Astronomy

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The Arizona CDFS Environment Survey (ACES): A Magellan/IMACS Spectroscopic Survey of the Chandra Deep Field-South*
(The American Astronomical Society, 2012) Cooper, M.C.; Yan, R.; Dickinson, M.; Juneau, S.; Lotz, J.M.; Newman, J.A.; Papovich, C.; Salim, S.; Walth, G.; Weiner, B.J.; Willmer, C.N.A.
We present the Arizona CDFS Environment Survey (ACES), a recently completed spectroscopic redshift survey of the Chandra Deep Field-South (CDFS) conducted using the Inamori-Magellan Areal Camera and Spectrograph on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of $R_{AB} = 24.1$, yielding 5080 secure redshifts across the $\sim30 arcmin × 30 arcmin$ extended CDFS region. The ACES data set delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously published spectroscopic redshifts, ACES now creates a highly complete survey of the galaxy population at $R < 23$, enabling the local galaxy density (or environment) on relatively small scales ($\sim 1 \text{Mpc}$) to be measured at $z < 1$ in one of the most heavily studied and data-rich fields in the sky. Here, we describe the motivation, design and implementation of the survey and present a preliminary redshift and environment catalogue. In addition, we utilize the ACES spectroscopic redshift catalogue to assess the quality of photometric redshifts from both the COMBO-17 and Multiwavelength Survey by Yale-Chile imaging surveys of the CDFS.
Average metallicity and star formation rate of Ly$\alpha$ emitters probed by a triple narrowband survey*
(The American Astronomical Society, 2012) Nakajima, K.; Ouchi, M.; Shimasaku, K.; Ono, Y.; Lee, J.C.; Foucad, S.; Ly, C.; Dale, D.A.; Salim, S.; Finn, R.; Almaini, O.; Okamura, S.
We present the average metallicity and star formation rate (SFR) of $Ly\alpha$ emitters (LAEs) measured from our large-area survey with three narrowband (NB) filters covering the $Ly\alpha, \big[O II\big]\lambda3727$, and $\text{H}\alpha+\big[\text{N} II\big]$ lines of LAEs at $z = 2.2$. We select 919 $z = 2.2$ LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted $\big[\text{O} II\big]$ and $\text{H}\alpha$ nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by NB imaging or deep spectroscopy. The stacked object has an Hα luminosity of $1.7 × 10^{42} erg s^{–1}$ corresponding to an SFR of $14 M_{\odot} yr6{–1}$. We place, for the first time, a firm lower limit to the average metallicity of LAEs of $Z \gtrsim 0.09 Z_{\odot} \big(2\sigma\big)$ based on the $\big[\text{O} II\big]/\big(\text{H}\alpha+\big[\text{N} II\big]\big)$ index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at $z \sim 2$, are extremely metal-poor $\big(Z < 2 × 10–2 Z_{\odot}\big)$ galaxies at the $4\sigma$ level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of $z \sim 2$ UV-selected galaxies toward lower masses $\big(5 × 108 M_{\odot}\big)$, but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The $\text{H}\alpha$ and $\text{Ly}\alpha$ luminosities of our NB-selected LAEs indicate that the escape fraction of $\text{Ly}\alpha$ photons is $\sim12%-30%$, much higher than the values derived for other galaxy populations at $z \sim 2$.
Calibrating the star formation rate at $z \sim 1$ from optical data
(The American Astronomical Society, 2012) Mostek, N.; Coil, A.L.; Moustakas, J.; Salim, S.; Weiner, B.J.
