Infrared Emission from Clusters in the Starforming Disk of He2-10

We have made subarcsecond-resolution images of the central 10" of the Wolf-Rayet dwarf galaxy He 2-10 at 11.7 microns, using the Long Wavelength Spectrometer on the Keck Telescope. The spatial distribution of the infrared emission roughly agrees with that of the rising spectrum radio sources seen by Kobulnicky & Johnson (1999) and confirms that those sources are compact HII regions rather than SNR or other objects. The infrared sources are more extended than the subarcsecond rising spectrum radio sources, although the entire complex is still less than 5" in extent. On sizescales of 1" the infrared and radio emission are in excellent agreement, with each source requiring several hundred to a thousand O stars for excitation. The nebulae lie in a flattened disk-like distribution about 240 by 100 pc and provide all of the flux measured by IRAS for the entire galaxy in the 12 micron band; 30% of the total IRAS flux from the galaxy emanates from one 15-30 pc source. In this galaxy, intense star formation, probably triggered by an accretion event, is confined to a central disk which breaks up into distinct nebulae which presumably mark the sites of young super star clusters.Comment: Accepted for Publication in the Astronomical Journa

A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei

We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035) Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features or multiple nuclei. The incidence of inner starburst rings is about 10% in both classes of Sy galaxies. In contrast, galaxies with H II region emission line spectra appear substantially more irregular because of their much higher specific rates of star formation. An unresolved central continuum source in our HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1 point sources are saturated in our images; we use their wings to estimate their magnitudes. The converse is not however true, as over a third of Sy's with direct spectroscopic evidence for broad Balmer wings show no nuclear point source. Like the Sy2's, they have central surface brightnesses consistent with those expected for the bulges of normal galaxies. The frequency of bars in Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more likely to show nuclear dust absorption, especially in lanes and patches which are irregular or reach close to the nucleus. The difference cannot be explained by different average redshifts or selection techniques. This is confirmed by our morphology classifications, which show that Sy1 nuclei reside in earlier type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy properties may undermine the strong unification hypothesis for Sy galaxies that they appear different due to the orientation of their central engine. The excess galactic dust we see in Sy2's may cause substantial absorption which obscures their hypothesized broad emission-line regions and central nonstellar continua. This galactic dust could produce much of the absorption in Sy2 nuclei which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9 figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as anonymous and give your e-mail address as the password. The images are in the /pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included here and can be printed using the lpr command in unix system

Spitzer observations of a gravitationally lensed quasar, QSO 2237+0305

The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by stars in the lens galaxy. The amplitude of microlensing variability can be used to infer the relative size of the quasar as a function of wavelength; this provides a test of quasar models. Toward this end, we present Spitzer Space Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy distribution (SED) is similar to that of other bright radio-quiet quasars, contrary to an earlier claim. (2) A dusty torus model with a small opening angle fits the overall shape of the IR SED well, but the quantitative agreement is poor due to an offset in wavelength of the silicate feature. (3) The flux ratios of the four lensed images can be derived from the IRAC data despite being unresolved. We find that the near-IR fluxes are increasingly affected by microlensing toward shorter wavelengths. (4) The wavelength dependence of the IRAC flux ratios is consistent with the standard quasar model in which an accretion disk and a dusty torus both contribute near 1 micron in the rest frame. This is also consistent with recent IR spectropolarimetry of nearby quasars

Dynamics and Formation of the Near-Resonant K2-24 System: Insights from Transit-Timing Variations and Radial Velocities

While planets between the size of Uranus and Saturn are absent within the Solar System, the star K2-24 hosts two such planets, K2-24b and c, with radii equal to $5.4~R_E$ and $7.5~R_E$, respectively. The two planets have orbital periods of 20.9 days and 42.4 days, residing only 1% outside the nominal 2:1 mean-motion resonance. In this work, we present results from a coordinated observing campaign to measure planet masses and eccentricities that combines radial velocity (RV) measurements from Keck/HIRES and transit-timing measurements from K2 and Spitzer. K2-24b and c have low, but non-zero, eccentricities of $e_1 \sim e_2 \sim 0.08$. The low observed eccentricities provide clues regarding the formation and dynamical evolution of K2-24b and K2-24c, suggesting that they could be the result of stochastic gravitational interactions with a turbulent protoplanetary disk, among other mechanisms. K2-24b and c are $19\pm2~M_E$ and $15\pm2~M_E$, respectively; K2-24c is 20% less massive than K2-24b, despite being 40% larger. Their large sizes and low masses imply large envelope fractions, which we estimate at $26^{+3}_{-3}\%$ and $52^{+5}_{-3}\%$. In particular, K2-24c's large envelope presents an intriguing challenge to the standard model of core nucleated accretion that predicts the onset of runaway accretion when $f_{env} \approx 50\%$.Comment: 14 pages, 9 figures, 2 tables, accepted to A

First Views of a Nearby LIRG: Star Formation and Molecular Gas in IRAS 04296+2923

