Browsing by Author "Keel, WC"
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Item Active nuclei and star-forming objects at z > 2: Metallicities, winds, and formation histories(University of Chicago Press, 2002-06) Keel, WC; Wu, WT; Waddington, I; Windhorst, RA; Pascarelle, SM; University of Alabama Tuscaloosa; Arizona State University; Arizona State University-TempeWe present near-infrared observations of the active galactic nuclei (AGNs) and star-forming objects in the field of the radio galaxy 53W002 at z = 2.39. The star-forming objects are of special interest as candidate protogalactic objects. The 1.1-2.2 mum passbands sample the emitted-optical range at this redshift, providing new diagnostics of the structure, metal abundance, and age of the members of this grouping originally selected through Lyalpha emission. The star-forming objects are uniformly very blue in continuum slope, which fits with the strong Lyalpha emission in indicating metal abundances that are less than half solar; some are as blue as the most metal-poor local objects. They fall in a range of luminosity and metallicity that is not populated by local objects, indicating a shorter star-forming history at this early epoch. The best local analogs, such as Mrk 66 and 357, either have several times lower luminosity at comparable [O/H] or significantly higher [O/H] for comparable luminosity. Spectroscopy from the Near-Infrared Camera and Multi-Object Spectrometer yields detections of [O III] emission for two objects and interesting [O III] and Hbeta limits for the rest, augmented by Halpha limits from Infrared Telescope Facility imaging. These data are satisfied by model stellar populations that have been forming stars for the last 2-5 x 10(6) yr before z = 2.39. We do not see evidence for older preexisting stellar populations, either in the broadband colors or as redder halos in which the star-forming regions are imbedded. These results suggest that the compact star-forming objects we see at z = 2.0-2.5 are indeed early stages in the building of galaxies rather than transient star-forming events in larger pre-existing dynamical systems. The results also allow an alternative scheme, in which these are low-mass systems that are blowing winds rather than self-enriching, in which case they should fade rapidly with cosmic epoch. For the three prominent AGNs at z = 2.39, Halpha and [O III] emission were measured. Unlike the fainter star-forming objects, their line ratios (specifically Lyalpha/Halpha) show metallicities just as high as in nearby systems. If the AGNs occur in those systems that started with the highest density and began active star formation before the less massive surrounding objects, they will have higher metallicity ( as we see in their emitted-ultraviolet line ratios). The "ionization cones" seen prominently in Lyalpha also appear in [O III] and Halpha, with a role for continuum reflection in some cases as well. The contrast between the AGNs and fainter star-forming objects can be broadly accommodated in a hierarchical formation picture, although there are still important unknowns as to the fate of the star-forming objects.Item An atlas of warm active galactic nuclei and starbursts from the IRAS deep fields(University of Chicago Press, 2005-06) Keel, WC; Irby, BK; May, A; Miley, GK; Golombek, D; de Grijp, MHK; Gallimore, JF; University of Alabama Tuscaloosa; Leiden University; Leiden University - Excl LUMC; Space Telescope Science Institute; Bucknell UniversityWe present a set of 180 active galactic nucleus (AGN) candidates based on color selection from the IRAS slow-scan deep observations, with color criteria broadened from the initial Point Source Catalog samples so as to include similar objects with redshifts up to z = 1 and allowing for two-band detections. Spectroscopic identifications have been obtained for 80 (44%); some additional identifications are secure based on radio detections or optical morphology, although yet unobserved spectroscopically. These spectroscopic identifications include 13 type 1 Seyfert galaxies, 17 type 2 Seyferts, 29 starburst galaxies, 7 LINER systems, and 13 emission-line galaxies so heavily reddened as to remain of ambiguous classification. The optical magnitudes range from R = 12.0 to 20.5; the counts suggest that incompleteness is important fainter than R = 15.5. Redshifts extend to z = 0.51, with a significant part of the sample at z > 0.2. Even with the relaxed color criteria, this sample includes slightly more AGNs than star-forming systems among those where the spectra contain enough diagnostic feature to make the distinction. The active nuclei include several broad-line objects with strong Fe II emission, and composite objects with the absorption-line signatures of fading starbursts. These AGNs with warm far-IR colors have little overlap with the "red AGNs'' identified with 2MASS; only a single Seyfert 1 was detected by 2MASS with J - K > 2. Some reliable IRAS detections have either very faint optical counterparts or only absorption-line galaxies, potentially being deeply obscured AGNs. The IRAS detections