We present a star formation rate (SFR) calibration based on optical data that is consistent with average observed rates in both the red and blue galaxy populations at $z \sim 1$. The motivation for this study is to calculate SFRs for DEEP2 Redshift Survey galaxies in the $0.7 < z < 1.4$ redshift range, but our results are generally applicable to similar optically selected galaxy samples without requiring UV or IR data. Using SFR fits from UV/optical spectral energy distributions (SEDs) in the All-Wavelength Extended Groth Strip International Survey, we explore the behavior of rest-frame B-band magnitude, observed [O II] luminosity, and rest-frame color with SED-fit SFR for both red sequence and blue cloud galaxies. The resulting SFR calibration is based on three optical-band observables: $M_{B} , \big(U – B\big)$, and $\big(B – V\big)$. The best-fit linear relation produces residual errors of 0.3 dex rms scatter for the full color-independent sample with minimal correlated residual error in $L\big[O_{II}\big]$ or stellar mass. We then compare the calibrated $z \sim 1$ SFRs to two diagnostics that use $L\big[O_{II}\big]$ as a tracer in local galaxies and correct for dust extinction at intermediate redshifts through either galaxy $B$-band luminosity or stellar mass. We find that an$ L\big[O_{II}\big]-M_{B}$ SFR calibration commonly used in the literature agrees well with our calculated SFRs after correcting for the average B-band luminosity evolution in $L_{*}$ galaxies. However, we find better agreement with a local $L\big[O_{II}\big]$-based SFR calibration that includes stellar mass to correct for reddening effects, indicating that stellar mass is a better tracer of dust extinction for all galaxy types and less affected by systematic evolution than galaxy luminosity from $z = 1$ to the current epoch.
Convergence studies of mass transport in disks with gravitational instabilities. I. the constant cooling time case
(The American Astronomical Society, 2012) Michael, S.; Steiman-Cameron, T.Y.; Durisen, R.H.; Boley, A.C.
We conduct a convergence study of a protostellar disk, subject to a constant global cooling time and susceptible to gravitational instabilities (GIs), at a time when heating and cooling are roughly balanced. Our goal is to determine the gravitational torques produced by GIs, the level to which transport can be represented by a simple α-disk formulation, and to examine fragmentation criteria. Four simulations are conducted, identical except for the number of azimuthal computational grid points used. A Fourier decomposition of non-axisymmetric density structures in cos ($m\phi$), sin ($m\phi$) is performed to evaluate the amplitudes $A_{m}$ of these structures. The $A_{m}$, gravitational torques, and the effective Shakura & Sunyaev α arising from gravitational stresses are determined for each resolution. We find nonzero $A_{m}$ for all $m$-values and that $A_{m}$ summed over all $m$ is essentially independent of resolution. Because the number of measurable $m$-values is limited to half the number of azimuthal grid points, higher-resolution simulations have a larger fraction of their total amplitude in higher-order structures. These structures act more locally than lower-order structures. Therefore, as the resolution increases the total gravitational stress decreases as well, leading higher-resolution simulations to experience weaker average gravitational torques than lower-resolution simulations. The effective $\alpha$ also depends upon the magnitude of the stresses, thus $\alpha_{\text{eff}}$ also decreases with increasing resolution. Our converged $\alpha_{\text{eff}}$ is consistent with predictions from an analytic local theory for thin disks by Gammie, but only over many dynamic times when averaged over a substantial volume of the disk.
Deep ultraviolet luminosity functions at the infall region of the coma cluster
(The American Astronomical Society, 2012) Salim, S.; Hammer, D.M.; Hornschemeier, A.E.; Smith, R.; Jenkins, L.; Mobasher, B.; Miller, N.; Ferguson, H.
We have used deep $\textit{GALEX}$ observations at the infall region of the Coma cluster to measure the faintest ultraviolet (UV) luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are measured to $M_{UV} = –10.5$ in the $\textit{GALEX}$ FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach the dwarf early-type galaxy population in Coma for the first time. The Schechter faint-end slopes ($\alpha \approx –1.39$ in both $\textit{GALEX}$ bands) are shallower than reported in previous Coma UV LF studies owing to a flatter LF at faint magnitudes. A Gaussian-plus-Schechter model provides a slightly better parameterization of the UV LFs resulting in a faint-end slope of $\alpha \approx –1.15$ in both $\textit{GALEX}$ bands. The two-component model gives faint-end slopes shallower than $\alpha = –1$ (a turnover) for the LFs constructed separately for passive and star-forming galaxies. The UV LFs for star-forming galaxies show a turnover at $M_{UV} \approx –14$ owing to a deficit of dwarf star-forming galaxies in Coma with stellar masses below $M_{*} = 108 M_{\odot}$. A similar turnover is identified in recent UV LFs measured for the Virgo cluster suggesting this may be a common feature of local galaxy clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did not identify an excess of passive galaxies as would be expected if the missing dwarf star-forming galaxies were quenched inside the cluster. In fact, the LFs for both dwarf passive and star-forming galaxies show the same turnover at faint magnitudes. We discuss the possible origin of the missing dwarf star-forming galaxies in Coma and their expected properties based on comparisons to local field galaxies.
