Angela Adamo1, Erik Zackrisson1, Goeran Ostlin1, Matthew Hayes2
1Stockholm University, 2Observatory of Geneva
Haro 11 is one of the most studied local blue compact galaxies. It shows a complex morphology, with three active and very luminous starburst regions and irregular kinematics (Ostlin et al. 2001, Ostlin et al. in prep.). A photometric study of the halo of Haro11 (Micheva et al., in prep.) confirms that the stellar population in the outskirts of the system is consistent with a 10 Gyr old population and low metallicity. The coexistence of old stellar populations, active star forming regions, and unrelaxed kinematics indicates that the present galaxy is the result of a previous merger between an evolved system and a gas-rich dwarf galaxy. In order to trace the origin and evolution of the current starburst phase we have performed a multi-wavelength (from far-UV to far-IR) photometric analysis of the star cluster population. About 300 confirmed cluster candidates have been detected in high-resolution HST images. We show here the results of the SED (spectral energy distribution) analysis we have done to estimate the cluster ages, masses, extinctions, and metallicities (Adamo et al., in prep.). We find that the clusters have an age distribution between 0.5 Myr and 100 Myr with a peak around 3 Myr; the estimated masses are between 103 and 106 solar masses; and extinctions, E(B-V), between 0.0 and 0.5. We noticed that the youngest clusters (ages between 1 and 10 Myr) show an I-band flux excess, impossible to match with the current stellar population models. Few clusters show also an excess at the IR wavelengths. Reines et al. (2008) have already noticed a similar behavior for the young star clusters in the nearby starburst galaxy NGC 4449, but the real physical reason for these effects remains unexplained. Due to its extremely young and rich cluster population, Haro 11 is one of the most interesting and key objects for studying the earliest phases of the clustered star formation and evolution.
Hugh H. Crowl1, Jeffrey D.P. Kenney2, Aeree Chung3, Jacqueline van Gorkom4
1University of Massachusetts, Amherst, 2Yale, 3NRAO, 4Columbia
I present results from a study of the stellar populations of HI-stripped spiral galaxies in the nearby Virgo Cluster. Virgo provides an ideal laboratory to study galaxy-galaxy and galaxy-cluster interactions at a level of detail impossible at higher redshift. In Virgo, there exists a large population of spiral galaxies with mostly undisturbed stellar disks, but truncated gas disks. By combining optical spectroscopy and UV imaging of these galaxies, we can understand when and where in the cluster galaxies are affected by interactions. Analysis of disk stellar populations shows that star formation was cut off in these galaxies within the last 500 Myr, consistent in several cases with being stripped outside the cluster core. This suggests that the "reach" of the intracluster medium is greater than is suggested by simple ICM models. Such interactions appear to transform blue star forming galaxies into red, passively-evolving disks.
Locating mergers is an important empirical task but difficult to carry out in practice. Close-pairs and non-parametric methods (such as CAS and Gini-M20) are prone to contamination whereas visual inspection by individuals is impractical for large modern surveys such as the SDSS. The Galaxy Zoo project overcomes this latter problem by enlisting hundred's of thousands of volunteers on the world-wide web who can collectively (and reliably) classify galactic morphologies and flag mergers interacting systems. Here we present the results of the largest and most homogenous catalogue of binary mergers in the local universe. We also discuss recent work on (major) multi-mergers as well as the preliminary results of the sequel project Galaxy Zoo 2.
G. E. de Messières, R. W. O'Connell, B. R. McNamara, M. Donahue, P. E. J. Nulsen, G. M. Voit, M. W. Wise
University of Virginia
My research team has obtained mid-infrared spectra of nine cool-core galaxy clusters with the Infrared Spectrograph aboard the Spitzer Space Telescope. X-ray, ultraviolet and optical observations have demonstrated that each of these clusters hosts a cooling flow which seems to be fueling vigorous star formation in the brightest cluster galaxy. My goal is to use the advantages of the mid-infrared band to improve estimates of star formation. Our spectra are characterized by diverse morphologies ranging from classic starbursts to flat spectra with surprisingly weak dust features. For some of the targets, the implied rates of star formation are very low compared to previously published estimates from optical and ultraviolet data. We propose that star formation is proceeding strongly in these clusters, but in unusually dust-deficient circumgalactic environments such as the interface between the cooling flow and the relativistic jets from the active galactic nucleus.
