Testing linear-theory predictions of galaxy formation

The angular momentum of galaxies is routinely ascribed to a process of tidal torques acting during the early stages of gravitational collapse, and is predicted from the initial mass distribution using second-order perturbation theory and the Zel'dovich approximation. We have tested this theory for a flat hierarchical cosmogony using a large N-body simulation with sufficient dynamic range to include tidal fields, allow resolution of individual galaxies, and thereby expand on previous studies. We find relatively good correlation between the predictions of linear theory and actual galaxy evolution. While structure formation from early times is a complex history of hierarchical merging, salient features are well described by the simple spherical-collapse model. Most notably, we test several methods for determining the turnaround epoch, and find that turnaround is succesfully described by the spherical collapse model. The angular momentum of collapsing structures grows linearly until turnaround, as predicted, and continues quasi-linearly until shell crossing. The predicted angular momentum for well-resolved galaxies at turnaround overestimates the true turnaround and final values by a factor of ~3 with a scatter of ~70 percent, and only marginally yields the correct direction of the angular momentum vector. We recover the prediction that final angular momentum scales as mass to the 5/3 power. We find that mass and angular momentum also vary proportionally with peak height.Comment: 20 pages, 16 figures, Accepted for publication in MNRA

Disentangling the Origin and Heating Mechanism of Supernova Dust: Late-Time Spitzer Spectroscopy of the Type IIn SN 2005ip

This paper presents late-time near-infrared and {\it Spitzer} mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest the warmer dust has a mass of $\sim 5 \times 10^{-4}~$\msolar, originates from newly formed dust in the ejecta, or possibly the cool, dense shell, and is continuously heated by the circumstellar interaction. By contrast, the cooler component likely originates from a circumstellar shock echo that forms from the heating of a large, pre-existing dust shell $\sim 0.01 - 0.05$~\msolar~by the late-time circumstellar interaction. The progenitor wind velocity derived from the blue edge of the He 1 1.083 \micron~P Cygni profile indicates a progenitor eruption likely formed this dust shell $\sim$100 years prior to the supernova explosion, which is consistent with a Luminous Blue Variable (LBV) progenitor star.Comment: 12 pages, 10 figures, Accepted to Ap

Late-time Light Curves of Type II Supernovae: Physical Properties of SNe and Their Environment

We present BVRIJHK band photometry of 6 core-collapse supernovae, SNe 1999bw, 2002hh, 2003gd, 2004et, 2005cs, and 2006bc measured at late epochs (>2 yrs) based on Hubble Space Telescope (HST), Gemini north, and WIYN telescopes. We also show the JHK lightcurves of a supernova impostor SN 2008S up to day 575. Of our 43 HST observations in total, 36 observations are successful in detecting the light from the SNe alone and measuring magnitudes of all the targets. HST observations show a resolved scattered light echo around SN 2003gd at day 1520 and around SN 2002hh at day 1717. Our Gemini and WIYN observations detected SNe 2002hh and 2004et, as well. Combining our data with previously published data, we show VRIJHK-band lightcurves and estimate decline magnitude rates at each band in 4 different phases. Our prior work on these lightcurves and other data indicate that dust is forming in our targets from day ~300-400, supporting SN dust formation theory. In this paper we focus on other physical properties derived from the late time light curves. We estimate 56Ni masses for our targets (0.5-14 x 10^{-2} Msun) from the bolometric lightcurve of each for days ~150-300 using SN 1987A as a standard (7.5 x 10^{-2} Msun). The flattening or sometimes increasing fluxes in the late time light curves of SNe 2002hh, 2003gd, 2004et and 2006bc indicate the presence of light echos. We estimate the circumstellar hydrogen density of the material causing the light echo and find that SN 2002hh is surrounded by relatively dense materials (n(H) >400 cm^{-3}) and SNe 2003gd and 2004et have densities more typical of the interstellar medium (~1 cm^{-3}). The 56Ni mass appears well correlated with progenitor mass with a slope of 0.31 x 10^{-2}, supporting the previous work by Maeda et al. (2010), who focus on more massive Type II SNe. The dust mass does not appear to be correlated with progenitor mass.Comment: We corrected the 56Ni mass of SN2005cs and Figures 8 (a) and 8 (c

Early Dust Formation and a Massive Progenitor for SN 2011ja?

SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby edge on spiral galaxy NGC 4945. Flat-topped and multi-peaked H-alpha and H-beta spectral emission lines appear between 64 - 84 days post-explosion, indicating interaction with a disc-like circumstellar medium inclined 30-45 degrees from edge-on. After day 84 an increase in the H- and K-band flux along with heavy attenuation of the red wing of the emission lines are strong indications of early dust formation, likely located in the cool dense shell created between the forward shock of the SN ejecta and the reverse shock created as the ejecta plows into the existing CSM. Radiative transfer modeling reveals both ~1.5 x 10^-4 Msun of pre-existing dust located ~ 10^16.7 cm away and ~ 5 x 10^-5 Msun of newly formed dust. Spectral observations after 1.5 years reveal the possibility that the fading SN is located within a young (3-6 Myr) massive stellar cluster, which when combined with tentative 56Ni mass estimates of 0.2 Msun may indicate a massive (> 25 Msun) progenitor for SN 2011ja.Comment: 13 pages, 8 figures, submitted to MNRAS awaiting final referee repor