include a newly identified symbiotic star, and several possible examples of the "Vega phenomenon,'' including dwarfs as cool as type K. Appendices detail these candidate stars, and the optical-identification content of a particularly deep set of high-latitude IRAS scans ( probing the limits of optical identification from IRAS data alone).Item An atlas of warm active galactic nuclei and starbursts from the IRAS deep fields(University of Chicago Press, 2005-06) Keel, WC; Irby, BK; May, A; Miley, GK; Golombek, D; de Grijp, MHK; Gallimore, JF; University of Alabama Tuscaloosa; Leiden University; Leiden University - Excl LUMC; Space Telescope Science Institute; Bucknell UniversityWe present a set of 180 active galactic nucleus (AGN) candidates based on color selection from the IRAS slow-scan deep observations, with color criteria broadened from the initial Point Source Catalog samples so as to include similar objects with redshifts up to z = 1 and allowing for two-band detections. Spectroscopic identifications have been obtained for 80 (44%); some additional identifications are secure based on radio detections or optical morphology, although yet unobserved spectroscopically. These spectroscopic identifications include 13 type 1 Seyfert galaxies, 17 type 2 Seyferts, 29 starburst galaxies, 7 LINER systems, and 13 emission-line galaxies so heavily reddened as to remain of ambiguous classification. The optical magnitudes range from R = 12.0 to 20.5; the counts suggest that incompleteness is important fainter than R = 15.5. Redshifts extend to z = 0.51, with a significant part of the sample at z > 0.2. Even with the relaxed color criteria, this sample includes slightly more AGNs than star-forming systems among those where the spectra contain enough diagnostic feature to make the distinction. The active nuclei include several broad-line objects with strong Fe II emission, and composite objects with the absorption-line signatures of fading starbursts. These AGNs with warm far-IR colors have little overlap with the "red AGNs'' identified with 2MASS; only a single Seyfert 1 was detected by 2MASS with J - K > 2. Some reliable IRAS detections have either very faint optical counterparts or only absorption-line galaxies, potentially being deeply obscured AGNs. The IRAS detections include a newly identified symbiotic star, and several possible examples of the "Vega phenomenon,'' including dwarfs as cool as type K. Appendices detail these candidate stars, and the optical-identification content of a particularly deep set of high-latitude IRAS scans ( probing the limits of optical identification from IRAS data alone).Item A deep radio survey of Abell 2125. I. Radio, optical, and near-infrared observations(University of Chicago Press, 2005-01) Owen, FN; Keel, WC; Ledlow, MJ; Morrison, GE; Windhorst, RA; National Radio Astronomy Observatory (NRAO); University of Alabama Tuscaloosa; National Optical Astronomy Observatory; Arizona State University; Arizona State University-TempeWe present a description of deep radio, optical, and near-IR observations taken with the VLA, the KPNO 2 m telescope, and the KPNO 4 m telescope of the region containing the rich cluster of galaxies Abell 2125. The reduction of each data set is described. A catalog of radio sources apparently not associated with members of A2125 and the associated R-band magnitudes is presented.Item A deep radio survey of Abell 2125. II. Accelerated galaxy evolution during a cluster-cluster merger(University of Chicago Press, 2005-01) Owen, FN; Ledlow, MJ; Keel, WC; Wang, QD; Morrison, GE; National Radio Astronomy Observatory (NRAO); University of Alabama Tuscaloosa; University of Massachusetts System; University of Massachusetts Amherst; National Optical Astronomy ObservatoryUsing our extensive radio, optical, near-IR, and X-ray imaging and spectroscopy, we consider the reason for the unusually large number of radio-detected galaxies, mostly found outside the cluster core, in Abell 2125 (z = 0.2465, richness class 4). With 20 cm VLA data, we detect continuum emission from 90 cluster members. The multiwavelength properties of these galaxies suggest that most of the radio emission is due to an enhanced star formation rate. The recent dynamical study of Miller et al. suggests that A2125 is undergoing a major cluster-cluster merger, with our view within 30degrees of the merger axis and within 0.2 Gyr of core passage. The combination of projection effects and the physical processes at work during this special time in the cluster's evolution seem likely to be responsible for the unusual level of activity we see in the cluster. We argue that tidal effects on individual cluster members, often far from the cluster core, are responsible for the increased star formation. Our results are consistent with the idea that disk galaxies during this phase of a cluster's evolution undergo rapid evolution through a burst of star formation on their way to becoming S0 galaxies.Item The diversity of extremely red objects(IOP Publishing, 2002-12-20) Smail, I; Owen, FN; Morrison, GE; Keel, WC; Ivison, RJ; Ledlow, MJ; Durham