Linda C. Watson

The Sloan Digital Sky Survey - II:supernova survey: technical summary

The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5° wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for the discovery of new objects. Supernova imaging observations are being acquired between September 1 and November 30 of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

First-year spectroscopy for the sloan digital sky survey - II. Supernova survey

This paper presents spectroscopy of supernovae (SNe) discovered in the first season of the Sloan Digital Sky Survey-II SN Survey. This program searches for and measures multi-band light curves of SNe in the redshift range z = 0.05-0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the SN population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our SN spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the SN and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host-galaxy contamination existing in the majority of our SN spectra.

DISCOVERY OF A VERY BRIGHT, NEARBY GRAVITATIONAL MICROLENSING EVENT

We report the serendipitous detection of a very bright, very nearby microlensing event. In late 2006 October, an otherwise unremarkable A0 star at a distance of � 1 kpc (GSC 3656� 1328) brightened achromatically by a factor of nearly 40 over the span of several days and then decayed in an apparently symmetrical way. We present a light curve of the event based on optical photometry from the Center for Backyard Astrophysics and the All Sky Automated Survey, as well as near-infrared photometry from the Peters Automated Infrared Imaging Telescope. This light curve is well fit by a generic microlensing model. We also report optical spectra and Swift X-ray and UVobservations that are consistent with the microlensing interpretation. We discuss and reject alternative explanations for this variability. The lens star is probably a low-mass star or brown dwarf, with a relatively high proper motion of k20 mas yr � 1 , and may be visible using precise optical/infrared imaging taken several years from now. A modest, all-sky survey telescope could detect � 10 such events per year, which would enable searches for very low mass planetary companions to relatively nearby stars. Subject headingg gravitational lensing — stars: individual (GSC 3656� 1328) Online material: color figures

Revisiting the Black Hole Masses of Soft X-Ray-Selected Active Galactic Nuclei

In our previous work, using luminosity and the Hβ FWHM as surrogates for black hole mass (MBH), we compared the black hole masses of narrow-line Seyfert 1 galaxies (NLS1s) and broad-line Seyfert 1 galaxies (BLS1s) in a sample of soft X-ray-selected active galactic nuclei. We found that the distributions of black hole masses in the two populations are statistically different. Recent work shows that the second moment of the Hβ emission line (the line dispersion) is a better estimator of black hole mass than FWHM. To test whether changing the width measure affects our results, we calculate line dispersion-based black hole masses for our soft X-ray-selected sample. We find that using the line dispersion rather than the FWHM as a measure of the gas velocity shifts NLS1 and BLS1 virial product distributions closer together, but they remain distinct. On the MBH-σ* plane, we find that using the line dispersion leaves NLS1s below the MBH-σ* relation, but to a less significant degree than when FWHM is used to calculate black hole masses (the [O III] λ5007 FWHM is used as a surrogate for the bulge stellar velocity dispersion). The level of significance of our findings is such that we cannot draw firm conclusions on the location of the two samples on the MBH-σ* plane. We are still left with two alternative scenarios: either (1) NLS1s lie below the MBH-σ* relation, indicating that their black hole masses are growing, or (2) NLS1s lie on the MBH-σ* relation, so they preferentially reside in smaller mass, less luminous galaxies; the present data do not allow us to choose one over the other. More trustworthy stellar velocity dispersions and accurate black hole mass measurements with reverberation mapping are required for a firmer statement about the locus of NLS1s on the MBH-σ* plane.

PROPERTIES OF BULGELESS DISK GALAXIES. I. ATOMIC GAS

We study the neutral hydrogen properties of a sample of 20 bulgeless disk galaxies (Sd-Sdm Hubble types), an interesting class that can be used to constrain galaxy formation and evolution, especially the role of mergers versus internal processes. Our sample is composed of nearby (within 32 Mpc), moderately inclined galaxies that bracket the circular velocity of 120 km s?1, which has been found to be associated with a transition in dust scale heights in edge-on, late-type disks. Here, we present H I channel maps, line profiles, and integrated intensity maps. We also derive kinematic parameters, including the circular velocity, from rotation curve analyses and calculate the integrated H I flux and H I mass for each galaxy in the sample. Three of the 20 galaxies in our sample have kinematically distinct outer components with major axes that differ by 30?-90? from the main disk. These distinct outer components may be due to a recent interaction, which would be somewhat surprising because the disks do not contain bulges. We will use the data products and derived properties in subsequent investigations into star formation and secular evolution in bulgeless disks with circular velocities above and below 120 km s?1.