The dependence of quenching upon the inner structure of galaxies at 0.5 ≤ $z$ < 0.8 in the DEEP2/AEGIS survey
(The American Astronomical Society, 2012) Cheung, E.; Faber, S.M.; Koo, D.C.; Dutton, A.A.; Simard, L.; McGrath, E.J.; Huang, J.-S.; Bell, E.F.; Dekel, A.; Fang, J.J.; Salim, S.; Barro, G.; Bundy, K.; Coil, A.L.; Cooper, M.C.; Conselice, C.J.; Davis, M.; Domínguez, A.; Kassin, S.A.; Kocevski, D.D.; Koekemoer, A.M.; Lin, L.; Lotz, J.M.; Newman, J.a.; Phillips, A.C.; Rosario, D.J.; Weiner, B.J.; Willmer, C.N.A.
The shutdown of star formation in galaxies is generally termed "quenching." Quenching may occur through a variety of processes, e.g., active galactic nucleus (AGN) feedback, stellar feedback, or the shock heating of gas in the dark matter halo. However, which mechanism(s) is, in fact, responsible for quenching is still in question. This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy structural parameters such as stellar mass ($M_{\ast }$), $M_{\ast }/r_{e}$, surface stellar mass density ($\sim M_{\ast }/r^{2}_{e}$), and Sérsic index ($n$). We analyze the rest-frame $U - B$ color correlations versus these structural parameters using a sample of galaxies in the redshift range $0.5 \lesssim z < 0.8$ from the DEEP2/AEGIS survey. In addition to global radii, stellar masses, and Sérsic parameters, we also use "bulge" and "disk" photometric measurements from GIM2D fits to $\textit{HST/ACS V}$ and $I$ images. We assess the tightness of the color relationships by measuring their "overlap regions," defined as the area in color-parameter space in which red and blue galaxies overlap; the parameter that minimizes these overlap regions is considered to be the most effective color discriminator. We find that Sérsic index ($n$) has the smallest overlap region among all tested parameters and resembles a step function with a threshold value of $n$ = 2.3. There exists, however, a significant population of outliers with blue colors yet high n values that seem to contradict this behavior; they make up $\approx$ 40% of $n$ > 2.3 galaxies. We hypothesize that their Sérsic values may be distorted by bursts of star formation, AGNs, and/or poor fits, leading us to consider central surface stellar mass density, $\sum^{\ast }_{1 \:\text{kpc}}$, as an alternative to Sérsic index. Not only does $\sum^{\ast }_{1 \:\text{kpc}}$ correct the outliers, but it also forms a tight relationship with color, suggesting that the $\textit{innermost structure of galaxies is most physically linked with quenching}$. Furthermore, at $z \sim 0.65$, the majority of the blue cloud galaxies cannot simply fade onto the red sequence since their GIM2D bulge masses are only half as large on average as the bulge masses of similar red sequence galaxies, thus demonstrating that stellar mass must absolutely increase at the centers of galaxies as they quench. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass buildup. The mass buildup is naturally explained by any non-axisymmetric features in the potential, such as those induced by mergers and/or disk instabilities. However, the identity of the second quenching agent is still unknown. We have placed our data catalog online
Direct oxygen abundances for low-luminosity LVL galaxies
(The American Astronomical Society, 2012) Berg, D.A.; Skillman, E.D.; Marble, A.R.; Van Zee, L.; Engelbracht, C.W.; Lee, J.C.; Kennicutt, R.C.; Calzetti, D.; Dale, D.A.; Johnson, B.D.