University of Exeter
Whilst hydrodynamical simulations of grand design galaxies have often adopted a static potential, capturing the full dynamics requires modeling interacting galaxies. We present simulations of the interaction of M51 with NGC 5195, which include both the stars and gas. The M51 galaxy shows a transition from flocculent to grand design spiral structure as the interaction progresses, with the main m=2 mode propagating inwards through the disc. However the comparatively high amplitude of other modes in the disc indicate the complex underlying dynamics. We also compare substructure in the stellar and gas distributions, and show that once a more long-standing 2 armed perturbation develops, spurs and feathers occur along the spiral arms similar to previous calculations with density waves imposed (e.g. Kim & Ostriker 2002, Dobbs & Bonnell 2006).
D. Domingue, C. K. Xu, Y. Cheng, T.H. Jarrett, R. Cutri, N. Lu, J. Mazarella, J. Surace, Y. Gao,J. Huang, W. Sun
Georgia College & State University, Caltech, Purple Mt. Obs., China, CfA, NCU, Taiwan
We select a close ``major-merger candidate" galaxy pair sample in order to calculate the K_s luminosity function (LF),pair fraction, merger rates and representative star formation rates (SFR) of the merger/interaction component of galaxy evolution in the local universe. The pair sample is selected by combining the Two Micron All Sky Survey (2MASS) with the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). The resulting data set of 340 galaxies suggests that major-merger candidate pairs in the z<0.1 universe are developed from 1.6% of the galaxy population without dependence on galaxy mass below 1011 solar masses. Combined with merger model time scales, this LF gives local merger rates per unit volume which decrease with masses greater than 1011 solar masses. Spitzer observations of a subsample of these pairs show only moderate SFR in a majority of that subsample as opposed to the high rates found in FIR selected samples.
Astronomical Institute ASCR, Czech Republic
Shell galaxies are galaxies containing fine stellar structures in their luminous profile. These structures forms open, concentric arcs - the shells. It is widely believed that the shells are a signature of a merger experienced by the host galaxy. The model of a radial merger is quite successful in reproducing the regular kind of shell systems. We are trying to improve our semi-analytical simulations of the shell origin by including the dynamical friction and the gradual disruption. We used radial symmetry of our galaxies to include the dynamical friction by the means of an improved version of the Chandrasekhar formula. It seems that the dynamical friction and gradual disruption have significant influence on the shell structure.
Max Planck Institute, Germany
We investigate the star formation and merger history of NGC6240 using new integral field data at resolutions down to 0.15arcsec, and new hydrodynamical simulations. Despite a clear rotational signature, the stellar kinematics in the two nuclei are dominated by dispersion (which is anomalously high across the northern half of the southern nucleus due to the superposition of two stellar populations). Jeans modelling yields the dynamical masses and mass-to-light ratios of the nuclei. Combining these with spatial variations in the Br-gamma equivalent width both on and off the nuclei shows that only about 1/3 of the K-band continuum from the nuclei is associated with the most recent star formation episode. As such, only about 30-50% of the bolometric luminosity, and 10% of the stellar mass, is due to this starburst. The apparent gas concentration between the nuclei is a projection effect. Our models, which match as far as possible the systems' characteristics, suggest instead that the gas is distributed along a tidally induced bridge connecting the nuclei that contains only a small fraction of the total gas mass.
Morgan Fouesneau, Ariane Lançon
Observatoire Astronomique de Strasbourg
The integrated spectrophotometric properties of young star clusters are subject to large cluster-to-cluster variations distributed in non trivial ways around the average properties predicted by standard population synthesis models. This directly depends on the stochastic mass distribution of the finite (small) number of luminous stars in each cluster, stars which may be either particularly blue or particularly red. The distribution is widely spread and usually far from Gaussian for the colors of young and intermediate age clusters. Determination of intrinsic properties of most star clusters, especially age estimation, is strongly affected by these variations. We developed a Bayesian approach to the study of ages and masses of star clusters that cannot be resolved into stars. Based on Monte-Carlo simulations, we explored the distributions of star cluster properties with a given multi- wavelength photometry. This poster presents the technical aspects of the implementation, which make a new use of the population synthesis suite Pégase and also presents applications of this Bayesian method to multi-wavelength observations of star clusters in interacting galaxies, such as the Antennae.
