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DOE OSTI2015

A COMPARATIVE ANALYSIS OF THE SUPERNOVA LEGACY SURVEY SAMPLE WITH ΛCDM AND THE R{sub h}=ct UNIVERSE

The use of Type Ia supernovae (SNe Ia) has thus far produced the most reliable measurement of the expansion history of the universe, suggesting that ΛCDM offers the best explanation for the redshift–luminosity distribution observed in these events. However, analysis of other kinds of sources, such as cosmic chronometers, gamma-ray bursts, and high-z quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the R{sub h} = ct universe is a better fit to the data. The central difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing supernova (SN) luminosities simultaneously with the parameters of an expansion model. Hence, in comparing competing models, one must reduce the data independently for each. We carry out such a comparison of ΛCDM and the R{sub h} = ct universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. However, since R{sub h} = ct has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over ΛCDM, the minimalist version of which has three (the Hubble constant, the scaled matter density, and either the spatial curvature constant or the dark energy equation-of-state parameter). We estimate using the Bayes Information Criterion that in a pairwise comparison, the likelihood of R{sub h} = ct is ∼90%, compared with only ∼10% for a minimalist form of ΛCDM, in which dark energy is simply a cosmological constant. Compared to R{sub h} = ct, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HST imaging of fading AGN candidates. I. Host-galaxy properties and origin of the extended gas

We present narrow- and medium-band Hubble Space Telescope imaging, with additional supporting ground-based imaging, spectrophotometry, and Fabry–Perot interferometric data, for eight galaxies identified as hosting a fading active galactic nucleus (AGN). These are selected to have AGN-ionized gas projected >10 kpc from the nucleus and energy budgets with a significant shortfall of ionizing radiation between the requirement to ionize the distant gas and the AGN as observed directly, indicating fading of the AGN on ≈50,000 yr timescales. This paper focuses on the host-galaxy properties and origin of the gas. In every galaxy, we identify evidence of ongoing or past interactions, including tidal tails, shells, and warped or chaotic dust structures; a similarly selected sample of obscured AGNs with extended ionized clouds shares this high incidence of disturbed morphologies. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material viewed ∼1.5 Gyr after its initial arrival. The host systems are of early Hubble type; most show nearly pure de Vaucouleurs surface brightness profiles and Sérsic indices appropriate for classical bulges, with one S0 and one SB0 galaxy. The gas has a systematically lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. Unlike extended emission regions around many radio-loud AGNs, these clouds are kinematically dominated by rotation, in some cases in warped disks. Outflows can play important kinematic roles only in localized regions near some of the AGNs. We find only a few sets of young star clusters potentially triggered by AGN outflows. In UGC 7342 and UGC 11185, multiple luminous star clusters are seen just within the projected ionization cones, potentially marking star formation triggered by outflows. As in the discovery example, Hanny’s Voorwerp/IC 2497, there are regions in these clouds where the lack of a strong correlation between Hα surface brightness and ionization parameter indicates that there is unresolved fine structure in the clouds. Together with thin coherent filaments spanning several kpc, persistence of these structures over their orbital lifetimes may require a role for magnetic confinement. Overall, we find that the sample of fading AGNs occur in interacting and merging systems, that the very extended ionized gas is composed of tidal debris rather than galactic winds, and that these host systems are bulge-dominated and show no strong evidence of triggered star formation in luminous clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Far-ultraviolet spectroscopy of old novae. I. V603 Aquila

We present the results of a synthetic spectral analysis of the far-ultraviolet archival International Ultraviolet Explorer, Hubble Space Telescope (HST), and FUSE observations of the fast old nova V603 Aql, obtained some 90 years after its 1918 nova outburst. Our analysis utilizes the new Hubble fine guidance sensor parallax distance for this nearly face-on old nova, a high white dwarf (WD) mass, and a low reddening. Our analysis includes non-truncated optically thick accretion disks since V603 Aql is neither a polar nor an intermediate polar. Our synthetic spectral modeling of the FUSE and HST spectra analyzed separately indicate a mass transfer rate of M-dot =1.5−2.2×10{sup −9}M{sub ⊙} yr{sup −1} for the FUSE and HST spectra, respectively, assuming a WD mass of 1.2M{sub ⊙}. The mass accretion rate also depends on the assumed WD mass and increases by a factor of two for a WD mass of 0.8M{sub ⊙}. Combining the FUSE and HST spectra lead to the same results. Potential implications are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A TEST OF COSMOLOGICAL MODELS USING HIGH-z MEASUREMENTS OF H(z)