We present MMT spectroscopic observations of H II regions in 42 low luminosity galaxies in the Spitzer Local Volume Legacy survey. For 31 of the 42 galaxies in our sample, we were able to measure the temperature sensitive [O III] $\lambda$4363 line at a strength of $4\sigma$ or greater, and thus determine oxygen abundances using the "direct" method. Our results provide the first "direct" estimates of oxygen abundance for 19 of these galaxies. "Direct" oxygen abundances were compared to $B$-band luminosities, 4.5 $\mu$m luminosities, and stellar masses in order to characterize the luminosity-metallicity and mass-metallicity relationships at low luminosity. We present and analyze a "Combined Select" sample composed of 38 objects (drawn from a sub-set of our parent sample and the literature) with "direct" oxygen abundances and reliable distance determinations (based on the tip of the red giant branch or Cepheid variables). Consistent with previous studies, the $B$ band and 4.5 $\mu$m luminosity-metallicity relationships for the 38 objects were found to be$12 + log(O/H) = (6.27 \pm 0.21) + (- 0.11 \pm 0.01)M_{B}$and$12+log(O/H) = (6.10 \pm 0.21) + (- 0.10 \pm 0.01)M_{[4.5]}$with dispersions of $\sigma$ = 0.15 and 0.14, respectively. The slopes of the optical and near-IR L-Z relationships have been reported to be different for galaxies with luminosities greater than that of the LMC. However, the similarity of the slopes of the optical and near-IR L-Z relationships for our sample probably reflects little influence by dust extinction in the low luminosity galaxies. For this sample, we derive a mass-metallicity relationship of $12 + log\big(O/H\big) = \big(5.61 \pm 0.24\big) + \big(0.29 \pm 0.03\big)log \big(M_{\star}\big)$, which agrees with previous studies; however, the dispersion ($\sigma$ = 0.15) is not significantly lower than that of the L-Z relationships. Because of the low dispersions in these relationships, if an accurate distance is available, the luminosity of a low luminosity galaxy is often a better indicator of metallicity than that derived using certain "strong-line" methods, so significant departures from the L-Z relationships may indicate that caution is prudent in such cases. With these new "direct" metallicities we also revisit the 70/160 $\mu$m color metallicity relationship. Additionally, we examine N/O abundance trends with respect to oxygen abundance and B - V color. We find a positive correlation between N/O ratio and B - V color for $0.05 \lesssim B - V \lesssim 0.75: log (N/O) = (1.18 \pm 0.9\big) × (B - V) + (- 1.92 \pm 0.08)$, with a dispersion of $\sigma$ = 0.14, which is in agreement with previous studies.
Elemental abundance ratios in stars of the outer galactic disk. IV. A new sample of open clusters
(The American Astronomical Society, 2012) Yong, D.; Carney, B.W.; Friel, E.D.
We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be18, Be21, Be22, Be32, and PWM4. For Be18 and PWM4, these are the first chemical abundance measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. For this combined sample, we study the chemical abundances of open clusters as a function of distance, age, and metallicity. We confirm that the metallicity gradient in the outer disk is flatter than the gradient in the vicinity of the solar neighborhood. We also confirm that the open clusters in the outer disk are metal-poor with enhancements in the ratios [$\alpha$/Fe] and perhaps [Eu/Fe]. All elements show negligible or small trends between [X/Fe] and distance (<0.02dexkpc$^{-1}$), but for some elements, there is a hint that the local (R$_{GC}$< 13kpc) and distant (R$_{GC}$> 13kpc) samples may have different trends with distance. There is no evidence for significant abundance trends versus age (<0.04dex Gyr$^{-1}$). We measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find that the scatter about the mean trend is comparable to the measurement uncertainties. Comparison with solar neighborhood field giants shows that the open clusters share similar abundance ratios [X/Fe] at a given metallicity. While the flattening of the metallicity gradient and enhanced [$\alpha$/Fe] ratios in the outer disk suggest a chemical enrichment history different from that of the solar neighborhood, we echo the sentiments expressed by Friel etal. that definitive conclusions await homogeneous analyses of larger samples of stars in larger numbers of clusters. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.
Exploring the correlations between globular cluster populations and supermassive black holes in giant galaxies
(The American Astronomical Society, 2012) Rhode, K.L.
