Lossless Astronomical Image Compression and the Effects of Noise

We compare a variety of lossless image compression methods on a large sample of astronomical images and show how the compression ratios and speeds of the algorithms are affected by the amount of noise in the images. In the ideal case where the image pixel values have a random Gaussian distribution, the equivalent number of uncompressible noise bits per pixel is given by Nbits =log2(sigma * sqrt(12)) and the lossless compression ratio is given by R = BITPIX / Nbits + K where BITPIX is the bit length of the pixel values and K is a measure of the efficiency of the compression algorithm. We perform image compression tests on a large sample of integer astronomical CCD images using the GZIP compression program and using a newer FITS tiled-image compression method that currently supports 4 compression algorithms: Rice, Hcompress, PLIO, and GZIP. Overall, the Rice compression algorithm strikes the best balance of compression and computational efficiency; it is 2--3 times faster and produces about 1.4 times greater compression than GZIP. The Rice algorithm produces 75%--90% (depending on the amount of noise in the image) as much compression as an ideal algorithm with K = 0. The image compression and uncompression utility programs used in this study (called fpack and funpack) are publicly available from the HEASARC web site. A simple command-line interface may be used to compress or uncompress any FITS image file.Comment: 20 pages, 9 figures, to be published in PAS

Optimal Compression of Floating-point Astronomical Images Without Significant Loss of Information

We describe a compression method for floating-point astronomical images that gives compression ratios of 6 -- 10 while still preserving the scientifically important information in the image. The pixel values are first preprocessed by quantizing them into scaled integer intensity levels, which removes some of the uncompressible noise in the image. The integers are then losslessly compressed using the fast and efficient Rice algorithm and stored in a portable FITS format file. Quantizing an image more coarsely gives greater image compression, but it also increases the noise and degrades the precision of the photometric and astrometric measurements in the quantized image. Dithering the pixel values during the quantization process can greatly improve the precision of measurements in the images. This is especially important if the analysis algorithm relies on the mode or the median which would be similarly quantized if the pixel values are not dithered. We perform a series of experiments on both synthetic and real astronomical CCD images to quantitatively demonstrate that the magnitudes and positions of stars in the quantized images can be measured with the predicted amount of precision. In order to encourage wider use of these image compression methods, we have made available a pair of general-purpose image compression programs, called fpack and funpack, which can be used to compress any FITS format image.Comment: Accepted PAS

DDR2 controls breast tumor stiffness and metastasis by regulating integrin mediated mechanotransduction in CAFs

Biomechanical changes in the tumor microenvironment influence tumor progression and metastases. Collagen content and fiber organization within the tumor stroma are major contributors to biomechanical changes (e., tumor stiffness) and correlated with tumor aggressiveness and outcome. What signals and in what cells control collagen organization within the tumors, and how, is not fully understood. We show in mouse breast tumors that the action of the collagen receptor DDR2 in CAFs controls tumor stiffness by reorganizing collagen fibers specifically at the tumor-stromal boundary. These changes were associated with lung metastases. The action of DDR2 in mouse and human CAFs, and tumors in vivo, was found to influence mechanotransduction by controlling full collagen-binding integrin activation via Rap1-mediated Talin1 and Kindlin2 recruitment. The action of DDR2 in tumor CAFs is thus critical for remodeling collagen fibers at the tumor-stromal boundary to generate a physically permissive tumor microenvironment for tumor cell invasion and metastases

Comparison of chromogenic media for recovery of carbapenemase-producing enterobacteriaceae (CPE) and evaluation of CPE prevalence at a tertiary care academic medical center

We evaluated the performance characteristics of chromID CARBA and HardyCHROM Carbapenemase for the detection of carbapenemase-producing Enterobacteriaceae (CPE). A CPE prevalence study was conducted using chromID CARBA; this demonstrated that in low-prevalence settings, CPE screening agars may lack specificity, and confirmation of putative isolates is necessary

Finding Galaxy Clusters using Voronoi Tessellations

We present an objective and automated procedure for detecting clusters of galaxies in imaging galaxy surveys. Our Voronoi Galaxy Cluster Finder (VGCF) uses galaxy positions and magnitudes to find clusters and determine their main features: size, richness and contrast above the background. The VGCF uses the Voronoi tessellation to evaluate the local density and to identify clusters as significative density fluctuations above the background. The significance threshold needs to be set by the user, but experimenting with different choices is very easy since it does not require a whole new run of the algorithm. The VGCF is non-parametric and does not smooth the data. As a consequence, clusters are identified irrispective of their shape and their identification is only slightly affected by border effects and by holes in the galaxy distribution on the sky. The algorithm is fast, and automatically assigns members to structures.Comment: 11 pages, 11 figures. It uses aa.cls (included). Accepted by A&

