Search Publications
Evidence of Cosmic Evolution of the Stellar Initial Mass Function
van Dokkum, Pieter G.
Theoretical arguments and indirect observational evidence suggest that the stellar IMF may evolve with time, such that it is more weighted toward high-mass stars at higher redshift. Here we test this idea by comparing the rate of luminosity evolution of massive early-type galaxies in clusters at 0.02 <= z<= 0.83 to the rate of their color ev…
The Low-z Intergalactic Medium. III. H I and Metal Absorbers at z < 0.4
Shull, J. Michael; Danforth, Charles W.
We conduct an ultraviolet (HST and FUSE) spectroscopic survey of H I (Lyman lines) and seven metal ions (O VI, N V, C IV, C III, Si IV, Si III, Fe III) in the low-redshift IGM at z < 0.4. We analyzed 650 Lyα absorbers over redshift path length Δ z = 5.27, detecting numerous absorbers: 83 O VI systems, 39 C III, 53 Si III, 24 C IV, 24 N V, and s…
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
Faucher-Giguère, Claude-André; Hernquist, Lars; Lidz, Adam +1 more
We investigate the implications of the intergalactic opacity for the evolution of the cosmic UV luminosity density and its sources. Our main constraint is our measurement of the Lyα forest opacity at redshifts 2 <= z <= 4.2 from 86 high-resolution quasar spectra. In addition, we impose the requirements that H I must be reionized by z = 6 and…
The Hard X-Ray Spectrum as a Probe for Black Hole Growth in Radio-Quiet Active Galactic Nuclei
Maiolino, Roberto; Brandt, W. N.; Kaspi, Shai +2 more
We study the hard X-ray spectral properties of 10 highly luminous radio-quiet (RQ) active galactic nuclei (AGNs) at z = 1.3-3.2, including new XMM-Newton observations of four of these sources. We find a significant correlation between the normalized accretion rate (L/LEdd) and the hard X-ray photon index (Γ) for 35 moderate- to high-lum…
Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge
Bouchet, L.; Porter, Troy A.; Strong, Andrew W. +2 more
A recent redetermination of the nonthermal component of the hard X-ray to soft γ-ray emission from the Galactic ridge, using the SPI instrument on the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), is shown to be well reproduced as inverse Compton emission from the interstellar medium. Both cosmic-ray primary electrons and secondary e…
A Highly Complete Spectroscopic Survey of the GOODS-N Field
Wang, W. -H.; Barger, A. J.; Cowie, L. L.
We present a table of redshifts for 2907 galaxies and stars in the 145 arcmin2 HST ACS GOODS-North, making this the most spectroscopically complete redshift sample obtained to date in a field of this size. We also include the redshifts, where available, in a table containing just under 7000 galaxies from the ACS area with Ks, AB
A Spitzer View of Protoplanetary Disks in the γ Velorum Cluster
Jeffries, R. D.; Gutermuth, R.; Stauffer, J. +4 more
We present new Spitzer Space Telescope observations of stars in the young (~5 Myr) γ Velorum stellar cluster. Combining optical and 2MASS photometry, we have selected 579 stars as candidate members of the cluster. With the addition of the Spitzer mid-infrared data, we have identified five debris disks around A-type stars and five to six debris dis…
Gemini and Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in ω Centauri
Gebhardt, Karl; Noyola, Eva; Bergmann, Marcel
The globular cluster ω Centauri is one of the largest and most massive members of the galactic system. However, its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this together with the fact that it has one of the largest velocity dispersions for star clusters…
Jets in Coronal Holes: Hinode Observations and Three-dimensional Computer Modeling
Galsgaard, K.; Moreno-Insertis, F.; Ugarte-Urra, I.
Recent observations of coronal hole areas with the XRT and EIS instruments on board the Hinode satellite have shown with unprecedented detail the launching of fast, hot jets away from the solar surface. In some cases these events coincide with episodes of flux emergence from beneath the photosphere. In this Letter we show results of a three-dimens…
Vigorous Star Formation with Low Efficiency in Massive Disk Galaxies at z = 1.5
Daddi, E.; Elbaz, D.; Morrison, G. +4 more
We present the first detection of molecular gas cooling CO emission lines from ordinary massive galaxies at z = 1.5. Two sources were observed with the IRAM Plateau de Bure Interferometer, selected to lie in the mass-star formation rate correlation at their redshift, thus being representative of massive high-z galaxies. Both sources were detected …