[show abstract][hide abstract] ABSTRACT: We have detected an X-ray absorption feature against the core of the galaxy cluster A2029 (z = 0.0767) that we identify with the foreground galaxy UZC J151054.6+054313 (z = 0.0221). Optical observations (B, V, R, and I) indicate that it is an Scd galaxy seen nearly edge-on at an inclination of 87° ± 3°. H I observations give a rotation velocity of 108 km s-1 and an atomic hydrogen mass of M = 3.1 × 109d M☉, where d90 is the distance to the galaxy in units of 90 Mpc. X-ray spectral fits to the Chandra absorption feature yield a hydrogen column density of (2.0 ± 0.4) × 1021 cm-2, assuming solar abundances. If the absorber is uniformly distributed over the disk of the galaxy, the implied hydrogen mass is MH = (6.2 ± 1.2) × 108d M☉. Since the absorbing gas in the galaxy is probably concentrated toward the center of the galaxy and the middle of the disk, this is a lower limit to the total hydrogen mass. On the other hand, the absorption measurements imply that the dark matter in UZC J151054.6+054313 is not distributed in a relatively uniform diffuse gas.
The Astrophysical Journal 12/2008; 601(2):798. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We recently reported the discovery of a regular corrugation pattern in the H I disk of the isolated, edge-on spiral galaxy IC 2233. Here we present measurements of the vertical structure of this galaxy at several additional wavelengths, ranging from the far-ultraviolet to the far-infrared. We find that undular patterns with amplitude 5'' ( 250 pc) are visible in a variety of Population I tracers in IC 2233, including the young to intermediate-age stars, the H II regions, and the dust. However, the vertical excursions become less pronounced in the older stellar populations traced by the mid-infrared light. This suggests that the process leading to the vertical displacements may be linked with the regulation of star formation in the galaxy. We have also identified a relationship between the locations of the density corrugations and small-amplitude ( 5 km s−1) velocity undulations in the H I rotation curve. We are able to exclude several possible mechanisms for the origin of the observed corrugations, including tidal interaction from a companion, Parker instabilities, or a galactic bore. Global gravitational instabilities appear to be the most likely explanation, although local perturbations may also be important.
The Astrophysical Journal 12/2008; 688(1):237. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Astronomical imaging using aperture synthesis telescopes requires deconvolution of the point spread function as well as calibration of instrumental and atmospheric effects. In general, such effects are time-variable and vary across the field of view as well, resulting in direction-dependent (DD), time-varying gains. Most existing imaging and calibration algorithms assume that the corruptions are direction independent, preventing even moderate dynamic range full-beam, full-Stokes imaging. We present a general framework for imaging algorithms which incorporate DD errors. We describe as well an iterative deconvolution algorithm that corrects known DD errors due to the antenna power patterns and pointing errors for high dynamic range full-beam polarimetric imaging. Using simulations we demonstrate that errors due to realistic primary beams as well as antenna pointing errors will limit the dynamic range of upcoming higher sensitivity instruments and that our new algorithm can be used to correct for such errors. We have applied this algorithm to VLA 1.4 GHz observations of a field that contains two ``4C'' sources and have obtained Stokes-I and -V images with systematic errors that are one order of magnitude lower than those obtained with conventional imaging tools. Our simulations show that on data with no other calibration errors, the algorithm corrects pointing errors as well as errors due to known asymmetries in the antenna pattern. Comment: submitted to A&A; some clarifications added in the text; accepted for publication in A&A
Astronomy and Astrophysics 05/2008; · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have used the Very Large Array to image the isolated "superthin" galaxy UGC 7321 in the H I line with a spatial resolution of 16'' and a spectral resolution of 24 kHz (5.2 km s-1). We have reached a sensitivity of (0.36–0.40) mJy beam-1 channel-1, which correspond to a column density of (8–9) × 1018 atoms cm-2 (1 σ). UGC 7321 has a gas-rich disk, with MH I = (1.06 ± 0.01) × 109 d M and MH I/LB = 1.0 (d10 is the distance to UGC 7321 in units of 10 Mpc, the value adopted in this paper), and no detectable radio continuum emission (FCONT = 0.41 ± 0.25 mJy). The global H I distribution of UGC 7321 is rather symmetric and extends to ~1.5 times the optical radius (DH I = 865 ± 015 at nH I = 3 × 1019 atoms cm-2). An "integral sign" warp is observed in the H I disk, commencing near the edge of the stellar distribution and twisting back toward the equatorial plane in the outermost regions. In addition, the position-velocity diagram suggests the presence of a bar or inner arm within ~40'' from the center. The rotation curve of UGC 7321 is slowly rising; it reaches its asymptotic velocity of ~110 km s-1 at ~25 from the center (about 0.9 optical radii) and declines near the edge of the H I disk. The ratio of the inferred dynamical mass to the mass in gas and stars is ~12d, implying that UGC 7321 is a highly dark-matter–dominated galaxy.