This paper presents an analysis of the correlation between the number of globular clusters ($N_{GC}$) in giant galaxies and the mass of the galaxies' central supermassive black hole ( $M_{SMBH}$). I construct a sample of 20 elliptical, spiral, and S0 galaxies with known SMBH masses and with accurately measured GC system properties derived from wide-field imaging studies. The coefficients of the best-fitting $N_{GC}-M_{SMBH}$ relation for the early-type galaxies are consistent with those from previous work but in some cases have smaller relative errors. I examine the correlation between $N_{GC}$ and $M_{SMBH}$ for various subsamples and find that elliptical galaxies show the strongest correlation, while S0 and pseudobulge galaxies exhibit increased scatter. I also compare the quality of the fit of the numbers of metal-poor GCs versus SMBH mass and the corresponding fit for metal-rich GCs. I supplement the 20 galaxy sample with 10 additional galaxies with reliable $N_{GC}$ determinations but without measured $M_{SMBH}$. I use this larger sample to investigate correlations between $N_{GC}$ and host galaxy properties like total galaxy luminosity and stellar mass, and bulge luminosity and mass. I find that the tightest correlation is between $N_{GC}$ and total galaxy stellar mass. This lends support to the notion that $N_{GC}$ and $M_{SMBH}$ are not directly linked but are correlated because both quantities depend on the host galaxy potential. Finally, I use the $N_{GC}-M_{SMBH}$ relation derived from the 20 galaxy sample to calculate predicted $M_{SMBH}$ values for the 10 galaxies with accurate $N_{GC}$ measurements but without measured SMBH masses.
Galaxy-scale star formation on the red sequence: The continued growth of S0s and the quiescence of ellipticals
(The American Astronomical Society, 2012) Salim, S.; Fang, J.J.; Rich, R.M.; Faber, S.M.; Thilker, D.A.
This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at $z \sim 0.1$. A sample is drawn from bulge-dominated Galaxy Evolution Explorer/Sloan Digital Sky Survey (GALEX/SDSS) galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such ETGs using Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) reveals structured UV morphology in 93% of the sample, consistent with low-level ongoing SF ($\sim0.5 M_{\odot} yr^{–1}$). In 3/4 of the sample the SF is extended on galaxy scales (25-75 kpc), while the rest contains smaller (5-15 kpc) SF patches in the vicinity of an ETG—presumably gas-rich satellites being disrupted. Optical imaging reveals that all ETGs with galaxy-scale SF in our sample have old stellar disks (mostly S0 type). None is classified as a true elliptical. In our sample, galaxy-scale SF takes the form of UV rings of varying sizes and morphologies. For the majority of such objects we conclude that the gas needed to fuel current SF has been accreted from the intergalactic medium, probably in a prolonged, quasi-static manner, leading in some cases to additional disk buildup. The remaining ETGs with galaxy-scale SF have UV and optical morphologies consistent with minor merger-driven SF or with the final stages of SF in fading spirals. Our analysis excludes that all recent SF on the red sequence resulted from gas-rich mergers. We find further evidence that galaxy-scale SF is almost exclusively an S0 phenomenon ($\sim$20% S0s have SF) by examining the overall optically red SDSS ETGs. Conclusion is that significant number of field S0s maintain or resume low-level SF because the preventive feedback is not in place or is intermittent. True ellipticals, on the other hand, stay entirely quiescent even in the field.
Generic effective source for scalar self-force calculations
(American Physical Society, 2012) Wardell, B.; Vega, I.; Thornburg, J.; Diener, P.
A leading approach to the modeling of extreme mass ratio inspirals involves the treatment of the smaller mass as a point particle and the computation of a regularized self-force acting on that particle. In turn, this computation requires knowledge of the regularized retarded field generated by the particle. A direct calculation of this regularized field may be achieved by replacing the point particle with an effective source and solving directly a wave equation for the regularized field. This has the advantage that all quantities are finite and require no further regularization. In this work, we present a method for computing an effective source which is finite and continuous everywhere, and which is valid for a scalar point particle in arbitrary geodesic motion in an arbitrary background spacetime. We explain in detail various technical and practical considerations that underlie its use in several numerical self-force calculations. We consider as examples the cases of a particle in a circular orbit about Schwarzschild and Kerr black holes, and also the case of a particle following a generic timelike geodesic about a highly spinning Kerr black hole. We provide numerical C code for computing an effective source for various orbital configurations about Schwarzschild and Kerr black holes.
