Showing papers by "Carol J. Lonsdale published in 2003"

SWIRE: The SIRTF Wide‐Area Infrared Extragalactic Survey

Abstract: The SIRTF Wide‐Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide‐area imaging survey to trace the evolution of dusty, star‐forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current epoch. SWIRE will survey seven high‐latitude fields, totaling 60–65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 μm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 μm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR‐selected galaxies, dominated by (1) ∼150,000 luminous infrared galaxies (LIRGs; LFIR > 1011 L⊙) detected by MIPS (and significantly more detected by IRAC), ∼7000 of these with ; (2) 1 million IRAC‐detected early‐type galaxies (∼ with and ∼10,000 with ); and (3) ∼20,000 classical AGNs detected with MIPS, plus significantly more dust‐obscured quasi‐stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs. The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to determine the evolutionary relationship between “normal galaxies” and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects. The SWIRE fields are likely to become the next generation of large “cosmic windows” into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes ∼9 deg2 of the unique large‐area XMM Large Scale Structure hard X‐ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near‐IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented.

SWIRE: The SIRTF Wide-area InfraRed Extragalactic Survey

Abstract: The SIRTF Wide-area InfraRed Extragalactic survey (SWIRE), the largest SIRTF Legacy program, is a wide-area, imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and AGN as a function of environment, from redshifts z~3 to the current epoch. SWIRE will survey 7 high-latitude fields, totaling 60 - 65 sq. deg. in all 7 SIRTF bands: IRAC 3.6, 4.5, 5.6, 8 microns and MIPS 24, 70, 160 microns. The Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) ~150,000 luminous infrared galaxies (LIRGs: L{FIR}>10^11 L_sun), ~7000 of these with z>2; (2) 1 million early-type galaxies, ~10,000 with z>2; and (3) \~20,000 classical AGN, plus significantly more dust-obscured QSO/AGN among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGN. The key scientific goals of SWIRE are: (1) to determine the evolution of actively star-forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts and AGN in the key redshift range, 0.5

VLBI Imaging of Luminous Infrared Galaxies: Active Galactic Nucleus Cores in Markarian 231, UGC 5101, and NGC 7469*

Abstract: We report 18 cm VLBI continuum imaging observations at ~5 mas resolution for UGC 5101, NGC 7469, and Mrk 231, all part of a sample of luminous infrared galaxies that were shown to have strong VLBI radio cores in a previous 18 cm VLBI survey. Mrk 231, generally considered to be a dust-enshrouded quasi-stellar object (QSO), shares many characteristics with quasars, including a broad Sy1 optical emission spectrum, optical and radio variability, and a broad absorption line spectrum. NGC 7469 is a classical Sy1 galaxy, and UGC 5101 is a LINER system. The radio morphology of these three systems on VLBI scales is like that of an active galactic nucleus (AGN), with well-defined ridgelines and high-brightness yet spatially resolved components. The structure and flux densities of these VLBI components are not consistent with starburst-generated radio supernovae of the type found in Arp 220. On scales of ~100 pc and perhaps beyond, the radio continuum in all three objects appears to be dominated by an AGN, not a starburst. Radio emission on larger scales may well originate, in part or in total, in a less compact circumnuclear star-forming region. This is in contrast to the situation thought to prevail in many luminous infrared galaxies (LIGs), which involves a very compact and dense nuclear star-forming region. By placing a lower limit on the AGN-related radio emission, it is possible to shed light on the relative luminosities of the AGN and starburst in these objects. Using the far-infrared-radio correlation for starburst-related radio emission, we show that, despite the unambiguous evidence for AGN activity in these systems, the AGN luminosity, although energetically important, may be exceeded by the extended starburst luminosity in all three cases, unless the bolometric luminosity of the entire system has been underestimated. The lower limits on AGN-related radio emission indicate that these AGNs are somewhat overluminous in the radio compared with radio-quiet Palomar-Green (PG) QSOs and thus that the AGN radio luminosity cannot be used to estimate the bolometric luminosity of the AGN. However, comparing near- and mid-IR luminosities of the LIGs to those of PG QSOs, we find evidence that a significant fraction of the bolometric luminosity of the AGN in Mrk 231 and to a lesser extent UGC 5101 may be radiated away from Earth and thus not detected at any wavelength. The VLBI structure observed in Mrk 231 allows additional interpretation. Confirming and extending VLBI imaging by Ulvestad, Wrobel, and Carilli, our continuum image shows a triple structure, with a core and two lobes, causing it to be classied as a compact symmetric object. It has been suggested that these sources are young, ? 106 yr, with the hot spots representing the working surface of a relativistic jet on the ambient medium. If the southern (primary) lobe/hot-spot in Mrk 231 is confined by ram pressure, we estimate a lobe advance speed, va ~ 10-4c, and an age for the jet/compact source, ? < 106 yr. We have also imaged the 1667 MHz OH maser emission in Mrk 231, which is extended on scales of 50-100 mas (40-80 pc) and probably coincides with the inner region of the disk, which is seen in CO emission and H I absorption. Among OH megamaser sources studied at high sensitivity with milliarcsecond resolution, Mrk 231 is unique in the stringent upper limits placed on the flux density of compact OH structures of the type found in Arp 220 and other LIGs. It is possible that the circumnuclear environment of Mrk 231 has been sufficiently disrupted by the emergent QSO that the cool dense clouds necessary for such compact masers no longer exist.

