Search Publications
New Constraints on Mass-dependent Disruption of Star Clusters in M51
Calzetti, Daniela; Schinnerer, Eva; Whitmore, Bradley C. +4 more
We use UBVI Hα images of the Whirlpool galaxy, M51, taken with the Advanced Camera for Surveys and WFPC2 cameras on the Hubble Space Telescope (HST) to select star clusters, and to estimate their masses and ages by comparing their observed colors with predictions from population synthesis models. We construct the mass function of intermediate-age …
Measuring Turbulence in the Interstellar Medium by Comparing N(H I; Lyα) and N(H I; 21 cm)
Lockman, Felix J.; Wakker, Bart P.; Brown, Jonathan M.
We present a study of the small-scale structure of the interstellar medium (ISM) in the Milky Way. We used HST STIS data to measure N(H I) in a pencil beam toward 59 active galactic nuclei and compared the results with the values seen at 9'-36' resolution in the same directions using radio telescopes (Green Bank Telescope, Green Bank 140-ft, and L…
Detection of Current Sheets and Magnetic Reconnections at the Turbulent Leading Edge of an Interplanetary Coronal Mass Ejection
Chian, Abraham C. -L.; Muñoz, Pablo R.
The relation between current sheets, turbulence, and magnetic reconnections at the leading edge of an interplanetary coronal mass ejection detected by four Cluster spacecraft on 2005 January 21 is studied. We report the observational evidence of two magnetically reconnected current sheets in the vicinity of a front magnetic cloud boundary layer wi…
Star Clusters in the Tidal Tails of Interacting Galaxies: Cluster Populations Across a Variety of Tail Environments
Bastian, N.; Konstantopoulos, I. S.; Gallagher, S. C. +17 more
We have searched for compact stellar structures within 17 tidal tails in 13 different interacting galaxies using F606W- and F814W-band images from the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The sample of tidal tails includes a diverse population of optical properties, merging galaxy mass ratios, H I content, and ages. Combini…
Evolution of Currents of Opposite Signs in the Flare-productive Solar Active Region NOAA 10930
Tiwari, Sanjiv Kumar; Venkatakrishnan, P.; Ravindra, B. +1 more
Analysis of a time series of high spatial resolution vector magnetograms of the active region NOAA 10930 available from the Solar Optical Telescope SpectroPolarimeter on board Hinode revealed that there is a mixture of upward and downward currents in the two footpoints of an emerging flux rope. The flux emergence rate is almost the same in both th…
The UDF05 Follow-up of the Hubble Ultra Deep Field. III. The Luminosity Function at z ~ 6
Ferguson, Henry C.; Giavalisco, Mauro; Lucas, Ray A. +13 more
In this paper, we present a derivation of the rest-frame 1400 Å luminosity function (LF) at redshift six from a new application of the maximum likelihood method by exploring the five deepest Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) fields, i.e., the Hubble Ultra Deep Field, two UDF05 fields, and two Great Observatories Origins …
Optical Properties of the Ultraluminous X-Ray Source Holmberg IX X-1 and Its Stellar Environment
Motch, C.; Kaaret, P.; Pakull, M. W. +1 more
Holmberg IX X-1 is an archetypal ultraluminous X-ray source (ULX). Here we study the properties of the optical counterpart and of its stellar environment using optical data from SUBARU/Faint Object Camera and Spectrograph, GEMINI/GMOS-N and Hubble Space Telescope (HST)/Advanced Camera for Surveys, as well as simultaneous Chandra X-ray data. The V …
New Evidence for High Activity of the Supermassive Black Hole in our Galaxy
Koyama, K.; Nobukawa, M.; Tsuru, T. G. +1 more
Prominent K-shell emission lines of neutral iron (hereafter Fe I-K lines) and hard-continuum X-rays from molecular clouds (MCs) in the Sagittarius B (Sgr B) region were found in two separate Suzaku observations in 2005 and 2009. The X-ray flux of the Fe I-K lines decreased in correlation with the hard-continuum flux by a factor of 0.4-0.5 in four …
Revisiting the Abundance Gradient in the Maser Host Galaxy NGC 4258
Bresolin, Fabio
New spectroscopic observations of 36 H II regions in NGC 4258 obtained with the Gemini telescope are combined with existing data from the literature to measure the radial oxygen abundance gradient in this galaxy. The [O III]λ4363 auroral line was detected in four of the outermost targets (17-22 kpc from the galaxy center), allowing a determination…
A Study of the X-rayed Outflow of APM 08279+5255 through Photoionization Codes
Chartas, George; Saez, Cristian
We present new results from our study of the X-rayed outflow of the z = 3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. These results are based on spectral fits to all the long exposure observations of APM 08279+5255 using a new quasar-outflow model. This model is based on CLOUDY 3 CLOUDY is a photoionization co…