The Astronomical Journal 12/2007; 125(5):2455. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have used the Very Large Array to image the H I 21 cm line emission in the edge-on Sd galaxy IC 2233 and the blue compact dwarf NGC 2537. We also present new optical B, R, and Hα imaging of IC 2233 obtained with the WIYN telescope. Despite evidence of localized massive star formation in the form of prominent H II regions and shells, supergiant stars, and a blue integrated color, IC 2233 is a low surface brightness system with a very low global star formation rate (0.05 M☉ yr−1), and we detect no significant 21 cm radio continuum emission from the galaxy. The H I and ionized gas disks of IC 2233 are clumpy and vertically distended, with scale heights comparable to that of the young stellar disk. Both the stellar and H I disks of IC 2233 appear flared, and we also find a vertically extended, rotationally anomalous component of H I extending to ~ 2.4d10 kpc from the midplane. The H I disk exhibits a mild lopsidedness as well as a global corrugation pattern with a period of ~7d10 kpc and an amplitude of ~150d10 pc. To our knowledge, this is the first time corrugations of the gas disk have been reported in an external galaxy; these undulations may be linked to bending instabilities or to underlying spiral structure and suggest that the disk is largely self-gravitating. Lying at a projected distance of from IC 2233, NGC 2537 has an H I disk with a bright, tilted inner ring and a flocculent, dynamically cold outer region that extends to ~3.5 times the extent of the stellar light (D25). Although NGC 2537 is rotationally-dominated, we measure H I velocity dispersions as high as km s−1 near its center, indicative of significant turbulent motions. The inner rotation curve rises steeply, implying a strong central mass concentration. Our data indicate that IC 2233 and NGC 2537 do not constitute a bound pair and most likely lie at different distances. We also find no compelling evidence of a recent minor merger in either IC 2233 or NGC 2537, suggesting that both are examples of small disk galaxies evolving in relative isolation.
The Astronomical Journal 12/2007; 135(1):291. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have used the VLA to image the HI 21-cm line emission in the edge-on Sd galaxy IC2233 and the blue compact dwarf NGC2537. We also present new optical B,R, and H alpha imaging of IC2233 obtained with the WIYN telescope. Despite evidence of localized massive star formation, IC2233 has a low surface brightness disk with a low global star formation rate (~0.05 M_sun/yr), and no significant 21-cm radio continuum emission. The HI and ionized gas disks of IC2233 are clumpy and vertically distended, with scale heights comparable to the young stars. Both the stellar and HI disks of IC2233 appear flared, and we also find a vertically extended, rotationally anomalous HI component extending to z~2.4 kpc. The HI disk exhibits a mild lopsidedness as well as a global corrugation pattern with a period of ~7 kpc and an amplitude of ~150 pc. To our knowledge, this is the first time corrugations of the gas disk have been reported in an external galaxy; these undulations may be linked to bending instabilities or to underlying spiral structure and suggest that the disk is largely self-gravitating. Lying at a projected distance of 16.7' from IC2233, NGC2537 has an HI disk with a bright, tilted inner ring and a flocculent, dynamically cold outer region that extends to ~3.5D_25. Although NGC2537 is rotationally-dominated, it shows significant turbulence near its center. The inner rotation curve rises steeply, implying a strong central mass concentration. Our data indicate that IC2233 and NGC2537 do not constitute a bound pair and most likely lie at different distances. We also find no compelling evidence of a recent minor merger in either galaxy, suggesting that both are examples of small disk galaxies evolving in relative isolation. (Abridged)
[show abstract][hide abstract] ABSTRACT: UGC10043 is an edge-on Sbc spiral galaxy with several peculiar morphological characteristics that distinguish it from typical Sb-Sc galaxies, suggesting a complex formation history and evolution. Despite its thin, dynamically cold stellar disk, it shows a vertically elongated, triaxial bulge that is bisected on its SW quadrant by a dust lane perpendicular to its major axis. It also exhibits a large-scale galactic wind powered by a faint central starburst. Such features relate UGC10043 to families of relatively rare objects such as polar ring galaxies, orthogonally decoupled bulge systems, and minor-axis dust-lane ellipticals, suggesting that its evolution must have included a significant merger or accretion event. New HI spectral imaging observations carried out with the VLA in its C and D configurations have provided us with new insight into the complex evolutionary history of UGC10043. Our observations reveal that the galaxy is located in a small group, and we detect HI emission from four of its galaxies. We also have uncovered a kinematically continuous HI bridge parallel to the major axis of UGC10043 that connects it to a previously unknown companion, MGC+04-37-035, which is being dynamically heated by the interaction. We will discuss how the current interaction has likely affected the present morphological and kinematic peculiarities of UGC10043 and more generally how studies of this system can offer important insights into how the group environment affects the structure and evolution of typical disk galaxies.
