Download or read book The Molecular Gas Content and Ionization Processes in Distant Powerful Radio Galaxies and Hyperluminous Infrared Galaxies written by Aaron S. Evans and published by . This book was released on 1996 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Molecular Gas Content of Ultraluminous Infrared Galaxies written by Stefano Venturini and published by . This book was released on 2004 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Annual Review of Astronomy and Astrophysics written by Leo Goldberg and published by . This book was released on 1996-09 with total page 844 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides abstracts and full text for articles on astronomy and astrophysics.
Download or read book Acquisition List written by University of Hawaii at Manoa. Library. Hawaiian Collection and published by . This book was released on 1997 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Exploration of Inter stellar Gas and Its Role in Galaxy Assembly Over Cosmic Time written by Riccardo Pavesi and published by . This book was released on 2019 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt: The key physical processes driving galaxy formation and evolution are controlled by gas and, in particular, the process of star formation from cold, dense gas is not well understood since it depends upon the gas cooling ability, its dynamical state and complex feedback processes. Galaxies were observed to form stars much more rapidly in the past (~10-11 billion years ago), which may be due to larger gas reservoirs or more efficient star formation processes. While previous studies have identified large molecular gas reservoirs in a few pre-selected star-forming galaxies, an unbiased survey for molecular gas is necessary to provide robust statistical constraints to the gas content of galaxies at the peak epoch of cosmic star formation. Taking advantage of the improved frequency coverage, sensitivity and bandwidth of the upgraded Very Large Array we have carried out the first unbiased survey by performing a deep-field blind search for CO(1-0) line emission at z~2-3 and CO(2-1) line emission at z~5-7, targeting CO(1-0) which is the most commonly used tracer of the cold, dense molecular gas which fuels star formation. Having detected the first CO(1-0)-selected galaxies at high redshift, we have used their luminosity and abundance to provide robust statistical constraints to the CO luminosity function at z~2-3, finding conclusive evidence for a much higher gas mass content relative to galaxies in the local Universe. This finding suggested that evolution in the mechanisms of star formation may not be the dominant contribution to the high observed star formation rates, but rather large amounts of available cold gas. In order to explore how this finding may apply to even higher redshift, we have also achieved the first detection of CO emission in "normal" galaxies at z>5 (in the first billion years of cosmic time) together with far-infrared fine structure line tracers of the atomic and ionized gas using the sensitive Atacama Large(sub-)Millimeter Array. We found that early galaxies appear to be extremely gas rich, relative to their stellar content, and to display comparable star formation efficiency to typical lower redshift "normal" galaxies. However, the interstellar medium in a fraction of such galaxies also appears to be strongly affected by lower metallicity, affecting the phase structure of the interstellar medium, and the usefulness of CO as a tracer of molecular gas.
Download or read book Dense Molecular Gas in Galaxies and the Evolution of Luminous Infrared Galaxies written by Yu Gao and published by . This book was released on 1996 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Galaxies Through Cosmic Time written by Amber Bauermeister and published by . This book was released on 2012 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past decade, molecular gas observations have begun probing the high redshift universe in a systematic way using increasingly powerful millimeter instruments. This work has significantly advanced our understanding of the history of gas consumption by star formation in galaxies, revealing the high redshift universe to be similar in many ways to what we know locally. Specifically, molecular gas studies suggest that at both high and low redshift, the molecular gas reservoir in galaxies is insufficient to support on-going star formation. This is the molecular gas depletion problem, and motivates the research presented in this dissertation. I first investigate the molecular gas depletion problem on cosmic scales. Using the observed cosmic densities of the star formation rate, atomic gas and molecular gas, combined with measurements of the molecular gas depletion time in local galaxies, I derive the history of gas consumption by star formation from z = 0 to z ~ 4. I show that models in which the molecular gas is not replenished, or is only replenished by atomic gas, are not consistent with observational constraints. I find that star formation on cosmic timescales must be fueled by intergalactic ionized gas at an average rate that roughly traces the star formation rate density of the universe. Further, I predict the volume averaged density of molecular gas to increase by a factor of 1.5 - 10 to z ~ 1.5 over the currently measured value, which implies that galaxies at high redshift must, on average, be more molecular gas-rich than they are at the present epoch, consistent with observations. Next I focus on the observational constraints on the molecular gas content of galaxies from z ~ 1 - 2 to today. Recent observations suggest z ~ 1 - 2 galaxies harbor molecular gas reservoirs an order of magnitude larger than their local counterparts, implying significant evolution of the molecular gas content of galaxies over the past 8 billion years. However, this period of time has been relatively un-observed in molecular gas. To fill in this observational gap, I carry out the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey, a study of molecular gas in 31 star-forming galaxies from z = 0.05 to z = 0.5. With observations of the CO(1-0) and CO(3-2) rotational lines using the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the EGNoG survey accomplishes two goals: tracing the evolution of the molecular gas content of galaxies at intermediate redshifts and constraining the excitation of the molecular gas in these galaxies. With 24 detections out of 31 observed galaxies, I calculate an average molecular gas fraction of 7 - 20% at z ~ 0.05 - 0.5, which is in line with observations at high and low redshift and agrees well with the evolution predicted by a simple empirical prescription for gas consumption by star formation in galaxies from z ~ 1 - 2 to today. The EGNoG observations of four galaxies at z = 0.3 (the gas excitation subsample) yield robust detections of both lines in three galaxies (and an upper limit on the fourth). I find an average line ratio, r31 = L'(CO(3-2)) / L'(CO(1-0)), of 0.46 ± 0.07 (with systematic errors less than 40%), which implies sub-thermal excitation of the CO(3-2) line. As the EGNoG galaxies are representative of the main sequence of star-forming galaxies, I extend this result to include main sequence galaxies at high redshift. To support the observations carried out at CARMA as part of the EGNoG survey, I give two appendices. The first details the data reduction and flux measurement for the EGNoG survey, including a description of the use of polarized calibrators to calibrate data from single, linearly polarized feeds. In the second appendix, I describe the absolute flux calibration of CARMA data and the automated monitoring system I helped put in place in order to maintain a historical record of the flux of common calibrators. Finally, I return to the gas depletion problem in the local universe. I carry out a pilot study of atomic (HI) gas in groups of galaxies in order to investigate the role of tidal interactions in transporting atomic gas from the outskirts of galaxy disks to the central regions so that it may replenish the molecular gas and fuel ongoing star formation. I image three groups of galaxies in the 21 cm line of HI with the Allen Telescope Array (ATA), detecting many galaxies not previously observed in HI as well as four previously undetected clouds of HI between galaxies that account for up to 3% of the HI reservoir of the groups. To investigate the potential role of this gas in the ongoing star formation in the group, I compare the mass of the detected HI gas in and between galaxies in the group to the estimated star formation rates of the group members.