University of Wisconsin
As the most common environment in the universe, groups of galaxies are likely to contain a significant fraction of the missing baryons in the form of intergalactic gas. The density of this gas is an important factor in whether ram pressure stripping and strangulation affect the evolution of galaxies in these systems. We present a method for measuring the density of intergalactic gas using bent-double radio sources. We use this method to probe intergalactic gas in different environments and find significant reservoirs of baryons. Additionally, we combine our knowledge of the density with archival X-ray observations to place an upper limit on the temperature of the intergalactic gas in one group of galaxies.
Mark Giroux1, Beverly Smith1, Curt Struck2, Mark Hancock3, and Sabrina Hurlock1
1East Tennessee State University, 2Iowa State University, 3University of California Riverside
We present an Atlas of GALEX UV images for a sample of 3 dozen pre-merger interacting galaxies selected from the Arp Atlas. We compare with available Spitzer infrared and ground-based optical and 21 cm HI images.
University of Glasgow, UK
The proposed Laser Interferometer Space Antenna, planned for launch late next decade, will open up a new window on the Universe through the observation of very low frequency gravitational waves from sources at cosmological distances. The strongest sources that LISA will detect will be the inspirals and mergers of supermassive binary black hole systems. These systems should be detectable to very high redshift - essentially their detection will be limited by their intrinsic redshift and mass distribution, and not by observational selection effects resulting from LISA's sensitivity. In this poster I will briefly describe the prospects for using LISA observations as a probe supermassive black hole mergers, and the constraints these observations might place on models of galaxy formation. Analysis of the inspiral waveforms detected by LISA, combined with the adoption of an assumed luminosity distance redshift relation (e.g. from Planck observations) should permit the inference of the SMBH masses to very high precision. Consequently, therefore, LISA data should provide important, new constraints on the mass and redshift distribution of SMBH merger events, at redshifts beyond the reach of electromagnetic observations.
Anthony Holincheck, John Wallin, Chris Lintott, Lucy Fortson, Jordan Raddick, Geza Gyuk, Mark SubbaRao, and Kirk Borne
George Mason University
In the last decade several automated or semi-automated systems have been developed for determining the best-fit orbital parameters for interacting galaxies. These systems make use of a fitness function or pattern matching capability for rating how well simulation outputs match the observed galaxies. The fitness functions are then optimized to find the best-fit parameters, frequently with a genetic algorithm. However, the success of these systems often relies on extensive manual tuning of simulation parameters. Due to the need for tuning, the existing systems have only been applied to a limited number of interacting pairs. The galaxy collision project is a set of software tools used to simulate pairs of interacting disk galaxies on-line. In this system, public volunteers with the Galaxy Zoo project act as Citizen Scientists using the tools to perform a series of restricted three-body simulations and rate the output. We present the preliminary results for several interacting pairs including an analysis of the uniqueness of the best-fit orbital parameters. Future work will include using the parameters from this simple model in a more sophisticated full N-body simulation using SPH.
Jeong-Sun Hwang and Curtis Struck
Iowa State University
We use Smoothed Particle Hydrodynamics models to study the large-scale morphology and dynamical evolution of the intergalactic gas in Stephan's Quintet, and compare to multiwavelength observations. Specifically, we model the formation of the hot X-ray gas, the large-scale shock, and emission line gas as the result of NGC 7318b colliding with the group. We also reproduce the N-body model of Renaud and Appleton for the tidal structures in the group.