University; National Radio Astronomy Observatory (NRAO); California Institute of Technology; University of Alabama Tuscaloosa; University of EdinburghWe present the results from a sensitive multiwavelength analysis of the properties of extremely red objects (EROs). Our analysis employs deep RIzJHK photometry of an 8.'5 x 8.'5 region to select a sample of 68 EROs with (R-K) greater than or equal to 5.3 and brighter than K = 20.5(5sigma). We combine this photometric data set with an extremely deep 1.4 GHz radio map of the field obtained from the VLA. This map reaches a 1 sigma limiting flux density of 3.5 muJy, making it the deepest 1.4 GHz map taken, and is sensitive enough to detect an active galaxy with L-1.4 greater than or similar to 10(23) WHz(-1) at z > 1. If powered by a starburst, this radio luminosity is equivalent to a star formation rate of greater than or similar to 25 M-. yr(-1) for stars more massive than 5 M-.. We identify radio counterparts to 21 of the EROs in this field with radio fluxes above 12.6 muJy and resolve one-third of these with our 1."6 FWHM beam. The spectral energy distributions of the majority of these galaxies are consistent with those expected for dust-reddened starbursts at z similar to 1. At these redshifts the radio luminosities of these galaxies indicate a median far-infrared luminosity of this population of L-FIR greater than or similar to 10(12) L-., meaning that half of the radio-detected sample are ultraluminous infrared galaxies (ULIRGs). We conclude that greater than or similar to16% +/- 5% of the ERO population brighter than K = 20.5 are luminous infrared galaxies (LIRGs) at z similar to 1. We also use photometric classification of the colors of the EROs to investigate the mix of dusty active and evolved passive systems in the remaining ERO population that is undetected in our radio map. Based on this we suggest that at least 30% and possibly up to similar to60% of all EROs with (R-K) greater than or equal to 5.3 and K less than or equal to 20.5 are dusty, star-forming systems at z greater than or similar to 1. Our best estimate of the star formation density in this highly obscured and optically faint (R greater than or similar to 26) population is (rho) over dot(*) (0.1-100 M-.) = 0.11 +/- 0.03 M-. yr(-1) Mpc(-3), comparable to estimates of that in Halpha-emitting galaxies at z 1 and greater than the estimates from UV- selected samples at these epochs. This lends support to the claims of a strong increase in the contribution from obscured systems to the star formation density at high redshifts. Using the observed counts of the radio-detected ERO population, we model the apparent break in the K-band number counts of the whole ERO population at K 19 20 and propose that the passive ERO class dominates the total population in a relatively narrow magnitude range around K less than or similar to 20, with dusty, active EROs making up the bulk of the population at fainter limits.Item Dust in spiral galaxies: Comparing emission and absorption to constrain small-scale and very cold structures(IOP Publishing, 1999-10) Domingue, DL; Keel, WC; Ryder, SD; White, RE; University of Alabama TuscaloosaThe detailed distribution of dust in the disks of spiral galaxies is important to understanding the radiative transfer within disks and to measuring overall dust masses if significant quantities of dust are either very opaque or very cold. We address this issue by comparing measures of dust absorption, using the galaxy-overlap technique in the optical, with measures of the dust grains' thermal emission from 50-2000 mu m, using ISOPHOT on board Infrared Space Observatory (ISO) and SCUBA at the James Clerk Maxwell Telescope. We examine three spiral galaxies projected partially in front of E/S0 galaxies: AM 1316-241, NGC 5545, and NGC 5091 (for NGC 5091 we have only optical and ISO data). Adopting an empirical exponential model for the dust distribution, we compare column densities and dust masses derived from the absorption and emission techniques. This comparison is sensitive to the amount of dust mass in small, opaque structures, which would not contribute strongly to area-weighted absorption measures, and to very cold dust, which would contribute to optical absorption but provide only a small fraction of the submillimeter emission. In AM 1316-241, we find global dust masses of 2-5 x 10(7) M., with the two techniques agreeing at the 50% level. NGC 5545 has about half this dust mass. The concordance of dust masses is well within the errors expected from our knowledge of the radial distribution of dust and argues against any dominant part of the dust mass being so cold or opaque. The 50-2000 mu m data are well fitted by modified Planck functions with an emissivity law beta = -2, at 21 +/- 2 K; a modest contribution from warmer dust is required to fit only the 50 mu m measurement of NGC 5545. We incorporate empirical corrections to the flux scale of ISOPHOT P32 data, which can reach a factor 2 from comparison of IRAS and ISO fluxes for objects in two programs. We also present 12 mu m ISOCAM observations of these pairs. The light