The recently constructed Hubble diagram using a combined sample of SNLS and SDSS-II SNe Ia, and an application of the Alcock–Paczyński (AP) test using model-independent Baryon Acoustic Oscillation (BAO) data, have suggested that the principal constraint underlying the cosmic expansion is the total equation-of-state of the cosmic fluid, rather than that of its dark energy. These studies have focused on the critical redshift range (0 ≲ z ≲ 2) within which the transition from decelerated to accelerated expansion is thought to have occurred, and they suggest that the cosmic fluid has zero active mass, consistent with a constant expansion rate. The evident impact of this conclusion on cosmological theory calls for an independent confirmation. In this paper, we carry out this crucial one-on-one comparison between the R{sub h} = ct universe (a Friedmann–Robertson–Walker cosmology with zero active mass) and wCDM/ΛCDM, using the latest high-z measurements of H(z). Whereas the SNe Ia yield the integrated luminosity distance, while the AP diagnostic tests the geometry of the universe, the Hubble parameter directly samples the expansion rate itself. We find that the model-independent cosmic chronometer data prefer R{sub h} = ct over wCDM/ΛCDM with a Bayes Information Criterion likelihood of ∼95% versus only ∼5%, in strong support of the earlier SNe Ia and AP results. This contrasts with a recent analysis of H(z) data based solely on BAO measurements which, however, strongly depend on the assumed cosmology. We discuss why the latter approach is inappropriate for model comparisons, and emphasize again the need for truly model-independent observations to be used in cosmological tests.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE MEGAMASER COSMOLOGY PROJECT. II. THE ANGULAR-DIAMETER DISTANCE TO UGC 3789

The Megamaser Cosmology Project (MCP) aims to determine H {sub 0} by measuring angular-diameter distances to galaxies in the Hubble flow using observations of water vapor megamasers in the circumnuclear accretion disks of active galaxies. The technique is based only on geometry and determines H {sub 0} in one step, independent of standard candles and the extragalactic distance ladder. In Paper I, we presented a very long baseline interferometry map of the maser emission from the Seyfert 2 galaxy UGC 3789. The map reveals an edge-on, sub-parsec disk in Keplerian rotation, analogous to the megamaser disk in NGC 4258. Here, we present 3.2 years of monthly Green Bank Telescope observations of the megamaser disk in UGC 3789. We use these observations to measure the centripetal accelerations of both the systemic and high-velocity maser components. The measured accelerations suggest that maser emission lines near the systemic velocity originate on the front side of the accretion disk, primarily from segments of two narrow rings. Adopting a two-ring model for the systemic features, we determine the angular-diameter distance to UGC 3789 to be 49.9 {+-} 7.0 Mpc. This is the most accurate geometric distance to a galaxy in the Hubble flow yet obtained. Based on this distance, we determine H {sub 0} = 69 {+-} 11 km s{sup -1} Mpc{sup -1}. We also measure the mass of the central black hole to be 1.09 x 10{sup 7} M{sub sun} {+-}14%. With additional observations, the uncertainty in the distance to this galaxy can be reduced to under 10%. Observations of megamaser disks in other galaxies will further reduce the uncertainty in H {sub 0} as measured by the MCP.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE NATURE OF STARBURSTS. I. THE STAR FORMATION HISTORIES OF EIGHTEEN NEARBY STARBURST DWARF GALAXIES

We use archival Hubble Space Telescope observations of resolved stellar populations to derive the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In this first paper, we present the observations, color-magnitude diagrams (CMDs), and the SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data reduction, differential extinction, and treatment of photometric completeness. We adopt a star formation rate (SFR) threshold normalized to the average SFR of the individual system as a metric for classifying starbursts in SFHs derived from resolved stellar populations. This choice facilitates finding not only the currently bursting galaxies but also 'fossil' bursts increasing the sample size of starburst galaxies in the nearby (D < 8 Mpc) universe. Thirteen of the eighteen galaxies are experiencing ongoing bursts and five galaxies show fossil bursts. From our reconstructed SFHs, it is evident that the elevated SFRs of a burst are sustained for hundreds of Myr with variations on small timescales. A long >100 Myr temporal baseline is thus fundamental to any starburst definition or identification method. The longer lived bursts rule out rapid 'self-quenching' of starbursts on global scales. The bursting galaxies' gas consumption timescales are shorter than the Hubble time for all but one galaxy confirming the short-lived nature of starbursts based on fuel limitations. Additionally, we find that the strength of the H{alpha} emission usually correlates with the CMD-based SFR during the last 4-10 Myr. However, in four cases, the H{alpha} emission is significantly less than what is expected for models of starbursts; the discrepancy is due to the SFR changing on timescales of a few Myr. The inherently short timescale of the H{alpha} emission limits identifying galaxies as starbursts based on the current characteristics which may or may not be representative of the recent SFH of a galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