PROPERTIES OF BULGELESS DISK GALAXIES. II. STAR FORMATION AS A FUNCTION OF CIRCULAR VELOCITY

L.C.W. gratefully acknowledges support from an NSF Graduate Research Fellowship and an Ohio State University Distinguished University Fellowship. PM is grateful for support from the NSF via award AST-0705170. U.L. acknowledges financial support from the research projects AYA2007-67625-C02-02 and AYA2011-24728 from the Spanish Ministerio de Ciencia y Educacion and from the Junta de Andalucia.

Testing the molecular-hydrogen Kennicutt–Schmidt law in the low-density environments of extended ultraviolet disc galaxies

Studying star formation beyond the optical radius of galaxies allows us to test empirical relations in extreme conditions with low average gas density and low molecular fraction. Previous studies discovered galaxies with extended ultraviolet (XUV) disks, which often contain star forming regions with lower Halpha-to-far-UV (FUV) flux ratios compared to inner disk star forming regions. However, most previous studies lack measurements of molecular gas, which is presumably the component of the interstellar medium out of which stars form. We analyzed published CO measurements and upper limits for fifteen star forming regions in the XUV or outer disk of three nearby spiral galaxies and a new CO upper limit from the IRAM 30 m telescope in one star forming region at r = 3.4 r_25 in the XUV disk of NGC 4625. We found that the star forming regions are in general consistent with the same molecular-hydrogen Kennicutt-Schmidt law that applies within the optical radius, independent of whether we used Halpha or FUV as the star formation rate (SFR) tracer. However, a number of the CO detections are significantly offset towards higher SFR surface density for their molecular hydrogen surface density. Deeper CO data may enable us to use the presence or absence of molecular gas as an evolutionary probe to break the degeneracy between age and stochastic sampling of the initial mass function as the explanation for the low Halpha-to-FUV flux ratios in XUV disks.

Discovery of a Large Population of Ultraluminous X-Ray Sources in the Bulgeless Galaxies NGC 337 and ESO 501-23

We have used Chandra observations of eight bulgeless disk galaxies to identify new ultraluminous X-ray source (ULX) candidates, study their high-mass X-ray binary (HMXB) population, and search for low-luminosity active galactic nuclei (AGNs). We report the discovery of 16 new ULX candidates in our sample of galaxies. Eight of these are found in the star forming galaxy NGC?337, none of which are expected to be background contaminants. The?HMXB luminosity function of NGC?337 implies a star formation rate (SFR) of 6.8 M ??yr?1, consistent at 1.5? with a recent state of the art SFR determination. We also report the discovery of a bright ULX candidate (X-1) in ESO 501-23. X-1s spectrum is well fit by an absorbed power law with and N H = 1.13?cm?2, implying a 0.3-8?keV flux of ?erg?s?1?cm?2. Its X-ray luminosity (LX ) is poorly constrained due to uncertainties in the host galaxys distance, but we argue that its spectrum implies LX > 1040?erg?s?1. An optical counterpart to this object may be present in an Hubble Space Telescope image. We also identify ULX candidates in IC 1291, PGC 3853, NGC?5964, and NGC?2805. We find no evidence of nuclear activity in the galaxies in our sample, placing a flux upper limit of 4 ? 10?15?erg?s?1?cm?2 on putative AGN. Additionally, the Type?II-P supernova SN 2011DQ in NGC?337, which exploded two?months before our X-ray observation, is undetected.

Angular Momentum in Disk Wind Revealed in the Young Star MWC 349A

Disk winds are thought to play a critical role in star birth. As winds extract excess angular momentum from accretion disks, matter in the disk can be transported inward to the star to fuel mass growth. However, the observational evidence of wind carrying angular momentum has been very limited. We present Submillimeter Array (SMA) observations of the young star MWC349A in the H26

A Study of Hydrogen Recombination Masers in MWC349A

\alpha