J. E. Beckman

The Hα Galaxy Survey ⋆ I. The galaxy sample, Hα narrow-band observations and star formation parameters for 334 galaxies

We discuss the selection and observations of a large sample of nearby galaxies, which we are using to quantify the star formation activity in the local Universe. The sample consists of 334 galaxies across all Hubble types from S0/a to Im and with recession velocities of between 0 and 3000 km s 1 . The basic data for each galaxy are narrow band H�+(Nii) and R-band imaging, from which we derive star formation rates, H�+(Nii) equivalent widths and surface brightnesses, and R-band total magnitudes. A strong correlation is found between total star formation rate and Hubble type, with the strongest star formation in isolated galaxies occurring in Sc and Sbc types. More surprisingly, no significant trend is found between H�+(Nii) equivalent width and galaxy R-band luminosity. More detailed analyses of the data set presented here will be described in subsequent papers.

A new chemo-evolutionary population synthesis model for early-type galaxies .2. Observations and results

We present the results of applying a new chemo-evolutionary stellar population model, developed in a previous paper, to new high-quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the Sombrero galaxy. Here we fit in detail ~20 absorption lines and six optical and near-infrared colors, following two approaches: fitting a single-age, single-metallicity model and fitting our full chemical evolutionary model. We find that all the iron lines are weaker than the best-fitting models predict, indicating that the iron abundance is anomalous and deficient. We also find that the Ca I index at 4227 A is much lower than predicted by the models. We can obtain good fits for all the other lines and observed colors with models of old and metal-rich stellar populations and can show that the observed radial gradients are due to metallicity decreasing outward. We find that good fits are obtained both with fully evolutionary models and with single-age, single-metallicity models. This is due to the fact that in the evolutionary model more than 80% of the stars form within 1.5 Gyr after the formation of the galaxies. The fact that slightly better fits are obtained with evolutionary models indicates that these galaxies contain a small spread in metallicity.

The Evolution of Galaxies on Cosmological Timescales

The 9.2 m Hobby-Eberly Telescope (HET) is beginning science operations. It provides a unique approach to very large telescope development, with high performance at modest cost. The HET is already being cloned in the Southern hemisphere and may be the basis for the development of signi cantly larger telescopes for the new Millennium. We describe the current performance of the HET and of the newly commissioned Marcario Low Resolution Spectrograph (LRS), for which the author is the PI. Projects on high redshift clustering are already underway, and early results are presented here. In particular, the TexasOxford high redshift cluster survey has already yielded several clusters with LRS redshifts as high as z=0.6.

When Is a Bulge Not a Bulge? Inner Disks Masquerading as Bulges in NGC 2787 and NGC 3945

We present a detailed morphological, photometric, and kinematic analysis of two barred S0 galaxies with large, luminous inner disks inside their bars. We show that these structures, in addition to being geometrically disk-like, have exponential profiles (scale lengths � 300–500 pc) distinct from the central, non-exponential bulges. We also find them to be kinematically disk-like. The inner disk in NGC 2787 has a luminosity roughly twice that of the bulge; but in NGC 3945, the inner disk is almost ten times more luminous than the bulge, which itself is extremely small (half-light radius � 100 pc, in a galaxy with an outer ring of radius � 14 kpc) and only � 5% of the total luminosity — a bulge/total ratio much more typical of an Sc galaxy. We estimate that at least 20% of (barred) S0 galaxies may have similar structures, which means that their bulge/disk ratios may be significantly overestimated. These inner disks dominate the central light of their galaxies; they are at least an order of magnitude larger than typical “nuclear disks” found in ellipticals and early-type spirals. Consequently, they must affect the dynamics of the bars in which they reside.

Multiple major outbursts from a restless luminous blue variable in NGC 3432

We present new photometric and spectroscopic observations of an unusual luminous blue variable (LBV) in NGC 3432, covering three major outbursts in 2008 October, 2009 April and 2009 November. Previously, this star experienced an outburst also in 2000 (known as SN 2000ch). During outbursts the star reached an absolute magnitude between −12.1 and −12.8. Its spectrum showed H, He i and Fe ii lines with P-Cygni profiles during and soon after the eruptive phases, while only intermediate-width lines in pure emission (including He iiλ4686) were visible during quiescence. The fast-evolving light curve soon after the outbursts, the quasi-modulated light curve, the peak magnitude and the overall spectral properties are consistent with multiple episodes of variability of an extremely active LBV. However, the widths of the spectral lines indicate unusually high wind velocities (1500–2800 km s^(−1)), similar to those observed in Wolf–Rayet stars. Although modulated light curves are typical of LBVs during the S-Dor variability phase, the luminous maxima and the high frequency of outbursts are unexpected in S-Dor variables. Such extreme variability may be associated with repeated ejection episodes during a giant eruption of an LBV. Alternatively, it may be indicative of a high level of instability shortly preceding the core-collapse or due to interaction with a massive, binary companion. In this context, the variable in NGC 3432 shares some similarities with the famous stellar system HD 5980 in the Small Magellanic Cloud, which includes an erupting LBV and an early Wolf–Rayet star.