GALAXY EVOLUTION IN A COMPLEX ENVIRONMENT: A MULTI-WAVELENGTH STUDY OF HCG 7

The environment where galaxies are found heavily influences their evolution. Close groupings, like the ones in the cores of galaxy clusters or compact groups, evolve in ways far more dramatic than their isolated counterparts. We have conducted a multi-wavelength study of Hickson Compact Group 7 (HCG 7), consisting of four giant galaxies: three spirals and one lenticular. We use Hubble Space Telescope (HST) imaging to identify and characterize the young and old star cluster populations. We find young massive clusters (YMCs) mostly in the three spirals, while the lenticular features a large, unimodal population of globular clusters (GCs) but no detectable clusters with ages less than a few Gyr. The spatial and approximate age distributions of the {approx}300 YMCs and {approx}150 GCs thus hint at a regular star formation history in the group over a Hubble time. While at first glance the HST data show the galaxies as undisturbed, our deep ground-based, wide-field imaging that extends the HST coverage reveals faint signatures of stellar material in the intragroup medium (IGM). We do not, however, detect the IGM in H I or Chandra X-ray observations, signatures that would be expected to arise from major mergers. Despite this fact, we find that the H I gas content of the individual galaxies and the group as a whole are a third of the expected abundance. The appearance of quiescence is challenged by spectroscopy that reveals an intense ionization continuum in one galaxy nucleus, and post-burst characteristics in another. Our spectroscopic survey of dwarf galaxy members yields a single dwarf elliptical galaxy in an apparent stellar tidal feature. Based on all this information, we suggest an evolutionary scenario for HCG 7, whereby the galaxies convert most of their available gas into stars without the influence of major mergers and ultimately result in a dry merger. As the conditions governing compact groups are reminiscent of galaxies at intermediate redshift, we propose that HCGs are appropriate for studying galaxy evolution at z {approx} 1-2.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

LOW-METALLICITY STAR FORMATION IN HIGH-REDSHIFT GALAXIES AT z {approx} 8

Based on the recent very deep near-infrared imaging of the Hubble Ultra Deep Field with WFC3 on the Hubble Space Telescope, five groups published the most probable samples of galaxies at z {approx} 8, selected by the so-called dropout method or photometric redshift; e.g., Y{sub 105}-dropouts (Y{sub 105} - J{sub 125} > 0.8). These studies are highly useful for investigating both the early star formation history of galaxies and the sources of cosmic re-ionization. In order to better understand these issues, we carefully examine whether there are low-z interlopers in the samples of z {approx} 8 galaxy candidates. We focus on the strong emission-line galaxies at z {approx} 2 in this paper. Such galaxies may be selected as Y{sub 105}-dropouts since the [O III] {lambda}5007 emission line is redshifted into the J{sub 125} band. We have found that the contamination from such low-z interlopers is negligibly small. Therefore, all objects found by the five groups are free from this type of contamination. However, it remains difficult to extract real z {approx} 8 galaxies because all the sources are very faint and the different groups have found different candidates. With this in mind, we construct a robust sample of eight galaxies at z {approx} 8 from the objects found by the five groups: each of these eight objects has been selected by at least two groups. Using this sample, we discuss their UV continuum slope. We also discuss the escape fraction of ionizing photons adopting various metallicities. Our analysis suggests that massive stars forming in low-metallicity gas (Z {approx} 5 x 10{sup -4} Z{sub sun}) can be responsible for the completion of cosmic re-ionization if the escape fraction of the ionizing continuum from galaxies is as large as 0.5, and this is consistent with the observed blue UV continua.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE RED NOVA-LIKE VARIABLE IN M31-A BLUE CANDIDATE IN QUIESCENCE