Thirty years of SN 1980K: Evidence for light echoes

We report optical and mid-infrared photometry of SN 1980K between 2004 and 2010, which show slow monotonic fading consistent with previous spectroscopic and photometric observations made 8 to 17 years after outburst. The slow rate-of-change over two decades suggests that this evolution may result from scattered and thermal light echoes off of extended circumstellar material. We present a semi- analytic dust radiative-transfer model that uses an empirically corrected effective optical depth to provide a fast and robust alternative to full Monte-Carlo radiative transfer modeling for homogenous dust at low to intermediate optical depths. We find that unresolved echoes from a thin circumstellar shell 14-15 lt-yr from the progenitor, and containing about 0.02 Msun of carbon-rich dust, can explain the broadband spectral and temporal evolution. The size, mass and dust composition are in good agreement with the contact discontinuity observed in scattered echoes around SN 1987A. The origin of slowly-changing high-velocity [O I] and Halpha lines is also considered. We propose an origin in shocked high-velocity metal-rich clumps of ejecta, rather than arising in the impact of ejecta on slowly-moving circumstellar material, as is the case with hot spots in SN 1987A.Comment: Accepted 2/14/12 to be published in ApJ. 15 pages, 10 figure

The Three-Dimensional Circumstellar Environment of SN 1987A

We present the detailed construction and analysis of the most complete map to date of the circumstellar environment around SN 1987A, using ground and space-based imaging from the past 16 years. PSF-matched difference-imaging analyses of data from 1988 through 1997 reveal material between 1 and 28 ly from the SN. Careful analyses allows the reconstruction of the probable circumstellar environment, revealing a richly-structured bipolar nebula. An outer, double-lobed ``Peanut,'' which is believed to be the contact discontinuity between red supergiant and main sequence winds, is a prolate shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's Hat, previously believed to be an independent structure, is the waist of this Peanut, which is pinched to a radius of 6 ly. Interior to this is a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the Peanut by a thick equatorial disk. The nebulae are inclined 41\degr south and 8\degr east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN. From the hourglass to the large, bipolar lobes, echo fluxes suggest that the gas density drops from 1--3 cm^{-3} to >0.03 cm^{-3}, while the maximum dust-grain size increases from ~0.2 micron to 2 micron, and the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun. The geometry of the three rings is studied, suggesting the northern and southern rings are located 1.3 and 1.0 ly from the SN, while the equatorial ring is elliptical (b/a < 0.98), and spatially offset in the same direction as the hourglass.Comment: Accepted for publication in the ApJ Supplements. 38 pages in apjemulate format, with 52 figure

An Extremely Bright Echo Associated With SN 2002hh

We present new, very late-time optical photometry and spectroscopy of the interesting Type II-P supernova, SN 2002hh, in NGC 6946. Gemini/GMOS-N has been used to acquire visible spectra at six epochs between 2004 August and 2006 July, following the evolution of the SN from age 661 to 1358 days. Few optical spectra of Type II supernovae with ages greater than one year exist. In addition, g'r'i' images were acquired at all six epochs. The spectral and photometric evolution of SN 2002hh has been very unusual. Measures of the brightness of this SN, both in the R and I bands as well as in the H-alpha emission flux, show no significant fading over an interval of nearly two years. The most straightforward explanation for this behavior is that the light being measured comes not only from the SN itself but also from an echo off of nearby dust. Echoes have been detected previously around several SNe but these echoes, at their brightest, were ~8 mag below the maximum brightness of the SN. At V~21 mag, the putative echo dominates the light of SN 2002hh and is only ~4 mag below the outburst's peak brightness. There is an estimated 6 magnitudes of total extinction in V towards SN 2002hh. The proposed explanation of a differential echo/SN absorption is inconsistent with the observed BVRI colors.Comment: 24 pages, 6 figures. Accepted for publication in the Ap

A New View of the Circumstellar Environment of SN 1987A

We summarize the analysis of a uniform set of both previously-known and newly-discovered scattered-light echoes, detected within 30" of SN 1987A in ten years of optical imaging, and with which we have constructed the most complete three-dimensional model of the progenitor's circumstellar environment. Surrounding the SN is a richly-structured bipolar nebula. An outer, double-lobed ``peanut,'' which we believe is the contact discontinuity between the red supergiant and main sequence winds, is a prolate shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's Hat, previously believed to be an independent structure, is the waist of this peanut, which is pinched to a radius of 6 ly. Interior, the innermost circumstellar material lies along a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the peanut by a thick equatorial disk. The nebulae are inclined 41o south and 8o east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN. The 3-D geometry of the three circumstellar rings is studied, suggesting the equatorial ring is elliptical (b/a<0.98), and spatially offset in the same direction as the hourglass. Dust-scattering models suggest that between the hourglass and bipolar lobes: the gas density drops from 1--3 cm^{-3} to >0.03 cm^{-3}; the maximum dust-grain size increases from ~0.2 micron to 2 micron; and the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun, yielding a red-supergiant mass loss around 5*10^{-6} Msun yr^{-1}.Comment: Accepted for publication in ApJ 2/14/05. 16 pages in emualteapj forma

HST-COS Observations of Hydrogen, Helium, Carbon and Nitrogen Emission from the SN 1987A Reverse Shock

We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (dv \sim 300 km/s) emission lines from the circumstellar ring, broad (dv \sim 10 -- 20 x 10^3 km/s) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise (> 40 per resolution element) broad LyA emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at \lambda > 1350A can be explained by HI 2-photon emission from the same region. We confirm our earlier, tentative detection of NV \lambda 1240 emission from the reverse shock and we present the first detections of broad HeII \lambda1640, CIV \lambda1550, and NIV] \lambda1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 +/- 0.06. The NV/H-alpha line ratio requires partial ion-electron equilibration (T_{e}/T_{p} \approx 0.14 - 0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance ratio may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring.Comment: 12 pages, 8 figures. ApJ - accepte