profiles at this wavelength exhibit shorter disk scale lengths than in the optical. Comparison of H alpha and 12 mu m images of NGC 5545 indicate that ISOCAM images are reliable tracers of star formation.Item The dynamics of A2125(IOP Publishing, 2004-10-01) Miller, NA; Owen, FN; Hill, JM; Keel, WC; Ledlow, MJ; Oegerle, WR; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; National Radio Astronomy Observatory (NRAO); University of Arizona; University of Alabama TuscaloosaWe present 371 galaxy velocities in the field of the very rich cluster A2125 (z approximate to 0.25). These were determined using optical spectroscopy collected over several years from both the WIYN 3.5 m telescope and NOAO Mayall 4 m telescope. Prior studies at a variety of wavelengths ( radio, optical, and X-ray) have indicated that A2125 is a likely cluster-cluster merger, a scenario that we are able to test using our large velocity database. We identified 224 cluster galaxies, which were subjected to a broad range of statistical tests using both positional and velocity information to evaluate the cluster dynamics and substructure. The tests confirmed the presence of substructures within the A2125 system at high significance, demonstrating that A2125 is a complex dynamical system. Comparison of the test results with existing simulations strengthens the merger hypothesis and provides clues about the merger geometry and stage. The merger model for the system can reconcile A2125's low X-ray temperature and luminosity with its apparently high richness and might also explain A2125's high fraction of active galaxies identified in prior radio and optical studies.Item Escape of Ly alpha emission in the starburst galaxy Markarian 357: A wind's far side(IOP Publishing, 2005-04) Keel, WC; University of Alabama TuscaloosaHubble Space Telescope imaging and slitless spectroscopy are used to examine where the strong Ly alpha emission escapes from the interstellar medium in the starburst galaxy Mrk 357. An H alpha image shows that the ionized gas is mostly in a global wind, rather than associated with the individual star-forming regions seen in the optical and UV continuum. The Ly alpha emission comes predominantly from the northwest side of the wind structure spatially, and shows a significant redshift relative to the optical lines. Both of these properties are signatures of seeing the line photons backscattered from the far side of a prolate or bipolar starburst wind, fitting both with escape calculations and evidence for winds in high-redshift galaxies with net Ly alpha emission. Scattering is most important within this wind itself, rather than involving a surrounding neutral medium, as shown by the decreasing relative redshift of the line peak from 250 to approximate to 30 km s(-1) between the center and edge of the detected emission. The Ly alpha emission exhibits strong asymmetry in comparison with both the starlight and H alpha structures. These results add to the evidence that kinematics, rather than gas metallicity or dust content, are the dominant effect in determining which galaxies have strong Ly alpha emission, and that powerful ( and perhaps episodic) starbursts are common among Lyman break galaxies as well as those discovered from Ly alpha line emission.Item Far-ultraviolet spectroscopy of star-forming regions in nearby galaxies: Stellar populations and abundance indicators(University of Chicago Press, 2004-07) Keel, WC; Holberg, JB; Treuthardt, PM; University of Alabama Tuscaloosa; University of ArizonaWe present Far Ultraviolet Spectroscopic Explorer spectroscopy and supporting data for star-forming regions in nearby galaxies, to examine their massive-star content and explore the use of abundance and population indicators in this spectral range for high-redshift galaxies. New far-ultraviolet spectra are shown for four bright H II regions in M33 (NGC 588, 592, 595, and 604), the H II region NGC 5461 in M101, and the starburst nucleus of NGC 7714, supplemented by the very low metallicity galaxy I Zw 18. In each case we see strong Milky Way absorption systems from H-2, but intrinsic absorption within each galaxy is weak or undetectable, perhaps because of the "UV bias'' in which reddened stars that lie behind molecular-rich areas are also heavily reddened. We see striking changes in the stellar wind lines from these populations with metallicity, suggesting that C II, C III, C IV, N II, N III, and P v lines are potential tracers of stellar metallicity in star-forming galaxies. Three of these relations - involving N IV, C III, and P v - are nearly linear over the range from O/H = 0.05 - 0.8 solar. The major difference in continuum shapes among these systems is that the giant H II complex NGC 604 has a stronger continuum shortward of 950 Angstrom than any other object in this sample. Small number statistics would likely go in the other direction; we favor this as the result of a discrete star-forming event approximate to 3 Myr ago, as suggested by previous studies of its stellar population.Item Gemini Multi-Object Spectrograph observations of SCUBA galaxies behind A851(University of Chicago Press, 2002-10-01) Ledlow, MJ; Smail, I; Owen, FN; Keel, WC; Ivison, RJ; Morrison, GE; Durham University; National Radio Astronomy Observatory (NRAO); University of Alabama Tuscaloosa; University of Edinburgh; California Institute of TechnologyWe have identified counterparts to two submillimeter (submm) sources, SMM J09429+4659 and SMM J09431+4700, seen through the core of the z = 0.41 cluster A851. We employ deep 1.4 GHz observations and the far-infrared/radio correlation to refine the submm positions and then optical and near-infrared imaging to locate their counterparts. We identify an extremely red counterpart to SMM J09429+4659, while Gemini Multi-Object Spectrograph spectroscopy with Gemini North shows that the radio source identified with SMM J09431+4700 is a hyperluminous infrared galaxy (L-FIR similar to 1.5 x 10(13) L.) at, the highest spectroscopic redshift so far for a galaxy discovered in the submm. The emission-line properties of this galaxy are characteristic of a narrow-line Seyfert 1 galaxy, although the lack of detected X-ray emission in a deep XMM-Newton observation suggests that the bulk of the luminosity of this galaxy is derived from massive star formation. We suggest that active nuclei, and the outflows they engender, may be an important part of the evolution of the brightest submm galaxies at high redshifts.Item GRB 991216 joins the jet set: Discovery and monitoring of its optical afterglow(University of Chicago Press, 2000-11-10) Halpern, JP; Uglesich, R; Mirabal, N; Kassin, S; Thorstensen, J; Keel, WC; Diercks, A; Bloom, JS; Harrison, F; Mattox, J; Eracleous, M; Columbia University; University System of Ohio; Ohio State University; Dartmouth College; University of Alabama Tuscaloosa; California Institute of Technology; Boston University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University ParkThe optical light curve of the energetic gamma -ray burst GRB 991216 is consistent with jetlike behavior in which a power-law decay steepens from t(-1.22+/-0.04) at early times to t(-1.53+/-0.05) in a gradual transition at around 2 days. The derivation of the late-time decay slope takes into account the constant contribution of a host or intervening galaxy, which was measured 110 days after the event at R = 24.56 +/- 0.14, although the light curve deviates from a single power law whether or not a constant term is included. The early-time spectral energy distribution of the afterglow can be described as F-nu proportional to nu (-0.74+/-0.05) or flatter between optical and X-ray, which, together with the slow initial decay, is characteristic of standard adiabatic evolution in a uniformly dense medium. Assuming that a reported absorption-line redshift of 1.02 is correct, the apparent isotropic energy of 6.7 x 10(53) ergs is reduced by a factor of approximate to 200 in the jet model, and the initial half-opening angle is approximate to 6 degrees. GRB 991216 is the third good example of a jetlike afterglow (following GRB 990123 and GRB 990510), supporting a trend in which the apparently most energetic gamma -ray events have the narrowest collimation and a uniform interstellar medium environment. This, plus the absence of evidence for supernovae associated with jetlike afterglows, suggests that these events may originate from a progenitor in which angular momentum plays an important role but a massive stellar envelope or wind does not, e.g., in the coalescence of a compact binary.Item The infrared counterparts of the optically unidentified Chandra Deep Field-South 1 Ms sources(University of Chicago Press, 2003) Yan, HJ; Windhorst, RA; Rottgering, HJA; Cohen, SH; Odewahn, SC; Chapman, SC; Keel, WC; Arizona State University; Arizona State University-Tempe; Leiden University; Leiden University - Excl LUMC; California Institute of Technology; University of Alabama TuscaloosaThe Chandra Deep Field South (CDF-S) 1 Ms exposure produced a catalog of 346 X-ray sources, of which 59 were not visible on the Very Large Telescope ( VLT)/FORS1 and the ESO-MPI/WFI deep R-band images to a limit of R-vega=26.1-26.7 mag. Using the first release of the ESO VLT/ISAAC JHK(s) data on the CDF-S, we identified six of the 12 such objects that were within the coverage of these IR observations. The VLT/FORS1 I-band data further confirm that five of these six objects are undetected in the optical. The photometric properties of these six counterparts are compared against those of the optically brighter counterparts of Chandra sources in the same field. We found that the location of these optically brighter Chandra sources in the near-IR color space was bifurcated, with the color of one branch being consistent with that of E/S0 galaxies at 0less than or equal tozless than or equal to1.5, and the other branch being consistent with that of unreddened active galactic nuclei/quasi-stellar objects (AGNs/QSOs) at 0less than or equal tozless than or equal to3.5. The six counterparts that we identified seemed to lie on the E/S0 branch and its extension, suggesting that these X-ray source hosts are mostly luminous E/S0 galaxies (M-V similar to -20 mag in the AB system) at 1less than or equal tozless than or equal to2.5. On the other hand, some of them can also be explained by AGNs/QSOs over a wide redshift range (0less than or equal tozless than or equal to5), if a range of internal extinction (A(V)=0-1 mag) is allowed. However, the later interpretation requires fine-tuning extinction together with redshift for these objects individually. If they are indeed AGNs/QSOs, the most luminous of them is just barely qualified for being a QSO. Finally, we point out that neither high-redshift (z>5) star-forming galaxies nor irregular galaxies at lower redshift can be a viable explanation to the nature of these six counterparts.Item Infrared Space Observatory observations of the 53W002 group at 6.7 microns: In search of the oldest stellar populations at z=2.4(IOP Publishing, 2004) Keel, WC; Wu, WT; van der Werf, PP; Windhorst, RA; Dunlop, JS; Eales, SA; Waddington, I; Holmes, M; University of Alabama Tuscaloosa; Leiden University; Leiden University - Excl LUMC; Arizona State University; Arizona State University-Tempe; University of Edinburgh; Cardiff University; University of Sussex; Vanderbilt UniversityWe present a deep Infrared Space Observatory (ISO) observation at 6.7 mum of the 53W002 group of galaxies and active galactic nuclei (AGNs) at z = 2.4. This approximately samples the emitted K band. Faint, blue star-forming objects are not detected, as expected from their very blue color across the emitted optical and UV spectrum. However, 53W002 itself is detected at the similar to3 sigma level, with an emitted color that is appropriate V - K for a population that formed starting at z = 3.6-7.0 most likely z = 4.7. This fits with shorter wavelength data, suggesting that the more massive members of this group, which may all host AGNs, began star formation earlier in deeper potential wells than the compact Lyalpha emission objects. Two foreground galaxies are detected, as are several stars. One additional 6.7 mum source closely coincides with an optically faint galaxy, potentially at z p. The overall source counts are consistent ( within the errors of such a small sample) with the other ISO deep 2 - 3 fields at 6.7 mum.Item Massive star clusters in ongoing galaxy interactions: Clues to cluster formation(University of Chicago Press, 2003-09) Keel, WC; Borne, KD; University of Alabama Tuscaloosa; Raytheon Technologies; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight CenterWe present HST WFPC2 observations, supplemented by ground-based Halpha data, of the star-cluster populations in two pairs of interacting galaxies selected for being in very different kinds of encounters seen at different stages. Dynamical information and n-body simulations provide the details of encounter geometry, mass ratio, and timing. In NGC 5752/4 we are seeing a weak encounter, well past closest approach, after about 2.5 x 10(8) yr. The large spiral NGC 5754 has a normal population of disk clusters, while the fainter companion NGC 5752 exhibits a rich population of luminous clusters with a flatter luminosity function. The strong, ongoing encounter in NGC 6621/2, seen about 1.0 x 10(8) yr past closest approach between roughly equal-mass galaxies, has produced an extensive population of luminous clusters, particularly young and luminous in a small region between the two nuclei. This region is dynamically interesting, with such a strong perturbation in the velocity field that the rotation curve reverses sign. From these results, in comparison with other strongly interacting systems discussed in the literature, cluster formation requires a threshold level of perturbation, with stage of the interaction a less important factor. The location of the most active star formation in NGC 6621/2 draws attention to a possible role for the Toomre stability threshold in shaping star formation in interacting galaxies. The rich cluster populations in NGC 5752 and NGC 6621 show that direct contact between gas-rich galaxy disks is not a requirement to form luminous clusters and that they can be triggered by processes happening within a single galaxy disk ( albeit triggered by external perturbations).Item Ongoing mass transfer in the interacting galaxy pair NGC 1409/1410(University of Chicago Press, 2004-03) Keel, WC; University of Alabama TuscaloosaI present two-band Hubble Space Telescope (HST) STIS imaging and WIYN spectral mapping of ongoing mass transfer in the interacting galaxy pair NGC 1409/1410 ( where NGC 1410 is the Seyfert galaxy also cataloged as III Zw 55). Archival snapshot WFPC2 imaging from the survey by Malkan and coworkers showed a dust feature stretching between the galaxies, apparently being captured by NGC 1409. The new images allow estimates of the mass being transferred and the rate of transfer. An absorption lane typically 0."25 ( 100 pc) wide, with a representative optical depth tau(B) = 0.2, cuts across the spiral structure of NGC 1410, crosses the 7 kpc projected space between the nuclei, wraps in front of and, at the limits of detection, behind NGC 1409 and becomes a denser (tau(B) = 0.4) polar feature around the core of NGC 1409. The combination of extinction data in two passbands allows a crude three-dimensional recovery of the dust structure, supporting the front/back geometry derived from colors and extinction estimates. The whole feature contains on the order of 2 x 10(6) M-. in dust, implying about 3 x 10(8) M-. of gas and requiring a mass transfer rate averaging approximate to 1 M-. yr(-1), unless we are particularly unlucky in viewing angle. Curiously, this demonstrable case of mass transfer seems to be independent of the occurrence of a Seyfert nucleus, since the Seyfert galaxy in this pair is the donor of the material. Likewise, the recipient shows no signs of recent star formation from incoming gas, although NGC 1410 has numerous luminous young star clusters and widespread Halpha emission.Item Optical and near-infrared integral field spectroscopy of the SCUBA galaxy N2 850.4(Blackwell, 2005) Swinbank, AM; Smail, I; Bower, RG; Borys, C; Chapman, SC; Blain, AW; Ivison, RJ; Howat, SR; Keel, WC; Bunker, AJ; Durham University; California Institute of Technology; University of Edinburgh; University of Alabama Tuscaloosa; University of ExeterWe present optical and near-infrared integral field spectroscopy of the SCUBA galaxy SMMJ163650.43+ 405734.5 (ELAIS N2 850.4) at z = 2.385. We combine Ly alpha and H alpha emission line maps and velocity structure with high-resolution HST ACS and NICMOS imaging to probe the complex dynamics of this vigorous starburst galaxy. The imaging data show a complex morphology, consisting of at least three components separated by similar to 1 arcsec (8 kpc) in projection. When combined with the Ha velocity field from UKIRT UIST IFU observations we identify two components whose redshifts are coincident with the systemic redshift, measured from previous CO observations, one of which shows signs of AGN activity. A third component is offset by 220 +/- 50 km s(-1) from the systemic velocity. The total star-formation rate of the whole system ( estimated from the narrow-line H alpha and uncorrected for reddening) is 340 +/- 50 M-. yr(-1). The Ly alpha emission mapped by the GMOS IFU covers the complete galaxy and is offset by + 270 +/- 40 km s(-1) from the systemic velocity. This velocity offset is comparable to that seen in rest-frame UV-selected galaxies at similar redshifts and usually interpreted as a starburst-driven wind. The extended structure of the Ly alpha emission suggests that this wind is not a nuclear phenomenon, but is instead a galactic-scale outflow. Our observations suggest that the vigorous activity in N2 850.4 is arising as a result of an interaction between at least two dynamically-distinct components, resulting in a strong starburst, a starburst-driven wind and actively-fuelled AGN activity. Whilst these observations are based on a single object, our results clearly show the power of combining optical and near-infrared integral field spectroscopy to probe the power sources, masses and metallicities of far-infrared luminous galaxies, as well as understanding the role of AGN- and starburst-driven feedback processes in these high-redshift systems.Item Radio-selected galaxies in very rich clusters at z <= 0.25. I. Multiwavelength observations and data reduction techniques(University of Chicago Press, 2003-06) Morrison, GE; Owen, FN; Ledlow, MJ; Keel, WC; Hill, JM; Voges, W; Herter, T; National Radio Astronomy Observatory (NRAO); University of New Mexico; University of Alabama Tuscaloosa; University of Arizona; Max Planck Society; Cornell UniversityRadio observations were used to detect the "active" galaxy population within rich clusters of galaxies in a nonbiased manner that is not plagued by dust extinction or the K-correction. We present wide-field radio, optical (imaging and spectroscopy), and ROSAT All-Sky Survey (RASS) X-ray data for a sample of 30 very rich Abell (Rgreater than or equal to2) clusters with zless than or equal to0.25. The VLA radio data samples the ultrafaint radio (L(1.4)greater than or equal to2x10(22) W Hz(-1)) galaxy population within these extremely rich clusters for galaxies with M(R)less than or equal to-21. This is the largest sample of low-luminosity 20 cm radio galaxies within rich Abell clusters collected to date. The radio-selected galaxy sample represents the starburst (star formation rate greater than or equal to5 M-circle dot yr(-1)) and active galactic nuclei populations contained within each cluster. Archival and newly acquired redshifts were used to verify cluster membership for most (similar to95%) of the optical identifications. Thus, we can identify all the starbursting galaxies within these clusters, regardless of the level of dust obscuration that would affect these galaxies being identified from their optical signature. Cluster sample selection, observations, and data reduction techniques for all wavelengths are discussed.Item The rest-frame optical spectra of SCUBA galaxies(University of Chicago Press, 2004-12-10) Swinbank, AM; Smail, I; Chapman, SC; Blain, AW; Ivison, RJ; Keel, WC; Durham University; California Institute of Technology; University of Edinburgh; University of Alabama TuscaloosaWe present near-infrared spectroscopy and narrowband imaging at the wavelength of redshifted Halpha for a sample of 30 high-redshift, far-infrared luminous galaxies. This sample is selected from surveys in the submillimeter, millimeter, and radio wave bands and has complete redshift coverage with a median redshift of zsimilar to2.4. We use our data to measure the Halpha properties of these systems and to gauge the prevalence of active galactic nuclei (AGNs) in these galaxies through their [N II]/Halpha ratios and Halpha line widths. Removing obvious AGNs, we find that the predicted Halpha star formation rates in this diverse population are suppressed (by a factor of similar to10) compared to those derived from their far-infrared luminosities. Using the AGN indicators provided by our near-infrared spectra, we estimate that AGNs are present in at least 40% of the galaxies in our sample. To further investigate this, we construct a composite rest-frame spectrum for both the entire sample and those galaxies that individually show no signs of nuclear activity. We find [N II]/Halpha ratios for both composite spectra that suggest that the energy output of the galaxies is star formation rather than AGN dominated. However, we also find that the Halpha line in the composite non-AGN spectrum is best fitted with an underlying broad-line component with a narrow/broad flux ratio of 0.45+/-0.20. The median Halpha line width for our sample (removing obvious AGNs) is 400+/-70 km s(-1) (FWHM), and the typical spatial extent of the Halpha emission in our narrowband observations is less than or similar to4-8 kpc, which indicates a dynamical mass of (1-)x10(11) M-circle dot with corresponding dynamical times of 10-20 Myr. Using both high-resolution imaging and spectroscopically identified velocity offsets, we find that seven of the far-infrared luminous galaxies have companions, suggesting that they are undergoing interactions/mergers, and from their relative velocities we can determine a dynamical mass of (1.5+/-0.9)x10(11) M-circle dot. These measurements are comparable to millimeter CO estimates for the dynamical masses of these systems on similar scales and larger than recent estimates of the dynamical masses of UV-selected galaxies at similar redshifts derived in an identical manner. Using the [N II]/Halpha index to predict abundances, we investigate the luminosity-metallicity relation for these galaxies and find that many have metallicities consistent with UV-selected high-redshift galaxies and slightly lower than local luminous infrared and elliptical galaxies (although we caution that our metallicity estimates have possible systematic uncertainties). We also compared our Halpha and far-infrared luminosities with deep Chandra observations of a subset of our survey fields and use these data to further assess their AGN content. We conclude that these high-redshift, far-infrared luminous galaxies represent a population of massive, metal-rich, merging systems with high instantaneous star formation rates, strong dust obscuration, and actively fueled AGNs that are likely to be the progenitors of massive local elliptical galaxies.Item Seeing galaxies through thick and thin. I. Optical opacity measures in overlapping galaxies(IOP Publishing, 2000-10-20) White, RE; Keel, WC; Conselice, CJ; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University of Alabama Tuscaloosa; University of ChicagoWe describe the use of partially overlapping galaxies to provide direct measurements of the effective absorption in galaxy disks, independent of assumptions about internal disk structure. The nonoverlapping parts of the galaxies and symmetry considerations are used to reconstruct, via differential photometry, how much background galaxy light is lost in passing through the foreground disks. Extensive catalog searches and follow-up imaging yield similar to 15-25 nearby galaxy pairs suitable for varying degrees of our analysis; 11 of the best such examples are presented here. From these pairs, we find that interarm extinction is modest, declining from A(B) similar to 1 mag at 0.3R(25)(B) to essentially zero by R(25)(B); the interarm dust has a scale length consistent with that of the disk starlight. In contrast, dust in spiral arms and resonance rings may be optically thick (A(B) > 2) at virtually any radius. Some disks have flatter extinction curves than the Galaxy, with A(B)/A(I) approximate to 1.6; this is probably the signature of clumpy dust distributions. Even though typical spirals are not optically thick throughout their disks, where they are optically thick is correlated with where they are most luminous: in spiral arms and inner disks. This correlation between absorption and emission regions may account for their apparent surface brightness being only mildly dependent on inclination, erroneously indicating that spirals are generally optically thick. Taken as an ensemble, the opacities of spiral galaxies may be just great enough to significantly affect QSO counts, though not enough to cause their high-redshift cutoff.