M31-RV was an extraordinarily luminous ({approx}10{sup 6} L{sub sun}) eruptive variable, displaying very cool temperatures (roughly 1000 K) as it faded. While this object's peak luminosity matched or exceeded those of the brightest known classical novae, its red colors and cool spectra were very different from those of classical novae. The photometric behavior of M31-RV (and several other very red novae, i.e., luminous eruptive red variables) has led to several models of this apparently new class of astrophysical object. We list these models, which predict very red eruptions and very red remnants decades after the eruptions. One of the most detailed models is that of 'mergebursts'. Mergebursts are (hypothetical) mergers of close binary stars, predicted to rival or exceed the brightest classical novae in luminosity, but to be much cooler and redder than classical novae, and to become slowly hotter and bluer as they age. This prediction suggests two stringent and definitive tests of the mergeburst hypothesis. First, there should always be a cool red remnant, and NOT a hot blue remnant at the site of such an outburst. Second, the inflated envelope of a mergeburst event should be slowly contracting; hence, it must display a slowly rising effective temperature. We have searched the location of M31-RV in multiple observatory archives. Our search revealed a luminous, UV-bright object within 0.''4 (1.5{sigma} of the astrometric position) of M31-RV in archival WFPC2 images taken 10 years after the outburst. Recent Hubble imagery, 20 years after the outburst, determines that this object is still hot and fading; it remains much too hot to be a mergeburst. Furthermore, the effective temperature of this object is declining, contrary to the prediction for mergebursts. If we have correctly identified M31-RV's remnant, it cannot be a mergeburst-but its behavior is consistent with theoretical nova models which erupt on a low-mass white dwarf. Future Hubble UV and visible images could determine if the M31-RV analogs (in M85 and in M99) are also much more blue than mergeburst theory predicts, and if they, too, are cooling in contradiction to mergeburst theory.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

High-Resolution Spectroscopy of Feige 24 in the Extreme-Ultraviolet

We report the first high-resolution (R = 4000) spectroscopic observation of the binary DA white dwarf Feige 24 in the extreme-ultraviolet band 220-250 {angstrom}. A stellar atmosphere model assuming a homogeneous element distribution yields a best fit to the data that excludes a significant abundance of photospheric helium. The upper limit on the photospheric helium abundance is 2.5 x 10{sup -6} (90% confidence), equivalent to a lower limit of 1.2 x 10{sup -13} M {sub {circle_dot}} on the overlying layer of hydrogen. An ionized interstellar He component (3.9 x 1017 cm{sup -2}) is clearly present along the line of sight, which implies an He ionization fraction of 0.72, considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption line doublet in a Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE DISCOVERY AND NATURE OF THE OPTICAL TRANSIENT CSS100217:102913+404220

We report on the discovery and observations of the extremely luminous optical transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic observations showed that this transient was coincident with a galaxy at redshift z = 0.147 and reached an apparent magnitude of V {approx} 16.3. After correcting for foreground Galactic extinction we determine the absolute magnitude to be M{sub V} = -22.7 approximately 45 days after maximum light. Over a period of 287 rest-frame days, this event had an integrated bolometric luminosity of 1.3 x 10{sup 52} erg based on time-averaged bolometric corrections of {approx}15 from V- and R-band observations. Analysis of the pre-outburst Sloan Digital Sky Survey (SDSS) spectrum of the source shows features consistent with a narrow-line Seyfert 1 galaxy. High-resolution Hubble Space Telescope and Keck follow-up observations show that the event occurred within 150 pc of the nucleus of the galaxy, suggesting a possible link to the active nuclear region. However, the rapid outburst along with photometric and spectroscopic evolution are much more consistent with a luminous supernova. Line diagnostics suggest that the host galaxy is undergoing significant star formation. We use extensive follow-up of the event along with archival Catalina Sky Survey NEO search and SDSS data to investigate the three most likely sources of such an event: (1) an extremely luminous supernova, (2) the tidal disruption of a star by the massive nuclear black hole, and (3) variability of the central active galactic nucleus (AGN). We find that CSS100217 was likely an extremely luminous Type IIn supernova and occurred within the range of the narrow-line region of an AGN. We discuss how similar events may have been missed in past supernova surveys because of confusion with AGN activity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