[show abstract][hide abstract] ABSTRACT: Using the IRAM 30-m telescope, we have obtained 12CO J=1-0 and 2-1 spectral line observations toward the nuclear regions of 15 edge-on, low surface brightness (LSB) spiral galaxies. Our sample comprises extreme late-type LSB spirals with disk-dominated morphologies and rotational velocities V_rot<~120 km/s. We report detections of four galaxies in at least one transition (>5sigma); for the remainder of the sample we provide upper limits on the nuclear CO content. Adopting a standard Galactic I_CO-to-H_2 conversion factor implies molecular gas masses of (3.3-9.8)x10**6 M_sun in the nuclear regions (inner 1.1-1.8 kpc) of the detected galaxies. Combining our new data with samples of late-type spirals from the literature, we find that the CO-detected LSB spirals adhere to the same M_H2-FIR correlation as more luminous and higher surface brightness galaxies. The amount of CO in the central regions of late-type spirals appears to depend more strongly on mass than on central optical surface brightness, and CO detectability declines significantly for moderate-to-low surface brightness spirals with V_rot<~90 km/s; no LSB spirals have so far been detected in CO below this threshold. Metallicity effects alone are unlikely to account for this trend, and we speculate that we are seeing the effects of a decrease in the mean fraction of a galaxy disk able to support giant molecular cloud formation with decreasing galaxy mass. Comment: accepted to AJ
The Astronomical Journal 01/2005; · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: We summarize results from an HI+optical imaging study of the ``Integral Sign'' galaxy, UGC3697. UGC3697 is a low-mass, Sd spiral that exhibits a ``superthin'' disk morphology despite a prounced gasous and stellar warp. Our new observations show evidence for a recent minor merger in this system that could account for its large-scale warp and a number of other properties of this galaxy. We speculate that UGC3697 has been caught in a rather short-lived dynamical state, and may soon undergo significant structural and morphological changes.
[show abstract][hide abstract] ABSTRACT: Many searches for baryonic dark matter have been conducted but, so far, all have been unsuccessful. Indeed, no more than 1% of the dark matter can be in the form of hydrogen burning stars. It has recently been suggested that most of the baryons in the universe are still in the form of ionized gas so that it is possible that there is no baryonic dark matter. Although it is likely that a significant fraction of the dark matter in the Milky Way is in a halo of non-baryonic matter, the data do not exclude the possibility that a considerable amount, perhaps most of it, could be in a tenuous halo of diffuse ionized gas.
Nuclear Physics B - Proceedings Supplements. 06/2000;
[show abstract][hide abstract] ABSTRACT: High-quality images of fields larger than the field-of-view of the
elements of an array of radio telescopes can be obtained from a mosaic
of overlapping pointings. The addition of "single-dish" observations
made with a telescope of the same size as the array elements suffices to
produce images in which all Fourier components from the zero spatial
frequency up to the maximum allowed by the array are properly
represented. Image quality is then limited by systematic errors. Images
with dynamic range exceeding 1000:1 and a fidelity index of about 20
require antennas with rms surface accuracy of ˜λ/4O and
pointing accuracy of ˜6% of the half-power beamwidth.
