Eric M. Wilcots

The Arecibo Legacy Fast ALFA Survey: the α.40 H I source catalog, its characteristics and their impact on the derivation of the H I mass function

We present a current catalog of 21 cm H I line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800 deg^2 of sky: the α.40 catalog. Covering 40% of the final survey area, the α.40 catalog contains 15,855 sources in the regions 07^h30^m < R.A. < 16^h30^m, +04° < decl. <+16°, and +24° < decl. <+28° and 22^h < R.A. < 03^h, +14° < decl. <+16°, and +24° < decl. < + 32°. Of those, 15,041 are certainly extragalactic, yielding a source density of 5.3 galaxies per deg^2, a factor of 29 improvement over the catalog extracted from the H I Parkes All-Sky Survey. In addition to the source centroid positions, H I line flux densities, recessional velocities, and line widths, the catalog includes the coordinates of the most probable optical counterpart of each H I line detection, and a separate compilation provides a cross-match to identifications given in the photometric and spectroscopic catalogs associated with the Sloan Digital Sky Survey Data Release 7. Fewer than 2% of the extragalactic H I line sources cannot be identified with a feasible optical counterpart; some of those may be rare OH megamasers at 0.16 < z < 0.25. A detailed analysis is presented of the completeness, width-dependent sensitivity function and bias inherent of the α.40 catalog. The impact of survey selection, distance errors, current volume coverage, and local large-scale structure on the derivation of the H I mass function is assessed. While α.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the H I mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.

The Kinematics and Distribution of H I in IC 10

We present the results of an extensive study of the neutral hydrogen content of IC 10, a dwarf irregular in the Local Group that is rightly considered a starburst. The H I content of IC 10 is characterized by a regularly rotating disk embedded within an extended and complex distribution of gas. The distribution of gas within the disk is dominated by holes and shells and has been and continues to be shaped by stellar winds associated with the numerous Wolf-Rayet and O stars. The stellar winds have likely triggered secondary generations of star formation within the shells surrounding many of the holes. We have detected the kinematic signature of the previously reported young superbubble in a large H I cloud at the southeastern tip of the optical galaxy. Finally, the complex distribution and kinematics of the extended gas around IC 10 suggest that this is a galaxy that is still forming via the accretion of the surrounding gas.

A Measurement of Disk Ellipticity in Nearby Spiral Galaxies

We have measured the intrinsic disk ellipticity for seven nearby, nearly face-on spiral galaxies by combining Densepak integral-field spectroscopy with I-band imaging from the WIYN telescope. Initially assuming an axisymmetric model, we determine the kinematic inclinations and position angles from Hα velocity fields and the photometric axis ratios and position angles from imaging data. We interpret the observed disparities between kinematic and photometric disk parameters in terms of an intrinsic nonzero ellipticity . The mean ellipticity of our sample is 0.05. If the majority of disk galaxies have such intrinsic axis ratios, this would account for roughly 50% of the scatter in the Tully-Fisher relation. This result, in turn, places tighter constraints on other sources of scatter in this relation, the most astrophysically compelling of which is galaxy mass-to-light ratios.

The Infrared Light Curve of SN 2011fe in M101 and the Distance to M101

We present near-infrared light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting 14 days before maximum brightness in the B band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera. When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band maximum of 10.85 ± 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used.

THE ROLE OF THE MAGNETIC FIELD IN THE INTERSTELLAR MEDIUM OF THE POST-STARBURST DWARF IRREGULAR GALAXY NGC 1569

NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10-40 Myr ago. We present observations that reach surface brightnesses 2-80 times fainter than previous radio continuum observations and the first radio continuum polarization observations of this galaxy at 20 cm, 13 cm, 6 cm, and 3 cm. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium (ISM). We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Hα arm at wavelengths shorter than 20 cm. Although, in general, the spectral indices derived for this galaxy steepen as one moves into the halo of the galaxy, there are filamentary regions of flat spectral indices extending to the edge of the galaxy. The spectral index trends in this galaxy support the theory that there is a convective wind at work in this galaxy. There is strong polarized emission at 3 cm and 6 cm and weak polarized emission at 20 cm and 13 cm. We estimate that the thermal fraction is 40%-50% in the center of the galaxy and falls off rapidly with height above the disk. Using this estimate, we derive a total magnetic field strength of 38 μG in the central regions and 10-15 μG in the halo. The magnetic field is largely random in the center of the galaxy; the uniform field is ~3-9 μG and is strongest in the halo. Using our total magnetic field strength estimates and the results of previous observations of NGC 1569, we find that the magnetic pressure is the same order of magnitude but, in general, a factor of a few less than the other components of the ISM in this galaxy. The uniform magnetic field in NGC 1569 is closely associated with the Hα bubbles and filaments. We suggest that a supernova-driven dynamo may be operating in this galaxy. Based on our pressure estimates and the morphology of the magnetic field, the outflow of hot gas from NGC 1569 is clearly shaping the magnetic field, but the magnetic field in turn may be aiding the outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with extended radio continuum halos like that of NGC 1569 may play an important role in magnetizing the intergalactic medium.

