We present super(12)CO(J= 110) observations of the high-redshift quasi-stellar objects (QSOs) BR 1202-0725 (z =4.69), PSS J2322+1944 (z = 4.12), and APM 08279+5255 (z = 3.91)using the NRAO Green Bank ...Telescope (GBT) and the MPIfR Effelsberg 100 m telescope. We detect, for the first time, the CO ground-level transition in BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations result in line fluxes that are consistent with previous NRAO Very Large Array (VLA) observations, but they reveal the full line profiles. We report a typical lensing-corrected velocity-integrated intrinsic super(12)CO(J = 110 line luminosity of L super('CO)=5 x 10 super(10) K km s super(-1) pc super(2) and a typical total H sub(2) mass of M(H sub(2)) = 4 x 10 super(10) M sub( )for the sources in our sample. The CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies, leading to a combined solution of log L sub(FIR) = (1.39 c 0.05) log L sub(CO) -1.76. It has previously been suggested that the molecular gas reservoirs in some quasar host galaxies may exhibit luminous, extended super(12)CO(J = 110) components that are not observed in the higher J CO transitions. Using the line profiles and the total intensities of our observations and large velocity gradient (LVG) models based on previous results for higher JCO transitions, we derive that emission from all CO transitions is described well by a single gas component in which all molecular gas is concentrated in a compact nuclear region. Thus, our observations and models show no indication of aluminous extended, low surface brightness molecular gas component in any of the high-redshift QSOs in our sample. If such extended components exist, their contribution to the overall luminosity is limited to at most 30%.
New super(13)CO data from the BU-FCRAO Milky Way Galactic Ring Survey (GRS) are analyzed to elucidate the shape and internal motions of molecular clouds. For a sample of more than 500 molecular ...clouds, we find that they are preferentially elongated along the Galactic plane. On the other hand, their spin axes are randomly oriented. We therefore conclude that the elongation is not supported by internal spin but by internal velocity anisotropy. It has been known that some driving mechanisms are necessary to sustain the supersonic velocity dispersion within molecular clouds. The mechanism for generating the velocity dispersion must also account for the preferred elongation. This excludes some driving mechanisms, such as stellar winds and supernovae, because they do not produce the systemic elongation along the Galactic plane. Driving energy is more likely to come from large-scale motions, such as Galactic rotation.
We present the first catalog of 67 strong galaxy-galaxy lens candidates discovered In the 1.64 deg super(2) Hubble Space Telescope COSMOS survey. Twenty of these systems display multiple images or ...strongly curved large arcs. Our initial search is performed by visual inspection of the data and is restricted, for practical considerations, to massive early-type lens galaxies with arcs found at radii smaller than similar to 5". Simple mass models are constructed for the best lens candidates, and our results are compared to the strong lensing catalogs of the SLACS survey and the CASTLES database. These new strong galaxy-galaxy lensing systems constitute a valuable sample to study the mass distribution of early-type galaxies and their associated dark matter halos. We further expect this sample to play an important role in the testing of software algorithms designed to automatically search for strong gravitational lenses. From our analysis a robust lower limit is derived for the expected occurrence of strong galaxy-galaxy systems in current and future space-based wide-field imaging surveys. We expect that such surveys should uncover a large number of strong lensing systems (more than 10 systems per square degree), which will allow for a detailed statistical analysis of galaxy properties and will likely lead to constraints on models of gravitational structure formation and cosmology.
We present infrared, optical, and X-ray data of 48 X-ray bright, optically dull active galactic nuclei (AGNs) in the COSMOS field. These objects exhibit the X-ray luminosity of an AGN but lack broad ...and narrow emission lines in their optical spectrum. We show that despite the lack of optical emission lines, most of these optically dull AGNs are not well described by a typical passive red galaxy spectrum: instead they exhibit weak but significant blue emission like an unobscured AGN. Photometric observations over several years additionally show significant variability in the blue emission of four optically dull AGNs. The nature of the blue and infrared emission suggest that the optically inactive appearance of these AGNs cannot be caused by obscuration intrinsic to the AGNs. Instead, up to ~70% of optically dull AGNs are diluted by their hosts, with bright or simply edge-on hosts lying preferentially within the spectroscopic aperture. The remaining ~30% of optically dull AGNs have anomalously high fX /fO ratios and are intrinsically weak, not obscured, in the optical. These optically dull AGNs are best described as a weakly accreting AGN with a truncated accretion disk from a radiatively inefficient accretion flow.
We report a discovery of six massive galaxies with both extremely large Ly alpha equivalent widths (EWs) and evolved stellar populations at z ~ 3. These MAssive Extremely STrong Ly alpha emitting ...Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Ly alpha emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW sub(0) (Ly alpha ) ~ 100-300 Angstrom, (2) Mlow * ~ 10 super(10.5)-10 super(11.1) M sub(middot in circle), and (3) relatively low specific star formation rates of SFR/Mlow * ~ 0.03-1 Gyr super(-1). Three of the six MAESTLOs have extended Ly alpha emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Ly alpha emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.
For a mass-selected sample of 66544 galaxies with photometric redshifts (z phot) from the Cosmic Evolution Survey (COSMOS), we examine the evolution of star-formation activity as a function of ...stellar mass in galaxies. We estimate the cosmic star-formation rates (SFRs) over the range 0.2 < z phot < 1.2, using the rest-frame 2800 A flux (corrected for extinction). We find the mean SFR to be a strong function of the galactic stellar mass at any given redshift, with massive systems (log(M/M )>10.5) contributing less (by a factor of ~5) to the total star-formation rate density (SFRD). Combining data from the COSMOS and Gemini Deep Deep Survey, we extend the SFRD-z relation as a function of stellar mass to z ~ 2. For massive galaxies, we find a steep increase in the SFRD-z relation to z ~ 2; for the less-massive systems, the SFRD which also increases from z = 0 to 1 levels off at z ~ 1. This implies that the massive systems have had their major star-formation activity at earlier epochs (z > 2) than the lower-mass galaxies. We study changes in the SFRDs as a function of both redshift and stellar mass for galaxies of different spectral types. We find that the slope of the SFRD-z relation for different spectral types of galaxies is a strong function of their stellar mass. For low- and intermediate-mass systems, the main contribution to the cosmic SFRD comes from the star-forming galaxies while, for more-massive systems, the evolved galaxies are the most dominant population.
We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to ...model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of {approx}90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.
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