H II REGION LUMINOSITY FUNCTION OF THE INTERACTING GALAXY M51

We present a study of H II regions in M51 using the Hubble Space Telescope Advanced Camera for Surveys images taken as part of the Hubble Heritage Program. We have cataloged about 19,600 H II regions in M51 with H{alpha} luminosity in the range of L = 10{sup 35.5}-10{sup 39.0} erg s{sup -1}. The H{alpha} luminosity function of H II regions (H II LF) in M51 is well represented by a double power law with its index {alpha} = -2.25 {+-} 0.02 for the bright part and {alpha} = -1.42 {+-} 0.01 for the faint part, separated at a break point L = 10{sup 37.1} erg s{sup -1}. This break was not found in previous studies of M51 H II regions. Comparison with simulated H II LFs suggests that this break is caused by the transition of H II region ionizing sources, from low-mass clusters (with {approx}10{sup 3} M{sub sun}, including several OB stars) to more massive clusters (including several tens of OB stars). The H II LFs with L < 10{sup 37.1} erg s{sup -1}are found to have different slopes for different parts in M51: the H II LF for the interarm region is steeper than those for the arm and the nuclear regions. This observed difference in H II LFs can be explained by evolutionary effects: H II regions in the interarm region are relatively older than those in the other parts of M51.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Photometric type Ia supernova candidates from the three-year SDSS-II SN survey data

We analyze the three-year Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey data and identify a sample of 1070 photometric Type Ia supernova (SN Ia) candidates based on their multiband light curve data. This sample consists of SN candidates with no spectroscopic confirmation, with a subset of 210 candidates having spectroscopic redshifts of their host galaxies measured while the remaining 860 candidates are purely photometric in their identification. We describe a method for estimating the efficiency and purity of photometric SN Ia classification when spectroscopic confirmation of only a limited sample is available, and demonstrate that SN Ia candidates from SDSS-II can be identified photometrically with {approx}91% efficiency and with a contamination of {approx}6%. Although this is the largest uniform sample of SN candidates to date for studying photometric identification, we find that a larger spectroscopic sample of contaminating sources is required to obtain a better characterization of the background events. A Hubble diagram using SN candidates with no spectroscopic confirmation, but with host galaxy spectroscopic redshifts, yields a distance modulus dispersion that is only {approx}20%-40% larger than that of the spectroscopically confirmed SN Ia sample alone with no significant bias. A Hubble diagram with purely photometric classification and redshift-distance measurements, however, exhibits biases that require further investigation for precision cosmology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

PHOTOMETRIC TYPE Ia SUPERNOVA CANDIDATES FROM THE THREE-YEAR SDSS-II SN SURVEY DATA

We analyze the three-year Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey data and identify a sample of 1070 photometric Type Ia supernova (SN Ia) candidates based on their multiband light curve data. This sample consists of SN candidates with no spectroscopic confirmation, with a subset of 210 candidates having spectroscopic redshifts of their host galaxies measured while the remaining 860 candidates are purely photometric in their identification. We describe a method for estimating the efficiency and purity of photometric SN Ia classification when spectroscopic confirmation of only a limited sample is available, and demonstrate that SN Ia candidates from SDSS-II can be identified photometrically with {approx}91% efficiency and with a contamination of {approx}6%. Although this is the largest uniform sample of SN candidates to date for studying photometric identification, we find that a larger spectroscopic sample of contaminating sources is required to obtain a better characterization of the background events. A Hubble diagram using SN candidates with no spectroscopic confirmation, but with host galaxy spectroscopic redshifts, yields a distance modulus dispersion that is only {approx}20%-40% larger than that of the spectroscopically confirmed SN Ia sample alone with no significant bias. A Hubble diagram with purely photometric classification and redshift-distance measurements, however, exhibits biases that require further investigation for precision cosmology.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

GALAXY STRUCTURE AND MODE OF STAR FORMATION IN THE SFR-MASS PLANE FROM z {approx} 2.5 TO z {approx} 0.1

We analyze the dependence of galaxy structure (size and Sersic index) and mode of star formation ({Sigma}{sub SFR} and SFR{sub IR}/SFR{sub UV}) on the position of galaxies in the star formation rate (SFR) versus mass diagram. Our sample comprises roughly 640,000 galaxies at z {approx} 0.1, 130,000 galaxies at z {approx} 1, and 36,000 galaxies at z {approx} 2. Structural measurements for all but the z {approx} 0.1 galaxies are based on Hubble Space Telescope imaging, and SFRs are derived using a Herschel-calibrated ladder of SFR indicators. We find that a correlation between the structure and stellar population of galaxies (i.e., a 'Hubble sequence') is already in place since at least z {approx} 2.5. At all epochs, typical star-forming galaxies on the main sequence are well approximated by exponential disks, while the profiles of quiescent galaxies are better described by de Vaucouleurs profiles. In the upper envelope of the main sequence, the relation between the SFR and Sersic index reverses, suggesting a rapid buildup of the central mass concentration in these starbursting outliers. We observe quiescent, moderately and highly star-forming systems to co-exist over an order of magnitude or more in stellar mass. At each mass and redshift, galaxies on the main sequence have the largest size. The rate of size growth correlates with specific SFR, and so does {Sigma}{sub SFR} at each redshift. A simple model using an empirically determined star formation law and metallicity scaling, in combination with an assumed geometry for dust and stars, is able to relate the observed {Sigma}{sub SFR} and SFR{sub IR}/SFR{sub UV}, provided a more patchy dust geometry is assumed for high-redshift galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE REST-FRAME ULTRAVIOLET LIGHT PROFILE SHAPES OF Ly{alpha}-EMITTING GALAXIES AT z = 3.1