Astronomy and Astrophysics 03/1993; 271:697. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The microwave background radiation is a remnant of the early Universe. It is blackbody radiation with a temperature TCBR = 2.735 ± 0.060 (0.017) K and no measured spectral distortions. It is isotropic to (ΔT/T) < 5 × 10−5 over all angular scales, except for a dipole component which is attributed to our motion with respect to the preferred reference frame of the radiation.A small-scale anisotropy has been detected towards a few dense clusters of galaxies that is attributed to inverse-Compton scattering of the photons of the background radiation by the hot gas that is responsible for the X-ray emission from these clusters. This is the Sunyaev-Zel'dovich effect.
Nuclear Physics B - Proceedings Supplements. 07/1992;
[show abstract][hide abstract] ABSTRACT: We analyze two methods of continuum subtraction in radio interferometric
imaging of spectral lines. These perform a linear fit to determine the
continuum emission. In the two methods, UVLIN and IMLIN, the fitting is
performed on the original visibilities and dirty images respectively. We
find that both work very well when the continuum emission is spread over
a small field of view and there are negligible instrumental errors. We
give simple expressions for the typical error level for both methods in
this regime. Both remain robust for significant instrumental errors in
the sense that the dynamic range is then proportional to the peak line
strength rather than the peak continuum strength. Hybrid methods
consisting of one of these methods preceded by the conventionally used
UVSUB method should work well when imaging emission spread over a large
field of view. We show examples of the application of these methods,
including a demonstration of the dangers inherent in the UVBAS method in
which linear fits to the visibility amplitude and phase are performed.
Astronomy and Astrophysics 04/1992; 258:583-590. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Universe is well described by the standard “Hot Big-Bang” model. Indeed, the consensus of observational results supports a homogeneous and isotropic model of the Universe which is expanding as described by Hubble's law. The ratio of the relative velocity of two (moderately) distant objects to their distance is Hubble's constant, Ho = (30 – 120) km s−1 Mpc−1.There is a background of blackbody radiation with a temperature, TCBR = 2.735±0.06 (0.017) K, isotropic to 3 parts in 105 on all angular scales except for a dipole component.The age of the Universe is probably in the range (14 – 18) × 109 years.The light-element abundances are consistent with 3 neutrino species and . As , there is likely to be baryonic dark matter. Since , there could be some non-baryonic dark matter.We do not know qo, Λo and probably never will.We might not yet have probed in detail a “fair sample” of the Universe.
Nuclear Physics B - Proceedings Supplements. 01/1992;
[show abstract][hide abstract] ABSTRACT: We have used the Very Large Array to search for ‘‘21-cm’’ narrow-band signals from neutral hydrogen at redshift Z=3.4. We detect absorption at Z=3.3968±0.0004 against a radio source that has been previously identified with a ‘‘normal’’ galaxy at Z=3.395±0.005. We detect emission at Z=3.3970±0.0003 separated from the absorption by 33’ (7–24 Mpc, depending on the cosmological model). This narrow-band emission signal is due to about 3×1014 M⊙ of neutral hydrogen as expected from a protocluster of galaxies. We identify it as the first example of a Zel’dovich ‘‘pancake.’’
[show abstract][hide abstract] ABSTRACT: The VLA to search for highly redshifted (Z = 3.3) '21 cm' line emission
from protoclusters of galaxies. The sensitivity, about 3.5 mJy per
synthesized beam for spectral channels of width about 100 kHz, was
limited at this level by statistical noise. The existence of any
Zel'dovich 'pancake' in the surveyed volume with a component of neutral
hydrogen with mass greater than about 10 to the 14th solar mass is ruled
out. This limit does not depend on the degree of fragmentation of such a
The Astrophysical Journal 07/1991; 377:L65-L68. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The P-band is the most recently completed observing band at the VLA. The aperture efficiency of the antennas is 0.4 and the system temperature is about 130 K. The primary beam is slightly off-axis and its half-power width is steeply frequency dependent, which induces abnormal spectral indices on off-axis sources. A search has been made for Zel'dovich 'pancakes' and a level of Delta S(rms) about 3.5 mJy has been reached for spectral channels of width of about 100 kHz. No pancake with M(HI) greater than about 5 x 10 exp 14 solar mass has been found.
[show abstract][hide abstract] ABSTRACT: An observational test has been performed of the 'Homogeneous Array' concept utilized in the MMA design, whereby the array elements are used in total power mode to provide the shortest spacings. Using the VLA in interferometric mode and a VLBA element measuring total power, a mosaic image of the Crab Nebula has been reconstructed, which fits the data adequately and is of good visual appearance.