A Pilot for a Very Large Array H I Deep Field

High-resolution 21-cm HI deep fields provide spatially and kinematically resolved images of neutral hydrogen at different redshifts, which are key to understanding galaxy evolution across cosmic time and testing predictions of cosmological simulations. Here we present results from a pilot for an HI deep field done with the Karl G. Jansky Very Large Array (VLA). We take advantage of the newly expanded capabilities of the telescope to probe the redshift interval 0 < z < 0.193 in one observation. We observe the COSMOS field for 50 hours, which contains 413 galaxies with optical spectroscopic redshifts in the imaged field of 34′ × 34′ and the observed redshift interval. We have detected neutral hydrogen gas in 33 galaxies in different environments spanning the probed redshift range, including three without a previously known spectroscopic redshift. The detections have a range of HI and stellar masses, indicating the diversity of galaxies we are probing. We discuss the observations, data reduction, results and highlight interesting detections. We find that the VLA’s B-array is the ideal configuration for HI deep fields since its long spacings mitigate RFI. This pilot shows that the VLA is ready to carry out such a survey, and serves as a test for future HI deep fields planned with other SKA pathfinders.

Triggering and Feedback: The Relation between the H I Gas and the Starburst in the Dwarf Galaxy NGC 1569

As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (H I) in the starburst dwarf galaxy NGC 1569. High-resolution measurements with the Very Large Array (B, C, and D configuration) are aimed at identifying morphological and kinematical signatures in H I caused by the starburst. Our kinematical data suggest a huge hole in the H I distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale H I structure, we confirm the existence of a possible H I companion and a so-called H I bridge east of NGC 1569. Furthermore, we report the detection of additional low-intensity H I halo emission, which leads us to suggest a revised halo structure. On the basis of our new picture, we discuss the origin of the halo gas and possible implications for the evolution of the starburst in NGC 1569.

THE H I DISTRIBUTION AND DYNAMICS IN TWO LATE-TYPE BARRED SPIRAL GALAXIES : NGC 925 AND NGC 1744

We present H I observations of NGC 925 and NGC 1744, two late-type barred spiral galaxies that are quite comparable in mass and optical morphology. NGC 925 is a very asymmetric galaxy with a strong spiral arm in the south and flocculent arms in the north. The rotation curves of the east and west sides of the galaxy are consistent with this asymmetry as well. In addition, NGC 925s dynamical center may be slightly offset (215, or ~1 kpc) from its optical center. The ratio of the H I to optical diameter of NGC 925 is small compared with other galaxies. We detected a ~107 M⊙ H I cloud and streamer, with little or no stellar component, apparently interacting with NGC 925. While the interaction between NGC 925 and the cloud may be responsible for the observed asymmetries, given the weakness of the interaction we postulate that NGC 925 has suffered other gravitational encounters over the past few gigayears. NGC 1744, on the other hand, is an unperturbed galaxy having a textbook example of a velocity field for a disk galaxy. It has a symmetric, albeit weak, spiral structure. Both NGC 925 and NGC 1744 have small streaming motions (~10 km s-1) associated with the bar and spiral arms.

H I OBSERVATIONS OF BARRED MAGELLANIC SPIRALS. II. THE FREQUENCY AND IMPACT OF COMPANIONS

The results of an H I 21 cm line survey of a sample of Magellanic spiral galaxies with apparent optical companions reveal that only four of 13 systems have confirmed H I–detected neighbors. The current interactions are affecting the morphology of the main galaxy in only two cases, NGC 3664 and NGC 3995. The presence of companions near NGC 2537 and UGC 5391 appears to have no effect on the morphology of those galaxies. Overall, there is little difference between the asymmetry of the H I profiles of those galaxies with and without companions, and on average, these Magellanic spirals have H I profiles that are no more asymmetric than a random sample of spirals in the field. We conclude that current interactions cannot be responsible for the lopsided morphology of most of the galaxies in this sample and that, whatever its original cause, lopsidedness must be a long-lived characteristic of these galaxies.

Massive compact galaxies with high-velocity outflows : Morphological analysis and constraints on AGN activity

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