The Disk and Dark Halo Mass of the Barred Galaxy NGC 4123. I. Observations

The non-circular streaming motions in barred galaxies are sensitive to the mass of the bar and can be used to lift the degeneracy between disk and dark matter halo encountered when fitting axisymmetric rotation curves of disk galaxies. In this paper, we present photometric and kinematic observations of NGC 4123, a barred galaxy of modest size (V_rot = 130 km/sec, L = 0.7 L_*), which reveal strong non-circular motions. The bar has straight dust lanes and an inner Lindblad resonance. The disk of NGC 4123 has no sign of truncation out to 10 scale lengths, and star-forming regions are found well outside R_25. A Fabry-Perot H-alpha velocity field shows velocity jumps of >100 km/sec at the location of the dust lanes within the bar, indicating shocks in the gas flow. VLA observations yield the velocity field of the H I disk. Axisymmetric mass models yield good fits to the rotation curve outside the bar regionfor disk I-band M/L of 2.25 or less, and dark halos with either isothermal or power-law profiles can fit the data well. In a companion paper, we model the full 2-D velocity field, including non-circular motions, to determine the stellar M/L and the mass of the dark halo.Comment: accepted by ApJ, 16 pages, 9 figures (1 color), uses emulateapj.sty, onecolfloat.st

Physical Structure and Nature of Supernova Remnants in M101

Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have been previously identified from ground-based H-alpha and [SII] images. We have used archival Hubble Space Telescope (HST) H-alpha and broad-band images as well as stellar photometry of 55 SNR candidates to examine their physical structure, interstellar environment, and underlying stellar population. We have also obtained high-dispersion echelle spectra to search for shocked high-velocity gas in 18 SNR candidates, and identified X-ray counterparts to SNR candidates using data from archival observations made by the Chandra X-ray Observatory. Twenty-one of these 55 SNR candidates studied have X-ray counterparts, although one of them is a known ultra-luminous X-ray source. The multi-wavelength information has been used to assess the nature of each SNR candidate. We find that within this limited sample, ~16% are likely remnants of Type Ia SNe and ~45% are remnants of core-collapse SNe. In addition, about ~36% are large candidates which we suggest are either superbubbles or OB/HII complexes. Existing radio observations are not sensitive enough to detect the non-thermal emission from these SNR candidates. Several radio sources are coincident with X-ray sources, but they are associated with either giant HII regions in M101 or background galaxies. The archival HST H-alpha images do not cover the entire galaxy and thus prevents a complete study of M101. Furthermore, the lack of HST [SII] images precludes searches for small SNR candidates which could not be identified by ground-based observations. Such high-resolution images are needed in order to obtain a complete census of SNRs in M101 for a comprehensive investigation of the distribution, population, and rates of SNe in this galaxy.Comment: 37 pages, 4 Tables, 7 Figures, accepted for publication in the Astronomical Journa

The properties of the Galactic bar implied by gas kinematics in the inner Milky Way

Longitude-velocity (l-V) diagrams of H I and CO gas in the inner Milky Way have long been known to be inconsistent with circular motion in an axisymmetric potential. Several lines of evidence suggest that the Galaxy is barred, and gas flow in a barred potential could be consistent with the observed ``forbidden'' velocities and other features in the data. We compare the H I observations to l-V diagrams synthesized from 2-D fluid dynamical simulations of gas flows in a family of barred potentials. The gas flow pattern is very sensitive to the parameters of the assumed potential, which allows us to discriminate among models. We present a model that reproduces the outer contour of the H I l-V diagram reasonably well; this model has a strong bar with a semimajor axis of 3.6 kpc, an axis ratio of approximately 3:1, an inner Lindblad resonance (ILR), and a pattern speed of 42 km/s/kpc, and matches the data best when viewed from 34\deg to the bar major axis. The behavior of the models, combined with the constraint that the shocks in the Milky Way bar should resemble those in external barred galaxies, leads us to conclude that wide ranges of parameter space are incompatible with the observations. In particular we suggest that the bar must be fairly strong, must have an ILR, and cannot be too end-on, with the bar major axis at 35\deg +/- 5\deg to the line of sight. The H I data exhibit larger forbidden velocities over a wider longitude range than are seen in molecular gas; this important difference is the reason our favored model differs so significantly from other recently proposed models.Comment: 23 pages, 14 figures, 1 table, uses emulateapj and psfig, 640 kb. Submitted to Ap

The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters

AIMS: We present in this work low and intermediate resolution spectroscopic data collected for 152 early type galaxies in 8 nearby clusters with z $\leq$ 0.10. METHODS: We use low resolution data to produce the redshift and the K-correction for every individual galaxy, as well as to give their overall spectral energy distribution, and some spectral indicators, including the 4000\AA break, the Mg$_2$ strength, and the NaD equivalent width.We have also obtained higher resolution data for early type galaxies in three of the clusters, to determine their central velocity dispersion. RESULTS: The effect of the resolution on the measured parameters is discussed. CONCLUSIONS: New accurate systemic redshift and velocity dispersion is presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39. We have found that the K-correction values for E/S0 bright galaxies in a given nearby clusters are very similar. We also find that the distribution of the line indicators significantly differ from cluster to cluster.Comment: 16 pages, 9 figures, Accepted in A&