SN 2002cv: a heavily obscured Type Ia supernova

We present V RIJHK photometry, and optical and near-infrared spectroscopy, of the heavily extinguished Type Ia supernova (SN) 2002cv, located in NGC 3190, which is also the parent galaxy of the Type Ia SN 2002bo. SN 2002cv, not visible in the blue, has a total visual extinction of 8.74±0.21 mag. In spite of this we were able to obtain the light curves between 10 and +207 days from the maximum in the I band, and also to follow the spectral evolution, deriving its key parameters. We found the peak I-band brightness to be Imax = 16.57±0.10 mag, the maximum absolute I magnitude to be M max I

The Massive Progenitor of the Possible Type II-Linear Supernova 2009hd in Messier 66

We present early- and late-time photometric and spectroscopic observations of supernova (SN) 2009hd in the nearby spiral galaxy NGC 3627 (M66). This SN is one of the closest to us in recent years and provides an uncommon opportunity to observe and study the nature of SNe. However, the object was heavily obscured by dust, rendering it unusually faint in the optical given its proximity. We find that the observed properties of SN 2009hd support its classification as a possible Type II-Linear SN (SN II-L), a relatively rare subclass of core-collapse SNe. High-precision relative astrometry has been employed to attempt to identify an SN progenitor candidate, based on a pixel-by-pixel comparison between Hubble Space Telescope (HST) F555W and F814W images of the SN site prior to explosion and at late times. A progenitor candidate is identified in the F814W images only; this object is undetected in F555W. Significant uncertainty exists in the astrometry, such that we cannot definitively identify this object as the SN progenitor. Via insertion of artificial stars into the pre-SN HST images, we are able to constrain the progenitors properties to those of a possible supergiant, with intrinsic absolute magnitude M^0_(F555W) ≳ –7.6 mag and intrinsic color (V – I)^0 ≳ 0.99 mag. The magnitude and color limits are consistent with a luminous red supergiant (RSG); however, they also allow for the possibility that the star could have been more yellow than red. From a comparison with theoretical massive-star evolutionary tracks which include rotation and pulsationally enhanced mass loss, we can place a conservative upper limit on the initial mass for the progenitor of M_(ini) ≾ 20 M_☉. If the actual mass of the progenitor is near the upper range allowed by our derived mass limit, then it would be consistent with that for the identified progenitors of the SN II-L 2009kr and the high-luminosity SN II-Plateau (II-P) 2008cn. The progenitors of these three SNe may possibly bridge the gap between lower-mass RSGs that explode as SNe II-P and luminous blue variables, or more extreme RSGs, from which the more exotic SNe II-narrow may arise. Very late time imaging of the SN 2009hd site may provide us with more clues regarding the true nature of its progenitor.

Scale lengths in disk surface brightness as probes of dust extinction in three spiral galaxies: M51, NGC 3631, and NGC 4321

We have measured the radial brightness distributions in the disks of three nearby face-on spiral galaxies, M51, NGC 3631, and NGC 4321 (M100), in the photometric bands B through I, with the addition of the K band for M51 only. The measurements were made by averaging azimuthally, in three modes, the two-dimensional surface brightness over the disks in photometric images of the objects in each band: (1) over each disk as a whole, (2) over the spiral arms alone, and (3) over the interarm zones alone. From these profiles, scale lengths were derived for comparison with schematic exponential disk models that incorporate interstellar dust. These models include both absorption and scattering in their treatment of radiative transfer. The model fits show that the arms exhibit greater optical depth in dust than the interarm zones. The average fraction of emitted stellar light in V that is extinguished by dust within 3 scale lengths of the center of each galaxy does not rise above 20% in any of them. We show that this conclusion is also valid for models with similar overall quantities of dust but in which this is concentrated in lanes. These can also account for the observed scale lengths and their variations.

Photoionization Models of NGC 346

We have compared direct estimates of the ionizing photon ux from the stars observed within the H II region NGC 346 in the Small Magellanic Cloud with its observed H luminosity using a series of photoionization models of the region. The tests were based on the use of the photoionization code Cloudy (Ferland 2000), aided by H, He, N, O, Ne, S, Ar, and Fe emission line observations of Peimbert, Peimbert, & Ruiz (2000, hereinafter PPR). A key result is that some 46% of the Lyman continuum photons escape from the region. The abundances of N, O, Ne, S, Ar, and Fe relative to H were determined using the ionization structure of the best model, and are compared with those derived from empirical ionization correction factors. We estimate directly the photoionization spectrum that will be used for the models based on the spectral classication of the blue stars presented by Massey, Parker, & Garmany (1989). We assume that these stars are blackbodies emitting at specied eectiv e temperatures. This assumption is plausible since the stars have high Te . To derive the ionizing ux, we have adopted the stellar parameters presented by Vacca, Garmany, & Shull (1996) and found that the total ionizing ux amounts to 40:06 10 39 erg s 1 . Using this ionizing luminosity as an input to a homogeneous spherical model for NGC 346 and assuming that all the ionizing photons are absorbed within the nebula, we obtain, using Cloudy a value for the H luminosity of the H II region of 1:78 10 39 erg s 1 .

Generation of galactic disc warps due to intergalactic accretion flows onto the disc

The accretion of the intergalactic medium onto the gaseous disc is used to explain the generation of galactic warps. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small for most incident inflow angles and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shaped warp. The torque produced by a flow of velocity ~100 km/s and baryon density ~10^{-25} kg/m^3, which is within the possible values for the intergalactic medium, is enough to generate the observed warps and this mechanism offers quite a plausible explanation. The inferred rate of infall of matter, ~1 M_sun/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of chemical evolution resolving key issues, notably the G-dwarf problem. Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because it would produce a dependence of the scaleheight of the disc with the Galactocentric azimuth in the outer disc, but rather than being an objection this is another argument in favour of the mechanism because this dependence is actually observed in our Galaxy.