The globular cluster populations of giant galaxies: Mosaic imaging of five moderate-luminosity early-type galaxies
(The American Astronomical Society, 2012) Hargis, J.R.; Rhode, K.L.
This paper presents results from wide-field imaging of the globular cluster (GC) systems of five intermediate-luminosity ($M_{V}$ ~ –21 to –22) early-type galaxies. The aim is to accurately quantify the global properties of the GC systems by measuring them out to large radii. We obtained BVR imaging of four lenticular galaxies (NGC 5866, NGC 4762, NGC 4754, NGC 3384) and one elliptical galaxy (NGC 5813) using the KPNO 4 m telescope and Mosaic imager and traced the GC population to projected galactocentric radii ranging from ~20 kpc to 120 kpc. We combine our imaging with Hubble Space Telescope data to measure the GC surface density close to the galaxy center. We calculate the total number of GCs (N GC) from the integrated radial profile and find $N_{GC}$ = 340 ± 80 for NGC 5866, $N_{GC}$ = 2900 ± 400 for NGC 5813, $N_{GC}$ = 270 ± 30 for NGC 4762, $N_{GC}$ = 115 ± 15 for NGC 4754, and $N_{GC}$ = 120 ± 30 for NGC 3384. The measured GC specific frequencies are SN between 0.6 and 3.6 and T in the range 0.9-4.2. These values are consistent with the mean specific frequencies for the galaxies' morphological types found by our survey and other published data. Three galaxies (NGC 5866, NGC 5813, and NGC 4762) had sufficient numbers of GC candidates to investigate color bimodality and color gradients in the GC systems. NGC 5813 shows strong evidence (>3σ) for bimodality and a B – R color gradient resulting from a more centrally concentrated red (metal-rich) GC subpopulation. We find no evidence for statistically significant color gradients in the other two galaxies.
Globular cluster systems of spiral and S0 galaxies: Results from WIYN imaging of NGC1023, NGC1055, NGC7332, and NGC7339
(The American Astronomical Society, 2012) Young, M.D.; Dowell, J.L.; Rhode, K.L.
We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies - the SB0 galaxy NGC1023, the SBb galaxy NGC1055, and an isolated pair comprised of the Sbc galaxy NGC7339 and the S0 galaxy NGC7332 - were observed in BVR filters with the WIYN 3.5m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously published data from the $\textit{Hubble Space Telescope}$ and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs ($N_{GC}$). We find $N_{GC}$ = 490 ± 30, 210 ± 40, 175 ± 15, and 75 ± 10 for NGC1023, NGC1055, NGC7332, and NGC7339, respectively. We also calculate the GC specific frequency (N GC normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. The two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the $B - R$ distribution of the GC system of NGC1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC1023A, which is a satellite of NGC1023.
The infrared light curve of SN 2011fe in M101 and the distance to M101
(The American Astronomical Society, 2012) Matheson, T.; Joyce, R.R.; Allen, L.E.; Saha, A.; Silva, D.R.; Wood-Vasey, W.M.; Adams, J.J.; Anderson, R.E.; Beck, T.L.; Bentz, M.C.; Bershady, M.A.; Binkert, W.S.; Butler, K.; Camarata, M.A.; Eigenbrot, A.; Everett, M.; Gallagher, J.S.; Garnavich, P.M.; Glikman, E.; Harbeck, D.; Hargis, J.R.; Herbst, H.; Horch, E.P.; Howell, S.B.; Jha, S.; Kaczmarek, J.F.; Knezek, P.; Manne-Nicholas, E.; Mathieu, R.D.; Meixner, M.; Milliman, K.; Power, J.; Rajagopal, J.; Reetz, K.; Rhode, K.L.; Schechtman-Rook, A.; Schwamb, M.E.; Schweiker, H.; Simmons, B.; Simon, J.D.; Summers, D.; Young, M.D.; Weyant, A.; Wilcots, E.M.; Will, G.; Williams, D.