We present a morphological analysis of the rest-frame ultraviolet emission of 78 resolved, high signal-to-noise z {approx} 3.1 Ly{alpha} emitters (LAEs) in the Extended Chandra Deep Field-South. Using Hubble Space Telescope/Advanced Camera for Surveys V-band images taken as part of the Galaxy Evolution from Morphology and SEDs, Great Observatories Origins Deep Survey, and Hubble Ultra Deep Field surveys, we investigate both single-component and multi-component LAEs, and derive concentration indices, Sersic indices, ellipticities, and half-light radii for all resolved components and systems with a signal-to-noise >30. We show that, although the LAE population is heterogeneous in nature, most LAEs are highly concentrated, with a distribution of C values similar to that measured for field stars; this suggests that the diagnostic is a poor discriminator near the resolution limit. The LAEs also display a wide range of Sersic indices (0 < n < 12), similar to that seen for galaxies in the local neighborhood. However, the majority of LAEs have n < 2, and a visual inspection of the images suggests that the small-n objects have extended or multimodal luminosity profiles, while the LAEs with n > 2 have compact components surrounded by diffuse emission. Moreover, unlike nearby spiral galaxies, whose distribution of ellipticities is flat, the LAE ellipticity distribution peaks near 1 - b/a {approx} 0.55. Thus, the population has more in common with z {approx} 3 Lyman-break galaxies than local star-forming objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ACTIVE AND PASSIVE GALAXIES AT z {approx} 2: REST-FRAME OPTICAL MORPHOLOGIES WITH WFC3

We use the high angular resolution in the near-infrared of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to determine YHVz color-color-selection criteria to identify and characterize 1.5 < z < 3.5 galaxies in the Hubble Ultra Deep Field 2009 (HUDF09) and Early Release Science (GOODS-South) fields. The WFC3 NIR images reveal galaxies at these redshifts that were undetected in the rest-frame UV HUDF/GOODS images, as well as true centers and regular disks in galaxies classified as highly irregular in rest-frame UV light. Across the 1.5 < z < 2.15 redshift range, regular disks are unveiled in the WFC3 images of {approx}25% of both intermediate and high mass galaxies, i.e., above 10{sup 10} M{sub Sun }. Meanwhile, galaxies maintaining diffuse and/or irregular morphologies in the rest-frame optical light-i.e., not yet dynamically settled-at these epochs are almost entirely restricted to masses below 10{sup 11} M{sub Sun }. In contrast at 2.25 < z < 3.5 these diffuse and/or irregular structures overwhelmingly dominate the morphological mix in both the intermediate and high mass regimes, while no regular disks, and only a small fraction ({approx}25%) of smooth spheroids, are evident above 10{sup 11} M{sub Sun }. Strikingly, by 1.5 < z < 2.25 roughly two out of every three galaxies at the highest masses are spheroids. In our small sample, the fraction of star-forming galaxies at these mass scales decreases concurrently from {approx}60% to {approx}5%. If confirmed, this indicates that z {approx} 2 is the epoch of both the morphological transformation and quenching of star formation which assemble the first substantial population of massive ellipticals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE COSMIC ORIGINS SPECTROGRAPH

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in 2009 May, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F{sub {lambda}} Almost-Equal-To 1.0 Multiplication-Sign 10{sup -14} erg cm{sup -2} s{sup -1} A{sup -1}, COS can achieve comparable signal to noise (when compared to Space Telescope Imaging Spectrograph echelle modes) in 1%-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (2009 September-2011 June) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is nine times than sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of 2011 June. COS has measured, for the first time with high reliability, broad Ly{alpha} absorbers and Ne VIII in the intergalactic medium, and observed the He II reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