VLBI Imaging of Luminous Infrared Galaxies: AGN Cores in Mrk231, UGC 5101 & NGC 7469

Abstract: We report 18cm VLBI continuum imaging observations at 5 mas resolution for UGC 5101, NGC 7469, and Mrk 231, all part of a sample of Luminous Infrared Galaxies which have been shown to have strong VLBI radio cores. The radio morphology of these three systems on VLBI scales is AGN-like, with well-defined ridgelines and high-brightness yet spatially resolved components. The structure and flux densities of these VLBI components are not consistent with starburst generated radio supernovae of the type found in Arp 220. On scales of 100pc the radio continuum in all three objects appears to be dominated by an AGN, not a starburst. Radio emission on larger scales may well originate in a less compact circumnuclear star-forming region. Confirming and extending VLBI imaging of Mrk 231 by Ulvestad et al. (1999), our continuum image shows a triple structure, with a core and two lobes, classifying it as a Compact Symmetric Object (CS0). If the southern (primary) lobe/hot-spot in Mrk 231 is confined by ram pressure, we estimate a lobe advance speed, $v_a \sim 10^{-4}c$, and an age for the jet/compact source, $< 10^6 yr$. We have also imaged the 1667 MHz OH maser emission in Mrk 231, which is extended on scales of 50--100 milliarcsec (40--80 pc) and probably coincides with the inner region of the disk which is seen in CO emission and HI absorption. Among OH megamasers studied at high sensitivity with mas resolution, Mrk 231 is unique in the stringent upper limits placed upon the flux density of compact OH structures of the type found in Arp 220 and other LIGs. It is possible that the circumnuclear environment of Mrk 231 has been sufficiently disrupted by the emergent QSO that the cool, dense clouds necessary for such compact masers no longer exist.

Continuum and spectral line observations of the OH Megamaser galaxy Arp 220

Abstract: We present MERLIN observations of the continuum (both 1.6 and 5 GHz) and OH maser emission towards Arp220. the correct spatial configuration of the various componnents of the galaxy is revealed. In the eastern component the masers are shown to be generally coincident with the larger scale continuum emission; in the west, the masers and continuum do not generally arise from the same location. A velocity gradient (0.32+/-0.03km/s/pc) is found in the eastern nuclear region in MERLIN scales; this gradient is three times smaller than seen in OH and implies that the OH gas lies inside the HI. A re-analysis of previously presented global VLBI data (Lonsdale et al. 1998) reveals a very high velocity gradient (18.67+/-0.12km/s/pc) in one component, possibly the site of a heavily obscured AGN.

The Far‐Infrared Spectral Energy Distributions of X‐Ray–selected Active Galaxies

Abstract: This paper reports the ISO results on hard X-ray selected AGN which are less biased against red/obscured objects than other selection wavebands. We find that, as predicted, the IR continuum of these sources extends to redder sources than in optically/radio selected sample. This indicates that the latter samples miss a portion of the population which is fainter in the optical but can be easily picked up in the hard X-ray. The range of IR SEDs is roughly consistent with reddening of the IR continuum up to column densities of around 10(exp 23)/cu cm. Modeling of the full SED using dusty disk models demonstrated that varying the viewing angle can explain the observed SEDs, though rather large disks are required to fit the cooler, long wavelength emission. From the fits we can obtain estimates of the mass and inclination of the system.

Models for Evolution of Dusty and E/S0 Galaxies Seen in Multiband Surveys

Abstract: Phenomenological models for evolution of dusty and E/S0 galaxies, respectively, are developed to address two major questions concerning galaxy populations in deep infrared (IR) surveys: (1) Do normal late-type galaxies or starburst galaxies (including galaxies with obscured active galactic nuclei) dominate among sources in deep IR surveys? (2) How much do E/S0 galaxies contribute to the counts in deep mid-infrared (MIR: 3-20 μm) surveys? Among three new models for evolution of dusty galaxies, it is assumed in model S1 that starburst galaxies are the dominant population and in model S2 that normal galaxies dominate. Model S3 is an intermediate model. Comparing the model predictions with a wide range of observational data collected from the literature, we find that none of these models can be ruled out, given the uncertainties of the data. We show that the most direct method to distinguish these models is to compare the predicted color distributions of IR galaxies with observations, which will soon be available from the SIRTF Wide-Area Infrared Extragalactic (SWIRE) survey. The models for E/S0 galaxies follow a simple passive evolution approach. Among the three E/S0 models (E1, E2, and E3) investigated in this paper, model E2, which is specified by a peak formation redshift zpeak = 2 and an e-folding formation timescale ω = 2 Gyr, fits the data best. This suggests a synchronization between the evolution of E/S0 galaxies and that of starburst galaxies, in the sense that the peak of the formation function of E/S0 galaxies (zpeak = 2) is close to the peak of the evolution functions of starburst galaxies (zpeak = 1.4). We find that E/S0 galaxies contribute about 10%-30% of the counts in the MIR bands of less than 10 μm and up to 30%-50% of the optical/near-IR counts in the bright end. Their contributions to counts in the UV (2000 A) and in the longer wavelength IR (≥12 μm) bands are negligible. Taking into account this contribution, new predictions for counts and confusion limits in the SIRTF bands are presented.

Multi-Wavelength Image Space: Another Grid-Enabled Science

Abstract: We describe how the Grid enables new research possibilities in astronomy through multi-wavelength images. To see sky images in the same pixel space, they must be projected to that space, a computer-intensive process. There is thus a virtual data space induced that is defined by an image and the applied projection. This virtual data can be created and replicated with Planners and Replica catalog technology developed under the GriPhyN project. We plan to deploy our system (MONTAGE) on the U.S. Teragrid. Grid computing is also needed for ingesting data—computing background correction on each image—which forms a separate virtual data space. Multi-wavelength images can be used for pushing source detection and statistics by an order of magnitude from current techniques; for optimization of multi-wavelength image registration for detection and characterization of extended sources; and for detection of new classes of essentially multi-wavelength astronomical phenomena. The paper discusses both the Grid architecture and the scientific goals.