L. Jilkova1, I. Ebrova2, B. Jungwiert2, T. Kratka1, M. Krizek2, I. Stoklasova2
1Department of Theoretical Physics & Astrophysics, Masaryk University, Brno, Czech Republic, 2Astronomical Institute ASCR, Prague, Czech Republic
In the context of exploring mass distributions of dark matter haloes in giant ellipticals, we extend the analysis carried out by Merrifield & Kuijken (1998) for stellar line profiles of shells created in nearly radial mergers of galaxies. We simulate shell formation in realistic multi-component potentials and show that the resulting line-of-sight velocity distributions are more complex than previously predicted. We analyze the detectability of spectroscopic signatures of shells after convolving them with spatial and spectral PSFs of currently available instruments. We also evaluate the possibility of constraining the halo properties from the shell kinematics.
William C. Keel1 and Lisa Frattare2
1University of Alabama, 2Space Telescope Science Institute
We present results from a study of the populations of H II regions in interacting systems based on H-alpha imaging. The most robust results come from spatial distributions, especially those with luminosity weighting. The H II regions are more centrally concentrated than in similar noninteracting galaxies, and are often concentrated in annular regions, a trend which is enhanced for the more luminous ones. Asymmetries in the H II regions' locations are not simply related to the current interaction geometry, although we do see preferred dynamical locations in a few systems. The luminosity functions are more difficult to interpret, largely because of a wide distance range and issues of blending (as well as defining single H II regions). We have used positions of the stellar associations from HST imagery to help separate blended H II regions in ground-based H-alpha imagery, and see whether the flatter luminosity functions in some of these systems actually trace more luminous individual star-forming regions or result from clumping of smaller episodes. Our aim is to use these data to address whether the interactions shape normal star formation (`more of the same') or set off new modes of starbirth, which may differ in its spatial properties or characteristic cluster masses.
Univ. of Colorado - Boulder
I will present broadband HST+WFPC2 images, ground-based Halpha images and optical spectra, and VLA HI 21 cm emission maps of the nearby galaxy ESO 1327-2041 (cz_gal = 5340 km/s), which is located 38 arcsec west of the QSO PKS 1327-206 (z_em = 1.17). We find HI 21 cm absorption in the QSO spectrum at cz_abs = 5250 and 5500 km/s, the same velocities that metal lines of Na I and Ca II were previously discovered. We attribute this absorption to disk gas from a disrupted spiral arm revealed by our HST images. Our optical spectra show Halpha emission from several clumps of material along this disrupted spiral arm that are located ~5 arcsec from the QSO position (~2 kpc at cz_gal). ESO 1327-2041 appears to be the result of a recent 3-body merger that ejected the smallest galaxy's nucleus from the system. Our ground-based Halpha images reveal the presence of several HII regions in an inclined disk near the galaxy's center, which likely represent star formation triggered by the merger.
Arizona State University
How does the tidal debris of minor galaxy mergers contribute to structures in spiral galaxies or in the intergalactic medium? While major mergers are known to create structures such as tidal dwarf galaxies and star clusters within their tidal debris, less is known about minor mergers (mass ratios between a dwarf galaxy and disk galaxy of less than one-third) and their tidal debris. This work surveys 15 minor mergers using optical broad-band and H-alpha narrow-band imaging to characterize star formation in their tidal debris. For example, NGC 2782, a minor merger having a mass ratio of 0.25 that occurred 200 Myr ago, has a population of young star clusters which formed along both tidal tails. In particular, the presence of young clusters in the Western tail is unexpected due to the lack of molecular gas observed in previous studies. Also, the star cluster populations of each tidal tail have different masses with the Western tail having smaller mass clusters. This result has implications for the wider field of star formation, suggesting that star cluster formation is a common outcome of minor mergers regardless of the molecular gas content in the tidal debris. However, the properties of the star clusters formed may be dependent on local properties such as metallicity, gas pressure density, gas content, etc. Even if minor mergers contribute less tidal debris per interaction than major mergers, they are more common and possibly contribute structure to all types of galaxies and to the intergalactic medium throughout the history of the universe.