Download or read book Gas in Distant Radio Galaxies Probung the Early Universe written by Robert van Ojik and published by . This book was released on 1995 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Extent and Content of Low Ionization Gas in Galaxies written by Donna S. Womble and published by . This book was released on 1992 with total page 650 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High resolution Observations of the Molecular Gas in Luminous Infrared Galaxies written by Peter M. Bryant and published by . This book was released on 1997 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Gas in Distant Radio Galaxies written by Robert van Ojik and published by . This book was released on 1995 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Metal Enriched Gaseous Halos Around Distant Radio Galaxies written by and published by . This book was released on 2006 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present the results of an optical and near-IR spectroscopic study of giant nebular emission line halos associated with three z> 3 radio galaxies, 4C 41.17, 4C 60.07 and B2 0902+34. Previous deep narrow band Ly[alpha] imaging had revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s−1, and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions>1000 km s−1. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of H"60 kpc along the radio-axis. The dynamical structures traced in the Ly[alpha] line are, in most cases, closely echoed in the Carbon and Oxygen lines. This shows that the Ly[alpha] line is produced in a highly clumped medium of small filling factor, and can therefore be used as a tracer of the dynamics of HzRGs. We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming 'red and dead' Elliptical galaxies.
Download or read book Radio Galaxies at TeV Energies written by Dorit Glawion and published by . This book was released on 2020 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is common believe that the centers of all galaxies exhibit supermassive black holes with masses ranging from millions up to billions of the mass of our Sun. By accreting surrounding matter, the luminosity of these galactic nuclei can outshine the emission of their host galaxies. If this is the case, they are called active galactic nuclei. Some of these objects eject powerful outflows composed of plasma, called jets. These jets can produce non-thermal radiation which observable across the entire electromagnetic spectrum from radio up to the gamma-ray frequencies. At highest frequencies (TeV range) most of the detected active galaxies have jets directed along or close to the line of sight. However, also galaxies with larger angles to the line of sight showing fascinating features were discovered, in seeming contradiction to traditional models for these so-called radio galaxies. Thus, the latter are of particular importance for understanding active galactic nuclei in general. This Special Issue contains reviews and research articles about the current knowledge of radio galaxies at TeV energies, including observational results and theoretical models. It is intended to guide the interested reader deeper into this fascinating discipline of modern day astronomy.
Download or read book Quantifying Feedback from Narrow Line Region Outflows in Nearby Active Galaxies written by Mitchell D. Revalski and published by . This book was released on 2019 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: Observations reveal that supermassive black holes (SMBHs) grow through the accretion of gas at the centers of galaxies as luminous active galactic nuclei (AGN), releasing radiation that drives powerful outflows of ionized and molecular gas. These winds are thought to play a critical role in galaxy evolution by regulating star formation and the growth of galaxies and their SMBHs. To test this model, we must quantify the dynamic impact of outflows by measuring their mass outflow rates and energetics. Using spatially resolved spectroscopy and imaging from the Hubble Space Telescope and Cloudy photoionization models we mapped the ionized gas kinematics and mass distributions of narrow line region (NLR) outflows in nearby active galaxies. We find that the outflows contain up to several million solar masses of ionized gas and are limited to distances of 1 - 2 kiloparsecs from the nucleus. The maximum mass outflow rates are M = 3 - 12 solar masses per year and the outflow gas mass, velocity, radial extent, and energetics are positively correlated with AGN luminosity. We use our results to test simplified techniques with less stringent data requirements and find that they significantly overestimate the gas mass. These results are crucial for modeling powerful outflows at higher redshift that may considerably influence star formation rates and the formation of galactic structure.
Download or read book Star Formation in the Inner Galaxy A Far infrared and Radio Study of Two H2 Regions written by and published by . This book was released on 1985 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Most Distant Radio Galaxies Probes of Massive Galaxy Formation written by Laura Pentericci and published by . This book was released on 1999 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Low Ionization Gaseous Content in Intermediate Redshift Galaxies written by Christopher W. Churchill and published by . This book was released on 1997 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:
