 to date, reaching to V ~ 28. The color-magnitude diagram of the field shows a clearly-defined red clump at V = 25.25 and a red giant branch consistent with [Fe/H] ~ -0.7. The lack of a blue horizontal branch contrasts with other M31 halo fields, the Andromeda dwarf spheroidals, and with the nearby globular cluster G1. Comparing the observed luminosity function to the Padova models, we find that at least some of the stellar population must be younger than 6 - 8 Gyr. The outermost detected neutral hydrogen gas disk of M31 lies only 2 kpc in projection from our field. The finding that some giants in the field have radial velocities close to that of the neutral hydrogen gas (Reitzel, Guhathakurta, & Rich 2003) leads us to conclude that our field samples the old, low-surface-brightness disk rather than the true Population II spheroid.Comment: 15 pages, 3 figures. accepted for publication in the A

BVRI Surface Photometry of Isolated Spiral Galaxies

A release of multicolor broad band (BVRI) photometry for a subsample of 44 isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is presented. Total magnitudes and colors at various circular apertures, as well as some global structural/morphological parameters are estimated. Morphology is reevaluated through optical and sharp/filtered R band images, (B-I) color index maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS structural parameters (Concentration, Asymmetry, and Clumpiness) were calculated from the images in each one of the bands. The fraction of galaxies with well identified optical/near-IR bars (SB) is 63%, while a 17% more shows evidence of weak or suspected bars (SAB). The sample average value of the maximum bar ellipticity is 0.4. Half of the galaxies in the sample shows rings. We identify two candidates for isolated galaxies with disturbed morphology. The structural CAS parameters change with the observed band, and the tendencies they follow with the morphological type and global color are more evident in the redder bands. In any band, the major difference between our isolated spirals and a sample of interacting spirals is revealed in the A-S plane. A deep and uniformly observed sample of isolated galaxies is intended for various purposes including (i) comparative studies of environmental effects, (ii) confronting model predictions of galaxy evolution and (iii) evaluating the change of galaxy properties with redshift.Comment: 44 pages, 9 figures and 7 tables included. To appear in The Astronomical Journal. For the 43 appendix figures 4.1-4.43 see http://www.astroscu.unam.mx/~avila/Figs4.1_4.43.tar.gz (7.2 Mb tar.gz file

Magnitude bias of microlensed sources towards the Large Magellanic Cloud

There are lines of evidence suggesting that some of the observed microlensing events in the direction of the Large Magellanic Cloud (LMC) are caused by ordinary star lenses as opposed to dark Machos in the Galactic halo. Efficient lensing by ordinary stars generally requires the presence of one or more additional concentrations of stars along the line of sight to the LMC disk. If such a population behind the LMC disk exists, then the source stars (for lensing by LMC disk objects) will be drawn preferentially from the background population and will show systematic differences from LMC field stars. One such difference is that the (lensed) source stars will be farther away than the average LMC field stars, and this should be reflected in their apparent baseline magnitudes. We focus on red clump stars: these should appear in the color-magnitude diagram at a few tenths of a magnitude fainter than the field red clump. Suggestively, one of the two near-clump confirmed events, MACHO-LMC-1, is a few tenths of magnitude fainter than the clump.Comment: To appear in ApJ Letters. Shortened to match the accepted version, 8 pages plus 1 ps figur

The non-specific lethal (NSL) complex at the crossroads of transcriptional control and cellular homeostasis

The functionality of chromatin is tightly regulated by post-translational modifications that modulate transcriptional output from target loci. Among the post-translational modifications of chromatin, reversible ε-lysine acetylation of histone proteins is prominent at transcriptionally active genes. Lysine acetylation is catalyzed by lysine acetyltransferases (KATs), which utilize the central cellular metabolite acetyl-CoA as their substrate. Among the KATs that mediate lysine acetylation, males absent on the first (MOF/KAT8) is particularly notable for its ability to acetylate histone 4 lysine 16 (H4K16ac), a modification that decompacts chromatin structure. MOF and its non-specific lethal (NSL) complex members have been shown to localize to gene promoters and enhancers in the nucleus, as well as to microtubules and mitochondria to regulate key cellular processes. Highlighting their importance, mutations or deregulation of NSL complex members has been reported in both human neurodevelopmental disorders and cancer. Based on insight gained from studies in human, mouse, and Drosophila model systems, this review discusses the role of NSL-mediated lysine acetylation in a myriad of cellular functions in both health and disease. Through these studies, the importance of the NSL complex in regulating core transcriptional and signaling networks required for normal development and cellular homeostasis is beginning to emerge

Investigating the Andromeda Stream: II. Orbital Fits and Properties of the Progenitor

We construct test-particle orbits and simple N-body models that match the properties of the giant stellar stream observed to the south of M31, using the model of M31's potential derived in the companion paper by Geehan et al. (2006). We introduce a simple approximation to account for the difference in position between the stream and the orbit of the progenitor; this significantly affects the best-fitting orbits. The progenitor orbits we derive have orbital apocenter \sim 60 \kpc and pericenter \sim 3 \kpc, though these quantities vary somewhat with the current orbital phase of the progenitor which is as yet unknown. Our best combined fit to the stream and galaxy properties implies a mass within 125 kpc of M31 of (7.4 \pm 1.2) \times 10^{11} \Msun. Based on its length, width, luminosity, and velocity dispersion, we conclude that the stream originates from a progenitor satellite with mass M_s \sim 10^9 \Msun, and at most modest amounts of dark matter; the estimate of $M_s$ is again correlated with the phase of the progenitor. M31 displays a large number of faint features in its inner halo which may be progenitors or continuations of the stream. While the orbital fits are not constrained enough for us to conclusively identify the progenitor, we can identify several plausible candidates, of which a feature in the planetary nebula distribution found by Merrett et al. is the most plausible, and rule out several others. We make predictions for the kinematic properties of the successful candidates. These may aid in observational identification of the progenitor object, which would greatly constrain the allowed models of the stream.Comment: 17 pages, 10 color figures, 4 tables. Accepted by Monthly Notices; some minor revisions and corrected typo