Rebecca A. Koopmann1, Riccardo Giovanelli2, Martha P. Haynes2, Brian R. Kent3, Noah Brosch4
1Union College, 2Cornell University, 3NRAO, 4Wise Observatory/Tel Aviv University
Early-type dwarf galaxies dominate cluster populations, but their formation and evolutionary histories are poorly understood. The ALFALFA (Arecibo Legacy Fast ALFA) survey has completed observations of the Virgo Cluster in the declination range of 4 - 16 degrees. Less than 2% of the early-type dwarf population is detected, a significantly lower fraction than reported in previous papers based on more limited samples. In contrast ~30-35% of the irregular/BCD dwarf population is detected. Most of the dwarfs detected in HI also show evidence for ongoing/recent star formation. Early-type galaxies with HI tend to be located in the outer regions of the cluster. Galaxies such as these may be undergoing morphological transition due to cluster environmental effects.
Astronomical Institute Utrecht, Utrecht University; Leiden Observatory, Leiden University
The observed mass-to-light ratios of Galactic globular clusters (GCs) are about 25% lower than expected from their respective metallicities. Recent studies have indicated that the mass-to-light ratios could be decreased by cluster dissolution. This would occur due to the preferential loss of low-mass stars ensuing from two-body relaxation. Using analytical cluster models in which this effect is accounted for, we model the mass-to-light ratios of 24 GCs and compare these to the observed values. We obtain an average mass-to-light ratio drop of 20% and show that within the statistical uncertainty the mass-to-light ratios of GCs can indeed be explained by low-mass star depletion.
Astronomical Institute Utrecht, Utrecht University; Leiden Observatory, Leiden University
In past years, the shape of the globular cluster mass function (GCMF) has been the subject of extensive discussion. However, not much attention has been given to the fact that it is always derived from the globular cluster luminosity function (GCLF) using a constant mass-to-light ratio for all globular clusters (GCs). We elaborate on the variability of the mass-to-light ratio with cluster mass and how this by necessity leads to a revision of the relation between the GCLF and the GCMF. We show that accounting for the preferential loss of low-mass stars yields a Galactic GCMF with low-mass slope equal to 0.7 instead of 1.0. Another implication of this more detailed translation from GCLF to GCMF is a lower turnover mass than would arise when assuming a canonical value of the mass-to-light ratio.
University of North Carolina
The recent discovery of extended ultraviolet (XUV) disks around ordinary disk galaxies provides evidence for disk building at recent epochs. Extending this line of inquiry to the occurrence of disk rebuilding after mergers, we examine whether E/S0 galaxies show evidence of newly developing UV disks as well. Combining GALEX observations with deep optical imaging, we explore various methods of identifying XUV structures in a sample of nearby low-mass E/S0 galaxies and the frequency with which XUV structures can be discerned using these methods. We also discuss how the optical and UV morphologies of these galaxies depend on their star formation and dust characteristics. Identifying such trends will allow us to better understand the evolutionary histories that distinguish E/S0 galaxies with and without XUV disks and the relationship of this phenomenon to disk rebirth.
L.M. Oskinova1, R. Ignace2
1University of Potsdam, 2East Tennessee State University
The mass and energy input from massive stars are among essential agents, which determine fate of massive star clusters, and is perhaps a key mechanism responsible for the cluster mass distribution. The massive star feedback is also pivotal in triggering consequent waves of starformation within already existing stellar conglomerates. X-ray observations provide excellent means to trace the input of mass and mechanic energy and determine the tipping point in cluster evolution, when the input of mechanic energy becomes dominant over the input of radiative energy. I will briefly review the X-ray observations of massive star forming regions in the Galaxy and beyond, and try to address the following questions: What are the links between evolution of massive star clusters and hot cluster winds? What giant supershells in the interacting galaxies can tell about the history of star formation? Do bursts of star formation in matter and metal poor regions always require triggering by mechanic energy form SNe and/or stellar winds?
A. Parker and J. S. Gallagher III
University of Wisconsin- Madison
Strongly interacting galaxy pairs provide a basis for studies of stellar tidal bridges. Moderately deep, multi-color optical images were obtained with the WIYN 0.9-m telescope for a variety of systems with stellar tidal bridges. The bridges in these systems range from complexly structured with evidence for star formation to extremely smooth and extended, as in Arp 104. Photometric measurements quantify the amplitudes of the structural elements within these features and provide a basis for comparison with tidal bridge formation models. The bridge structures and colors also yield insights into the importance of star formation within these low density regions. Research supported in part by the National Science Foundation through grant AST-0708967 to the University of Wisconsin Research also supported in part by the National Space Grant College and Fellowship Program and the Wisconsin Space Grant Consortium
Bradley W. Peterson
Iowa State University
We present results from a study of proto-globular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5). Studies of the Antennae and M51 have suggested that the majority of these star clusters dissolve within 20 Myr due to mass loss. We obtain cluster colors using archival HST data, and estimate ages and extinctions for over 150 clusters using evolutionary synthesis models. We find that clusters in NGC 7714 are generally less than 20 Myr old, while the data in the bridge is too limited to allow good estimates for individual clusters. We also examine H II region complexes with lower-resolution Spitzer and GALEX images.
Washington State University
Spectral feature index diagrams with integrated globular clusters and simple stellar population models often show that some clusters have weak H-beta lines, so weak that even the oldest models cannot match the oberved feature depths. In this work, we rule out the possibility that abundance mixture effects are responsible for the weak indices. We discuss this result in the context of other explanations, including horizontal branch morphology, blue straggler populations, and nebular or stellar emission fill-in.
P. Repetto, M. Rosado, I. Fuentes-Carrera and R. Gabbasov
Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM),
Escuela Superior de Fisica y Matematicas, IPN, Mexico
In this work we present Ha observations of the isolated interacting galaxy pair NGC 5278/79 using the scanning Fabry-Perot interferometer PUMA. For each component of this pair, velocity fields, various kinematic parameters and rotation curves were derived. The residual velocity map of both galaxies was also obtained to study the non-circular motions in these galaxies. Using the observed rotation curves, a range of possible masses was computed for each galaxy. These were compared with the orbital mass of their pair derived from the relative motion of the members. Finally, we present an analysis of the interaction process.
Naval Research Laboratory
Over the last three decades, multi-wavelength observations and numerical simulations have demonstrated spiral-spiral mergers are capable of forming elliptical galaxies. Recently, controversy has erupted over whether these mergers are capable of forming m > m* ellipticals. Both observations of the Red Sequence out to z = 1, and σ derived from the 2.29 micron CO bandhead for local LIRG/ULIRGs, suggest they are not. IR-bright mergers are often cited as the best candidates for forming massive ellipticals, so the recent observations have raised doubts about both the Toomre Merger Hypothesis and the fundamental assumptions of many lambda-CDM galaxy formation models. On the other hand, kinematics obtained with the Calcium II Triplet (CaT) at 8500 Angstrom suggest all types of mergers are forming m > m* ellipticals. Using comparison samples of merger remnants and elliptical galaxies in the local universe, I will show that kinematics derived from the CO stellar absorption bandhead leads to a severe underestimation of the dynamical masses of local LIRGs/ULIRGs. This is primarily due to the dominant effects on the derived kinematics of a young stellar populations during this phase of the merger.
Institute for Astronomy, University of Hawaii
Recent results have shown that interacting galaxies do not follow the mass-metallicity realtion. Instead, nuclear, gas-phase oxygen abundances are depressed in strongly interacting galaxies. We present the first ever metallicity gradient studies of strongly interacting galaxies, using multi-object Keck spectroscopy and numerical simulations. We confirm that these lowered abundances are caused by interaction-driven gas inflows that flatten the gradients, compared to those of the progenitor systems.
Nitza A. Santiago1, Mary Putman1, Jessica Werk1,2, Emma Ryan-Weber3, Gerhardt R. Meurer4
1Columbia University, 2University of Michigan, 3Swinburne University, 4John Hopkins University
We obtained VLA 21-cm observations of the galaxy ESO 481-G017 to determine the environment of remote star formation traced by a HII region found 43 kpc from the galaxy (in projection). ESO 481-G017 is an early type spiral galaxy with an HI mass of 1.1 x 109 Msun and a distance of 55 Mpc. The isolated HII region was detected as a discrete dot in H-alpha images and has minimal continuum emission, suggesting that new stars have formed in a region where few stars previously existed. The spectrum of the HII region reveals a velocity of 4701 ± 80 km s-1, while ESO 481-G017 has a velocity range 3840-3985 km s-1. The large diference in velocity (~ 900 km s-1) indicates that the isolated HII region may represent star formation in a tidal feature of a gas-rich group or a low surface brightness companion galaxy. The VLA observations shed light on the nature of this young object and the gaseous environment of ESO 481-G017.
Washington State University
Emission infill corrections for the Balmer series of the Sloan Digital Sky Survey(SDSS) quiescent stacked galaxy spectra are derived, along with corrections for continuum shape and stellar content, as a function of the Mg $b$ Lick Index strength.. These corrections are obtained by comparing the observed lick index measurements of the SDSS and comparing them to observed measurement of 13 Virgo Cluster galaxies, and checked with model grids. These two data sets are compared using index index plots of H-alpha vs. Mg b. From this a line correction for the observed measurement is constructed using best fit trend lines. Then corrections for H-beta, H-gamma and H-delta are constructed using models to predict continuum shape changes as a function of Mg b, the Lick index definitions, and Balmer series intensities typical of LINERS.
N. Shafi1, T. Oosterloo2, R. Morganti2, R. Booth1
1 HartRAO and University of the Witwatersrand, South Africa
2ASTRON, The Netherlands
Very deep neutral hydrogen (HI) observations of the edge-on spiral galaxy NGC3079 with the Westerbork Synthesis Radio Telescope (WSRT) are presented. The galaxy has been studied extensively in different wavelengths and is known for its several unique and complex features. However, the new data obtained from WSRT reveal new features and show that the galaxy is even more complicated and interesting than previously thought. With these new observations a large stream of gas, encircling the entire galaxy, has been discovered, while the data also show, for the first time, that not only hot gas is blown into space by the burst of star formation, but also large amounts of cold gas, despite the high energies involved in the outflow.
Beverly J. Smith et al.
East Tennessee State University
The key to understanding the physical processes occuring during galaxy interactions is dynamical modeling, and in particular, the detailed matching of numerical models to specific systems. To make modeling interacting galaxies more efficient, we have constructed the `automatic galaxy collision' (AGC) code, which requires less human intervention in finding good matches of models to data. We present some preliminary results from this code, and address questions of uniqueness of solutions and uncertainties in the interaction parameters.
University of Virginia / Observatorio Nacional, Brazil
I present the results of Integral Field spectroscopy on the prototype HII galaxy II Zw 40 from a combination of two complementary collaborations. Using Gemini GMOS-IFU in the red part of the visible spectrum Bordalo, Plana & Telles (2009) derived Ha monochromatic, velocity and dispersion maps on the central star forming knot. We show that II Zw 40 has a kinematic core which is dominated by random motions with a core velocity dispersion of 34 km s-1. It also shows a lower limit supersonic velocity dispersion of ~ 26 km s-1, unaffected by stellar evolution, which permeates the whole star forming region, likely to represent the dispersion associated with gravity. Diagnostic diagrams, such as the Intensity versus sigma diagram, are used to identify the kinematic features as shells and filaments due to the stellar driven winds. A single Gaussian fit to the integrated spectrum Ha line over the whole star forming region will measure exactly the same width as a single Gaussian fit to the one pixel core Ha line. Using SINFONI integral field in the near-infrared with adaptive optics on the VLT, Vanzi, Cresci, Telles & Melnick (2008) analysed the spatial distribution of extinction, ionized Hydrogen, Helium, [Fe II] and molecular hydrogen (H2) emission and velocity fields. We show that II Zw 40 is solely powered by one super stellar cluster (knot A) producing all the present ionizing radiation. It is also responsible for the photo-excitation of H2, although this has a peculiar velocity field detached from Br and [Fe II]. Both of these studies are in good agreement revealing that the age of the stellar population in the main cluster is such that no supernova (SN) should be present yet so that the gas kinematics must be dominated by the young stars with a dominant turbulent random component in the core. We do not see, in the starbursting region, any geometrical or dynamical structure that can be related to the large scale morphology of the galaxy.