We present near-infrared light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting 14 days before maximum brightness in the B band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera. When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band maximum of 10.85 ± 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used.
Migration of Gas Giant Planets in Gravitationally Unstable Disks
(2011-05-25) Michael, Scott; Durisen, Richard H.; Boley, Aaron C.
Characterization of migration in gravitationally unstable disks is necessary to understand the fate of protoplanets formed by disk instability. As part of a larger study, we are using a 3D radiative hydrodynamics code to investigate how an embedded gas giant planet interacts with a gas disk that undergoes gravitational instabilities (GIs). This Letter presents preliminary results from simulations with a Jupiter-mass planet placed in orbit at 25 AU within a 0.14 M_sun disk. The disk spans 5 to 40 AU around a 1 M_sun star and is initially close to marginal stability. In one simulation, the planet is inserted prior to the eruption of GIs; in another, it is inserted only after the disk has settled into a quasi-steady GI-active state, where heating by GIs roughly balances radiative cooling. When the planet is present from the beginning, its own wake stimulates growth of a particular global mode with which it strongly interacts, and the planet plunges inward six AU in about 1000 years. In both cases with embedded planets, there are times when the planet's radial motion is slow and varies in direction. At other times, when the planet appears to be interacting with strong spiral modes, migration both inward and outward can be relatively rapid, covering several AUs over hundreds of years. Migration in both cases appears to stall near the inner Lindblad resonance of a dominant low-order mode. Planet orbit eccentricities fluctuate rapidly between about 0.02 to 0.1 throughout the GI-active phases of the simulations.
Modeling the effects of star formation histories on H$\alpha$ and ultraviolet fluxes in nearby dwarf galaxies
(The American Astronomical Society, 2012) Weisz, D.R.; Johnson, B.D.; Johnson, L.C.; Skillman, E.D.; Lee, J.C.; Kennicutt, R.C.; Calzetti, D.; Van Zee, L.; Bothwell, M.S.; Dalcanton, J.J.; Dale, D.A.; Williams, B.F.
We consider the effects of non-constant star formation histories (SFHs) on $\text{H}\alpha$ and GALEX far-ultraviolet (FUV) star formation rate (SFR) indicators. Under the assumption of a fully populated Chabrier initial mass function (IMF), we compare the distribution of $\text{H}\alpha$-to-FUV flux ratios from ~1500 simple, periodic model SFHs with observations of 185 galaxies from the $\textit{Spitzer}$ Local Volume Legacy survey. We find a set of SFH models that are well matched to the data, such that more massive galaxies are best characterized by nearly constant SFHs, while low-mass systems experience burst amplitudes of ~30 (i.e., an increase in the SFR by a factor of 30 over the SFR during the inter-burst period), burst durations of tens of Myr, and periods of ~250 Myr; these SFHs are broadly consistent with the increased stochastic star formation expected in systems with lower SFRs. We analyze the predicted temporal evolution of galaxy stellar mass, R-band surface brightness, $\text{H}\alpha$-derived SFR, and blue luminosity, and find that they provide a reasonable match to observed flux distributions. We find that our model SFHs are generally able to reproduce both the observed systematic decline and increased scatter in $\text{H}\alpha$-to-FUV ratios toward low-mass systems, without invoking other physical mechanisms. We also compare our predictions with those from the Integrated Galactic IMF theory with a constant SFR. We find that while both predict a systematic decline in the observed ratios, only the time variable SFH models are capable of producing the observed population of low-mass galaxies $\big(M_{*} \lesssim 10^{7} M_{\odot}\big)$ with normal $\text{H}\alpha$-to-FUV ratios. These results demonstrate that a variable IMF alone has difficulty explaining the observed scatter in the $\text{H}\alpha$-to-FUV ratios. We conclude by considering the limitations of the model SFHs and discuss the use of additional empirical constraints to improve future SFH modeling efforts.
Multiwavelength observations of massive stellar cluster candidates in the galaxy
(The American Astronomical Society, 2012) Richards, E.E.; Lang, C.C.; Trombley, C.; Figer, D.F.