We present a first look at the local LIRG, IRAS04296+2923. This barred spiral, overlooked because of its location in the Galactic plane, is among the half dozen closest LIRGs. More IR-luminous than either M82 or the Antennae, it may be the best local example of a nuclear starburst caused by bar-mediated secular evolution. We present Palomar J and Pa beta images, VLA maps from 20-1.3cm, a Keck LWS image at 11.7mic and OVRO CO(1-0) and ^13CO(1-0), and 2.7 mm continuum images. The J-band image shows a symmetric barred spiral. Two bright, compact mid-IR/radio sources in the nucleus comprise a starburst that is equivalent to 10^5 O7 stars, probably a pair of young super star clusters separated by 30pc. The nuclear starburst is forming stars at the rate of ~12Msun/yr, half of the total star formation rate for the galaxy of ~25Msun/yr. IRAS04296 is bright in CO, and among the most gas-rich galaxies in the local universe. The CO luminosity of the inner half kpc is equivalent to that of the entire Milky Way. While the most intense CO emission extends over a 15"(2 kpc) region, the nuclear starburst is confined to ~1-2"(150-250 pc) of the dynamical center. From ^13CO, we find that the CO conversion factor in the nucleus is higher than the Galactic value by a factor 3-4, typical of gas-rich spiral nuclei. The nuclear star formation efficiency is M_gas/SFR^nuc = 2.7x10^-8 yr^-1, corresponding to gas consumption timescale, tau_SF^nuc~4x10^7 yrs. The star formation efficiency is ten times lower in the disk, tau_SF^disk~3.3x10^8 yrs. The low absolute star formation efficiency in the disk implies that the molecular gas is not completely consumed before it drifts into the nucleus, and is capable of fueling a sustained nuclear starburst. IRAS04296 is beginning a 100Myr period as a LIRG, during which it will turn much of its 6x10^9Msun of molecular gas into a nuclear cluster of stars. (abridged)Comment: Accepted, Astronomical Journa

Aperture Photometry Tool

Aperture Photometry Tool (APT) is software for astronomers and students interested in manually exploring the photometric qualities of astronomical images. It is a graphical user interface (GUI) designed to allow the image data associated with aperture photometry calculations for point and extended sources to be visualized and, therefore, more effectively analyzed. The finely tuned layout of the GUI, along with judicious use of color-coding and alerting, is intended to give maximal user utility and convenience. Simply mouse-clicking on a source in the displayed image will instantly draw a circular or elliptical aperture and sky annulus around the source and will compute the source intensity and its uncertainty, along with several commonly used measures of the local sky background and its variability. The results are displayed and can be optionally saved to an aperture-photometry-table file and plotted on graphs in various ways using functions available in the software. APT is geared toward processing sources in a small number of images and is not suitable for bulk processing a large number of images, unlike other aperture photometry packages (e.g., SExtractor). However, APT does have a convenient source-list tool that enables calculations for a large number of detections in a given image. The source-list tool can be run either in automatic mode to generate an aperture photometry table quickly or in manual mode to permit inspection and adjustment of the calculation for each individual detection. APT displays a variety of useful graphs with just the push of a button, including image histogram, x and y aperture slices, source scatter plot, sky scatter plot, sky histogram, radial profile, curve of growth, and aperture-photometry-table scatter plots and histograms. APT has many functions for customizing the calculations, including outlier rejection, pixel “picking” and “zapping,” and a selection of source and sky models. The radial-profile-interpolation source model, which is accessed via the radial-profile-plot panel, allows recovery of source intensity from pixels with missing data and can be especially beneficial in crowded fields

Revisiting the HIP 41378 System with K2 and Spitzer

We present new observations of the multiplanet system HIP 41378, a bright star (V = 8.9, K s = 7.7) with five known transiting planets. Previous K2 observations showed multiple transits of two Neptune-sized bodies and single transits of three larger planets (R P = 0.33R J , 0.47R J , 0.88R J ). K2 recently observed the system again in Campaign 18 (C18). We observe one new transit each of two of the larger planets d/f, giving maximal orbital periods of 1114/1084 days, as well as integer divisions of these values down to a lower limit of about 50 days. We use all available photometry to determine the eccentricity distributions of HIP 41378 d & f, finding that periods lesssim300 days require non-zero eccentricity. We check for overlapping orbits of planets d and f to constrain their mutual periods, finding that short periods (P < 300 days) for planet f are disfavored. We also observe transits of planets b and c with Spitzer/Infrared Array Camera (IRAC), which we combine with the K2 observations to search for transit timing variations (TTVs). We find a linear ephemeris for planet b, but see a significant TTV signal for planet c. The ability to recover the two smaller planets with Spitzer shows that this fascinating system will continue to be detectable with Spitzer, CHEOPS, TESS, and other observatories, allowing us to precisely determine the periods of d and f, characterize the TTVs of planet c, recover the transits of planet e, and further enhance our view of this remarkable dynamical laboratory