Gelys Trancho1, Nate Bastian2
1Gemini Observatory, Chile; 2University of Cambridge, UK
We present optical spectroscopy of 16 star clusters in the merging galaxies NGC 4038/39 (The Antennae) and supplement this dataset with U, B, V, I, & Halpha HST imaging. We derive the age and metallicity of each cluster through a comparison between observed Balmer and metal line strengths with simple stellar population models. We then estimate extinctions and masses using the photometry. We find clusters with ages between 3 - 200 Myr, consistent with the expected increase in the star-formation rate due to the merger. Most of the clusters appear to take part in the general rotation of the galaxy, hence star/cluster formation is still taking place within the galactic disks. However, two clusters have radial velocities consistent with being part of the halo, which is surprising given their young (200 - 500 Myr) ages. We find evidence for spatially distributed cluster formation throughout the duration of the merger. Finally, we explore the impact of various assumptions about the star/cluster formation rate on the interpretation of the cluster age distribution, and do not find evidence for long term infant mortality as has been previously suggested.
Lisa May Walker, Kelsey E. Johnson, Sarah C. Gallagher, John E. Hibbard, Ann E. Hornschemeier, Jane C. Charlton, Jason Young, Caryl Gronwall
University of Virginia
We investigate the mid-infrared distribution in colorspace of 42 galaxies from 12 Hickson Compact Groups (HCGs) and the distributions of several comparison samples including the SINGS galaxies, KISS galaxies, galaxies from the Coma Cluster, interacting galaxies, and starburst galaxies. We find that the HCG galaxies are not uniformly distributed in colorspace, as well as qualitative evidence for a gap. Galaxies in the infall region of the Coma cluster also exhibit a non-uniform distribution and a less well defined gap, which may reflect a similarity with the compact group environment. None of the other samples we studied show evidence of a gap, leading us to speculate that it is unique to the dense environment present in compact groups and clusters.
Lisa H. Wei, Sheila J. Kannappan, Stuart N. Vogel, Andrew J. Baker
University of Maryland
Recent work has identified a population of low-mass, field ellipticals and S0s that occupy the ``blue sequence'' in color vs. stellar mass parameter space, where spiral galaxies typically reside. While some seem to be young merger remnants destined to fade onto the red sequence, commonly associated with E/S0s, many appear to be settled products of long-ago mergers that are now rebuilding disks. We present observations of cold gas in blue- and red-sequence E/S0s. Based on the size of the cold gas reservoir, stellar mass content, and current star formation rate, we probe the current evolutionary state as well as the extent of morphological transformation possible in the future for blue-sequence E/S0s.
Kenneth Wong1, Michael Blanton2, Alison Coil3, Richard Cool4, Daniel Eisenstein1, John Moustakas2, Wiphu Rujopakarn1, Guangtun Zhu2
1The University of Arizona, 2NYU, 3UC San Diego, 4Princeton University
The Prism Multi-Object Survey (PRIMUS) is a galaxy redshift survey covering ~10 square degrees to a flux limit of i ~ 23 mag. We acquire roughly 200,000 spectra of galaxies out to z ~ 1 in fields with existing multiwavelength data in the UV, X-ray, and infrared. By mutiplexing in the wavelength direction, we sacrifice spectral resolution for throughput, allowing us to observe ~3000 objects per mask for 121 masks over just 39 dark nights at Magellan. Our goal is to combine our redshifts with the existing data to study various aspects of galaxy evolution with redshift, such as star formation rates, stellar mass, luminosity functions, and clustering properties. One of the initial science projects will be to use UV data from the Galaxy Evolution Explorer (GALEX) to derive specific star formation rates for close galaxy pairs (projected separation < 50 h-1 kpc) and compare the enhancement of UV luminosity to isolated galaxies in the field. We will use our redshifts to identify interlopers that are close in projected separation but separated in redshift space to improve the quality of our sample.
Washington State University
At a fairly hefty velocity dispersion of 200 km s-1, the relative ratios of elements C, N, O, Na, Mg, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr, and Ba can be determined to scientifically useful precision. Cases of interest that are borderline because they suffer internal degeneracies (although plenty of signal is present) are Al and the trio C, N, and O. The elements S, K, Cu, and Eu are too difficult to measure at this velocity dispersion, and V is borderline. The effects of abundance ratios on the final spectra are quite large. The effects of abundance ratios on the underlying isochrones are varied, but can easily reach severities where population ages become completely buried under the abundance uncertainties.