The Galaxy appears to be richer in young, massive stellar clusters than previously known, due to advances in infrared surveys that have uncovered deeply embedded regions of star formation. Young, massive clusters can significantly impact the surrounding interstellar medium (ISM) and hence radio observations can also be an important tracer of their activity. Several hundred cluster candidates are now known by examining survey data. Here, we report on multiwavelength observations of six of these candidates in the Galaxy. We carried out 4.9 and 8.5 GHz Very Large Array observations of the radio emission associated with these clusters to obtain the physical characteristics of the surrounding gas, including the Lyman continuum photon flux and ionized gas mass. $\textit{Spitzer}$ Infrared Array Camera observations were also made of these regions, and provide details on the stellar population as well as the dust continuum and polycyclic aromatic hydrocarbon emission. When compared to the known young, massive clusters in the Galaxy, the six cluster candidates have less powerful Lyman ionizing fluxes and ionize less of the H II mass in the surrounding ISM. Therefore, these cluster candidates appear to be more consistent with intermediate-mass clusters ($10^{3}-10^{4} M_{\odot}$)
Oxygen and sodium abundances in M13 (NGC6205) giants: Linking globular cluster formation scenarios, deep mixing, and post-RGB evolution
(The American Astronomical Society, 2012) Johnson, C.I.; Pilachowski, C.A.
We present O, Na, and Fe abundances, as well as radial velocities, for 113 red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular cluster M13. The abundances and velocities are based on spectra obtained with the WIYN-Hydra spectrograph, and the observations range in luminosity from the horizontal branch (HB) to RGB tip. The results are examined in the context of recent globular cluster formation scenarios. We find that M13 exhibits many key characteristics that suggest its formation and chemical enrichment are well described by current models. Some of these observations include the central concentration of O-poor stars, the notable decrease in [O/Fe] (but small increase in [Na/Fe]) with increasing luminosity that affects primarily the "extreme" population, the small fraction of stars with halo-like composition, and the paucity of O-poor AGB stars. In agreement with recent work, we conclude that the most O-poor M13 giants are likely He-enriched and that most (all?) O-poor RGB stars evolve to become extreme HB and AGB-manqué stars. In contrast, the "primordial" and "intermediate" population stars appear to experience standard HB and AGB evolution.
Planet Migration Induced by Gravitational Instabilities
(Indiana University, 2011-02-18) Michael, Scott
The study of gravitational instabilities (GIs) and their effects in protoplanetary disks has been an area of active research for over a decade. Although some studies have indicated that GIs cannot form gas giant planets directly, it is clear that they can have a significant effect on a protoplanetary disk. In this dissertation I present several areas where GIs may play a key role in the evolution of a protoplanetary disk. These studies are carried out using three dimensional numerical simulations. I have carried out and analyzed nearly twenty simulations with varying initial conditions, resolutions, and physical effects. Although all indications from these simulations are that GIs cannot form gas giant planets directly at radii smaller than 40 AU, they have shown that GIs can have a dramatic effect on protoplanetary disk structure and planets embedded in a protoplanetary disk. I present several key results including: the effects of a varied initial surface density profile azimuthal resolution, the amplitude of the initial random perturbation, and the adiabatic index used on the onset, strength and general evolution of GIs in protoplanetary disks. Additionally, I present results on studies of the interaction of the instabilities with the central star when it is allowed to move freely in response to the action of the GIs. Finally, I present several results regarding the interaction of embedded massive planets and GI active disks. I find that the presence of massive planets can have a dramatic effect on the evolution of GIs in an active disk, and the GIs can also dramatically effect them migration of the embedded planet. In fact, the action of the GIs may planets to migrate outward, contrary to the standard theory of the planet migration in laminar disks.
QU Carinae: Type Ia supernova in the making?
(Oxford University Press on behalf of the Royal Astronomical Society, 2012) Kafka, S.; Honeycutt, R.K.; Williams, R.
Variable Na I absorption lines have been reported in a number of Type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a giant donor star may be the progenitors of these SNeIa. We present echelle spectra of the CV QU Carinae which strengthen the connection between CVs of the V Sge class, the accretion wind evolution scenario, variable wind features, variable Na I absorption and SNeIa. This thread not only provides insight into the spectral peculiarities of QU Car, but also links SNeIa as a class with their parent systems.

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